B cells in cancer: functions, mechanisms and therapeutic advances

Abstract

Across various cancer entities, a wide array of subtypes of B cells that infiltrate tumors can be identified. These subtypes confer these cells with high adaptability in their functions and significant involvement in tumor progression. Tumor-infiltrating B cells act as distinctive microenvironmental mediators that build tertiary lymphoid structures, secrete diverse factors, and generate a wide antibody repertoire, thereby offering a valuable indicator of immunotherapy response. Recent clinical trials have demonstrated that intervening in tumor-infiltrating B cells can be an effective treatment strategy for tumors, including common types such as breast cancer, colorectal carcinoma, and non-small cell lung cancer. These findings suggest that tumor-infiltrating B cells should not be overlooked as therapeutic targets, as they offer significant potential to reduce the incidence of nonresponse, drug resistance, and immune-related adverse effects commonly seen in current treatment techniques. In this review, we explore the historical development of B cells in the context of tumors. We then discuss the various subtypes of tumor-infiltrating B cells, analyzing their diverse roles in tumor development. Additionally, we delve into the signaling pathways of tumor-infiltrating B cells, intercellular crosstalk, and multilevel regulatory mechanisms. Finally, based on immune checkpoints and therapeutic targets on the surface of tumor-infiltrating B cells, we summarize the current understanding which can lead to the development of new intervention methods targeting tumor-infiltrating B cells in the future. This review aims to provide a comprehensive summary of B-cell classification and therapeutic potential, emphasizing their critical role in guiding clinical treatment strategies.

Introduction

The tumor microenvironment (TME) is divided into a nonimmune microenvironment dominated by fibroblasts, vascular endothelial cells, and other noncellular elements, such as cytokines and extracellular matrix proteins, and an immune microenvironment dominated by immune cells such as myeloid cells, T lymphocytes, and B lymphocytes.¹ The TME is not static but varies depending on the tissue type and evolves as the cancer progresses.² Multiple immune cells play diverse roles, exerting either tumor-promoting or tumor-suppressing effects.³ Neutrophils, tumor-associated macrophages (TAMs), T cells, and fibroblasts have all been studied in the context of the TME across various cancer entities, providing plenty of evidence in tumor progression and patient prognosis.^2,4–7 Currently, research on tumor-infiltrating B cells (TIBs) is gradually increasing, likewise revealing their functional heterogeneity in the TME and their significant relationship with tumor progression and prognosis.

TIBs are crucial immune cells in the TME, referring to B cells infiltrating into tumor tissues.⁸ Among TIBs, various types can be identified based on their functions and developmental stages. Functionally, TIBs can be further categorized into regulatory B cells (Bregs) and antibody presenting cells (APCs).⁹ Similar to B cells in nonneoplastic conditions, TIBs undergo somatic hypermutation and clonal expansion and can secrete antibodies. Within tumors, various differentiation stages of TIBs exist, which are embedded within distinct microenvironmental structures.¹⁰ TIBs exist in tertiary lymphoid structures (TLSs), which account for a large proportion of all TIBs. Similarly, lympho-myeloid aggregates (LMAs) are various nonfollicular aggregates of poorly organized B cells, T cells, and myeloid cells found in tumors. LMAs also accommodate naive and memory B cells.⁸ Visible B-cell germinal centers and adjacent T cell areas allow them to respond quickly to inflammation and immune stimulation in tumors.¹¹ Moreover, TIBs are scattered throughout the tumor stroma, but this phenomenon is only observed in some tumors, where they can interact with tumor cells to perform various functions.^8,12 A more widely accepted classification method is based on the differentiation stages of B cells, including naive B cells, activated B cells, memory B cells, plasmablasts, and plasma cells. All these B cells can infiltrate tumors as TIBs.

TIBs exhibit dual effects. On the one hand, they play significant roles in promoting tumor cell proliferation, inducing tumor immune tolerance, and enhancing tumor cell invasion and metastasis.¹³ On the other hand, they inhibit tumor progression and promote immune cell infiltration.¹⁴ TIBs are closely related to nonimmune cells in the TME. TIBs interact with tumor cells, enhancing CD8⁺ T-cells function through antigen presentation,¹⁵ which also facilitates TAM polarization and antibody production.¹⁶ Additionally, TIBs interact with multiple immune cells, forming TLSs that actively participate in initiating and maintaining adaptive immune responses.¹⁷ TLS, as an essential component of the TME, are composed of multiple immune cell types. They form organized aggregations under chronic inflammatory stimuli, thereby enhancing antitumor immune responses.¹⁸ The presence of TLSs often indicates a good response to immunotherapy and is associated with prolonged survival for patients.¹⁹ However, some TLSs exert conflicting effects on prognosis.²⁰

In the past decade, the clinical success of immune checkpoint inhibitors (ICIs) has proven that modulating immune cells in the TME is highly effective. However, the overall effective rate of immune checkpoint therapy is 20–30%.²¹ Research has already confirmed that interventions targeting immune cells in tumors are practical, such as chimeric antigen receptor T-cell therapy (CAR-T),²² CAR-NK therapy,²³ and CAR-M therapy (a cell-based immunotherapy that uses genetically engineered macrophages expressing chimeric antigen receptor to target and eliminate tumor cells).²⁴ At present, studies about TIBs are progressively expanding, similarly uncovering their diverse functions within the TME and their notable impact on tumor progression and prognosis.²⁵ Adoptive B-cell therapy, which leverages B cells’ antibody-producing capabilities, is being explored as a novel approach to enhance antitumor immunity and address limitations of current treatments. TIBs, as an essential component of the TME, have become one of the significant research directions and are expected to play a significant role in cancer treatment.

This review aims to provide a comprehensive overview of the relationship between TIBs and cancer. It begins by retracing the historical research on B cells in the context of cancer, highlighting key milestones and discoveries. The review then delves into the heterogeneity of TIBs, examining their diverse phenotypes and functions. It further explores the dual roles that TIBs can play, either by promoting or inhibiting tumor progression. By analyzing the signaling pathways of TIBs, as well as the intricate intracellular and intercellular signaling crosstalk and multilevel regulatory mechanisms, this review elucidates how these cells function within the TME. Finally, it summarizes current therapeutic strategies targeting TIBs, evaluates their potential feasibility, and offers valuable insights for the development of future cancer treatments.

The research history of B cells is rich and tortuous. In 1875, Heinrich H. von Hartz-Waldeyer was the first to propose the term “plasma cells”, describing a type of cell with a large, granular cytoplasm.²⁶ In the 1890s, the German physiologist Emil von Behring proposed that the human body contains a type of cell capable of “remembering” past infections and producing antibodies upon re-encountering such infections.^27,28 In 1948, Astrid Fagraeus discovered that plasma cells are the cells responsible for antibody production through observation and analysis of cells during immune responses.²⁹ This discovery demonstrated the central role of plasma cells in humoral immunity. In 1960, Max Cooper discovered B cells and unveiled their functions.³⁰ Through experiments, he demonstrated that once the bursa of Fabricius—the key site for B-cell development in birds—was surgically removed, irradiated chickens could no longer produce antibodies. In 1963, Kurt Hirschhorn discovered that antigens could sensitize cells in the plasma, and upon reintroduction of the same antigen, some of these cells differentiated to produce gamma globulins.³¹ In 1975, scientists first observed the existence of memory B cells in mice.³² Initially, Bregs were described as transitional B cells capable of secreting interleukin (IL)-10 by Paul A. Blair in 2010.³³ As research progressed, it was recognized that Bregs represent a state with immunoregulatory functions, playing a key role in maintaining immune tolerance and regulating immune responses.

The research history of TIBs related to cancer is relatively extensive. In 1953, Foley E. J. first proposed the concept of immune surveillance, which refers to the immune system’s ability to detect and eliminate abnormal cells, including cancer cells, thereby preventing the development of malignancies.³⁴ In 1960, George D. Snell discovered that humoral immunity can recognize tumor antigens.³⁵ In 1973, IgA and IgG were reduced, and IgM was increased, and in 1/3 breast cancers, correlating with immunoglobulin production, suggesting plasma cell infiltration by M. Maureen Roberts.³⁶ In 1990, Joachim Hombach identified the components of the B-cell receptor (BCR), laying the foundation for subsequent research on how the BCR recognizes antigens and activates B-cell signaling pathways.³⁷ In 1991, P. van der Bruggen first discovered tumor-associated antigens (TAAs) that lymphocytes could recognize.³⁸ The earliest article reporting toll-like receptors (TLRs) was published by Ruslan Medzhitov and Charles Janeway in 1997, revealing the crucial role of TLR4 in activating immune responses.³⁹ The study that first described the prognostic significance of TIBs in solid tumors, indicating a better prognosis, was published by Zhihai Qin et al. in 1998.⁴⁰ The article reporting high infiltration of TIBs in patients with advanced breast cancer and its indication of cancer progression was reported by E. F. Murta in 2000.⁴¹ In 2010, Massimo Ammirante found that inflammation attracts TIBs to prostate cancer foci, releasing cytokines such as nuclear factor kappa-B kinase subunit β (Ikkβ) and Nuclear Factor Kappa-light-chain-enhancer of activated B cells (NF-κB), which promote cancer cell growth and reactivate suppressed cells.⁴² In 2016, Pucci found that melanoma-derived vesicles enter the lymph node cortex via disrupted CD169⁺ macrophage barriers in tumor-draining lymph nodes (tdLNs), promoting tumor-associated humoral immunity.⁴³ In 2020, Yiwen Lu discovered the emergence of an inducible T-cell costimulatory ligand (ICOSL)⁺ TIB subset after chemotherapy, indicating that ICOSL in TIBs enhances antitumor immunity by increasing the ratio of effector cells to regulatory T cells (Tregs).⁴⁴ In the same year, Beth A Helmink discovered that, by analyzing the immune cell composition in tumor tissues from metastatic melanoma and renal cell carcinoma (RCC) cohorts, TIBs and TLSs were positively correlated with patients’ response to immunotherapy.⁴⁵ During the same year, the team led by Wolf H. Fridman and Hussein A. Tawbi found, through analyzing clinical cohort studies of soft tissue sarcomas, that TIBs, TLSs, and patient prognosis and response to immunotherapy were positively correlated.⁴⁶ In 2020, the Rita Cabrita team found that CD8⁺ T cells and CD20⁺ TIBs in tumor tissues predicted better overall survival (OS) in metastatic melanoma patients, based on their analysis of tumor samples and clinical outcomes.⁴⁷ In 2021, Baihao Zhang established that TIB-derived gamma-aminobutyric acid (GABA) promotes the differentiation of monocytes into anti-inflammatory macrophages that secrete IL-10 and inhibit the cytotoxic function of CD8⁺ T cells.¹⁶ In that same year, the team led by Subir Biswas discovered that polymerized immunoglobulin (Ig) A orchestrates a protective humoral response, with IgA antagonizing the growth of ovarian cancer by regulating coordinated responses of tumor cells, T cells, and TIBs.⁴⁸ In the same year, Cai Cui discovered that tumor neoantigens can regulate the fate of tumor-specific CD4⁺ T cells by promoting their interaction with TIBs, which enhances antitumor immunity by boosting CD8⁺ T-cell effector function.¹⁵ In 2023, Lloyd Bod identified a key immune checkpoint, T-cell immunoglobulin and mucin domain (TIM)-1, activated in TIBs. Targeted inhibition of TIM-1 in TIBs enhanced antitumor CD8⁺ and CD4⁺ T-cell responses and suppressed tumor growth, which holds significant implications for cancer treatment.⁴⁹ With the continuous development of bioinformatics technology, in 2024, Yu Yang, Jiaqiang Ma, and Evelyn Fitzsimons elucidated the different differentiation stages from naive B cells to plasma cells through single-cell RNA sequencing (scRNA-seq) technology, and revealed the prognostic associations of different subpopulations with cancer patients.^4,50–52

TLSs, as a novel yet significant form of TIB infiltration in tumors, are also a key research focus in the study of TIBs.¹⁰ (Fig. 1) In 2006, Fabrizio Aloisi and Ramon Pujol-Borrell defined and described TLSs, a form of ectopic lymphoid organization of TIBs.⁵³ In 2015, Shlomi Finkin and Nikhil S Joshi suggested that TLSs can promote tumor progression from different perspectives.^54,55 In 2020, Beth A Helmink and Rita Cabrita identified that TIBs and TLSs promote immune therapy responses.^45,47 In 2024, Yifan Zhang et al. found that C-C motif chemokine ligand (CCL) 19-producing fibroblasts promote TLS formation, enhancing antitumor IgG response in colorectal carcinoma (CRC) liver metastasis.⁵⁶

Fig. 1.

The timeline of key milestones in the study of B cells and cancer. We have summarized the relationship between B cells, antibodies, tumors, and TLSs since the discovery of plasma cells in 1875. Over the past 150 years, scientists have gradually established an understanding of B cells and antibodies and effectively linked them to cancer. With in-depth research on monoclonal antibodies and immune checkpoints, immune checkpoint inhibitors have emerged as an important therapeutic approach, opening up new directions for cancer treatment. The discovery and definition of the unique structure of TLSs have further laid the foundation for researchers to gain a deeper understanding of the behavior and function of TIBs. Along with the advancement of technology, high-throughput sequencing has provided a brand-new perspective for elucidating the functions of TIBs. Figures were created with Adobe Illustrator. TLR toll-like receptors, PD-1 programmed death 1, GABA gamma-aminobutyric acid, scRNA-seq single-cell RNA sequencing, IL interleukin, TLS tertiary lymphoid structure, FDA Food and Drug Administration, BCR B Cell Receptor

In vitro, monoclonal antibodies produced by B cells and their derived drugs serve as a crucial tool for tumor treatment. In 1890, Emil von Behring discovered antibodies and was awarded the Nobel Prize in 1901.⁵⁷ In 1959 and 1960, Rodney Porter and Gerald Edelman elucidated the structure of antibodies.^58,59 In 1971, Niels Jerne was the first to propose the natural selection theory of antibody formation.⁶⁰ George Koehler and Caesar Milstein were the first to produce monoclonal antibodies in 1975 and were awarded the Nobel Prize in 1984 for their achievement.⁶¹ In 1976, Susumu Tonegawa discovered the genetic principles underlying antibody diversity and was awarded the Nobel Prize in 1987 for this discovery.⁶² In 1992, Tasuku Honjo discovered programmed death 1 (PD-1).⁶³ Ipilimumab, an anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) agent, was the first ICI approved by the Food and Drug Administration (FDA) for the treatment of stage IV melanoma in 2011.⁶⁴ The second class of ICI, anti-PD-1, named pembrolizumab, was approved for the treatment of melanoma in 2014.⁶⁵

The heterogeneity of B cells in the tumor microenvironment

TIBs are prevalent and ubiquitous within the TME and exhibit considerable heterogeneity and diversity in their classification. Advances in scRNA-seq have progressively elucidated and refined the intricate processes underlying the maturation and differentiation of TIBs, revealing a spectrum of functional roles attributed to TIBs at various developmental stages.

Classification and functional diversity of TIBs

TIBs can be classified based on their differentiation stages and functions. Naive B cells mature in the bone marrow, express BCR without somatic hypermutation, and have surface markers such as CD19, CD20, CD22, CD79a and low CD24 but no CD27.⁶⁶ Upon antigen encounter, they activate and differentiate into effector or memory B cells. Activated B cells are those that have encountered an antigen and subsequently undergo activation, initiating further proliferation and differentiation.⁶⁷ They express CD19, CD20, CD22, CD79a, high CD86, and CD40, with possible CD23 upregulation.

Memory B cells, derived from activated B cells, have long lifespans, express high-affinity BCRs, and rapidly differentiate into plasma cells upon re-exposure to antigens. Their markers include CD19, CD20, CD22, CD79a, high CD27, CD80, and CD86.⁶⁸ Plasmablasts are short-lived, proliferating B cells that secrete antibodies with lower affinity in early immune responses.⁶⁹ They had low CD19, high CD27 and CD38, and weak CD138 expression. Plasma cells are the main antibody producers, differentiated from B cells, with lost BCR and long lifespans. They express CD19, high CD138, CD27, and CD38, but no CD20.⁷⁰

In the TME with TLSs, follicular B cells and GC B cells may also be present. GC B cells participate in somatic hypermutation and affinity maturation, differentiating into memory B cells or plasma cells through interactions with follicular dendritic cells and follicular helper T cells (Tfh cells).⁷¹ They express CD19, CD20, and CD22 and CD77, CD10, and CD38 at high levels.

Functionally, TIBs can be divided into Bregs, which regulate immune responses by secreting inhibitory cytokines such as IL-10, transforming growth factor-β (TGF-β) and IL-35, or through intercellular contacts, and immunocompetent B cells.⁷² Additionally, exhausted B cells lose normal functions under prolonged antigenic stimulation.^73,74 B-1 cells are a subset of B cells with the phenotype CD19⁺B220^lowCD23⁻CD43⁺IgM^highIgD^low, which are mainly enriched in the peritoneal cavity and have the ability to self-renew.⁷⁵

Application of novel technologies in B-cell classification

The differences in the types of TIBs may significantly impact the prognosis of tumor patients. The application of novel technologies has provided fresh insights into the diversity and mechanisms of action of TIBs in cancer. With the assistance of scRNA-seq technology, preliminary evidence has been provided that in breast cancer patients, TIBs can be classified into two significant populations: one comprising memory B cells and naive B cells, and the other consisting of plasmablasts.⁷⁶ 12 TIB subsets are defined in lung adenocarcinoma (LUAD) and normal tissues, showing extensive TIB remodeling.⁷⁷ Memory B cells and plasma cells are enriched in tumors, with high differentiation and somatic mutations. TIBs are mainly located in the C-X-C motif chemokine ligand (CXCL)13⁺ LMA. Double-negative B cells are a unique subset of B cells that do not express CD27 and IgD molecules on their surface.⁷⁸ Unique innate and GC B-cell clusters have been identified in nasopharyngeal carcinoma (NPC), contributing to the interpatient heterogeneity of B cells within the NPC microenvironment.⁷⁹ Further analysis confirms that plasma cells and double-negative B cells are more prone to infiltrating the NPC microenvironment. In CRC, IgG plasma cells are more abundant at the tumor site than in normal mucosa. The CCL28-CC motif chemokine receptor (CCR)10 axis drives migration from the TLS periphery to the tumor stroma.⁸⁰ B-cell-rich populations with strong antigen presentation, IgG accumulation, high microsatellite instability, and high tumor mutation burden may serve as predictive biomarkers for immunotherapy. In melanoma, TIBs produce antibodies with higher nonproductive sequences and unique CDR3 features compared to blood antibodies.⁸¹ These antibodies show affinity maturation and polyreactivity, indicating dysregulated B-cell lineages with distinct antibody repertoires. Through scRNA-seq, it was found that TIBs from right-sided and left-sided CRCs exhibit distinct developmental trajectories.⁸² CD20⁺ TIBs are associated with a favorable prognosis in CRC patients, especially in right-sided tumors. Using spatial transcriptomics, we investigated the nature of the TIB response within TLSs in RCC.⁸³ TIBs are abundant in TLSs, and within these structures, we can identify all stages of TIB maturation leading to the formation of plasma cells. In bladder cancer, an immunosuppressive subset of atypical B cells exists, particularly in aged female mice compared to male mice.⁸⁴ Based on scRNA-seq data, the infiltration of TIBs in NPC tissues is significantly higher than that in normal tissues.⁸⁵ TIBs with high expression of the makers of proliferation Ki-67 (MKI67) and DNA topoisomerase II alpha (TOP2A) genes are associated with poor outcomes. In contrast, TIBs expressing Human Leukocyte Antigen (HLA)-Class II, DQ Alpha 2 (DQA2) and X inactive specific transcript (XIST) genes are associated with better outcomes.

TIBs show preference in certain cancers, influenced by organ structure and the TME. Key subsets such as pre-GC B cells and plasmablasts have been identified, with intratumoral GC-like reactions observed.⁵⁰ Tumor-enriched Fc receptor like 4 (FCRL4)⁺ memory B cells are revealed to be potentially involved in antigen presentation. TME stimuli may affect antibody repertoires. Similarly, a cross-cancer scRNA-seq atlas was constructed to systematically analyze the heterogeneity and functional diversity of TIBs and plasma cells.⁵¹ This study also focused on exploring the complex immune regulation between B cells and T cells. Recent data show prevalent somatic copy number alterations in major histocompatibility complex (MHC) class I polypeptide-related sequence A and B genes, linked to antibody-dependent cell-mediated cytotoxicity (ADCC) in tumors with high TIB activity.⁷

Different types of tumors often have unique TIB infiltration patterns. Therefore, in-depth research on the types and characteristics of TIB infiltration in different tumor categories is of great significance for understanding the biological behavior of tumors and developing targeted treatment strategies.

Variability in TIB infiltration across cancer entities

The infiltration quantity of TIBs exhibits variability across different cancer entities. (Fig. 2a) The abundance of IgM⁺IgD⁺ TIBs in tumors is more significant than that in peripheral blood, leading to the speculation that TIBs primarily originate from the continuous differentiation of in situ memory B cells.⁸⁶ In CRC tissues, compared to normal tissues, GC B cells show increased clonal expansion, heavy chain mutations, and differentiation into memory B cells, but plasma cells, especially IgA-secreting ones, are significantly reduced in the TME.⁸⁷

Fig. 2.

Heterogeneity of TIBs in the TME. a TIB infiltration types and their impacts. For different kinds of cancers, there are distinct types of TIB infiltration that regulate the TME and either promote or inhibit tumor growth. b Distinct TIB subpopulations exhibit divergent behaviors within the tumor microenvironment. Plasma cells (PCs) secrete antibodies that subsequently mediate antitumor effects such as ADCC, ADCP, and CDC. IgA rises in premalignancy, whereas IgG increases in established tumors. Memory B cells differentiate into IgG-producing plasma cells that correlate with prolonged survival. Within metastases they convert into suppressive tumor-infiltrating B cells. Rich memory B cells predict superior checkpoint blockade responses. Bregs secrete multiple cytokines that shape the tumor microenvironment: they suppress CD8⁺ T cells and dendritic cells (DCs) while promoting M2 TAMs and expanding Treg populations. GC B cells recruit B cells to form TLSs and are the hallmark cells of TLSs. CD20⁺ TIBs frequently colocalize with CD8⁺ cells. B-1 cells secrete IL-10 to promote metastasis. c TIBs may undergo different metabolic and differentiation pathways under various stimuli. When TIBs are stimulated with IL-2, IFN-γ, and activated TLRs, they activate distinct transcription factors (TFs) that promote lipid metabolism, glucose metabolism and oxidative phosphorylation in TIBs. Metabolites like α-ketoglutaric acid (α-KG), play important roles in this process. GC-derived PCs secrete IgG and IgA; under IL-10, IL-21, and glutamine, TIBs instead use an extrafollicular route to yield IgM/IgA plasmablasts and PCs while upregulating nitrogen metabolism. GC-born memory B cells enhance TIB antitumor function, whereas extrafollicular AtM B cells diminish it. GC B cells show heightened pyruvate metabolism. Figures were created with Adobe Illustrator. ADCC Antibody-Dependent Cellular Cytotoxicity, ADCP Antibody-Dependent Cellular Phagocytosis, CDC Complement-Dependent Cytotoxicity, TCA cycle Tricarboxylic acid cycle; BRCA Breast Invasive Carcinoma, RCC Renal Cell Carcinoma, NSCLC Non-small cell lung cancer, NPC Nasopharyngeal Carcinoma, LIHC Liver Hepatocellular Carcinoma, COAD Colon Adenocarcinoma, PAAD Pancreatic Adenocarcinoma, STAD Stomach Adenocarcinoma, OV Ovarian Serous Cystadenocarcinoma, LUAD Lung Adenocarcinoma, PFS Progression-free survival, OS Overall survival, GC B cells Germinal Center B cells, MKI67 Marker of proliferation Ki-67, TOP2A DNA Topoisomerase II Alpha, XIST X Inactive Specific Transcript, HLA-DQA2 Major Histocompatibility Complex, Class II DQ Alpha 2, TLS Tertiary lymphoid structure, TIBs Tumor-infiltrating B cells

Near tumor tissues, TIBs can aggregate and exert an influence on tumor progression. CD20⁺ B cells and plasma cells are significantly less infiltrated in multifocal hepatocellular carcinoma (HCC) than in solitary tumors, and higher CD20 expression is positively associated with better prognosis in patients with multifocal disease.⁸⁸ Higher TIBs levels at the inner tumor margin predict longer tumor-free intervals and extended recurrence times. An increased ratio of CD20⁺ TIBs at the inner margin compared to the outer margin correlates with better tumor-free survival and recurrence outcomes.

Different immune cells form various structures, including TLSs and LMAs. These spatial structures serve as assemblies of immune cells, exerting complex influences on the TME. For example, an elevated quantity of TLSs within the TME has been associated with improved disease-free survival rates.⁸⁹ In the context of gastric cancer, the presence of TLSs is linked to tumor size and grade.⁹⁰ A higher density of TLSs is associated with increased OS rates postsurgery and enhances the efficacy of anti-PD-1 inhibitor treatment. Primary cutaneous melanomas without metastasis contain significantly more TIBs than metastatic tumors.⁹¹ A higher number of TIBs is associated with a significantly improved OS rate in patients with primary cutaneous melanomas with a Breslow depth greater than 1 mm. Most melanoma patient samples contain a high abundance of TIBs, primarily dispersed within the stroma surrounding the tumor deposits.⁹² In 26% of the samples, follicular-like aggregates of TIBs were also observed. In non-small cell lung cancer (NSCLC), follicular B cells, GC B cells, and plasma cells participate in the formation of TLSs, improving patient survival.⁹³ In high-grade serous ovarian cancer, elevated CXCL13 correlates with longer survival, and CD20⁺ TIBs predict improved survival outcomes only when CXCL13 is present.⁹⁴ CXCL13 colocalizes with TLSs, and TLSs’ prognostic benefits are seen only with CXCL13 expression. CD20⁺ TIBs form follicular-like structures within tumors in some bladder cancer patients, which is associated with prolonged survival in these patients.⁹⁵

Heterogeneous TIB behaviors shape tumor immunity

The changes in the number and function of TIBs and different types of immune cells may have an impact on the TME and patient prognosis. (Fig. 2b) In pancreatic cancer, naive B cells contribute to the formation of TLSs, which are associated with a favorable prognosis for patients.⁹⁶ In ovarian cancer, long-term survival patients have more stromal TIB infiltration than compared to medium and short-term survival patients, with nearly fivefold increased odds.⁹⁷ Additionally, some TLS-bearing cells contain GC B cells. The presence of these TIB subsets indicates the formation of TLS, which may be beneficial to patient prognosis.⁹⁸ In the TME of human papillomavirus(HPV)-positive head and neck cancer patients, there are activated B cells, GC B cells, and antibody-secreting cells, which are mainly concentrated in the tumor stroma, forming well-organized germinal center reaction clusters.⁹⁹ In high-grade serous ovarian cancer, CD20⁺ TIBs exhibit antigen experience but lack the canonical memory marker CD27.¹⁰⁰ They colocalize with activated CD8⁺ T cells and express antigen-presenting markers. Their coexistence with CD8⁺ T cells is associated with increased patient survival. In gastric cancer, TIBs can be recruited by the upregulation of genes such as C-X-C chemokine receptor(CXCR) 4.¹⁰¹ Plasma cells also play an essential role in cancer. An abundant presence of IgA⁺ plasma cells is found in the precancerous microenvironment of gastric cancer.¹⁰² In gastric cancer samples, the number of CD138⁺ cells is significantly lower than that in noncancerous gastric mucosa, whereas the number of IgG4⁺ plasma cells is considerably higher.¹⁰³ Patients with a high number of IgG4⁺ plasma cells have a significantly poorer prognosis than those with a low number of IgG4⁺ plasma cells. ScRNA-seq has also confirmed that an increased proportion of plasma cells is a new characteristic of diffuse-type gastric cancer tumors.¹⁰⁴ In gastric cancer and esophageal cancer, high expression of the plasma cell marker gene immunoglobulin kappa constant (IGKC) is an independent predictor of prolonged OS and time to recurrence, whereas CD138 expression only has prognostic significance.¹⁰⁵

CD20⁺ TIB infiltration correlates with T-cell infiltration and is linked to low lymph node metastasis and low TNM stage.¹⁰⁶ High levels of CD20⁺ TIB infiltration, class-switched memory B cells, and plasma cells are associated with better OS and disease-free survival. Differential infiltration of naive B cells and Tregs in canine CRC tumors indicates an immunosuppressive state within the TME.¹⁰⁷ Immunohistochemical analysis of CD20 and CD138 expression was conducted in 221 patients with CRC, and it was found that the TIBs/plasma cell score was associated with a longer survival duration.¹⁰⁸ Immunoglobulin heavy constant gamma (IGHG)1/3⁺ plasma cells concentrate at the transition between normal tissue and adenoma tissue, significantly influencing the transformation of colorectal tissue from normal to adenoma and cancer.¹⁰⁹

Double-negative B cells were more common in lung tumors than in the normal adjacent control group. They are negatively correlated with the presence of affinity-matured CD 27⁺IgD^- B cells with affinity within the cancer.¹¹⁰ In NPC, exhausted B cells are not significantly associated with patient OS.¹¹¹ CD11c⁻CD21⁻ double negative B cells accumulate in the blood and tumors of patients with head and neck squamous cell carcinoma and portend poor prognosis.¹¹² These cells are hyporesponsive to antigen stimulation, produce low levels of antibodies, and fail to differentiate into antibody-secreting cells.

Within the same type of cancer, there are also differences in the categories of TIBs. HPV⁺ head and neck squamous cell carcinoma contains GC B cells in addition to naive B cells, memory B cells, plasmablasts, and plasma cells.⁹⁸ In contrast, HPV^- head and neck squamous cell carcinoma possesses GC B cells in relatively small numbers. In surgical specimens of untreated pancreatic ductal adenocarcinoma (PDAC), 46% of tumors contain distinct aggregates of T and B cells reflecting “early TLS”, which are enriched with IgG1 class-switched memory B cells and are associated with longer OS and progression-free survival (PFS).¹¹³ In liver tumors, particularly in metastatic foci, activated memory B cells gradually transform into suppressive B cells.¹¹⁴

The heterogeneity of TIBs is also reflected in their diverse expression of immune checkpoints and cellular signaling molecules.¹¹⁵ Many studies have shown that TIBs can be distinguished by clusters of differentiation molecules, and their functions have been speculated. TIBs can promote or suppress tumors via immune checkpoints such as PD-1 or by secreting products such as IL-10, GABA, and antibodies.^116,117 Additionally, B-1 cells can regulate inflammatory responses through the secretion of immune regulatory molecules such as IL-10, thereby increasing the metastatic potential of B16 melanoma cells.¹¹⁸ In melanoma immunotherapy, studies have found that the coinfiltration of CD8⁺ T cells and CD20⁺ TIBs within tumors is associated with improved survival, independent of other clinical variables.⁴⁷ In most NSCLC tumors, all B-cell differentiation stages, including plasma cell production are detected.¹⁷ Mechanisms of centrosome somatic hypermutation and class switch recombination are activated. High follicular B-cell densities correlate with long-term survival in both early-stage and advanced NSCLC patients undergoing chemotherapy.

In neuroendocrine tumors, TIBs and their impact on outcomes have been less studied due to the rarity and heterogeneity of these tumors. In pituitary neuroendocrine tumors, higher CD20⁺ TIBs are associated with rounder vascular structures, indicating that TIBs may influence vascular architecture and contribute to angiogenesis.¹¹⁹ In colorectal neuroendocrine tumors with liver metastases, TIBs demonstrated significantly higher stress scores than those from the primary lesions and exhibited higher expression levels of CXCR4.¹²⁰

The regulation of the TME and patient prognosis by different types of TIBs is highly diverse. This diversity reflects the complex mechanisms of action they play in tumor initiation, progression, and metastasis.

Factors influencing TIB heterogeneity

TIBs are influenced by or secrete cytokines or immune molecules, leading to different effects and exhibiting heterogeneity. In ovarian cancer with a high prevalence of plasma cells, some TIBs express TNF receptor superfamily member 17 (TNFRSF17), which activates the X-box binding protein 1 (XBP1) gene, promoting plasma cell differentiation and immunoglobulin production, and is crucial for the survival of long-lived plasma cells.¹²¹ Interferon-γ (IFN-γ) secreted by NK cells is related to the differentiation of memory B cells, and the number of memory B cells is associated with the formation of GCs. A decrease in the number of memory B cells or an increase in the number of naive B cells suggests a higher risk of metastasis in NSCLC.¹²²

In terms of metabolism, TIBs also exhibit heterogeneity. (Fig. 2c) In HCC tissues, activated TIBs have higher lipid metabolic activity than plasma cells and other TIBs, while other TIBs show reduced metabolic activity.⁷⁴ Three energy metabolic pathways—oxidative phosphorylation, nitrogen, and sulfur metabolism—differ among TIB subpopulations, with plasma cells having the highest oxidative phosphorylation activity and other TIBs showing incomplete metabolism. Glutamine-derived metabolites promote the differentiation of TIBs through the extrafollicular pathway, generating atypical memory B cells (AtM B cells), which express dual specificity phosphatase 4 (DUSP4), integrin subunit alpha X (ITGAX), Fc receptor-like 5 (FCRL5) zinc finger e-box binding homeobox 2 (ZEB2), and FGR proto-oncogene (FGR), which may lead to cancer progression.⁴ Stronger signals of CD56⁺ NK cells and immature dendritic cells were found in the high-metabolism tumor areas of cervical squamous cell carcinoma, while more eosinophils, immature TIBs, and Treg cells were observed in the low-metabolism tumor areas.¹²³ TIBs expressing tyrosine typically exhibit a proinflammatory phenotype, whereas TIBs expressing arginine demonstrate a regulatory phenotype in melanoma.¹²⁴ In NPC, GC B cells differentiate into plasma cells.¹²⁵ GC B cells show activated pyruvate metabolism and the MYC proto-oncogene (MYC) pathway, while plasma cells upregulate glycolysis and macrophage chemotaxis pathways.

Lifestyle may also contribute to the heterogeneity of TIBs. Smokers exhibited significantly elevated plasma cells with different differentiation trajectories. TIBs in smokers with LUAD are mainly located in CXCL13⁺ LMA, with increased diversity of BCR clonal types, but as the pathological stage of LUAD increases, there is an elevated fraction of CD4⁺ Tregs.⁷⁷ In LUAD patients, smokers have an increasing number of mature TLSs, with higher CCL21 secretion.¹²⁶ Benzopyrene in tobacco boosts CCL21 expression by retaining the aryl hydrocarbon receptor on its promoter. The CCL21-CCR7 axis enhances CD4⁺ T-cell and CD20⁺ TIB interactions, potentially promoting TLS formation.

In summary, TIBs exhibit significant heterogeneity in tumors, which poses challenges in TIBs research. However, this also indicates ample room for intervention to modulate TIBs, enhancing the response to ICI treatments and ultimately improving patient outcomes.

Multifaceted role of B cells in the tumor microenvironment

The TIBs in cancers can influence immunity and tumor development through various mechanisms. Among 69 reports on 19 types of cancer, 50.0% of the patients reported positive prognostic effects of CD20⁺ TIBs, while the remaining patients showed neutral (40.7%) or negative (9.3%) effects.¹²⁷

The antitumor effect of TIBs in cancers

In HCC, “hot” tumors with high immunological activity show increased TIBs infiltration. These tumors have significant immune cell infiltration, especially effector lymphocytes, which are activated and can attack tumor cells.¹²⁸ (Fig. 3a) This pattern of infiltration is indicative of a favorable prognosis, suggesting that the presence of TIBs may actively enhance antitumor immune responses in HCC patients.^129,130 In HCC, IgD^-IgG⁺CD27^-CD38^- TIBs are mainly concentrated at the tumor invasive margin.¹³¹ A high density of margin-infiltrating TIBs is significantly associated with improved OS and recurrence-free survival. The expression of CCL5 in HCC tissue is lower than that in adjacent nontumorous tissues. A deficiency in CCL5 may result in diminished recruitment of TIBs and reduced IgM secretion, potentially facilitating tumor progression.¹³² In hepatic malignancies, HCC tissues show a reduced proportion of total TIBs compared to nonneoplastic tissues, but plasma cell abundance remains unchanged.¹³³ There is also reduced expression of antigen presentation-related genes. Increased TIBs infiltration in the TME correlates with better prognosis for HCC patients. TIBs frequently express the precursor of nociceptin (PNOC), and an increased level of TIB infiltration has been correlated with improved prognoses in patients with cholangiocarcinoma.¹³⁴ In breast cancer, TIBs are mainly in the stroma, separate from the cancer epithelium, with most breast cancers showing widespread TIB infiltration. Higher TIB counts in the TME correlate with better outcomes for patients.¹³⁵ In breast cancer, memory B cells are associated with a good therapeutic response.¹³⁶ Multivariate analysis revealed that a lower percentage of CD19⁺ TIBs and a positive Epstein-Barr virus (EBV) DNA test independently predicted poorer 5-year PFS in NPC patients.¹³⁷ Based on scRNA-seq data, in the cohort of HPV⁺ cervical cancer patients, CD8⁺ T cells and B cells are downregulated.¹³⁸ In contrast, Treg cells and CD4⁺ T cells are upregulated. An increase in the expression of naive B cells or CD8⁺ T cells favors the survival probability of cervical cancer patients. TIBs and cytotoxic cells demonstrate significant predictive accuracy for lymph node metastasis in papillary thyroid carcinoma.¹³⁹ TIBs and NK cells are associated with favorable prognoses in papillary thyroid carcinoma patients, whereas tumor-associated CD56^high NK cells correlate with poor prognoses in patients with papillary thyroid carcinoma. In metastatic melanoma, the presence of CD8⁺ T cells and CD20⁺ TIBs is linked to better survival. Tumors with high TIB density often have more T-cell factor 7 (TCF7)⁺ naive or memory T cells.⁴⁷ This suggests a synergistic interaction between TIBs and other immune cells in the TME, enhancing antitumor responses.

Fig. 3.

Antitumoral and protumoral roles of TIBs. a Anti-tumor effect of TIBs: Tumor-associated antigens (TAAs) are phagocytosed by dendritic cells and recognized by the BCRs on TIBs. TIBs present processed antigens on major histocompatibility complex (MHC)-I and MHC-II to CD8⁺ and CD4⁺ T cells while providing CD80 costimulation, and T-cell CD40L reciprocally drives TIB proliferation and differentiation into memory B cells, plasmablasts, and plasma cells (PCs). Within the tumor microenvironment CCL5 recruits TIBs and enhances antibody production, complement C3 ligation of CR2 promotes expansion activate T cells. TLS further suppress M2 tumor-associated macrophages (TAMs) and regulatory T cells. b The protumor effect of TIBs: Through receptor–ligand interactions, cytokine secretion, metabolic editing, exosome release, and Breg expansion, they suppress CD8⁺ T-cell cytotoxicity and DC priming, polarize M2 TAMs, trigger epithelial–mesenchymal transition and expand Tregs, thereby fostering immune tolerance and tumor progression. Figures were created with Adobe Illustrator. FcγRII Fcγ receptor II, LIHC Liver Hepatocellular Carcinoma, COAD Colon Adenocarcinoma, PAAD Pancreatic Adenocarcinoma, SKCM Skin Cutaneous Melanoma, BRCA Breast Invasive Carcinoma, LUNG Lung Cancer, ESCA Esophageal Carcinoma, STAD Stomach Adenocarcinoma, RCC Renal Cell Carcinoma, OV Ovarian Serous Cystadenocarcinoma, NSCLC Non-Small Cell Lung Cancer, TCR T-cell receptor, BCR B-cell receptor, TAMs tumor-associated macrophages, CR2 Complement C3d receptor 2, CCL5 C-C motif chemokine ligand 5, BCL-2 BCL2 apoptosis regulator, TGF-β Transforming Growth Factor-β, BAFFR B-cell activating factor receptor, HMGB1 High mobility group box1, TIM-1 T-cell immunoglobulin and mucin domain-containing protein, Acar acylcarnitine, Treg Regulatory T cell, Breg Regulatory B cell, TLR toll-like receptors, TLS Tertiary lymphoid structure, TIBs tumor-infiltrating B cells

TIBs possess the capability to modulate the TME through complex interactions, thereby exerting inhibitory effects on cancer progression. In breast cancer, chemotherapy-induced phosphatidylserine externalization activates complement C3, engaging TIBs via complement receptor (CR) 2.⁴⁴ This process upregulates ICOSL on TIBs, which costimulates T cells via the ICOSL-ICOS axis, activating their tumoricidal functions and enhancing antitumor immunity. In hepatitis B virus (HBV)-related HCC, CXCR5⁺CD8⁺ T cells induce tumor apoptosis while sparing TIBs.^140,141 In melanoma, plasmablast-like CD20⁺ TIBs express chemokines that facilitate the recruitment of T cells, thereby increasing the efficacy of anti-PD-1 antibodies and enhancing T-cell activation.¹⁴² Furthermore, B cells possess the intrinsic capability to exert antitumor effects through the direct elimination of tumor cells.¹⁴³ In breast cancer, blocking IL-10 can boost the function of B cells from tumor-draining lymph nodes.¹⁴⁴ These activated B cells can express factor-related apoptosis ligand (FasL) and directly kill tumor cells through a FasL dependent, antigen-specific mechanism in vitro. In soft tissue sarcoma, the subpopulation of exhausted B cells is reduced in patients who have received treatment for more than 12 months.¹⁴⁵ The unique natural IgM repertoire of B-1 cells can inhibit tumor growth and induce tumor cell death.¹⁴⁶ These cells can also specifically recognize tumor spheroids through monoclonal natural IgM antibodies.

Antitumor effects of B cells in the immune response

TIBs are essential for the formation of a robust immune response against antigens, underscoring the critical nature of TIBs in orchestrating effective antitumor immunity. (Fig. 3a)

TAAs are a class of antigen molecules present on both tumor cells and their normal counterparts. TAA expression is often upregulated during the proliferative and malignant transformation phase of tumor cells.¹⁴⁷ Historically, it was postulated that TAAs were insufficient in generating robust antitumor immune responses, given that the proteins expressed by most tumor cells closely resemble those of normal tissue cells, with only a minority of tumor cells producing specific antigens detectable by the immune system. However, within the TME, TIBs can be activated by autoantigens, thereby exhibiting characteristics similar to those observed in autoimmune conditions and shaping the humoral immune response.¹⁴⁸ Furthermore, following ICI therapy, patients often experience immune-related adverse events (irAEs), which have been linked to the dysregulation of TIBs’ immune functions.^149,150

Enhancing the function of APCs can bolster the body’s ability to combat cancer. In patients with CRC liver metastasis, applying IL-10 neutralizing antibodies has been shown to improve the functionality of MHC-I or MHC-II and increase the effectiveness of CAR-T therapy.¹⁵¹

Researchers have acknowledged that TAAs have the potential to overcome immune tolerance and induce antitumor immunity. Studies have revealed two types of tumor-reactive autoantibodies: one that relies on somatic hypermutation to acquire tumor-binding capacity, and another that is autoreactive at the germline-encoded stage.^152,153 This implies that tumor-reactive autoantibodies can either be innate or evolve through an antigen-driven selection process. Significantly, the inoculation of tumor cells characterized by a high tumor mutation burden, induced by ultraviolet light, in close proximity to tumor tissues with a lower mutation burden, has been observed to cause the regression of the entire tumor effectively.¹⁵⁴ This phenomenon highlights the critical role of epitope spreading in activating tumor immunity and the subsequent enhancement of antitumor immune responses. APCs isolated from tumor-draining lymph nodes of cancer patients show an increased percentage of tumor antigen-specific B cells.¹⁵⁵ They are capable of inducing autologous T-cell responses in vitro. A total of 68.3% of patients expressed ≥5 TAAs and coregulatory clusters simultaneously, and endogenous humoral responses against ≥1 TAA were detected in 53.7% of patients.¹⁵⁶ We found that T-cell abundance was correlated with the expression of genes related to TAAs and antigen presentation, and that autologous CD40-activated B cells could induce and enhance T-cell immune responses.

Antigen epitope spreading encompasses a variety of mechanisms that can be broadly categorized into two types: intramolecular and intermolecular spreading. Intramolecular spreading refers to immune responses initiated by different epitopes within the same protein. In contrast, intermolecular spreading involves immune responses triggered by epitopes from distinct proteins due to immunological stimulation.¹⁵⁷ The concept of intermolecular immunity involves targeting highly immunogenic epitopes, with antigen spreading occurring as the immune response intensifies.¹⁵⁸ This plays a key role in autoimmune diseases. In breast cancer mouse models, a vascular endothelial growth factor receptor (VEGFR)-2 vaccine based on a single peptide segment induces epitope spreading. Among the various peptides, kinase insert domain receptor (Flk-E1) and Flk-I1 showed the most significant effects, while Flk-E2 showed the least. Similarly, in the context of autoimmune diseases, TLSs have been implicated in epitope spreading, leading to immune dysregulation and the generation of immune responses against self-antigens.¹⁵⁹

The existence of TAAs triggers the production of tumor-associated autoantibodies. It is worth noting that tumor-associated autoantibodies are widely present in cancer patients and are helpful for cancer diagnosis and predicting cancer stage. In breast cancer patients, the diversity of autoantibodies increases and is associated with the cancer stage.¹⁶⁰ Before and after surgery, glioblastomas and meningiomas have 350-800 differentially reactive antigens.¹⁶¹ The preoperative and postoperative sera have approximately 20-30% similarity and 10-15% similarity in tumor-associated autoantibodies, respectively. Tumor-associated autoantibodies have been proven to have the potential as biomarkers for cancer detection.¹⁶² We have compiled recently reported tumor-associated autoantibodies and their combinations, which provide an important basis for the early diagnosis of cancer and treatment monitoring.^163–190 (Table 1)

Table 1.

Antibody functionality about B cells in tumor

Cancer entities	Sample size	Methods	Protein abbreviation		References
Lung cancer	377 patients with pulmonary nodules	ELISA	P53, PGP9.5, SOX2, GAGE7, GBU4-5, CAGE, and MAGE-A1	Individuals with elevated antibody levels have an increased risk of developing lung cancer.	163
Pancreatic adenocarcinoma	338 Pancreatic adenocarcinoma patients, 294 normal healthy volunteers, 122 chronic pancreatitis patients and 100 patients with non-PAAC malignancies	ELISA	CLDN17, KCNN3, SLAMF7, SLC22A11, and OR51F2	Individuals with elevated antibody levels have an increased risk of developing pancreatic adenocarcinoma	164
Lung cancer	533 lung cancer cases and 454 controls	ELISA	CEA, NSE, CA 125, SCC, CA 15 -3, pro-GRP, and CYFRA 21 -1	Individuals with elevated antibody levels have an increased risk of developing lung cancer.	165
Pancreatic adenocarcinoma	20 pancreatic cancer patients and 20 controls	Engineered glycopeptides on nanoparticle	MUC1	Individuals with elevated antibody levels have an increased risk of developing pancreatic adenocarcinoma	166
Lung, Pancreatic, Ovarian, Esophageal, and Liver cancers	>2,800 individuals with or without cancer	ELISA	ORF 1 p and ORF 2 p	Individuals with elevated antibody levels have an increased risk of developing tumor.	167
Hepatocellular Carcinoma (HCC)	30 HCC sera and 22 normal control sera for the Human Proteome Microarray and 1625 human serum samples for ELISA	ELISA and the Human Proteome Microarray	RAD23A, CAST, RUNX1T1, PAIP1, SARS, and PRKCZ	Individuals with elevated antibody levels have an increased risk of developing HCC.	168
Esophageal Squamous Cell Carcinoma (ESCC)	243 ESCC patients and 243 controls	ELISA	P53, SLC2A1, GNA11, and MMP 1	Individuals with elevated antibody levels have an increased risk of developing ESCC.	169
Non-small Cell Lung Cancer (NSCLC)	97 advanced NSCLC patients with ICIs treatment	the serum positivity	P53, CAGE, MAGEA 4, GAGE 7, UTP 14 A, IMP 2, and PSMC 1	Individuals with elevated antibody levels have an increased risk of developing NSCLC.	170
Lung cancer	433 patients diagnosed with lung cancer and 76 patients with benign lung disease	ELISA	P53, PGP9.5, SOX2, GBU4-5, MAGE A1, CAGE, and GAGE7	Individuals with elevated antibody levels have an increased risk of developing lung cancer.	171
Lung cancer	354 patients with lung cancer and 108 patients with benign pulmonary disease	ELISA	P53, PGP9.5, SOX2, GAGE7, GBU4-5, MAGEA1, and CAGE	Individuals with elevated antibody levels have an increased risk of developing lung cancer.	172
Gastric cancer	570 gastric cancer patients and 373 controls	ELISA	CLDN18, CAGE1, CTAG1A, PBRM1, RASSF7, IMMP2L and COPB1	Individuals with elevated antibody levels have an increased risk of developing gastric cancer.	173
Gastric cancer	51 precancerous lesion, 78 early gastric cancer, 113 advanced gastric cancer	ELISA	RAE 1、PGK 1、NPM 1 and ARF 4	Individuals with elevated antibody levels have an increased risk of developing gastric cancer.	174
Lung cancer	212 lung cancer tissues and 212 control	High-throughput protein microarray and ELISA	SARS, ZPR 1, FAM 131 A, GGA 3, PRKCZ, HDAC 1, GOLPH 3, NSG 1, CD 84, and EEA1	Individuals with elevated antibody levels have an increased risk of developing lung cancer.	175
HCC	25 patients with HCC, 28 patients with liver cirrhosis, and 27 patients with chronic hepatitis	ELISA	PAX5, PTCH1, and GNA11	Individuals with elevated antibody levels have an increased risk of developing HCC.	176
HCC	8 healthy controls, 5 patients with chronic hepatitis B, 5 patients with B-related cirrhosis, and 11 patients with HCC	ELISA	UBE2Z, CNOT3, and EID3	Individuals with elevated antibody levels have an increased risk of developing HCC.	177
AFP-negative HCC	85 negative hepatocellular carcinoma and 85 control	ELISA	BIRC5	Individuals with elevated antibody levels have an increased risk of developing AFP-negative HCC.	178
HBV-Associated HCC	783 samples	ELISA	ZIC2, CDC37L1, and DUSP6	Individuals with elevated antibody levels have an increased risk of developing HBV-associated HCC.	179
Oral squamous cell carcinoma	20 patients and 20 controls	ELISA	NUBP 2	Individuals with elevated antibody levels have an increased risk of developing Oral squamous cell carcinoma.	180
Lung cancer	15,430 individuals	ELISA	P53, PGP9.5, SOX2, GAGE7, GBU4-5, MAGEA1, and CAG	Individuals with elevated antibody levels have an increased risk of developing lung cancer.	181
ESCC	161 patients with ESCC, 49 patients with high-grade intraepithelial neoplasia, and 176 controls	ELISA	CETN 2 and POFUT 1	Individuals with elevated antibody levels have an increased risk of developing ESCC.	182
Urothelial bladder cancer	20 healthy controls, and 10 autoimmune patients	two-dimensional gel electrophoresis and mass spectrometry	ENO1, VDAC2, AKR1B1, SDF2L1, PRDX6, PSME1, HSPB1, and PHB1	Individuals with elevated antibody levels have an increased risk of developing urothelial bladder cancer.	183
HBV-Associated HCC	133 controls, 105 patients with chronic hepatitis, 105 with liver cirrhosis, and 173 with HCC	ELISA	APEX2, RCSD 1, and TP53	Individuals with elevated antibody levels have an increased risk of developing HBV-associated HCC.	184
HCC	119 patients with HCC and 130 controls	ELISA	ANXA1 and MYC	Individuals with elevated antibody levels have an increased risk of developing HBV-associated HCC.	185
ESCC	119 with ESCC and 114 healthy people	ELISA	P53, PGP9.5, SOX2, GAGE7, GBU4-5, MAGE A1, and CAGE	Individuals with elevated antibody levels have an increased risk of developing ESCC.	186
Lung cancer	101 lung benign lesions and 105 early-stage lung cancer patients	The HuProt array	CKAP2, DEPDC1B, DPP4, PARP11, TCP11L2, and TIPARP	Individuals with elevated antibody levels have an decreased risk of developing lung cancer.	187
Pancreatic ductal adenocarcinoma	30 pancreatic ductal adenocarcinoma and 16 chronic pancreatitis, 13 non-ulcer dyspepsia	The serum autoantibody and lectin microarray assays	ACVR2B, GAGE1, LEMD1, MAG EB1 and PAGE1(lgG) and AURKA, GAGE1, MAGEA10, PLEKHA5 and XAGE3aV1(IgA)	Individuals with elevated antibody levels have an increased risk of developing pancreatic ductal adenocarcinoma.	188
Lung cancer	316 patients with lung cancer	ELISA	CAGE, GAGE7, GBU4-5, MAGEA1, P53, PGP9.5, SOX2	Individuals with elevated antibody levels have an increased risk of developing lung cancer.	189
Colorectal cancer	4 colorectal cancer and 3 controls	The high-density protein arrays	RPRD1A	Individuals with elevated antibody levels have an increased risk of developing colorectal cancer.	190

We provides an overview of the antibody functionality related to B cells within the tumor microenvironment. We categorize studies by cancer entities, details the sample size involved in each study, outlines the methods used for analysis, lists relevant protein abbreviations, and cites the corresponding references for further reading

ELISA Enzyme linked immunosorbent assay, P53 Tumor Protein 53, PGP9.5 Protein Gene Product 9.5, GAGE7 G Antigen Family 4 Member 7, G Antigen Family 4 Member 7, RNA helicase autoantibodies 4-5, CAGE Cancer-Testis Antigen, MAGE-A1 Melanoma Antigen Family A 1, PAAC Pancreatic adenocarcinoma, CLDN17 Claudin 17, KCNN3 Potassium Intermediate/Small Conductance Calcium-Activated Channel, Subfamily N, Member 3, SLAMF7 Signaling Lymphocytic Activation Molecule Family, Member 7, SLC22A11 Solute Carrier Family 22 Member 11, OR51F2 Olfactory Receptor Family 51 Subfamily F Member 2, CEA Carcinoembryonic Antigen, NSE Neuron-Specific Enolase, CA 125 Cancer Antigen 125, SCC Squamous Cell Carcinoma Antigen, CA 15-3 Carbohydrate Antigen 15-3, pro-GRP Pro-Gastrin Releasing Peptide, CYFRA 21-1 Cytokeratin 19 Fragment Antigen 21-1, MUC1 Mucin 1, ORF Open Reading Frame, RAD23A RAD23 homolog A, CAST Calpastatin, RUNX1T1 Runt-related transcription factor 1, PAIP1 Poly(A) binding protein interacting protein 1, PRKCZ Protein kinase C zeta, SLC2A1 Solute Carrier Family 2 Member 1, GNA11 G Protein Subunit Alpha 11, MMP1 Matrix Metalloproteinase 1, AURKA Aurora Kinase A, CXCL10 C-X-C Motif Chemokine Ligand 10, FOXM1 Forkhead Box M1, MAGEA4 Melanoma Antigen Family A 4, UTP14A U3 Small Nucleolar RNA-Associated Protein 14 Homolog A, PSMC1 Proteasome 26S Subunit ATPase 1, SOX2 SRY-Box Transcription Factor 2, CFL1 Cofilin 1, EZR Ezrin, PFN1 Profilin 1, CLDN18 Claudin 18, CAGE1 Cancer Testis Antigen 1, CTAG1A CancerTestis Antigen Family 1, Member A, PBRM1 Polybromo 1, RASSF7 Ras Association Domain Family Member 7, IMMP2L Inner Mitochondrial Membrane Peptidase-Like 2, COPB1 Coatomer Protein Complex, Subunit Beta 1, RAE1 Retinoic Acid Early Inducible 1, PGK1 Phosphoglycerate Kinase 1, NPM1 Nucleophosmin 1, ARF4 ADP-Ribosylation Factor 4, ZPR1 Zinc Finger Protein 1, FAM131A Family With Sequence Similarity 131 Member A, GGA3 Golgi-Localized Gamma Ear-Containing ARF-Binding Protein 3, PRKCZ Protein Kinase C Zeta, HDAC1 Histone Deacetylase 1, GOLPH3 Golgi Phosphoprotein 3, NSG1 Neuron-Specific Gene Family Member 1, CD84 Cluster of Differentiation 84, EEA1 Early Endosome Antigen 1, PAX5 Paired Box 5, PTCH1 Patched 1, GNA11 Guanine Nucleotide Binding Protein Alpha 11, UBE2Z Ubiquitin-Conjugating Enzyme E2Z, CNOT3 CCR4-NOT Transcription Complex Subunit 3, EID3 EP300 Interacting Inhibitor of Differentiation 3, BIRC5 Baculoviral IAP Repeat Containing 5, p16 Cyclin-Dependent Kinase Inhibitor 2A, IMP2 Insulin-Like Growth Factor 2 mRNA Binding Protein 2, ZIC2 Zic Family Member 2, CDC37L1 Cell Division Cycle 37-Like 1, DUSP6 Dual Specificity Phosphatase 6, NUBP2 Nucleotide Binding Protein 2, CETN2 Centrin 2, POFUT1 Protein O-Fucosyltransferase 1, ENO1 Enolase 1, VDAC2 Voltage-Dependent Anion Channel 2, AKR1B1 Aldo-Keto Reductase Family 1 Member B1, SDF2L1 Stromal Cell-Derived Factor 2-Like 1, PRDX6 Peroxiredoxin 6, PSME1 Proteasome Activator Subunit 1, HSPB1 Heat Shock Protein Family B Member 1, PHB1 Prohibitin 1, ANXA1 Annexin A1, CKAP2 Cytoskeleton Associated Protein 2, DEPDC1B DEP Domain Containing 1B, DPP4 Dipeptidyl Peptidase 4, PARP11 Poly(ADP-Ribose) Polymerase Family Member 11, TCP11L2 T-Complex Protein 11 Like 2, TIPARP TCDD Inducible Poly(ADP-Ribose) Polymerase, ACVR2B Activin A Receptor Type 2B, GAGE1 G Antigen 1, LEMD1 LEM Domain Containing 1, MAGEB1 Melanoma Antigen Family B Member 1, PAGE1 P Antigen Family Member 1, AURKA Aurora Kinase A, GAGE1 G Antigen 1, MAGEA10 Melanoma Antigen Family A Member 10, PLEKHA5 Pleckstrin Homology Domain Containing Family A Member 5, XAGE3aV1 X Antigen Family Member 3a Variant 1

Although studies have shown that TIBs in the TME can function as APCs, their antigen-presenting capacity is relatively weak, limiting the proliferation of CD4⁺ T cells.¹⁹¹ Epitope spreading is likely in TLSs or LMAs in “hot” tumors. Do TIBs in autoimmune diseases develop similarly? Understanding the mechanisms of autoimmune responses in immunotherapy could help explore antitumor responses.

Antibody—induced antitumor mechanisms

Engineered antibodies designed for therapeutic applications can play a significant role in antitumor immunity, presenting a promising strategy for cancer treatment. For example, recombinant adinbitor (rAdinbitor) has demonstrated efficacy in reducing the expression of vascular endothelial growth factor (VEGF) in murine tumors.¹⁹² This reduction correlates with a decrease in both the quantity and size of tumor vasculature, while simultaneously increasing serum levels of IgG and IL-18. In the context of human IgG1, a specific substitution at glycine 396 to arginine 396 has been shown to promote the differentiation of transitional TIBs into plasma cells.¹⁹³ This process enhances antibody production and improves TAA presentation and antibody-dependent phagocytosis of tumor cells, thereby strengthening the immune response against cancer.

The type of antibody is conducive to our understanding of the antitumor response. The IgG1/IgA ratio serves as a prognostic indicator for bladder cancer subtypes and in the IMVigor 210 study cohort, demonstrating significant correlations with cytotoxic gene signatures, T-cell receptor signals, and IL-21-mediated signaling.¹⁹⁴ In high-grade serous ovarian cancer, the humoral response is predominantly characterized by the production of polyclonal IgA.⁴⁸ This IgA binds to the polymeric immunoglobulin receptor (pIgR), leading to alterations in cancer cell transcriptional programs, notably upregulating IFN-γ-related pathways and augmenting T-cell cytotoxicity, thereby exerting anticancer effects. In patients with RCC, tumors positive for TLSs that demonstrate a high prevalence of IgG⁺ plasma cells and IgG staining on apoptotic malignant cells are indicative of active antitumor effects.⁸³ The presence of IgG-stained tumor cells is positively correlated with responsiveness to ICI therapy and PFS.

Tertiary lymphoid structures—antitumor immunity

TLSs containing a large number of TIBs also play a crucial role in the antitumor process. (Fig. 3a) In the context of gastric cancer, the presence of TLSs is linked to tumor size and grade.⁹⁰ A higher density of TLS is associated with increased OS rates postsurgery and enhances the efficacy of anti-PD-1 inhibitor treatment. The proliferation of TLS is positively associated with the infiltration of memory B cells and plasma cells. Concurrently, an increase in TLSs is inversely correlated with M2 TAMs and Tregs.¹⁹⁵ The expression levels of Killer cell lectin-like receptor K1 (KLRK1) and Granzyme A (GZMA) are implicated in TLS formation, which is indicative of a favorable prognosis. In high-grade serous ovarian cancer, a substantial aggregation of plasma cells is observed encircling the TLS.¹⁹⁶ These plasma cells exhibit mature oligoclonal IgG transcripts, suggesting an antigen-specific immune. TLSs are present in metastatic melanoma, where they produce IgA, and both cellular and humoral immune responses are mounted against the melanoma.¹⁹⁷ In resectable and unresectable HCC patients treated with atezolizumab and bevacizumab, CD4⁺ and CD8⁺ stem-like T cells are primarily localized within T-cell aggregates.¹⁹⁸ The differentiation of CXCL13⁺CD4⁺ T cells correlates with the establishment of a plasma cell microenvironment, which is predictive of clinical outcomes. In advanced NSCLC patients treated with PD-1 inhibitors and anlotinib, higher TLS counts, higher CD20⁺ TIB proportion in TLSs, higher CD8⁺ T-cell density in tumors, and more TLSs within 20 micrometers of tumor cells correlate with higher objective response rates and PFS.¹⁹⁹ Papillary thyroid carcinoma patients with higher B-cell gene expression and more mature TLSs tend to have higher survival rates and better prognoses.²⁰⁰

The pro-tumor effect of TIBs in cancers

B-cell-mediated immunosuppression is common. TIBs with immunosuppressive features in the TME weaken immune responses, affect immune cells, and remodel the microenvironment. (Fig. 3b)

TIBs are pivotal in promoting immune evasion within the TME. IL-17a can inhibit the expression of miR-15a/16, promote the activation of NF-κB and signal transducer and activator of transcription-1 (STAT1), and reduce the production of chemokines CXCL9 and CXCL10, thereby decreasing the chemotaxis of IgA⁺ plasma cells and promoting the occurrence and development of colon cancer.²⁰¹ In advanced CRC, leucine-tRNA-synthase-2 (LARS2)⁺ TIBs are identified in both mice and humans, and are characterized by TGF-β1 regulation, leucine preference, and active mitochondrial aminoacyl-tRNA synthesis.²⁰² These cells are located outside TLSs, and are associated with CRC proliferation and shorter patient survival. Erbin gene expression in platelets suppresses mitochondrial oxidative phosphorylation and reduces acylcarnitine secretion, impairing mitochondrial function in TIBs and weakening antitumor immunity.²⁰³ Furthermore, IL-10⁺ TIBs secrete GABA, which facilitates the differentiation of monocytes into M2 TAMs and inhibits the cytotoxic function of CD8⁺ T cells.¹⁶ In LUAD, G protein-coupled receptor (GPR) 56⁺ TIBs correlate with reduced HLA-DR⁺ and CD40⁺ cells, indicating increased plasmablasts and decreased memory B cells.²⁰⁴ This phenotype is associated with tumor markers and a low TIB activation state, contributing to cancer progression. Additionally, overexpression of B-cell activating factor (BAFF) in 4T1 cells enhances the production of IL-10 in CD5⁺ TIBs through interaction with B-cell activating factor receptor (BAFFR), subsequently inhibiting the secretion of IFN-γ by T cells.²⁰⁵ Melanoma resistance to BRAF/mitogen-activated extracellular signal-regulated kinase (MEK) inhibitors is linked to elevated CD20 and IGF-1 transcripts in tumors and increased insulin-like growth factor 1 (IGF-1) expression by TIBs.²⁰⁶ Human melanoma cells produce fibroblast growth factor 2 (FGF-2), which activates TIBs to secrete IGF-1. B-cell-derived IGF-1 is crucial for this resistance, due to heterogeneous subpopulations and fibroblast growth factor receptor 3 (FGFR-3) activation. In NSCLC, CD21⁻CD27⁻IgD⁻ TIBs resemble the phenotype of exhausted B cells seen in chronic infections and are associated with a lack of response to ICIs.²⁰⁷

Regulatory B cells in tumor progression

Bregs play a pivotal role within the TIB population. Current research indicates that Bregs encompass various subtypes, including naive B cells, plasmablasts, and plasma cells, which can potentially facilitate tumor development.²⁰⁸ Bregs, distinguished by elevated levels of CD25, CD27, CD86, CD1d, IL-10, and TGF-β, exhibit the capacity to attenuate the proliferative potential of CD4⁺ T cells when cocultured with them.²⁰⁹

IL-10⁺ TIBs primarily provide inflammatory signals during early activation, with IL-10 production peaking at 48 h.²¹⁰ CD25⁺CD39^highIL-10⁺ TIBs exhibit stronger proinflammatory characteristics. The frequency of IL-10⁺ producing circulating B cells in HCC tissues was markedly higher than that in healthy control tissues. Additionally, serum IL-10 levels in HCC patients show a positive correlation with these circulating B cells.²¹¹ An increase in the percentage of IL-10⁺ circulating B cells and elevated serum IL-10 levels indicate tumor progression in the liver. In liver cancer, the activation of monocytes results in over 50% of TIBs exhibiting a low or absent Fcγ receptor II (FcγRII) activation phenotype.²¹² The substantial infiltration of these cells is positively associated with cancer progression, as they can inhibit the function of cytotoxic T cells via IL-10 signaling. In squamous cell carcinoma, TNF-α exhibits anticancer properties by inhibiting Bregs.²¹³ This inhibition is characterized by the suppression of IL-10 secretion and an increase in the production of CD8⁺ T cells that generate IFN-γ.

Exosomes from esophageal squamous cell carcinoma patients inhibit circulating B-cell proliferation and increase circulating IL-10⁺ B cells and PD-1^high Bregs.²¹⁴ Exosome-derived high mobility group box 1 (HMGB1) activates TIBs and promotes the expansion of Tim-1⁺ Bregs via TLR2/4 and mitogen-activated protein kinase (MAPK) signaling pathways.²¹⁵

In HCC, TIBs with high expression of PD-1 display a CD5^highCD24^-/+CD27^high/+CD38^low phenotype.²¹⁶ The upregulation of Bcl6 mediated by TLR4 is crucial for the induction of PD-1^high TIBs, which can obstruct the PD-1/PD-L1 interaction in T cells through IL-10 signaling. Using anti-PD-1 or anti-PD-L1 can eliminate the inhibitory effect of Bregs. IgA⁺ TIBs express PD-L1 and IL-10, and directly inhibit cytotoxic CD8⁺ T cells, accelerating the occurrence of liver cancer.²¹⁷ In tongue cancer, the levels of TIBs are higher than those in the adjacent normal tissue.²¹⁸ This elevation in TIBs is linked to increased Bcl-2 apoptosis regulator (BCL-2) levels, which correlate with a rise in Bregs. These Bregs facilitate the conversion of CD4⁺CD25^- T cells into Tregs. The level of Breg in bladder cancer tissues is higher than that in adjacent tissues, and positively correlates with the degree of malignancy.²¹⁹ Risk signatures constructed based on Breg-related genes (such as CD96, 2’-5’-Oligoadenylate synthetase 1 (OAS1), and Chorionic somatomammotropin hormone 1 (CSH1)) can robustly classify prognosis and predict the sensitivity to immunotherapy.

Naive B cells may exhibit immune-suppressive functions in certain TMEs and can inhibit T-cell responses through high expression of PD-L1. PD-L1⁺ TIBs are upregulated in advanced melanoma and enriched in metastatic tumors, exhibiting a naive B-cell-like phenotype.²²⁰ In early-stage patients, naive B cells express low levels of PD-L1 and are unable to suppress T-cell responses, whereas in advanced-stage patients, naive B cells with moderate PD-L1 expression can significantly suppress T-cell responses in a PD-L1-dependent manner. Neuroendocrine-differentiated gastric cancer exhibits a significantly stronger suppressive TME, with increased but immature TLSs and high densities of naive B cells and follicular Tregs, and is significantly correlated with tumor growth and invasion.²²¹ Furthermore, a positive correlation has been identified between the expression of genes associated with glycolysis and cholesterol biosynthesis and the infiltration of naive B cells.²²² Notably, reduced infiltration of naive B cells into the TME is indicative of extended survival in patients with HCC. Reduced infiltration of naive B cells is associated with extended patient survival, which is similar to the prognostic significance of Bregs in some tumors.

B cells in tumor metastasis

In addition to their presence in tumors and peritumoral regions, B cells within tdLNs significantly influence disease progression. In breast cancer, TIBs secrete high levels of IgG antibodies targeting heat shock protein (HSP) A4, which upregulates cyclooxygenase 2 (COX2)-mediated prostaglandin E2 (PGE2) secretion. This induces lymph node stromal cells to secrete stromal cell-derived factor-1α (SDF1α), accumulating B cells in tdLNs.²²³ This process is crucial for establishing a premetastatic niche and enhancing tumor cell migration to draining lymph nodes, promoting metastasis. In the tdLNs of mouse triple-negative breast cancer, significant expansion of total B cells and plasma cells was observed.²²⁴ According to the results of the scRNA-seq data, LAG-3 expression may serve as a marker of T-dependent activation in B cells, and patients with LAG-3^high B-cell transcription levels exhibited longer progression-free intervals. Neutrophils recruit innate-like B cells by inducing CXCL13 expression.²²⁵ These B cells expand regulatory T cells via IL-10 secretion, promoting early-stage ovarian cancer omental metastasis.

Antibody—mediated protumor mechanisms

Antibodies secreted by TIBs are recognized for their substantial influence on the TME, affecting the course of cancer progression. A correlation has been observed between autoimmune diseases and the development of cholangiocarcinoma, with antibodies targeting glycoprotein 2 (GP2) implicated in the pathogenesis of large bile duct diseases, consequently increasing the risk of cholangiocarcinoma.²²⁶ In HCC, IgG⁺ plasma cells are recruited by TAMs via the CXCR3-CXCL10 axis, while in colorectal liver metastases, IgA⁺ plasma cells are attracted by tumor cells via the CCR10-CCL28 pathway.²²⁷ Increased IgG⁺ plasma cells and TAMs in liver cancer are linked to poorer survival, whereas higher IgA⁺ plasma cells and neutrophils in colorectal liver metastases indicate a worse prognosis. In melanoma, CD22⁺ TIBs and IgG4⁺ plasma cells accumulate within the TME and express IL-10, IL-4, and tumor-reactive IgG4, which can inhibit IgG1-mediated antitumor functions by reducing FcγRI activation.²²⁸ The overexpression of the Fc fragment of IgG binding protein in HCC is associated with poor prognosis.²²⁹ The Fc fragment of the IgG binding protein is closely related to classical tumor regulatory targets and signaling pathways and is involved in the regulation of immune infiltration in HCC. In glioblastoma, CCL2-CCR2-recruited plasma cells secrete IgG that drives glioma stem cell proliferation via the FcγRIIA–AKT–mTOR axis.²³⁰

Furthermore, the posttranslational modifications of antibodies are intricately associated with the pathogenesis of cancer. In lung cancer, the octamer-binding transcription factor 4 (OCT4) and sex determining region Y-box 2 (SOX2) have been identified as pivotal factors that enhance the expression of sialic acid immunoglobulin G (SIA-cIgG), thereby activating the c-Met-SOX2 signaling cascade, which promotes the stem-like properties of cancer cells.²³¹ Similarly, tumor-derived IgG that activates SOX2 has been reported to sustain the stemness of prostate cancer cells.²³² Neutralization of the neutrophil surface receptor Siglec-9 enhances neutrophil cytotoxicity, thereby inhibiting the progression of breast cancer.²³³ Furthermore, inhibiting immune checkpoints can promote the sialylation of IgG antibodies, facilitating their interaction with TAM FcγR.²³⁴ This interaction subsequently suppresses the STING signaling pathway, reduces the production of type I IFN, and ultimately diminishes the effectiveness of immunotherapy. Cancer cells are capable of secreting IgG into the TME, where aberrantly sialylated Cancer-IgG directly inhibits the proliferation of effector T cells by engaging sialic acid-binding immunoglobulin-type lectins (Siglecs) on CD4⁺ and CD8⁺ T cells.²³⁵ This interaction diminishes the infiltration of these T cells into the tumor tissue, thereby significantly promoting tumor growth. Targeting specific Siglecs, such as Siglec-7/SIA-IgG, offers a potential strategy to enhance immune function and sensitize cancer cells to immune-mediated attacks.²³⁶ In patients with lung cancer, a significant reduction in the galactosylation of IgG, accompanied by an increase in sialic acid content and the presence of more complex, highly branched N-glycan structures, is characteristic of both chronic obstructive pulmonary disease and lung cancer.²³⁷

Antibody secretion is linked to the TME regulation of TIBs. Antibody modification expands their application and complexity, and intervening in this process can help suppress tumors. Further exploration of tumor-related antibodies is needed to uncover new immunotherapy methods.

Tertiary lymphoid structures and tumor—promoting microenvironment

The formation of mature TLSs occurs in the early stages of liver cancer, facilitating the recruitment of T cells, TIBs, and dendritic cells.²³⁸ This process may contribute to immune evasion by cancer cells and promote tumor progression. An increased presence of TLSs in the peritumoral region has been correlated with a poorer prognosis in liver cancer patients, frequently accompanied by heightened infiltration of neutrophils.²³⁹ The higher density of early/primary TLS at the invasive margin is associated with poorer prognosis in NSCLC patients, possibly due to the suppression of TLS maturation caused by an increased density of suppressive immune cells at the tumor invasion front.²⁴⁰ In estrogen receptor (ER)⁺ epidermal growth factor receptor 2 (HER2)^- cases, the infiltration of TLSs into the tumor tissue is associated with an increased pathological lymph node stage and lymph node involvement.²⁴¹ Gastric cancer-derived peritoneal metastases often contain immature TLSs associated with immunosuppressive regulatory leukocytes.²⁴² These immature TLSs are linked to protumorigenic pathways, including T-cell exhaustion and the enhancement of DNA repair pathways in the corresponding cancers. In vitro, CD169⁺ monocyte-derived macrophages promote antibody secretion and IL-6 production by activated B cells.²⁴³ In the primary breast TME, CD169⁺ monocyte-derived macrophages are associated with immunosuppression and TLS functionality. In mature TLSs, progenitor exhausted CD4⁺ T cells promote antitumor immunity by activating B cells to generate plasma cells within the germinal center.²⁴⁴

The functional heterogeneity of TIBs may be caused by differences in surface receptor activation, intracellular signaling pathways, and immune checkpoint expression, leading to immune activation or tolerance. TLS formation and angiogenesis may also play a role. We will discuss these mechanisms further in the following sections.

Signaling pathways and markers of immune regulation by B cells

TIBs influence tumor progression through signaling pathways and receptor interactions, highlighting their potential as therapeutic targets in cancer immunotherapy. We summarize how TIBs influence tumor progression through signaling pathways and receptor interactions, highlighting their potential as therapeutic targets in cancer immunotherapy.

Signaling pathways in TIBs

Cytokine receptor interactions

TIBs express various receptors that receive external signals and elicit responses, playing key roles in B cells.²⁴⁵ We analyzed TIBs’ signaling pathways, focusing on surface receptors and intracellular responses to stimuli, and explored their antitumor mechanisms. Cytokines gather signals from cells such as cancer cells and lymphocytes, mediating effects on TIBs’ proliferation and differentiation and ultimately influencing cancer progression. (Fig. 4)

Fig. 4.

Signaling Pathways in the TIBs. We have summarized multiple signaling pathways in TIBs, including the BCR signaling pathway, the TLR signaling pathway, the CXCR/CCR-related G protein-coupled signaling pathway, the TGF-β signaling pathway, the IFN signaling pathway, the interleukin signaling pathway, and the TNF receptor superfamily signaling pathway, which are involved in functions such as TIBs’ survival, proliferation, differentiation, metabolism, maturation, and immune regulation. Figures were created with Adobe Illustrator. TIBs Tumor-Infiltrating B cells, p phosphate, CCL C-C motif chemokine ligand, CCR CC motif chemokine receptor, CCL C-C motif chemokine ligand, CXCL C-X-C motif chemokine ligand, CXCR C-X-C chemokine receptor, p50 NF-κB p50 subunit, p100 Nuclear Factor Kappa B Subunit 2, NF-κB Nuclear Factor Kappa-light-chain-enhancer of activated B cells, MAPKs Mitogen-Activated Protein Kinases, JNK Jun N-terminal Kinase, TF Transcription Factor, PIP3 Phosphatidylinositol 3,4,5-triphosphate, PI3k Phosphatidylinositol 3-kinase, p38 p38 Mitogen-Activated Protein Kinase, RelB transcription factor RelB, CREB cAMP-response element binding protein, IRAKs Interleukin 1 receptor associated kinases, AKT RAC-alpha serine/threonine-protein kinase, MKK Mitogen-activated Protein Kinase Kinase, TLRs Toll-like receptors, LTβR Lymphotoxin Beta Receptor, BAFFR B-cell activating factor receptor, TGF-β Transforming Growth Factor-β, TβR Transforming Growth Factor-β Receptor, PKC Protein Kinase C, TNFR TNF Receptor, TNF Tumor Necrosis Factor, GDP Guanosine diphosphate, GTP Guanosine triphosphate, IFN Interferon, IFNR Interferon receptor, IKK IκB Kinase, MyD88 Myeloid Differentiation Primary Response Protein 88, TBK1 TANK Binding Kinase 1, NIK NF-κB-inducing kinase, ERK Extracellular regulated protein kinases, MEK Mitogen-activated protein kinase kinase, eIF4B/E Eukaryotic Translation Initiation Factor 4 B/E, BTK B cell Progenitor Kinase, SYK Spleen Tyrosine Kinase, PDCD4 Programmed Cell Death 4, CaM Calmodulin, IRF Interferon Regulatory Factor, STAT Signal transducer and activator of transcription, mTOR mammalian target of rapamycin, AP-1 Activator protein-1, c -FOS Fos proto-oncogene protein, MYC Myc proto-oncogene protein, ETS E26 transformation-specific family, ELK ETS Transcription Factor ELK, JAKs Janus Kinases, CCR(L) CC motif chemokine receptor (ligand), CXCR(L) C-X-C chemokine receptor(ligand), eIF4B Eukaryotic Translation Initiation Factor 4 B

Interleukins

Interleukins exert dual roles of antitumor immunity and immunosuppression in the TME by regulating the activation, differentiation, and antibody secretion of TIBs, as well as their interactions with other immune cells, thereby influencing tumor progression and the efficacy of immunotherapy.²⁴⁶ In the LUAD model, the recognition of tumor antigens by TIBs and T cells is necessary for the generation of IL-21-producing Tfh cells.²⁴⁷ Similar to germinal centers generated by other chronic inflammatory stimuli, within tumor tissues and under the influence of tumors, cytokines such as IL-4 and IL-21 can also promote the differentiation and maturation of TIBs into plasma cells within the TME, which is crucial for the immune response against tumors.²⁴⁸ During the process of TIB survival and development, IL-15 is also required to maintain the activation and survival of TIBs.²⁴⁹ Similarly, IL-12 acts as a cytokine switch. It directly acts on TIBs to promote extrafollicular responses and inhibit germinal center responses.²⁵⁰ Moreover, IL-12 derived from TIBs enhances plasmablast responses and Th1 cell polarization. Secreted IgM regulates immune homeostasis by binding to receptors such as FcμR on the surface of TIBs, which inhibits the expansion of IL-10⁺ TIBs.²⁵¹ However, this phenomenon still needs to be verified in cancer.

Interferons

In tumor tissues, similar to viral infections and autoimmune diseases, interferons play a crucial role in regulating immune responses, specifically by promoting the differentiation of TIBs into plasma cells.²⁵² ScRNA-seq shows that IFN-induced TIBs subsets expand during mucosal healing, mainly in damaged areas, and correlate with colitis severity.²⁵³ Activated B cells disrupt epithelial-stromal crosstalk needed for organoid survival, and chronic inflammation and hyperplasia can lead to cancer. Pathway analysis of TIBs reveals that TIBs derived from NPC are also significantly affected by excessive release of IFN-γ and IFN-α.²⁵⁴ Conversely, B cells derived from nasopharyngeal lymphoid hyperplasia undergo alterations due to inflammatory dysregulation and are significantly associated with better PFS in NPC patients, suggesting that TIBs play a positive role in anti-NPC immunity. Broad IFN signaling convergence across immune cells in HCC patients correlates with immunotherapy response, indicating enhanced TIB function and predicting treatment outcomes.²⁵⁵

Chemokines

The role of the chemokines CXCL/CCL in TIBs primarily lies in regulating the chemotaxis and functions of immune cells, thereby influencing the immune response within the TME.²⁵⁶ Pre-mRNA processing factor 19 (PRP19) is highly expressed in tissues with low TIB infiltration.²⁵⁷ Through its interaction with DEAD-box helicase 5 (DDX5), PRP19 leads to the ubiquitination and degradation of DDX5, disrupting the stability of CXCL12 mRNA. This, in turn, inhibits TIB recruitment and plasma cell differentiation, thereby promoting the development of HCC. After neoadjuvant durvalumab chemotherapy for basal-like triple-negative breast cancer, cases with residual disease exhibited higher expression of macrophage markers and various chemokines, whereas cases with complete response showed higher expression of markers such as IFN-γ and IL-2, as well as markers of activated T cells and B cells.²⁵⁸ TIB subsets stimulated by interferons and TIB subsets associated with germinal centers are significantly enriched in muscle-invasive bladder cancer (MIBC).²⁵⁹ CellChat analysis revealed that CXCL13⁺ T cells play a pivotal role in recruiting CXCR5⁺ B cells and contribute to the formation of TLSs exhibiting distinct follicular structures. Similarly, we found that CXCL12 is associated with increased infiltration of naive B cells in bladder cancer and contributes to prolonged survival times for patients.²⁶⁰ In gastric cancer, tumor cells can influence and recruit plasma cells through CCL28-CCR10 signaling.²⁶¹ Targeting CCL28 can significantly promote the infiltration and function of CD8⁺ T cells in the TME by modulating the function of TIBs and plasma cells. By analyzing RNA-seq data from LUAD, it was found that monocytes or macrophages interact with tissue stem cells and NK cells through the SPP1 signaling pathway, while tissue stem cells interact with T cells and TIBs through the CXCL signaling pathway.²⁶² CXCL9 exerts an antitumor effect in triple-negative breast cancer by recruiting and activating immune cells.²⁶³ High expression of CXCL9 positively correlates with the expression of CXCL10 and CXCL11 and the infiltration of CD19⁺ TIBs, and is associated with prolonged disease-free survival and OS in patients.

Toll Like Receptors

TLRs are a class of pattern recognition receptors primarily located on the surface of immune cells or within cells. They are capable of recognizing pathogen-associated molecular patterns and damage-associated molecular patterns, initiating inflammatory responses, and modulating adaptive immune responses.²⁶⁴ In B16 melanoma mice, it was found that CD40⁺ TIBs contribute to enhancing antitumor immunity and are crucial for the efficacy of combined therapy against PD-L1 with TLR-7/8 agonists, but have no effect on CTLA-4 blockade.²⁶⁵ The presence of CD40⁺ TIBs is closely associated with improved OS. TLR agonist treatment induces rapid production of natural IgM by B-1a cells, activating the classical complement pathway and thereby inhibiting peritoneal tumor growth and ascites development.²⁶⁶ Macrophages significantly enhance the TIBs activity potentiation induced by tumor-derived autophagosomes through cell-cell contact.²⁶⁷ This process relies on the CD40/CD40L interaction, TLR4, and myeloid differentiation primary response protein 88 (MyD88) signaling pathways, and augments the antigen-presenting function of TIBs, facilitating the activation of specific T cells. Upon TLR activation, TIBs producing IL-10 can differentiate into IgA⁺ plasma cells.²⁶⁸ IL-10 derived from TIBs limits Th1/Th17 cell responses in chronic colitis and affects the microbiota through IgA, thereby controlling chronic inflammation and tumorigenesis. A study has shown that TIBs from melanoma patients respond ineffectively to CD40 and TLR9 agonists by upregulating immunomodulatory molecules and secreting cytokines weakly, marked by a relative and absolute loss of CD27⁺ memory B cells, and this is associated with abnormal systemic plasmacytosis.²⁶⁹ This evidence confirms that TLRs play a significant role in the regulation of TIBs, often contributing to tumor prevention and immunity in most cases.

Other Important Receptors on TIBs

In addition, various TIB receptors are involved in immune regulation. There is a negative correlation between serum vitamin D levels and the expression of IL-10 in peripheral B cells in patients with pituitary tumors.²⁷⁰ The vitamin D receptor binds to the transcription factors of IL-10, thereby interfering with the expression of IL-10 in peripheral B cells. In mouse fibrosarcomas, the production of specific antibodies depends on CD11b⁺ myeloid cells, which promote TIB responses, proliferation, activation, and survival by secreting TNF-α.²⁷¹ TIBs secrete tumor necrosis factor-alpha (TNF-α), a cytokine that promotes tumor growth by inducing the production of inflammatory cytokines and simultaneously diminishes the effectiveness of ICIs.²⁷² Additionally, membrane BAFF on tumor-associated neutrophils significantly promotes IgG production through interaction with BAFFR, and induces phenotypic modulation of B cells, facilitating their differentiation into CD45^-B220⁺CD138⁺ plasma cells.²⁷³ In melanoma, BAFF enhances TIB antigen presentation to CD4⁺ helper T cells (Th cells) by upregulating the expression of TIB costimulatory molecules and IL-12a.²⁷⁴ Simultaneously, it upregulates the expression of CD40 and PD-L1 on TIBs, augments the expression of the proinflammatory chemokine receptor CCR6, and promotes the formation of memory phenotypes. These effects are positively correlated with OS. Flow cytometry has confirmed that, compared to healthy individuals, patients with head and neck squamous cell carcinoma exhibit lower levels of TIB expression of transmembrane TNF, FasL, lymphotoxin (LT) α1β2, and TNF-related apoptosis-inducing ligand (TRAIL), resulting in a weakened innate ability for anticancer cytotoxicity.²⁷⁵

TIBs have diverse cytokine receptors that regulate signaling pathways. Targeting these receptors can help TIBs exert antitumor effects and form an antitumor TME.

Intracellular signaling pathways

Upon receiving stimulation from the external environment, TIBs elicit various responses that activate signaling molecules within the cells. This, in turn, prompts TIBs to secrete cytokines themselves and exert significant influences on other cells within the TME (Fig. 4).

BCR signaling pathway

The BCR signaling pathway serves as a classic and crucial intracellular signaling pathway in B cells, playing a vital role in B-cell immune responses to TAAs, as well as in B-cell survival, proliferation, and differentiation.²⁷⁶ The BCR comprises membrane-bound immunoglobulin and the CD79a/CD79b heterodimer. Upon recognition and binding of an antigen by the BCR, the receptor clusters and activates a series of downstream signaling molecules.²⁷⁷ These signaling molecules include the activation of kinase cascades: following BCR clustering, SRC Proto-Oncogene (SRC) family kinases, as well as tyrosine kinases spleen tyrosine kinase (SYK) and Bruton’s tyrosine kinase (BTK), are activated.^278,279 Formation of signalosomes: The activated kinases further activate adapter proteins (such as CD19 and B-cell linker protein (BLNK)) and signaling enzymes (such as phospholipase C gamma 2 (PLCγ2), phosphatidylinositol 3-kinase (PI3K), and Vav guanine nucleotide exchange factor 1 (Vav)), leading to the formation of signalosomes.²⁸⁰ Regulation of cellular behavior: The signals emanating from the signalosomes activate multiple signaling cascades, leading to changes in cellular metabolism, gene expression, and cytoskeletal organization. These changes, in turn, regulate B-cell survival, proliferation, and differentiation into antibody-producing cells or memory B cells.²⁸¹ The CD5 molecule on the surface of B cells promotes B-cell survival by inhibiting BCR signaling events, reducing intracellular Ca²⁺ mobilization, and subsequently stimulating the production of IL-10.²⁸² Conversely, TLRs play a significant role in B-cell responses to external antigen stimulation. The activation of BCR synergizes with signals mediated by CD40 and TLR9 to drive the proliferation of human memory B cells, cell cycle progression, costimulatory molecule expression, cytokine production, and immunoglobulin generation.²⁸³ The interactions between TLR1/2, TLR4, TLR7, and TLR9 in modulating BCR and CD40 during the induction of immunoglobulin class switch DNA recombination, as well as TLR-dependent Ig class switch DNA recombination, enhance the secretion of class-switched Ig and influence B-cell proliferation or IgM expression.²⁸⁴

STAT-related signaling pathways

In liver tumors associated with metabolic dysfunction-induced steatohepatitis, elevated expression of the IL-21 receptor induces and activates IgA⁺ plasma cells via the IL-21R-STAT1-c-Jun/c-Fos signaling pathway.²⁸⁵ In the peripheral blood of patients with cutaneous squamous cell carcinoma, CD19⁺ TIBs are enriched, and the surface TIM-1 modulates the STAT3 signaling pathway, exerting inhibitory functions through the secretion of IL-10.²⁸⁶ The survival of plasma cells relies on STAT-3 phosphorylation, which is typically induced by IL-10, IL-21, and IL-6.²⁸⁷ This process aids B cells in maintaining the expression of cytokines and cytokine ligands, including proliferation-inducing ligand (APRIL), BAFF, IGF-1, VEGF, and stromal cell-derived factor-1α (SDF-1α), thereby facilitating normal B-cell function.

NF-κB-related signaling pathway

Membrane-bound HMGB1 on intact autophagosomes released by mouse tumor cells plays a crucial role in inducing Breg differentiation by activating the TLR2-MyD88-NF-κB signaling pathway in TIBs.²⁸⁸ Exosomes secreted by MC38 mouse colon cancer cells can promote the activation of the NF-κB pathway in TIBs, significantly inhibiting gene pathways related to BCR signaling and antigen processing and presentation in TIBs, while upregulating genes associated with apoptotic pathways, endowing TIBs with Breg characteristics, including the upregulation of IL-10 and TGF-β.²⁸⁹

Other important signaling pathways in TIBs

Other signaling pathways within B cells also play crucial roles in the occurrence and development of cancer. Increased CXCL13 promotes CXCR5⁺ TIB infiltration and BCR diversity, thereby enhancing the activation of CD4⁺ Tfh and tumor-reactive CD8⁺ T cells.²⁹⁰ Following ICI therapy, patients exhibited higher BCR diversity and IFN-γ pathway scores, which were significantly associated with prolonged patient survival. Under hypoxic conditions, TIBs in human NPC activate the MAPK pathway, triggering epidermal growth factor receptor (EGFR)1 and EGFR3 activation, which regulate immunosuppressive factors such as TGF-β1 and IL-10.²⁹¹ EGFR1^highEGFR3⁺ TIBs also activate Treg maturation and immunosuppressive function by secreting IL-16 and TNF-α. CpG island (CpG) stimulation can significantly induce the upregulation of PD-L1 expression in TIBs in pancreatic cancer, potentially through the activation of STAT1 and STAT3.²⁹²

Activated B cells are significantly depleted in CRC with liver metastasis, and immature plasma cell populations correlate highly with metastasis. Mechanistically, the Wnt and TGF-β pathways in cancer cells upregulate the RAC-alpha serine/threonine-protein kinase (AKT)—extracellular signal-regulated kinase (ERK) signaling pathway in activated B cells via the SDF-1-CXCR4 axis, promoting migration through downstream target genes such as matrix metalloproteinase (MMP)-9.²⁹³

Targeting these signaling pathways or modulating TIBs’ functions can enhance antitumor immune responses, providing new strategies for cancer treatment.¹⁴

TIB-specific checkpoint molecules and related pathways

With the rapid development of immunotherapy, understanding of how tumors evade immune attacks has deepened, with immune checkpoints emerging as a research focus. Blocking inhibitory checkpoints can restore immune cells’ antitumor ability, showing efficacy in cancer treatment.²⁹⁴ However, while T-cell checkpoints are well studied, TIB checkpoints remain underexplored. Investigating TIB checkpoints could be key to overcoming drug resistance and improving cancer treatment, offering new strategies for patients.

The immune checkpoint PD-1/PD-L1 is primarily expressed on the surface of activated immune cells, thereby serving as a regulatory mechanism that maintains immune homeostasis. This immune checkpoint has also been identified within TIBs. Targeting PD-1/PD-L1 in TIBs has demonstrated efficacy.²⁹⁵ A study found that the density of CD19⁺ TIBs in invasive breast cancer is higher than that in benign fibroadenomas.²⁹⁶ These TIBs highly express IL-10 and PD-L1 and can differentiate into CD19⁺CD24⁺CD38⁺ TIBs, which induce the formation of CD4⁺CD25⁺ Forkhead box protein p3 (FOXP3)⁺ Tregs. This process is mediated by PD-L1, and blocking PD-L1 contributes to long-term patient survival. In NSCLC, the number of Tfh cells is increased while IL-21 levels are decreased, especially in advanced-stage patients, indicating impaired function.²⁹⁷ Tfh cells induce the differentiation of Bregs, which is negatively correlated with disease-free survival after surgery. In breast cancer, the expression of PD-L1 on TIBs is positively correlated with the presence of tumor-infiltrating T cells.²⁹⁸ It may facilitate the generation of CD4⁺CD25⁺CD127^- Tregs, which inhibit IL-15-mediated NK cell proliferation and T-cell antitumor responses. Furthermore, patients with advanced esophageal squamous cell carcinoma treated with PD-1/PD-L1 inhibitors exhibited a significant increase in plasma cell numbers and achieved prolonged PFS and OS.²⁹⁹ In prostate cancer, a specific subpopulation of PD-L1 expressing plasma cells has been identified, which expresses IL-10 and is associated with the suppression of T-cell function.³⁰⁰

Beyond the PD-1/PD-L1 axis, a range of immunosuppressive checkpoints, such as B and T lymphocyte attenuator (BTLA), CD24, LAG-3, Tim-1/3/4, and T-cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT), play crucial roles in modulating the behavior of TIBs. Under the influence of the cytokines IL-6 and IL-10, there is an increased induction of BTLA⁺CD19^high TIBs via the AKT and STAT3 signaling pathways, which may be indicative of a poor prognosis for patients with epithelial ovarian cancer.^301,302 In breast cancer, CD24^highCD27⁺ Bregs markedly contribute to enhancing multidrug resistance and acquiring stem-like properties in breast cancer cells through the secretion of IL-6 and TNF-α.³⁰³ Consequently, these breast cancer cells promote the activation of CD24^highCD27⁺ Bregs via CD40L-dependent and PD-L1-dependent signaling pathways, thereby establishing a positive feedback loop. CD103⁺LAG-3⁺ TIBs combined with the CXCL13/BIRC3 signature stratify prognosis, drug sensitivity, molecular-immune profiles and immunotherapy outcomes in breast cancer.³⁰⁴ In melanoma, despite the heterogeneous expression of multiple molecules by TIBs, the role of Tim-1 is particularly significant, as it inhibits the type I interferon response and antigen presentation, thereby promoting tumor development.⁴⁹ In PDAC, CD38⁺ TIBs, which express elevated levels of Tim-1 and secrete IL-10 and TGF-β, suppress the cytotoxic activity of NK cells.³⁰⁵ Infiltrating TIM-1⁺ plasmablasts in CRC also inhibit the expression of IFN-γ and TNF-α.³⁰⁶ In a contrasting role, TIM-4⁺ B cells are enriched with proinflammatory TIBs, which reduce the metastasis and growth of B16-F10 melanoma through an IFN-γ-dependent mechanism, whereas TIM-1⁺ B cells are enriched with Bregs that secrete IL-10, thereby suppressing immune responses.³⁰⁷ Furthermore, TIGIT⁺CD20⁺ TIBs are present within gastric cancer and are associated with poor clinical outcomes in patients, who may benefit from adjuvant chemotherapy.³⁰⁸

TIBs express a variety of costimulatory immune checkpoint molecules on their surface, including ICOS/ICOSL, tumor necrosis factor receptor superfamily member 9 (4-1BBL), tumor necrosis factor receptor superfamily member 4 (OX40), CD27, and CD40. The increase in 4-1BBL-expressing B cells induces Granzyme B (GZMB)⁺CD8⁺ T cells via the 4-1BBL/4-1BB axis, enhancing antitumor responses in aged mice.³⁰⁹ In the elderly population, 4-1BBL⁺ TIBs can enhance the aggregation of GranzymeB⁺CD8⁺ T cells by presenting endogenous antigens and upregulating membrane TNF-α protein, thereby augmenting antitumor efficacy.³¹⁰ The application of agonistic OX40 antibodies has been shown to effectively stimulate the immune response of T cells and TIBs against TAAs.³¹¹ In CRC, CD1^lowCD27^high plasmablasts secrete IL-10, which inhibits monocyte expression of IL-17. This inhibition is associated with a favorable prognosis in CRC by mitigating deleterious Th17-mediated inflammation.³¹² In early-stage NSCLC and NPC samples, CD27^-IgD^- TIBs are enriched, exhibiting a negative correlation with the density of CD27⁺IgD^- TIBs.^110,254 In CRC, activation of the CD40 protein on the surface of TIBs can trigger NF-κB signaling, thereby facilitating the recruitment and activation of CD8⁺ T cells.³¹³ This process renders the TME proinflammatory and enhances antitumor immunity. Following chemotherapy for esophageal squamous cell carcinoma, enhanced CD40 signaling in TIBs has been observed to increase antibody production, correlating with prolonged survival.³¹⁴ Nevertheless, some studies have indicated that TIBs with elevated CD40 expression secrete IL-10, IL-35, and TGF-β, potentially inhibiting IFN-γ and suppressing the activity of effector cells such as T cells.³¹⁵ After CTLA-4 inhibition, tumor regression is accompanied by the expansion of T and B cells, leading to the formation of TLSs, which contain follicles, germinal centers, and plasma cells, and some of these TIBs exhibit tumor reactivity.³¹⁶ The glucocorticoid-induced TNF receptor (GITR) agonist DTA-1 enhances antitumor immunity by activating both B cells and T cells. B cells are essential for DTA-1-induced tumor regression, which differentiates GITR costimulation from CTLA-4 blockade and OX40 agonism.³¹⁷ This finding suggests that attenuating B-cell functions may not be beneficial in immunotherapies based on GITR agonism. Notably, research indicates that the therapeutic effectiveness of agonistic GITR antibodies is dependent on the prior depletion of Tregs, underscoring the intricate interaction between stimulatory and inhibitory immune checkpoints in the regulation of the TME.³¹⁸ The infiltration of CD19⁺CD73⁺ TIBs in gastric cancer tissues is significantly higher than that in normal tissues.³¹⁹ These cells produce IL-10 and TGF-β1, which strongly correlate with poorer OS and reduced responsiveness to neoadjuvant immunotherapy, suggesting adenosine metabolism and CD8⁺ T-cell exhaustion. However, the function of CD73 is controversial. The highest expression of CD73 on TIBs is found on class-switched memory B cells, and higher infiltration of CD73⁺ TIBs in CRC is associated with better OS.³²⁰

It is worth noting that many TIBs express more than one immune checkpoint on their surfaces. In HPV⁺ cervical cancer, TIBs may possess both CD39 and PD-L1 as targets, and these TIBs exhibit reduced MHC-II expression and can inhibit the activity of NK cells and CD8⁺ T cells.³²¹ Female patients with high-grade non-MIBC exhibit significantly increased expression of genes related to TIB recruitment and function, as well as immune checkpoint genes, including PD-L1.³²² Targeting LAG-3, TIM-3, and TIGIT for cancer immunotherapy may prove effective, with multitarget interventions implying better therapeutic outcomes.³²³ TIBs are also associated with the expression of immune checkpoints on other immune cells within the TME. In patients with high levels of TIBs in renal clear cell carcinoma, the favorable rates of PD-1, CTLA-4, and TIM-3 are significantly increased in CD4⁺ T cells. This indicates the diversity and complexity of immune checkpoint therapies.³²⁴

Signaling pathways and immune checkpoints regulate TIBs’ behavior, affecting their activation, proliferation, differentiation, and function, and impacting the TME. Researching these mechanisms is crucial for developing new immunotherapy strategies.

Intracellular and intercellular crosstalk in tumor-infiltrating B cells

TIBs are significant immune cells in the TME that play complex roles in tumor onset, progression, and the immune response. Their intracellular signaling involves cytokines, chemokines, and pathways, affecting TIB differentiation and function, and modulating the TME. (Fig. 5)

Fig. 5.

Crosstalk between TIBs and other cells in the TME. In the TME, TIBs are recruited and differentiated by CXCL13, CCL20, CD40L recognition, and IL-2/21 signaling. They secrete IL-10, IL-35, and TGF-β to upregulate T-cell IL-10 and CTLA-4, driving tumor progression, but they also release TNF to induce GZMB-mediated cytotoxicity and IgG to activate FcR on TAMs, prompting IL-6, IL-10, and CCL20 production. BTLA–Herpesvirus Entry Mediator (HVEM) engagement dampens BCR signaling and steers TAMs toward an M2 phenotype, whereas FasL upregulation on TIBs can trigger tumor cell apoptosis. Tumor cells, stimulated by IL-17, suppress CXCL9/10 expression to limit TIB recruitment. Thus, TIBs exert multifaceted and context-dependent regulation within the TME. Figures were created with Adobe Illustrator. TIBs Tumor-Infiltrating B cells, TME Tumor Microenvironment, p phosphate, TF Transcription Factor, TRAF TNF Receptor Associated Factor, NF-κB Nuclear Factor Kappa-light-chain-enhancer of activated B cells, MAPKs Mitogen-Activated Protein Kinases, AKT RAC-alpha serine/threonine-protein kinase, IL Interleukin, cIAP2 Cellular inhibitor of apoptosis-2, CREB cAMP-response element binding protein, NTAF nuclear factor of activated T-cells, JAKs Janus Kinases, SHP SH2-containing Protein Tyrosine Phos-phatase, TLRs Toll-like receptors, TGF-β Transforming Growth Factor-β, TβR Transforming Growth Factor-β Receptor, PKC Protein Kinase C, TNFR TNF Receptor, TNF Tumor Necrosis Factor, SYK Spleen Tyrosine Kinase, AP-1 Activator protein-1, ERK Extracellular regulated protein kinases, MEK Mitogen-activated protein kinase kinase, TCR T-cell receptor, BCR B-cell receptor, TAMs Tumor-associated macrophages, SF1 Tumor Necrosis Factor Receptor Superfamily Member 1, IL4I1 Interleukin 4 induced 1, Fas(L) Factor-related apoptosis (ligand), IgG Immunoglobulin G, CTLA-4 Cytotoxic T-lymphocyte-associated protein 4, FcR Fc Receptors, CCR(L) CC motif chemokine receptor (ligand), CXCR(L) C-X-C chemokine receptor(ligand), BTLA B and T lymphocyte attenuator, STAT Signal transducer and activator of transcription, ICOS(L) Inducible T cell costimulatory (ligand), ELK1 ETS Transcription Factor ELK1, GZMB Granzyme B, IRAKs Interleukin 1 Receptor Associated Kinases, PI3k Phosphatidylinositol 3-kinase, IKK IκB Kinase

Crosstalk of intracellular signals in B cells

Intracellular signaling network in TIBs coordinates multiple signaling pathways within TIBs, working together to regulate various biological behaviors, such as TIB proliferation and differentiation. Induction of granzymeB⁺ TIBs by IL-21 integrates signals mediated by surface BCR and TLRs, which is augmented with the expression of the B-cell marker CD5.³²⁵ Furthermore, we present some examples of intracellular signaling pathway crosstalk in nontumor B cells, which may facilitate our future research endeavors. Complement C3d receptor 2 (CR2) tightly regulates BCR signaling during B-cell differentiation.³²⁶ CR2 is detected in both immature and mature B cells, with high expression on the surface of marginal zone B cells. Notch signaling can regulate CR2 promoter activity in the mature B-cell lineage. Peripheral B cells inhibit B-lymphopoiesis in the bone marrow through the TNF-α/insulin like growth factor binding protein 1(IGFBP-1)/IGF-1 axis, thereby maintaining immune balance.³²⁷ Administration of IGF-1 or anti-TNF-α antibodies to mice can restore B-lymphopoiesis in the bone marrow. Complement impacts B-cell signaling. GC B cells inhibit CD55 and upregulate CD59 via BCL6, allowing C3 cleavage and C3a/C5a signaling without the membrane attack complex.³²⁸ Rapamycin boosts BCR-CD40 signaling, aiding germinal center formation and B-cell affinity maturation.

MiRNAs play a crucial regulatory role in signal transduction within TIBs by modulating RNA transcription and translation processes.³²⁹ Using TCGA data, an analysis of 379 HCC samples showed significant changes in memory B cells.³³⁰ A prognostic ceRNA network was built, revealing a novel pathway involving LINC00261, MiR105-5p, and Selectin L (SELL), which may be potential biomarkers for prognosis and immunotherapy. The upregulation of miR-21 expression in NPC cells and tissues can increase the expression of nuclear factor I A (NFI-A) and IL-10 in B cells, induce the generation of IL-10⁺ TIBs, and subsequently inhibit the activity of CD8⁺ T cells.³³¹ MiRNAs are also crucial in the survival and differentiation of B cells. However, this needs to be validated in tumor tissues. MiR-212/132 are upregulated in B cells in response to BCR signaling, and miR-132 may block early B-cell development and induce B-apoptosis by inhibiting the expression of SRY-box transcription factor 4 (SOX4).³³²

TIBs exhibit diverse and intricate intracellular signaling crosstalk mechanisms, which collectively shape their behavior and function. These complex interactions offer highly promising intervention targets for cancer therapy.

B cells interact with tumor cells, stromal cells, and other immune cells

In this section, we will delve into the complex and multifaceted interactions and communications that occur among various cell types and signaling pathways within the TME. These exchanges include direct cell-to-cell contacts and indirect signaling mediated through soluble factors.³³³ Each direct or indirect interaction type is crucial in orchestrating the intricate and comprehensive immune response, and further examination is warranted to explore whether this interpretation potentially overlaps with established concepts of extracellular B-cell regulation. (Fig. 5)

Direct interactions

Bregs with high expression of CD19⁺ and CD25⁺ in human peripheral blood can promote an increase in Tregs while reducing Th17 cells.³³⁴ In patients with MIBC, CD19⁺ TIBs express surface markers of APCs, demonstrating antigen-presenting function, and colocalize with activated CD4⁺ T cells, indicating a significant increase in OS after adjuvant chemotherapy.³³⁵ RCC can recruit TIBs and induce these cells to overexpress Delta-like canonical notch ligand 4 (DLL4), which promotes renal cancer metastasis by inducing the downstream Notch 1 signaling pathway and activating IL-1β/hypoxia inducible factor 2 subunit alpha (HIF-2α) signaling within cancer cells.³³⁶ Recent studies have elucidated that interactions between ICOS⁺ type 2 innate lymphoid cells (ILC2a) and naive B cells, which exhibit strong ICOSL expression, can induce the activation of the HSP70 gene in advanced liver cancer.³³⁷ This activation leads to the elevated expression of HSP1A and HSP1B in ILC2s, subsequently inhibiting antitumor immune responses and correlating with a poor prognosis for patients. PD-1 blockade increases the infiltration of CD4⁺ T cells into germinal centers, upregulates ICOS expression, and activates ERK signaling, which promotes B-cell differentiation.³³⁸ Inhibition of ERK signaling attenuates ICOS expression and IgG production. In LMAs of esophageal squamous cell carcinoma, double negative B cells are abundant and spatially proximal to Tregs. High-level infiltration of TIBs is associated with shortened OS.³³⁹ In gastric cancer, the HLA-E-KLRC1/KLRC2 pair may mediate interactions between T-cell-like B cells (expressing CD79A, CD20, CD19, CD40) and NK cells, as well as between T-cell-like TIBs and cytotoxic/exhausted CD8⁺ T cells.³⁴⁰ In human NPC, CXCL13⁺cancer-associated fibroblasts promote TIB adhesion and antibody production.³⁴¹ These plasma cells are interspersed among tumor cell aggregates, facilitating apoptosis of EBV-associated malignant cells and enhancing immune therapeutic responses. Muc1^highIL-18^high tumor cells recruit CD24⁺CD44^-CD40^- TIBs, which, in turn, drive macrophage-mediated adaptive immune tolerance through CD200 and BTLA, and facilitate liver metastasis of tumor cells.³⁴² In HCC, TIBs are in close contact with tumor-infiltrating T cells. TIB density correlates with higher granzyme B and IFN-γ expression by T and NK cells.³⁴³ TIBs expressing costimulatory molecules CD27 and CD40 and the activation marker CD38 are also linked to patient survival.

Indirect interactions

Critical intermediaries such as cytokines, metabolites, and exosomes mediate immune cell communication. Cytokines, small signaling proteins secreted by immune cells including TIBs, influence other cells in the TME. In turn, other cells regulate TIB functions via cytokine secretion and metabolic modulation, forming a complex interaction network.

Activated CD4⁺ T cells from HCC stimulate macrophages to produce CXCL10, which binds to CXCR3 on TIBs and differentiates them into IgG⁺ plasma cells.³⁴⁴ Secreted IgG subsequently activates FcR (Fc receptors) on macrophages, producing IL-6, IL-10, and CCL20, facilitating tumor progression. IL-10 secreted by Bregs can significantly inhibit the production of proinflammatory cytokines (including IFN-γ, IL-2, and TNF) in follicular cytotoxic T cells.³⁴⁵ In gastric cancer, activated B cells interact with CD103⁺CD8⁺ Trm cells, enhancing CXCL13 and GZMB secretion and glycolysis via the LTα/TNFR2 axis.³⁴⁶ This is regulated by mammalian target of rapamycin (mTOR) signaling and is TNFR2-dependent for anti-PD-1 therapy efficacy. CD27⁺CD10^- TIBs are enriched in the TME and highly express IL-10, which also significantly enhances IL-10 production from CD4⁺ and CD8⁺ T cells in an IL-10-dependent manner.³⁴⁷ In patients with differentiated thyroid cancer, the IL-10⁺ subset is enriched within CD27⁺ TIBs, inhibiting the expression of IFN-γ from CD4⁺ T cells and the expression of IFN-γ, perforin, and GZMB from CD8⁺ T cells, while promoting the survival of both CD4⁺ and CD8⁺ T cells.³⁴⁸ The density of Tfh cells and innate T cells increases, while the density of most T-cell subsets decreases as the tumor progresses.³⁴⁹ In this process, TIBs are key participants in the core immune network and are associated with prolonged survival. CXCL13 and IL-21 are crucial factors in the Tfh cell/TIB axis. In PDAC, IL-35 secreted by TIBs inhibits the expression of CXCR3, CCR5, and IFN-γ by activating the STAT3 signaling pathway in CD8⁺ T cells, leading to impaired infiltration and effector functions of CD8⁺ T cells, thereby promoting resistance to immunotherapy.³⁵⁰ In CRC, the significant interplay between TIBs and myeloid cell signaling, particularly the CCL8⁺ circulating B-cell/CCR5⁺ T-cell interaction, may represent an antitumor mechanism in advanced CRC tumors.³⁵¹ In cutaneous melanoma, immature and follicular TIBs protect against tumor progression by promoting effector memory T cells and limiting MDSC recruitment.³⁵² However, this effect is weakened by interleukin 4-induced 1 (IL4I1) overexpression, impairing TIB function and enhancing immunosuppression. In immunotherapy cohorts for HCC, patients with a good response exhibit higher infiltration of CCL19⁺ fibroblasts and plasma cells.³⁵³ This process occurs through the CCL19-CCR7 axis, where plasma cells secrete chemokines and promote T-cell activation and leukocyte migration.

In scientific research and clinical settings, we cannot simply categorize the interactions among various cells in the TME as direct or indirect. In neuroblastoma patients, the frequency of γδ Tfh cells in the peripheral blood is significantly higher than that in the normal control group.³⁵⁴ It positively correlates with the number of CD19⁺CD27^high plasma cells but negatively correlates with CD19⁺ TIBs. In microsatellite-stable CRC, CD8⁺CXCR5⁺ follicular cytotoxic T cells may regulate antitumor functions by modulating CD19⁺CD38⁺ TIBs and TLSs.³⁵⁵ The formation of a reticulated network by cancer-associated fibroblasts is mediated by CD8⁺ T cells and relies on CXCL13-induced recruitment of LTα1β2-expressing TIBs.³⁵⁶ This process contributes to developing TLSs composed of discrete T and B-cell zones, which correlate with the overall response to checkpoint immunotherapy. MDSCs secrete TGF-β, which impairs IL-7 and STAT5 signaling in TIBs via cell-to-cell contact.³⁵⁷ This results in suppressed TIB proliferation and differentiation, reduced IgG expression, and weakened TIB-mediated immune responses. In a mouse model of ovarian cancer, a significant influx of MDSCs was found to be associated with the depletion of TIB subsets.³⁵⁸ There was a marked reduction in B1 cells in the peritoneal cavity ascites, and selective loss of B1 and marginal zone B-cell subsets was also observed in the spleen.

TIBs interact with T cells, TAMs, and tumor cells, producing both anti-tumor and tumor-promoting effects. Understanding these interactions can reveal mechanisms of tumorigenesis and progression. Targeting these interactions may offer new cancer treatment strategies.

B-cell activation, tolerance, and multilevel regulatory mechanisms

Understanding the regulatory mechanisms of TIB activation and differentiation is crucial for elucidating their functions in the TME. This section will explore how these multilevel mechanisms respond to external stimuli and mediate biological effects.

B-cell activation or tolerance mechanisms

During B-cell activation and differentiation, naive B cells recognize antigens via BCR, leading to T-cell-dependent or T-cell-independent activation. In the TME, T-cell-dependent activation by TAAs is most common. B cells capture antigens, process them into peptides, and present them to Th cells via MHC II⁺ Th cells bind to B cells via CD40L-CD40, providing costimulatory signals and secreting cytokines such as IL-4 and IL-21, which promote B-cell proliferation and differentiation.^359,360 Activated B cells rapidly proliferate, driven by pathways such as PI3K-Akt-mTOR and NF-κB, which alter metabolism and gene expression. After proliferation, B cells differentiate into memory B cells, plasmablasts, and plasma cells. Memory B cells possess long-term survival ability. Upon re-encountering the same antigen, they can rapidly activate, differentiate into plasma cells, or re-enter germinal centers for antibody affinity maturation.³⁶¹ Plasmablasts are an early differentiated form of activated B cells capable of secreting antibodies but with a relatively short lifespan. Plasma cells, on the other hand, are terminally differentiated B cells that are capable of synthesizing and secreting large amounts of antibodies.³⁶² The differentiation of plasma cells requires the regulation of transcription factors such as B lymphocyte-induced maturation protein 1 (Blimp-1), XBP1, and interferon regulatory factor 4 (IRF4).³⁶³ B cells at different stages possess distinct surface markers.

The regulation of the tolerance mechanism of TIBs involves multiple complex biological processes, possibly leading to immune suppression and tumor progression. First, immune checkpoint molecules can induce the suppression of TIB function, including the regulation of TIM-1, PD-1, TIM-3, TIGIT, and LAG-3.^{308,364–366} These molecules, by binding to their corresponding ligands, transmit inhibitory signals, resulting in TIB dysfunction or exhaustion, thereby weakening the antitumor immune response. Second, metabolites also exert an influence on TIBs differentiation and function.⁴ Additionally, metabolic disorders may affect TIBs’ activation and antibody secretion capabilities by altering their energy metabolic status.³⁶⁷ The intercellular interactions between TIBs and other immune cells in the TME lead to immunosuppressive effects on TIBs. For instance, when TIBs interact with myeloid cells, they may inhibit T-cell function by secreting immunosuppressive cytokines or overexpressing immune checkpoint molecules.³⁶⁸ Furthermore, the interaction between TIBs and Tregs may also enhance immune suppression.³⁶⁹

Comprehensive single-cell multiomics approaches have collectively revealed two distinct developmental pathways of TIBs.⁵² The Extrafollicular (EF) pathway refers to the process in which B cells rapidly differentiate into plasma cells or effector B cells in nonfollicular areas after antigen stimulation.³⁷⁰ This pathway typically involves the help of T cells but does not depend on the formation of germinal centers. Antibodies produced via the EF pathway usually have lower affinity. The germinal center pathway involves B cells differentiating into high-affinity plasma cells or memory B cells through somatic hypermutation and clonal selection in lymphoid follicles or ectopic structures stimulated by tumor inflammation.³⁷¹ The germinal center is crucial for antibody affinity maturation and memory cell generation. Cancer entities categorized under the EF pathway are associated with poorer clinical outcomes and resistance to immunotherapy. Additionally, dysfunctional EF programs have been found to be related to glutamine-derived metabolites through epigenetic-metabolic crosstalk.⁴

Gene expression regulation

Transcription factors regulate gene expression by specifically binding to DNA sequences. B-cell lymphoma 6 (BCL-6) is a key transcription factor regulating B-cell proliferation and differentiation.³⁷² In human B cells, IL-10 upregulates Absent in Melanoma 2 (AIM2) via DNA demethylation, leading to decreased Blimp-1 and increased BCL-6 expression, which promotes the expansion of memory B cells and plasma cells.³⁷³ The BCL-2 protein family regulates apoptosis and B cell survival.³⁷⁴ In memory B cells, decreased NF-κB-driven BCL-2 expression impairs long-term survival.³⁷⁵ In naive B cells, lower NF-κB activity may reduce BCL2 like 1 (BCL-XL) mRNA levels, affecting germinal center survival. IL-21 and CD40 stimulation boosts Bcl-XL levels, rescuing function in both naive and memory B cells.³⁷⁶ Paired box 5 (PAX5) is a key transcription factor in B-cell development that regulates B-cell activation and function via BCR signaling pathways.³⁷⁷ Rack1 maintains PAX5 protein levels, preventing ubiquitination and supporting B-cell maturation, while PAX5 boosts BCR and TLR signaling in mature B cells.³⁷⁸ IRF4 is crucial for B-cell differentiation and affects antibody secretion by regulating immunoglobulin gene expression.⁶⁹ IRF4 regulates XBP1 expression and endoplasmic reticulum structure, modulates mitochondrial quality and reactive oxygen species (ROS) production, and biases B cells toward aerobic metabolism, promoting differentiation into long-lived plasma cells.³⁷⁹ Mice lacking IRF4 in B cells show increased IL-27⁺ Bregs via the interferon regulatory factor 8 (IRF8)/basic leucine aipper ATF-like transcription factor (BATF) axis, while IRF4/BATF activation biases B cells toward IL-35⁺ Breg differentiation.³⁸⁰

Posttranscriptional regulation encompasses the modulation of mRNA splicing and stability.³⁸¹ Protein arginine methyltransferase 5 (PRMT5) in mouse CD19⁺ B cells inhibits CCL22, IGHG1, and IL12a expression while increasing JAK3 and STAT5b expression. CCL22 and IGHG1 expression may be related to poly(A) tail length, and JAK3, STAT5b, and IL12a may be regulated by m6A modification.³⁸² These changes can promote CRC development in mice. The actin-regulatory protein ENAH actin (hMENA) undergoes tissue-specific splicing, with hMENAΔv6 found in LUAD aggressive cancer cells and tumor-associated fibroblasts.³⁸³ hMENAΔv6 inhibits the lymphotoxin β receptor (LTβR) -NF-κB pathway, reduces CXCL13 secretion, and promotes fibronectin production, leading to decreased memory B cells and shorter survival. In esophageal squamous cell carcinoma, XBP1 splicing in response to ER stress activates the innate immune system, increasing the lymphocyte ratio and initiating plasma cell migration.³⁸⁴ In LUAD, high PIMREG expression correlates with poor outcomes and negatively correlates with TIB levels.³⁸⁵

Epigenetic regulation, involving DNA methylation, histone modifications, and noncoding RNA activity, affects gene expression without changing the DNA sequence, adding a regulatory dimension to the functional diversity of TIBs.³⁸⁶ In tumor-bearing mice, TIBs have higher H3K27 acetylation than splenic B cells.³⁸⁷ Lactate enhances H3K27 acetylation and induces IL-10 expression in TIBs, boosting CD40 signaling and cyclic adenosine monophosphate (cAMP)-mediated pathways and promoting Breg generation in the TME. Tet methylcytosine dioxygenase 2 (TET2), an important epigenetic enzyme in TIBs, regulates gene expression by demethylating 5-methylcytosine to 5-hydroxymethylcytosine.³⁸⁸ TET2 activation promotes high IL-10 expression, indicating poor prognosis in liver cancer patients.

Intracellular signals in B cells can also interact with epigenetic modifications of genes. BTB domain and CNC homolog 2 (Bach2) recruits the histone deacetylase 3 (HDAC3) –nuclear receptor corepressor (NCoR) complex to deacetylate and silence Prdm1, restraining plasma-cell differentiation in B cells.³⁸⁹ The CCCTC-binding factor binds to Bcl-6 intron 1 and exon 1A, inducing chromatin modifications that prevent Bcl-6 autoregulation and maintain germinal center cells from differentiating into plasma cells.³⁹⁰

Though reports on epigenetic regulation of TIBs are limited, evidence suggests that multilevel mechanisms significantly influence TIB differentiation and function in the TME. Further research in this area is highly anticipated to better understand its role in tumors.

Mechanisms of extracellular regulation in tumor-infiltrating B cells

TLSs are regularly arranged immune cell structures induced by chronic inflammatory stimuli such as allergies, infections, chronic inflammation, and cancer.³⁹¹ Depending on the nature of the tumor, the proportion of tumors with TLSs varies.^392,393

TIBs are a vital component of TLSs, where they form B-cell follicles to participate in antigen-driven immune responses.³⁹⁴ (Fig. 6) These TIBs are closely related to the maturity and function of TLSs, jointly promoting antitumor immunity.³⁹⁵ The development of TLSs is a multifaceted process analogous to the formation of secondary lymphoid organs. Initially, hematopoietic lymphoid tissue inducer (LTi) cells, characterized as CD3^-CD4⁺CD45⁺ innate lymphoid cells, are recruited to the site. These LTi cells interact with lymphoid tissue organizer (LTo) cells via LTα1β2 and its receptor, LTβR, thereby initiating the foundational assembly of TLSs.³⁹⁶ This interaction induces the production of CCL9 and CXCL5 lymphokines, which, along with the subsequent recruitment of leukocytes facilitated by adjacent high endothelial venules, promote the maturation of TLSs.^397,398 Studies suggest that CCL19⁺ fibroblasts recruit CCR7⁺ TIBs in TLS-positive tumors and liver tissue, with this role being more critical in early stages.⁵⁶ Within TLSs, TIBs undergo low somatic hypermutation, antibody affinity maturation, proliferation, and differentiation, ultimately giving rise to plasma cells and memory B cells.^399,400 Surrounding TLSs, CXCL12⁺ reticular cells, and fibroblasts are strategically positioned, recruiting immune cells via the CXCL12-CXCR4 axis and facilitating prolonged antibody secretion by plasma cells.⁴⁰¹ Follicular dendritic cells attract TIBs through the CXCL13-CXCR5 axis, further promoting antibody affinity maturation of TIBs.⁴⁰² Additionally, Tfh cells play a crucial role in the maturation of TIBs, assisting in antibody class switching through the action of IL-4 and IL-21.^403,404 TLSs serve as a venue for the interaction between T cells and B cells, with TIBs providing costimulatory signals for CD8⁺ T-cell maturation, ultimately enhancing the density of CD8⁺ T cells within tumors.⁴⁰⁵ Correspondingly, TIBs can also mature outside the TLS structure. In the extrafollicular pathway, TIBs are stimulated by TAAs and differentiate directly through the extrafollicular pathway.⁴⁰⁶ In this process, TIBs respond quickly to antigens and differentiate into plasmablasts and memory B cells.

Fig. 6.

Differentiation of TIBs and formation of TLSs. Lymphoid tissue inducer (LTi) cells are recruited by IL-7 and CXCL13 from lymphocytes and stromal cells, respond by secreting IL-17, and attract lymphoid tissue organizer (LTo) cells via LTα1β2. vascular endothelial growth factor C (VEGFC) drives high endothelial venule (HEV) differentiation, and subsequent CXCL13, CCL19, and CCL21 release promotes lymphocyte extravasation to form tertiary lymphoid structures with central dendritic cells encircled by B-cell follicles and T-cell zones. In germinal center pathways, (1) TIBs initially form centroblasts, which proliferate and differentiate with the aid of CXCL12⁺ reticular cells. CCL19⁺ fibroblasts can recruit CCR7⁺ TIBs. (2) Guided by CXCL13, centroblasts migrate toward the center. (3) With the assistance of dendritic cells, TIBs undergo low somatic hypermutation to achieve antibody affinity maturation. (4) Then TIBs gradually decrease the expression of CXCR5 and increase the expression of CXCR4, exiting the TLS center. In this process, TIBs interact with Tfh cells and complete the screening with the help of IL-4 and IL-21. (5) Subsequently, some TIBs differentiate into memory B cells, while others differentiate into plasmablasts and PCs. Plasma cells (PCs) continuously secrete antibodies, primarily IgA and IgG, with the help of CXCL12⁺ fibroblasts. However, some TIBs do not form TLSs but instead follow an extrafollicular pathway. Upon activation by TAAs, they form immunoblasts, which further differentiate into memory B cells, plasmablasts, and PCs that secrete antibodies, primarily IgM and IgG. Figures were created with Adobe Illustrator. TIBs Tumor-Infiltrating B cells, TLS Tertiary lymphoid structure, TAAs Tumor-Associated Antigens, HEVs Tfh cells, Follicular Helper T cells, Th cells T Helper cells, LTα1β2 Lymphotoxin α1β2, LTβR lymphotoxin receptor, AtM B cells Atypical memory B cells

Lymphonets, networks of interacting lymphocytes, form from T-cell clusters and incorporate B cells.⁴⁰⁷ CXCR3 regulates their size and number, while T-cell antigen expression directs their localization within tumors. TLS in ovarian tumors are less developed than in fallopian tube or omental tumors.⁴⁰⁸ A prognostic TLS signature from high-grade serous ovarian cancers indicates that normal mesenchymal stem cells support B-cell function and TLS formation, while cancer-educated mesenchymal stem cells negate this benefit.

Solid tumors can reprogram the host immune system, causing systemic immune suppression. Tumors induce two B-cell abnormality patterns: impaired B-cell generation and systemic accumulation of early B-cell.⁴⁰⁹ These are linked to abnormal myeloid hematopoiesis in the bone marrow. Early B-cell in the latter pattern impair antitumor immunity via nonantigen-specific mechanisms, reducing ICI therapy efficacy.

B lymphocytes are attracted to areas where new blood vessels form and help with new blood vessel growth in both tumors and wounds.⁴¹⁰ In the blood of tumor-bearing mice, CD45⁺CD31^lowVEGFR1^- cells, which represent a subset of naive B cells, serve as a surrogate marker for tumor angiogenesis.⁴¹¹ Their levels increase during active tumor angiogenesis. IL-35 secreted by Bregs inhibits the binding of the proinflammatory transcription factor AP-1 to the intercellular cell adhesion molecule-1 (ICAM-1) promoter and suppresses the activation of vascular endothelial cells.⁴¹²

TIBs significantly influence cellular structures and tumor tissues, facilitating diverse tissue formation and exerting complex effects on tumor immunity. The extracellular regulatory mechanisms of TIBs need further exploration and could become effective therapeutic targets, potentially enhancing the tumor immune response.

B-cell based therapeutic targets and clinical research progress

The methods of tumor treatment have become increasingly diverse, and combined therapy has become one of the approaches to counter tumor drug resistance, enhance treatment effects, and improve patient prognosis.

TIBs in the TME play different roles in tumor suppression. First, TIBs can cooperate with other immune cells, such as CD8⁺ T cells and TAMs, to exert tumor-suppressing effects.⁴¹³ Second, TIBs can act as APCs to activate specific immune responses.⁴¹⁴ Third, TIBs can provide a costimulatory signal for T-cell activation, expanding the immune response.⁴¹⁵ Given the limited number of specific molecules on the surface of TIBs, apart from BCR, CD19, CD20, CD22, CD138, and CD79a/CD79b, current reports have yet to identify other proteins that are specifically expressed on the surface of B cells. At present, in the field of solid tumors, the number of drugs undergoing clinical trials is relatively limited, with only CD20-targeted drugs currently being studied. The clinical trial numbers for these studies are NCT03893019, NCT04787042, NCT0137671380, NCT01032122, and NCT01326702. Therefore, the impact of broadly acting drugs on TIBs is of vital importance.

FDA-approved drugs and registered clinical trials currently

The subpopulations and numbers of TIBs often change during immunotherapy, indicating the potential for developing personalized therapies targeting B cells. ScRNA-seq reveals that gemcitabine plus cisplatin chemotherapy activates an antitumor immune response via CD27⁺IgD⁺IgM⁺ innate-like B cells, which boost Tfh and Th1 cells through the ICOSL-ICOS axis, enhancing cytotoxic T cells in TLS postchemotherapy.⁴¹⁶ Neoadjuvant pembrolizumab immunotherapy enhances the enrichment of memory B cells through the expression of the CPR183 gene in NSCLC and tumor tissues, increasing the infiltration of TIBs in NSCLC tissues and thereby facilitating antitumor responses.⁴¹⁷ In the circulating lymphocytes of patients with RCC, after treatment with nivolumab and/or ipilimumab, the proportion of plasmablasts among total B cells increased significantly, while there was a trend toward an increase in the proportion of switched memory B cells among total B cells. Additionally, the proportion of B cells in peripheral blood decreased markedly.⁴¹⁸ In recurrent and/or metastatic head and neck squamous cell carcinoma, stromal enrichment of TIBs-related genes has been shown to correlate with response to nivolumab.⁴¹⁹ A combination of PD-L1 positivity and a high TIB count in the stroma predicts significantly prolonged PFS and OS. Compared to before treatment, there is a significant decrease in CD4⁺ T cells and CD8⁺ T cells in the peripheral blood of gastric cancer patients after neoadjuvant therapy, while there is no significant difference in the number of TIBs and plasma cells.⁴²⁰ Emerging evidence suggests a correlation between the expression of EIF2S2 and the expression of immune checkpoints PDCD1, TIGIT, and CTLA-4.⁴²¹ This relationship appears to facilitate the infiltration of TIBs and plasma cells into tumor tissues, thereby enhancing the tumor’s responsiveness to therapeutic agents such as paclitaxel and sunitinib and ultimately improving patient prognosis. In patients with well-controlled HBsAg, the combined administration of PD-1 ICIs and tyrosine kinase inhibitors has been shown to reduce TIB infiltration and extend survival time.⁴²² Additionally, neoadjuvant chemotherapy with cabozantinib and nivolumab can enhance the immune response within the TME by activating the key regulatory factor PAX5, which governs TIB activation, promotes TIB maturation, and contributes to antitumor efficacy.⁴²³ The CD73-specific antibody Mupadolimab binds to CD73 on TIBs, promoting the transformation of TIBs into plasmablast-like morphology, and enhancing MHC-II expression on TIBs, thereby promoting antibody production and tumor regression.⁴²⁴ In patients with differentiated thyroid tumors, those who have undergone thyroidectomy and ¹³¹I treatment exhibit significantly lower frequencies of PD-1⁺ TIBs, which facilitates the proliferation and activation of CD4⁺ and CD8⁺ T cells.⁴²⁵

In addition, there are also therapeutic approaches targeting checkpoints on the surface of TIBs, but these studies are still relatively limited and have not yet been approved by the FDA. Targeting TIBs’ receptors or signaling pathways can enhance their antigen presentation and tumor eradication. Agonistic anti-CD40 antibodies or CD40 overexpression via adenoviral vaccines boost TIB infiltration in tumors, strengthening antitumor immunity and improving patient outcomes.^426,427 Activating 4-1BBL⁺TIBs to form potent APCs using CD40 agonists, IFN-γ, and BAFF can enhance T-cell activation and proliferation through the IL-15/IL-15Ra mechanism.^428,429 The TLR9 agonist CpG activates TIBs to adopt a phenotype characterized by high expression of IL-2Rα and ICOS, along with low expression of CD39.⁴³⁰ This phenotype enhances direct interactions between TIBs and T cells, promoting the expansion of potent CD8⁺ T cells with distinct phenotypic traits and antitumor capabilities. Rapamycin inhibits STAT3 and modulates the expression of c-Myc, thereby obstructing the proliferation of TIBs and subsequently inhibiting liver tumor growth.⁴³¹ Administration of a TLR agonist (OK-432, a TLR 2/4/9 agonist) in glioma-bearing mice facilitates the induction of TLS and the maturation of tumor-infiltrating lymphocytes through the interaction between LTα/β and LTβR.⁴³² CAR-T therapy exhibits analogous effects. Post-CAR-T therapy, an enhancement in the antigen-presenting function of TIBs has been observed, which contributes to the synergistic eradication of tumor cells.⁴³³

Therapeutic approaches targeting nonimmune checkpoints on the surface of TIBs are also worth paying attention to, even though these methods have not been approved by the FDA. The humanized antibody protein tyrosine phosphatase 4a3 (PRL3)-zumab specifically targets PRL3, facilitating the recruitment of TIBs, NK cells, and TAMs to the TME, thereby exerting antitumor effects.⁴³⁴ For patients with high levels of IgG1, blocking the inhibitory NK cell lectin-like receptor subfamily C member 1 (NKG2A) receptor with monalizumab makes it easier to activate NK cells and CD8⁺ T cells, which further inhibits tumor growth.⁴³⁵ Furthermore, peroxisome proliferator-activated receptor (PPAR)-δ is markedly upregulated in tumor-induced IL-10⁺ TIBs exhibiting CD19⁺CD24^highIgD^low/-CD38^low or CD38^high phenotypes.⁴³⁶ Treatment with the PPAR-δ inhibitor GSK3787 diminishes the induction of IL-10⁺ TIBs by tumor cells and CD40 binding.

Furthermore, various FDA-approved drugs exert an influence on TIBs, which in turn affects the TME of tumors and treatment responses. We have summarized the clinical trials of FDA-approved drugs (Table 2) and the clinical trials of other drugs (Table 3). Delving deeper into these results can aid in optimizing treatment strategies and enhancing therapeutic outcomes for cancer patients.

Table 2.

The clinical trials of FDA-approved drugs involving TIBs for tumor treatment

Antibody name	Types of antibody	Treatment strategy	Combinational therapy	Cancer entities	Results and mechanism	Clinical trial number
Pertuzumab	IgG1	HER2	Trastuzumab	HER2-amplified cancers that aren’t breast, gastric, or colorectal	Inhibiting the Her2 signaling pathway and enhancing the activation and proliferation of Th1 cells and CD8+ T cells, thereby suppressing tumor growth	NCT06136897
Cetuximab	IgG1	EGFR	Erlotinib hydrochloride	Gastrointestinal Cancer, Head and Neck Cancer, NSCLC and CRC	Blocking the EGFR signal transduction pathway within cells, thereby inhibiting the proliferation of cancer cells. Reducing the production of matrix metalloproteinases and VEGF	NCT00397384
Necitumumab	IgG1	EGFR	Trastuzumab	NSCLC		NCT04285671
Margetuximab	IgG1	EGFR	Retifanlimab and Tebotelimab	Gastric Cancer and Gastroesophageal Junction Cancer		NCT04082364
Siltuximab	IgG1	IL-6	NA	Olid malignant tumors	Tumor cells, promoting cancer cell apoptosis and metastasis inhibition, as well as inhibiting angiogenesis.	NCT00841191
Bevacizumab	IgG1	VEGF	NA	Ovarian Epithelial Cancer and Primary Peritoneal Cancer	Inhibit tumor angiogenesis, and suppress ligand-induced tumor cell proliferation and migration.	NCT00022659
Bevacizumab	IgG1	VEGF	Pembrolizumab and low-dose cyclophosphamide	Ovarian cancer		NCT06083844
Bevacizumab	IgG1	VEGF	CDX-1140	Recurrent serous, endometrioid, clear cell recurrent epithelial ovarian, fallopian tube and primary peritoneal cancer		NCT05231122
Ramucirumab	IgG1	VEGFR2	NA	Gastric carcinoma		NCT01148849
Ramucirumab	IgG1	VEGFR2	NA	Liver Cancer		NCT00627042
Relatlimib	IgG4	LAG-3	Nivolumab	Gastroesophageal Cancer	Weakening the immunosuppressive effects of B cells, enhancing the antigen-presenting activity of B cells. Restoring the cytotoxic activity of T cells, reducing the suppressive effects of regulatory T cells on effector T cells, and strengthening the killing effect on tumors. When used in combination with PD-1/PD-L1, it enhances the therapeutic efficacy.	NCT03610711
Relatlimib	IgG4	LAG-3	Nivolumab and Ipilimumab	head and neck squamous cell carcinoma		NCT04080804
Obinutuzumab	IgG1	CD20	ST-067 and pembrolizumab	Melanoma	Killing Bregs and CD20+ tumor cells.	NCT04787042
Ofatumumab	IgG1	CD20	Dacarbazine			NCT01376713
Rituximab	IgG1	CD20	NA			NCT01032122
Rituximab	IgG1	CD20	veliparib and bendamustine hydrochloride	Solid Tumors		NCT01326702
Daratumumab	IgG1	CD38	Pancreatic Ductal Adenocarcinoma and Refractory NSCLC	KRAS vaccine and Nivolumab	Reduce the immunosuppression of CD38+Bregs and promote T-cell expansion and increased activity.	NCT06015724
Daratumumab	IgG1	CD38	NA	metastatic renal cell carcinoma and muscle invasive bladder cancer		NCT03473730
Daratumumab	IgG1	CD38	JNJ-40346527	Prostate Adenocarcinoma		NCT03177460
Daratumumab	IgG1	CD38	NA	Prostate Cancer		NCT03035357
Isatuximab	IgG1	CD38	Cemiplimab	Prostate Cancer and NSCLC	Promote tumor cell apoptosis. Inhibit CD38+Breg, recruit NK cells, and enhance anti-tumor immune response.	NCT03367819
Nivolumab	IgG4	PD-1	NA	Recurrent and/or metastatic head and neck squamous cell cancer	TIBs are associated with the response to nivolumab. Subgroups with higher TIBs predict significantly prolonged PFS and OS.	NCT03652142
Nivolumab	IgG4	PD-1	Cabozantinib	HCC	Enhance TME immune response by activating PAX5 to promote TIBs activation and maturation.	NCT03299946
Pembrolizumab	IgG4	PD-1	G100	Soft tissue sarcomas	Promote the formation of TLS	NCT02406781
Gemcitabine	NA	Nucleoside metabolism	Cisplatin	NPC	Activate an anti-tumor immune response dominated by innate-like B cells.	NCT01417546

We provide a concise overview of FDA-approved drugs utilizing Tumor-Infiltrating B cells (TIBs) for cancer treatment. We detail therapeutic strategies, mechanisms of action, and targeted cancer types. Information includes antibody names, classes, specific targeting strategies, and whether used in combination with other therapies

Her-2 Human Epidermal Growth Factor Receptor 2, IgG Immunoglobulin G, EGFR Epidermal Growth Factor Receptor, Th1 cells Helper T cells type 1, VEGF Vascular Endothelial Growth Factor, NSCLC Non-Small Cell Lung Cancer, CRC Colorectal Cancer, IL-6 Interleukin-6, VEGFR2 Vascular Endothelial Growth Factor Receptor 2, LAG-3 Lymphocyte-Activation Gene 3, KRAS Kirsten Rat Sarcoma Viral Oncogene; Bregs, Regulatory B cells, PAX5 Paired Box 5, PD-1 Programmed Cell Death Protein 1, HCC Hepatocellular Carcinoma, NPC Nasopharyngeal Carcinoma, PFS Progression-Free Survival, OS Overall Survival, TLS Tertiary Lymphoid Structures, TIBs Tumor-Infiltrating B Cells, TME Tumor Microenvironment, PD-L1 Programmed Death-Ligand 1

Table 3.

Ongoing and emerging clinical trials affecting or involving TIBs in tumor treatment

Antibody name	Treatment strategy	Combinational therapy	Cancer entities	Results and mechanism	Clinical trial number
BI-1910	TNFR2	Pembrolizumab	Solid tumors and NSCLC	Inhibit tumor immune evasion, slow down tumor growth, and weaken resistance to checkpoint inhibitors.	NCT06205706
DS-8201a	Her-2	NA	Gastric and gastro-esophageal junction cancer	Inhibiting the Her2 signaling pathway and enhancing the activation and proliferation of Th1 cells and CD8 + T cells, thereby suppressing tumor growth	NCT04014075
MGAH22	Her-2	NA	Breast Cancer and Gastric Cancer		NCT01148849
S095029	NKG2A	pembrolizumab	unresectable or metastatic gastric and adenocarcinomas	Enhance anti-tumor immune responses mediated by NK cells and cytotoxic T lymphocytes	NCT06116136
BGB-A445	OX40	Docetaxel and Ramucirumab	NSCLC	Enhancing T cell activity induces an anti-tumor immune response and promotes TABs to secrete immunoglobulins.	NCT06029127
INBRX-106	OX40	Pembrolizumab	NSCLC, Melanoma, Head and Neck Cancer, Gastric Cancer, Renal Cell Carcinoma and Urothelial Carcinoma		NCT04198766
MEDI6469	OX40	Stereotactic ablative radiotherapy	metastatic breast cancer		NCT01862900
PF-04518600	OX40	PF-05082566	Melanoma and NSCLC		NCT02315066
JS004	BTLA	Toripalimab	advanced lung cancer	Promoting the proliferation of T lymphocytes and enhancing the function of tumor-infiltrating lymphocytes inhibits tumor progression	NCT05664971
HLX07	EGFR	lenvatinib	Advanced HCC	Blocking the EGFR signal transduction pathway within cells, thereby inhibiting the proliferation of cancer cells. Reducing the production of matrix metalloproteinases and VEGF	NCT05290220
AU-007	IL-2	NA	melanoma and renal cell cancer, Merkel	Bind to IL-2 and inhibit IL-2Rα, thereby preventing STAT5 phosphorylation of CD8 + T cells and maintaining the tumor killing function of CD8 + T cells	NCT05267626
BI 765063	CD47	Cetuximab and ezabenlimab	Head and Neck Squamous Cell Carcinoma or HCC	Inhibit the formation of CD47-SIRPα signaling complex and promote macrophage-mediated phagocytic function	NCT05249426
COM902	TIGIT	COM701	Ovarian Cancer, Lung Cancer and Colon Cance	Enhance the tumor killing function of NK cells and T cells	NCT04354246
EOS-448	TIGIT	Pembrolizumab, Inupadenant and Dostarlimab	Lung Cancer, Head and Neck Cancer, Melanoma		NCT05060432
TSR-033	LAG-3	Dostarlimab	metastatic solid tumor	To weaken the immunosuppressive effects of B cells, enhance their antigen-presenting activity, enable T cells to regain cytotoxic activity, reduce the inhibition of effector T cells by Tregs, and strengthen the killing effect on tumors	NCT03250832
CDX-1140	CD40	CDX-301	NSCLC	Activate APCs to promote the initiation of antigen-specific T cells and enhance their anti-tumor potential.	NCT04940325
CDX-1140	CD40	CDX-301 and Embrolizumab	Advanced Malignancies		NCT03329950
APX005M	CD40	NSCLC and metastatic melanoma			NCT03123783
Mitazalimab	CD40	Irreversible electroporation	Pancreatic Cancer		NCT06205849
CDX-1127	CD27	Cobimetinib and Atezolizumab	biliary cancers	Recruit lymphocytes, facilitate the activation of T and B cells, increase the secretion of the cytokine IFN-γ, and promote macrophage phagocytic function.	NCT04941287
Varlilumab	CD27	Nivolumab	Squamous Cell Carcinoma of the Head and Neck, Ovarian Carcinoma and CRC		NCT02335918
NGM120	GFRAL	NA	Advanced Solid Tumors, Pancreatic Cancer, and Prostate Cancer	Blocking GDF15 signal transduction to prevent cachexia in advanced cancer	NCT04068896
VX15/2503	SEMA4D	Ipilimumab and nivolumab	NSCLC	Overcome myeloid suppression, enhance T-cell infiltration and activity, and produce a synergistic effect with other immune checkpoint inhibitors.	NCT03373188
Rilotumumab	HGF	Erlotinib Hydrochloride	Squamous Cell Lung Cancer	Inhibit HGF/MET-driven signal transduction to reduce tumor cell proliferation.	NCT02926638
Rilotumumab	HGF	Cisplatin and Capecitabine	Gastric Cancer		NCT02137343
Fresolimumab	TGF-β	Stereotactic ablative radiotherapy	early stage NSCLC	Inhibit tumor growth, weaken the function of Treg and Bregs, enhance the function of CD8 + T cells, and suppress epithelial-mesenchymal transition.	NCT02581787
SAR439459	TGF-β	cemiplimab	Advanced or Unresectable Solid Tumors		NCT04729725
NIS793	TGF-β	standard of care anti-cancer therapy	Metastatic CRC		NCT04952753
Rovalpituzumab	DLL3	Cisplatin and Etoposide	small cell lung cancer	Inhibit the Notch signaling pathway, thereby inhibiting cancer development.	NCT02819999
Enoblituzumab	B7-H3	Ipilimumab	B7-H3 expressing cancers	By increasing soluble 4-1BB and IL-17, immune responses are promoted, leading to an increase in CD8 + T cell levels and stimulating antibody secretion by PCs.	NCT02381314
CM-24	CEACAM1	Pembrolizumab	gastrointestinal, ovarian, melanoma, non-small cell lung adenocarcinoma and bladder	Blocking the intercellular CEACAM1-CEACAM1 interaction reverses the inhibition of activated lymphocytes by restoring the phosphorylation of ZAP70.	NCT02346955
RO5323441	PlGF	Sorafenib	HCC	Indirectly inhibiting tumor angiogenesis by suppressing VEGF-driven angiogenesis and reducing pro-angiogenic myeloid cells.	NCT01308723
Olaratumab	PDGFRα	liposomal doxorubicin	Ovarian Cancer	Inhibiting the excessive activation of PDGFRα and its downstream signaling pathways exerts anti-tumor activity.	NCT00913835
Mapatumumab	TRAIL-R1	Sorafenib	Advanced HCC	Activate the apoptotic signaling pathway in tumor cells to promote their apoptosis. Reduce the number of Tregs in the tumor microenvironment.	NCT01258608 and NCT00712855
AMG 479	IGF-1R	NA	Recurrent Platinum-sensitive Ovarian Cancer	Kill non-replicative state cancer cells and inhibit the proliferation of tumor cells.	NCT00719212
AVE1642	IGF-1R	Sorafenib and Erlotinib	Liver Cancer		NCT00791544
Cixutumumab	IGF-1R	NA	Neuroendocrine cancer		NCT01204476
Cixutumumab	IGF-1R	GDC-0449, cisplatin and etoposide	Gastric Cancer and Adenocarcinoma		NCT00887159
Cixutumumab	IGF-1R	NA	malignant solid tumors		NCT00831844
Cixutumumab	IGF-1R	NA	Liver Cancer		NCT00639509
MK-0646	IGF-1R	Cisplatin and Etoposide	Small cell lung cancer		NCT00869752
MVT-5873	CA19.9	NA	Pancreatic Cancers, Cholangiocarcinomas, and Metastatic CRCs	Mediate the complement-dependent cytotoxicity and antibody-dependent cell-mediated cytotoxicity. Reduce recurrence rates and prolong survival after resection.	NCT03801915
Hu3S193	Lewis-Y	NA	Small Cell Lung Cancer	Target Lewis antigens to kill tumor cells through Antibody-Dependent Cellular Cytotoxicity.	NCT00084799
Hu3S193	Lewis-Y	NA	Ovarian Epithelial, Primary Peritoneal and Fallopian Tube Cancer		NCT00617773
PD 0360324	M-CSF	Cyclophosphamide	High-Grade Epithelial Ovarian, Primary Peritoneal, or Fallopian Tube Cancer	Help the body’s immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread	NCT02948101
OR502	LILRB2	Cemiplimab	Ovarian cancer and cutaneous squamous cell carcinoma	Reversing the immunosuppressive state of macrophages and enhancing the function of APCs can subsequently boost the tumor-killing efficacy of T cells.	NCT06090266
KY1044	ICOS	Atezolizumab	Squamous Cell Carcinoma of Head and Neck, NSCLC and HCC	Suppressing Treg and Bregs in solid tumors can enhance the activity of TABs and their antigen-presenting capabilities. Targeting and killing ICOS+ tumor cells.	NCT03829501
Feladilimab	ICOS	Pembrolizumab	Neoplasms, Head and Neck		NCT04428333
CPI-006	CD73	pembrolizumab or ciforadenant	Advanced Cancers	Activat CD69POS B cells redistribute to lymphoid tissues and reduce tumor volume	NCT03454451251
TAB004	BTLA	NA	Advanced Malignancies	Increase the frequency of killing CD8 + T cells and the production of effector cytokines to improve the efficacy of ICIs therapy.	NCT04137900
BMS 986016	LAG-3	Nivolumab	Glioblastoma, Gliosarcoma and Recurrent Brain Neoplasm	Weakening the immunosuppressive effects of B cells, enhancing the antigen-presenting activity of B cells. Restoring the cytotoxic activity of T cells, reducing the suppressive effects of regulatory T cells on effector T cells, and strengthening the killing effect on tumors.	NCT02658981
HLX26	LAG-3	Serplulimab	NSCLC		NCT05787613
Sym022	LAG-3	Sym021 and irinotecan	biliary tract carcinomas and esophageal squamous cell carcinoma		NCT04641871
fianlimab	LAG-3	cemiplimab	Prostate Cancer		NCT04989946
IMP321	LAG-3	Gemcitabine	Pancreatic Neoplasms		NCT00732082
IMP321	LAG-3	paclitaxel	metastatic breast carcinoma		NCT00349934
IMP321	LAG-3	Pembrolizumab	NSCLC and head and neck squamous cell carcinoma		NCT03625323
IMP321	LAG-3	Pembrolizumab	head and neck squamous cell carcinoma		NCT04811027
XmAb22841	LAG-3 and CTLA-4	NA	Metastatic Melanoma	Weakening the immunosuppressive effects of B cells, enhancing the antigen-presenting activity of B cells. Restoring the cytotoxic activity of T cells, reducing the suppressive effects of regulatory T cells on effector T cells, and strengthening the killing effect on tumors. When used in combination with CTLA4, it enhances the therapeutic efficacy.	NCT05695898
INCA 32459	LAG-3 and PD-1	NA	Advanced Malignancies	Weakening the immunosuppressive effects of B cells, enhancing the antigen-presenting activity of B cells. Restoring the cytotoxic activity of T cells, reducing the suppressive effects of regulatory T cells on effector T cells, and strengthening the killing effect on tumors. When used in combination with PD-1/PD-L1, it enhances the therapeutic efficacy.	NCT05577182
TSR-033	LAG-3	Dostarlimab	metastatic solid tumor		NCT03250832
ABL501	LAG-3 and PD-L1	NA	Metastatic Solid Tumors		NCT05101109
EMB-02	LAG-3 and PD-1	NA	Advanced Solid Tumors		NCT04618393
MGD013	LAG-3 and PD-1	MGA012 and enoblituzumab	head and neck squamous cell carcinoma		NCT04129320
LVGN 7409	CD40	LVGN 3616 and LVGN 6051	Head and Neck Squamous Cell Carcinoma	Enhancing the antigen-presenting capabilities of TABs promotes T cell differentiation, and combination therapy with PD-1 antibodies and CD137 agonistic antibodies can enhance therapeutic efficacy.	NCT06159621
TQB2916	CD40	NA	Advanced Malignant Tumors	Enhancing the antigen-presenting capabilities of TABs boosts the killing ability of T cells against tumors and increases the secretion of IFN-γ, thereby promoting tumor regression.	NCT05213767
mitazalimab	CD40	Irreversible electroporation	Pancreatic Cancer	Activate APCs, initiate specific anti-tumor responses, and promote the activation and anti-tumor potential of antigen-specific T cells.	NCT06205849
mitazalimab	CD40	the standard of care chemotherapy mFOLFIRINOX	metastatic pancreatic ductal adenocarcinoma		NCT04888312
APX005M	CD40	domvanalimab and zimberelimab		Agonistic CD40 antibodies induce effective anti-tumor immune responses, inhibiting tumor metastasis and dissemination.	NCT05419479
RO7300490	CD40 and FAP	Atezolizumab	Solid Tumors	Activate immune cells in the tumor microenvironment to inhibit cancer development.	NCT04857138
MP0317	CD40 and FAP	NA	Advanced Malignant Solid Tumor		NCT05098405
2141-V11	CD40	NA	Prostate Cancer	Activation of the CD40 signaling pathway promotes APCs, enhances the anti-tumor capabilities of T cells, and generates a synergistic effect with the IL-15 cytokine to inhibit tumor growth.	NCT06347705
2141-V11	CD40	NA	Non-muscle Invasive Bladder Cancer		NCT05126472
SEA-CD40	CD40	pembrolizumab, pemetrexed and carboplatin	NSCLC and Melanoma	Increase the secretion of cytokines, including IP-10, monocyte chemoattractant protein-1, MIG, and MIP-1b, to promote tumor regression.	NCT04993677
MEM-288	CD40	Nivolumab	NSCLC		NCT05076760
CDX-1140	CD40	Pembrolizumab	Malignant Epithelial Neoplasms	Activate APCs to promote the initiation of antigen-specific T cells and enhance their anti-tumor potential.	NCT05349890
CDX-1140	CD40	Pembrolizumab	Ovarian Clear Cell Adenocarcinoma		NCT05231122
CDX-1140	CD40	capecitabine, oxaliplatin, Keytruda	Biliary tract carcinoma		NCT05849480
CDX-1140	CD40	odetiglucan	Metastatic Pancreatic Adenocarcinoma		NCT05484011
CDX-1140	CD40	CDX-301	HER2-negative Breast Cancer		NCT05029999
Chi Lob 7/4	CD40	NA	Advanced Malignancies		NCT01561911 245
MB-CART20.1	CD20	NA	Melanoma	Trials of CAR-T cells targeting CD20 in melanoma, aimed at killing Bregs and CD20+ tumor cells.	NCT03893019
KY1044	ICOS	atezolizumab	Squamous Cell Carcinoma of Head and Neck, NSCLC and HCC	Suppress the function of Treg and Bregs in solid tumors, enhance the activity of antitumor effector T cells and the antigen-presenting capabilities of TABs, and kill ICOS+ tumor cells.	NCT03829501
XmAb23104	ICOS and PD-1	NA	Sarcoma	Simultaneously inhibiting the immune suppressive effects of the PD-1 pathway and activating the immune stimulatory effects of the ICOS pathway, thereby enhancing the antitumor immune response.	NCT05879185
XmAb23104	ICOS and PD-1	XmAb22841	Metastatic Melanoma		NCT05695898
Vopratelimab	ICOS	Ipilimumab	Urothelial carcinoma and NSCLC	Inhibit the function of Treg and Bregs in solid tumors, enhance the activity and antigen-presenting capabilities of TABs, and kill ICOS+ tumor cells.	NCT03989362
Vopratelimab	ICOS	Pimivalimab	NSCLC		NCT04549025
Vopratelimab	ICOS	Nivolumab, Ipilimumab and Pembrolizumab	Solid Tumor Malignancies		NCT02904226
Feladilimab	ICOS	Pembrolizumab	Neoplasms, Head and Neck	Suppress Treg and Bregs in solid tumors, enhance the secretion of IFN-γ, and reduce the expression of PD-1.	NCT04428333
Feladilimab	ICOS	Ipilimumab and Docetaxel	NSCLC		NCT03739710
Feladilimab	ICOS	Tremelimumab and Docetaxel	Head and Neck Squamous Cell Carcinomas		NCT03693612
GSK3174998	OX40	GSK1795091 and GSK3359609	Squamous Cell Carcinoma of Head and Neck, NSCLC and HCC	Enhancing T cell activity induces an anti-tumor immune response and promotes TABs to secrete immunoglobulins.	NCT03447314
MBG453	Tim-3	PDR001 and Decitabine	advanced or metastatic solid tumors	Enhance the antigen-presenting function of TABs, reduce the number of Tregs, and increase the killing activity of CD8 + T cells.	NCT02608268
TQB2618	Tim-3	TQB2450	Advanced Solid Tumor		NCT05645315
NB002	Tim-3	NA	Advanced Solid Tumor		NCT05924906
INCAGN02390	Tim-3	INCMGA00012 and INCAGN02385	Melanoma		NCT04370704
MBG453	Tim-3	spartalizumab and stereotactic radiosurgery	Glioblastoma Multiforme		NCT03961971
Sym023	Tim-3	NA	metastatic solid tumor malignancies		NCT03489343
BGB-A425	Tim-3	Tislelizumab and LBL-007	HNSCC, NSCLC and RCC		NCT03744468
TSR-022	Tim-3	Nivolumab and Dostarlimab	Advanced Solid Tumors		NCT02817633
TSR-022	Tim-3	Dostarlimab	Primary Liver Cancer	Simultaneously inhibiting the immunosuppressive effect of the PD-1 pathway and blocking the Tim-3 pathway contribute to improving the immune microenvironment.	NCT03680508
LB1410	Tim-3 and PD-1	LB4330	Solid Tumor		NCT06468358
AZD7789	Tim-3 and PD-1	NA	Gastric Cance, Gastroesophageal Junction Cancer and NSCLC		NCT04931654
Lomvastomig	Tim-3 and PD-1	NA	Melanoma and NSCLC		NCT03708328
Lomvastomig	Tim-3 and PD-1	Nivolumab and Tobemstomig	Esophageal Squamous Cell Carcinoma		NCT04785820
LY3321367	Tim-3 and PD-L1	LY3300054	advanced relapsed/refractory solid tumors		NCT03099109
LY3415244	Tim-3 and PD-L1	NA	advanced solid tumors		NCT03752177
varlilumab	CD27	nivolumab	Squamous Cell Carcinoma of the Head and Neck, Ovarian Carcinoma and Colorectal Cance	Recruit lymphocytes, promote the activation of T cells and B cells, increase the secretion of the cytokine IFN-γ, and enhance the phagocytic function of macrophages.	NCT02335918
varlilumab	CD27	ONT 10	Breast Carcinoma and Ovarian Carcinoma		NCT02270372
varlilumab	CD27	sunitinib	metastatic clear cell renal cell carcinoma		NCT02386111
varlilumab	CD27	radiation therapy and concurrent temozolomide	Glioblastoma		NCT03688178
Varlilumab	CD27	polyICLC and IMA950	Glioma		NCT02924038
Varlilumab	CD27	CDX-1401 and ipilimumab	Melanoma		NCT02413827
6MHP	CD27	ontanide ISA-51, polyICLC and varlilumab	Melanoma	A T-cell vaccine that recruits lymphocytes, promotes the activation of T cells and B cells, and facilitates tumor regression.	NCT03617328
STI-6129	CD38	NA	advanced solid tumor	Antibody-drug conjugate, targeting the elimination of both CD38+Bregs and tumor cells, promotes T-cell expansion and enhanced activity.	NCT05584709
ES014	CD39 and PD-1	NA	Advanced or Metastatic Solid Tumors	Reduce adenosine formation, maintain ATP levels, decrease Treg cell activity, and enhance anti-tumor immune responses.	NCT05717348
IAE0972	EGFR and IL-10	NA	Advanced Malignant Solid Tumors	By blocking the EGFR signal transduction pathway within cells, the proliferation of cancer cells is inhibited, concurrently diminishing the production of matrix metalloproteinases and VEGF.	NCT05396339
LGX818	BRAF	BGJ398	advanced or metastatic BRAF mutant melanoma	Inhibiting the sustained activation of the MAPK signaling pathway inhibits tumor growth.	NCT01820364
IBB0979	IL-10R and CD276	NA	advanced Malignant Tumors	Enhance anti-tumor immune response and inhibit tumor metastasis.	NCT05991583
PM8001	TGF-β and PD-L1	PM1021	Advanced Solid Tumors	Inhibit tumor growth, weaken the function of Treg and Bregs, enhance the function of CD8 + T cells, and suppress epithelial-mesenchymal transition.	NCT05537051
AK130	TGF-β and TIGIT	NA	Advanced Malignant Tumors		NCT05653284
bintrafusp α	TGF-β and PD-L1	carboplatin and paclitaxel	paclitaxel and carboplatin		NCT04481256
LY2157299	TGF-βR	Enzalutamide	Prostate Cancer		NCT02452008
LY2157299	TGF-βR	Sorafenib	Advanced HCC		NCT02178358
LY2157299	TGF-βR	MEDI4736	Metastatic Pancreatic Cancer		NCT02734160

We outline ongoing and emerging clinical trials involving Tumor-Infiltrating B cells (TIBs) in cancer treatment, including those that may not yet have FDA approval. The table details the antibody names, treatment strategies, and combination therapies used. The results and mechanisms column describes how these treatments affect tumor growth and immune evasion

ICIs immune checkpoint inhibitors, BTLA B-cell Lymphoma 2-Associated Protein 3, ICOS Inducible T cell co-stimulator, LILRB2 Leukocyte Immunoglobulin Like Receptor Subfamily B Member 2, M-CSF macrophage colony-stimulating factor, CA19.9 Carbohydrate antigen 19-9, CRC colorectal cancer, VEGFR2 Vascular Endothelial Growth Factor Receptor 2, VEGFR2 Vascular Endothelial Growth Factor, IGF-1R Insulin-like Growth Factor 1 Receptor, TRAIL-R1 TNF-related apoptosis-inducing ligand receptor 1, PDGFRα Platelet-derived Growth Factor Receptor Alpha, CEACAM1 Carcinoembryonic Antigen Related Cell Adhesion Molecule 1, PlGF Placental Growth Factor, B7-H3 B7 homolog 3, TGF-β Transforming Growth Factor-β, HGF Hepatocyte Growth Factor, TIGIT T cell Immunoreceptor with Ig and ITIM domains, LAG-3 Lymphocyte Activation Gene-3, DLL3 Delta-like protein 3, SEMA4D Semaphorin 4D, GFRAL GDNF Family Receptor Alpha-Like, EGFR Epidermal Growth Factor Receptor, OX40 Tumor Necrosis Factor Receptor Superfamily Member 4, TNFR2 Tumor Necrosis Factor Receptor 2, NKG2A NK cell lectin-like receptor subfamily C member 1, NSCLC Non-small Cell Lung Cancer, HCC Hepatocellular Carcinoma, r, Tim-3 T cell immunoglobulin domain and mucin domain protein 3, PD-1 Programmed Death 1, PD-L1 Programmed Death-Ligand 1, CTLA-4 Cytotoxic T Lymphocyte-Associated Protein 4, BRAF v-raf murine sarcoma viral oncogene homolog B1

Feasible directions for intervening with TIBs and potential pathways reported in the literature

Tertiary lymphoid structures and cancer therapy

The extensive application of ICIs and targeted therapies has elevated investigating their effects on TLSs to a prominent area of interest in oncological research. Anti-PD-1 antibodies, such as nivolumab and cabozantinib, may increase TLS in tumors, enhancing local immune responses.⁴³⁷ This effect may be linked to higher TNF-α and CCR7 levels, showing a complex interaction between these drugs and the TME. The use of adeno-associated virus vectors to express LIGHT in the vasculature of glioma therapy can induce the formation of HEVs and TLSs in glioblastoma, promoting the infiltration of transcription factor (TCF1)⁺CD8 stem-like T cells, reducing T-cell exhaustion, and extending the survival of mice resistant to αPD-1 treatment.⁴³⁸ Through mouse experiments and scRNA-seq analysis, CXCL13⁺ T cells were enriched in samples of anaplastic thyroid cancer.⁴³⁹ The combination of famitinib and an anti-PD-1 antibody can promote the development of TLSs in thyroid cancer, indicating a better sensitivity to immunotherapy. Tryptophan-rich metabolic microenvironments created by malignant cells skew TLS maturation in HCC.⁴⁴⁰ Inhibiting tryptophan metabolism promotes TLS maturation in tumors, enhances tumor control, and synergizes with anti-PD-1 therapy. In addition to PD-1/PD-L1 inhibitors, CTLA-4 antibodies facilitate the recruitment of TIBs and the formation of TLSs, which can be utilized in treating liver cancer.⁴⁴¹ In brain metastases, CTLA4⁺ Tfh cells, together with BAFF/APRIL from M1-like macrophages, recruit and activate B cells to form TLSs, enabling synergistic antitumor efficacy of combined anti-CTLA4 and anti-PD-1 therapy.⁴⁴²

Other therapies also have an impact on TLSs. In lung cancer, it has been discovered that TLSs are correlated with the production of tumor-binding antibodies, with endogenous retroviral envelope glycoproteins serving as key targets.⁴⁴³ Immune checkpoint inhibition and KRAS-targeted inhibition can augment the endogenous retrovirus-targeted TIB response. G100, a potent TLR4 agonist, when combined with pembrolizumab, aids in the formation of TLSs.⁴⁴⁴ However, with a 6-month PFS rate of 11.8%, the first endpoint of the study was not met, indicating limited clinical activity when used in combination. IL-33-induced TLS in the TME promote TLS formation by activating ILC2s that express lymphotoxin.⁴⁴⁵ These ILC2s work with myeloid cells to drive TLS development. Higher IL-33 in TLSs is linked to better prognosis, and recombinant human IL-33 can expand TLSs and boost antitumor activity in PDAC mouse models. Following cisplatin treatment, there is an observed increase in the number of TLSs in hepatoblastoma associated with adenomatous polyposis coli germline mutations.⁴⁴⁶ A low systemic inflammatory status is significantly associated with pathological complete response (pCR) in gastric cancer patients undergoing radical gastrectomy. Additionally, high TLS density is correlated with pCR.⁴⁴⁷

Tumor vaccine and tumor-infiltrating B cells

The administration of biological vaccines or TAA protein vaccines can effectively stimulate specific immune responses, enhance TIB immune responses, and exert antitumor effects.⁴⁴⁸ Targeted aspartate beta-hydroxylase (ASPH) knockout λ phage vaccines combined with PD-L1 monoclonal antibodies increase B-cell germinal centers and TLS in the TME, significantly improving survival and prognosis in liver cancer patients.⁴⁴⁹ This is based on the ASPH-MYC signaling cascade that upregulates PD-L1 in breast and liver tumor cells. The antigen-cluster nanovaccine, which clusters HER2⁺ TIBs or CD4⁺ T-cell epitopes on gold nanoparticles, can enhance the presentation of TIB antigens, promote CD4⁺ T-cell activation, reshape the TME, and facilitate tumor regression.⁴⁵⁰ The administration of a combination of two B-cell epitope vaccines, engineered to mimic the binding sites of trastuzumab and pertuzumab, was employed in treating patients with metastatic carcinoma or advanced solid carcinoma.⁴⁵¹ This approach elicited a humoral response attributable to the conformational B-cell epitope vaccine.

BVAC-B is an immunosuppressive vaccine derived from autologous B cells and monocytes that includes cells transfected with recombinant HER-2 and loaded with the natural killer T-cell ligand α-galactosylceramide.⁴⁵² After BVAC-B treatment, IFN-γ, TNF-α, and IL-6 all increase, which can effectively improve the prognosis of patients with gastric cancer. A stimulator that integrates the B-cell antigen receptor CD40, TLR4, and TLR7 as a B-cell vaccine (Bvac) has enhanced the OS rate of mice with melanoma and reduced tumor size.⁴⁵³ Bvac upregulates TIB antigen presentation molecules, stimulates the activation of CD4⁺ and CD8⁺ T cells, and induces T-cell migration. By activating B cells with CD40 agonists, IFN-γ, and BAFF, a potent vaccine called BVax is generated.⁴²⁸ Compared to naive B cells, BVax exhibits improved potential for antigen cross-presentation and utilizes the IL-15-IL-15Ra mechanism to enhance T-cell activation. In glioblastoma, this BVax vaccine differentiates into Ab-producing plasmablasts, generating antibodies with unique reactivity that primarily target factors associated with cell motility and the extracellular matrix.⁴⁵⁴ Following intramuscular therapeutic vaccination with the HPV16 E6/E7 antigen, TLSs can be observed in tissues affected by high-grade cervical intraepithelial neoplasia, accompanied by increased expression of CXCR3, T-box transcription factor 21 (T-bet), and IFN-β genes, thereby promoting immune cell infiltration.⁴⁵⁵ In PDAC, PI3k-γ inhibitors with an alpha-enolase DNA vaccine boost circular anti-alpha-enolase IgG levels and IFN-γ secretion by T cells. This TIBs-dependent response inhibits tumor progression.⁴⁵⁶

Additionally, for pancreatic cancer, the development of an mRNA vaccine targeting FA Complementation Group D2 can potentially enhance TIBs’ immune score and the level of immune infiltration.⁴⁵⁷ This, in turn, may improve overall patient survival and increase sensitivity to therapeutic agents. Montanide ISA-51 is an incomplete Freund’s adjuvant that enhances systemic immune responses and promotes the formation of TLSs, as well as the expression of IFN-γ and STAT1.⁴⁵⁸

Immune-related adverse events and tumor-infiltrating B cells

IrAEs are adverse reactions linked to immune mechanisms in clinical trials or with antitumor drugs. ICIs help TIBs reshape the TME and inhibit cancer, but excessive TIB activation can cause IrAEs.⁴⁵⁹ When treating advanced NSCLC with pembrolizumab, some patients experience high-grade irAEs. In these patients, the function of IL-10⁺ Bregs is impaired, leading to enhanced autoreactive T-cell activity and autoantibody formation.⁴⁶⁰ TIB repertoire analysis before treatment can provide an important tool for identifying lung cancer patients at high risk of developing severe irAEs following checkpoint blockade. Anti-PD-1 therapy induces irAE-like multi-organ dysfunction in elderly tumor-bearing mice, involving the upregulation of CXCL13 by CD4⁺ T cells secreting IL-21, which promotes the homing of TIBs and the formation of TLSs. Depletion of TIBs or blockade of IL-21/CXCL13 can alleviate toxicity.⁴⁶¹ A case of an advanced lung cancer patient experienced a delayed-onset visual irAE after anti-PD-1 therapy, accompanied by significant increases in cytokines, autoantibodies, and plasmablasts.⁴⁶² Corticosteroid treatment rapidly reduced the levels of cytokines, autoantibodies, and inflammatory cells. A study found a nonsense mutation in a family with sequence similarity 187 member B (TMEM162), which is associated with increased peripheral and TIBs and suppression of Tregs, leading to an elevated risk of irAEs.⁴⁶³ Severe irAEs occurred in cancer patients receiving combined anti-CTLA-4/PD-1 immunotherapy. Mice treated with ipilimumab-antacid showed excessive T-cell proliferation and differentiation into effector cells, causing TIB depletion.⁴⁶⁴ This was mediated by CD4⁺ and CD8⁺ T cells, and partially rescued by an anti-TNF-α antibody. In patients with neuro-irAEs, there was a significant decrease in IgD⁻CD11c⁺CD21^low and IgD⁻CD24⁺CD21^high circulating B cells.⁴⁶⁵ In 214 melanoma patients treated with ICIs, carriers of the minor allele at rs16906115 had a higher risk of severe irAEs.⁴⁶⁶ This locus, in the IL7 gene intron, is a B-cell-specific expression quantitative trait locus linked to IL-7 levels.

Assessment and recommendations based on safety, efficacy, cost-effectiveness, and patient acceptability

With advancements in bioinformatics technology, the development of antigen peptides that activate B cells, based on the structures of MHC-I/II molecules and the target antigen, has facilitated tumor immunology.⁴⁶⁷ MHC-based B-cell-targeting vaccines enable precise immune activation against tumor-specific antigens or neoantigens, enhancing B-cell-mediated humoral immune responses. Compared to cellular adoptive therapies (such as CAR-T), antigen peptide vaccines have lower production costs and do not require complex cell culture and processing procedures. However, due to the need for personalized design and customization, their fees are still higher than those of traditional nonpersonalized therapies. Furthermore, uncertainties in their clinical efficacy may impact the overall cost-effectiveness. The vaccination process is relatively simple, with mild adverse reactions, translating to higher patient acceptability.⁴⁶⁸

The application of nanoparticles in tumor immunotherapy is a cutting-edge research direction in cancer treatment. It enables precise delivery of drugs to tumor sites through passive or active targeting mechanisms, thereby reducing drug distribution in healthy tissues and minimizing systemic toxicity.⁴⁶⁹ However, potential long-term toxicity remains a concern that warrants further investigation. Nanoparticles can enhance the efficacy of immunotherapy, particularly in B-cell therapies, with preclinical studies demonstrating significant improvements in antitumor effects when using nanoparticle delivery systems.⁴⁷⁰ The production costs of nanoparticles are relatively low and scalable. Nanoparticle-based therapies are associated with mild adverse reactions, leading to high patient acceptability. Additionally, the treatment process is relatively straightforward, eliminating the need for complex cellular manipulations.

The therapy of activating B cells ex vivo and reinfusing them into patients is called B-cell activation therapy. Compared to CAR-T therapy, it may offer higher safety, mitigating severe adverse reactions such as cytokine release syndrome and neurotoxicity, which are commonly seen in CAR-T therapy.⁴⁷¹ Although it has demonstrated promising results in vitro and in animal models, its broad-spectrum effectiveness against different types of tumors still needs to be verified in clinical applications. Furthermore, tumor heterogeneity and immune evasion mechanisms may limit its efficacy in certain patients. The production cost of this therapy is lower than that of CAR-T therapy.⁴⁷² However, the costs associated with personalized customization and clinical trial development remain high, and the cost-effectiveness requires further evaluation in large-scale clinical applications.

The safety of ICIs has been extensively studied in multiple clinical trials. Overall, these drugs exhibit good safety profiles, although they may still induce irAEs. ICIs have demonstrated significant antitumor activity across various cancer entities, attributed to their broad range of action.^473,474 However, there is individual variability in the efficacy of ICIs, with some patients showing no response to treatment.⁴⁷⁵ This is related to tumor heterogeneity, the TME, and the patient’s own immune status. While ICIs demonstrate high cost-effectiveness in specific cancer entities and treatment stages, particularly in combination therapies, their relevance to B-cell mechanisms requires further exploration.⁴⁷⁶ The relatively low toxicity and convenient treatment process of ICIs contribute to their high patient acceptance, but their impact on B-cell functions and interactions should be considered in the context of B-cell-focused therapies.

Immunomodulatory therapy targeting B-cell proteins, by targeting specific B-cell proteins (such as CD40 and TLRs), can enhance antitumor immune responses and reduce adverse reactions associated with nonspecific immune activation.⁴⁷⁷ Its effectiveness may vary depending on the drug delivery method, tumor type, and individual patient differences. The production cost of B-cell-targeted immunotherapy is relatively low, as it does not require complex cell culture and gene engineering.⁴⁷⁸ However, the long-term cost-effectiveness needs further evaluation in large-scale clinical applications. The treatment process is relatively simple, with mild adverse reactions, resulting in high patient acceptability.

In addition to antigen peptide vaccines, ICIs, agonists targeting B-cell surface checkpoints, and B-cell adoptive therapies, methods such as oncolytic virotherapy,⁴⁷⁹ cytokine-induced killer cell therapy,⁴⁸⁰ and combined dendritic cell vaccine therapy⁴⁸¹ can directly or indirectly affect TIBs to exert antitumor effects. For example, adoptively transferred Th17 cells, via CD40L and IL-21, promote host B-cell expansion, germinal-center formation, and tumor-specific antibody production, collaboratively establishing durable antitumor immunity and suppressing distant metastases.⁴⁸² More strategies will emerge with advancements in tumor immunotherapy.

Conclusion and perspective

This review comprehensively examines the current understanding of TIBs within the TME, systematically summarizing their classification, functional diversity, signaling regulatory mechanisms, and clinical translational potential. As a critical immune cell population in the TME, TIBs exhibit remarkable phenotypic and functional heterogeneity. On the one hand, they can enhance antitumor immune responses through antigen presentation, antibody secretion, and TLS formation. On the other hand, they may promote immune evasion and tumor progression by secreting immunosuppressive factors such as IL-10, TGF-β, and GABA or expressing immune checkpoint molecules including PD-L1, TIM-1, and TIGIT. The widespread application of single-cell sequencing technologies has revealed the distinct subpopulations of TIBs across various cancer types and their associations with patient prognosis, further highlighting their value as potential biomarkers and therapeutic targets.

At the mechanistic level, TIBs are regulated by diverse signaling pathways such as BCR, NF-κB, STAT, TLR and metabolic circuits including glutamine metabolism and oxidative phosphorylation. They form intricate intercellular networks with T cells and TAMs. TLSs serve as the essential structural basis for TIBs to exert their functions, and their maturity and spatial distribution directly shape antitumor immunity. Regulatory mechanisms underlying TLS formation, such as the CXCL13-CXCR5 axis and LTβR signaling, have become focal points of current research.⁴⁸³ Moreover, TIBs display a dual role in immunotherapy: they can enhance efficacy by cooperating with immune checkpoint inhibitors, yet excessive activation may trigger immune-related adverse events, underscoring the need to balance their stimulatory and suppressive functions.

Although current research has laid a solid foundation for the clinical translation of TIBs, several challenges remain. First, the rules governing the dynamic evolution of TIB subpopulations are unclear, especially because time-series single-cell data before and after therapy are scarce. Second, the mechanisms that underlie the functional heterogeneity of TLSs are poorly understood; we need to dissect the molecular basis by which TLS maturity interacts with the immune microenvironment. Third, no predictive model exists for TIB-mediated immune-related adverse events; multilayer omics data must be used to build risk-stratification systems. Fourth, therapeutic strategies that target TIBs remain monotonous, with most clinical trials restricted to anti-CD20 antibodies; specific interventions for Bregs or TLSs are still lacking.

Future research should focus on the following directions: construct spatiotemporal atlases of TIBs across cancer types by integrating single-cell multiomics, spatial transcriptomics and longitudinal clinical data to reveal how TIB differentiation trajectories relate to therapeutic response. Elucidate combined metabolic and epigenetic control mechanisms, exploring how glutamine metabolism, lactylation and other modifications remodel TIB function. Optimize TLS-based immunotherapy through the development of novel combination regimens that pair LTβR agonists or CXCL13–CXCR5 axis modulators with immune checkpoint inhibitors. Design personalized B-cell vaccines that merge tumor neoantigens with B-cell epitopes to overcome T-cell exhaustion.⁴⁸⁴ Investigate microbiome–TIB interactions, clarifying how the gut microbiota regulates TIBs via metabolites such as short-chain fatty acids or immune mediators.

Crucially, combined immune therapy that simultaneously targets TIBs and T-cell antigens can activate T cells, enhance tumor-cell killing, modulate TIBs immune responses and synergize with T-cell functions to boost antitumor efficacy.⁴⁸⁵ Preliminary data suggest that such dual targeting yields stronger and more durable responses than either strategy alone,⁴⁸⁶ indicating that it should become a central component of the next wave of clinical trials. Further prospective studies across diverse cancer types are now needed to validate these findings, refine dosing and sequencing, and ultimately optimize therapeutic outcomes for patients.

Author contributions

H.Z., K.C. and J.M. collected the related papers and were major contributors to the writing of the manuscript. H.Z. and Z.W. prepared the figures and tables. M.C., Z.Z., Z.W. and Z.Y. drafted the paper and revised it critically for important intellectual content. X.C. and W.Z. provided final approval for the version to be published and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All authors have read and approved the review article.

Competing interests

The authors declare no competing interests.