Migration of immune cells in tumors and inflammation: molecular mechanisms and therapeutic targets

Abstract

Cancer and inflammatory diseases are critically influenced by dynamic interactions between pathological tissues and the host immune system. The precise migration of immune cells into the local microenvironments of tumors or inflammation is a fundamental prerequisite for them to exert their functions. Immune reservoirs, including tertiary lymphoid structures, secondary lymphoid structures, bone marrow and the intestinal tract, serve as critical mobilization hubs for diverse lymphoid and myeloid populations to infiltrate tumors or inflamed sites. The directional migration of immune cells is orchestrated through complex regulatory networks involving chemokine or cytokine-receptor pairs, adhesion molecule interactions, extracellular vesicle signaling, metabolic reprogramming and microbiota modulation. In both tumors and inflammation, immune cell trafficking shapes the local immune landscape, contributing to either immune protection or pathological progression. Contemporary therapeutic strategies targeting immune cell migration encompass the following axes: precision modulation of chemokine or cytokine networks, architectural reprogramming of lymphatic structures or extracellular matrix, dietary intervention and strategic manipulation of microbiome. Nevertheless, clinical translation remains hindered by microenvironmental heterogeneity, suboptimal migratory efficiency, and technical limitations in longitudinal tracking of cellular dynamics. This review integrates recent findings from oncology and inflammatory diseases to explore the origins, phenotypes and trafficking mechanisms of migratory immune cells, highlighting how advances in understanding immune migration across cancer and inflammation can inform therapeutic innovation and precision immunomodulation.

Introduction

The intricate interplay between the immune system and pathological tissues, such as tumors and inflammatory diseases, has long been recognized as a critical determinant of disease progression or alleviation.¹ Whether in cancer or inflammatory disorders, migratory immune cells not only participate in host defense but also contribute to disease exacerbation, reflecting their context-dependent dual functionality.^2,3 While substantial studies have illuminated the phenotypic and functional characteristics of immune cells within tumor and inflamed tissues, fundamental challenges concerning the comprehensive nature of immune responses and therapeutic efficacy remain unresolved.^4,5 In cancer therapy, immune checkpoint blockade (ICB) still faces significant limitations in efficacy, evident in persistent disease progression or rapid relapse after initial response.⁶ Similarly, treatments for chronic inflammatory conditions such as rheumatoid arthritis or inflammatory bowel disease (IBD) frequently exhibit therapeutic resistance or partial remission, necessitating continuous, intensive management.^7,8 These impasses strongly indicate unexplored regulatory dimensions in current therapeutic strategies, potentially mediated by the broader immunological macroenvironment.

Emerging evidence indicates that peripheral immune cells mobilized from reservoirs such as secondary lymphoid organs (SLOs), bone marrow, and the gastrointestinal tract play critical yet often underappreciated roles in modulating disease.^9–11 In cancer, peripheral immune cells, including diverse lymphoid and myeloid subsets, migrate toward tumor sites under specific chemokine gradients and adhesion molecule interactions.¹² Importantly, these recruited immune cells exhibit significant functional heterogeneity and are capable of either promoting robust antitumor immunity or facilitating tumor progression. Similarly, during inflammation, peripheral immune cell migration profoundly shapes disease outcomes. For instance, gut-derived immune cells, including mucosal-associated invariant T cells, can exacerbate joint inflammation in rheumatoid arthritis through targeted trafficking mediated by upregulated E-selectin, ICAM1, and VCAM1.¹³ Conversely, gut-origin IgA⁺ plasma cells traffic into the central nervous system (CNS), alleviating neuroinflammation through the elevation of IL-10, thereby highlighting the dual potential of migrating peripheral cells.¹⁴

In this review, we comprehensively delineate the multidimensional characteristics of immune cell migration in cancer and inflammation, including acute and chronic inflammatory diseases. Specifically, we describe the origins, phenotypic diversities, and dynamic migratory trajectories of these immune cells, examining the intricate regulatory networks that govern their mobilization and functional polarization. The discussion extends to advanced methodologies enabling high-resolution tracking of immune cell trajectories, providing novel insights into the dynamic interactions underpinning effective tumor and inflammatory immunity. Furthermore, a systematic analysis of the molecular determinants governing immune cell trafficking was conducted. Concurrently, we performed a critical evaluation of innovative therapeutic strategies aimed at modulating these pathways. By connecting the mechanisms of immune cell migration to clinical applications, our discussion establishes a cohesive framework that links fundamental insights with therapeutic strategies. This integration ultimately aims to identify precision immunomodulation for treating cancer and inflammatory diseases.

Origin of migratory immune cells

The migration of distinct immune cell subsets from their reservoirs, including lymphoid structures, bone marrow and gut, exerts profound influences on the intralesional microenvironment.^11,15–17 Immune cells derived from different origins exhibit distinct functional properties. For instance, myeloid-derived suppressor cells (MDSCs) from bone marrow exhibit immunosuppressive properties that promote tumor progression, whereas gut-derived Th17 cells can drive inflammatory responses, contributing to the pathogenesis of autoimmune disorders.^18,19 Meanwhile, the migration of immunocytes is governed by sophisticated molecular networks. These specific mechanisms, from chemokine signaling to the modulation of adhesion molecules, ensure precise spatiotemporal control over immune responses.

Tertiary lymphoid structures

Prior investigations have predominantly focused on alterations in immune cell populations within diseased tissues. However, intralesional migration of immune cells plays a pivotal role in driving microenvironmental remodeling²⁰ (Fig. 1). Tertiary lymphoid structure (TLS) initiation involves the recruitment of lymphoid tissue-inducer-like (LTi-like) cells, whose secretion of LTα and TNF drives stromal cell differentiation into lymphoid tissue organizer (LTo) cells.²¹ These LTo cells orchestrate T and B cell recruitment and segregation via the CCL21-CCR7 and CXCL13-CXCR5 axes, establishing a self-amplifying loop that promotes TLS maturation and expansion.²² Mature TLSs, situated within stromal regions of tumors and adjacent to tumor cell nests, constitute critical structures for mediating intratumoral migration of immunocytes.^21,23 High endothelial venules (HEVs) serve as critical structures for recruiting immune cells within mature TLSs. These specialized vessels express peripheral node addressin (PNAd), which binds to L-selectin (CD62L) on circulating immune cells, mediating their trafficking into the tumor parenchyma.²⁴ Intratumoral TLSs can recruit B cells, sustaining their maturation and subsequent antibody production, which is associated with the response to immunotherapy.²⁵ In metastatic melanoma and lung cancer, these tumor-specific antibodies promote natural killer (NK) cell infiltration and mediate antibody-dependent cell-mediated cytotoxicity (ADCC), thereby augmenting the adaptive immune response against tumor cells.^26,27 Within T-B cell segregation, B cells activate T follicular helper (Tfh) cells via the costimulatory molecules ICOSL/CD40L and the cytokine IL-21, which subsequently promote the intratumoral migration of NK cells.²⁸ However, in murine models of non-small cell lung cancer (NSCLC), regulatory T cells (Tregs) have been observed to infiltrate TLSs via the CCL17/CCL22-CCR4 axis, a process associated with adverse prognosis.²⁹ While the upstream mechanisms governing Treg infiltration remain elusive, emerging evidence suggests that these cells may participate in TLS neogenesis.³⁰

Fig. 1.

The origin of migratory immune cells in cancer and inflammation. Immune cells originate from three main sources: secondary lymphoid organs (including spleen and lymph nodes), intestines and bone marrow. Distinct immune cells infiltrate tumors or inflammatory tissues from their reservoirs via unique migratory patterns. Conversely, immune cells within these lesions can also circulate back to their sites of origin, thereby executing their effector functions. Additionally, immune cell migration within the tumor or inflammatory microenvironment may be orchestrated by tertiary lymphoid structures (TLSs), which serve as organized hubs for immune coordination. Purple, red, green, and blue arrows represent the migration pathways of immune cells originating from the spleen, intestines, lymph nodes, and bone marrow, respectively. The black arrows represent the migration of immune cells within tissues or organ axes. Created with BioRender.com. TLS tertiary lymphoid structures, HSCs hematopoietic stem cells, GMPs granulocyte-monocyte progenitors, MDSCs myeloid-derived suppressor cells, MAIT mucosal-associated invariant T cells, FDC follicular dendritic cell, NK cells natural killer cells, T_CM cells central memory T cells, DCs dendritic cells, CTLs cytotoxic T lymphocytes, Tregs regulatory T cells, Tfh T follicular helper cells, Tpex progenitor-exhausted T cells

While the formation of TLSs can be seen as a response to chronic inflammation, immune cells within TLSs often paradoxically exacerbate the inflammatory milieu, contributing to disease progression. This detrimental effect is mediated through immune cell recruitment and subsequent amplification of local inflammatory responses. In lupus nephritis, for example, the presence of the formation of TLSs was associated with a longer disease course together with elevated CXCL13, a chemokine that promotes B cel recruitment and impairs renal function.³¹ Similarly, during atherogenesis, M1-polarized macrophages in TLSs induce vascular smooth muscle cells to express CCL19, CCL20, and CXCL16 via the TNF-α/TNFR signaling pathway.³² This process effectively recruits B cells and T helper cells, whose accumulation significantly amplifies the local inflammatory milieu, ultimately promoting the progression of atherosclerotic plaques.³² Beyond direct recruitment, TLSs serve as crucial niches for immune cell activation and cytokine production, contributing to tissue damage. In chronic obstructive pulmonary disease (COPD), IL-18⁺ M1 macrophages and dendritic cells (DCs) initially localize within pulmonary TLSs, which stimulate responsive lymphocytes to release IFN-γ, promoting tissue damage and inflammation.³³ In progressive multiple sclerosis, TLSs in the subarachnoid space are associated with extensive periventricular infiltration predominantly composed of B cells and follicular dendritic cells (FDCs).³⁴ These immune cells further secrete inflammatory cytokines such as IFN-γ and TNF-α, eliciting microglial activation that exacerbates neuronal and axonal damage.³⁴ Furthermore, TLSs can structurally modify their microenvironment, impacting immune cell trafficking and local immune responses. Within the inflamed intestinal mucosa of IBD patients, TLSs can remodel lymphatic architecture and disturb lymph fluid flow, thereby impeding plasma cell and dendritic cell trafficking. This compromised drainage promotes excessive local antibody production, ultimately exacerbating intestinal inflammation.³⁵

Although TLSs establish privileged migratory routes for intratumoral immune cell trafficking, malignant cells actively counteract immune infiltration through diverse strategies. Cancer cells can impair the physical interactions between tumor and immune cells, including MHC class I:TCR and CD58:CD2, thereby mediating T cell exclusion.³⁶ Physical obstruction of the stroma is another important factor in T cell exclusion. Chi3l1 produced by tumors can promote neutrophil recruitment and neutrophil extracellular trap (NET) formation, which blocks T cell infiltration by forming a physical barrier around tumors.³⁷ Therefore, elucidating the mechanisms by which TLSs orchestrate intralesional immune cell migration and how physical and biological barriers counteract this process is crucial for identifying vulnerabilities to enhance immunotherapy efficacy.

Secondary lymphoid organs

SLOs, including the spleen and lymph nodes, serve as hubs for the initiation of effective adaptive immune responses^38–40 (Fig. 1). Following lymphocyte activation within SLOs, effector and memory lymphocytes egress and migrate to peripheral sites of tumor and inflammation to execute their immune functions.³⁸

In tumor and chronic inflammatory diseases such as atherosclerosis and IBD, the spleen undergoes distinct adaptive alterations, particularly manifesting as splenic extramedullary hematopoiesis.^41–43 Specifically, myeloid precursors such as hematopoietic stem cells (HSCs) display myeloid-biased differentiation at the expense of erythropoiesis and lymphopoiesis.⁴⁴ Primed by IL-6-producing stromal cells, these splenic HSCs subsequently differentiate into MDSCs and migrate to tumors and chronic inflammatory sites, contributing to systematic immunosuppression.⁴¹ Tumor and chronic inflammation facilitate the spleen’s role as a reservoir for immune cells migrating toward distal diseased sites.⁴⁴ For instance, excessive secretion of the peptide hormone angiotensin II (AngII) in murine models of lung adenocarcinoma enhances the self-renewal of HSCs within the spleen, thereby inducing the generation of classical monocytes.⁴⁵ These monocytes egress from the spleen via the S1P1 receptor and migrate into the tumor microenvironment (TME), where they further differentiate into tumor-associated macrophages (TAMs) to facilitate cancer progression.⁴⁵ Similarly, during atherosclerosis, CD45⁺ leukocytes within the splenic red pulp robustly produce GM-CSF and IL-3, inducing the differentiation of HSCs into classical monocytes.⁴² Monocytes born in such extramedullary niches intravasate, circulate, and accumulate abundantly in atheromata, where they exacerbate inflammation by secreting IL-1β, reactive oxygen species (ROS), and proteolytic enzymes.⁴² In contrast, during infection, the spleen primarily regulates the immune response by recruiting immune cells into its compartment rather than functioning as a reservoir for immune cell egress.⁴⁶ Bacterial infection recruits innate response activator B cells to the red pulp in the spleen via VLA-4 and LFA-1 adhesion.⁴⁷ As infection persists, abundant CX3CR1⁺ classical monocytes are recruited to the marginal zone and T cell zone of the spleen and then differentiate into pro-inflammatory TNF- and iNOS-producing DCs (Tip-DCs), triggering a cytokine storm that causes severe tissue injury.⁴⁸ Crucially for the differentiation of these pathogenic Tip-DCs, NK cells have been reported to be a major contributor during Listeria infection.⁴⁹ Once recruited in a CCR5-dependent manner, these NK cells locally produce IFN-γ, which is essential for differentiating monocytes into cytokine-producing Tip-DCs.⁴⁹

Unlike the spleen’s primary role in systemic immune regulation, lymph nodes play a more prominent role in orchestrating immune responses within their local drainage areas.⁴⁰ During tumor development and inflammation, lymph nodes function as crucial sites for antigen capture and serve as sources of migratory immune cells that initiate immune responses.^9,50 The critical entry gateway for immune cells into lymph nodes is HEVs. During tumors and inflammation, HEVs switch to an immature phenotype, with endothelial cells upregulating chemokines and adhesion proteins such as CXCL9, P-selectin, and E-selectin.^51,52 Once across the HEV endothelium, tissue-migratory CCR7⁺ DCs are recruited to T-cell rich zones within the lymph nodes via a CCL21 chemokine gradient secreted by the lymphatic endothelium.⁵³ Within the lymph nodes, these DCs further secrete lymphotoxin to activate LT-βR on the surface of HEV endothelial cells.⁵⁴ Activation of LT-βR maintains the expression of adhesion molecules on HEVs such as GLYCAM-1, thereby ensuring the efficient homing of lymphocytes.⁵⁴ The major function of DCs within lymph nodes is to orchestrate the dual priming of CD4⁺ and CD8⁺ T cells, a process essential for effective CD8⁺ T cell activation.⁵⁵ Initially, activated CD4⁺ T cells license DCs through CD40L-CD40 interactions, enhancing the antigen-presenting and co-stimulatory capacity of DCs.⁵⁶ Subsequently, licensed DCs, along with CD4⁺ T cells, secrete cytokines such as IL-2 and IL-12 that are essential for the full activation and polarization of CD8⁺ T cells. This dual mechanism ensures robust and sustained CD8⁺ T cell responses against tumor or pathogen-derived antigens.⁵⁷ The egress of T cells from lymph nodes to tumor or inflammatory sites is regulated by sphingosine-1-phosphate (S1P) gradients and their interaction with the S1P receptor (S1PR1).⁵⁸ Intrinsically, S1PR1 is indispensable for effector T cell emigration, as its deletion prevents lymphatic sinus entry despite downregulation of retention signals such as CCR7.⁵⁹ The establishment of the S1P gradient within lymphatic vessels depends critically on the activity of the Spinster homolog 2 (SPNS2), which mediates transcellular S1P transport on lymphatic endothelial cells.⁶⁰ Furthermore, desensitization of S1PR1 via G-protein coupled receptor kinase-2 (GRK2) terminates sustained egress signaling in circulation and enables effector T cells to re-enter lymphoid tissues, thus preventing tissue damage caused by excessive effector lymphocyte egress.⁶¹ Collectively, S1PR1 signaling, SPNS2-mediated S1P availability, and GRK2-dependent receptor desensitization constitute the core mechanism governing effector T cell egress from lymph nodes.

During inflammation, LNs are instructive hubs where the geography of lymphatic drainage and the site of priming determine whether immunity is amplified, specialized, tolerogenic or pathogenic. During herpes simplex virus infections, tissue conventional dendritic cells (cDCs) undergo CCR7-dependent migration to draining LNs and transfer antigens to LN-resident DCs for efficient cytotoxic T lymphocyte (CTL) priming and antiviral response amplification.⁶² Building on this principle, LN specialization along distinct drainage basins dictates antibacterial efficacy. After dermal infection with Staphylococcus aureus, skin-draining LNs recruit neutrophils through IL-17-dependent signals mediated by Th17-polarized γδ T cells, thereby orchestrating bacterial clearance.⁶³ In contrast, gut-draining mesenteric LNs fail to effectively combat such infection owing to the absence of such Th17-like γδ T cells populations.⁶³ Moreover, networks of co-draining LNs can impose cross-organ tolerance. Within the co-draining LNs shared by the pancreas, liver, and duodenum, DC1 cells with high Aldh1a2 expression drive retinoic acid-dependent Treg differentiation to establish immunological tolerance and restrain pancreas-directed autoimmunity.⁶⁴ However, intestinal rotavirus infection aberrantly activates DCs across all co-draining LNs via dysregulated interferon signaling, skewing pancreas-reactive T cells toward pro-inflammatory phenotypes and contributing to the pathogenesis of type I diabetes.⁶⁴ Critically, the anatomical location of LNs where T helper cells undergo initial priming dictates their functional phenotype upon homing to distal tissues. T helper cells originating from the mesenteric LNs upregulate P2rx7 and rarely infiltrate the gray matter, whereas those primed in the inguinal LNs exhibit elevated expression of Cxcr6 and preferentially infiltrate both the gray and white matter.⁶⁵ In autoimmune encephalomyelitis, these infiltrating CXCR6⁺ Th cells propagate neuroinflammation by producing IL-17, IFN-γ, and GM-CSF. Furthermore, these cells constitutively express high levels of SerpinB1, which inhibits granzyme-mediated suicidal cell death and sustains the expansion of pathogenic CXCR6⁺ Th cells to perpetuate neuroinflammation.⁶⁶

Tumor-draining lymph nodes (TDLNs) are lymph nodes that are located along the lymphatic drainage pathway of primary tumors.⁶⁷ While lymph nodes in infection and autoimmunity primarily serve as rapid effector priming sites, immune responses within TDLNs are functionally diversified to balance sustained antitumor immunity with the risk of immunosuppression.^69,71 This distinction is further reflected in the composition and functionality of immune cells emigrating from TDLNs. Although ICB induces local expansion of T cells within the TME, T cells originating from TDLNs may play a more critical role in antitumor immunity.⁶⁸ The local TDLN environment serves as a reservoir that maintains the stem-like state of precursor exhausted T (T_PEX) cells by providing a spatially segregated niche for sustained antigenic stimulation.⁶⁹ Upon tumor antigen recognition via TCR, T_PEX cells upregulate CXCR3 and migrate from TDLNs to tumors, where they continuously supply stem-like progeny to the intratumoral T-cell compartment.⁷⁰ By maintaining a pool of responsive precursors within the TME, this process helps sustain ongoing antitumor immunity and may contribute to therapeutic responsiveness, particularly in immunologically cold tumors.⁶⁹ Within the TME, T_PEX cells undergo further differentiation into terminally differentiated (TD) CD8⁺ T cells upon receiving CD28 costimulatory signals from DCs.⁷⁰ These TD CD8⁺ T cells paradoxically retain self-renewal capacity while directly mediating tumor cytolysis through granzyme B (GZMB) and IFN-γ.⁷⁰ Notably, TDLNs can also establish an immunosuppressive microenvironment that impairs immune cell infiltration and function.⁷¹ Primary tumor cells can reportedly induce substantial B cell recruitment in TDLNs, potentially resulting in the production of pathogenic antibodies targeting HSPA4/ITGB5 that can activate Src/NF-κB signaling within tumor cells, ultimately supporting tumor metastasis via the CXCR4/CXCL12α axis.⁷² In a mouse mammary tumor model, high levels of immunosuppressive Treg infiltration in TDLNs were also noted during primary tumor growth, wherein these cells were able to suppress NK cell activation and migration.⁷³ Tumor cells can hijack the lymph nodes to facilitate their metastatic dissemination to other tissue compartments.⁷⁴ Upon invasion by metastatic tumor cells, TDLNs exhibit a profoundly suppressed immune status, characterized by functional impairment of antitumor effector cells and increased infiltration of immunosuppressive cells.⁷⁴ Metastatic tumor cells within TDLNs sustain upregulation of PD-L1 and MHC class I subunits, which in turn suppress cytotoxic functions of T cells and NK cells, respectively.⁷⁵ In a lung carcinoma metastasis model, DCs located in the subcapsular regions of metastatic lymph nodes were found to induce the recruitment of Tregs through the COX-2/EP3-dependent production of stromal cell-derived factor 1 (CXCL12).⁷⁶ These metastatic niches further drive the de novo differentiation of antigen-specific Tregs through cytokines such as TGF-β.⁷⁵ The expanded Treg pool accumulates within metastatic TDLNs and subsequently disseminates systemically, engendering widespread immune suppression.⁷⁵ Therefore, leveraging the dual roles of TDLNs in promoting antitumor immunity and fostering immunosuppression offers a promising direction to optimize immunotherapy and develop novel therapeutic strategies. However, challenges such as lymphocyte activation driven by tumor-nonspecific antigens and broader systemic immune perturbations should be acknowledged. For instance, administration of ICB induces nonspecific activation of highly cytotoxic CD8⁺ T cells and IFN-γ/TNF-α-secreting myeloid cells, culminating the development of colitis.⁷⁷ Beyond this, ICB elevates pro-inflammatory cytokines such as IL-6 and TNF-α across multiple organs, driving nonspecific tissue damage and resulting in systemic immune disruption.⁷⁸ Given that TDLNs are often overlooked in preclinical and clinical studies, we recommend that future work explicitly investigate TDLN-focused strategies to harness their antitumor functions while mitigating their immunosuppressive potential.

Bone marrow

Extramedullary inflammatory diseases and nonhaematological malignancies have been found to profoundly disrupt the bone marrow ecosystem (BME), yet their perturbation patterns exhibit distinct features^1,79 (Fig. 1).

In inflammatory diseases, the bone marrow remodels the hematopoietic system through emergency myelopoiesis (EM) mechanisms, which involve differentiation reprogramming of HSCs.¹¹ Specifically, IL-1 induces the expression of the critical myeloid transcription factor PU.1 to direct myeloid differentiation at the expense of self-renewal in HSCs.⁸⁰ Hence, HSCs function as sustained reservoirs for the generation of hyperinflammatory myeloid cells, which are major contributors to chronic inflammatory pathology.⁸¹ During systemic lupus erythematosus, HSCs constitutively differentiate into M1 macrophages that produce TNF-α and IL-6 to exacerbate inflammation.⁸² Even after resolution of primary inflammation, these HSCs can persist within the bone marrow for extended periods and rapidly differentiate into hyperinflammatory macrophages upon stimulation, triggering systemic lupus erythematosus (SLE) relapse.⁸² Such myeloid differentiation bias during EM is further amplified by dysregulation of the WNT/β-catenin-IRF8 signaling axis. Upregulated β-catenin suppresses IRF8, triggering aberrant self-renewal and abnormal clustered aggregation of granulocyte-monocyte progenitors (GMPs) that accelerate myeloid amplification.⁸³ In IBD, these GMPs massively accumulate in the gut and differentiate into short-lived neutrophils and inflammatory monocytes, thereby exacerbating intestinal inflammation.⁴³ Although tumors similarly induce EM and skewed progenitor differentiation in the bone marrow, the underlying mechanisms involved differ from those in inflammatory diseases. Cancer-induced EM, initiated by cytokines, including G-CSF, GM-CSF and IL-6, profoundly modulates the expansion and differentiation of multiple progenitor populations in the bone marrow.^84,85 Within the context of EM, hyperactivation of STAT3 and/or STAT5 suppresses IRF8 expression, resulting in aberrant self-renewal of GMPs and induction of MDSCs.⁸³ These tumor-induced alterations, particularly the expansion and immunosuppressive function of MDSCs, critically impair immune cell function within tumors.¹⁹ Moreover, the G-CSF-suppressed IRF8 axis not only promotes MDSC emergence but also simultaneously represses the production of cDCs from myeloid progenitors, augmenting immune evasion of tumor antigens.⁸⁶ HtrA serine peptidase 1 (HTRA1) carried by tumor-derived small extracellular vesicles also drives expansion of granulocyte-monocyte progenitors and HSCs, generating an EM-promoting niche at the endosteum through the production of MMP13.⁸⁷ Notably, these alterations persist long after primary tumor resection, indicating durable effects on hematopoiesis.⁸⁷ Collectively, these studies exemplify how cancer cells can manipulate the EM mechanism and hematopoietic-stromal niche unit to alter the number and entrained functions of myeloid cells reaching the tumor.

Aging is another contributor to BME remodeling. However, current research lacks in-depth investigation into the molecular mechanisms by which senescence directly regulates immunocyte egress from the bone marrow. Existing evidence indicates that senescence-mediated BME remodeling affects hematopoietic differentiation processes and alters the composition of immune cell output. During organismal aging, degeneration of bone marrow sympathetic nervous function attenuates β3-adrenergic receptor (ADRβ3) signaling, thereby contributing to the senescence of HSCs.⁸⁸ These aged HSCs exhibit a significantly rapid cell cycle, declined regenerative capacity, minimal efficacy in homing to bone marrow and generate a higher number of myeloid cells.⁸⁹ In addition to senescent HSCs, bone marrow adipocytes (BMAds) also contribute to the egress of myeloid cells. A large increase in the abundance of BMAds with altered secretory profiles occurs during ageing.⁹⁰ For instance, higher DPP4 levels expressed by BMAds cleave key hematopoietic regulators, including G-CSF, GM-CSF and IL-3, impairing HSC retention and promoting myeloid-biased differentiation.⁹¹ Collectively, these mechanisms promote the expansion of myeloid cells within bone marrow. These myeloid cells are recruited into the TME via CSF-1/CSF-1R signaling and subsequently differentiate into TAMs, thereby promoting tumor progression.⁹² Beyond altered differentiation, senescence also perturbs the trafficking and effector function of mature myeloid cells. As age increases, loss of rhythmic Kruppel-like factor 4 (KLF4) expression in senescent macrophages disrupts diurnal trafficking from the bone marrow and impairs phagocytic activity, thereby heightening patients’ susceptibility to infection.⁹³

Gut

Clinical and experimental observations have established the gut as a central organ for several inflammatory diseases of extraintestinal organs and demonstrated disease-relevant communication via the gut-liver, gut-joint and gut-brain axes^94–96 (Fig. 1). In gut-liver axis, aberrant expression of gut-specific adhesion molecules such as MADCAM1 on hepatic vessels in patients with primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC) provided strong evidence for hepatic recruitment of mucosal T helper cells that are primed initially in the intestinal environment.^97,98 Notably, liver sinusoidal endothelial cells might promote gut tropism by upregulating gut-homing markers α4β7 and CCR9 in a retinoic acid-dependent manner, supporting an enterohepatic lymphocyte circulation from the liver back to the gut.⁹⁹ The gut-joint axis operates through a similar mechanism but involves a broader spectrum of immune cell types. During the pre-arthritic phase, upregulation of zonulin reduces the expression of intestinal tight junction proteins such as ZO-1 and occludin, thereby enhancing gut permeability and facilitating translocation of intestinal Th1 and Th17 cells into circulation.¹⁸ Following migration to the synovial tissue, these cells induce osteoclast accumulation that promotes joint erosive damage and inflammation.¹⁸ Mucosal associated invariant T (MAIT) cells are another lymphocyte subset that undergoes targeted trafficking to the joints. This process is enabled by the TNF-α and IL-1β-induced upregulation of E-selectin, ICAM1, and VCAM1 on synovial endothelial cells in the inflammatory milieu.¹⁰⁰ While the gut-liver and gut-joint axes predominantly exacerbate tissue inflammation and damage, immune cell trafficking via the gut-brain axis possesses broader functions, including mediating both pro-inflammatory and anti-inflammatory effects. During multiple sclerosis, intestinal IgA⁺ plasma cells are recruited into the brain and spinal cord to attenuate neuroinflammation in an IL-10-dependent manner.¹⁴ Local immune cells of the CNS may also be programmed by gut-derived cells. For example, a subset of IFN-γ-producing meningeal NK cells derived from the gut promotes the development of neuroimmunoregulatory astrocytes that express LAMP1 and TRAIL.¹⁰¹

In addition to the gut-liver, gut-joint and gut-brain axes in inflammation, the gut-bone marrow circuit plays a crucial role in the regulation of tumor immunity. In leukemic mice, immunogenic chemotherapy has been shown to prime central memory T (T_CM) cells with enhanced gut-to-bone marrow trafficking capacity, thereby potentiating immune-mediated leukemic cell clearance.¹⁰² Beyond hematological malignancies, this circuit also impacts solid tumors. Gut-bone crosstalk has been shown to modulate melanoma metastasis and growth by recruiting intestinal NK and Th1 cells to the tumor-associated bone marrow, and clinical evidence further indicates that disruption of intestinal homeostasis is associated with inferior outcomes in patients with melanoma.¹⁰³ Nutritional interventions such as dietary restriction induce immunocyte redistribution from the gut to the bone marrow.¹⁰⁴ Specifically, during fasting, naive B cells traffic from the small intestinal Peyer’s patches to the bone marrow and return to the small intestine after refeeding.¹⁰⁵ This nutritional stress-induced redistribution of immune cells exemplifies a fundamental mechanism by which systemic metabolism reshapes immune cell dynamics, indicating that dietary interventions enhance anti-tumor immunity by reprogramming bone marrow-immune crosstalk.^102,104

Types and properties of migratory immune cells

The immunological landscape of cellular constituents fundamentally governs tumor immunity and inflammatory responses. For instance, intratumoral infiltration of CTLs correlates with prolonged disease-free survival across multiple malignancies, whereas Treg infiltration is frequently associated with adverse clinical outcomes.¹⁰⁶ This principle extends to chronic inflammatory diseases, such as rheumatoid arthritis. Synovial enrichment dominated by CTLs drives potent destructive inflammation, whereas myeloid cell-mediated inflammation predisposes toward chronic maintenance and tissue remodeling.¹⁰⁷ Nevertheless, the immune landscape is governed by multifactorial determinants. For instance, low-grade gliomas exhibit sparse lymphocytic infiltration with predominant M2 macrophage polarization. In contrast, gastric and ovarian carcinomas demonstrate M1 macrophage profiles coincide with enriched CD8⁺ T cell signatures.¹⁰⁸ These findings underscore that cancer subtypes and the TME are key determinants of immune landscape composition. Additionally, a study in patients with asthma revealed progressive neutrophilic predominance in sputum with advancing age, underscoring age as an additional determinant of immune cell composition within inflammatory tissue microenvironments.¹⁰⁹ However, the precise spatiotemporal positioning of immune cells within pathological niches is fundamentally contingent on their migratory dynamics, thereby representing a fundamental prerequisite for immunocyte functional impact (Fig. 2) (Table 1). Consequently, understanding the molecular mechanisms governing immune cell trafficking is pivotal for deciphering disease pathogenesis and developing targeted immunomodulatory strategies.

Fig. 2.

Subtypes of migratory immune cells. Distinct subsets of adaptive and innate immune cells employ specialized migratory mechanisms to traffic into tumor or inflammatory sites, where they orchestrate specific effector functions. Created with BioRender.com. DCs dendritic cells, cDCs conventional DCs, mregDCs mature regulatory DCs, pDCs plasmacytoid DCs, moDCs Monocyte-derived DCs, Tfh T follicular helper cells, Tregs Regulatory T cells, Breg regulatory B cells, T_CM central memory T cells, Tpex progenitor-exhausted T cells, CD8⁺ TA effector T cells, TAM tumor-associated macrophages, ILC Innate. lymphoid cells, NK cells natural killer cells, MDSCs myeloid-derived suppressor cells, TANs tumor-associated neutrophils

Table 1.

Functions of migratory immune cells in the tumor microenvironment

Cell type	Subtype marker	Origin	Species	Effects on tumor cells	Refs
Adaptive immune cells
CD8+T cell	CMKLR1+	Adjacent normal liver and lung tissue	Human and mouse	Cytotoxic effects similar to NK cells.	ref. 113
	TCRαβ+	Induced by CRISPR/Cas9 in vitro	Human	Antibody-dependent cell-mediated cytotoxicity.	ref. 114
	NKp30+
	CD161+
	CD62L+	Tumor-draining lymph nodes	Human	Mounting a rapid and pronounced immune response upon re-encounter with the tumor antigen.	ref. 518
	CCR7+
	TCF1+	Tumor-draining lymph nodes	Human and mouse	Sustained anti-tumor immune response.	ref. 69
	CX3CR1+	Tumor-draining lymph nodes	Mouse	Producing cytotoxic molecules and pro-inflammatory cytokines in TME.	ref. 519
	TCF1-
	CD39+	Tumor-draining lymph nodes	Human and mouse	Irrecoverable loss of intrinsic and therapeutically inducible anti-tumor activity, exhibiting immunosuppressive effects.	ref. 121
	TIM-3+
CD4+T cell	CD195+	Tumor-draining lymph node	Human	Early response to anti-PD-L1 plus anti-CTLA4 therapy.	ref. 520
	CD26+	Peripheral blood	Human and mouse	Cytotoxic effects, self-renewal and maintenance of long-term antitumor activity.	ref. 521
	S1P1+	Thymus and lymph node	Mouse	Improving immunosurveillance and tumor-specific immune responses.	ref. 522
	PDLIM4+
Treg	GPR15+	Thymus	Human and mouse	Inhibiting antitumoral CD8+T cell immunity and facilitating tumorigenesis by producing IL17 and TNFα.	ref. 148
	CXCR3+	Tumor-draining lymph nodes	Mouse	Inhibiting cross-presentation of tumor antigens by DC1s, thereby limiting activation and function of anti-tumor CD8+T cells.	ref. 523
	CCR4+	Peripheral lymph nodes	Human and mouse	Suppressing effector T cell function and promoting tumor resistance to immunotherapy.	ref. 293
	CCR6+	Peripheral blood and lymphatic tissue	Human and mouse	Promoting immune evasion by expressing high levels of CD25 and inhibiting effector T cell activity.	ref. 302
B cell	ICOSL+	Peripheral blood	Human and mouse	Stimulate the generation of Th1 cells and CTLs.	ref. 524
	CD45+	Spleen	Mouse	Differentiating into plasma cells upon contact with neutrophils, resulting in IgG production.	ref. 312
	B220+
	CD138-
	MUM1+	Tertiary lymphoid structures	Human	Producing IgG antibodies that mediate apoptosis of tumor cells via effector macrophages.	ref. 525
Innate immune cells
Dendritic cells	CD103+	Bone marrow	Human	Activating CD8+T cells by cross-presentation of tumor-associated antigens.	ref. 526
	CD11b+	Bone marrow	Human and mouse	Activating CD4+T cells by presentation of MHC II-associated tumor antigens.	ref. 527
	CD303+	Bone marrow	Mouse	Inducting cDC1 maturation by type I interferon production and enhancing effector functions of CD8+ T cells and NK cells.	ref. 528
	CD304+
	CD123+
	CD64+	Bone marrow	Mouse	Inducing CD4+T cell activation and IL-17 production.	ref. 529
	IRF8+
NK cells	CX3CR1+	Peripheral blood	Human and mouse	Inhibiting tumor cell metastasis through the STAT3 pathway.	ref. 530
	CXCR6+	Peripheral blood	Human	A subpopulation of immune cell responding to irradiation.	ref. 531
	CXCR3+	Peripheral blood and lymphatic tissue	Mouse	Directly eliminating tumor cells and promoting the formation of immune memory.	ref. 532
	NKG2D+	Peripheral blood	Human	Mediating cytotoxic function by recognizing stress proteins on tumor cells.	ref. 533
	XCL1+	Peripheral blood	Human	Recruiting cross-presenting dendritic cells and activating T-cell immunity.	ref. 534
	XCL2+
	ATF3+	Peripheral blood	Human	Exhibiting higher cellular stress response, immunosuppressive signaling, and metabolic activation.	ref. 535
	BAG3+
	GADD45B+
	DUSP1+
Innate lymphoid cells-2	KLRG1+	Gut	Human and mouse	Induce tertiary lymphoid structures.	ref. 218
	GATA3+	Skin or small intestine	Human and mouse	Secreting GM-CSF, IL-5 and IL-13 recruiting anti-tumor immune cell infiltration.	ref. 536,537
	Sca-1+
	RORγt-
	IL10+	Peripheral blood	Human and mouse	Suppressing T cell activity under hypoxic conditions by secreting immunosuppressive factors, such as IL-10.	ref. 547
	CD103-
	ST2+	Bone marrow and spleen	Human and mouse	Secreting cytokines such as IL-5 and activating eosinophils, thereby promoting tumor growth and progression.	ref. 538
	Sca-1+
Monocyte/Macrophage	Ly6Chigh	Bone marrow	Mouse	Enriched in hypoxic regions, pro-angiogenic and inhibiting T cell proliferation after differentiation into tumor-associated macrophages (TAMs).	ref. 539
	CX3CR1low
	Ly6Chigh	Bone marrow	Mouse	Promotes endothelial translocation and colonization of tumor cells in distant organs by secreting SDF-1 after differentiation into CXCR4high TAMs.	ref. 540
	CCR2+
	CXCR4+
	Gr-1+	Bone marrow	Human and mouse	Promoting tumor metastasis by secreting VEGF after differentiation into TAMs.	ref. 181
	CCR2+	Bone marrow	Human and mouse	Promoting tumor survival, proliferation and angiogenesis by secreting a variety of cytokines after differentiation into TAMs.	ref. 541
	CX3CR1−
	CCR2+	Bone marrow	Mouse	Supporting tumor progression by inducing apoptosis of cytotoxic T cells, promoting angiogenesis, triggering fibrosis and remodeling the ECM.	ref. 542
	CX3CR1+
Myeloid-derived suppressor cells	DPP-4+	Bone marrow	Human and mouse	Leading to immunosuppression through high expression of integrin β1 and DPP-4.	ref. 192
	CD11b+	Bone marrow and spleen	Mouse	Suppressing T cell and NK cell function and inducing tumor epithelial-mesenchymal transition.	ref. 543
	Gr-1+
	CX3CR1+	Bone marrow	Mouse	Inhibiting the anti-tumor activity of CD8+T cells, thereby promoting tumor growth and metastasis.	ref. 544
Neutrophils	CD49d+	Skull bone marrow	Human and mouse	Activating T cells in an MHCII-dependent manner to control tumor growth.	ref. 205
	CXCR2-Ly6Glow/high
	CXCR2+	Bone marrow	Human and mouse	Inducing tumor resistance to chemotherapy and immunotherapy.	ref. 545
	Ly6G+	Bone marrow	Human and mouse	Inducing the formation of neutrophil extracellular traps that support tumor colonization and growth in the lung.	ref. 546
	CD11b+
	Ly6G+	Bone marrow	Human and mouse	Activating AXL receptors on tumor cells to promote tumor regeneration.	ref. 547
	Gas6+

Adaptive immune cells

CD8⁺ T cells

Among adaptive immune cells, distinct subtypes of CD8⁺ T cells, including effector CD8⁺ T cells, central memory CD8⁺ T cells and precursor exhausted T cells, exhibit disparate migration properties and unique immunoregulatory functions. Activated CD8⁺ T cells (CD8⁺ TA) serve as primary mediators that directly eliminate malignant or infected target cells.^110,111 Conventional theory reveals that CD8⁺ TAs can be recruited to targeted cells by antigen-dependent and antigen-independent mechanisms. Key inflammatory mediators, including IFNγ, TNF and IL-1, potentiate this trafficking through stereotyped integrin upregulation, directing CD8⁺ TA homing to TMEs and infection sites.¹¹² Recent studies have identified CD8⁺ TAs with distinct activation or differentiation states. Chemerin chemokine-like receptor 1 (CMKLR1⁺) CD8⁺ TAs recruited by chemerin and α4β1 integrin develop NK cell-like properties at the tumor site, significantly enhancing their cytotoxic capacity.¹¹³ B-cell lymphoma/leukemia 11B (BCL11B)-deficient CD8⁺ TA cells effectively infiltrate tumors via transendothelial migration, maintaining both cytotoxicity and memory properties to ensure sustained anti-tumor efficacy.¹¹⁴ Conversely, the formidable trafficking and effector capacity of CD8⁺ TAs can be misdirected, precipitating severe immunopathology. For instance, immune checkpoint inhibitors can promote the aberrant migration of CXCR6-expressing CD8⁺ TA cells to the thyroid gland, where they secrete IFN-γ and granzyme B to mediate the pathogenesis of autoimmune thyroiditis.¹¹⁵ Similarly, in multiple sclerosis, CD8⁺ TA cells driven by myelin basic protein antigen-presenting signals preferentially home to cerebral parenchyma over the spinal cord.¹¹⁶ Subsequently, CD8⁺ TA cells activate myeloid populations in a FasL-dependent manner and potentiate intracerebral ROS production, thereby exacerbating neuroinflammation in multiple sclerosis.¹¹⁶

Additionally, the potent effector response of CD8⁺ TA can be maintained and replenished by a reservoir of central memory CD8⁺ T cells (T_CMs), which differentiate from naive CD8⁺ T cells following antigenic stimulation. The expression of CCR7 and CD62L on T_CM enables their homing to lymphoid organs from circulation.^117,118 Residing in the SLOs, T_CM cells possess self-renewal capacity and multilineage differentiation potential, thereby conferring a significant advantage for long-term immune protection and robust secondary immune responses.^117,118 Upon viral infection, T_CM cells rapidly differentiate into CD8⁺ TA cells that substantially reduce viral loads.^117,118 Similarly, T_CM is capable of mediating long-term tumor control through memory recall responses.¹¹⁹ Upon activation by tumor antigens, T_CM cells egress from TDLNs and enter the circulation to differentiate into CD8⁺ TA cells, thereby mediating IFN-γ-mediated immune activation and enhancing the efficacy of immunotherapy.¹²⁰

Sustained antigen exposure ultimately drives the progression of CD8⁺ TA into exhausted states. While exhausted T cells (T_EX) and terminally exhausted T cells (T_EX-term) exhibit restricted tissue penetration and are retained in the tumor core via metabolic constraints,¹²¹ T_PEX exhibit a propensity to migrate to SLOs and retain the capacity for self-renewal.^110,122 The homing and retention of T_PEX cells within lymph nodes are governed by TGF-β-mediated regulation of integrin α4β1/α4β7 expression during chronic infection.¹²³ However, the egress of T_PEX cells from lymphoid organs accelerates their differentiation, thereby attenuating stemness properties. CXCR3-mediated intratumoral trafficking of T_PEX cells coincides with their differentiation toward CD8⁺ TA cell lineages.¹²⁴ Although this transition is associated with attenuated stemness, concomitant upregulation of granzyme B and IFNγ enhances effector functionality.^124,125 This migratory property of T_PEX cells further underscores their targetability in anti-PD-1 therapy.¹²⁴

CD4⁺ T cells

Among CD4⁺ T cell subsets, the functional competence of Th17, Tfh, and Tregs is intimately linked to their migratory potential.

Steady-state Th17 cells primarily reside in mucosal barriers such as the intestinal lamina propria, where they secrete IL-17A, IL-17F, and IL-22 to prevent microbial invasion and mediate tissue homeostasis.^126,127 However, these intestinal-originated Th17 cells can be converted to pathogenic CXCR6⁺ Th17 cells under the stimulation of inflammatory signals mediated by IL-23 and migrate out of the gut to participate in extra-intestinal autoimmune disease.^128,129 Recruitment of Th17 cells in the context of malignancies further exemplifies their role in pathogenic progression. In diffuse large B-cell lymphoma, overexpression of miR130b downregulated tumor OX40L expression by directly targeting the IFNAR1/p-STAT1 axis. This alleviates OX40/OX40L interaction-mediated suppression of Th17 cells, promoting their recruitment into the lymphoma microenvironment.¹³⁰ These recruited Th17 cells induce an immunosuppressive TME by stimulating tumor cell stemness, proliferation, migration, and invasion.¹³⁰ Cytokine TWEAK-secreting Th17 cells, recruited by CD163L1⁺ macrophages, can promote epithelial-mesenchymal transition (EMT) by binding TWEAK to receptor Fn14 on tumor cells, therefore enhancing tumor migration and invasion.¹³¹

Tfh cells are the specialized CD4⁺ T cell subset that promote the germinal center (GC) reaction and differentiation of B cells.¹³² Under the guidance of CXCL13, Tfh cells migrate from the T cell zone to the T-B cell border, where they interact with B cells through ICOS-ICOSL and CD40L-CD40 interactions and ultimately migrate into the GC in the B cell zone.¹³³ In autoimmune diseases, Tfh cells at the T-B cell border tend to travel through efferent lymph to the blood and are referred to as circulating Tfh (cTfh) cells.¹³⁴ These cTfh cells exacerbate autoimmune responses by eliciting pathogenic IL-21 secretion from B cells, which antagonizes the immunosuppressive function of regulatory T cells.¹³⁵ Treatment with the drug FTY720, which prevents lymph node exit, can dramatically decrease the number of c Tfh cells.¹³⁶ Migratory Tfh cells can also respond to tumor immunotherapy, exemplified by their increased frequencies of infiltration after ICB administration in different types of cancer.^137,138 Within the TME and TDLNs, IL-21 secreted by Tfh cells restores CD8⁺ T cell-dependent antitumor immunity by enhancing the expression of IFN-γ and granzyme B.¹³⁹ Notably, CD8⁺ TAs further recruit IL-12-producing Tfh cells via CXCL13-CXCR5 axis, thereby sustaining their effector functions.¹³⁹

Whereas the majority of immune cells function to promote inflammation to fight pathogens and cancers, Tregs keep immunity in check to maintain homeostasis and prevent pathology.¹⁴⁰ Tregs exhibit tissue-agnostic migratory patterns by bearing TCRs that recognize common tissue antigens rather than highly restricted tissue-specific antigens.¹⁴¹ This migratory pattern is further regulated by key transcription factors including BATF and GATA3.^142,143 Ablation of BATF in Tregs impairs their migratory capacity to multiple peripheral sites, particularly visceral adipose tissue, lung, colon and bone marrow.¹⁴² Along with BATF, GATA3 has also been recognized as a pivotal regulator critical for the trafficking of Tregs into tissues and the maintenance of tissue residency.¹⁴⁴ Within the TME, Tregs are an immunosuppressive subset of CD4⁺ T cells with an essential role in tumor progression.¹⁴⁵ The infiltration of Tregs into tumor tissues has been associated with poor prognosis for patients with cancer.¹⁴⁶ Tumor-infiltrating Tregs expressing high levels of CCR4 were specifically recruited into the tumor via their interaction with CCL22, expressed by both ovarian cancer cells and TAMs.¹⁴⁷ GPR15^high Tregs can directly migrate from the thymus to tumors under inflammatory stimuli. These cells adopt a Th17-like phenotype to suppress anti-tumor immunity.¹⁴⁸ After entering the tumor, upregulated expression of CCR8 on Tregs might play a pivotal role in cell retention that prevents Tregs from trafficking out of the TME.¹⁴⁹

B cells

The migratory activity of B cells occurs predominantly within lymphoid organs, where distinct subsets exhibit specialized migratory mechanisms. Conventional B (B-2) cells chemotaxis into inflammatory lesions are amplified by CCL5 released from T cells, which are sequentially recruited through an autocrine CCL5-CCR1 signaling axis established by CCR1^high/CCL5^high macrophages.¹⁵⁰ Once positioned, these B-2 cells engage cognate T cells to initiate robust BCR-driven activation and differentiation programs that underpin autoantibody production.¹⁵⁰ Memory B cells recruited by CXCL9-CXCR3 or CXCL13-CXCR5 axis significantly contribute to the formation of TLS.^52,151 The presence of intratumoral TLSs has been associated with favorable clinical outcomes in patients with ovarian cancer.⁵² While in giant cell arteritis, memory B cells induced TLSs may exacerbate the inflammatory response and contribute to vascular injury.¹⁵¹ Whereas mature plasma cells remain largely nonmotile, immature plasma cells exhibit CXCL12-CXCR4 axis-directed migratory activity, orchestrated by Wnt and TGF-β pathways in cancer cells.¹⁵² Infiltration of these immature plasma cells suppresses colorectal cancer liver metastasis by enhancing cytotoxic T cell activation and is associated with improved patient survival.¹⁵²

The migration and spatial localization of regulatory B cells (Bregs) are pivotal determinants of their immunomodulatory functions, orchestrating divergent outcomes in cancer and autoimmune diseases. In the TME, Breg trafficking and infiltration are primarily modulated by local signals. For instance, intratumoral CXCL9/CXCL10 promotes their infiltration through microRNA 15A and 16-1-mediated activation of the IκB kinase complex.¹⁵³ Additionally, knockdown of tumor cell-derived IL-1β resulted in diminished frequencies of Bregs, suggesting that IL-1β signaling modulates the Breg trafficking mechanism.¹⁵⁴ Once positioned within the TME, Bregs that produce IL-35 primarily aggregate within TLSs, hindering endogenous antitumor T cell immunity via a STAT3-mediated decrease in CD8⁺ T cell infiltration.¹⁵⁵ Complementing this, another subset of Bregs is characterized by high expression of LARS. These LARS⁺ Bregs can secrete TGF-β1 through activation of the mTORC1 signaling pathway, thereby suppressing CD8⁺T cell effector functions and attenuating antitumor immune responses.¹⁵⁶ In contrast to their pro-tumoral role, the migratory capacity of Bregs is instrumental in ameliorating inflammation in autoimmune settings. In a preclinical multiple sclerosis model, dopamine receptor D3 (DRD3) signaling upregulates the homing molecule CD49d on Bregs, facilitating their entry into the CNS.¹⁵⁷ Within the CNS, IL-10 secreted by Bregs not only suppresses microglial production of pro-inflammatory TNF-α and IL-6 but also inhibits T cell polarization toward pathogenic Th1/Th17.¹⁵⁸ This dual functionality establishes Bregs as critical regulators restraining the progression of autoimmune encephalomyelitis.¹⁵⁸ Beyond the site of inflammation, intravital imaging has revealed that Bregs can selectively migrate into T-cell zones of lymph nodes and directly contact T cells.¹⁵⁹ This interaction physically limits T cell access to DCs and reduces the contact of T cells and DCs, thereby curbing the priming of pathogenic T cells.¹⁵⁹

Innate immune cells

Dendritic cells

As pivotal bridges connecting innate immunity and adaptive immunity, DCs require precise migratory positioning to fulfill their antigen-presenting functions.^15,160 After stimulated by inflammatory and tumor signals, cDCs upregulate the expression of MHC class II, costimulatory molecules and the chemokine receptor CCR7, guiding cDC trafficking toward lymph nodes via afferent lymphatics.^15,161 cDCs are subdivided into cDC1 and cDC2 subpopulations. Both cDC1s and cDC2s can present antigens through MHC class I and MHC class II pathways, and the presentation efficiency of each subset is regulated by local activation signals.¹⁶² cDC1s can be recruited into the TME by XCL1 and CCL5, produced by intratumoral NK cells.¹⁶³ Within the melanoma, cDC1s acquire antigens from necrotic tumor cells and specifically migrate to TDLNs, where they present antigens to naive CD8⁺ T cells and prime cytotoxic effector CD8⁺ T cells.¹⁶⁴ During asthma exacerbations, cDC2s that specifically infiltrate inflamed airways interact with Th2 cells via costimulatory molecules.¹⁶⁵ The localized DC2-Th2 crosstalk establishes Th2 residence in the airways, induces pathogenic Th2 phenotypes, and promotes IL-9 production through PPARγ activation, establishing a positive feedback loop that amplifies type 2 inflammation.¹⁶⁵ However, a recent study identified a new subset of cDCs that preferentially resides within tumors. These cDCs progressively downregulate the expression of molecules involved in antigen presentation and pro-inflammatory transcripts, serving as a potential marker for predicting therapeutic response.¹⁶⁶ Beyond their antigen-presenting function, migratory cDCs can directly recruit immune cells and drive tumor progression. For instance, cDCs expressing LAMP3 can recruit immunosuppressive Tregs through the CCL17/CCL22-CCR4 axis, thus driving tumor progression.¹⁶⁷ Further investigations identify these LAMP3⁺ CCR7⁺ cDCs as mature regulatory DCs (mregDCs) based on their distinct molecular profile, which features the coordinated expression of immunoregulatory molecules, including PD-L1, PD-L2, and CD200.^162,168 mregDCs rely on the CCR7-CCL19/CCL21 chemokine axis for migration to lymph nodes, where they mediate immunomodulatory functions while retaining their capacity to activate T cells.^168,169 Within the TDLN, mregDCs upregulate PD-L1 via the AXL signaling pathway following antigen uptake, thereby impairing CTL activity and ultimately curtailing anti-tumor immunity.¹⁶⁸ Similarly, during sepsis, mregDCs in the lymph nodes promote the polarization of CD4⁺T cells toward Treg and Th2 cells through the secretion of IL-4i1 and CCL22, which attenuates excessive inflammation.¹⁷⁰ Beyond these immunomodulatory roles, mregDCs are critical for sustaining adaptive immune responses. mregDCs promote the formation and maturation of TLSs through the high expression of costimulatory molecules CD80, CD86 and CD40 alongside cytokines IL12B and IL15.¹⁷¹ These molecules also serve as vital signaling cues that sustain T cell differentiation, activation, and survival.¹⁷¹ Furthermore, mregDCs can recruit T_PEX via CXCL9 and CCL5 while sustaining T_PEX expansion and self-renewal through CD80-CD28 costimulatory signaling, ultimately promoting durable responses to ICB.¹⁷²

Monocyte-derived DCs (moDCs) and plasmacytoid DCs (pDCs) are inflammatory DC subsets that predominantly operate within inflammatory contexts instead of tumors. Notably, in solid tumors, most intratumoral DCs are monocyte-derived DCs, whereas cDCs are less frequent and pDCs often represent a minor subset.^173,174 During parasitic infection, moDCs originate from CCR2-mediated recruitment of blood classical monocytes and are capable of activating protective Th1 responses at the site of infection.¹⁷⁴ In the inflamed colon, CX3CR1^intLy6C^low moDCs with the capacity for antigen presentation and T-cell priming can also egress from the colonic lamina propria toward the mesenteric lymph nodes, contributing to colon inflammation.¹⁷⁵ Commonly distributed in peripheral blood and lymphoid organs, pDCs are potent producers of type I interferon (IFN) with unique migratory properties.¹⁵ After CCR7-mediated extravasation into lymphoid tissues, pDCs further upregulate CCR6 and migrate to the inflamed epithelium in response to CCL20 and CCL27. Subsequently, pDCs contribute to the production of IFN I, which facilitates pathogen clearance and suppresses local inflammation.¹⁷⁶

Monocyte/Macrophage

Based on the expression levels of Ly6C, monocytes in peripheral blood can be classified into classical (Ly6C^high) and nonclassical (Ly6C^low) subsets.¹⁷⁷ Classical monocytes, primarily utilizing the CCL2-CCR2 signaling axis for migration, often play a pro-pathogenic role. For instance, during nonalcoholic steatohepatitis, classical monocytes migrate to the liver, where they subsequently differentiate into pro-inflammatory monocyte-derived Kupffer cells.¹⁷⁸ This migratory process displaces intrahepatic tolerogenic resident Kupffer cells, thereby exacerbating hepatic inflammation and injury.¹⁷⁸ Similarly, in the context of severe COVID-19, CCL2-driven recruitment of classical monocytes into the airways establishes a self-amplifying inflammatory loop and promotes pulmonary fibrosis through their differentiation into TGF-β-secreting macrophages.^179,180 The pro-pathogenic capacity of classical monocytes extends to oncology. In breast cancer, classical monocytes are preferentially recruited to pulmonary metastases via CCL2-CCR2 axis.¹⁸¹ During the early stages of metastasis, tumor cell extravasation is critically dependent on VEGF secreted by classical monocytes. Subsequently, classical monocytes differentiate into metastasis-associated macrophages, which sustain the proliferation of tumor cells within established metastatic lesions.¹⁸¹ Nonclassical monocytes typically infiltrate diseased tissue via CX3CR1-dependent patrolling. During inflammatory primary graft dysfunction, infiltration of nonclassical monocytes and subsequent activation of MyD88/TRIF signaling trigger the secretion of CXCL2, which recruits neutrophils and drives pulmonary inflammatory injury.¹⁸² Moreover, in colorectal cancer, nonclassical monocytes recruitment by peritumoral vascular endothelia establish an immunosuppressive microenvironment, where nonclassical monocytes produce IL-10 and promote resistance to anti-VEGFR2 therapy.¹⁸³ Conversely, nonclassical monocytes can also exert potent anti-tumor effects. In lung metastasis models, nonclassical monocytes recruited by the CX3CR1-CX3CL1 subsequently secrete chemokines including CCL4 and CCL5, which further recruit NK cells to potentiate cancer immunosurveillance.¹⁸⁴

During tumorigenesis and inflammation, the trafficking of macrophages is predominantly mediated by blood monocytes that infiltrate tissues and differentiate into diverse functional subsets.^185,186 Following infiltration, TAMs undergo further directed migration and spatial redistribution into specialized niches, particularly in perivascular regions, where they orchestrate critical steps of tumor progression. Tumor hypoxia-induced ANGPT2 expression stimulated the recruitment and revascularization of perivascular aggregates of TIE2-expressing TAMs.¹⁸⁷ Upon perivascular localization, TIE2⁺ TAMs drive VEGF-A-mediated signaling, leading to the disruption of endothelial junctions and transient vascular hyperpermeability that facilitates tumor distant metastasis.¹⁸⁷ Complementing this, tumor-derived TGF-β upregulates CXCR4 expression on TAMs, while perivascular cancer-associated fibroblasts (CAFs) secrete the corresponding ligand CXCL12 to recruit CXCR4⁺ TAMs toward the vasculature.¹⁸⁸ TAMs co-localized in perivascular sites engage in physical interactions with cancer cells and endothelial cells to assemble TMEs of metastasis, which can directly facilitate cancer cell intravasation into the bloodstream.¹⁸⁸ Furthermore, TAM-mediated perivascular organization extends to the lymphatic vasculature. Tumor-derived IL-6 induces CCR5 expression in lymphatic vessel endothelial hyaluronan receptor-1-expressing (LYVE-1⁺) TAMs, which drive LYVE-1⁺ TAMs migration and perivascular clustering, forming specialized niche structures. Within the perivascular niches, LYVE-1⁺ TAMs further express the immune-suppressive enzyme heme oxygenase-1 to restrict CD8⁺ T cell infiltration into the TME, thereby orchestrating chemotherapy resistance and immune exclusion.¹⁸⁹ Research in an MMTV-PyMT spontaneous breast cancer mouse model further demonstrated that perivascular LYVE-1⁺ TAMs can promote the proliferation of αSMA⁺ mesenchymal cells via PDGF-CC signaling, fostering a proangiogenic niche and accelerating tumor progression.¹⁹⁰

MDSCs and neutrophils

MDSCs, primarily classified into polymorphonuclear (PMN-MDSCs) and monocytic (M-MDSCs) subgroups, exhibit distinct migratory dominance that critically dictates their functional impact on both tumorigenesis and inflammatory diseases.¹⁹¹ Within the TME, M-MDSCs are the predominant population and exhibit heightened immunosuppressive activity compared to PMN-MDSCs. In glioblastoma, M-MDSCs leverage high expression of integrin β1 and DPP-4 to enhance their migratory capacity.¹⁹² M-MDSC recruitment can be further modulated by therapeutic interventions. Local radiotherapy in tumor-bearing mice has been shown to induce tumor cell secretion of CCL2, which selectively facilitates the infiltration of CCR2-high M-MDSCs.¹⁹³ Upon migration to tumors, M-MDSCs can induce Treg proliferation through the secretion of IL-10 and TGF-β.¹⁹⁴ Furthermore, MDSCs induce the acquisition of an epithelial–mesenchymal transition (EMT) phenotype in tumor cells, thereby triggering tumor cell dissemination.¹⁹⁵ In contrast to M-MDSCs, PMN-MDSCs are less prevalent within primary tumors and are preferentially recruited to metastatic foci. In multiple preclinical models of head and neck cancer, galectin-1 increases STING stability in cancer cells that activates NF-κB signaling and CXCL2 expression to promote PMN-MDSC trafficking.¹⁹⁶ These recruited PMN-MDSCs are instrumental in establishing a premetastatic niche in distant organs, such as the lungs, by remodeling the extracellular matrix (ECM).¹⁹⁶ Within metastatic sites, PMN-MDSCs promote tumor outgrowth by inducing the reversion of tumor cells from an EMT phenotype.¹⁹⁵ Beyond oncology, the differential migration of MDSC subsets is also pivotal in regulating inflammatory conditions. During liver ischemia‒reperfusion injury (IRI), PMN-MDSCs represent the predominant subset recruited via CXCL17, whose expression is upregulated following hypoxia-reoxygenation-induced activation of the YAP/TEAD1 complex.¹⁹⁷ These PMN-MDSCs subsequently attenuate hepatic IRI-induced inflammation and damage by inhibiting M1 macrophage polarization.¹⁹⁷ In parallel, during acute graft-versus-host disease, adenosine triphosphate (ATP) released by inflammation or tissue damage mediates the directional migration of M-MDSCs via the P2X7 receptor. Locally, M-MDSCs secrete IL-1β, thereby exerting immunosuppressive functions and maintaining immune homeostasis.¹⁹⁸

Neutrophil recruitment across diverse tissues typically adheres to a canonical, sequentially ordered cascade encompassing initial tethering, rolling, firm adhesion and intraluminal crawling and culminating in transendothelial migration.¹⁹⁹ Spatiotemporal gradients of chemoattractants govern the directional orientation of neutrophil crawling within the vasculature, thereby guiding these cells to precise sites of inflammation.²⁰⁰ Crucially, neutrophil chemotaxis is orchestrated primarily through key signaling pathways, including the PI3K pathway, the ERK pathway and the p38 MAPK pathway.^201,202 Tumor-associated neutrophils (TANs) are categorized into N1 and N2 subtypes based on their demonstrated antitumor or protumor functions within the TME.²⁰³ TANs recruited by CXCL2 presented an N1-like anti-tumor phenotype, with increased NETs causing tumor cell apoptosis through cell-to-cell contact.²⁰⁴ Recent investigation has identified a novel subset of TANs exhibiting dendritic morphology and functional properties, which are recruited from the skull bone marrow to glioblastoma.²⁰⁵ The functional repertoire of these dendritic-like TANs encompasses morphological complexity, expression of genes associated with antigen presentation and the capacity to process exogenous peptides and robustly stimulate MHC class II-dependent T cell activation.²⁰⁵

Innate lymphoid cells

Innate lymphoid cells (ILCs) encompass a diverse array of subpopulations, including NK cells, ILC1s, ILC2s, and ILC3s.²⁰⁶

Directed NK cells are a pivotal determinant of immunological outcomes, exhibiting a dual role in both constraining and amplifying immune responses. During lymphocytic choriomeningitis virus infection, NK cells translocate from the splenic red pulp to T cell-enriched white pulp (WP) regions via CXCR3-dependent trafficking.²⁰⁷ Within the WP, NK cells directly eliminate activated CD4⁺ T cells through perforin-mediated cytotoxicity, thereby constraining T cell responses and mitigating immunopathology.²⁰⁷ Conversely, in a Leishmania major infection model, the same CXCL9/10/11-CXCR3 chemokine axis directs NK cells to lymph nodes. Subsequently, NK cell-derived IFN-γ enhances IL-12 production by DCs, thereby driving Th1 polarization and potentiating anti-infective immunity.²⁰⁸ However, this potent pro-inflammatory capacity can become pathogenic in the context of autoimmune cells. In psoriatic skin lesions, NK cells are recruited by keratinocyte-derived CXCL10 and CCL5 and are activated by skin-resident DCs. Activated NK cells subsequently release high levels of IFN-γ and exacerbate local inflammation.²⁰⁹ Similarly, NK cells expressing the CXCR3 receptor are recruited to the synovium via neutrophil-derived CXCL10 in a mouse model of experimental osteoarthritis.²¹⁰ Infiltrating NK cells further exacerbate cartilage degradation and bone erosion by promoting osteoclast differentiation and suppressing osteoblast function.²¹⁰

NK cells infiltrate the TME via coordinated chemokine-receptor interactions, such as the CXCR3-CXCL10, CX3CR1-CX3CL1, and CCR5-CCL5 axes.¹⁶ Upon successful infiltration, activated NK cells can lyse tumor cells by directly releasing perforin and granzymes and inducing apoptosis with ADCC, FasL, or TRAIL.²¹¹ Additionally, they orchestrate broader immune responses by producing IFN-γ and chemokines, including CCL5 and XCL1/2, which recruit cDC1s and enhance T cell priming.¹⁶³ The critical nature of NK cell infiltration is highlighted in breast cancer models, where reduced NK cell trafficking leads to increased tumor burden.²¹² Despite the migration-dependent antitumor capabilities, the therapeutic efficacy of NK cells is frequently curtailed by impaired trafficking, especially into solid tumors.²¹³ Multiple mechanisms have been implicated in the impaired trafficking of NK cells within the solid-tumor microenvironment. Investigation of the TME in endometrial carcinoma identified diminished levels of key chemokines, including CXCL12, CXCL10, and CCL27. Such chemokine downregulation could compromise the recruitment of NK cells to the tumor.²¹⁴ Additionally, aberrantly accumulated metabolites within the TME, such as adenosine and lactate, disrupt chemotactic responsiveness of NK cells through interference with cellular metabolism and chemokine receptor expression, thereby impairing NK cell infiltration to solid tumors.^215,216

The migratory dynamics of ILCs critically influence immune responses in both neoplastic and inflammatory settings, exhibiting subset-specific trafficking patterns with profound functional consequences. Within colorectal cancer, ILC2s infiltrate tumors via an IL-33-dependent pathway and mediate tumor immune surveillance by promoting CTL responses.²¹⁷ Beyond this direct anti-tumor role, IL-33-activated ILC2s can migrate from the gut to pancreatic adenocarcinoma and engage putative lymphotoxin β receptor (LTβR⁺) myeloid organizer cells to initiate tertiary lymphoneogenesis.²¹⁸ During inflammation, a distinct subset of ILC2s named inflammatory ILC2s (iILC2s) can be mobilized from blood and lymph.²¹⁹ The trafficking of iILC2s to peripheral infection sites is IL-25-signaling dependent, whereupon they acquire IL-17 production capacity for host defense against invasive fungal pathogens.²¹⁹ Similarly, ILC3s exhibit dynamic migratory behaviors that underpin their dual roles in tumor immunology and inflammation. ILC3s migrate to tumors via the CCL20-CCR6 chemokine axis. Within the TME, IL-1β-activated ILC3s secrete CXCL10 to recruit CD4⁺ and CD8⁺ T cells, thereby converting immunologically “cold” tumors into “hot” tumors and potentiating response to immunotherapy.²²⁰ This process is further exemplified in lung cancer, where NCR⁺ ILC3s recognize tumor cells via the NKp44 receptor and secrete TNF-α. These cytokines upregulate ICAM-1 and VCAM-1 on endothelial cells, thereby facilitating the infiltration of ILC3s into TLS.²²¹ Within TLSs, ILC3s secrete TNF-α, IL-8, and IL-2, contributing to TLS formation while simultaneously potentiating lymphocyte infiltration and activation.²²¹ Beyond chemokine-driven migration, ILC3 trafficking can be modulated by distinct classes of G protein-coupled receptors (GPCRs) during inflammation. GPR183-expressing ILC3s respond to inflammation-induced 7α,25-hydroxycholesterol and migrate to intestinal mucosal sites, where they potentiate colonic inflammation through sustained cytokine amplification.²²² Conversely, GPR34-mediated sensing of ILC3 trafficking to tissue injury sites, where these cells orchestrate epithelial regeneration through IL-22-dependent mechanisms.²²³

Detection techniques for immune cell migration

Sequencing technique

Cell migration often induces alterations in gene expression, which can serve as an indirect reflection of a cell’s migratory status²²⁴ (Fig. 3). Bulk RNA sequencing (bulk RNA-seq) has emerged as a potential tool for tracking immune cell migration by detecting tissue-specific gene expression signatures.^225,226 For example, researchers utilized bulk RNA-seq in a study investigating immune cell migration between bone marrow and the intestine, identifying key T-cell subpopulations involved in this migration pathway.¹⁰² Nonetheless, this sequencing method exhibits certain deficiencies including low precision and limited resolution in discerning heterogeneous cell populations.²²⁶ Single-cell sequencing (scRNA-seq) technologies have partially addressed these deficiencies and revolutionized the field by offering a more granular perspective on cell migration. By combining scRNA-seq with RNA velocity analysis, researchers can track the dynamic states of individual cells and predict their migration trajectories with high precision.²²⁷ In a multi-tissue Treg model study, researchers employed scRNA-seq to reveal the shared phenotypes, transient residency and multi-tissue migration characteristics of Tregs, further highlighting the potential of scRNA-seq in deconstructing immune cell migration at cellular resolution.¹⁴¹

Fig. 3.

Sequencing techniques and in vivo/in vitro models for immune cell migration detection. Detection techniques for immune cell migration involve sequencing technology and animal and in vitro models. These techniques are capable of resolving immune cell migration in multiple dimensions. Created with BioRender.com

For specific immune cell populations, advances in T-cell/B-cell receptor sequencing (TCR/BCR-seq) have paved the way for more precise tracking of T and B cell migratory routes.^228,229 TCR sequencing leverages the high specificity and stability of TCR sequences, allowing for tracking T cell migration by comparing TCR sequences in samples from different tissues or time points.²²⁵ To enhance tracking resolution beyond natural TCR sequences, researchers developed an embedded viral barcode-assisted high-throughput sequencing technology.²³⁰ This technology artificially inserts unique DNA barcodes into cellular genomes and analyses the distribution and abundance of the barcodes by high-throughput sequencing, thus effectively mapping the trafficking patterns and dynamics of cells.²³⁰ Advances in single-cell TCR sequencing (sc-TCR) further refine the capability to track individual T-cell migratory patterns.²³¹ Unlike traditional TCR sequencing, which examines T-cell migration patterns at the population level, sc-TCR sequencing allows for more precise monitoring of migratory trajectories at single-cell resolution.²³² By integrating single-cell sequencing with TCR sequencing, the STARTRAC-migr index was developed to quantify T-cell migration capacity and track dynamic migration patterns with unprecedented precision.²²⁶ Likewise, parallel approaches have been developed for B cells. Studies demonstrate that BCR-seq, in conjunction with longitudinal analysis of single-cell sequencing, also facilitates the tracking of the time course and pattern of cell migration during the process of immune response.²³³ However, existing studies on BCR-seq combined with single-cell sequencing to detect cell migration remain limited, and further exploration is warranted.

In vivo and in vitro models

Animal models remain indispensable for investigating immune cell migration dynamics in vivo, with genetically engineered systems providing unprecedented spatial-temporal resolution²³⁴ (Fig. 3). The Kaede transgenic animal model exemplifies this capability through its photoconvertible fluorescent reporter protein that irreversibly shifts emission from green to red upon UV exposure.²³⁵ Through these findings, researchers demonstrated extensive multi-tissue migration of intestinal immune cells, shedding light on the dynamic behavior of immune cells in the body.²³⁶ Complementing this approach, the Kit-CreER/Rosa26-tdTomato dual reporter model enables tamoxifen-inducible Cre recombinase activity, which specifically induces tdTomato fluorescent protein expression in c-Kit⁺ cells, enabling their visualization through fluorescence microscopy.²³⁷ This model has been used to reveal the migration and differentiation of c-Kit⁺ cells during the atherosclerotic process.²³⁷ In addition to fluorescent labeling of proteins, genetic reporter systems also enable noninvasive tracking of immune cell dynamics in animal models.^238,239 The DiLiCre model exemplifies this approach through doxycycline-controlled and light-controlled Cre recombinase activation.²³⁸ This precision tool mediates FLEx (Flip-Excision) reporter cassette switching at loxP sites, generating permanent fluorescent markers that permit longitudinal monitoring of cellular migration via in vivo imaging without the need to sacrifice animals.²³⁸ While the DiLiCre system provides broad applicability, specialized immune cell tracking requires more targeted approaches. For neutrophil-specific tracking, the Catchup model employs targeted tdTomato insertion at the Ly6g locus, creating definitive genetic tagging of granulocyte populations.²³⁹ When integrated with intravital two-photon microscopy, this model reveals neutrophil trafficking patterns in native microenvironments without the need for adoptive cell transplantation.²³⁹

In vitro models primarily rely on mathematical algorithms or deep learning methods to systematically analyze and process multidimensional signals generated during cell migration, enabling the visualization and quantitative analysis of cellular migratory behavior.^240,241 One such model, Tracking Cells by Footprint (TCF), employs a mechano-optical biosensor to map 2D cellular migration trajectories via fluorescent signals generated by DNA/PNA hybrid duplex disassembly under cellular mechanical forces.²⁴² Recent research further explored the integration of sequencing technologies with in vitro models. The bidirectional single-cell migration chip (BM-Chip) exemplifies this paradigm by synergizing sequencing technologies with bidirectional migration channels, permitting high-throughput detection of cellular migratory phenotypes via time-lapse imaging.²⁴³ Building upon conventional 2D imaging, a microchip-based time-lapse imaging system incorporating temporal analysis achieved 12-h continuous monitoring of NK cells, enabling comprehensive tracking of individual NK cell migration trajectories and documentation of cytotoxic events.²⁴⁴ While 2D systems provide foundational insights, their physiological relevance is constrained by dimensional limitations. To overcome this limitation, researchers have progressively developed higher-dimensional analysis algorithms to depict cell movements more comprehensively. Based on a 3D U-net deep neural network architecture, cell position and motion fields (CPMF) offer high-precision tracking of complex migration dynamics by analyzing cellular spatial position and motion vector fields.²⁴⁵ The Automatic Feature Extraction for Cell Migration Examination (ACME) system extends this capability by integrating 3D convolutional neural networks with temporal dimensions for real-time intravascular tracking, offering valuable insights into immune cell movement during cancer treatment.²⁴⁶ Parallel advancements in microengineered platforms address spatiotemporal resolution gaps through tracking single-cell migration from spatial and temporal perspectives.²⁴⁷ This platform enables real-time monitoring and quantitative analysis of cell movement, providing a powerful tool for in-depth investigation of the differentiation mechanisms and functional regulatory alterations during cell migration.²⁴⁷

Clinical imaging technology

Conventional clinical imaging methods for tracking and monitoring cell migration are contingent upon the development and implementation of novel contrast agents^248,249 (Fig. 4). The selection of appropriate imaging techniques for cell tracking studies depends on the imaging mechanisms and properties of different contrast agents.^248,249

Fig. 4.

Clinical imaging techniques for immune cell migration detection. Clinical imaging techniques include ultrasound, computed tomography, magnetic resonance imaging, positron emission tomography and advanced imaging technologies. These techniques enable real-time visualization of immune cell migratory trajectories, allowing for dynamic and high-precision tracking of their spatial behavior. Created with BioRender.com

Ultrasound imaging has been revolutionized by phase-change peptide nanoemulsion contrast agents that generate enhanced acoustic signals upon ultrasound excitation.²⁵⁰ Functionalization of these nanoemulsions with an integrin-targeted peptide emulsifier enables efficient macrophage uptake, thus permitting sustained real-time visualization of migration trajectories by ultrasonography imaging.²⁵⁰ Additionally, gold nanoparticles used as contrast agents in computed tomography (CT) imaging enable multidimensional tracking and quantitative analysis of T cell migration patterns across tissue compartments.²⁵¹ This technology holds considerable promise for evaluating the efficacy of adoptive T cells therapy and providing a basis for optimizing clinical therapeutic regimens.²⁵¹ Magnetic resonance imaging (MRI) has also proved advantageous in tracking cell migration, particularly through a nanomaterial-enhanced contrast mechanism.²⁵² DCs labeled with superparamagnetic iron oxide (SPIO) nanoparticles generate hypointense signals on T2-weighted imaging.²⁵³ By optimizing the imaging pulse sequence parameters, researchers have enhanced the single-cell detection sensitivity of SPIO-labeled DCs, thus providing a reliable imaging basis for monitoring DC-based immunotherapeutic responses.²⁵³

Distinguished from nanomaterial-dependent imaging modalities, Positron emission tomography (PET) uses radionuclides to label cells through metabolic mechanisms. Integrated with bioorthogonal chemistry, CTLs can be effectively radiolabeled with ⁶⁴Cu, thereby enabling PET imaging to visualize their migration under diverse treatment conditions.²⁵⁴ Quantitative analysis of CTL accumulation within TME through this methodology provides invaluable prognostic insights for early-phase prediction of adoptive cell therapies.²⁵⁴ Complementary PET strategies employ genetic reporters for enhanced tracking specificity. The engineered hdCK3mut reporter system exhibits particular utility for cell tracking in immunotherapy, where its specific binding affinity for [18F]-L-FMAU generates quantifiable PET signals proportional to cell migration activity.²⁵⁵

In addition to the phenomenal techniques that are routinely employed in the clinic, researchers have also developed novel imaging methodologies for tracking cell migration. Optical Coherence Tomography (OCT), originally developed for ophthalmic applications, has been repurposed for high-resolution glioblastoma tracking through nanoparticle-enhanced contrast mechanisms.²⁵⁶ However, traditional OCT suffers from limitations in cell tracking, particularly due to speckle noise. Recent development of the Speckle-Modulating Optical Coherence Tomography (SM-OCT) system has addressed this limitation by implementing noise suppression algorithms during imaging, achieving unprecedented clarity in TAM tracking within the TME.²⁵⁷ This advancement leverages large gold nanorods as photostable molecular tracers that enable spatiotemporal mapping of TAM migratory patterns, revealing insights into the potential role of TAMs as nanoparticle-based drug delivery vectors in immunotherapy.²⁵⁷ Beyond advancements in single-modality imaging, a multimodal approach offers distinct advantages, with OCT being integrated with Photoacoustic Microscopy for enhanced long-term cell tracking.²⁵⁸ In a study of in vivo tracking progenitor cells, this technique enabled longitudinal monitoring of transplanted retinal pigment epithelial cells for 3 months and systematically elucidated the migration dynamics of these cells in the damaged area.²⁵⁸ Complementing these optical approaches, Phototruncation-assisted Cell Tracking (PACT) has emerged as an innovative technique that employs photosensitive dyes and light-induced chemical reactions to label and track cells.²⁵⁹ This technique permits quantitative analysis of spatial distribution and migration efficiency of immune cells in TDLNs.^259,260 Parallel innovations in biphotonic include All-engineered Bioluminescence Imaging (AkaBLI), which incorporates genetically modified firefly luciferase to significantly enhance tissue barrier penetration, enabling single-cell resolution tracking in deep tissues.²⁶¹ This technology has been successfully applied to track cellular responses in the hippocampus and migration within deep lung vessels, demonstrating its potential for non-invasive, in vivo tracking of cellar dynamics.²⁶¹

Factors influencing immune cell migration

Immune cells exhibit distinct infiltration patterns in the contexts of tumors and inflammation. For instance, immune-cold tumors frequently drive the infiltration of immunosuppressive cells or impede antitumor immunocyte migration through physical and biological barriers. In contrast, immune-hot tumors are characterized by enrichment of antitumor immune cells.²⁶² During infection, the inflammatory site primarily recruits immune cells capable of pathogen clearance.^15,263 Whereas in autoimmune diseases, infiltrating immune cells exacerbate local inflammatory responses and promote tissue injury.^2,264 Such infiltration pattern heterogeneity is regulated by the tumor or inflammatory microenvironment and systemic determinants. Local microenvironmental factors primarily encompass chemokines, cytokines, and adhesion molecules. Furthermore, systemic factors such as organismal metabolic reprogramming and the gut microbiota also significantly influence infiltration patterns.

Cytokines and chemokines

Across diverse pathophysiological landscapes, including oncology, autoimmunity, and infection, chemokine and cytokine networks play a critical role in orchestrating immune cell trafficking (Fig. 5). Malignant cells exploit this chemotactic system by constitutively expressing chemokines or cytokines that sculpt immunosuppressive niches.¹² In a panel of mouse pancreatic ductal adenocarcinoma (PDAC) tumors derived from clones of an autochthonous model, MYC-driven expression of CXCL1 by cancer cells inversely correlates with intratumoral infiltration, mechanistically impeding cytotoxic lymphocyte recruitment.²⁶⁵ Frequent expression of chemokine ligand(s) and their cognate receptors by tumor cells establishes self-sustaining autocrine circuits, amplifying ligand-receptor signaling to drive pathway hyperactivity.²⁶⁶ In one such instance, the autocrine CCL5-CCR5 axis induces MDSC infiltration via the JAK/STAT signaling pathway, which restricts T cell chemotaxis and antitumor function.²⁶⁷ Alternative to the expression of chemokines, cancer cell-intrinsic mechanisms can also modulate the secretion of cytokines to regulate immune cell migration. Immunogenic cell death (ICD) is an attractive strategy for counteracting tumor-mediated immune evasion by inducing interferon production and influencing immune cell trafficking.^268,269

Fig. 5.

Factors influencing immune cell migration. Factors influencing immune cell migration include cytokine and chemokine signaling pathways, cellular interactions, the extracellular matrix, metabolic reprogramming, and microbiota. a Cytokines and chemokines regulate immune cell recruitment through ligand-receptor signals derived from tumor cells, immune cells, stromal cells and epithelial cells. b Cellular interactions regulate immune cell migration through adhesion molecules, soluble mediators, EVs-associated signals. c Extracellular matrix components and remodeling shape migratory routes by providing structural support or physical barriers to immune cell movement. d Metabolic factors, including nutrient utilization, hypoxia, and metabolite signaling, modulate the migratory capacity of immune cells. e Microbiota-derived signals regulate immune cell trafficking through effects on chemokines, homing receptors and lymphatic network expansion. Created with BioRender.com. EVs extracellular vesicles, OPN osteopontin, MIF macrophage migration inhibitory factor, HC heavy chain, HA hyaluronan, LOX lysyl oxidase, ECM extracellular matrix, FPP farnesyl pyrophosphate, SFA short-chain fatty acid, SBA secondary bile acid, KA kynurenic acid

For instance, ICD induction in PERK-ablated tumors stimulates type I interferon production in DCs, which primes CCR2-dependent recruitment of common monocytic precursors to bolster anti-tumor responses.²⁷⁰ Separately, in tumor signaling pathways, STAT3 expression in multiple tumors is closely associated with poor prognosis.^271,272 Mechanistically, constitutively activated STAT3 in tumors promotes cytokine Chi3l1-mediated neutrophil recruitment and NET formation that physically constrain CD8⁺ T cell infiltration.³⁷

Endothelial and epithelial cells function as critical regulators of immune cell trafficking by secreting specific chemokines, thereby orchestrating the pathogenesis of inflammatory diseases. Within the vasculature, endothelial cells can initiate and amplify localized inflammation. For instance, in IBD, intestinal microvascular endothelial cells upregulate the expression of CX3CL1, which mediates the recruitment of CX3CR1⁺ CD8⁺ T cells into the intestinal mucosa. Upon infiltration, CX3CR1⁺ CD8⁺ T cells release type I cytokines such as IFN-γ and cytotoxic molecules, which collectively drive the pathogenesis of intestinal inflammation.²⁷³ Furthermore, in an experimental autoimmune model, pulmonary vascular endothelial cells mediate the secretion of CCL5 via the cGAS-STING pathway, which recruits CCR5⁺ CD8⁺ T cells to the lungs, thereby initiating TLS formation and exacerbating autoimmune pathogenesis.²⁷⁴ Beyond the vasculature, epithelial cells lining various organs are also key contributors to chemokine secretion. CXCL12 secreted by glomerular and tubular epithelial cells can recruit CXCR4⁺ B cells, which subsequently differentiate into plasma cells and generate anti-double-stranded DNA antibodies to exacerbate lupus nephritis.²⁷⁵ In the context of pulmonary inflammation, the role of epithelial-derived chemokines is equally prominent. During allergic asthma, pulmonary epithelial cells secrete CCL2 to recruit CCR2-expressing classical monocytes that can differentiate into MoDCs, thereby promoting Th2 cell-mediated immune responses and exacerbating allergic inflammation.²⁷⁶ Similarly, in acute viral infections such as COVID-19, alveolar epithelial cells upregulate CXCL16 to guide the migration of monocytes into the lung parenchyma via CXCR6, contributing to pulmonary inflammation.²⁷⁷ Conversely, patients with long COVID-19 exhibit sustained downregulation of COX2 and CXCR2 expression, impairing monocyte responsiveness to inflammatory signals.²⁷⁷

Mesenchymal stromal cells, including adipocytes, fibroblasts, and fibroblastic reticular cells (FRCs), establish chemokine gradients that profoundly modulate immunocyte trafficking in both inflammation and tumors. Adipocytes adopt a pro-inflammatory role during diabetes and acute hepatic inflammation. Adipocyte-derived CCL2 and IL-29 facilitate the recruitment of monocytes, which subsequently differentiate into M1 macrophages and secrete pro-inflammatory cytokines such as TNF-α and IL-1β, thereby contributing to the development of insulin resistance.^278–280 The pro-pathogenic function of adipocytes extends to the TME. In breast cancer (BC), peritumoral cancer-associated adipocytes (CAAs) are located predominantly at the invasive front of BC.²⁸¹ Mechanistic investigations revealed that CAA-derived CXCL8 exerts immunosuppressive effects by suppressing CD8⁺ T cell infiltration while upregulating CD274 expression in BC, thereby promoting EMT and metastasis progression.²⁸² The chemokine network orchestrated by fibroblasts also exhibits a pathogenic function. Dermal fibroblasts stimulated by IFNγ can secrete the chemokines CXCL9 and CXCL10 to recruit cytotoxic CD8⁺ T cells, which specifically target epidermal melanocytes, thereby driving the progression of vitiligo.²⁸³ Similarly, during Staphylococcus aureus (S. aureus) skin infection and psoriasis, both IL-17A and TNFα have been observed to induce the secretion of CXCL12 via the NFKBIZ pathway in dermal fibroblasts, thereby orchestrating the recruitment of neutrophils. CXCL12-recruited neutrophils contribute to bacterial clearance during S. aureus infection but exacerbate tissue damage in psoriasis.²⁸⁴ Fibroblast-like synoviocytes (FLS) are a specialized fibroblast subtype that serve as major contributors to CCL25 elevation during arthritis. Following recruitment to the joint via the CCL25-CCR9 signaling axis, monocytes undergo CCL25-driven differentiation into proinflammatory M1 macrophages, which subsequently secrete IL-8 and CCL2 to exacerbate synovial inflammation.²⁸⁵ Additionally, FLSs also produce CCL20 to mediate the migration of CCR6⁺ Th17 cells to inflamed joints. Th17-secreted IL-17A further activates FLSs to produce pro-inflammatory cytokines, thereby establishing a pathogenic positive feedback loop that exacerbates rheumatoid arthritis.²⁸⁶ Within the tumor stroma, CAFs similarly adopt CXCL12 to modulate immune cell behavior. Perivascular CAF-derived CXCL12 activates CXCR4 on immune cells, including monocyte-derived TAM.¹⁸⁸ This CXCL12-CXCR4 axis impedes the direct migration of immune cells through inhibiting the chemotactic functions of chemokine receptors, including CXCR1, CXCR3 and CCR2.²⁸⁷ Therefore, the effects of CXCL12 extend beyond impairing cellular migration to orchestrating systemic immunosuppression. While CAFs hinder immune cell migration through CXCL12, FRCs within the stromal niche exhibit immunostimulatory properties. CCL19 and CCL21 secreted by FRCs are fundamental for recruiting dendritic cells, T helper cells and B cells, which is essential for initiating adaptive immunity against chronic infections and for fostering a protective anti-tumor immunity.^288,289 Further investigations confirmed that the FRC-derived CCL19 gradient promotes T cell infiltration and fosters a protective intratumoral T cell environment, critically regulating the potency and durability of antitumor T cell immunity.²⁹⁰ Beyond CCL19 and CCL21, CXCL12 produced by FRCs via the LTβR signaling pathway plays a protective role in limiting pathological inflammation. During allograft rejection, Tregs recruited by CXCL12 exert their potent immunoregulatory capacity by inhibiting Th1 and Th17 lineage differentiation, thereby attenuating the inflammatory rejection process.²⁸⁴

Immune cells also constitute self-regulatory chemokine networks during inflammation and tumors. In advanced-stage tumors, Th17-mediated immunosuppression operates through IL-17A/STAT3 signaling to downregulate CXCR3 expression, systemically impairing CD8⁺ T-cell trafficking.²⁹¹ TAMs and DCs further shape immune landscapes by secreting CCR4 ligands such as CCL17 and CCL22, which promote the recruitment of Tregs to the tumor site.^147,292 Interestingly, treatment with immune checkpoint inhibitors facilitates CCR4 ligand expression and Treg infiltration, suggesting a mechanism by which immune evasion is facilitated.²⁹³ Furthermore, Treg-derived IL-10 reinforces this immunosuppressive axis by suppressing the recruitment of M1-type macrophages and promoting the activation of immunosuppressive M2-type macrophages.²⁹⁴ Counterbalancing these inhibitory mechanisms, cDC1s drive anti-tumor immunity through CXCL9/CXCL10 production, creating chemotactic gradients that recruit effector CD8⁺ T cells.²⁹⁵ Therapeutic amplification of these chemokines by injecting Flt3 ligand-derived DCs significantly enhances T cell recruitment and anti-tumor immunity.²⁹⁶ Interferon-γ (IFN-γ) production is mainly regulated by NK cells in innate immunity, while CD8⁺ and CD4⁺ T cells serve as principal paracrine producers in adaptive immunity.^297,298 IFN-γ establishes a self-reinforcing recruitment circuit by initiating CXCL9/10 secretion from DCs and malignant cells upon detection by sparse tumor-infiltrating T/NK cells, thereby amplifying the influx of IFN-γ-producing T cells to sustain this immunostimulatory cascade.^296,299 Beyond the T-cell-centric feedback mechanisms, DC-derived chemokines are also pivotal in directing humoral responses and autoimmune pathology. CXCL13 secreted by renal DCs promotes the recruitment of CXCR5⁺ B cells to the kidney, fostering a proinflammatory environment that contributes to tissue damage in lupus nephritis.³⁰⁰ Similarly, during asthma, pulmonary DCs stimulated by IL-13 can secrete CCL22 and CCL17, which recruit CCR4⁺ Th2 lymphocytes into the airways. Upon infiltration, production of IL-13 by Th2 cells establishes a positive-feedback loop that amplifies eosinophilic inflammation and airway hyperresponsiveness.³⁰¹

Beyond the pivotal roles played by dendritic cells and T lymphocytes, macrophages emerge as a critical source of chemokines. In the TME, TAMs frequently foster immunosuppression by recruiting Tregs. In hepatocellular carcinoma, activation of the DGAT1-catalyzed and DGAT2-catalyzed triglyceride biosynthetic pathway in TAMs drives lipid droplet accumulation, which in turn promotes CCL20 expression to recruit CCR6⁺ Tregs.³⁰² In addition to direct recruitment of Tregs, CCL18 secreted by TAMs also recruits naive CD4⁺ T cells, which subsequently differentiate into Tregs within the tumor niche.³⁰³ Conversely, macrophages can also mediate potent anti-tumor immunity. Dual PD-1/CTLA-4 blockade has been reported to induce the secretion of CXCL9 and CXCL10 from macrophages. CXCR3-expressing CD8⁺ T cells recruited by CXCL9 and CXCL10 subsequently mediate antitumor immunity through the production of IFN-γ and TNF-α.³⁰⁴ This CXCL9-CXCR3 axis is also fundamental in infection defense. Under IFN-γ stimulation, the transcription factor PU.1 in macrophages induces the expression of CXCL9, which subsequently mediates CXCR3⁺ CTL and NK cell migration to sites of inflammation and controls infection progression.³⁰⁵ Beyond infection, macrophage-derived chemokines are pivotal drivers of inflammatory pathologies. During asthma, pulmonary macrophages activated by IL-14 secrete CCL11 and CCL24. These ligands engage CCR3 on eosinophils, promoting their infiltration into the airways, which drives the pathogenesis of allergic airway inflammation.³⁰¹ In the context of autoimmune diabetes, IL-1β-stimulated pancreatic macrophages orchestrate neutrophil infiltration into pancreatic islets through the CXCL1/CXCL2-CXCR2 axis.³⁰⁶ Within pancreatic islets, neutrophils exacerbate tissue inflammation and propagate autoimmune diabetes through NETosis-mediated excessive release of neutrophil elastase and proteinase 3.³⁰⁷

Subsequent to recruitment by chemokines from macrophages and other sources, neutrophils themselves act as both effector cells and chemokine producers. A fundamental mechanism underpinning the localized infiltration and accumulation of neutrophils is the establishment of a CXCL1/CXCL2-CXCR2 autocrine self-amplifying loop, which perpetuates inflammation in conditions such as arthritis.³⁰⁸ A comparable self-amplifying recruitment of neutrophils occurs during infection.³⁰⁹ However, elevated local chemoattractant concentrations trigger GRK2-mediated site-specific phosphorylation of serine/threonine residues within GPCR intracellular domains, which sterically hinders G protein coupling to terminate downstream signaling.³¹⁰ This negative feedback mechanism induces neutrophil migratory arrest and prevents pathological accumulation.³¹⁰ In the context of oncology, neutrophils polarize into TANs and exert a profound influence over other immune lineages through chemokines and cytokines. For instance, hepatocellular carcinoma cells activate the PI3K/Akt and p38/MAPK signaling pathways in neutrophils, promoting their polarization into TANs and stimulating the secretion of CCL2 and CCL17. These chemokines facilitate the recruitment of macrophages and Tregs via CCR2 and CCR4, respectively, thereby establishing an immunosuppressive microenvironment and contributing to resistance to Sorafenib.³¹¹Beyond typical chemokine-mediated recruitment, TNFα derived from TANs directly regulates B cell chemotaxis and migration through a novel mechanism independent of CXCL12, CXCL13, and CXCL9. Following infiltration into tumors, B cells are further induced by TANs via membrane-bound BAFF to differentiate into IgG-producing plasma cells that exert either anti-tumor or pro-tumor functions.³¹²

The aforementioned migratory network, centered on the chemokine-receptor axis, constitutes a localized immune response subject to feedback regulation. However, dysregulation of cytokine secretion induced by aberrant pathogenic signals can precipitate a deleterious systemic inflammatory cascade, commonly referred to as a cytokine storm.³¹³ Pathogen recognition occurs via Toll-like receptors (TLRs) engaging pathogen-associated molecular patterns and damage-associated molecular patterns, subsequently activating both the canonical TLRs/MyD88/MAPK pathway and noncanonical TLRs/TRIF/IRF3 pathway, which drive massive uncontrollable release of proinflammatory cytokines.³¹⁴ Neutrophils recruited by elevated CXCL8 during cytokine storms induce the formation of NETs, which trigger TLR2/4-dependent upregulation of IL-6 and pro-IL-1β in macrophages.^313,315 This amplified pro-inflammatory cytokine milieu further drives Th17 cell differentiation and myeloid cell recruitment that exacerbate systemic inflammation.³¹⁵ Notably, IL-1β and IL-18 can in turn facilitate the recruitment of neutrophils and T helper cells to the site of infection, resulting in the release of secondary wave cytokines such as IL-6 and TNF.^314,316 Additionally, dysregulation of cytolytic activity during cytokine storm undermined the cytotoxicity of CTL and NK cells, resulting in pathological retention of undegraded lymphocytes.³¹⁷ These lymphocytes undergo prolonged crosstalk between antigen-presenting cells, substantially enhancing the production of proinflammatory cytokines such as IFN-γ that amplify the inflammatory response.³¹⁸

Cellular interaction

In addition to their role in cytokine and chemokine networks, cellular interactions mediated by adhesion molecules, soluble signaling proteins and extracellular vesicles critically regulate immune cell trafficking (Fig. 5). Specifically, MAdCAM-1 expression on HEVs engages α4β7 integrins to mediate lymphocyte extravasation into tissues.³¹⁹ This interaction not only promotes the recruitment of immune cells across organ barriers but also intensifies local inflammation within the TME. Beyond commonly expressed adhesion molecules, individual organs also harbor tissue-specific adhesion molecules that govern immunocyte trafficking. For instance, neuro-oncology studies have revealed that T cells in intracranial melanoma preferentially utilize ICAM-1-dependent pathways for peritumoral venous adhesion, suggesting central nervous system-specific immune trafficking mechanisms.³²⁰ During multiple sclerosis, Th17 cells employ their constitutively high surface expression of DICAM to engage cognate DICAM ligands and αVβ3 integrin on blood-brain barrier endothelial cells, thereby facilitating transendothelial migration into the CNS.³²¹ Infiltrated Th17 cells further secrete IL-17 to promote blood‒brain barrier disruption and CNS inflammation.³²¹ Conversely, endothelial cells (ECs) can also actively restrict immune trafficking by modulating the availability of adhesion molecules. For instance, EC autophagy remodels intercellular junctions through ATG16L1-dependent degradation of adhesion molecules, including PECAM-1 and E-cadherin.³²² Genetic ablation of EC autophagy led to excessive neutrophil transendothelial cell migration and uncontrolled leukocyte migration in murine inflammatory models.³²² In addition to the above adhesion molecules, emerging evidence highlights noncanonical molecular regulators that paradoxically impede rather than promote immune cell migration. EDIL3 is a secreted multifunctional protein that interacts with integrins.³²³ Endothelial cell-derived EDIL3 primarily regulates inflammatory initiation by restraining ITGAL- and ICAM1-dependent neutrophil recruitment.³²⁴ When secreted by CAFs, EDIL3 disrupts the cellular adhesion cascade by antagonizing LFA-1/ICAM-1 binding and effectively impedes T-cell transmigration. This spatial regulation of adhesion molecule interactions establishes EDIL3 as a multifaceted regulator of tumor immune evasion.³²⁵

Beyond direct cellular contact, the migration of immune cells is also regulated by soluble proteins or extracellular vesicles secreted by neighboring cells. POSTN secreted by glioblastoma stem cells recruits αVβ3⁺ microglia and upregulates CD70 expression, subsequently fostering Treg development and facilitating tumor progression.³²⁶ Parallel mechanisms operate in hepatocellular carcinoma, where tumor-overexpressed osteopontin (OPN) initiates the migration of M2 macrophages through the OPN/CSF1R axis coupled with PD-L1 upregulation to blunt cytotoxic T cell responses.³²⁷ Ongoing research is elucidating the mechanistic underpinnings of tumor-mediated protein secretion. Myosin II is a molecular motor that converts chemical energy derived from ATP hydrolysis into mechanical work.³²⁸ Surprisingly, enhanced Myosin II activity in ameboid cancer cells triggers the release of immunomodulatory proteins that recruit monocytes and direct their differentiation into tumor-promoting macrophages.³²⁹ Epigenetic modifications further fine-tune this protein secretory landscape that mediates cellular interaction and migration. METTL3-mediated N6-methyladenosine (m6A) modification sustains MDSC migration through a BHLHE41-dependent pathway and inhibits antitumor immunity.³³⁰

Extracellular vesicles (EVs) are nanosized, membranous structures secreted into the extracellular space that participate in cellular interactions.³³¹ Decorated with membrane proteins derived from their parental cells, EVs are significant carriers for signal proteins.³³² For instance, CCL2 bound to proteoglycans on the surface of cancer cell-derived EVs recruits NK cells and MDSCs, promoting an immunosuppressive microenvironment that may play a role in tumor metastasis.³³³ In diabetes, chronic exposure to pro-inflammatory cytokines has been shown to perturb β cell communication and function.³³⁴ For instance, EVs with the expression of the chemokine CXCL10 on their surface can facilitate leukocyte recruitment to islets, leading to β cell dysfunction.³³⁵ Integrins, selectins, and immunoglobulin superfamily molecules constitute another critical class of EV surface determinants. These molecules mediate immune cell transendothelial migration by engaging cognate receptors on vascular endothelial cells.³³¹ EVs with the expression of integrin β1 have been identified as a key contributor to the hepatic recruitment of monocyte-derived macrophages from circulation, which exacerbates inflammation in nonalcoholic steatohepatitis.³³⁶

Additionally, EVs carry a wide range of cargo mediating immunocyte migration, including signaling proteins and nucleic acids.³³¹ EVs released by neutrophils, macrophages and other immune cells that contain cytokines and chemokines can promote or resolve inflammatory reactions.³³⁷ Although most cytokines are secreted predominantly in soluble forms, EVs can cotransport cytokines intraluminally.³³² Compared with their secretion of free cytokines, the phospholipid bilayer of EVs can prevent EV-associated cytokines from rapid degradation, thereby supporting sustained signaling.³³² Interestingly, pancreatic cancer-secreted EVs that carry macrophage migration inhibitory factors (MIFs) have been demonstrated to promote the recruitment of bone marrow-derived macrophages, which further initiate premetastatic niche formation in the liver.³³⁸ In addition to cytokines, EVs can modulate immune cell migration through miRNA-mediated regulation of gene expression within target immune cells. During sepsis-related acute lung injury, neutrophil-derived EVs enriched with miR-30d-5p drive M1 macrophage polarization and migration via activation of the NF-κB signaling pathway.³³⁹ Conversely, TAM-secreted EVs harbor miR-21-5p and miR-29a-3p, which induce Treg/Th17 imbalance through STAT3 pathway activation, thereby promoting Treg trafficking into the TME.³⁴⁰ Additionally, hepatocyte-derived EVs in fatty liver are reported to transfer YAP signaling-regulating microRNAs into cancer cells, resulting in the establishment of an immunosuppressive microenvironment by M2 macrophage infiltration through CYR61 production.³⁴¹

Metabolic reprogramming

Disruptions in lipid, glucose and energy metabolism not only affect immune cell metabolism but also act as signaling molecules to regulate their migration³⁴² (Fig. 5). Lipids execute important physiological roles in energy storage and membrane fluidity modulation, making them key participants in cell trafficking.^343,344 As a TME-derived lipid mediator, prostaglandin E2 (PGE2) orchestrates metabolic suppression through c-Myc and PGC-1 downregulation, concurrently impairing oxidative phosphorylation, glycolysis, and ribosomal biogenesis.^345,346 This metabolic reprogramming compromises multiple functions of CD8⁺ T cells, particularly their migratory capacity and tumor-infiltrating potential.³⁴⁵ During SLE, aberrant cholesterol metabolism culminates in farnesyl pyrophosphate (FPP) accrual within mregDCs. FPP-mediated activation of RhoA fosters mitochondrial fusion and enhances oxidative metabolism, which collectively bolsters DC motility and exacerbates SLE progression.³⁴⁷ Additionally, inflammatory factors in the cellular microenvironment activate the immune response, thereby promoting glycolysis and increasing the production and release of lactate.^348,349 Lactate imported via SlC5A12 and SlC16A1 transporters into CD4⁺ and CD8⁺ T cells suppresses glycolytic enzymes such as hexokinase-1, compromising cellular bioenergetics and inducing motility arrest both in tumors and inflammation.^350,351 Accordingly, elevated expression of lactate dehydrogenase A not only correlates with enhanced macrophage infiltration but also induces TAM polarization toward the M2 subtype through a lactate-mediated mechanism, ultimately promoting tumor progression.³⁵² In recent years, an increasing number of studies have emerged in understanding ATP metabolism signals regulating immune cell migration. Malignant cells upregulate distinct energy metabolism programs that hijack essential nutrients and outcompete neighboring infiltrating immune cells.³⁵³ Adenosine monophosphate (AMP) contributes to immune suppression by preventing NK cell infiltration into the TME and impairing their anti-tumor activity.²¹⁵ Parallel findings demonstrate that adenosine signaling through A2AR attenuates antitumor immunity by inhibiting CD8⁺ T cell infiltration and effector functions.³⁵⁴ During inflammation, extracellular ATP released by damaged cells increases mregDC motility through CACNB3-mediated calcium release from the endoplasmic reticulum, thereby attenuating inflammation to prevent excessive tissue damage.³⁵⁵ In addition to the accumulation of metabolites, heightened metabolic activity in immune and neoplastic cells drives accelerated oxygen consumption during tumorigenesis and inflammatory processes, culminating in the establishment of localized hypoxic niches.^356–358 During acute inflammation, hypoxic niches resulting from neutrophil respiratory burst activate HIF signaling within epithelial cells.³⁵⁹ This fortifies epithelial barrier integrity, thereby restricting further neutrophil transmigration and accelerating inflammation resolution.³⁵⁹ Within GBM, hypoxia attracts and sequesters TAMs through CCL8 and IL-1β, where they are reprogrammed toward an immunosuppressive state.³⁶⁰ Furthermore, hypoxia modulates NK cell functionality by altering chemokine secretion patterns, ultimately impairing directional migration toward tumor sites.³⁶¹

Extracellular matrix

The ECM constitutes a critical spatial structure that bidirectionally regulates immune cell migration through biomechanical and biochemical cues, mediating both permissive and restrictive functions (Fig. 5). On the one hand, the physical structure and molecular composition of the ECM can serve as guidance cues for immune cell migration and positioning. Pores formed by interwoven collagen fibrils within the ECM are pivotal structural determinants. For instance, leukocytes will leverage nuclear positioning mechanisms to actively probe the ECM, preferentially navigating through larger pores of ECM to facilitate their migration.³⁶² Similarly, T cells have been demonstrated to preferentially move through tissue sites that are characterized by thin fibers, deliberately avoiding denser matrices that are made by lysyl oxidases (LOXs).³⁶³ Beyond these passive guidance cues offered by the ECM architecture, successful migration relies on the intrinsic ability of immune cells to actively adapt their morphology. After experiencing large cell shape changes caused by the physical structures in the ECM, DCs employ the ARP2/3-cPLA2 shape-sensing mechanism to potentiate myosin contractility, thereby enhancing DC motility and enabling their directional migration from peripheral tissues toward TDLNs.³⁶⁴ In addition to its physical structure, the ECM molecular composition serves as a significant biochemical regulator orchestrating directed immune cell migration. During inflammation, type I collagen protein in the ECM potently enhances the migratory capacity of ILC2s by inducing their polarization and remodeling the actin cytoskeleton.³⁶⁵ In inflamed skin, structural changes to fibronectin fibers of the ECM result in enhanced integrin binding, thereby guiding Th1 cells migrating to perivascular sites³⁶⁶ ECM to further facilitate directional cell guidance indirectly by mediating the presentation of signaling proteins. Heparan sulfate proteoglycans in ECM can bind and present chemokines within the vasculature as well as the tissue parenchyma to form gradients that direct immune cell movement.³⁶⁷ Similarly, ECM glycosaminoglycans can regulate whether chemokines were presented on cell surfaces or remain more soluble, thereby affecting chemokine availability and ensuring specificity of chemokine action that directs immune cell trafficking.³⁶⁸ This phenomenon elucidates the underlying mechanism by which immune cells achieve directional migration through intricate chemokine networks.

On the other hand, spatial confinement formed by the ECM structure fundamentally undermines the migration of immune cells.^369,370 Under homeostatic conditions, the glycocalyx in the ECM forms a 200-2000 nm barrier that blocks interaction with adhesion molecules on circulating leukocytes, preventing aberrant leukocyte recruitment.³⁷⁰ During injury and inflammation, hyaluronan (HA) becomes covalently modified with heavy chains (HCs) from the interalpha-inhibitor (IaI) family of proteoglycans, forming crosslinked HA matrices.^371,372 Crosslinked HC-HA complexes demonstrate enhanced CD44 binding affinity, trapping leukocytes within the lesional ECM by promoting adhesion and preventing their migration, thereby perpetuating inflammatory responses.^373,374 Clinical and translational studies further reveal that ECM-impaired T cell migration through the tumor parenchyma constitutes a major bottleneck for adoptive cell therapies.³⁷⁵ This limitation persists even in immunogenic tumors, as aligned stromal collagen fibers physically restrict T cells infiltration into tumor cores.³⁷⁶ For instance, lysyl oxidase-mediated collagen cross-linking increases matrix rigidity while creating steric hindrance for T cell migration.³⁷⁵ In addition to enzymes, CAFs are another significant mediator that contributes to ECM remodeling. CAFs comprise a heterogeneous cellular compartment with functionally distinct subpopulations. Among these, myofibroblastic CAFs (myCAFs) are the main regulators of ECM remodeling through the exertion of actomyosin-dependent contracting forces and secretion of matrix metalloproteinases.^377,378 The ECM protein network remodeled by myCAFs serves as a physical barrier for immune cells, especially T lymphocytes, thus inhibiting their recruitment into cancer sites and subsequently reducing their opportunities to participate in the immune response in the TME.³⁷⁹

Impact of microbiota

A previous study revealed that antibiotic-induced gut microbiota depletion inhibits systemic trafficking of intestinal immunocytes, highlighting the impact of microbiota on immune cell migration.²³⁶

The microbiota can modulate the expression of immune cell membrane proteins, thereby regulating their migratory capabilities (Fig. 5). In the context of preventing local excessive inflammation, commensal-derived metabolites play a crucial role. For instance, Clostridium scindens-produced short-chain fatty acids can stimulate colonic epithelial cells to secrete TGF-β1, which induces high expression of CD103 and β7 integrin on Tregs, thereby promoting Treg homing to the colonic mucosa to maintain intestinal immune homeostasis.³⁸⁰ Similarly, during intestinal inflammation, cyclic dinucleotides derived from Helicobacter hepaticus upregulate the expression of CCR7 on ILC3s through the STING/NF-κB signaling pathway, driving ILC3 migration from the intestinal lamina propria to the mesenteric lymph nodes to suppress inflammatory responses.³⁸¹ Beyond local immune regulation, microbial influence on cell trafficking is pivotal for systemic antitumor immunity. Secondary bile acids produced by Clostridium scindens and Enterocloster spp. downregulate MAdCAM-1 in the ileum, driving the emigration of enterotropic α4β7⁺ Th17 cells into the tumor.³⁸² Similarly, modifications in the Ligilactobacillus to Bacteroides ratio within the gut microbiota regulate the MAdCAM-1-dependent homing of IgA⁺ antibody-secreting cells, thereby enhancing the CD8⁺ T cell response in distal tumors.³⁸³ However, microbial modulation of immune cell trafficking can also precipitate pathology, particularly through mechanisms such as molecular mimicry. Clostridioides difficile expresses a surface layer protein A that contains a mimic epitope of myelin basic protein (MBP), leading to the activation of MBP-specific Th1/Th17 cells.³⁸⁴ Activated Th1/Th17 cells with elevated expression of α4β1 integrin then migrate to the CNS, thereby inducing multiple sclerosis.³⁸⁴ Additionally, segmented filamentous bacteria have been reported to directly elevate S1PR1 expression on Tfh cells, enabling their migration from Peyer’s patches to inflammatory sites and promoting systemic extraintestinal autoimmunity.³⁸⁵

Beyond directly modulating immune cell protein expression, the microbiota also orchestrates immunocyte migration by regulating the molecular and structural composition of the extracellular microenvironment (Fig. 5). Segmented filamentous bacteria have been proven to convert vitamin A into retinoic acid (RA) through retinaldehyde dehydrogenase. Local accumulation of RA further induces intestinal epithelial cells to express serum amyloid A, which facilitates Th17 cell homing to the inflammation site and defense against infection.³⁸⁶ This principle of metabolite-driven recruitment extends to autoimmune inflammation. Kynurenic acid produced by Sporosarcina pasteurii specifically recruits macrophages to mesenteric lymph nodes (mLNs) via GPR35 receptor activation. Within the mLNs, macrophages secrete IL-6 to facilitate Th17 cell migration from the mLNs to the spinal cord, where they secrete IL-17A and exacerbate neuroinflammation in multiple sclerosis.³⁸⁷ Microbial metabolite regulation of immune trafficking is equally pivotal in promoting antitumor immunity. Tumors infected by human papillomavirus (HPV) tend to secrete higher levels of chemokines such as CXCL9, CXCL10 and CXCL12 to recruit Th17, Th1 and CD8⁺T lymphocytes.³⁸⁸ Infiltrated CD4⁺T and CD8⁺T cells subsequently secrete IFN-γ and IL-17 to enhance anti-tumor immunity.³⁸⁸ Conversely, microbiota can also impede the migration of immunosuppressive cells. For example, urocanic acid derived from Muribaculum suppresses NF-κB signaling in tumor vascular endothelial cells, which reduces CXCL1 secretion and consequently impairs the recruitment of MDSCs toward tumors, thereby enhancing the tumor response to immune checkpoint inhibitors.³⁸⁹ In addition to microbiota-mediated chemoattractant gradients, investigations have also identified the microbiota contribution to the formation of lymphatic structures that facilitate the migration of immune cells. For instance, Helicobacter hepaticus has been demonstrated to promote colonic lymphatic network expansion through enhancement of lymphatic endothelial cell proliferation functional maturation, establishing optimized conduits for tumor-directed trafficking of anti-tumor T follicular helper cells.²⁸

Therapeutic approaches targeting immune cell migration

Although conventional therapies such as chemotherapy and radiotherapy in tumors and immunosuppressive agents in autoimmunity do not directly target immune cell migration mechanisms, evidence indicates that they can also modulate immune cell trafficking. These therapeutic effects on immunocyte migration in turn contribute to improved therapeutic outcomes. For instance, neoadjuvant chemotherapy with FOLFIRINOX is associated with increased recruitment of cytotoxic CD8⁺ T cells and M1 macrophages, significantly contributing to greater anti-tumor response and improved patient survival.³⁹⁰ In parallel, radiotherapy-induced upregulation of CXCL16, CXCL8, CXCL9 and CXCL10 within the TME facilitates the recruitment of NK cells and CTLs, thereby synergizing the ICB therapy.^391,392 The modulatory effect on immune cell migration extends to autoimmune diseases. Administration of methotrexate in psoriasis suppresses the infiltration of pathogenic T helper cells into lesional skin, thereby significantly ameliorating cutaneous inflammation.³⁹³ Therefore, targeting the process of immune cell migration represents a promising therapeutic strategy.

Targeting cytokine and chemokine signaling pathways

Therapeutic strategies targeting cytokine and chemokine signaling pathways primarily encompass two distinct approaches, including blockade of ligand‒receptor interactions and elevation of cytokine or chemokine levels (Fig. 6).

Fig. 6.

Principal strategies for immune cell directed therapy. a Targeting chemokine/cytokine pathways includes blockade of ligand-receptor interactions through antibodies or inhibitors and enhancement of local chemokine or cytokines activity such as nanoparticles, CAR immune cells, chemotherapy/ICB-induced chemokine production, engineered cytokines and fusion proteins. b Targeting tertiary lymphoid structures modulates organized immune-cell recruitment by promoting TLS formation and HEV maturation in tumors or suppressing pathogenic TLS responses in inflammatory diseases. c Targeting ECM reduces stromal barriers to immune cell infiltration by limiting collagen cross-linking, collagen deposition and fibroblast-driven ECM remodeling. d Targeting metabolic reprogramming restores immune-cell function by reshaping lactate and fatty acid metabolism through metabolic inhibitors, FAO modulation and dietary intervention. e Targeting microbiota reshapes microbial communities or microbial metabolites through antibiotics, prebiotics, fecal microbiota transplantation and engineered microbiota. Created with BioRender.com. CAR chimeric antigen receptor, ICB immune checkpoint blockade, TLS tertiary lymphoid structures, LOX lysyl oxidases, Hsp heat shock proteins, NIR-PIT infrared photoimmunotherapy, FAO fatty acid oxidation

Artificially engineered small-molecule inhibitors, antagonists and monoclonal antibodies can disrupt chemokine-receptor binding.^394,395 Within the TME, chemokines and their corresponding receptors mediate the recruitment of immunosuppressive cells. In contrast, similar chemokine-receptor axes in inflammatory disorders drive the infiltration of pro-inflammatory cells. Although the nature of the recruited immune cells is fundamentally distinct between malignant and inflammatory contexts, both contribute to disease progression. Consequently, targeting these chemokine-receptor axes has emerged as a pivotal area of therapeutic investigation. CXCR2 not only recruits N2 TANs and TAMs but also establishes an MDSC-mediated immunotherapy-resistant microenvironment, as evidenced by diminished PD-1 blockade efficacy.^396–399 Small molecule inhibitors and monoclonal antibodies against CXCR2, such as SB225002, Reparixin, Navarixin, AZD5069, SX682, ABX-IL8 and HuMax-IL8, have shown potential in enhancing cancer therapy by impairing the recruitment of immunosuppressive cells and angiogenesis.^400–402 In addition to CXCR2, myeloid immunosuppressive cells can also be recruited by CCR2 and CCR5.⁴⁰³ The CCR2 inhibitor PF04136309, combined with FOLFIRINOX (oxaliplatin, irinotecan, leucovorin and bolus fluorouracil) chemotherapy for pancreatic cancer, has demonstrated notable antitumor efficacy, with disease control achieved in 97% of patients and an objective response rate (ORR) of 49%.⁴⁰⁴ Although carlumab is a monoclonal antibody targeting CCR2 ligands, its therapeutic impact is modest. Stable disease was observed in a minority of patients, and no objective responses were achieved.⁴⁰⁵ Similarly, another monoclonal antibody that binds to CCL2, CNTO888, was also not effective at sustaining CCL2-CCR2 signaling blockade in a phase II study in patients with prostate cancer.⁴⁰⁶ These limited therapeutic efficacies may be attributed to compensatory surges in endogenous CCL2 production following its inhibition, thereby preventing sustained suppression of the target pathway.⁴⁰⁵ The CCR2 antagonist INCB3344 curbs M1 macrophage infiltration into vascular and renal compartments, thereby reducing inflammation, oxidative stress, and vascular remodeling. These effects suggest its potential utility in antihypertensive therapy.⁴⁰⁷ Preclinical studies in murine models also demonstrated that the CCR5 antagonist maraviroc exerts cardioprotective effects, mediated through reduced expression of endothelial adhesion molecules, which was associated with diminished lesional M1 macrophage infiltration.⁴⁰⁸ These protective effects were further substantiated in a phase IV clinical trial, wherein 24 weeks of maraviroc treatment reduced markers of arterial stiffness and early carotid atherosclerosis in patients with HIV infection.⁴⁰⁹ A dual antagonist targeting CCR2 and CCR5, cenicriviroc, has been developed to block mucosa-associated invariant T (MAIT) cell migration in cases of acute intestinal inflammation.⁴¹⁰ Preclinical models also identify the central role of cenicriviroc in blocking liver-infiltrating CCR2⁺ monocyte interaction with tissue-destructive CD8⁺ T cells in the pathogenesis of hepatitis.⁴¹¹ However, cenicriviroc demonstrated disappointing clinical outcomes. In the phase IIb TANDEM study, only 31.6% of patients achieved ≥1-point improvement in fibrosis stage without worsening steatohepatitis.⁴¹² The above negative outcomes may stem from the possibility that CCR2/CCR5-mediated immune cell recruitment does not constitute the dominant pathogenic driver in the progression of these diseases. CCR4 is another significant receptor that mediates the directional migration of Tregs to modulate the TME.^413–415 Blocking CCR4-dependent Treg accumulation can reverse CD8⁺ T cell exhaustion and PD-L1-mediated immune evasion, thereby potentiating ICB responsiveness.^395,416 Clinical translation of this approach is exemplified by mogamulizumab, a CCR4 antagonist that has undergone evaluation for cancer treatment in several clinical trials.^417–419 In a phase I clinical study, NCT02476123, the combination of mogamulizumab and the anti-PD-1 antibody nivolumab manifested an adequate safety profile and significant antitumor activity in solid tumors.⁴¹⁷ Specifically, in inflammation, dysregulation of cytokine and chemokine control during inflammatory responses drives aberrant recruitment of immune cells, ultimately leading to tissue damage or cytokine storms. For instance, IL-1 facilitates the recruitment of neutrophils and Th1 cells to the site of inflammation, resulting in the release of secondary wave cytokines that promote destructive inflammation.⁴²⁰ Anakinra, the recombinant IL-1Ra that specifically blocks the activity of both IL-1α and IL-1β, has been demonstrated to effectively alleviate cytokine syndrome during immune effector cell-associated neurotoxicity syndrome and rheumatic conditions, as well as improve cardiac contractility and outcomes in patients with fulminant myocarditis.^420–422 During the acute phase of COVID-19 infection, IL-6 is associated with increased infiltration of pro-inflammatory monocytes.⁴²³ The administration of tocilizumab, a recombinant human IL-6 monoclonal antibody, has demonstrated positive outcomes for patients with severe COVID-19 necessitating organ support in intensive care units.⁴²⁴

Apart from blocking cytokine and chemokine pathways, strategies aimed at breaching biological barriers within migratory paths have emerged. A prominent approach involves elevating cytokine and chemokine levels through endogenous production or exogenous delivery.⁴²⁵ Enhanced endogenous chemokine production involves targeting specific signaling molecules that stimulate resident cells within the TME. For instance, dual PD-1/CTLA-4 blockade significantly upregulated macrophage-derived CXCL9 and CXCL10 expression, promoting CD8⁺ T cell infiltration and therapeutic efficacy.³⁰⁴ In addition to targeting immune checkpoints, the administration of DPP4 inhibitors or COX-2 inhibitors similarly elevates CXCL9/CXCL10 expression, facilitating CD8⁺ T cell trafficking and thereby potentiating anti-PD-1 responses.^426–428 Combination therapy with carboplatin and PP4 inhibition specifically upregulates CXCL10, improving NK/T cell recruitment and tumor chemosensitivity.⁴²⁹ Additionally, chimeric antigen receptor (CAR)-engineered T and NK cells with chemokine/cytokine secreting capability represent a strategy to locally overcome chemotactic barriers. Preclinical studies in metastatic pancreatic cancer models have revealed that IL-15 co-expression not only facilitates the infiltration of CAR immune cells but also achieves substantial therapeutic responses with favorable safety profiles, providing a strong rationale for clinical application.⁴³⁰ Clinical validation of these barrier-overcoming strategies has been documented in multiple trials. A phase I clinical study, NCT04099797, reported that GD2. CAR-T cells engineered with Interleukin-7 receptor demonstrated favorable treatment response and safety tolerability.⁴³¹ Similarly, IL-7/CCL19-secreting CAR-T cells in a phase I trial, NCT03198546, showed disease control benefits across hepatic, prostatic, and ovarian malignancies.⁴³² Despite these advancements, CAR-NK applications in solid tumors remain clinically underexplored. Promisingly, the safety and efficacy of IL-15-expressing CAR-NK cells in B cell tumors have been demonstrated by a phase 1/2 trial, NCT03056339, with 70% of patients remaining in CR at 12 months and no patients suffering neurotoxicity or graft-versus-host disease.⁴³³ In cancer therapy, recent advances in nanotechnology have provided novel exogenous chemokine and cytokine delivery strategies for targeted transport in therapeutic applications.⁴³⁴ These nanocarriers can be precisely engineered to excel in releasing IL-1β and CXCL10, thereby establishing a local pro-inflammatory environment that promotes the influx of immune cells.⁴³⁵ Moreover, Chen et al. constructed a tumor acidity-responsive nanoparticle delivery system (NP-siCD47/CCL25) that enabled intratumoral delivery of CCL25, significantly enhancing CCR9⁺ CD8⁺ T cells infiltration and improving PD-1/PD-L1 blockade therapeutic efficacy.⁴³⁶ Intriguingly, the novel erythrocyte-anchored nanoparticle platform ImmunoBait enables CXCL10 chemokine delivery through tumor-associated vasculature, thereby bypassing vascular barriers and recruiting CD8⁺ T cells and NK cells to tumors.⁴³⁷ Parallel innovations involve a nanopolymer for IL-2 delivery, which is a biodegradable carrier with minimal toxicity.⁴³⁸ Peritumoural injection of this nanopolymer was reported to promote the infiltration of CD8⁺ and CD4⁺ T cells and NK cells into the TME, suppressing tumor growth in C57BL/6 mice.⁴³⁸ Unlike traditional adenovirus-based IL-2 delivery, which often necessitates multiple injections and results in dose-dependent toxicity, employment of nanotechnology enables reduced administration frequency while maintaining therapeutic efficacy, thereby significantly mitigating IL-2-associated adverse effects.^439,440 However, such nanopolymer delivery exhibits limited sustainability, necessitating frequent administration. Delivery of circular RNA (circRNA) via H1L1A1B3 lipid nanoparticles (LNPs) resolves this challenge by providing sustained therapeutic payload release.⁴⁴¹ A single intratumoral injection of H1L1A1B3 LNPs loaded with circRNA encoding interleukin-12 (IL-12) induces a robust immune response and significantly suppresses tumor growth in a Lewis lung carcinoma model.⁴⁴¹ Collectively, these studies demonstrate that modulating chemokine/cytokine gradients, either endogenously or via advanced delivery systems, constitutes a validated hypothesis for restoring immune cell infiltration by targeting their migratory mechanisms and helping them overcome the biological barriers present in the TME.

Given that supraphysiological cytokine levels in inflammatory disorders risk triggering cytokine release syndrome, the core strategy for targeting cytokines under inflammatory conditions lies in augmenting their beneficial effects at low dose rather than merely elevating their overall concentrations.³⁹⁴ Engineered IL-2 analogs with selectivity for the trimeric high-affinity IL-2R can selectively expand Tregs, which subsequently suppress pathogenic autoreactive T cell infiltration into inflamed tissues and promote protective regulatory immune responses.⁴⁴² However, due to its short half-life (<15 min), high amounts of intravenous IL-2 were required and were associated with severe nonspecific toxicities.⁴⁴³ Although low-dose IL-2 therapy avoids severe toxicities and demonstrates favorable efficacy in patients with systemic lupus erythematosus,⁴⁴⁴ its off-target effects prove challenging to circumvent and frequently precipitate treatment failure.^442,443 Engineered cytokine variants are another novel strategy to address the dose-limiting toxicities associated with high-dose cytokine administration. IL-10 variants with enhanced binding to IL-10Rβ display augmented potency, with robust activity even at low doses in monocytes, thereby limiting their ability to recruit inflammatory immune cell subsets.⁴⁴⁵ Additionally, prolongation of cytokine half-life achieved by protein fusions also demonstrates its potential in low-dose administration of cytokines without sacrificing efficiency.³⁹⁴ In mice with chronic autoimmune encephalomyelitis, IL-4-albumin fusion inhibits Th17 cell infiltration into the spinal cord and completely abrogates immune responses to myelin antigen in the spleen, demonstrating its prophylactically and therapeutically advantageous role in the treatment of multiple sclerosis.⁴⁴⁶

Targeting metabolic reprogramming

Although metabolic reprogramming has been demonstrated to modulate immune cell migration, current metabolically targeted therapeutic strategies primarily focus on modulating the overall functionality of immune cells rather than specifically intervening in their migratory capacity. Consequently, alterations in immune cell infiltration observed following treatment may represent a concomitant effect of metabolic targeting rather than its core therapeutic objective. This constitutes a fundamental distinction from the aforementioned therapeutic approaches directly targeting cytokine or chemokine pathways.

Targeting lactate metabolism has shown promise in modulating immune suppression within the TME. Inhibition of lactate dehydrogenase A (LDH-A) by oxamate in combination with PD-1 blockade pembrolizumab restores T cell function and enhances CD8⁺T cell infiltration by reducing lactic acid accumulation in tumors, thereby improving immunosurveillance and sensitizing immunotherapy.⁴⁴⁷ Similarly, preclinical trials have shown that the combination of monocarboxylate transporter 1 (MCT1) inhibitor AZD3965 and anti-PD-1 therapy can reduce lactate secretion into the TME, reduce the infiltration of Tregs in solid tumors, and improve antitumor immunity.⁴⁴⁸ In autoimmune or chronic inflammatory diseases, the glycolytic reprogramming of immune cells contributes to excessive inflammation and tissue infiltration. Dioscin can suppress glycolysis by inhibiting the HIF-1α/mTORC1 signaling pathway. During silica-induced pulmonary fibrosis, dioscin partially attenuates chronic pulmonary inflammation by suppressing the infiltration of M1 macrophages, B cells, and T helper cells.⁴⁴⁹ Similarly, inhibition of glycolysis via 2-DG in macrophages dampens LPS-induced chemokine secretion and impairs chemotactic migration, thereby limiting inflammatory T cell infiltration in models of acute lung injury.⁴⁵⁰

Recent advances have also demonstrated that targeting key nodes of lipid metabolism not only alters the bioenergetic state of immune cells but is also associated with increased immune cell infiltration, thereby indicating potential therapeutic effects in cancer and inflammatory diseases. Metabolic reprogramming within the TME often restricts glucose availability, forcing tumor-infiltrating lymphocytes (TILs), especially CD8⁺ T cells, to rely on fatty acid oxidation (FAO) for energy.⁴⁵¹ Activation of peroxisome proliferator-activated receptor alpha (PPAR-α) using fenofibrate enhances the FAO capacity of CD8⁺ TILs, thereby improving their survival, motility and cytotoxic function in lipid-rich, hypoglycemic environments.⁴⁵² Beyond enhancing FAO, modulating lipid uptake can also impact immune cell localization. CD36, a key scavenger receptor mediating fatty acid uptake, has been implicated in inducing lipid peroxidation and dysfunction in TILs within the TME.⁴⁵³ Pharmacological or genetic inhibition of CD36 restores CD8⁺ T cell fitness and promotes their accumulation at tumor sites, leading to suppressed tumor progression.^453,454 Similarly, in inflammatory diseases such as ulcerative colitis (UC), targeting lipid metabolic pathways modulates immune cell recruitment and activation in affected tissues. PPAR-α activation by fenofibrate reduces the infiltration of pro-inflammatory T helper subsets (Th1/Th17) by altering their metabolic programming, which in turn dampens the production of cytokines.⁴⁵⁵ This immune rebalancing contributes to the resolution of intestinal inflammation in susceptible models.

Dietary intervention offers a novel therapeutic paradigm for metabolically targeted approaches by modulating host metabolism at the macroenvironmental level. A fasting or fasting-mimicking diet (FMD) was shown to remodel the intratumoral immune landscape by promoting the infiltration of activated and cytotoxic immune cell populations, including CD8⁺ T cells, M1 macrophages, and NK cells.⁴⁵⁶ A recent phase II clinical trial (NCT04248998) demonstrated that the combination of FMD with chemotherapy achieved a pathologic complete response (pCR) rate of 56.6% in patients with early-stage triple-negative breast cancer, with a favorable safety profile.⁴⁵⁷ In the context of autoimmune disorders, intermittent fasting exerts protective effects by increasing the infiltration of Tregs and simultaneously diminishing the number of pro-inflammatory IL-17-producing T cells, thereby mitigating disease progression in multiple sclerosis.⁴⁵⁸ In addition to fasting, healthy dietary interventions also exert targeted immunomodulatory effects. Phenolic compounds in extravirgin olive oil, an essential component of the Mediterranean diet, attenuate immune cell infiltration and tissue damage in inflammatory arthritis models by suppressing pro-inflammatory cytokines and prostaglandin E₂ levels, thereby reducing joint edema, leukocyte infiltration and structural degradation.⁴⁵⁹ Similarly, dietary protein restriction or selective amino acid limitation, such as methionine or cystine, enhances the infiltration and tumoricidal activity of CD8⁺ T cells while curbing the recruitment of immunosuppressive MDSCs.⁴⁶⁰ Mechanistically, moderate protein restriction activates the unfolded protein response (UPR) in tumor cells via IRE1α, which potentiates CD8⁺ T cell recruitment and bolsters antitumor immunosurveillance.⁴⁶¹ In contrast, detrimental dietary patterns can promote pathological immune cell infiltration. High-fat diets (HFD) are implicated in fostering liver metastasis via hepatocyte-derived extracellular vesicles that propagate YAP-regulating microRNAs, culminating in nuclear CYR61 overexpression and M2-like macrophage infiltration.³⁴¹ HFD-induced adipose tissue hypoxia and inflammation further exemplify this mechanism, wherein inflammation-driven adipocyte dysfunction activates the NLRP3 inflammasome and promotes the infiltration of pro-inflammatory M1 macrophages, aggravating systemic insulin resistance.^462,463 Moreover, elevated intake of dietary salt can exacerbate autoimmune conditions by promoting the induction of pathogenic Th17 cells, contributing to the pathogenesis of multiple sclerosis.⁴⁶⁴ Interestingly, research has also shown that a high-salt diet can impair cytokine networks critical for MDSC expansion and thus attenuate the accumulation of MDSCs within the tumor niche.⁴⁶⁵ These results suggest that modification of detrimental dietary patterns may confer therapeutic benefits, although its potential warrants further rigorous investigation.

Targeting tertiary lymphoid structures

TLSs frequently undergo spatial structural remodeling in response to therapeutic interventions, creating a permissive destination for migratory immune cells⁴⁶⁶ (Fig. 6). However, therapeutic strategies targeting TLSs diverge substantially between oncology and inflammatory diseases. In oncology, the primary approach involves facilitating TLS maturation to augment the infiltration of antitumor immune cells. Conversely, in inflammatory disorders, therapeutic efforts are directed toward preventing the formation of TLSs, thereby reducing the migration of pathogenic immune cells.

Recent preclinical studies have underscored the therapeutic potential of promoting TLS formation and maturation to optimize immune cell infiltration and improve antitumor immunity. The administration of recombinant human IL-33 protein induces intratumoral expansion of lymphoneogenic ILC2s and facilitates the development of TLSs in PDAC mouse models, establishing organized hubs for adaptive immune activation.²¹⁸ The formation of TLSs can also be induced by a novel fusion protein, LIGHT-VTP, consisting of the TNF superfamily cytokine LIGHT and vascular targeting peptide (VTP).⁴⁶⁷ When combined with immune checkpoint inhibitors, LIGHT-VTP stimulates the trafficking of preexisting endogenous effector T cells and promotes their intratumoral activation, outperforming conventional immunotherapies in preclinical evaluations.⁴⁶⁷ Clinical translation is evidenced by neoadjuvant chemotherapy-induced TLS maturation in high-grade serous ovarian carcinoma, which maintains T cells with preserved responsiveness to ICB.⁴⁶⁸ Within the TLS, HEVs function as specialized lymphocyte trafficking conduits, whose functional status directly governs the recruitment efficiency of immune cells.^469–471 Emerging evidence demonstrates that targeted modulation of HEV functional status enhances TLS-mediated immunogenicity, providing a paradigm to refine contemporary immunotherapeutic regimens.⁴⁷⁰ Former studies reveal that HEV density positively correlates with both T and B cell infiltration while serving as a prognostic biomarker in malignant patients.⁴⁷² Mechanistically, the lymphotoxin (LT)/LTβR signaling pathway has been identified as the principal regulator of HEV maturation and maintenance.⁴⁷³ Therapeutic activation of this pathway through LTβR agonists has shown significant enhancement of immunotherapy efficacy in preclinical models.⁴⁷⁴ Recent advances highlight synergistic strategies for HEV maturation beyond LTβR agonists. Dual PD-1/CTLA-4 blockade substantially augments both the density and functional maturation of HEVs, thereby enhancing endogenous lymphocyte trafficking.⁴⁷⁵ Complementary approaches combining anti-angiogenic agents with PD-L1 inhibitors demonstrate similar potentiation of immunotherapeutic effects by inducing HEV maturation.⁴⁷⁶

In autoimmune diseases and chronic inflammatory conditions, which are typically characterized by the immune system’s attack on self-tissues, the emergence and maturation of TLSs are often associated with poorer prognoses.⁴⁷⁷ Thus, inhibition of TLS formation has become a potential therapeutic strategy. As pivotal drivers of TLS development, Th17 and Tfh cells constitute critical therapeutic targets in inflammatory disorders. During viral myocarditis (VMC), targeting Th17 cells by monoclonal antibodies (mAbs), such as podoplanin (PDPN) mAb, suppresses their proliferation and activation, thereby inhibiting the formation of ectopic TLSs.⁴⁷⁸ Consequently, the recruitment of pro-inflammatory CD68⁺ M1 macrophages and B cells mediated by ectopic TLS is blocked, leading to reduced production of anti-heart autoantibodies and ameliorating VMC symptoms.⁴⁷⁸ Similar experimental outcomes were replicated in a Sjögren’s syndrome model, where anti-IL-17A antibodies suppressed infiltration of GL7⁺ germinal center B cells, thereby ameliorating tissue damage due to autoimmune responses.⁴⁷⁹ Tfh cells also contribute to the recruitment and activation of B cells, mediating TLS formation.⁴⁸⁰ Targeting Tfh cells with ICOS-neutralizing antibodies significantly suppresses the formation of TLSs as well as the infiltration of B cells and plasma cells, thereby alleviating the process of renal fibrosis.⁴⁸¹

Targeting extracellular matrix

In contrast to TLSs, which typically facilitate immune cell trafficking into tumors, the ECM often serves as a predominant driver of the physical barrier, necessitating focused strategies for therapeutic targeting⁴⁸² (Fig. 6). In inflammatory diseases, ECM-targeted therapies are primarily aimed at mitigating fibroproliferative pathology, with no established role in modulating immune cell migration.⁴⁸³ One prominent therapeutic strategy targeting the ECM in oncology involves inhibiting the deposition and cross-linking of collagen. Hsp47 constitutes a critical regulator of collagen deposition within the ECM.⁴⁸⁴ Functioning as a molecular chaperone, Hsp47 facilitates procollagen folding and maturation in the endoplasmic reticulum, thereby enhancing collagen secretion into the ECM.⁴⁸⁵ Col003, an inhibitor disrupting the Hsp47-collagen association, suppresses collagen maturation and secretion, which in turn reduces ECM density and rigidity, thereby facilitating CTL infiltration and enhancing the efficacy of anti-PD-L1 immunotherapy.⁴⁸⁶ However, clinical trials evaluating Col003 have not yet been initiated, and its therapeutic potential in patients requires further investigation. Lysyl oxidases (LOX) are the major enzymes that catalyze covalent cross-linking of both collagens and elastin, contributing to the formation and increased stiffness of ECM.^487,488 Recombinant collagenase, such as LOX inhibitor, has gained traction as a potential oncological therapeutic by directly depleting collagen.³⁷⁵ Given their capacity to modulate ECM density and stiffness, LOX inhibitors may also restore immune cell infiltration by alleviating physical barriers to migration. PXS-5505, a pan-LOX inhibitor, has been reported not only to facilitate CTL infiltration but also to enhance the gemcitabine response in pancreatic cancer, suggesting a dual role in modifying both tumor stroma and migratory accessibility.⁴⁸⁹ However, clinical trials of PXS-5505 have thus far been conducted exclusively in myelofibrosis, with its efficacy and safety in solid malignancies remaining unexplored.⁴⁹⁰ Similarly, the anti-tumor efficacy of the dual LOX/LOXL2 inhibitor CCT36562 has been demonstrated solely in murine models, with no clinical trials conducted to date.⁴⁹¹ The efficacy of the selective LOXL2 inhibitor simtuzumab in combination with gemcitabine has been evaluated in a phase II randomized, double-blind study. Unfortunately, simtuzumab failed to confer additional clinical benefit over gemcitabine monotherapy for first-line treatment of pancreatic adenocarcinoma.⁴⁹² This may indicate that partial LOX axis blockade is insufficient to overcome redundant stromal mechanisms that continue to restrict immune cell infiltration, including persistently activated CAFs.⁴⁹³

Given the suboptimal clinical efficacy of directly targeting ECM-modifying enzymes, where CAFs represent a prominent confounding factor underlying these results, therapeutic strategies specifically directed against CAFs have thus emerged. One major approach is to directly eliminate CAFs by targeting specific surface markers such as FAP, thereby fundamentally blocking CAF-induced ECM remodeling and the impairment of immune cell infiltration.⁴⁹⁴ FAP-specific chimeric antigen receptor T cell treatment (CAR-T) can explicitly deplete FAP⁺ CAFs, overcoming stroma-dependent T cell exclusion and altering the immune landscape by reducing myeloid cell accumulation and increasing endogenous CD8⁺ T cell and NK cell infiltration.⁴⁹⁵ Recently, a phase I clinical trial (NCT01722149) investigating FAP-specific CAR-T cell therapy in four patients with metastatic pleural mesothelioma (MPM) demonstrated an acceptable safety profile.⁴⁹⁶ However, the limited sample size precluded definitive assessment of treatment efficacy, warranting further investigation.⁴⁹⁶ Infrared photoimmunotherapy (NIR-PIT) is another novel approach to remove CAFs. Mechanistically, NIR-PIT utilizes antibody-IRDye700DX (IR700) conjugates that bind to FAP⁺ CAFs. Subsequent near-infrared light irradiation drives a dramatic change in the solubility of conjugate, culminating in rapid plasma membrane disruption and highly ICD of targeted FAP⁺ CAFs.⁴⁹⁷ This technology constitutes a novel approach for CAF-targeted therapeutic strategies. However, its efficacy remains to be validated in further clinical trials.

Overall, these findings collectively support a conceptual framework whereby targeting ECM remodeling may facilitate immune cell migration by overcoming both physical and biochemical stromal barriers. Further investigations are warranted to explore whether combining these agents with chemokine axis modulators could synergistically restore effective immune cell trafficking into tumors.

Targeting microbiota

Therapeutic strategies targeting microbiota encompass selective depletion or supplementation of defined bacterial taxa and modulation of microbiota-derived metabolites (Fig. 6). Emerging insights into intratumoral microbiota dynamics are unveiling novel therapeutic opportunities for enhancing antitumor immunity.⁴⁹⁸ In breast cancer mouse models, F. nucleatum colonization exacerbates tumor metastatic potential through Gal-GalNAc-mediated impairment of T cell infiltration.⁴⁹⁹ Targeted clearance of Fusobacterium nucleatum within tumor niches through metronidazole or bacteriophage resulted in marked inhibition of both local tumor expansion and distal metastatic dissemination.^499,500 Neutrophil depletion leads to significant expansion of intratumoral bacteria such as Akkermansia. These bacteria boost B-cell infiltration via IL-17, thereby driving immune evasion and tumor cell proliferation.⁵⁰¹ In neutrophil-deficient mouse models, antibiotic depletion of Akkermansia ameliorates intratumoral dysbiosis and significantly attenuates tumor invasion, demonstrating therapeutic potential by disrupting this bacterial-immune axis.⁵⁰¹ In addition to targeted clearance of microbiota, engineered consortia introduction constitutes another potential strategy in oncological immunotherapy. Researchers designed an attenuated Salmonella typhimurium strain that released Vibrio trauma flagellum B (FlaB) in the tumor, promoting M1 macrophage infiltration through TLR4 signaling.⁵⁰² Additionally, a probiotic strain of E. coli Nissle 1917 was engineered to target mouse tumors and transform the accumulated metabolic product ammonia in the TME into L-arginine, which increased the number of tumor-infiltrating CD8⁺ T cells and had marked synergistic effects with PD-L1 blocking antibodies in the clearance of tumors.⁵⁰³

Beyond intratumoral microbiota, gut microbiomes exert increasingly recognized impacts on tumors and autoimmune diseases. Clostridium butyricum (C.B.), a bacterium that is found in the gut microbiota, has demonstrated antitumor potential in colorectal cancer (CRC).⁵⁰⁴ Treatment with CB results in proteasomal degradation of oncogenic MYC protein and enhanced infiltration of CD8⁺ T cells. These findings underscore the important mechanisms of microbiota in boosting the effectiveness of chemotherapy and immunotherapy in CRC.⁵⁰⁵ Contrary to C.B., a recent investigation identified a new strain of the bacterial genus Hominenteromicrobium (designated YB328) isolated from the feces of patients who responded to PD-1 blockade.⁵⁰⁶ Oral administration of YB328 augments the antitumor efficacy of PD-1 blockade by promoting the migration of cDCs from gut-associated lymphoid tissue to the TME, thereby enhancing CD8⁺ T cell activation.⁵⁰⁶ The impact of microbial metabolites on immune cell trafficking is increasingly recognized, consequently catalyzing the development of novel therapeutic approaches. Propionic acid and butyrate are significant short-chain fatty acids (SCFAs) produced by bacteria such as Coprococcus, Ruminococcaceae, and Clostridium.⁵⁰⁷ Propionic acid-mediated GPR43 activation has been reported to inhibit pathogenic CD4⁺ and CD8⁺ T cell egress from the colonic lamina propria, abrogating their CNS infiltration and attenuating autoimmune encephalomyelitis progression.⁵⁰⁸ Oral propionate administration has been demonstrated to significantly improve clinical outcomes and reduce the annual relapse rate in patients with multiple sclerosis (MS).⁵⁰⁹ In contrast, butyrate administration in drinking water promotes the egress of gut-derived Tregs in nonobese diabetic mice and increases their pancreatic infiltration, suggesting therapeutic potential in type I diabetes through induced immune tolerance.⁵¹⁰

Fecal microbiota transplantation (FMT) represents an emerging therapeutic strategy that remains under active investigation. Investigation reveals that FMT can reprogram the gut-tumor immune axis, systemically augmenting the trafficking competence of circulating CD8^±T cells to tumor-infiltrated niches.⁵¹¹ Clinical trials are currently evaluating FMT as an immune checkpoint inhibitor (ICI) adjuvant, with preliminary data showing restored anti-PD-1 responsiveness in refractory metastatic melanoma patients receiving microbiota from ICI-responsive donors.^512,513 FMT also exhibits potential in the treatment of autoimmune diseases. In SLE patients, FMT elevates Lactobacillus johnsonii-derived inosine, which suppresses the expression of B cell migration-associated genes via the ERK-HIF-1α pathway, thereby reducing renal B cell infiltration and ameliorating lupus symptoms.⁵¹⁴ Clinical trials further demonstrate that FMT mitigates autoimmune responses and preserves pancreatic β-cell function in type I diabetes by reducing pathogenic CD8⁺ T cell migration while promoting Treg infiltration.⁵¹⁵ However, a critical challenge in FMT lies in the current inability to establish standardized criteria defining an “optimized fecal microbiota”, which consequently constrains its clinical translation in contrast to prebiotic interventions. Water-soluble polysaccharide extracted from Ganoderma lucidum (GLP) has been demonstrated to suppress tumor and inflammation progression by inhibiting macrophage infiltration and downregulating the expression of pro-inflammatory mediators, including IL-1β, iNOS, and COX-2.⁵¹⁶ Conversely, inulin modulates the relative abundance of Lactobacillus, Dubosiella and the Prevotellaceae_NK3B31 group within the gut microbiota, thereby enhancing SCFA production and indirectly limiting Th17 cell infiltration into the CNS, ultimately attenuating autoimmune neuroinflammation.⁵¹⁷

Conclusion and perspective

Immune cell migration constitutes a cornerstone of effective cancer immunotherapy and inflammatory disease resolution by orchestrating the spatiotemporal dynamics of immune surveillance and effector functions across diverse pathological contexts. This review elucidates the navigation mechanisms by which immune cells from diverse sources infiltrate tumors and inflammatory microenvironments through coordinated cellular and molecular interactions. These migratory processes facilitate the recruitment, activation, and spatial reprogramming of immune subsets that either suppress or exacerbate disease progression. Overall, a nuanced understanding of immune cell trafficking not only enables the precise optimization of immune spatial distribution but also offers novel immunomodulatory avenues for restraining pathogenic inflammation.

Despite remarkable advances in mechanistic insights, critical challenges persist in translating immune migration into clinically actionable strategies. One principal obstacle is the heterogeneity of tumor or inflammatory microenvironments and interindividual variability that impact immune cell infiltration. This variability arises from complex factors such as chemokine gradients, adhesion molecule landscapes, ECM remodeling, metabolic reprogramming and microbiome modulation, which complicate therapeutic response, necessitating personalized stratification frameworks. Moreover, current limitations in imaging methodologies for tracking immune cell migration are further compounded by insufficient imaging safety profiles and suboptimal spatiotemporal resolution.^{250,251,253–255} These technical constraints, along with patient-specific variability in immune responses, complicate the development of standardized protocols for effectively harnessing immune cell migration. Addressing these challenges necessitates multidisciplinary innovation, including advancing real-time in vivo imaging, improving molecular tagging strategies, and developing integrated platforms that combine high-resolution data with functional clinical endpoints.

Future research on immune cell migration is entering a transformative phase driven by three synergistic frontiers: mechanistic dissection, therapeutic innovation, and technological convergence. Comprehensive investigation of the regulatory networks governing immune cell migration, particularly from nontraditional sources such as the gut, will not only uncover novel mechanistic insights into immune cell trafficking but also identify innovative therapeutic targets across both cancer and inflammatory diseases. The integration of multidisciplinary technologies prominently involves therapeutic strategies and imaging modalities. The strategic implementation of biomaterials has enabled precision-targeted therapeutic approaches through biologically engineered delivery mechanisms. While incorporation of material science and sequencing with intravital imaging multidimensional tracking of immune dynamics, resolving previously inaccessible spatiotemporal patterns of immune cell migration.^{242,243,245–247} Assimilating these molecular insights with technological innovations will ultimately pave the way for precision immunotherapies that effectively harness the full potential of immune cell migration to treat both malignancies and inflammation.

Author contributions

Yufeng Lu and Di Shao drafted and conceptualized the initial manuscript. Supervision and strategic direction were provided by Yi Xiao, Yi-Zhou Jiang and Zhi-Ming Shao. All authors have read and approved the review article.

Competing interests

The authors declare no competing interests.