Trial watch: anticancer vaccination with dendritic cells

ABSTRACT

Dendritic cells (DCs) are critical players at the intersection of innate and adaptive immunity, making them ideal candidates for anticancer vaccine development. DC-based immunotherapies typically involve isolating patient-derived DCs, pulsing them with tumor-associated antigens (TAAs) or tumor-specific antigens (TSAs), and utilizing maturation cocktails to ensure their effective activation. These matured DCs are then reinfused to elicit tumor-specific T-cell responses. While this approach has demonstrated the ability to generate potent immune responses, its clinical efficacy has been limited due to the immunosuppressive tumor microenvironment. Recent efforts have focused on enhancing the immunogenicity of DC-based vaccines, particularly through combination therapies with T cell-targeting immunotherapies. This Trial Watch summarizes recent advances in DC-based cancer treatments, including the development of new preclinical and clinical strategies, and discusses the future potential of DC-based vaccines in the evolving landscape of immuno-oncology.

Introduction

Dendritic cells (DCs) are pivotal at the interface of innate and adaptive immunity, positioning them as prime targets for anticancer vaccine research.^1,2 In 1973, Ralph Steinman first identified DCs³ and was awarded the Nobel Prize in 2011 for this groundbreaking discovery.⁴ Steinman’s pioneering research significantly advanced our understanding of the innate immune system.^5,6 These cells, which were named after the Greek term “dendron” because of their ‘tree-like’ shape, are now recognized as professional antigen-presenting cells (APCs).^3,5,7–11 Indeed, DCs are highly specialized in antigen presentation,^12,13 a process that is vital for initiating and regulating immune responses.¹⁴ They are capable of presenting extracellular antigens on major histocompatibility complex (MHC) class II molecules to CD4⁺ T helper (T_H)¹⁵ cells and intracellular antigens on MHC class I molecules to CD8⁺ cytotoxic T lymphocytes (CTLs). In addition, DCs have the ability to present extracellular antigens on major histocompatibility complex (MHC) class I, through a process known as cross-presentation.^{12,13,16–18} This ability to cross-present is particularly crucial for eliciting efficacious antitumor immune responses, highlighting the importance of DCs in cancer immunotherapy.^19–21

The field of DC research has expanded significantly since Steinman’s discovery, with extensive studies focusing on the functionality and interactions of DCs with CD4⁺ and CD8⁺ T cells,^22–25 This research has been propelled by advances in high-dimensional flow cytometry, single-cell transcriptomics, in vivo imaging, and sophisticated in vivo transgenics. These technologies have significantly refined the classification of dendritic cells (DCs) into distinct biological subsets, defined by their phenotype, ontogeny, and function.^22,26–30 These subsets include two types of ‘classical’ or ‘conventional’ DCs: type 1 cDC (cDC1)^31,32 and type 2 cDC (cDC2), as well as plasmacytoid DCs (pDCs)^33–38 Nowadays it is well known that cDCs and pDCs are completely distinct from monocyte-derived DCs (moDCs) in terms of lineage, whereas for a long time, it was traditionally believed that DCs originated from monocytes.^2,34,39,40 While cDC1 and cDC2 share a common DC progenitor, the developmental origins of pDCs⁴¹ remain a subject of debate.^29,42–45

Each subset of DCs exhibits unique functional specializations, contributing to their distinct roles in immune responses during health and disease. The pDCs are renowned for their robust type I interferon (IFN) responses, in particular the production of IFN-α,^{42-44,46–49} However, their presence in tumors is often associated with poor prognosis due to impaired type I IFN production in the tumor microenvironment (TME), leading to immunosuppression.^49,50 The cDC1s are particularly proficient in activating CD8⁺ T cells through cross-presentation and are essential for antitumor immunity, being the only canonical DCs capable of effectively prime tumor-specific CD8⁺ T cells.^29,51–56 They also produce interferon-λ, thereby manipulating T cell responses toward a helper T cell phenotype.⁵⁷ Their abundance in the TME frequently correlates with prolonged patient survival.^58,59 Conversely, cDC2s are primarily involved in presenting exogenous antigens to various CD4⁺ T helper cell subsets^60,61 and can secrete high levels of interleukin-12 (IL-12),^62,63 which is critical for the expansion and survival of T and natural killer (NK) cells.^64,65

In homeostatic conditions, both tissue-resident (found in the tissues where they are seeded) and circulating (found in peripheral blood) DCs exist in an immature state, which is crucial for immunosurveillance and maintaining tolerance to self-antigens,^66-68 Immature DCs (iDCs) excel at taking-up extracellular material and promoting the expansion of regulatory T cells (Treg) if DCs encounter self-antigens, thereby preventing autoimmunity,^69–73 Upon encountering activating, foreign, and/or non-self stimuli, iDCs undergo maturation,^74–82 which is characterized by decreased antigen uptake, increased expression of co-stimulatory molecules, and enhanced cytokine secretion, enabling them to efficiently prime T cells in lymph nodes.^69,73

Given their pivotal role in antigen presentation and T cell activation, DCs have become central to anticancer vaccination strategies,^83–90 Classically, in clinical studies, DC vaccines are generated by differentiating DCs ex vivo from patients’ autologous monocytes, followed by exposing these DCs to tumor-associated or specific antigens (TAAs or TSAs)^91,92 and maturation-inducing agents. These DC vaccines are then reinfused back into the patients.^{1,88,93–103} Although the precise relationship of such moDCs to the canonical DC lineages is not entirely clear, such cells become particularly prevalent under inflammatory conditions.^104,105,106 They are potent stimulators of CD4⁺ T cells and cross-present antigens and activate CD8⁺ T cells.^95,106 Despite some success in triggering anti-tumor immune responses, the therapeutic impact of DC-based vaccines in clinical trials has been constrained, largely due to the potent immunosuppressive mechanisms within the TME.^94,107–111

Although moDCs are commonly used for vaccine development due to practical advantages, increasing evidence indicates that cDCs may have superior T cell stimulatory capabilities.^{95,97,112,113} Consequently, there is growing interest in exploring naturally occurring DC subsets, such as cDCs, Langerhans cells (LCs) – cells that originate from the bone marrow and then migrate into the epithelium to perform the function of antigen recognition and presentation^114,115− and pDCs, in the context of DC vaccines. Early clinical trials show promising results, but further validation of the protocols for isolating or differentiating these cells in vitro is still needed.^31,115–120

To determine whether the historically low efficacy of moDC-based vaccines stems from their potentially less effective T cell stimulation or other unknown resistance mechanisms specific to DC vaccines, future clinical trials involving cDC- and pDC-based anticancer vaccines will be critical^121–125 Additionally, significant advancements have been made in the field of therapeutic DC vaccination, with a range of sophisticated strategies now being tested in preclinical and clinical trials. These strategies encompass the ex vivo loading of DCs with TAAs/TSAs, genetic modification of DCs to express TAAs or TSAs, and in vivo activation using various agents such as immunostimulatory cytokines or molecules like pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) that interact with toll-like receptors (TLRs).^{123,126–129}

In defiance of considerable progress, sipuleucel-T (Provenge®), a therapy integrating DCs (amongst other immune cells) for treating asymptomatic or minimally symptomatic metastatic castrate-resistant prostate cancer, remains the only FDA-approved DC-integrating therapy for the last 14 years. Indeed, sipuleucel-T is not a pure DC preparation but a mixture of various immune cells, which could have contributed to its mixed clinical performance.^130–134

Despite the challenges, numerous ongoing clinical studies are exploring DC vaccination as a cancer treatment, with many investigating multimodal therapeutic approaches that combine DC vaccines with immune checkpoint blockers (ICBs) and adoptive T cell transfer (ACT),^135–141 These innovative combinations offer promising prospects for enhancing DC-based cancer immunotherapy.¹⁴² This Trial Watch outlines the latest advances in preclinical and clinical research on DC vaccines, highlighting their potential as a powerful anticancer approach.

Recent preclinical developments

Numerous preclinical studies have been published since our last Trial Watch article on DC vaccination for cancer treatment in July 2022.¹⁴³ We have chosen a few key publications to highlight the main trends in the field (presented in no order).

Vedunova et al. (National Research Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia) reported the efficacy and molecular mechanism of glioma cell-loaded DC vaccines going through immunogenic cell death (ICD) induced by photosensitizer-based photodynamic therapy (PS-PDT). Herein, the transcriptional program induced in the DC vaccine following incubation with glioma cells undergoing ICD involved a T_H17-like footprint. Accordingly, in an orthotopic mouse model, the efficacy of ICD-based DC vaccine was dependent on retinoic acid receptor-related orphan receptor-(ROR)γt. Interestingly, analysis of the transcriptome of the ICD-based DC vaccine highlighted a predictive four-gene signature (CFH, GALNT3, SMC4, and VAV3) that was related to a better overall survival (OS) in glioma patients.¹⁴⁴

Adamik et al. (Parker Institute for Cancer Immunotherapy, San Francisco, USA) analyzed the transcriptomic and immuno-metabolic profiles of the DC vaccines from 35 subjects enrolled in a trial with late-stage melanoma patients. DC vaccines demonstrated alterations in multiple immune and metabolic pathways, a functional decrease in oxygen consumption rate (OCR)/oxidative phosphorylation (OXPHOS), and an increase in extracellular acidification rate (ECAR)/glycolysis. By using a technique called single-cell energetic metabolism by profiling translation inhibition (SCENITH), they showed that metabolic skewing and increased glycolysis in DC vaccines impacted OS in melanoma patients. Moreover, single-cell metabolic regulome profiling showed that the lactate transporter MCT1 (monocarboxylate transporter-1) was increased in melanoma patients' DCs as compared to healthy donors. In line with this, an increase in glucose uptake and lactate secretion was observed, the latter being described as an immune-inhibitory molecule in many immune-related processes.¹⁴⁵ This suggested that culture conditions that more tightly control metabolic pathways of monocytic cells might be necessary to create more effective DC vaccines capable of inducing efficacious antitumor T cell responses.¹⁴⁶

Sprooten et al.. (KU Leuven, Leuven, Belgium) used multi-omics analyses to find that clinical DC vaccines do not simply move from an immature state to functionally mature state after relevant clinical preparation steps, as widely expected based on previous data. Instead, the DC vaccines develop into three patient-dependent developmental trajectories i.e., a type I IFN response^HIGH T1 trajectory, which associated with efficacious in situ antigen-specific responses and prolonged patient survival. This contrasted with the other T2 (macrophage-like state) or T3 (mature regulatory/mreg DC-like state) trajectories, both of which correlated to weak in situ antigen-specific reactions and a shorter patient survival. However, contrary to the above expectations, pre-clinical version of DC vaccines following the T1 differentiation trajectory induced an unprecedented negative feedback loop that resulted in CD8⁺ T cell-suppressive programmed death-ligand 1 positive (PD-L1⁺) macrophages. This was evident in both preclinical settings and glioblastoma (GBM) patients (in an ongoing Phase II clinical trial). More specifically, they observed that DC vaccines, counter to expectations, created a unique niche of PD-L1⁺ lymph node-associated macrophages (LAMs) as well as tumor-associated macrophages (TAMs) across lymph nodes and tumors, respectively. These LAMs and TAMs killed CD8⁺ T cells via TNF-related apoptosis-inducing ligand (TRAIL) signaling in both these anatomical locations thereby inhibiting these DC vaccine’s ability to activate anticancer T cells. Accordingly, they showed that combining PD-L1 blockade (but not blockade of other immune-checkpoints) with DC vaccination achieved significant tumor regression by depleting PD-L1⁺TAMs/LAMs, suppressing myeloid inflammation, and de-inhibiting effector/stem-like memory T cells. Accordingly, they proposed a mandatory multimodal immunotherapy combined with DC vaccines exhibiting a type I IFN response^HIGH state, to robustly overcome T cell-depleted tumors.¹⁴⁷

Han et al. (University of Illinois at Urbana-Champaign, USA) to enable targeted modulation of adoptively transferred DCs for developing improved DC vaccines reported an easy metabolic labeling approach. Labeling with metabolic glycan showed a reduction of the membrane mobility of DCs, thereby activating DCs and improving their ability to present antigens and to subsequently prime T cells. Furthermore, the cell-surface chemical tags introduced via this labeling method also enabled in vivo conjugation of cytokines onto adoptively transferred DCs, which additionally enhanced cytotoxic T lymphocytes (CTL) response and antitumor efficacy.¹⁴⁸

Basirjafar et al. (School of Medicine, Rafsanjan University of Medical Sciences, Iran) used a murine breast cancer model to access the effects of leptin and/or lipopolysaccharide (LPS)-treated DC vaccines on multiple T cell-related immunological markers. Leptin/LPS-treated DC vaccines showed more efficacy in inhibiting breast cancer development and preventing metastasis. Increasing immune responses against tumor induced by leptin/LPS-treated DC vaccines was linked to a significant increase in the frequencies of splenic CTLs and T_H1 cells, an increased production of IFNγ and IL-12, a significant increase in T-box transcription factor TBX21 (best known as T-bet) and granzyme expression as well as a concomitant decrease in tumor growth factor beta (TGF-β) and forkhead box protein P3 (FOXP3) expression.¹⁴⁹

Chan et al. (University of Guelph, Canada) demonstrated the quick hiring of neutrophils to the draining lymph nodes of DC-vaccinated mice, a process that occurred together by an increased number of IFN-γ-producing NK cells expressing the degranulation marker CD107a. In line with this, the reduced numbers of NK cells in draining lymph nodes as compared to the controls arose from the decrease in neutrophils in DC-immunized mice. Notably, the authors also showed that DC vaccines induced IFNγ− and TNF-producing CD8⁺ T cells that expressed CD107a, and were not impacted by neutrophils depletion, suggesting that neutrophil-mediated antitumor immunity induced by DC vaccines might be targeted to enhance vaccination efficacy.¹⁵⁰

Because cancer vaccines based on peripheral blood monocytes or bone marrow treated with granulocyte-macrophage colony-stimulating factor (GM-CSF) i.e., GMDCs, were shown to depend on the transfer of antigens from the DC vaccine to the host cDC1, Ferris et al. (Washington University in St. Louis, Missouri) evaluated whether cDC1 are superior to GMDC-based vaccines. For this, they compared antitumor responses induced by GMDCs and cDC1s in mice with a deleted enhancer located at +32 kb of the interferon regulatory factor 8 (Irf8) transcriptional start site (Irf8 +32^−/− mice), which leads to a lack of endogenous cDC1s in these mice and are incapable of rejecting immunogenic fibrosarcoma. Both GMDCs and cDC1s could cross-present cell-associated antigens to CD8⁺ T cells in vitro. Still, tumor injection of GMDCs in Irf8 +32^−/− mice failed to trigger antitumor immunity, aligned with the reported dependence on host cDC1. On the other hand, tumor injection of cDC1 into Irf8 +32^−/− mice induced their migration to the draining lymph node, as well as CD8⁺ T cell activation and tumor rejection. This tumor rejection did not require antigen loading on cDC1, showing that in vivo acquisition of the antigen by cDC1 leads to antitumor responses.¹⁵¹

Silva et al.. (Oncology Research Institute (IPON), Federal University of Triângulo Mineiro (UFTM), Brazil) evaluated the behavior of the adhesion molecules, intercellular adhesion molecule (ICAM)-1 and ICAM-2, in DC-based immunotherapy. For this, tumor and lymph nodes of Balb/c mice were analyzed 7 and 14 days after therapy. This showed that ICAM-2 was associated with a reduction in tumor volume. This suggested that the DC vaccine enhances the immune system and that ICAM-2 might serve as a marker for high immunogenicity.¹⁵²

Sultan et al.. (Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO, USA) discovered that the efficacy of therapeutic peptide vaccines targeting tumor-specific neoantigens is strongly influenced by the dosage of the MHC-II neoantigens included in the vaccine. To achieve this, Sultan and his team used vaccines with MHC-I neoantigens and different doses of tumor-derived MHC-II neoantigens and observed that while low doses of MHC-II-restricted peptides promoted tumor rejection, high doses inhibited rejection in tumor-bearing mice. Inhibitory cells induced by the high-dosage vaccines were identified as type 1 regulatory T (Tr1) cells (identified as FOXP3-negative, IL-10-producing inhibitory cells.¹⁵³ These tumor-specific Tr1 cells suppressed tumor rejection driven by anti-PD1 therapy, or adoptively transferred tumor-specific effector T cells. Mechanistically, Tr1 cells selectively targeted and killed cDC1s, resulting in reduced cDC1 numbers within the tumors. Overall, these findings demonstrate that Tr1 cells have a role in suppressing antitumor responses and thus impeding immune control of cancer.¹⁵⁴

The studies selected above represent a small portion of the numerous preclinical studies on DC vaccines found in the published literature. This shows a significant interest in optimizing and advancing anticancer DC vaccines.

Completed clinical trials

Since the publication of our previous Trial Watch on this subject (July 2022),¹⁴³ we have identified 26 new clinical trials that investigated the safety and efficacy of DC-based therapeutic interventions in cancer patients, which have been published in the peer-reviewed scientific literature in the past 2 years (source http://www.ncbi.nlm.nih.gov/pubmed).

The findings from these published studies incorporate trials conducted across 11 distinct types of cancers, of which the most common were melanoma,^{120,155–158} followed by prostate cancer,^159–162 GBM,^163–165 multiple myeloma,^166,167 lung cancer^168,169 and ovarian cancer^170,171 (Figure 1). Compared to our previous Trial Watch,¹⁴³ the new clinical trials targeted mainly the same cancer types as in the years before.

Figure 1.

Overview of current strategies of dendritic cell (DC) vaccination for cancer therapy. DC, dendritic cell; MUC1, mucin 1, cell surface associated; NY-ESO-1 (official name: CTAG1B), cancer/testis antigen 1B; TAA, tumor-associated antigen; TSA, tumor-specific antigen; TERT, telomerase reverse transcriptase; WT1, WT1 transcription factor; CAR, chimeric antigen receptor; CTL, cytotoxic T lymphocyte; CTLA4, cytotoxic T-lymphocyte associated protein 4; ERBB, erb-b2 receptor tyrosine kinase; EBV, Epstein-Barr virus; GM-CSF, granulocyte-macrophage colony-stimulating factor; MAGE, melanoma-associated antigen; PD1, programmed death ligand 1; PDL1, programmed cell death 1 ligand 1; Tp53, tumor protein p53.

Most of the studies reviewed here present findings from clinical trials assessing autologous moDCs loaded with TAAs/TSAs or TAA-derived peptides,^{120,155,157,161,166,172–175} TAA/TSAs-coding RNAs,^162,166,176 and autologous/allogenic cancer cell lysates^{156,158,159,163,165,168,177,178} (Figure 1). This is in line with our previous report of July 2022¹⁴³. Additionally, one publication reported the use of cDC2 and pDC¹²⁰ instead of moDCs, and another study used immature DCs in combination with ICBs such as anti-programmed cell death-1 (PDCD1, best known as PD-1) and anti-cytotoxic T-lymphocyte associated protein 4 (CTLA-4) antibodies.¹⁶⁰

In contrast to our previous Trial Watch,¹⁴³ the use of individual antigens for DC pulsing has reduced substantially, such that most of the recently published studies focused on a range or mixture of TAAs (Figure 1). However, the TAAs targeted in some of these reports are in line with the general trend also reported previously, i.e., they target common TAAs, such as melanoma antigen family (MAGE) antigens,¹⁶⁶ Epstein–Barr virus (EBV) antigens,¹⁷³ WT1 transcription factor (WT1) antigen,¹⁶⁶ or baculoviral IAP repeat containing 5 (Survivin) antigen.¹⁷⁵

In the studies mentioned above, DC vaccines were evaluated either as a single agent therapy^{161,164–166,170,173,178} (usually after surgery) or in conjunction with conventional anticancer treatments, predominantly chemotherapeutics^{159,168,169,171,175,177} and other standard-of-care (SOC) regimens^{157,162,163,176} (Figure 1). Besides conventional treatments, other trials combined DC vaccines with immunotherapeutic agents such as ICBs (mainly anti-PD1 and anti-CTLA4 antibodies) or immunomodulatory factors such as GM-CSF.^{155,156,158,167,172,174,179}

The majority of these publications were on Phase I or II studies, including 9 Phase I studies, 8 Phase II studies, 5 Phase I/II studies followed by only 4 Phase III studies. Existing literature, and in line with our previous reports on the subject, indicates that DC vaccines were generally well tolerated, with the majority of studies reporting only mild-to-moderate adverse effects (grade 1–2) such as fatigue, fever, and influenza-like symptoms. However, two studies reported a significant number of severe adverse events (grade 3–4): (I) a Phase I study¹⁷⁴ where 57.9% of the patients had grade 3 or 4 treatment-related effects, and (II) a Phase I/II study¹⁷⁵ where all patients had at least one adverse event of grade 3 or higher, although these effects were associated with the adjuvant chemotherapy (carboplatin/paclitaxel) rather than the DC vaccines. Overall, in these trials, DC vaccination showed promising immunological changes, demonstrated by (but not limited to) the increased antigen-specific T or B cell activity and/or the tumor infiltration of lymphocytes.

Herein, the results of the 4 Phase III studies that assessed the clinical benefits of DC-based therapy need particular attention. One Phase III trial enrolled 1182 patients with metastatic castration-resistant prostate cancer (mCRPC), and evaluated the efficacy and safety of DCVAC/PCa (DC-based vaccine where DCs prepared from the patient’s monocytes were collected and subsequently exposed to a human prostate adenocarcinoma cell line (LNCaP) killed by immunogenic modality) combined with chemotherapy (docetaxel and prednisone) versus chemotherapy alone.¹⁵⁹ The study reported no difference in OS between the DCVAC/PCa plus chemotherapy and chemotherapy alone groups, with OS of 23.9 months and 24.3 months, respectively. Also, no differences in the secondary efficacy endpoints (radiological progression-free survival, time to prostate-specific antigen progression, or skeletal-related events) were observed. Another study evaluated the possible delayed clinical outcome caused by sipuleucel-T in men with mCRPC.¹⁶¹ Two cohorts of men were included: the prospective evaluation of chronic pancreatitis for epidemiologic and translational studies (PROCEED) which is the first prospective, observational cohort study of chronic pancreatitis in the USA; and the cohort of mCRPC patients treated with sipuleucel-T at Dana-Farber Cancer Institute (DFCI). From these cohorts, men who received three infusions of sipuleucel-T and did not initiate a new therapy for more than 6 months after completion of sipuleucel-T, were included. Prostate-specific antigen (PSA) response was observed in 19.9% of patients from the PROCEED cohort and 14.3% of patients from the DFCI cohort, and with a median OS of 49 and 60 months, respectively. In this analysis of mCRPC patients treated with sipuleucel-T, using two datasets, a delayed PSA response was observed in a subset of patients, suggesting a delayed but detectable clinical activity. On the basis of (previous) promising Phase I/II data, another Phase III trial in advanced renal cell carcinoma (RCC) further investigated the safety and efficacy of the combination therapy involving CMN001 (a DC-based immunotherapy, employing autologous DC electroporated with autologous tumor RNA) plus the SOC sunitinib.¹⁷⁶ In the trial, 426 patients were either treated with CMN-001 plus SOC treatment or SOC treatment alone. The study reported almost no difference in OS between the combinatorial group (27.7 months) and the SOC group (32.4 months). The last Phase III trial covered by our current survey, focused on investigating whether adding autologous tumor lysate-loaded DC vaccine (DCVax-L) to SOC extends survival among GBM patients.¹⁶³ The study involved 232 patients with newly diagnosed GBM or recurrent GBM in the DCVax-L group and 99 patients in the SOC only group. Median OS for patients with newly diagnosed GBM treated with DCVax-L was 19.3 months vs. 16.5 in SOC only groups. For recurrent GBM patients treated with DCVax-L this median OS was 13.2 months vs.7.8 in SOC only groups. This study demonstrated that incorporating DCVax-L with the SOC might extend survival in patients with both newly diagnosed GBM and recurrent GBM, compared to matched external controls who only received SOC. Although the results of this study require additional validation with compatible control arm.

Overall, the findings from these studies underscore the inconsistent clinical potential of DC vaccination. This suggests significant opportunities for enhancement in areas such as patient selection, tailoring for specific cancer types, personalizing antigens, and developing more targeted combinatorial strategies.

Ongoing clinical trials

This Trial Watch recorded 52 ‘ongoing’ clinical trials registered at http://www.clinicaltrials.gov/in the period between January 2022 and February 2024, evaluating the efficacy, safety, and therapeutic profile of anticancer DC vaccination. The details of these trials are summarized in Table 1.

Table 1.

Overview of clinical trials registered on clinicaltrials.gov between January 2022 and February 2024 testing dendritic cell (dc)-based immunotherapy in cancer patients.

Strategies	Indication	Phase	Status	TAA/TSA(s)	Combinatorial treatment	Reference
Autologous DCs	Gastrointestinal Tumors	II	Not yet recruiting	n. a	Pembrolizumab, Nivolumab, Sintilimab, Toripalimab, Camrelizumab, Tislelizumab	NCT05461235
	Glioma		Recruiting	n. a	Single agent	NCT06156150
			Recruiting	n. a		NCT06043232
	Hepatocellular Carcinoma	II	Not yet recruiting	n. a	Single agent	NCT06193733
	Liver Cancer	I/II	Not yet recruiting	n. a	Single agent	NCT05622825
	Pancreas Cancer	I/II	Not yet recruiting	n. a	ICBs	NCT06172634
		II/III	Recruiting	n. a	Tegafur	NCT05955157
	Pleural Mesotheliomas	I	Not yet recruiting	n. a	Single agent	NCT05304208
	Postoperative treatment	Early I	Not yet recruiting	n. a	Oral NMN	NCT06036355
	Prostate Cancer	I	Recruiting	n. a	Prodencel	NCT05533203
	Solid Tumors	I	Recruiting	n. a	Single agent	NCT06015269
Autologous DCs loaded with tumor lysate	Melanoma	I/II	Completed	Tumour Lysate, TAAs	PROLEUKIN	NCT06152367
	NSCLC	I/II	Recruiting	Tumour Lysate	N-803	NCT05642195
	Ovarian Cancer	I/II	Recruiting	Tumour Lysate	Single agent	NCT05773859
	Pancreatic Cancer	I	Completed	Tumour Lysate	Mitazalimab	NCT05650918
	Solid Tumors	I/II	Recruiting	Tumour Lysate	Nivolumab, Entinostat	NCT05898828
		II	Recruiting	Tumour Lysate	Single agent	NCT06175221
Autologous DCs transfected or pulsed with TAA-coding RNA(s)	Angiosarcoma	I	Recruiting	Tumor-derived mRNA, tumor lysate	Paclitaxel, Filgrastim, Pegylatedinterferin alpha-2A	NCT05799612
Autologous DCs loaded with recombinant TAAs or TAA-derived peptide(s)	Breast Cancer	I/II	Recruiting	ERBB2	Trastuzumab, Pepinemab	NCT05378464
		I	Recruiting	ERBB2, ERBB3	Single agent	NCT05504707
		II	Recruiting	ERBB2	Trastazumab, Pertuzumab, Paclitaxel	NCT05325632
		I	Not yet recruiting	Neoantigens	Single agent	NCT06195618
		I	Recruiting	Neoantigens	Single agent	NCT05809752
		II	Not yet recruiting	ERBB2	Pembrolizumab	NCT05539365
	Colorectal Carcinoma	II	Not yet recruiting	Neoantigens	Pembrolizumab	NCT05518032
	ESCC	I	Unknown status	Neoantigens	Single agent	NCT05317325
	Fallopian Tube Carcinosarcoma	I/II	Recruiting	Neoantigens	Pembrolizumab	NCT05920798
	Glioma	I	Not yet recruiting	Neoantigens	Ipilimumab, Nivolumab, Poly ICLC	NCT05457959
	Head and Neck Carcinoma	I/II	Recruiting	HPV	Poly-ICLC	NCT06007092
	Hematologic Neoplasms	I	Enrolling by invitation	EBV antigens	Single agent	NCT05635591
	Leukemia	I	Withdrawn	Neoantigens	STING Dependent Activators (STAVs)	NCT05321940
	Lung Carcinoma	I	Recruiting	Neoantigens	Pembrolizumab, Durvalumab	NCT05886439
	Lymphoma	Early I	Active, not recruiting	EBV antigens	Single agent	NCT05882305
	Nasopharyngeal Cancer	I/II	Recruiting	Neoantigens	Single agent	NCT05261750
	Neoplasms	I	Withdrawn	Neoantigens	Single agent	NCT05589844
	NSCLC	I	Recruiting	Personalized neoantigens	Low dose cyclophosphamide	NCT05195619
	Ovarian Cancer	I	Unknown status	Tumor-associated antigen and patient-specific neoantigens	Single agent	NCT05270720
		I/II	Not yet recruiting	Personalized neoantigens, tumor lysate	Low dose cyclophosphamide	NCT05714306
	Pleural Mesotheliomas	I/II	Recruiting	WT-1	Atezolizumab, Platinum/Pemetrexed based chemotherapy	NCT05765084
	Prostate Cancer	III	Not yet recruiting	Neoantigens	Sipuleucel-T	NCT06134232
		II	Recruiting	Neoantigens	Testoterone cypionate	NCT06100705
		I	Recruiting	Neoantigens	Single agent	NCT05806814
		II	Recruiting	Personalized neoantigens	Single agent	NCT05751941
	Solid Tumors	I/II	Recruiting	WT-1	Single agent	NCT05964361
			Recruiting	Neoantigens	Single agent	NCT05749627
		I	Recruiting	Neoantigens	Levatinib, Nivolumab	NCT05767684
		I	Recruiting	Tp53	Abraxane, Cyclophosphamide, anti-PD1, Anti-CTLA4	NCT05631886
Autologous DC-CIK/CTL combinations	Leukemia	I	Recruiting	n. a	Antigen-specific T cells CART/CTL	NCT05262673
		I	Recruiting	n. a	Antigen-specific T cells CART/CTL	NCT05277753
	Lymphoma	I	Recruiting	n. a	CD19 CAR-T	NCT05585996
	Solid Tumors	I	Unknown status	TAAs	Single agent	NCT05235607

Abbreviations: CAR, chimeric antigen receptor; CTL, cytotoxic T lymphocyte; CIK, cytokine-induced killer; DC, dendritic cell; ERBB, erb-b2 receptor tyrosine kinase; n.a., not applicable; NSCLC, non-small cell lung cancer; TAA, tumor-associated antigen; TBVA, tumor blood vessel antigen; WT1, WT1 transcription factor; Tp53, tumor protein p53; ESCC, esophageal squamous cell carcinoma; EBV, Epstein-Barr virus; HPV, Human papillomavirus.

In these ongoing clinical trials, the most common cancer being targeted is breast cancer followed by basket trials that enroll patients with multiple solid tumors (Figure 1 and Table 1). Such basket studies cover a range of tumor types like breast cancer, ovarian cancer, prostate cancer, non-small cell lung cancer, and leukemia (Figure 1 and Table 1). Notably, although the majority of studies are Phase I or II trials, at least two advanced-phase clinical trials are evaluating DC vaccination: a Phase III study enrolling mCRPC patients (NCT06134232), and a Phase II/III trial focusing on pancreatic ductal adenocarcinoma (NCT05955157). This suggests that some DC-based therapies have progressed to a more advanced clinical development.

In most of the ongoing trials, the DC vaccines consist of autologous DCs pulsed with TAAs/TSAs, TAA-derived peptides, or tumor lysates (Figure 1 and Table 1). However, several studies are focusing on DCs pulsed with personalized TSAs or neoantigens (Table 1). Trials reporting autologous DCs pulsed with TAAs show a variety of common TAAs as targets, such as WT1, and EBV antigens as described before (Figure 1 and Table 1).

Interestingly, most of the ongoing trials administer DC-based vaccination alone, or in combination with other cancer therapies, including (but not limited to) ICBs targeting PD-1 (pembrolizumab or nivolumab), or CTLA4 (ipilimumab). Besides ICBs, chemo- and radiotherapy and other immunotherapeutic strategies such as ACT and chimeric antigen receptor (CAR) T cells are also being used (Figure 1 and Table 1). The goal of these combinations is to improve the efficacy of these DC-based vaccines.

In summary, the field of clinical DC vaccines is moving toward the use of tailored TAAs or personalized TSA approaches with the tendency to combine DC-based therapies with other forms of immunotherapy and/or chemotherapy.

Status update on clinical trials

Since our previous Trial Watch (July 2022) several clinical trials listed previously on DC-based vaccination as cancer treatment have changed status. NCT04523688, NCT04348747, NCT04093323, and NCT05127824 are now “Recruiting”, after being previously listed as “Not yet recruiting”. NCT04552886, NCT04837547, and NCT04147078 have changed their status from “Recruiting” to “Completed”. NCT04105582 is now listed as “Completed” after having been listed as “Active not recruiting”. The following trials have changed to “Active, not recruiting” from “Recruiting”: NCT04487756, NCT04911621, NCT04968366, NCT03970746. NCT04078269 changed from “Unknown” to “Active, not recruiting”. Additionally, several trials are now listed with “Unknown” status: NCT04085159, NCT04571632, NCT04801147, NCT04317248, NCT04335890, NCT05023928, NCT04567069, NCT03914768, NCT04115761, NCT04888611, NCT04277221, NCT03870113, NCT04082182, NCT04292769, NCT05020119, NCT04672473, NCT04476641, NCT04388033. Lastly, the following trials have terminated: NCT04614051 and NCT04615845 (difficult recruitment), NCT04963413 (terminated by mutual agreement of sponsor and institution), NCT03927222 (resource shortage), and NCT04203901 (strategic corporate decision).

Concluding remarks

In comparison with our previous trial watch, we observe a slight decline in the number of ongoing clinical trials (from 55 to 52) using DC vaccines for cancer therapy.^135,180 This decrease is likely due to the quick adoption of ICBs as part of the SOC for multiple cancers, along with the limited-to-poor clinical performance of DC vaccines^180–184 However, ICBs are also not effective for all cancers, and both primary as well as adaptive or acquired resistance to ICBs remain significant challenges in many cancers^185–191 As a result, DC vaccines are finding niche applications, for example, in cancers characterized by an immune-cold microenvironment (e.g., GBM) and resistance to ICBs, ACTs and/or CAR-T cells^192–199 This reflects an increasing focus on pinpointing specific tumor types where DC vaccines may be effective, particularly when combined with other therapies,^{184,200–207} or when integrating the targeting of tumor-specific neoantigens^208,209,210 DC vaccines are also being explored to ‘pre-prime’ tumors for subsequent T cell-based therapies.^170,211,212

Also, there seems to be a disconnection between preclinical research, which focuses on increasing the immunogenicity of DC vaccines, and the clinical unmet needs.²¹³ Regardless of several compositions being tested,^214–218 the clinical outcomes have not matched the preclinical promise.²¹⁹ This suggests that issues beyond DC vaccine-associated immunogenicity, such as adaptive or acquired resistance pathways might be operating in the clinical context and require urgent preclinical as well as translational investigations.^6,220–226

Emerging technologies, such as personalized neoantigenic vaccines and multimodal combinatorial therapies, hold promise in addressing the limitations of DC vaccines by enhancing antigen specificity, boosting immunogenicity, and overcoming tumor immunosuppression.^21,134,140 By combining the precision of neoantigen targeting with the synergy of multiple therapeutic modalities, these emerging technologies have the potential to revolutionize cancer immunotherapy, enabling more robust and durable antitumor responses.^208,217,219

Of course, to advance the development of DC vaccines toward socio-economic impact, they must either demonstrate clear survival benefits in patients or mechanisms behind their clinical failures must be identified, to guide future improvements. The number of Phase III clinical trials for DC vaccines is limited^{159,161,163,176} and has not shown significant benefits.²²⁷ The results of other advanced trials, especially for cancers that do not respond to current ICBs, are eagerly awaited. Subsequent investigations should address the shortcomings of previous DC vaccine trials and explore alternative strategies, such as using physiological DCs instead of moDCs.¹⁴² However, generating large quantities of certain DC subsets, like cDC1/cDC2, remains a challenge^228–231 DC vaccine research must also address challenges similar to those faced by ICBs,²¹⁹ such as immunosuppressive TME, the emergence of antigen-loss variants, and patient-to-patient immune heterogeneity or diversity.^{13,91,232–234} Also, manufacturing costs must be reduced, potentially through higher automation or even using HLA-matched donors, to improve practicality. Moreover, ICBs have benefited immensely from the use of specific biomarkers^{183,235–237} to guide patient pre-selection for their personalized application. But there is a severe lack of robust biomarkers for similar patient pre-selection for DC vaccines. Using multi-omics and spatial biomarker profiling to identify predictors of positive responses to DC vaccines could help design better clinical trials focused on specific patient subsets rather than all cancer or patients, thereby improving response rates as well as possibility of robust regulatory approvals.^238–240

Finally, while success has been somewhat limited up to now, DC vaccines still possess substantial potential in the field of cancer immunotherapy.²⁴¹ Advances in biomarker profiling, understanding of clinical DC biology and immune resistance mechanisms, will together enable the development of more effective and personalized DC vaccines.^13,142,242 We believe that DC vaccines will play a crucial role in sensitizing and priming ‘immune cold’ tumors to overcome ICB resistance in various cancers.

Funding Statement

ADG is supported by Research Foundation Flanders (FWO) (Fundamental Research Grant, G0B4620N; Excellence of Science/EOS grant, 30837538, for ‘DECODE’ consortium; Strategic Basic Research or SBO grant, S000523N), KU Leuven (C1 grant, C14/24/122; and C3 grants, C3/23/067, C3/21/037, C3/22/022), Come Up Against Cancer or Kom op Tegen Kanker (KOTK/2018/11509/1 and KOTK/2019/11955/1), VLIR-UOS (iBOF grant, iBOF/21/048, for ‘MIMICRY’ consortium), Olivia Hendrickx Research Foundation (OHRF), and European Union (EU) Mission Cancer grant for the GLIOMATCH consortium (Project no. 101136670). IV and RSL are supported by FWO-SB PhD Fellowship (1S06821N and 1S44123N). JS was funded by Kom op tegen Kanker (Stand up to Cancer), the Flemish cancer society through the Emmanuel van der Schueren (EvDS) PhD fellowship (projectID: 12699).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

There is no relevant new data or dataset associated with this manuscript.