CD4 CAR-T cells targeting CD19 play a key role in exacerbating cytokine release syndrome, while maintaining long-term responses

CD4+ T cells in antitumor immunity

Advances in cancer immunotherapy have transformed cancer care and realized unprecedented responses in many patients. The growing arsenal of novel therapeutics - including immune checkpoint inhibition (ICI), adoptive T cell therapies (ACTs), and cancer vaccines - reflects the success of cancer immunotherapy. The therapeutic benefits of these treatment modalities are generally attributed to the enhanced quantity and quality of antitumor CD8+ T cell responses. Nevertheless, CD4+ T cells are now recognized to play key roles in both the priming and effector phases of the antitumor immune response. In addition to providing T cell help through co-stimulation and cytokine production, CD4+ T cells can also possess cytotoxicity either directly on MHC class II-expressing tumor cells or to other cells within the tumor microenvironment (TME). The presence of specific populations of CD4+ T cells, and their intrinsic plasticity, within the TME can represent an important determinant of clinical response to immune checkpoint inhibitors, vaccines, and chimeric antigen receptor (CAR) T cell therapies. Understanding how the antitumor functions of specific CD4+ T cell types are induced while limiting their protumorigenic attributes will enable more successful immunotherapies.

Modulation of PRC1 Promotes Anticancer Effects in Pancreatic Cancer

Background: Pancreatic cancer, while relatively uncommon, is extrapolated to become the second leading cause of cancer-related deaths worldwide. Despite identifying well-known markers like the KRAS gene, the exact regulation of pancreatic cancer progression remains elusive. Methods: Clinical value of PRC1 was analyzed using bioinformatics database. The role of PRC1 was further evaluated through cell-based assays, including viability, wound healing, and sensitivity with the drug. Results: We demonstrate that PRC1 was significantly overexpressed in pancreatic cancer compared to pancreases without cancer, as revealed through human databases and cell lines analysis. Furthermore, high PRC1 expression had a negative correlation with CD4+ T cells, which are crucial for the immune response against cancers. Additionally, PRC1 showed a positive correlation with established pancreatic cancer markers. Silencing PRC1 expression using siRNA significantly inhibited cancer cell proliferation and viability and increased chemotherapeutic drug sensitivity. Conclusions: These findings suggest that targeting PRC1 in pancreatic cancer may enhance immune cell infiltration and inhibit cancer cell proliferation, offering a promising avenue for developing anticancer therapies.

CAR T cells in solid tumors and metastasis: paving the way forward

CAR T cell therapy, hailed as a breakthrough in cancer treatment due to its remarkable outcomes in hematological malignancies, encounters significant hurdles when applied to solid tumors. While notable responses to CAR T cells remain sporadic in these patients, challenges persist due to issues such as on-target off-tumor toxicity, difficulties in their trafficking and infiltration into the tumor, and the presence of a hostile and immunosuppressive microenvironment. This review aims to explore recent endeavors aimed at overcoming these obstacles in CAR T cell therapy for solid tumors. Specifically, we will delve into promising strategies for enhancing tumor specificity through antigen targeting, addressing tumor heterogeneity, overcoming physical barriers, and counteracting the immune-suppressive microenvironment.

Absolute lymphocyte count after BCMA CAR-T therapy is a predictor of response and outcomes in relapsed multiple myeloma

ABSTRACT

B-cell maturation antigen (BCMA)-targeting chimeric antigen receptor T cells (CAR-Ts) used in multiple myeloma (MM) are rapidly becoming a mainstay in the treatment of relapsed/refractory (R/R) disease, and CAR-T expansion after infusion has been shown to inform depth and duration of response (DoR), but measuring this process remains investigational. This multicenter study describes the kinetics and prognostic impact of absolute lymphocyte count (ALC) in the first 15 days after CAR-T infusion in 156 patients with relapsed MM treated with the BCMA-targeting agents ciltacabtagene autoleucel and idecabtagene vicleucel. Patients with higher maximum ALC (ALCmax) had better depth of response, progression-free survival (PFS), and DoR. Patients with ALCmax >1.0 × 103/μL had a superior PFS (30.5 months vs 6 months; P < .001) compared with those with ≤1.0 × 103/μL, whereas patients with ALCmax ≤0.5 × 103/μL represent a high-risk group with early disease progression and short PFS (hazard ratio, 3.4; 95% confidence interval, 2-5.8; P < .001). In multivariate analysis, ALCmax >1.0 × 103/μL and nonparaskeletal extramedullary disease were the only independent predictors of PFS and DoR after accounting for international staging systemic staging, age, CAR-T product, high-risk cytogenetics, and the number of previous lines. Moreover, our flow cytometry data suggest that ALC is a surrogate for BCMA CAR-T expansion and can be used as an accessible prognostic marker. We report, to our knowledge, for the first time the association of ALC after BCMA CAR-T infusion with clinical outcomes and its utility in predicting response in patients with R/R MM.

Engineered NKG2C + NK-like T cells exhibit superior antitumor efficacy while mitigating cytokine release syndrome

Engineered T and NK cell therapies have widely been used to treat hematologic malignancies and solid tumors, with promising clinical results. Current chimeric antigen receptor (CAR) T cell therapeutics have, however, been associated with treatment-related adverse events such as cytokine release syndrome (CRS) and are prone to immunologic exhaustion. CAR-NK therapeutics, while not associated with CRS, have limited in vivo persistence. We now demonstrate that an NK-like TCRαβ + CD8 T cell subset, identified and expanded ex vivo through its expression of the activating receptor NKG2C (NKG2C + NK-like T cells), can be transduced to express a second-generation CD19 CAR (1928z), resulting in superior tumor clearance, longer persistence and decreased exhaustion compared to conventional 1928z CAR + CD8 T cells and 1928z CAR+ NK cells. Moreover, CAR-modified NKG2C + NK-like T cells resulted in significantly reduced CRS compared to conventional CAR + CD8 T cells. Similarly, NKG2C + NK-like T cells engineered with a TCR targeting the NY-ESO-1 antigen exhibit robust tumor control and minimal exhaustion compared to TCR-engineered conventional CD8 T cells. These data establish NKG2C + NK-like T cells as a robust platform for cell engineering, and offer a safer, more durable alternative to conventional CAR-T and CAR-NK therapies.

Deciphering CD4+ T cell-mediated responses against cancer

It's been long thought that CD8+ cytotoxic T cells play a major role in T cell-mediated antitumor responses, whereas CD4+ T cells merely provide some assistance to CD8+ T cells as the "helpers." In recent years, numerous studies support the notion that CD4+ T cells play an indispensable role in antitumor responses. Here, we summarize and discuss the current knowledge regarding the roles of CD4+ T cells in antitumor responses and immunotherapy, with a focus on the molecular and cellular mechanisms behind these observations. These new insights on CD4+ T cells may pave the way to further optimize cancer immunotherapy.

Highlight of 2023: Virtues and vices of CD4 CAR T cells

This article for the Highlights of 2023 Series explores recent work that suggests that targeting CD4 CAR T cells may be critical for both of these challenges.

UniCAR T-Cell Potency-A Matter of Affinity between Adaptor Molecules and Adaptor CAR T-Cells?

Although Chimeric Antigen Receptor (CAR) T-cells have shown high efficacy in hematologic malignancies, they can cause severe to life-threatening side effects. To address these safety concerns, we have developed adaptor CAR platforms, like the UniCAR system. The redirection of UniCAR T-cells to target cells relies on a Target Module (TM), containing the E5B9 epitope and a tumor-specific binding moiety. Appropriate UniCAR-T activation thus involves two interactions: between the TM and the CAR T-cell, and the TM and the target cell. Here, we investigate if and how alterations of the amino acid sequence of the E5B9 UniCAR epitope impact the interaction between TMs and the UniCAR. We identify the new epitope E5B9L, for which the monoclonal antibody 5B9 has the greatest affinity. We then integrate the E5B9L peptide in previously established TMs directed to Fibroblast Activation Protein (FAP) and assess if such changes in the UniCAR epitope of the TMs affect UniCAR T-cell potency. Binding properties of the newly generated anti-FAP-E5B9L TMs to UniCAR and their ability to redirect UniCAR T-cells were compared side-by-side with the ones of anti-FAP-E5B9 TMs. Despite a substantial variation in the affinity of the different TMs to the UniCAR, no significant differences were observed in the cytotoxic and cytokine-release profiles of the redirected T-cells. Overall, our work indicates that increasing affinity of the UniCAR to the TM does not play a crucial role in such adaptor CAR system, as it does not significantly impact the potency of the UniCAR T-cells.

DMPK perspective on quantitative model analysis for chimeric antigen receptor cell therapy: Advances and challenges

Chimeric antigen receptor (CAR) cells are genetically engineered immune cells that specifically target tumor-associated antigens and have revolutionized cancer treatment, particularly in hematological malignancies, with ongoing investigations into their potential applications in solid tumors. This review provides a comprehensive overview of the current status and challenges in drug metabolism and pharmacokinetics (DMPK) for CAR cell therapy, specifically emphasizing on quantitative modeling and simulation (M&S). Furthermore, the recent advances in quantitative model analysis have been reviewed, ranging from clinical data characterization to mechanism-based modeling that connects in vitro and in vivo nonclinical and clinical study data. Additionally, the future perspectives and areas for improvement in CAR cell therapy translation have been reviewed. This includes using formulation quality considerations, characterization of appropriate animal models, refinement of in vitro models for bottom-up approaches, and enhancement of quantitative bioanalytical methodology. Addressing these challenges within a DMPK framework is pivotal in facilitating the translation of CAR cell therapy, ultimately enhancing the patients' lives through efficient CAR cell therapies.

Expand available targets for CAR-T therapy to overcome tumor drug resistance based on the "Evolutionary Traps"

Based on the concept of "Evolutionary Traps", targeting survival essential genes obtained during tumor drug resistance can effectively eliminate resistant cells. While, it still faces limitations. In this study, lapatinib-resistant cells were used to test the concept of "Evolutionary Traps" and no suitable target stand out because of the identified genes without accessible drug. However, a membrane protein PDPN, which is low or non-expressed in normal tissues, is identified as highly expressed in lapatinib-resistant tumor cells. PDPN CAR-T cells were developed and showed high cytotoxicity against lapatinib-resistant tumor cells in vitro and in vivo, suggesting that CAR-T may be a feasible route for overcoming drug resistance of tumor based on "Evolutionary Trap". To test whether this concept is cell line or drug dependent, we analyzed 21 drug-resistant tumor cell expression profiles reveal that JAG1, GPC3, and L1CAM, which are suitable targets for CAR-T treatment, are significantly upregulated in various drug-resistant tumor cells. Our findings shed light on the feasibility of utilizing CAR-T therapy to treat drug-resistant tumors and broaden the concept of the "Evolutionary Trap".

Deleting the mitochondrial respiration negative regulator MCJ enhances the efficacy of CD8+ T cell adoptive therapies in pre-clinical studies

Mitochondrial respiration is essential for the survival and function of T cells used in adoptive cellular therapies. However, strategies that specifically enhance mitochondrial respiration to promote T cell function remain limited. Here, we investigate methylation-controlled J protein (MCJ), an endogenous negative regulator of mitochondrial complex I expressed in CD8 cells, as a target for improving the efficacy of adoptive T cell therapies. We demonstrate that MCJ inhibits mitochondrial respiration in murine CD8+ CAR-T cells and that deletion of MCJ increases their in vitro and in vivo efficacy against murine B cell leukaemia. Similarly, MCJ deletion in ovalbumin (OVA)-specific CD8+ T cells also increases their efficacy against established OVA-expressing melanoma tumors in vivo. Furthermore, we show for the first time that MCJ is expressed in human CD8 cells and that the level of MCJ expression correlates with the functional activity of CD8+ CAR-T cells. Silencing MCJ expression in human CD8 CAR-T cells increases their mitochondrial metabolism and enhances their anti-tumor activity. Thus, targeting MCJ may represent a potential therapeutic strategy to increase mitochondrial metabolism and improve the efficacy of adoptive T cell therapies.

Rebuilding and rebooting immunity with stem cells

Advances in modern medicine have enabled a rapid increase in lifespan and, consequently, have highlighted the immune system as a key driver of age-related disease. Immune regeneration therapies present exciting strategies to address age-related diseases by rebooting the host's primary lymphoid tissues or rebuilding the immune system directly via biomaterials or artificial tissue. Here, we identify important, unanswered questions regarding the safety and feasibility of these therapies. Further, we identify key design parameters that should be primary considerations guiding technology design, including timing of application, interaction with the host immune system, and functional characterization of the target patient population.

CAR T treatment beyond cancer: Hope for immunomodulatory therapy of non-cancerous diseases

Engineering a patient's own T cells to accurately identify and eliminate cancer cells has effectively cured individuals afflicted with previously incurable hematologic cancers. These findings have stimulated research into employing chimeric antigen receptor (CAR) T therapy across various areas within the field of oncology. However, evidence from both clinical and preclinical investigations emphasize the broader potential of CAR T therapy, extending beyond oncology to address autoimmune disorders, persistent infections, cardiac fibrosis, age-related ailments and other conditions. Concurrently, the advent of novel technologies and platforms presents additional avenues for utilizing CAR T therapy in non-cancerous contexts. This review provides an overview of the rationale behind CAR T therapy, delineates ongoing challenges in its application to cancer treatment, summarizes recent findings in non-cancerous diseases, and engages in discourse regarding emerging technologies that bear relevance. The review delves into prospective applications of this therapeutic approach across a diverse range of scenarios. Lastly, the review underscores concerns related to precision and safety, while also outlining the envisioned trajectory for extending CAR T therapy beyond cancer treatment.

CAR-T Cell Therapy: Advances in Kidney-Related Diseases

Background

Chimeric antigen receptor (CAR)-T cell therapy represents a significant advancement in the field of immunotherapy, providing targeted eradication of abnormal cells through the recognition between CAR and target antigens. This approach has garnered considerable attention due to its promising results in the clinical treatment of hematological malignancies and autoimmune diseases. As the focus shifts toward exploring novel targets and expanding the application of CAR-T cell therapy to solid tumors, including renal malignancies, researchers are pushing the boundaries of this innovative treatment. However, it is crucial to address the observed comorbidities associated with CAR-T cell therapy, particularly nephrotoxicity, due to the superseding release of cytokines and impairment of normal tissue.

Summary

Our review discusses the research strategies and nephrotoxicity related to CAR-T cell therapy in various kidney-related diseases and provides insights into enhancing investigation and optimization.

Key Messages

CAR-T cell therapy has captured the attention of researchers and clinicians in the treatment of renal malignancies, multiple myeloma, systemic lupus erythematosus, and acquired immunodeficiency syndrome, which may lead to potential nephrotoxicity as they involve primary or secondary kidney complications. Understanding and summarizing the current research progress of CAR-T cell therapies can provide valuable insights into novel targets and combinations to optimize research models and enhance their clinical value.

Universal CAR T cells targeted to HER2 with a biotin-trastuzumab soluble linker penetrate spheroids and large tumor xenografts that are inherently resistant to trastuzumab mediated ADCC

CAR T cell therapies face challenges in combating solid tumors due to their single-target approach, which becomes ineffective if the targeted antigen is absent or lost. Universal CAR T cells (UniCAR Ts) provide a promising solution by utilizing molecular tags (linkers), such as biotin conjugated to monoclonal antibodies, enabling them to target a variety of tumor antigens. Recently, we showed that conventional CAR T cells could penetrate the extracellular matrix (ECM) of ADCC-resistant tumors, which forms a barrier to therapeutic antibodies. This finding led us to investigate whether UniCAR T cells, targeted by soluble antibody-derived linkers, could similarly tackle ADCC-resistant tumors where ECM restricts antibody penetration. We engineered UniCAR T cells by incorporating a biotin-binding monomeric streptavidin 2 (mSA2) domain for targeting HER2 via biotinylated trastuzumab (BT). The activation and cytotoxicity of UniCAR T cells in the presence or absence of BT were evaluated in conventional immunoassays. A 3D spheroid coculture was set up to test the capability of UniCAR Ts to access ECM-masked HER2+ cells. For in vivo analysis, we utilized a HER2+ xenograft model in which intravenously administered UniCAR T cells were supplemented with intraperitoneal BT treatments. In vitro, BT-guided UniCAR T cells showed effective activation and distinct anti-tumor response. Upon target recognition, IFNγ secretion correlated with BT concentration. In the presence of BT, UniCAR T cells effectively penetrated HER2+ spheroids and induced cell death in their core regions. In vivo, upon intravenous administration of UniCAR Ts, circulating BT linkers immediately engaged the mSA2 domain and directed effector cells to the HER2+ tumors. However, these co-treated mice died early, possibly due to the lung infiltration of UniCAR T cells that could recognize both native biotin and HER2. Our results suggest that UniCAR T cells guided with soluble linkers present a viable alternative to conventional CAR T cells, especially for patients resistant to antibody therapy and those with solid tumors exhibiting high antigenic variability. Critical to their success, however, is the choice of an appropriate binding domain for the CAR and the corresponding soluble linker, ensuring both efficacy and safety in therapeutic applications.

Engineered T cells from induced pluripotent stem cells: from research towards clinical implementation

Induced pluripotent stem cell (iPSC)-derived T (iT) cells represent a groundbreaking frontier in adoptive cell therapies with engineered T cells, poised to overcome pivotal limitations associated with conventional manufacturing methods. iPSCs offer an off-the-shelf source of therapeutic T cells with the potential for infinite expansion and straightforward genetic manipulation to ensure hypo-immunogenicity and introduce specific therapeutic functions, such as antigen specificity through a chimeric antigen receptor (CAR). Importantly, genetic engineering of iPSC offers the benefit of generating fully modified clonal lines that are amenable to rigorous safety assessments. Critical to harnessing the potential of iT cells is the development of a robust and clinically compatible production process. Current protocols for genetic engineering as well as differentiation protocols designed to mirror human hematopoiesis and T cell development, vary in efficiency and often contain non-compliant components, thereby rendering them unsuitable for clinical implementation. This comprehensive review centers on the remarkable progress made over the last decade in generating functional engineered T cells from iPSCs. Emphasis is placed on alignment with good manufacturing practice (GMP) standards, scalability, safety measures and quality controls, which constitute the fundamental prerequisites for clinical application. In conclusion, the focus on iPSC as a source promises standardized, scalable, clinically relevant, and potentially safer production of engineered T cells. This groundbreaking approach holds the potential to extend hope to a broader spectrum of patients and diseases, leading in a new era in adoptive T cell therapy.

Rank aggregation of independent genetic screen results highlights new strategies for adoptive cellular transfer therapy of cancer

Efficient intratumoral infiltration of adoptively transferred cells is a significant barrier to effectively treating solid tumors with adoptive cellular transfer (ACT) therapies. Our recent forward genetic, whole-genome screen identified T cell-intrinsic gene candidates that may improve tumor infiltration of T cells. Here, results are combined with five independent genetic screens using rank aggregation to improve rigor. This resulted in a combined total of 1,523 candidate genes - including 1,464 genes not currently being evaluated as therapeutic targets - that may improve tumor infiltration of T cells. Gene set enrichment analysis of a published human dataset shows that these gene candidates are differentially expressed in tumor infiltrating compared to circulating T cells, supporting translational potential. Importantly, adoptive transfer of T cells overexpressing gain-of-function candidates (AAK1ΔN125, SPRR1B, and EHHADH) into tumor-bearing mice resulted in increased T cell infiltration into tumors. These novel gene candidates may be considered as potential therapeutic candidates that can aid adoptive cellular therapy in improving T cell infiltration into solid tumors.

A synthetic biology approach to engineering circuits in immune cells

A synthetic circuit in a biological system involves the designed assembly of genetic elements, biomolecules, or cells to create a defined function. These circuits are central in synthetic biology, enabling the reprogramming of cellular behavior and the engineering of cells with customized responses. In cancer therapeutics, engineering T cells with circuits have the potential to overcome the challenges of current approaches, for example, by allowing specific recognition and killing of cancer cells. Recent advances also facilitate engineering integrated circuits for the controlled release of therapeutic molecules at specified locations, for example, in a solid tumor. In this review, we discuss recent strategies and applications of synthetic receptor circuits aimed at enhancing immune cell functions for cancer immunotherapy. We begin by introducing the concept of circuits in networks at the molecular and cellular scales and provide an analysis of the development and implementation of several synthetic circuits in T cells that have the goal to overcome current challenges in cancer immunotherapy. These include specific targeting of cancer cells, increased T-cell proliferation, and persistence in the tumor microenvironment. By harnessing the power of synthetic biology, and the characteristics of certain circuit architectures, it is now possible to engineer a new generation of immune cells that recognize cancer cells, while minimizing off-target toxicities. We specifically discuss T-cell circuits for antigen density sensing. These circuits allow targeting of solid tumors that share antigens with normal tissues. Additionally, we explore designs for synthetic circuits that could control T-cell differentiation or T-cell fate as well as the concept of synthetic multicellular circuits that leverage cellular communication and division of labor to achieve improved therapeutic efficacy. As our understanding of cell biology expands and novel tools for genome, protein, and cell engineering are developed, we anticipate further innovative approaches to emerge in the design and engineering of circuits in immune cells.

Delivery of Plasmid DNA by Ionizable Lipid Nanoparticles to Induce CAR Expression in T Cells

Introduction

Chimeric antigen receptor (CAR) cell therapy represents a hallmark in cancer immunotherapy, with significant clinical results in the treatment of hematological tumors. However, current approved methods to engineer T cells to express CAR use viral vectors, which are integrative and have been associated with severe adverse effects due to constitutive expression of CAR. In this context, non-viral vectors such as ionizable lipid nanoparticles (LNPs) arise as an alternative to engineer CAR T cells with transient expression of CAR.

Methods

Here, we formulated a mini-library of LNPs to deliver pDNA to T cells by varying the molar ratios of excipient lipids in each formulation. LNPs were characterized and screened in vitro using a T cell line (Jurkat). The optimized formulation was used ex vivo to engineer T cells derived from human peripheral blood mononuclear cells (PBMCs) for the expression of an anti-CD19 CAR (CAR-CD19BBz). The effectiveness of these CAR T cells was assessed in vitro against Raji (CD19+) cells.

Results

LNPs formulated with different molar ratios of excipient lipids efficiently delivered pDNA to Jurkat cells with low cytotoxicity compared to conventional transfection methods, such as electroporation and lipofectamine. We show that CAR-CD19BBz expression in T cells was transient after transfection with LNPs. Jurkat cells transfected with our top-performing LNPs underwent activation when exposed to CD19+ target cells. Using our top-performing LNP-9-CAR, we were able to engineer human primary T cells to express CAR-CD19BBz, which elicited significant specific killing of CD19+ target cells in vitro.

Conclusion

Collectively, our results show that LNP-mediated delivery of pDNA is a suitable method to engineer human T cells to express CAR, which holds promise for improving the production methods and broader application of this therapy in the future.

A major role for CD4+ T cells in driving cytokine release syndrome during CAR T cell therapy

Anti-CD19 chimeric antigen receptor (CAR) T cell therapy represents a breakthrough for the treatment of B cell malignancies. Yet, it can lead to severe adverse events, including cytokine release syndrome (CRS), which may require urgent clinical management. Whether interpatient variability in CAR T cell subsets contributes to CRS is unclear. Here, we show that CD4+ CAR T cells are the main drivers of CRS. Using an immunocompetent model of anti-CD19 CAR T cell therapy, we report that CD4+, but not CD8+, CAR T cells elicit physiological CRS-like manifestations associated with the release of inflammatory cytokines. In CAR T cell-treated patients, CRS occurrence and severity are significantly associated with high absolute values of CD4+ CAR T cells in the blood. CRS in mice occurs independently of CAR T cell-derived interferon γ (IFN-γ) but requires elevated tumor burden. Thus, adjusting the CD4:CD8 CAR T cell ratio to patient tumor load may help mitigate CAR T cell-associated toxicities.

Learning from the microbes: exploiting the microbiome to enforce T cell immunotherapy

The opportunities genetic engineering has created in the field of adoptive cellular therapy for cancer are accelerating the development of novel treatment strategies using chimeric antigen receptor (CAR) and T cell receptor (TCR) T cells. The great success in the context of hematologic malignancies has made especially CAR T cell therapy a promising approach capable of achieving long-lasting remission. However, the causalities involved in mediating resistance to treatment or relapse are still barely investigated. Research on T cell exhaustion and dysfunction has drawn attention to host-derived factors that define both the immune and tumor microenvironment (TME) crucially influencing efficacy and toxicity of cellular immunotherapy. The microbiome, as one of the most complex host factors, has become a central topic of investigations due to its ability to impact on health and disease. Recent findings support the hypothesis that commensal bacteria and particularly microbiota-derived metabolites educate and modulate host immunity and TME, thereby contributing to the response to cancer immunotherapy. Hence, the composition of microbial strains as well as their soluble messengers are considered to have predictive value regarding CAR T cell efficacy and toxicity. The diversity of mechanisms underlying both beneficial and detrimental effects of microbiota comprise various epigenetic, metabolic and signaling-related pathways that have the potential to be exploited for the improvement of CAR T cell function. In this review, we will discuss the recent findings in the field of microbiome-cancer interaction, especially with respect to new trajectories that commensal factors can offer to advance cellular immunotherapy.

Cytotoxic CD4 T cells in the mucosa and in cancer

CD4 T cells were initially described as helper cells that promote either the cellular immune response (Th1 cells) or the humoral immune response (Th2 cells). Since then, a plethora of functionally distinct helper and regulatory CD4 T cell subsets have been described. CD4 T cells with cytotoxic function were first described in the setting of viral infections and autoimmunity, and more recently in cancer and gut dysbiosis. Regulatory CD4 T cell subsets such as Tregs and T-regulatory type 1 (Tr1) cells have also been shown to have cytotoxic potential. Indeed, Tr1 cells have been shown to be important for maintenance of stem cell niches in the bone marrow and the gut. This review will provide an overview of cytotoxic CD4 T cell development, and discuss the role of inflammatory and Tr1-like cytotoxic CD4 T cells in maintenance of intestinal stem cells and in anti-cancer immune responses.