MAIT cells regulate NK cell-mediated tumor immunity

Mucosal-associated invariant T cells modulate innate immune cells and inhibit colon cancer growth

Mucosal-associated invariant T (MAIT) cells are innate-like T cells that can be activated by microbial antigens and cytokines and are abundant in mucosal tissues including the colon. MAIT cells have cytotoxic and pro-inflammatory functions and have potentials for use as adoptive cell therapy. However, studies into their anti-cancer activity, including their role in colon cancer, are limited. Using an animal model of colon cancer, we showed that peritumoral injection of in vivo-expanded MAIT cells into RAG1-/- mice with MC38-derived tumours inhibits tumour growth compared to control. Multiplex cytokine analyses showed that tumours from the MAIT cell-treated group have higher expression of markers for eosinophil-activating cytokines, suggesting a potential association between eosinophil recruitment and tumour inhibition. In a human peripheral leukocyte co-culture model, we showed that leukocytes stimulated with MAIT ligand showed an increase in eotaxin-1 production and activation of eosinophils, associated with increased cancer cell killing. In conclusion, we showed that MAIT cells have a protective role in a murine colon cancer model, associated with modulation of the immune response to cancer, potentially involving eosinophil-associated mechanisms. Our results highlight the potential of MAIT cells for non-donor restricted colon cancer immunotherapy.

Mucosal-associated invariant T cells in cancer: dual roles, complex interactions and therapeutic potential

Mucosal-associated invariant T (MAIT) cells play diverse roles in cancer, infectious diseases, and immunotherapy. This review explores their intricate involvement in cancer, from early detection to their dual functions in promoting inflammation and mediating anti-tumor responses. Within the solid tumor microenvironment (TME), MAIT cells can acquire an 'exhausted' state and secrete tumor-promoting cytokines. On the other hand, MAIT cells are highly cytotoxic, and there is evidence that they may have an anti-tumor immune response. The frequency of MAIT cells and their subsets has also been shown to have prognostic value in several cancer types. Recent innovative approaches, such as programming MAIT cells with chimeric antigen receptors (CARs), provide a novel and exciting approach to utilizing these cells in cell-based cancer immunotherapy. Because MAIT cells have a restricted T cell receptor (TCR) and recognize a common antigen, this also mitigates potential graft-versus-host disease (GVHD) and opens the possibility of using allogeneic MAIT cells as off-the-shelf cell therapies in cancer. Additionally, we outline the interactions of MAIT cells with the microbiome and their critical role in infectious diseases and how this may impact the tumor responses of these cells. Understanding these complex roles can lead to novel therapeutic strategies harnessing the targeting capabilities of MAIT cells.

MAIT cells are associated with responsiveness to neoadjuvant immunotherapy in COPD-associated NSCLC

BACKGROUND

Patients with non-small cell lung cancer (NSCLC) and chronic obstructive pulmonary disease (COPD) experience worse clinical outcomes but respond better to immunotherapy than patients with NSCLC without COPD. Mucosal-associated invariant T (MAIT) cells, a versatile population of innate immune T lymphocytes, have a crucial function in the response to infection and tumors. This study investigated the distribution of MAIT cells in COPD-associated NSCLC and their involvement in the immune response.

METHODS

Flow cytometry, immunohistochemistry, and immunofluorescence were performed on tissue samples of patients with NSCLC, with or without COPD, treated with or without anti-programmed death 1 (PD1) immunotherapy. MAIT cells were stimulated with 5-OP-RU using a mouse subcutaneous tumor model.

RESULTS

Tumors contained significantly more MAIT cells than paraneoplastic tissues, and CD8+ MAIT cells accounted for more than 90% of these cells. Patients with NSCLC and COPD had higher CD8+ MAIT cell counts than those with NSCLC without COPD. Additionally, patients with NSCLC and COPD displayed reduced expression of the activation marker, CD69, and functional markers, granzyme B (GZMB) and interferon γ (IFNγ), and higher expression of the immune exhaustion marker, PD1. Among patients who received immunotherapy, the proportion with a complete or partial response was higher in those with COPD than in those without COPD. In patients with NSCLC and COPD, the major pathologic response (MPR) group had higher MAIT levels than those in the no major pathologic response (NPR) group. In the mouse subcutaneous tumor model stimulation of MAIT cells using 5-OP-RU enhanced the antitumor effects of anti-PD1.

CONCLUSIONS

In patients with NSCLC and COPD, response to immunotherapy is associated with accumulation of CD8+ MAIT cells showing immune exhaustion. These findings may contribute to innovative approaches for immunotherapy targeting CD8+ MAIT cells.

Immune checkpoint blockade improves the activation and function of circulating mucosal-associated invariant T (MAIT) cells in patients with non-small cell lung cancer

Mucosal-associated invariant T (MAIT) cells constitute one of the most numerous unconventional T cell subsets, and are characterized by rapid release of Th1- and Th17-associated cytokines and increased cytotoxic functions following activation. MAIT cells accumulate in tumor tissue but show an exhausted phenotype. Here, we investigated if immune checkpoint blockade (ICB) with antibodies to PD-1 or PD-L1 affects the function of circulating MAIT cells from non-small cell lung cancer patients. ICB increased the proliferation and co-expression of the activation markers HLA-DR and CD38 on MAIT cells in most patients after the first treatment cycle, irrespective of treatment outcome. Furthermore, production of cytokines, especially TNF and IL-2, also increased after treatment, as did MAIT cell polyfunctionality. These results indicate that MAIT cells respond to ICB, and that MAIT cell reinvigoration may contribute to tumor regression in patients undergoing immune checkpoint therapy.

MAIT Cells Modulate Innate Immune Cells and Inhibit Colon Cancer Growth

Mucosal-associated invariant T (MAIT) cells are innate-like T cells that can be activated by microbial antigens and cytokines and are abundant in mucosal tissues including the colon. MAIT cells have cytotoxic and pro-inflammatory functions and have potentials for use as adoptive cell therapy. However, studies into their anti-cancer activity, including their role in colon cancer, are limited. Using an animal model of colon cancer, we show that peritumoral injection of in vivo-expanded MAIT cells into RAG1-/- mice with MC38-derived tumors inhibits tumor growth compared to control. Multiplex cytokine analyses show that tumors from the MAIT cell-treated group have higher expression of markers for eosinophil-activating cytokines, suggesting an association between eosinophil recruitment and tumor inhibition. In a human peripheral leukocyte co-culture model, we show that leukocytes stimulated with MAIT ligand show an increase in eotaxin-1 production and activation of eosinophils, associated with increased cancer cell killing. In conclusion, we show that MAIT cells have a protective role in a murine colon cancer model, associated with modulation of the immune response to cancer, potentially involving eosinophil-associated mechanisms. Our results highlight the potential of MAIT cells for non-donor restricted colon cancer immunotherapy.

Transcriptomic and genomic profiling of multiple primary colorectal cancers reveals intratumor heterogeneity and a distinct immune microenvironment

This study reported on the intratumor genomic and immunological heterogeneity of different tumor lesions from a single patient with multiple primary colorectal cancer (MPCC). The goal of this study was to explore the molecular and microenvironment characteristics of tumor lesions from different primary sites in a patient with MPCC. A total of three tumor lesions located in the hepatic flexure of the transverse colon, sigmoid colon, and rectum were collected from a 72-year-old male patient with MPCC. All three tumor samples were examined by using whole-exome sequencing (WES) and single-cell RNA sequencing (scRNA-seq). The transcriptome data of The Cancer Genome Atlas (TCGA) colon cancer (COAD) dataset were explored to characterize the biological impacts of certain immune cells. Only three nonsynonymous mutations were shared by all of the tumor lesions, whereas a number of single nucleotide variant (SNV) and copy number variation (CNV) mutations were shared by tumor samples from the sigmoid colon and rectum. Transcriptomic analysis showed that tumor lesions derived from the transverse colon had decreased levels of RTK, ERK, and AKT pathway activity, thus suggesting lower oncogenic properties in the transverse lesion compared to the other two samples. Further immune landscape evaluation by using single-cell transcriptomic analysis displayed significant intratumor heterogeneity in MPCC. Specifically, more abundant mucosal-associated invariant T (MAIT) cell infiltration was found in transverse colon tumor lesions. Afterwards, we found that higher MAIT cell infiltration may correlate with a better prognosis of patients with colon cancer (immunohistochemical status was MSI-L/pMMR) by using a publicly available TCGA dataset.

MAIT cells in bacterial infectious diseases: heroes, villains, or both?

Due to the aggravation of bacterial drug resistance and the lag in the development of new antibiotics, it is crucial to develop novel therapeutic regimens for bacterial infectious diseases. Currently, immunotherapy is a promising regimen for the treatment of infectious diseases. Mucosal-associated invariant T (MAIT) cells, a subpopulation of innate-like T cells, are abundant in humans and can mount a rapid immune response to pathogens, thus becoming a potential target of immunotherapy for infectious diseases. At the site of infection, activated MAIT cells perform complex biological functions by secreting a variety of cytokines and cytotoxic substances. Many studies have shown that MAIT cells have immunoprotective effects because they can bridge innate and adaptive immune responses, leading to bacterial clearance, tissue repair, and homeostasis maintenance. MAIT cells also participate in cytokine storm generation, tissue fibrosis, and cancer progression, indicating that they play a role in immunopathology. In this article, we review recent studies of MAIT cells, discuss their dual roles in bacterial infectious diseases and provide some promising MAIT cell-targeting strategies for the treatment of bacterial infectious diseases.

Natural Killer T Cell Diversity and Immunotherapy

Invariant natural killer T cells (iNKTs), a type of unconventional T cells, share features with NK cells and have an invariant T cell receptor (TCR), which recognizes lipid antigens loaded on CD1d molecules, a major histocompatibility complex class I (MHC-I)-like protein. This interaction produces the secretion of a wide array of cytokines by these cells, including interferon gamma (IFN-γ) and interleukin 4 (IL-4), allowing iNKTs to link innate with adaptive responses. Interestingly, molecules that bind CD1d have been identified that enable the modulation of these cells, highlighting their potential pro-inflammatory and immunosuppressive capacities, as required in different clinical settings. In this review, we summarize key features of iNKTs and current understandings of modulatory α-galactosylceramide (α-GalCer) variants, a model iNKT cell activator that can shift the outcome of adaptive immune responses. Furthermore, we discuss advances in the development of strategies that modulate these cells to target pathologies that are considerable healthcare burdens. Finally, we recapitulate findings supporting a role for iNKTs in infectious diseases and tumor immunotherapy.

Exploiting innate immunity for cancer immunotherapy

Immunotherapies have revolutionized the treatment paradigms of various types of cancers. However, most of these immunomodulatory strategies focus on harnessing adaptive immunity, mainly by inhibiting immunosuppressive signaling with immune checkpoint blockade, or enhancing immunostimulatory signaling with bispecific T cell engager and chimeric antigen receptor (CAR)-T cell. Although these agents have already achieved great success, only a tiny percentage of patients could benefit from immunotherapies. Actually, immunotherapy efficacy is determined by multiple components in the tumor microenvironment beyond adaptive immunity. Cells from the innate arm of the immune system, such as macrophages, dendritic cells, myeloid-derived suppressor cells, neutrophils, natural killer cells, and unconventional T cells, also participate in cancer immune evasion and surveillance. Considering that the innate arm is the cornerstone of the antitumor immune response, utilizing innate immunity provides potential therapeutic options for cancer control. Up to now, strategies exploiting innate immunity, such as agonists of stimulator of interferon genes, CAR-macrophage or -natural killer cell therapies, metabolic regulators, and novel immune checkpoint blockade, have exhibited potent antitumor activities in preclinical and clinical studies. Here, we summarize the latest insights into the potential roles of innate cells in antitumor immunity and discuss the advances in innate arm-targeted therapeutic strategies.

Mucosal-associated invariant T cells in digestive tract: Local guardians or destroyers?

Mucosa-associated invariant T cells (MAIT) are a class of innate-like T lymphocytes mainly presenting CD8+ phenotype with a semi-invariant αβ T-cell receptor, which specifically recognises MR1-presented biosynthetic derivatives of riboflavin synthesis produced by various types of microbiomes. As innate-like T lymphocytes, MAIT can be activated by a variety of cytokines, leading to immediate immune responses to infection and tumour cues. As an organ that communicates with the external environment, the digestive tract, especially the gastrointestinal tract, contains abundant microbial populations. Communication between MAIT and local microbiomes is important for the homeostasis of mucosal immunity. In addition, accumulating evidence suggests changes in the abundance and structure of the microbial community during inflammation and tumorigenesis plays a critical role in disease progress partly through their impact on MAIT development and function. Therefore, it is essential for the understanding of MAIT response and their interaction with microbiomes in the digestive tract. Here, we summarised MAIT characteristics in the digestive tract and its alteration facing inflammation and tumour, raising that targeting MAIT can be a candidate for treatment of gastrointestinal diseases.

Aging unconventionally: γδ T cells, iNKT cells, and MAIT cells in aging

Unconventional T cells include γδ T cells, invariant Natural Killer T cells (iNKT) cells and Mucosal Associated Invariant T (MAIT) cells, which are distinguished from conventional T cells by their recognition of non-peptide ligands presented by non-polymorphic antigen presenting molecules and rapid effector functions that are pre-programmed during their development. Here we review current knowledge of the effect of age on unconventional T cells, from early life to old age, in both mice and humans. We then discuss the role of unconventional T cells in age-associated diseases and infections, highlighting the similarities between members of the unconventional T cell family in the context of aging.

Synthetic 5-amino-6-D-ribitylaminouracil paired with inflammatory stimuli facilitates MAIT cell expansion in vivo

Introduction

Mucosal-associated invariant T (MAIT) cells are a population of innate-like T cells, which mediate host immunity to microbial infection by recognizing metabolite antigens derived from microbial riboflavin synthesis presented by the MHC-I-related protein 1 (MR1). Namely, the potent MAIT cell antigens, 5-(2-oxopropylideneamino)-6-D-ribitylaminouracil (5-OP-RU) and 5-(2-oxoethylideneamino)-6-D-ribitylaminouracil (5-OE-RU), form via the condensation of the riboflavin precursor 5-amino-6-D-ribitylaminouracil (5-A-RU) with the reactive carbonyl species (RCS) methylglyoxal (MG) and glyoxal (G), respectively. Although MAIT cells are abundant in humans, they are rare in mice, and increasing their abundance using expansion protocols with antigen and adjuvant has been shown to facilitate their study in mouse models of infection and disease.

Methods

Here, we outline three methods to increase the abundance of MAIT cells in C57BL/6 mice using a combination of inflammatory stimuli, 5-A-RU and MG.

Results

Our data demonstrate that the administration of synthetic 5-A-RU in combination with one of three different inflammatory stimuli is sufficient to increase the frequency and absolute numbers of MAIT cells in C57BL/6 mice. The resultant boosted MAIT cells are functional and can provide protection against a lethal infection of Legionella longbeachae.

Conclusion

These results provide alternative methods for expanding MAIT cells with high doses of commercially available 5-A-RU (± MG) in the presence of various danger signals.

Tumor-associated macrophages trigger MAIT cell dysfunction at the HCC invasive margin

Mucosal-associated invariant T (MAIT) cells represent an abundant innate-like T cell subtype in the human liver. MAIT cells are assigned crucial roles in regulating immunity and inflammation, yet their role in liver cancer remains elusive. Here, we present a MAIT cell-centered profiling of hepatocellular carcinoma (HCC) using scRNA-seq, flow cytometry, and co-detection by indexing (CODEX) imaging of paired patient samples. These analyses highlight the heterogeneity and dysfunctionality of MAIT cells in HCC and their defective capacity to infiltrate liver tumors. Machine-learning tools were used to dissect the spatial cellular interaction network within the MAIT cell neighborhood. Co-localization in the adjacent liver and interaction between niche-occupying CSF1R+PD-L1+ tumor-associated macrophages (TAMs) and MAIT cells was identified as a key regulatory element of MAIT cell dysfunction. Perturbation of this cell-cell interaction in ex vivo co-culture studies using patient samples and murine models reinvigorated MAIT cell cytotoxicity. These studies suggest that aPD-1/aPD-L1 therapies target MAIT cells in HCC patients.

Classic costimulatory interactions in MAIT cell responses: from gene expression to immune regulation

Mucosa-associated invariant T (MAIT) cells are evolutionarily conserved, innate-like T lymphocytes with enormous immunomodulatory potentials. Due to their strategic localization, their invariant T cell receptor (iTCR) specificity for major histocompatibility complex-related protein 1 (MR1) ligands of commensal and pathogenic bacterial origin, and their sensitivity to infection-elicited cytokines, MAIT cells are best known for their antimicrobial characteristics. However, they are thought to also play important parts in the contexts of cancer, autoimmunity, vaccine-induced immunity, and tissue repair. While cognate MR1 ligands and cytokine cues govern MAIT cell maturation, polarization, and peripheral activation, other signal transduction pathways, including those mediated by costimulatory interactions, regulate MAIT cell responses. Activated MAIT cells exhibit cytolytic activities and secrete potent inflammatory cytokines of their own, thus transregulating the biological behaviors of several other cell types, including dendritic cells, macrophages, natural killer cells, conventional T cells, and B cells, with significant implications in health and disease. Therefore, an in-depth understanding of how costimulatory pathways control MAIT cell responses may introduce new targets for optimized MR1/MAIT cell-based interventions. Herein, we compare and contrast MAIT cells and mainstream T cells for their expression of classic costimulatory molecules belonging to the immunoglobulin superfamily and the tumor necrosis factor (TNF)/TNF receptor superfamily, based not only on the available literature but also on our transcriptomic analyses. We discuss how these molecules participate in MAIT cells' development and activities. Finally, we introduce several pressing questions vis-à-vis MAIT cell costimulation and offer new directions for future research in this area.

Deep Immunophenotyping of Human Whole Blood by Standardized Multi-parametric Flow Cytometry Analyses

Immunophenotyping is proving crucial to understanding the role of the immune system in health and disease. High-throughput flow cytometry has been used extensively to reveal changes in immune cell composition and function at the single-cell level. Here, we describe six optimized 11-color flow cytometry panels for deep immunophenotyping of human whole blood. A total of 51 surface antibodies, which are readily available and validated, were selected to identify the key immune cell populations and evaluate their functional state in a single assay. The gating strategies for effective flow cytometry data analysis are included in the protocol. To ensure data reproducibility, we provide detailed procedures in three parts, including (1) instrument characterization and detector gain optimization, (2) antibody titration and sample staining, and (3) data acquisition and quality checks. This standardized approach has been applied to a variety of donors for a better understanding of the complexity of the human immune system.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43657-022-00092-9.

NK Cells in Cancer: Mechanisms of Dysfunction and Therapeutic Potential

Natural killer cells (NK) are innate lymphocytes endowed with the ability to recognize and kill cancer cells. Consequently, adoptive transfer of autologous or allogeneic NK cells represents a novel opportunity in cancer treatment that is currently under clinical investigation. However, cancer renders NK cells dysfunctional, thus restraining the efficacy of cell therapies. Importantly, extensive effort has been employed to investigate the mechanisms that restrain NK cell anti-tumor function, and the results have offered forthcoming solutions to improve the efficiency of NK cell-based therapies. The present review will introduce the origin and features of NK cells, summarize the mechanisms of action and causes of dysfunction of NK cells in cancer, and frame NK cells in the tumoral microenvironment and in the context of immunotherapies. Finally, we will discuss therapeutic potential and current limitations of NK cell adoptive transfer in tumors.

Innate lymphoid cells and innate-like T cells in cancer - at the crossroads of innate and adaptive immunity

Immunotherapies targeting conventional T cells have revolutionized systemic treatment for many cancers, yet only a subset of patients benefit from these approaches. A better understanding of the complex immune microenvironment of tumours is needed to design the next generation of immunotherapeutics. Innate lymphoid cells (ILCs) and innate-like T cells (ILTCs) are abundant, tissue-resident lymphocytes that have recently been shown to have critical roles in many types of cancers. ILCs and ILTCs rapidly respond to changes in their surrounding environment and act as the first responders to bridge innate and adaptive immunity. This places ILCs and ILTCs as pivotal orchestrators of the final antitumour immune response. In this Review, we outline hallmarks of ILCs and ILTCs and discuss their emerging role in antitumour immunity, as well as the pathophysiological adaptations leading to their pro-tumorigenic function. We explore the pleiotropic, in parts redundant and sometimes opposing, mechanisms that underlie the delicate interplay between the different subsets of ILCs and ILTCs. Finally, we highlight their role in amplifying and complementing conventional T cell functions and summarize immunotherapeutic strategies for targeting ILCs and ILTCs in cancer.

Mucosal-associated invariant T cells for cancer immunotherapy

Human mucosal-associated invariant T (MAIT) cells are characterized by their expression of an invariant TCR α chain Vα7.2-Jα33/Jα20/Jα12 paired with a restricted TCR β chain. MAIT cells recognize microbial peptides presented by the highly conserved MHC class I-like molecule MR1 and bridge the innate and acquired immune systems to mediate augmented immune responses. Upon activation, MAIT cells rapidly proliferate, produce a variety of cytokines and cytotoxic molecules, and trigger efficient antitumor immunity. Administration of a representative MAIT cell ligand 5-OP-RU effectively activates MAIT cells and enhances their antitumor capacity. In this review, we introduce MAIT cell biology and their importance in antitumor immunity, summarize the current development of peripheral blood mononuclear cell-derived and stem cell-derived MAIT cell products for cancer treatment, and discuss the potential of genetic engineering of MAIT cells for off-the-shelf cancer immunotherapy.

Longitudinal analysis of mucosa-associated invariant T cells in sepsis reveals their early numerical decline with prognostic implications and a progressive loss of antimicrobial functions

Sepsis-elicited immunosuppression elevates the risk of secondary infections. We used a clinically relevant mouse model and serial peripheral blood samples from patients to assess the antimicrobial activities of mucosa-associated invariant T (MAIT) cells in sepsis. Hepatic and splenic MAIT cells from B6-MAIT^CAST mice displayed increased CD69 expression and a robust interferon-γ (IFNγ) production capacity shortly after sublethal cecal ligation and puncture, but not at a late timepoint. Peripheral blood MAIT cell frequencies were reduced in septic patients at the time of intensive care unit (ICU) admission, and more dramatically so among nonsurvivors, suggesting the predictive usefulness of early MAIT cell enumeration. In addition, at ICU admission, MAIT cells from sepsis survivors launched stronger IFNγ responses to several bacterial species compared with those from patients who subsequently died of sepsis. Of note, while low human leukocyte antigen (HLA)-DR⁺ monocyte frequencies, widely regarded as a surrogate indicator of sepsis-induced immunosuppression, were gradually corrected, the numerical insufficiency of MAIT cells was not resolved over time, and their CD69 expression continued to decline. MAIT cell responses to bacterial pathogens, a major histocompatibility complex-related protein 1 (MR1) ligand, and interleukin (IL)-12 and IL-18 were also progressively lost during sepsis and did not recover by the time of ICU/hospital discharge. We propose that MAIT cell dysfunctions contribute to post-sepsis immunosuppression.

Weaponizing natural killer cells for solid cancer immunotherapy

Enhancing natural killer (NK) cell-based innate immunity has become a promising strategy for immunotherapy against hard-to-cure solid cancers. Monoclonal antibody (mAb) therapy has been used to activate NK-cell-mediated antibody-dependent cellular cytotoxicity (ADCC) towards solid cancers. Cancer cells, however, can subvert immunosurveillance using multiple immunosuppressive mechanisms, which may hamper NK cell ADCC. Mechanisms to safely enhance ADCC by NK cells, such as utilizing temporary inhibition of receptor endocytosis to increase antibody presentation from target to effector cells can now be used to enhance NK-cell-mediated ADCC against solid tumors. This review summarizes and discusses the recent advances in the field and highlights current and potential future use of immunotherapies to maximize the therapeutic efficacy of innate anticancer immunity.

Enhancing Mucosal-Associated Invariant T Cell Function and Expansion with Human Selective Serum

Mucosal-associated invariant T (MAIT) cells are promising innate-like lymphocytes with potential for use in anti-tumor immunotherapy. Existing MAIT cell expansion protocols are associated with potentially decremental phenotypic changes, including increased frequency of CD4+ MAIT cells and higher inhibitory receptor expression. In this study, we compared the effect on expansion of human MAIT cells of a serum replacement, Physiologix XF SR (Phx), with traditional serum FBS for supplementing RPMI 1640 media. Using flow cytometry, we found that Phx supported a significantly higher proliferative capacity for MAIT cells and resulted in a lower frequency of CD4+ MAIT cells, which have been associated with reduced Th1 effector and cytolytic functions. We saw that culturing MAIT cells in Phx led to better survival of MAIT cells and lower frequency of PD-1+ MAIT cells than FBS-supplemented media. Functionally, we saw that Phx supplementation was associated with a higher frequency of IFN-γ+ MAIT cells after stimulation with Escherichia coli than FBS-supplemented RPMI. In conclusion, we show that MAIT cells cultured in Phx have higher proliferative capacity, lower expression of inhibitory receptors, and higher capacity to produce IFN-γ after E. coli stimulation than FBS-supplemented RPMI. This work shows that expanding MAIT cells with Phx compared with FBS-supplemented RPMI results in a more functionally desirable MAIT cell for future anti-tumor immunotherapy.

Harnessing the Power of Mucosal-Associated Invariant T (MAIT) Cells in Cancer Cell Therapy

Mucosal-associated invariant T (MAIT) cells, a burgeoning type of the innate-like T cells, play a crucial role in maintaining immune homeostasis, particularly in host defense. Although many studies have implied the use of MAIT cells in tumor immunity, whether MAIT cells are pro-tumor or anti-tumor has remained elusive, as in the case for other innate-like T cells that possess dichotomous roles in tumor immunity. Although this difficulty persists where endogenous MAIT cells are the target for therapeutic intervention, the advent of induced pluripotent stem-cell-derived MAIT cells (reMAIT cells) will make it possible to harness these cells for immune cell therapy. In this review, we will discuss possible roles of MAIT cells in tumor immunity and the potential of reMAIT cells to treat tumors.

MAIT cells ameliorate liver fibrosis by enhancing the cytotoxicity of NK cells in cholestatic murine models

BACKGROUND AND AIMS

Mucosal-associated invariant T (MAIT) cells are innate-like lymphocytes that display a critical role in various liver diseases. However, the role of MAIT cells in cholestatic liver fibrogenesis remains obscure. Our study aims to assess the contribution of MAIT cells and underlying mechanisms during this process.

METHODS

Cholestatic murine models using MAIT cell-deficient (MR1^- /^- ) and wild-type (WT) mice were established by feeding a 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-enriched diet or bile duct ligation (BDL). Liver samples were collected to determine the severity of fibrosis. Lymphocytes of the liver were isolated for analysing the phenotype and function of MAIT cells. Cell co-culture experiments were performed to investigate the cross-talk between MAIT and NK cells.

RESULTS

Liver MAIT cells were more activated with increased cytokines in cholestatic mice models than in control mice, although their frequency was decreased. MAIT cell deficiency led to severe liver inflammation and fibrosis with more activated HSCs in cholestatic mice. In addition, MR1^- /^- mice had an increased frequency of NK cells with higher expression of stimulatory receptors relative to WT mice. Paradoxically, activated MAIT cells significantly promoted the anti-fibrotic ability of NK cells by enhancing their cytotoxicity against HSCs in co-culture experiments. Importantly, this effect depended on direct cell-cell contact and TNF-α produced by MAIT cells.

CONCLUSION

Our findings indicate that MAIT cells ameliorate cholestatic liver fibrosis by enhancing the cytotoxicity of NK cells against HSCs. An in-depth understanding of the MAIT cell-mediated regulatory effect will provide more valuable immunotherapy strategies to treat liver fibrosis.

MAIT cells and their implication in human oral diseases

OBJECTIVE

Mucosal-associated invariant T (MAIT) cells are unique innate-like T cells that are abundant in humans, accounting for 1-10% of circulating T cells and about 2% of total T cells in human oral cavity. MAIT cells can mount a strong immune response quickly without exogenous antigens and undergo a phenotypic transformation in the development of diseases. They produce cytokines involved in the Th1 and Th17 immune response and cytotoxic proteins, promote the dysfunction of autoreactive B cell and inhibit the function of NK cells. MAIT cells have been widely explored in autoimmune diseases, inflammatory diseases and tumors, and these mechanisms may also be involved in the pathogenesis of some oral diseases, while MAIT cells have not been systematically discussed in oral diseases.

METHODS

We searched PubMed/MEDLINE, EMBASE and Microsoft Bing databases to review and analyze relevant literatures on the impact of MAIT cells in the pathogenesis of human oral diseases.

CONCLUSION

Collected evidence elucidated the characteristics of MAIT cells and emphasized the potential roles of MAIT cells in oral lichen planus (OLP), chronic graft-versus-host disease (cGVHD), oral squamous cell carcinoma (OSCC), apical periodontitis (AP) and primary Sjogren's syndrome (pSS).

Tumor-Associated Inflammation: The Tumor-Promoting Immunity in the Early Stages of Tumorigenesis

Tumorigenesis is a multistage progressive oncogenic process caused by alterations in the structure and expression level of multiple genes. Normal cells are continuously endowed with new capabilities in this evolution, leading to subsequent tumor formation. Immune cells are the most important components of inflammation, which is closely associated with tumorigenesis. There is a broad consensus in cancer research that inflammation and immune response facilitate tumor progression, infiltration, and metastasis via different mechanisms; however, their protumor effects are equally important in tumorigenesis at earlier stages. Previous studies have demonstrated that during the early stages of tumorigenesis, certain immune cells can promote the formation and proliferation of premalignant cells by inducing DNA damage and repair inhibition, releasing trophic/supporting signals, promoting immune escape, and activating inflammasomes, as well as enhance the characteristics of cancer stem cells. In this review, we focus on the potential mechanisms by which immune cells can promote tumor initiation and promotion in the early stages of tumorigenesis; furthermore, we discuss the interaction of the inflammatory environment and protumor immune cells with premalignant cells and cancer stem cells, as well as the possibility of early intervention in tumor formation by targeting these cellular mechanisms.

The duplexity of unconventional T cells in cancer

Unconventional T cells and their involvement in cancer are understudied in comparison to conventional T cells, but recent findings indicate that these cells play important roles in both cancer progression and inhibition. Here, we briefly review the dichotomous role of three unconventional T cell lineages: γδ T cells, MAIT cells and NKT cells. Studies using mouse models of cancer show how this unconventional trilogy interacts with cancer epithelial cells and other immune cell populations during tumour evolution. These reports highlight various potential avenues for therapeutic intervention that may be exploited for cancer immunotherapy.

Engineering-Induced Pluripotent Stem Cells for Cancer Immunotherapy

Simple Summary

Induced pluripotent stem cells (iPSCs) that can be genetically engineered and differentiated into different types of immune cells, providing an unlimited resource for developing off-the-shelf cell therapies. Here, we present a comprehensive review that describes the current stages of iPSC-based cell therapies, including iPSC-derived T, nature killer (NK), invariant natural killer T (iNKT), gamma delta T (γδ T), mucosal-associated invariant T (MAIT) cells, and macrophages (Mφs).

Abstract

Cell-based immunotherapy, such as chimeric antigen receptor (CAR) T cell therapy, has revolutionized the treatment of hematological malignancies, especially in patients who are refractory to other therapies. However, there are critical obstacles that hinder the widespread clinical applications of current autologous therapies, such as high cost, challenging large-scale manufacturing, and inaccessibility to the therapy for lymphopenia patients. Therefore, it is in great demand to generate the universal off-the-shelf cell products with significant scalability. Human induced pluripotent stem cells (iPSCs) provide an “unlimited supply” for cell therapy because of their unique self-renewal properties and the capacity to be genetically engineered. iPSCs can be differentiated into different immune cells, such as T cells, natural killer (NK) cells, invariant natural killer T (iNKT) cells, gamma delta T (γδ T), mucosal-associated invariant T (MAIT) cells, and macrophages (Mφs). In this review, we describe iPSC-based allogeneic cell therapy, the different culture methods of generating iPSC-derived immune cells (e.g., iPSC-T, iPSC-NK, iPSC-iNKT, iPSC-γδT, iPSC-MAIT and iPSC-Mφ), as well as the recent advances in iPSC-T and iPSC-NK cell therapies, particularly in combinations with CAR-engineering. We also discuss the current challenges and the future perspectives in this field towards the foreseeable applications of iPSC-based immune therapy.

Reprogramming and redifferentiation of mucosal-associated invariant T cells reveal tumor inhibitory activity

Mucosal-associated invariant T (MAIT) cells belong to a family of innate-like T cells that bridge innate and adaptive immunities. Although MAIT cells have been implicated in tumor immunity, it currently remains unclear whether they function as tumor-promoting or inhibitory cells. Therefore, we herein used induced pluripotent stem cell (iPSC) technology to investigate this issue. Murine MAIT cells were reprogrammed into iPSCs and redifferentiated towards MAIT-like cells (m-reMAIT cells). m-reMAIT cells were activated by an agonist in the presence and absence of antigen-presenting cells and MR1-tetramer, a reagent to detect MAIT cells. This activation accompanied protein tyrosine phosphorylation and the production of T helper (Th)1, Th2, and Th17 cytokines and inflammatory chemokines. Upon adoptive transfer, m-reMAIT cells migrated to different organs with maturation in mice. Furthermore, m-reMAIT cells inhibited tumor growth in the lung metastasis model and prolonged mouse survival upon tumor inoculation through the NK cell-mediated reinforcement of cytolytic activity. Collectively, the present results demonstrated the utility and role of m-reMAIT cells in tumor immunity and provide insights into the function of MAIT cells in immunity.

Double-negative T cells: Setting the stage for disease control or progression

Double-negative (DN) T cells are present at relatively low frequencies in human peripheral blood, and are characterized as expressing the alpha-beta or gamma-delta T-cell receptor (TCR), but not the CD4 nor the CD8 co-receptors. Despite their low frequencies, these cells are potent producers of cytokines and, thus, are key orchestrators of immune responses. DN T cells were initially associated with induction of peripheral immunological tolerance and immunomodulatory activities related to disease prevention. However, other studies demonstrated that these cells can also display effector functions associated with pathology development. This apparent contradiction highlighted the heterogeneity of the DN T-cell population. Here, we review phenotypic and functional characteristics of DN T cells, emphasizing their role in human diseases. The need for developing biomarkers to facilitate the translation of studies from animal models to humans will also be discussed. Finally, we will examine DN T cells as promising therapeutic targets to prevent or inhibit human disease development.

Mechanisms of immune activation and regulation: lessons from melanoma

Melanoma, a skin cancer that develops from pigment cells, has been studied intensively, particularly in terms of the immune response to tumours, and has been used as a model for the development of immunotherapy. This is due, in part, to the high mutational burden observed in melanomas, which increases both their immunogenicity and the infiltration of immune cells into the tumours, compared with other types of cancers. The immune response to melanomas involves a complex set of components and interactions. As the tumour evolves, it accumulates an increasing number of genetic and epigenetic alterations, some of which contribute to the immunogenicity of the tumour cells and the infiltration of immune cells. However, tumour evolution also enables the development of resistance mechanisms, which, in turn, lead to tumour immune escape. Understanding the interactions between melanoma tumour cells and the immune system, and the evolving changes within the melanoma tumour cells, the immune system and the microenvironment, is essential for the development of new cancer therapies. However, current research suggests that other extrinsic factors, such as the microbiome, may play a role in the immune response to melanomas. Here, we review the mechanisms underlying the immune response in the tumour and discuss recent advances as well as strategies for treatment development.

Mucosal-associated invariant T cells: a cryptic coordinator in HIV-infected immune reconstitution

Human immunodeficiency virus type 1 (HIV-1) infection causes considerable morbidity and mortality worldwide. Although antiretroviral therapy (ART) has largely transformed HIV infection from a fatal disease to a chronic condition, approximately 10%~40% of HIV-infected individuals who receive effective ART and sustain long-term viral suppression still cannot achieve optimal immune reconstitution. These patients are called immunological non-responders, a state associated with poor clinical prognosis. Mucosal-associated invariant T (MAIT) cells are an evolutionarily conserved unconventional T cell subset defined by expression of semi-invariant αβ T cell receptor (TCR), which recognizes metabolites derived from the riboflavin biosynthetic pathway presented on major histocompatibility complex (MHC)-related protein-1 (MR1). MAIT cells, which are considered to act as a bridge between innate and adaptive immunity, produce a wide range of cytokines and cytotoxic molecules upon activation through TCR-dependent and TCR-independent mechanisms, which is of major importance in defense against a variety of pathogens. In addition, MAIT cells are involved in autoimmune and immune-mediated diseases. The number of MAIT cells is dramatically and irreversibly decreased in the early stage of HIV infection and is not fully restored even after long-term suppressive ART. In light of the important role of MAIT cells in mucosal immunity and because microbial translocation is inversely associated with CD4⁺ T cell counts, we propose that MAIT cells participate in the maintenance of intestinal barrier integrity and microbial homeostasis, thus further affecting immune reconstitution in HIV-infected individuals. This article is protected by copyright. All rights reserved.

Cholangiocarcinoma: what are the most valuable therapeutic targets - cancer-associated fibroblasts, immune cells, or beyond T cells?

INTRODUCTION

CCAs are dense and desmoplastic tumors with an abundant tumor microenviroment (TME). The evolving TME is characterized by reciprocal interactions between cancer cells and their environment and is essential in facilitating tumor progression. The TME has nonimmune and immune components. Nonimmune cell types include cancer-associated fibroblasts (CAFs) and endothelial cells accompanying tumor angiogenesis. Immune cell types include elements of the innate and adaptive immune response, and can have pro-tumor or antitumor roles. The TME can shape treatment response and resistance. Therefore, elements of the TME are attractive therapeutic targets. TME targeting therapies have been evaluated in preclinical and clinical studies but only a small subset of patients has a meaningful response.

AREAS COVERED

We discuss the TME components and potential TME targeting strategies. Literature search was performed on PubMed and ClinicalTrials.gov until October 2021.

EXPERT OPINION

Elucidating the CCA TME is essential for developing effective treatment strategies. Preclinical models that recapitulate the disease (such as organoids) are important tools in uncovering the intricate cross talk in the CCA TME. Characterization of patient-derived specimens using multi-omic and single-omic technologies can dissect the cellular interplay in the CCA TME, which can guide development of effective treatment strategies and identify biomarkers for patient stratification.

Determination of Sample Concentrations by PULCON NMR Spectroscopy

PULCON (Pulse Length Based Concentration Determination) is a powerful, versatile, non-invasive, and accurate technique for measuring solution concentrations during routine NMR spectroscopy. As solutes are quantified directly by their unique resonances, this technique avoids weight-based errors caused by contaminants (e.g. moisture), allows NMR samples to be directly employed in biological assays, and is particularly useful for quantifying small molecules, peptides, unstable molecules, and other materials that are difficult to weigh or handle. This article provides an introductory guide for biological and medicinal chemists, and highlights the diversity of applications.

Deciphering the Pyroptosis-Related Prognostic Signature and Immune Cell Infiltration Characteristics of Colon Cancer

Background: Colon cancer (CC) remains one of the most common malignancies with a poor prognosis. Pyroptosis, referred to as cellular inflammatory necrosis, is thought to influence tumor development. However, the potential effects of pyroptosis-related regulators (PRRs) on the CC immune microenvironment remain unknown.

Methods: In this study, 27 PRRs reported in the previous study were used to cluster the 1,334 CC samples into three pyroptosis-related molecular patterns. Through subtype pattern differential analysis and structure network mining using Weighted Gene Co-expression Network Analysis (WGCNA), 854 signature genes associated with the PRRs were discovered. Further LASSO-penalized Cox regression of these genes established an eight-gene assessment model for predicting prognosis.

Results: The CC patients were subtyped based on three distinct pyroptosis-related molecular patterns. These pyroptosis-related patterns were correlated with different clinical outcomes and immune cell infiltration characteristics in the tumor microenvironment. The pyroptosis-related eight-signature model was established and used to assess the prognosis of CC patients with medium-to-high accuracy by employing the risk scores, which was named “PRM-scores.” Greater inflammatory cell infiltration was observed in tumors with low PRM-scores, indicating a potential benefit of immunotherapy in these patients.

Conclusions: This study suggests that PRRs have a significant effect on the tumor immune microenvironment and tumor development. Evaluating the pyroptosis-related patterns and related models will promote our understanding of immune cell infiltration characteristics in the tumor microenvironment and provide a theoretical basis for future research targeting pyroptosis in cancer.