Activation and Functional Alteration of Mucosal-Associated Invariant T Cells in Adult Patients With Community-Acquired Pneumonia

Community-acquired pneumonia (CAP) remains the significant infectious cause of morbidity and mortality worldwide. Although mucosal-associated invariant T cells (MAIT) play roles in the pathogenesis of children CAP and ICU-associated pneumonia, their roles in adult CAP are largely unexplored. In this study, we investigated the frequency, phenotype, and function of MAIT cells in peripheral blood and bronchoalveolar lavage fluid (BALF) of adult CAP patients. Our data indicate that MAIT-cell frequency is profoundly lower in the peripheral blood of CAP patients compared to that in healthy individuals. Furthermore, the circulatory MAIT cells express higher levels of CD69 and PD-1 compared to those in healthy individuals. In BALF of CAP patients, MAIT-cell frequency is higher and MAIT cells express higher levels of CD69 and PD-1 compared to their matched blood counterparts. Levels of IL-17A and IFN-γ are increased in BALF of CAP patients compared to those in BALF of patients with pulmonary small nodules. The IL-17A/IFN-γ ratio is significantly positively correlated with MAIT frequency in BALF of CAP patients, suggesting a pathogenic role of MAIT-17 cells in CAP. Of note, blood MAIT-cell frequency in CAP patients is strongly negatively correlated with high-sensitivity C-reactive protein (hsCRP) and neutrophil count percentage in blood. The ability of circulating MAIT cells in CAP patients to produce IFN-γ is significantly impaired compared to those in healthy individuals. In summary, our findings suggest the possible involvement of MAIT cells in the immunopathogenesis of adult CAP.

The Potential Roles of Mucosa-Associated Invariant T Cells in the Pathogenesis of Gut Graft-Versus-Host Disease after Hematopoietic Stem Cell Transplantation

Background & Purpose: Gut acute graft-versus-host disease (aGVHD) is a serious complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and is associated with high mortality. Mucosal-associated invariant T cells (MAITs) are a group of innate-like T cells enriched in the intestine that can be activated by riboflavin metabolites from various microorganisms. However, little is known about the function or mechanism of action of MAIT in the occurrence of gut aGVHD in the human body. Methods & Cases: In our study, multiparameter flow cytometry (FCM) was used to evaluate the number of MAIT cells (MAITs) and functional cytokines. 16S V34 region amplicon sequencing analysis was used to analyse the intestinal flora of transplant patients. In vitro stimulation and coculture assays were used to study the activation and function of MAITs. The number and distribution of MAITs in intestinal tissues were analysed by immunofluorescence technology. We prospectively studied the enrolled 150 consecutive patients who underwent allo-HSCT in our institute. Results: The number and frequency of MAITs in infused grafts in gut aGVHD patients were lower than those in non-gut aGVHD patients (Figure). Recipients with a high number of MAITs in infused grafts had a higher abundance of intestinal flora in the early post-transplantation period (+14 days). At the onset of gut aGVHD, the number of MAITs decreased in peripheral blood, and the activation marker CD69, chemokines CXCR3 and CXCR4 and transcription factors Rorγt and T-bet tended to increase. Furthermore, when gut aGVHD occurred, the proportion of MAIT17 was higher than that of MAIT1. The abundance of intestinal flora with non-riboflavin metabolic pathways tended to increase in gut aGVHD patients. MAITs secreted more granzyme B, TNF-α and IFN-γ under the stimulation of IL-12/IL-18 (non-TCR signal) and secreted most of the IL-17 under the stimulation of CD3/CD28 (TCR signal). MAITs inhibited the proliferation of CD4+ T cells in vitro. Conclusions: In conclusion, the lower number of MAITs in infused grafts was related to the higher incidence of gut aGVHD, and the number of MAITs in grafts may affect the composition of the intestinal flora of recipients early after transplantation. The flora of the riboflavin metabolism pathway activated MAITs and promoted the secretion of intestinal protective factors to affect the occurrence of gut aGVHD in humans. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

286 Sex differences in the transcriptional profiles of mucosal-associated invariant T cells in neoadjuvant anti-PD-1 treated non-small cell lung cancer (NSCLC)

BackgroundMucosal Associated Invariant T Cells (MAIT cells) are unconventional T cells that recognize vitamin B metabolites derived from bacteria and are mainly present in mucosal tissues and peripheral blood.1 Their activation by T Cell Receptor (TCR)-dependent and -independent pathways can result in effector function that can either promote or inhibit cytotoxic effects.2 MAIT cells are known to be involved in the pathogenesis of multiple diseases that involve mucosal tissues, such as non-small cell lung cancer (NSCLC).2 Recently, studies have shown that disparate outcomes to SARS-CoV-2-infection between males and females may involve a differential activation of MAIT cells in the lung mucosa.3 It is therefore conceivable to hypothesize that sex differences of MAIT cells in NSCLC may also impact outcome, however their involvement in progression and subsequent treatment response of NSCLC has never been explored.MethodsTo study the transcriptional program of MAIT cells in NSCLC as a function of sex, peripheral blood and tissue biospecimens were obtained from the first-in-human clinical trial of neoadjuvant anti-PD-1 (nivolumab) in resectable non-small cell lung cancer; NCT02259621.4 Coupled single-cell RNAseq/TCRseq was performed on tumor infiltrating lymphocytes (TIL), paired adjacent normal lung, and tumor-draining lymph nodes (TDLN). MAIT cells were identified by expression of SLC4A10 and the invariant TRAV1-2 and TRAJ33/12/20 TCR. Computational analysis revealed 4 distinct MAIT cell clusters and differentially expressed genes in the tumors and healthy normal lung of males as compared to females.ResultsIn MAIT cells from females, we found upregulation of CD8A, GNLY, and NKG7 genes. These genes are involved with T cell activation and cytolytic function, suggesting that the activation of these genes in MAIT cells could be contributing towards their cytolytic activity in females. In MAIT cells from males, we found upregulation of PDE3B and PCBP2 genes, which are known to be involved with immunosuppression and downregulation of cytotoxic T lymphocyte (CTL) responses. These findings were consistent in the healthy normal lung, suggesting these transcriptional programs may be due to the normal lung biology and not necessarily a byproduct of carcinogenesis.ConclusionsThese results highlight the potential for dual characteristics of MAIT cells in neoadjuvant anti-PD-1-treated NSCLCs and provide an important foundation in our study of the often dichotomous responses between males and females to immunotherapy. Future analyses will focus on the interplay of MAIT cells with other cells in the tumor microenvironment (TME) as a function of immunotherapy treatment and clinical response.ReferencesChen Z, Wang H, D’Souza C, et al. Mucosal-associated invariant T-cell activation and accumulation after in vivo infection depends on microbial riboflavin synthesis and co-stimulatory signals. Mucosal Immunol 2017;10:58–68.Wen X, Zhang X, et al. Title of article: mucosal-associated invariant T cells in lung cancers. Elsevier 2021;94.Yu C, Littleton S, et al. Mucosal-associated invariant T cell responses differ by sex in COVID-19. CellPress 2021;2:755–772.Caushi JX, Zhang J, Ji Z, et al. Transcriptional programs of neoantigen-specific TIL in anti-PD-1-treated lung cancers. Nature 2021.Ethics ApprovalThis study was approved by the Institutional Review Boards (IRB) at Johns Hopkins University (JHU) and Memorial Sloan Kettering Cancer Center and was conducted in accordance with the Declaration of Helsinki and the International Conference on Harmonization Good Clinical Practice guidelines. The patients described in this study provided written informed consent.