Expression Of MR1 Research Articles

MR1 Gene and Protein Expression Are Enhanced by Inhibition of the Extracellular Signal-Regulated Kinase ERK.

The MHC class I-related molecule MR1 is ubiquitously expressed, is highly conserved among mammals, and presents bacterial and endogenous antigens in tumor cells. These features indicate that tumor-specific T cells restricted to MR1 may represent ideal candidates for novel cancer-directed T-cell immunotherapy. The very low expression of the MR1 protein at the cell surface is a potential challenge limiting the possible use of MR1-directed immunotherapies. To overcome this challenge, it is important that understanding of the mechanisms regulating MR1 expression is increased, as little is known about this currently. This study identified ERK1/2 as negative regulators of the MR1 gene and protein expression. Inhibition of ERK1/2 in tumor cells or treatment of BRAF-mutant tumor cells with drugs specific for mutated BRAF increased MR1 protein expression and recognition by tumor-reactive and MR1-restricted T cells. The ERK1/2 inhibition of MR1 was mediated by the ELF1 transcription factor, which was required for MR1 gene expression. The effects of ERK1/2 inhibition also occurred in cancer cell lines of different tissue origins, cancer cell lines resistant to drugs that inhibit mutated BRAF, and primary cancer cells, making them potential targets of specific T cells. In contrast to tumor cells, the recognition of healthy cells was very poor or absent after ERK1/2 inhibition. These findings suggest a pharmaceutical approach to increase MR1 protein expression in tumor cells and the subsequent activation of MR1-restricted T cells, and they have potential therapeutic implications.

Potent Immunomodulators Developed from an Unstable Bacterial Metabolite of Vitamin B2 Biosynthesis

AbstractBacterial synthesis of vitamin B2 generates a by‐product, 5‐(2‐oxopropylideneamino)‐d‐ribityl‐aminouracil (5‐OP‐RU), with potent immunological properties in mammals, but it is rapidly degraded in water. This natural product covalently bonds to the key immunological protein MR1 in the endoplasmic reticulum of antigen presenting cells (APCs), enabling MR1 refolding and trafficking to the cell surface, where it interacts with T cell receptors (TCRs) on mucosal associated invariant T lymphocytes (MAIT cells), activating their immunological and antimicrobial properties. Here, we strategically modify this natural product to understand the molecular basis of its recognition by MR1. This culminated in the discovery of new water‐stable compounds with extremely powerful and distinctive immunological functions. We report their capacity to bind MR1 inside APCs, triggering its expression on the cell surface (EC50 17 nM), and their potent activation (EC50 56 pM) or inhibition (IC50 80 nM) of interacting MAIT cells. We further derivatize compounds with diazirine‐alkyne, biotin, or fluorophore (Cy5 or AF647) labels for detecting, monitoring, and studying cellular MR1. Computer modeling casts new light on the molecular mechanism of activation, revealing that potent activators are first captured in a tyrosine‐ and serine‐lined cleft in MR1 via specific pi‐interactions and H‐bonds, before more tightly attaching via a covalent bond to Lys43 in MR1. This chemical study advances our molecular understanding of how bacterial metabolites are captured by MR1, influence cell surface expression of MR1, interact with T cells to induce immunity, and offers novel clues for developing new vaccine adjuvants, immunotherapeutics, and anticancer drugs.

Potent Immunomodulators Developed from an Unstable Bacterial Metabolite of Vitamin B2 Biosynthesis.

Bacterial synthesis of vitamin B2 generates a by-product, 5-(2-oxopropylideneamino)-d-ribityl-aminouracil (5-OP-RU), with potent immunological properties in mammals, but it is rapidly degraded in water. This natural product covalently bonds to the key immunological protein MR1 in the endoplasmic reticulum of antigen presenting cells (APCs), enabling MR1 refolding and trafficking to the cell surface, where it interacts with T cell receptors (TCRs) on mucosal associated invariant T lymphocytes (MAIT cells), activating their immunological and antimicrobial properties. Here, we strategically modify this natural product to understand the molecular basis of its recognition by MR1. This culminated in the discovery of new water-stable compounds with extremely powerful and distinctive immunological functions. We report their capacity to bind MR1 inside APCs, triggering its expression on the cell surface (EC50 17 nM), and their potent activation (EC50 56 pM) or inhibition (IC50 80 nM) of interacting MAIT cells. We further derivatize compounds with diazirine-alkyne, biotin, or fluorophore (Cy5 or AF647) labels for detecting, monitoring, and studying cellular MR1. Computer modeling casts new light on the molecular mechanism of activation, revealing that potent activators are first captured in a tyrosine- and serine-lined cleft in MR1 via specific pi-interactions and H-bonds, before more tightly attaching via a covalent bond to Lys43 in MR1. This chemical study advances our molecular understanding of how bacterial metabolites are captured by MR1, influence cell surface expression of MR1, interact with T cells to induce immunity, and offers novel clues for developing new vaccine adjuvants, immunotherapeutics, and anticancer drugs.

Abstract 1590: The role of mucosal associated invariant T (MAIT) cells in pancreatic cancer liver metastasis

Abstract Pancreatic cancer liver metastasis (PCLM) is present in 50% of patients diagnosed with pancreatic ductal adenocarcinoma (PDAC) and leads to a median survival of <6 months. Here, we sought to identify urgently needed therapeutic options for treating PCLM by targeting mucosal associated invariant T (MAIT) cells, an invariant T cell restricted to MHCI related protein (MR1). MAIT cells are a unique subset of T cells that are classified as “protumor” MAIT17 and “antitumor” MAIT1 cells. We hypothesize that the PCLM tumor microenvironment (TME) induces direct MAIT cell activation via MR1 which primes MAIT cells towards a “protumor” phenotype. Using publicly available TCGA data, we found that PDAC tumors were enriched for MR1 gene expression compared to healthy tissue and patients with lower tumor MR1 expression had better overall survival. Next, immunostaining of MR1 on tumor samples from primary PDAC and PCLM revealed that that MR1 protein expression is highly enriched in the TME and localized to the surface of tumor cells. This suggests that MAIT cells in the PCLM TME are being activated directly via an MR1 dependent pathway. Next, we performed hemi-spleen injection of mouse pancreatic cancer cells into WT and MR1 KO (lacks MAIT cells) mice to model PCLM. Interestingly, MAIT cells in the WT PCLM mice were shifted towards the “pro-tumor” MAIT17 phenotype. Furthermore, the lack of MAIT cells in MR1 KO mice significantly reduced tumor burden compared to WT mice. Lastly, we found that MR1 KO mice had a reduction in exhausted NK and NKT cells which likely promoted anti-tumor immunity. Overall, we find that the PCLM TME promotes “pro-tumor” MAIT17 cells via MR1 mediated activation and these MAIT17 cells inhibit anti-tumor cells such as NK and NKT cells. This work identifies targeting MAIT cells as a novel immunotherapy approach for PCLM. Citation Format: Jugmohit Toor, Peter Dimitrion, Rachel Krevh, Kalpana Subedi, Bobby Zuniga, Jie Wang, Li Zhou, Qing-Sheng Mi. The role of mucosal associated invariant T (MAIT) cells in pancreatic cancer liver metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1590.

Topical antibiotics limit depigmentation in a mouse model ofvitiligo.

Oral neomycin administration impacts the gut microbiome and delays vitiligo development in mice, and topical antibiotics may likewise allow the microbiome to preserve skin health and delay depigmentation. Here, we examined the effects of 6-week topical antibiotic treatment on vitiligo-prone pmel-1 mice. Bacitracin, Neosporin, or Vaseline were applied to one denuded flank, while the contralateral flank was treated with Vaseline in all mice. Ventral depigmentation was quantified weekly. We found that topical Neosporin treatment significantly reduced depigmentation and exhibited effects beyond the treated area, while Bacitracin ointment had no effect. Stool samples collected from four representative mice/group during treatment revealed that Neosporin treatment aligned with reduced abundance of the Alistipes genus in the gut, while relevant changes to the skin microbiome at end point were less apparent. Either antibiotic treatment led to reduced expression of MR1, potentially limiting mucosal-associated invariant T-cell activation, while Neosporin-treated skin selectively revealed significantly reduced CD8+ T-cell abundance. The latter finding aligned with reduced expression of multiple inflammatory markers and markedly increased regulatory T-cell density. Our studies on favorable skin and oral antibiotic treatment share the neomycin compound, and in either case, microbial changes were most apparent in stool samples. Taken together, neomycin-containing antibiotic applications can mediate skin Treg infiltration to limit vitiligo development. Our study highlights the therapeutic potential of short-term antibiotic applications to limit depigmentation vitiligo.

MR1/MAIT Cell Axis Impacts Innate Immunity and Synaptic Proteins in 5XFAD Mice

Background:
 Amyloid beta (Aβ)-induced synaptic dysfunction and inflammation are features of Alzheimer’s disease (AD). One contributor to inflammation is mucosal-associated invariant T (MAIT) cells, an innate T cell that recognizes antigens presented by the MR1 molecule. Previously, we found increased MR1 expression in microglia near plaques and the loss of MR1/MAIT cell axis slowed the progression of Aβ pathology. This study aimed to determine contributions of the MR1/MAIT cell axis to immunity and synaptic proteins in the 5XFAD AD model mouse.
 Methods:
 We crossed 5XFAD mice with MR1-deficient mice (which lack MR1 and MAIT cells). At 2-, 4-, 6-, and 8-months of age, hippocampal and cortical brain tissue from wild-type, MR1KO, 5XFAD, and 5XFAD/MR1KO mice were analyzed by Western blot. Protein levels were analyzed with antibodies against GFAP (astrocytes), complement C3, and postsynaptic density protein (PSD)95. Additionally, Novel Object Recognition, Open Field, and Barnes Maze behavioral tests were performed in the 5XFAD mice to measure memory deficits.
 Results:
 Region-specific results were obtained for the hippocampus and cortex. The expression levels of PSD95 and C3 were significantly upregulated in the hippocampus of 5XFAD/MR1KO compared to 5XFAD mice at 6-8 months of age; in the cortex, GFAP levels were also significantly increased in 5XFAD/MR1KO mice. Finally, compared to wildtype C57BL/6 mice, 5XFAD mice showed memory deficits.
 Conclusions and Potential Impact:
 Approximately 6.7 million Americans are living with AD. This number is expected to double by 2050. Without any currently demonstrated therapy against AD, there is a need for therapeutic target(s) as part of novel treatment paradigms. Our results demonstrate an impact of the MR1/MAIT cell axis on postsynaptic proteins and consequent AD pathology. Thus, understanding the contribution of this axis could help reveal the role of innate immunity in AD and potentially serve as a future therapeutic target in AD patients.

Control of the temporal development of Alzheimer’s disease pathology by the MR1/MAIT cell axis

BackgroundNeuroinflammation is an important feature of Alzheimer’s disease (AD). Understanding which aspects of the immune system are important in AD may lead to new therapeutic approaches. We study the major histocompatibility complex class I-related immune molecule, MR1, which is recognized by an innate-like T cell population called mucosal-associated invariant T (MAIT) cells.MethodsHaving found that MR1 gene expression is elevated in the brain tissue of AD patients by mining the Agora database, we sought to examine the role of the MR1/MAIT cell axis in AD pathology. Brain tissue from AD patients and the 5XFAD mouse model of AD were used to analyze MR1 expression through qPCR, immunofluorescence, and flow cytometry. Furthermore, mice deficient in MR1 and MAIT cells were crossed with the 5XFAD mice to produce a model to study how the loss of this innate immune axis alters AD progression. Moreover, 5XFAD mice were also used to study brain-resident MAIT cells over time.ResultsIn tissue samples from AD patients and 5XFAD mice, MR1 expression was substantially elevated in the microglia surrounding plaques vs. those that are further away (human AD: P < 0.05; 5XFAD: P < 0.001). In 5XFAD mice lacking the MR1/MAIT cell axis, the development of amyloid-beta plaque pathology occurred at a significantly slower rate than in those mice with MR1 and MAIT cells. Furthermore, in brain tissue from 5XFAD mice, there was a temporal increase in MAIT cell numbers (P < 0.01) and their activation state, the latter determined by detecting an upregulation of both CD69 (P < 0.05) and the interleukin-2 receptor alpha chain (P < 0.05) via flow cytometry.ConclusionsTogether, these data reveal a previously unknown role for the MR1/MAIT cell innate immune axis in AD pathology and its potential utility as a novel therapeutic target.

Varicella Zoster Virus infects mucosal associated Invariant T cells.

Mucosal Associated Invariant T (MAIT) cells are innate-like T cells that respond to conserved pathogen-derived vitamin B metabolites presented by the MHC class I related-1 molecule (MR1) antigen presentation pathway. Whilst viruses do not synthesize these metabolites, we have reported that varicella zoster virus (VZV) profoundly suppresses MR1 expression, implicating this virus in manipulation of the MR1:MAIT cell axis. During primary infection, the lymphotropism of VZV is likely to be instrumental in hematogenous dissemination of virus to gain access to cutaneous sites where it clinically manifests as varicella (chickenpox). However, MAIT cells, which are found in the blood and at mucosal and other organ sites, have yet to be examined in the context of VZV infection. The goal of this study was to examine any direct impact of VZV on MAIT cells. Using flow cytometry, we interrogated whether primary blood derived MAIT cells are permissive to infection by VZV whilst further analysing differential levels of infection between various MAIT cell subpopulations. Changes in cell surface extravasation, skin homing, activation and proliferation markers after VZV infection of MAIT cells was also assessed via flow cytometry. Finally the capacity of MAIT cells to transfer infectious virus was tested through an infectious center assay and imaged via fluorescence microscopy. We identify primary blood-derived MAIT cells as being permissive to VZV infection. A consequence of VZV infection of MAIT cells was their capacity to transfer infectious virus to other permissive cells, consistent with MAIT cells supporting productive infection. When subgrouping MAIT cells by their co- expression of a variety cell surface markers, there was a higher proportion of VZV infected MAIT cells co-expressing CD4+ and CD4+/CD8+ MAIT cells compared to the more phenotypically dominant CD8+ MAIT cells, whereas infection was not associated with differences in co-expression of CD56 (MAIT cell subset with enhanced responsiveness to innate cytokine stimulation), CD27 (co-stimulatory) or PD-1 (immune checkpoint). Infected MAIT cells retained high expression of CCR2, CCR5, CCR6, CLA and CCR4, indicating a potentially intact capacity for transendothelial migration, extravasation and trafficking to skin sites. Infected MAIT cells also displayed increased expression of CD69 (early activation) and CD71 (proliferation) markers. These data identify MAIT cells as being permissive to VZV infection and identify impacts of such infection on co- expressed functional markers.

Suppression of MR1 by human cytomegalovirus inhibits MAIT cell activation.

The antigen presentation molecule MHC class I related protein-1 (MR1) is best characterized by its ability to present bacterially derived metabolites of vitamin B2 biosynthesis to mucosal-associated invariant T-cells (MAIT cells). Through in vitro human cytomegalovirus (HCMV) infection in the presence of MR1 ligand we investigate the modulation of MR1 expression. Using coimmunoprecipitation, mass spectrometry, expression by recombinant adenovirus and HCMV deletion mutants we investigate HCMV gpUS9 and its family members as potential regulators of MR1 expression. The functional consequences of MR1 modulation by HCMV infection are explored in coculture activation assays with either Jurkat cells engineered to express the MAIT cell TCR or primary MAIT cells. MR1 dependence in these activation assays is established by addition of MR1 neutralizing antibody and CRISPR/Cas-9 mediated MR1 knockout. Here we demonstrate that HCMV infection efficiently suppresses MR1 surface expression and reduces total MR1 protein levels. Expression of the viral glycoprotein gpUS9 in isolation could reduce both cell surface and total MR1 levels, with analysis of a specific US9 HCMV deletion mutant suggesting that the virus can target MR1 using multiple mechanisms. Functional assays with primary MAIT cells demonstrated the ability of HCMV infection to inhibit bacterially driven, MR1-dependent activation using both neutralizing antibodies and engineered MR1 knockout cells. This study identifies a strategy encoded by HCMV to disrupt the MR1:MAIT cell axis. This immune axis is less well characterized in the context of viral infection. HCMV encodes hundreds of proteins, some of which regulate the expression of antigen presentation molecules. However the ability of this virus to regulate the MR1:MAIT TCR axis has not been studied in detail.

DOP08 Cellular and molecular interaction of MAIT in mucosal tissue and their role in inflammatory bowel disease

Abstract Background Inflammatory bowel disease (IBD) manifests as chronic inflammation of the gastrointestinal tract and is characterized by a deregulated immune response targeting the gut microflora. Mucosal-associated invariant T (MAIT) cells have been identified as a possible key player in IBD. Activated MAIT cells produce cytokines including IL-26, a newly discovered cytokine involved in the pathology of IBD. Interestingly, IL-26 is not expressed in mice and therefore its effect on the course of inflammation has not been yet fully investigated. Similarly, studies employing human cell cultures often provide limited results as they cannot fully mimic the complex three-dimensional structure of the intestinal tissue. A great hope is placed in the development of models of human diseases using organoids - 3D structures that better recapitulate the architecture and functionality of tissues. Methods Our laboratory recently described a model of intestinal inflammation based on human iPSCs-derived intestinal organoids (IOs). Taking advantage of this model, we investigate the influence of the cytokine IL-26 on the course of IBD. Moreover, we elucidate the influence of MAIT cells on the pathogenesis of IBD by studying their pathways of activation in vitro, and subsequently their interaction with inflamed tissues through the co-culture with IOs. Results After stimulation, IOs mimic the pro-inflammatory microenvironment and express various cytokines and chemokines. Moreover, IOs express MR1 which is recognised by the invariant TCR receptor of the MAIT cells. IOs express functional IL-26 receptor and respond to this cytokine. MAIT cells isolated from human blood show production cytokines including IL-26 and effector molecules upon in vitro activation. Their response differs depending on the origin of the stimuli. Conclusion IOs form complex structures and immunocompetent environment allowing to study of intestinal inflammation. IOs consist of various cell types, but not immune cells. Taken together with MR1 and cytokines expression we show that IOs can activate MAIT cells, and they serve as a relevant model for in vitro study of their biology. Moreover, IOs respond to IL-26, so they also provide a relevant model to elucidate the role of this cytokine. We expect that this study will contribute to our understanding of the processes underlying the progression of IBD, and lead to the design of new therapeutic targets for the treatment of idiopathic intestinal inflammation.

IM-1 THE IMMUNOSUPPRESSIVE ROLE OF MAIT CELLS AND MR1 IN GBM THROUGH THE INDUCTION OF NEUTROPHILS AND MDSCS

Abstract Background Glioblastoma (GBM) is a devastating brain tumor, and its immunosuppressive microenvironment has been implicated in the poor prognosis. However, the mechanism of the induction of the microenvironment is not well understood. MHC class I-related protein (MR1) is an antigen-presenting molecule for Mucosal-Associated Invariant T (MAIT) cells. Recently, MR1 transcriptomic level was reported to correlate with glioma’s poor survival, and the infiltration of MAIT cells in GBM was reported previously. However, the role of MAIT cells and MR1 in GBM is poorly understood. We aimed to understand the mechanism by which MR1 levels affect GBM patient survival and any potential involvement of MAIT cells. Method RNA-sequencing data from TCGA-GBM was subjected to multi-layered analysis. Multiple methods, including comprehensive gene expression analysis and direct alignment-search using FASTQ data, were used to assess the immunological impact of MAIT cells in GBM. Using data from Pan-cancer TCGA, the role of MAIT cells in other cancer types was assessed. Result The survival of GBM patients was negatively correlated with the level of MR1 expression. 8.3% of TCGA-GBM samples were identified to have MAIT cell infiltration, and the expression of MR1, the amount of MAIT cell infiltration, and the activity of tumor-associated neutrophils (TANs)/myeloid-derived suppressor cells (MDSCs) were significantly correlated. Simultaneously, the TAN/MDSC activity was significantly correlated with the poor survival of GBM patients. In four more cancer types, similar relationships between MAIT/MR1 and TANs/MDSCs were observed. Conclusions Our observations shed light on the possible immunosuppressive role of MAIT cells and MR1. It was shown that MR1 up-regulation causes MAIT cell activation, which in turn causes TAN/MDSC induction. The current study implied the existence of a novel MAIT/MR1-TAN/MDSC immunosuppressive pathway, whose activation is associated with a worse prognosis for GBM. It was also suggested that a similar pathway might exist in other cancer types.

Ligand-dependent modulation of MR1-restricted antigen presentation

Mucosal-associated invariant T (MAIT) cells are innate T cells recognising intermediates of the vitamin B2 biosynthetic pathway presented by the monomorphic MR1 molecule. We have demonstrated that in addition to their cytolytic activity important in antimicrobial defence, MAIT cells have also immune-modulatory functions, enhancing DC maturation, in vitro and in vivo. Furthermore, through an in silico and in vitro screening of commercial libraries, we have identified novel compounds capable of activating MAIT cells and the first compounds that inhibits of MAIT cell activation through downregulation of MR1 expression. Identification of novel agonists and antagonists of MAIT cell function paves the way for potentially harnessing MAIT cell function in vivo .

Regulation of tumor-associated macrophage (TAM) differentiation by NDRG2 expression in breast cancer cells

Macrophages are a major cellular component of innate immunity and are mainly known to have phagocytic activity. In the tumor microenvironment (TME), they can be differentiated into tumor-associated macrophages (TAMs). As the most abundant immune cells in the TME, TAMs promote tumor progression by enhancing angiogenesis, suppressing T cells and increasing immunosuppressive cytokine production. N-myc downstream-regulated gene 2 (NDRG2) is a tumor suppressor gene, whose expression is down-regulated in various cancers. However, the effect of NDRG2 on the differentiation of macrophages into TAMs in breast cancer remains elusive. In this study, we investigated the effect of NDRG2 expression in breast cancer cells on the differentiation of macrophages into TAMs. Compared to tumor cell-conditioned medium (TCCM) from 4T1-mock cells, TCCM from NDRG2-overexpressing 4T1 mouse breast cancer cells did not significantly change the morphology of RAW 264.7 cells. However, TCCM from 4T1-NDRG2 cells reduced the mRNA levels of TAM-related genes, including MR1, IL-10, ARG1 and iNOS, in RAW 264.7 cells. In addition, TCCM from 4T1-NDRG2 cells reduced the expression of TAM-related surface markers, such as CD206, in peritoneal macrophages (PEM). The mRNA expression of TAM-related genes, including IL-10, YM1, FIZZ1, MR1, ARG1 and iNOS, was also downregulated by TCCM from 4T1-NDRG2 cells. Remarkably, TCCM from 4T1-NDRG2 cells reduced the expression of PD-L1 and Fra-1 as well as the production of GM-CSF, IL-10 and ROS, leading to the attenuation of T cell-inhibitory activity of PEM. These data showed that compared with TCCM from 4T1-mock cells, TCCM from 4T1-NDRG2 cells suppressed the TAM differentiation and activation. Collectively, these results suggest that NDRG2 expression in breast cancer may reduce the differentiation of macrophages into TAMs in the TME.

Magnetic Resonance Image in Monitor and Diagnosis of Patients with Neuromyelitis Optica.

This study was aimed to investigate the craniocerebral magnetic resonance imaging (MRI) measurement and clinical characteristics of patients with neuromyelitis optica (NMO) and multiple sclerosis (MS). 50 patients with NMO (NMO group) and 50 patients with MS (MS group) were studied. The clinical manifestations, brain injury morphology, MRI signal characteristics, brain distribution characteristics, and related laboratory tests (serum aquaporin 4 [AQP4] antibody) were statistically analyzed. The results showed that the analysis of clinical manifestations of patients revealed that optic neuritis (37 cases) was the most common disease in NMO patients, and myelitis (16 cases) was more common in MS patients than NMO patients. There were significant differences in gender ratio, abnormal expression of brain MR1, positive serum AQP4-IgG, and other immune diseases and symptoms between the two groups (P < 0.05). When the lesions measured by MRI were located in the white matter area of the cerebral hemisphere, the image showed blurred edges and a relatively symmetrical distribution. When the lesions measured by MRI were located around the medulla oblongata, the lesions mainly involved the central gray matter and white matter of the spinal cord, with patchy and line-like long T1 and long T2 signals. Moreover, in the late stage of recurrence of spinal cord disease, severe spinal cord atrophy may occur. In conclusion, craniocerebral MRI measurement in NMO patients can provide more basis for the diagnosis and differential diagnosis of the disease, so as to improve the diagnostic level of NMO.

Multiomic analysis reveals decidual-specific transcriptional programing of MAIT cells.

Mucosal-Associated Invariant T (MAIT) cells have been recently identified at the maternal-fetal interface. However, transcriptional programming of decidual MAIT cells in pregnancy remains poorly understood. We employed a multiomic approach to address this question. Mononuclear cells from the decidua basalis and parietalis, and control PBMCs, were analyzed via flow cytometry to investigate MAIT cells in the decidua and assess their transcription factor expression. In a separate study, both decidual and matched peripheral MAIT cells were analyzed using Cellular Indexing of Transcriptomes and Epitopes by Sequencing (CITE-seq) coupled with gene expression analysis. Lastly, decidual MAIT cells were stimulated with E.coli and expression of MR1 by antigen presenting cells was measured to evaluate decidual MAIT cell function. First, we identified MAIT cells in both the decidua basalis and parietalis. CITE-seq, coupled with scRNA-seq gene expression analysis, highlighted transcriptional programming differences between decidual and matched peripheral MAIT cells at a single cell resolution. Transcription factor expression analysis further highlighted transcriptional differences between decidual MAIT cells and non-matched peripheral MAIT cells. Functionally, MAIT cells are skewed towards IFNγ and TNFα production upon stimulation, with E.coli leading to IFNγ production. Lastly, we demonstrate that MR1, the antigen presenting molecule restricting MAIT cells, is expressed by decidual APCs. MAIT cells are present in the decidua basalis and obtain a unique gene expression profile. The presence of MR1 on APCs coupled with in vitro activation by E.coli suggests that MAIT cells might be involved in tissue-repair mechanisms at the maternal-fetal interface.

MR1, an immunological periscope of cellular metabolism.

The discovery that major histocompatibility complex (MHC) class I-related molecule 1 (MR1) presents microbial antigens to mucosal-associated invariant T (MAIT) cells was a significant scientific milestone in the last decade. Surveillance for foreign metabolically derived antigens added a new class of target structures for immune recognition. The recent identification of a second family of MR1-restricted T cells, called MR1T cells, which show self-reactivity suggests the microbial antigens characterized so far may only represent a handful of the potential structures presented by MR1. Furthermore, the reactivity of MR1T cells towards tumours and not healthy cells indicates tight regulation in the generation of self-antigens and in MR1 expression and antigen loading. These novel and exciting observations invite consideration of new perspectives of MR1-restricted antigen presentation and its wider role within immunity and disease.

Varicella Zoster Virus Impairs Expression of the Nonclassical Major Histocompatibility Complex Class I-Related Gene Protein (MR1).

The antigen presentation molecule MR1 (major histocompatibility complex, class I-related) presents ligands derived from the riboflavin (vitamin B) synthesis pathway, which is not present in mammalian species or viruses, to mucosal-associated invariant T (MAIT) cells. In this study, we demonstrate that varicella zoster virus (VZV) profoundly suppresses MR1 expression. We show that VZV targets the intracellular reservoir of immature MR1 for degradation, while preexisting, ligand-bound cell surface MR1 is protected from such targeting, thereby highlighting an intricate temporal relationship between infection and ligand availability. We also identify VZV open reading frame (ORF) 66 as functioning to suppress MR1 expression when this viral protein is expressed during transient transfection, but this is not apparent during infection with a VZV mutant virus lacking ORF66 expression. This indicates that VZV is likely to encode multiple viral genes that target MR1. Overall, we identify an immunomodulatory function of VZV whereby infection suppresses the MR1 biosynthesis pathway.

MR1 expression and surface translocation in airway epithelial cells from COPD or smoker lungs is altered following exposure to IFNγ or MAIT cells.

Abstract MAIT cells, a highly prevalent subset of T cells restricted by the MHC Class I-like molecule MR1, play a key role in early response to bacterial infection. Chronic obstructive pulmonary disease (COPD) pathogenesis is associated with airway inflammation, increased infiltration by CD8+ T lymphocytes, and infection-driven exacerbations. Cigarette smoke (CS), a leading cause of COPD, leads to impaired immune function of airway epithelial cells (AECs) and decreases surface expression of classical MHC Class I molecules. However, the impact of CS and COPD on MR1 expression and airway MAIT cell function is unknown. We have demonstrated that exposure to CS alters MAIT cell responses to primary AECs from healthy, COPD, or smoker lungs. Here, we examined whether CS impacts expression of MR1 mRNA or surface translocation of MR1 in these primary AEC populations as a possible mechanism for this dysregulation. Short-term treatment of AECs with CS or infection with S. pneumoniae (SP) did not alter MR1 expression in any of the donor AEC groups. However, incubating CS-treated or SP-infected AECs with MAIT cells increased MR1 expression. This upregulation may be mediated through IFNγ signaling pathways, as treatment with IFNγ alone resulted in MR1 upregulation. Our data further suggest MAIT cell- and IFNγ-mediated MR1 upregulation is altered in COPD cells. Additionally, we observed increased baseline surface expression of MR1 protein in smoker AECs and reduced surface translocation upon addition of exogenous ligand. COPD- and CS-mediated dysregulation of MR1 expression could impact MAIT cell function in airways, resulting in inflammation or reduced early response to bacteria, contributing to lower airway colonization and COPD exacerbations.

MR1 overexpression correlates with poor clinical prognosis in glioma patients.

BackgroundGlioblastoma is the most common adult primary brain tumor with near-universal fatality. Major histocompatibility complex (MHC) class I molecules are important mediators of CD8 activation and can be downregulated by cancer cells to escape immune surveillance. MR1 is a nonclassical MHC-I-like molecule responsible for the activation of a subset of T cells. Although high levels of MR1 expression should enhance cancer cell recognition, various tumors demonstrate MR1 overexpression with unknown implications. Here, we study the role of MR1 in glioma.MethodsUsing multi-omics data from the Cancer Genome Atlas (TCGA), we studied MR1 expression patterns and its impact on survival for various solid tumors. In glioma specifically, we validated MR1 expression by histology, elucidate transcriptomic profiles of MR1 high versus low gliomas. To understand MR1 expression, we analyzed the methylation status of the MR1 gene and MR1 gene-related transcription factor (TF) expression.Results MR1 is overexpressed in all grades of glioma and many other solid cancers. However, only in glioma, MR1 overexpression correlated with poor overall survival and demonstrated global dysregulation of many immune-related genes in an MR1-dependent manner. MR1 overexpression correlated with decreased MR1 gene methylation and upregulation of predicted MR1 promoter binding TFs, implying MR1 gene methylation might regulate MR1 expression in glioma.ConclusionsOur in silico analysis shows that MR1 expression is a predictor of clinical outcome in glioma patients and is potentially regulated at the epigenetic level, resulting in immune-related genes dysregulation. These findings need to be validated using independent in vitro and in vivo functional studies.

Rab6 regulates recycling and retrograde trafficking of MR1 molecules

Mucosal-associated invariant T (MAIT) cells are an innate-like T cell subset important in the early response to bacterial and viral lung pathogens. MAIT cells recognize bacterial small molecule metabolites presented on the Class I-like molecule MR1. As with other Class I and Class II molecules, MR1 can likely sample ligands in the intracellular environment through multiple cellular pathways. Rab6, a small GTPase that regulates a number of endosomal trafficking pathways including retrograde transport to the trans-Golgi network (TGN), is involved in the presentation of ligands from Mycobacterium tuberculosis (Mtb) to MAIT cells. The Rab6-mediated trafficking pathway contains endosomal compartments that share features with the Mtb intracellular compartment. Using inducible expression of MR1, this study demonstrates that Rab6 regulates the recycling of MR1 molecules from the cell surface through endosomal trafficking compartments to the TGN. This Rab6-dependent pool of recycled MR1, which is available for reloading with ligands from bacterial pathogens like Mtb, may be important for early recognition of infected cells by MAIT cells in the lung.