MAIT Cells Research Articles

CXCR6-positive circulating mucosal-associated invariant T cells can identify patients with non-small cell lung cancer responding to anti-PD-1 immunotherapy

BackgroundMucosal-associated invariant T (MAIT) cells have been reported to regulate tumor immunity. However, the immune characteristics of MAIT cells in non-small cell lung cancer (NSCLC) and their correlation with the treatment efficacy of immune checkpoint inhibitors (ICIs) remain unclear.Patients and methodsIn this study, we performed single-cell RNA sequencing (scRNA-seq), flow cytometry, and multiplex immunofluorescence assays to determine the proportion and characteristics of CD8+MAIT cells in patients with metastatic NSCLC who did and did not respond to anti-PD-1 therapy. Survival analyses were employed to determine the effects of MAIT proportion and C-X-C chemokine receptor 6 (CXCR6) expression on the prognosis of patients with advanced NSCLC.ResultsThe proportion of activated and proliferating CD8+MAIT cells were significantly higher in responders-derived peripheral blood mononuclear cells (PBMCs) and lung tissues before anti-PD-1 therapy, with enhanced expression of cytotoxicity-related genes including CCL4, KLRG1, PRF1, NCR3, NKG7, GZMB, and KLRK1. The responders’ peripheral and tumor-infiltrating CD8+MAIT cells showed an upregulated CXCR6 expression. Similarly, CXCR6+CD8+MAIT cells from responders showed higher expression of cytotoxicity-related genes, such as CST7, GNLY, KLRG1, NKG7, and PRF1. Patients with ≥15.1% CD8+MAIT cells to CD8+T cells ratio and ≥35.9% CXCR6+CD8+MAIT cells to CD8+MAIT cells ratio in peripheral blood showed better progression-free survival (PFS) after immunotherapy. The role of CD8+MAIT cells in lung cancer immunotherapy was potentially mediated by classical/non-classical monocytes through the CXCL16-CXCR6 axis.ConclusionCD8+MAIT cells are a potential predictive biomarker for patients with NSCLC responding to anti-PD-1 therapy. The correlation between CD8+MAIT cells and immunotherapy sensitivity may be ascribed to high CXCR6 expression.

Identification of T cell subpopulations exhibiting a high-degree of TCR-independent, IL-15-induced activation in pateints with acute hepatitis A

Abstract During acute hepatitis A, pre-existing memory CD8+ T cells specific to hepatitis A virus-unrelated antigens are activated by IL-15 in a T-cell receptor (TCR)-independent manner, which is termed bystander activation, and these T cells contribute to liver injury (Immunity 2018, 48:161). However, it has been remained to be elucidated if other types of T cells are also activated by IL-15 without TCR engagement during acute hepatitis A. Here, we performed CITE-seq analysis in combination with single-cell RNA sequencing (scRNA-seq) using peripheral blood mononuclear cells (PBMCs) from patients with acute hepatitis A at acute and convalescent phases and healthy controls. In the scRNA-seq analysis, we used a gene set that was previously known to be upregulated by IL-15 in the absence of TCR stimulation to identify T-cell clusters that undergo TCR-independent, IL-15-induced activation. Among CD8+ T and γδ T cells, subclusters expressing CD45RO, CD57, and KLRG1 exhibited the highest module score of TCR-independent, IL-15-induced activation. Among MAIT cells, subclusters expressing CD8 and CD226 showed the highest module score of TCR-independent, IL-15-induced activation. Notably, these subclusters with the highest module score were exclusively found at the acute stage compared to the convalescent phase. In summary, T cell subpopulations exhibiting a high-degree of TCR-independent, IL-15-induced activation express distinct cell surface protein markers in patients with acute hepatitis A.

EEPD1 is identified as a predictor of prognosis and immune microenvironment through pan-cancer analysis and related to progression of colorectal cancer

BackgroundEEPD1 is vital in homologous recombination, while its role in cancer remains unclear. MethodsWe performed multiple pan-cancer analyses of EEPD1 with bioinformatics methods, such as gene expression, gene alterations, Prognosis and enrichment analysis, tumor microenvironment, immune cell infiltration, TMB, MSI, immunotherapy, co-expression of genes, and drug resistance. Finally, RT-qPCR, EdU, and transwell assays helped investigate the impact of EEPD1 on CRC cells. ResultsEEPD1 was dysregulated and correlated with bad prognosis in several cancers. GSVA and GSEA revealed that EEPD1 was primarily associated with the "WNT_BETA_CATENIN_SIGNALING," "ribonucleoprotein complex biogenesis," "Ribosome," and "rRNA processing." The infiltration of CD8+ T cells, MAIT cells, iTreg cells, NK cells, Tc cells, Tex cells, Tfh cells, and Th1 cells were negatively correlated with EEPD1 expression. Additionally, EEPD1 is significantly associated with TMB and MSI in COAD, while enhanced CRC cell proliferation and migration. ConclusionsEEPD1 was dysregulated in human cancers and correlated with various cancer patient prognoses. The dysregulated EEPD1 expression can affect tumor-infiltrating immune cells and immunotherapy response. Therefore, EEPD1 could act as an oncogene associated with immune cell infiltration in CRC.

Single-cell sequencing analysis of chronic subdural hematoma cell subpopulations and their potential therapeutic mechanisms

BackgroundChronic subdural hematoma (CSDH) is a prevalent form of intracranial haemorrhage encountered in neurosurgical practice, and its incidence has notably risen in recent years. Currently, there is a lack of studies that have comprehensively classified the cells present in hematomas removed during surgery, and their correlation with CSDH recurrence remains elusive. This study aims to analyse the subcellular populations and occupancy levels within peripheral blood. MethodsThis study analyses the subcellular populations and occupancy levels within peripheral blood and postoperatively removed hematomas by single-cell sequencing and attempts to analyse the effect of different cell occupancies within peripheral blood and intraoperatively removed hematomas on CSDH. ResultsThe single-cell sequencing results showed that the cells were classified into 25 clusters by differential gene and UMAP dimensionality reduction clustering analyses and further classified into 17 significant cell populations by cell markers: pDCs, CD8 T cells, CD4 T cells, MigDCs, cDC2s, cDC1s, plasma cells, neutrophils, naive B cells, NK cells, memory B cells, M2 macrophages, CD8 Teffs, CD8 MAIT cells, CD4 Tregs, CD19 B cells, and monocytes. Further research showed that the presence of more cDC2 and M2 macrophages recruited at the focal site in patients with CSDH and the upregulation of the level of T-cell occupancy may be a red flag for further brain damage. ROS, a marker of oxidative stress, was significantly upregulated in cDC2 cells and may mediate the functioning of transcription proteins of inflammatory factors, such as NFκB, which induced T cells' activation. Moreover, cDC2 may regulate M2 macrophage immune infiltration and anti-inflammatory activity by secreting IL1β and binding to M2 macrophage IL1R protein. ConclusionThe detailed classification of cells in the peripheral blood and hematoma site of CSDH patients helps us to understand the mechanism of CSDH generation and the reduction in the probability of recurrence by regulating the ratio of cell subpopulations.

Chronic Viral Infection Compromises the Quality of Circulating Mucosal-Associated Invariant T Cells and Follicular T Helper Cells via Expression of Inhibitory Receptors.

Chronic viral infection results in impaired immune responses rendering viral persistence. Here, we compared the quality of T-cell responses among chronic hepatitis B virus (HBV), hepatitis C virus (HCV) and human immunodeficiency virus (HIV)-infected individuals by examining the levels of expression of selected immune activation and exhaustion molecules on circulating MAIT cells and Tfh cells. Cytokines were measured using a commercial Bio-plex Pro Human Cytokine Grp I Panel 17-plex kit (BioRad, Hercules, CA, USA). Inflammation was assessed by measuring an array of plasma cytokines, and phenotypic alterations in CD4+ T cells including circulating Tfh cells, CD8+ T cells, and TCR iVα7.2+ MAIT cells in chronic HBV, HCV, and HIV-infected patients and healthy controls. The cells were characterized based on markers pertaining to immune activation (CD69, ICOS, and CD27) proliferation (Ki67), cytokine production (TNF-α, IFN-γ) and exhaustion (PD-1). The cytokine levels and T cell phenotypes together with cell markers were correlated with surrogate markers of disease progression. The activation marker CD69 was significantly increased in CD4+hi T cells, while CD8+ MAIT cells producing IFN-γ were significantly increased in chronic HBV, HCV and HIV infections. Six cell phenotypes, viz., TNF-α+CD4+lo T cells, CD69+CD8+ T cells, CD69+CD4+ MAIT cells, PD-1+CD4+hi T cells, PD-1+CD8+ T cells, and Ki67+CD4+ MAIT cells, were independently associated with decelerating the plasma viral load (PVL). TNF-α levels showed a positive correlation with increase in cytokine levels and decrease in PVL. Chronic viral infection negatively impacts the quality of peripheral MAIT cells and Tfh cells via differential expression of both activating and inhibitory receptors.

Abstract 6708: MAIT engagers: Bispecific antibody-mediated redirection of mucosal associated invariant T cells to treat solid tumors

Abstract Background. Using bispecific antibodies (BiXAb) to redirect T cells to engage and kill cancer cells is an efficacious modality in the treatment of haematological cancers but has had limited success in the treatment of solid tumors. Mucosal-Associated Invariant T cells (MAITs) are an abundant subset of non-conventional T-cells with potent cytotoxic capacity (up to 20% of circulating T-cells) that are naturally resident in many tissues and solid tumors. MAIT cells utilize a semi-invariant TCR and recognize bacterial metabolites presented in the context of the MR1 protein. Biomunex has generated bispecific antibodies that bind the MAIT semi-invariant TCR (iTCR) and the HER2 receptor tyrosine kinase expressed on tumor cells. At difference to classical T-cell engagers that activate all T-cell subsets, MAIT engagers only modulate the activity of the cytotoxic MAIT cells leading to efficient tumor control and greater safety profile. Methods. Using the Biomunex proprietary BiXAb platform, bispecific, tetravalent antibodies were generated that target the MAIT iTCR and the HER2. MAIT-cell activation, proliferation and degranulation were followed by gating on MAIT cells within a purified CD8 cell population. Tumor cell lines (varying in [HER2] expression) were co-cultured with MAIT cells and the BiXAbs in several cytotoxic assays (evaluated by Chromium release). Cytokine release was assessed by Legend Plex assays or ELISA. Cytotoxicity of tumor-resident MAITs, from fresh patient samples, was determined by impedence measurements and in patient-derived 3D organoids by The Hub organoids (imaging). For in vivo analysis, sub-cutaneous tumor growth was measured with callipers. Results. MAIT engagers induce the rapid activation, proliferation and degranulation of MAIT cells leading to efficient killing of engaged HER2+ cancer cells with a potency similar to that of a classical HER2-directed TCE (in clinical development). The MAIT engager did not activate the regulatory T cells or other CD4/CD8 subsets. In addition, using PBMCs, total cytokine release was 1000-fold less with the MAIT engager compared to a classical TCE, opening up a large therapeutic window, which should permit effective treatment of solid tumors. Ex vivo cytotoxicity of tumor-resident MAIT cells using dissociated ovarian cancer samples at “real E:T ratios”, MAIT engager-mediated cytotoxicity of patient-derived organoids (CRC) and in vivo evaluation of tumor control will be shown. Conclusions. MAIT cell redirection is a promising approach for the treatment of solid tumors that has the potency and efficacy of a classical TCE but with a significantly improved cytokine safety profile leading to a larger therapeutic window. Citation Format: Simon Edward Plyte, Marie Fraudeau, Dorothee Winterberg, Claire Germain, Camille Rousseau, Gaetano Sodaro, Lise Fenou, Maxime Audin, Alexandre Ivagnes, Han-Heinrich Oberg, Pierre Emmanuel Gerard, Isabelle Navarro-Teulon, Daniela Wesch, Matthias Peipp, Julie Prigent. MAIT engagers: Bispecific antibody-mediated redirection of mucosal associated invariant T cells to treat solid tumors [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 6708.

Abstract 2062: Identification of functional MAIT-specific TCRs using MR1 dCODE Dextramer® reagents and evaluating antigen presentation

Abstract Objectives: To support TCR discovery and enable evaluation of TCR target expression on the surface of cells, we have established a streamlined workflow allowing TCR Discovery, validation and evaluation of MHC-antigen expression on target cells. As proof of concept, MR1 dCODE Dextramer® reagents were used to identify antigen-specific MAIT cells using single-cell sequencing, TCR sequences were extracted from the resulting data and then cloned and expressed as TCR monomers. The specificity of the TCRs was subsequently validated as TCR Dextramer® reagents and used to evaluate target MHC-peptide presentation on cell surface. Methods: Mixed PBMC samples from three healthy donors were stained with antibodies targeting relevant phenotypic markers as well as MR1 dCODE Dextramer® reagents carrying the MAIT cell-specific ligand 5-OP-RU. Following staining, sorting, and partitioning on a BD Rhapsody™ Single-Cell Analysis System, the cells underwent sequencing for a characterization of gene and surface marker expression as well as paired alpha-beta TCR sequences. Single alpha and beta chains were individually expressed, refolded together and purified. Refolded TCR monomer functionality was validated using an artificial cell assay. The functional TCRs can be multimerized on a Dextramer® backbone and used to evaluate expression of target on cell surface. Results: The majority of the identified CD161+ MAIT cells (~70%) expressed typical TCRs consisting of TRAV1-2 and TRAJ33 as well as TRBV6/20, TRBD1/2, and TRBJ2 gene segments. Three alpha-beta TCR sequences were selected: Two TCRs having common TRAV+TRAJ, TRBV+TRBJ combinations and one having a rare TRAV+TRAJ one. TCR alpha and beta chains were successfully expressed for all selected TCRs but only 2 TCRs showed a correctly refolded TCR as demonstrated by proper recognition of MR1/5-OP-RU. Based on these two functional TCRs, TCR Dextramer® reagents were generated and used to evaluate expression of target antigen on cell surface. Conclusion: We demonstrate a workflow allowing: (i) Identification of MAIT cells and their corresponding TCR sequences. (ii) Generation of soluble TCR molecules based on the identified sequences and validation of their specificity. (iii) Generation of TCR Dextramer® reagents allowing identification of target expression on surface of cells. This workflow is also useful for identification of other antigen-specific T cells and creates a new tool for evaluation of antigen-expression by MHC on surface of cells. By combining the high sensitivity of dCODE Dextramer® technology with TCR sequencing and creation of TCR Dextramer® reagents, both low-affinity interactions and rare cell types can be detected and studied in unique detail. Citation Format: Kevin Lenogue, Bjarke Hansen, Kivin Jacobsen, Liselotte Brix, Thomas Holberg Blicher. Identification of functional MAIT-specific TCRs using MR1 dCODE Dextramer® reagents and evaluating antigen presentation [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 2062.

Abstract 6724: Mechanistic validation of MAIT cell engagers in HUB patient-derived organoids (PDO) co-culture model

Abstract In the field of cancer immunotherapy, bispecific antibodies have emerged as a promising approach for redirecting T-cells to target and combat tumors. However, their efficacy is limited to only a subset of patients. A major challenge that hinders the development of bispecific antibody targets is the lack of preclinical models that preserve patient-specific tumor antigens and recapitulate the complex interaction between the human immune system and tumor cells. HUB Organoids technology presents a valuable platform for novel immunotherapies testing and validation as they are directly derived from patient tumor tissues, accurately reflecting patient-specific tumor antigens. BIOMUNEX Pharmaceuticals has developed the BiXAb® technology platform, a computational modeling approach that rapidly generates bispecific antibodies from various monospecific monoclonal antibodies, eliminating the need for extensive engineering. This platform includes a bivalent T cell engager specifically targeting MAIT cells and human epithelial growth factor receptor (HER2), a tumor antigen highly expressed in some colorectal cancer (CRC) patients. This innovative approach forms an efficient immunological synapse, allowing exclusive redirection of MAIT cells to directly eliminate cancer cells. In a collaborative research initiative between HUB Organoids® and BIOMUNEX Pharmaceuticals, the mechanisms by which BiXAb® induce tumor cell killing were confirmed using CRC patient-derived organoids (HUB Organoids® or PDOs) co-cultured with allogenic MAIT cells in an in vitro model. The study results depicted BiXAb® induced MAIT-cell activation in a dose-dependent manner, as detected by FACS and ELISA. Furthermore, BiXAb®-mediated MAIT-cell-specific killing of CRC PDOs was observed in a HER2-dependent manner, determined using an image-based viability assay. In conclusion, the co-culture platform of CRC PDOs-MAIT cells described here effectively captured the activation and targeted killing of MAIT cells mediated by BiXAb®, underscoring the added value of this PDO-based co-culture platform in developing novel immunotherapies. Citation Format: Yasmine Abouleila, Julie Prigent, Mayke Doorn, Claire Germain, Sylvia Boj, Simon Plyte, Carla Verissimo. Mechanistic validation of MAIT cell engagers in HUB patient-derived organoids (PDO) co-culture model [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 6724.

Abstract 4108: Safety and feasibility of personalized neoantigen DC vaccines in postoperative esophagus squamous cell carcinoma: A Phase 1b trial

Abstract Background: Immunotherapy, currently stands at the forefront of esophagus squamous cell carcinoma (ESCC) research. Yet, the landscape of post-surgical adjuvant therapy, particularly for patients resistant or unresponsive to initial immunotherapy, remains unexplored. Addressing this, our prospective study evaluates the efficacy of a personalized neoantigen-loaded dendritic cell vaccine (Neo-DCVac) as a novel adjuvant in ESCC patients after neoadjuvant immunochemotherapy (nICT). Methods: Neo-DCVac, designed for 12 ESCC patients post-radical mastectomy following nICT. The vaccine regimen included five doses at weeks 1, 2, 4, 6, and 8, followed by bi-monthly boosts for a year. The primary endpoints were safety and immune response post-vaccination, with 1- and 2-year overall survival (OS) and progression-free survival as secondary endpoints. The T-cell response to neoantigen peptides was evaluated using ELISPOT, flow cytometry, ELISA, and single-cell sequencing to investigate the vaccine's mechanism of action. Results: From April 2021 to October 2023, a total of 12 ESCC patients were enrolled. The occurrence of all-grade AEs was 38.5% (5/12), all of grade 1-2, with no dose-limiting toxicities. No treatment interruptions or treatment-related deaths were observed. Till October 27 2023, the median follow-up was 31.2 months. Survival analysis revealed 1-year and 2-year disease-free survival (DFS) and overall survival(OS) rates of 88.3%, 66.7%, and 100.0%, 91.7%, respectively. Patients with diver genes had a longer median DFS (not reached) compared with patients without diver genes (10.8 months, P = 0.001). Post-vaccine immunization, all patients showed a marked increase in peripheral blood T cell subtypes (CD3, CD4, CD8), with significant neoantigen peptide response in 75% (9/12) as evidenced by ELISPOT and ELISA tests. Single-cell sequencing coupled with CoNGA analysis revealed a distinct MAIT cell population, displaying 65 clonotypes and 146 cells with consistent GEX profiles and TCR sequences. GLIPH2 analysis on Neo-Vac immunotherapy patients identified shared peptide-MHC specificities, notably in patient ES0-01, and similar patterns in patients ES0-04 and ES0-07, suggesting T cell expansion and neoantigen-specific responses post-vaccination. Conclusions: The neoantigen DC vaccine demonstrated favorable safety and exhibited notable efficacy in ESCC. Clinical trial information: NCT05023928. Research Sponsor: No. Citation Format: Yueyun Chen, Hua-Shan Shi, Yang Hu, Yong Yuan, Yu-Shang Yang, Heng Xu, Li Yang, Zhen-Yu Ding. Safety and feasibility of personalized neoantigen DC vaccines in postoperative esophagus squamous cell carcinoma: A Phase 1b trial [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 4108.

Cytotoxic CD8+ Temra cells show loss of chromatin accessibility at genes associated with T cell activation.

As humans age, their memory T cell compartment expands due to the lifelong exposure to antigens. This expansion is characterized by terminally differentiated CD8+ T cells (Temra), which possess NK cell-like phenotype and are associated with chronic inflammatory conditions. Temra cells are predominantly driven by the sporadic reactivation of cytomegalovirus (CMV), yet their epigenomic patterns and cellular heterogeneity remain understudied. To address this gap, we correlated their gene expression profiles with chromatin openness and conducted single-cell transcriptome analysis, comparing them to other CD8+ subsets and CMV-responses. We confirmed that Temra cells exhibit high expression of genes associated with cytotoxicity and lower expression of costimulatory and chemokine genes. The data revealed that CMV-responsive CD8+ T cells (Tcmv) were predominantly derived from a mixed population of Temra and memory cells (Tcm/em) and shared their transcriptomic profiles. Using ATAC-seq analysis, we identified 1449 differentially accessible chromatin regions between CD8+ Temra and Tcm/em cells, of which only 127 sites gained chromatin accessibility in Temra cells. We further identified 51 gene loci, including costimulatory CD27, CD28, and ICOS genes, whose chromatin accessibility correlated with their gene expression. The differential chromatin regions Tcm/em cells were enriched in motifs that bind multiple transcriptional activators, such as Jun/Fos, NFkappaB, and STAT, whereas the open regions in Temra cells mainly contained binding sites of T-box transcription factors. Our single-cell analysis of CD8+CCR7loCD45RAhi sorted Temra population showed several subsets of Temra and NKT-like cells and CMC1+ Temra populations in older individuals that were shifted towards decreased cytotoxicity. Among CD8+CCR7loCD45RAhi sorted cells, we found a decreased proportion of IL7R+ Tcm/em-like and MAIT cells in individuals with high levels of CMV antibodies (CMVhi). These results shed new light on the molecular and cellular heterogeneity of CD8+ Temra cells and their relationship to aging and CMV infection.

Human MAIT cells inhibit alloreactive T cell responses and protect against acute graft-versus-host disease.

Adoptive transfer of immunoregulatory cells can prevent or ameliorate graft-versus-host disease (GVHD), which remains the main cause of nonrelapse mortality after allogeneic hematopoietic stem cell transplantation. Mucosal-associated invariant T (MAIT) cells were recently associated with tissue repair capacities and with lower rates of GVHD in humans. Here, we analyzed the immunosuppressive effect of MAIT cells in an in vitro model of alloreactivity and explored their adoptive transfer in a preclinical xenogeneic GVHD model. We found that MAIT cells, whether freshly purified or short-term expanded, dose-dependently inhibited proliferation and activation of alloreactive T cells. In immunodeficient mice injected with human PBMCs, MAIT cells greatly delayed GVHD onset and decreased severity when transferred early after PBMC injection but could also control ongoing GVHD when transferred at delayed time points. This effect was associated with decreased proliferation and effector function of human T cells infiltrating tissues of diseased mice and was correlated with lower circulating IFN-γ and TNF-α levels and increased IL-10 levels. MAIT cells acted partly in a contact-dependent manner, which likely required direct interaction of their T cell receptor with MHC class I-related molecule (MR1) induced on host-reactive T cells. These results support the setup of clinical trials using MAIT cells as universal therapeutic tools to control severe GVHD or mucosal inflammatory disorders.

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Transient MAIT Cell Recovery after Severe COVID-19 See article p. 389 Tim-3 and CD8+ T Cell Memory See article p. 466

MAIT cells play a role in liver tissue repair via growth factor secretion

MAIT cells play a role in liver tissue repair via growth factor secretion

Single Cell Rnaseq Identifies Chemokine Responses to BK Polyomavirus Infection and Novel Contribution of MAIT Cells

Single Cell Rnaseq Identifies Chemokine Responses to BK Polyomavirus Infection and Novel Contribution of MAIT Cells

KLRB1-high and GNLY-low MAIT Cells Are Enriched in Severe Sarcoidosis

KLRB1-high and GNLY-low MAIT Cells Are Enriched in Severe Sarcoidosis

A Novel Homozygous Germline Mutation in Transferrin Receptor 1 (TfR1) Leads to Combined Immunodeficiency and Provides New Insights into Iron-Immunity Axis

A homozygous missense mutation in the transferrin receptor 1 (TfR1), also known as CD71, leads to a rare inborn error of immunity (IEI) characterized by the impaired lymphocyte activation and proliferation due to defective iron uptake of cells. However, only one causative mutation (c.58T > C, p.Y20H) in the TFRC gene coding for TfR1 has been reported so far. We herein identified a new disease-causing homozygous germline mutation in the TFRC gene (c.64C > T, p.R22W) (referred to as TfR1R22W from now on) in a Turkish patient with combined immunodeficiency (CID). TfR1R22W results in impaired TfR1 internalization similar to previously defined TfR1Y20H mutation. We found that TfR1R22W is associated with severely restricted B and T lymphocyte clonal diversity and impaired T cell activation and cytokine production as well as defective mitochondrial oxidative phosphorylation in helper T cells. In addition, circulating NK, Treg, and MAIT cell populations were significantly decreased in the patient. Using whole transcriptome analysis, we found dysregulated immune homeostasis and novel biological processes associated with TfR1R22W. We also identified a considerable expansion of circulating low-density neutrophils (LDNs) in patient’s PBMCs. Overall, TfR1R22W mutation expands the current understanding of the IEI associated with TfR1 dysfunction and provides new insights underlying impaired immune function, lymphocyte diversity, and granulocyte homeostasis.

Mucosal-Associated Invariant T Cells are not susceptible in vitro to SARS-CoV-2 infection but accumulate into the lungs of COVID-19 patients

Prolonged T cell lymphopenia is common in COVID-19, caused by SARS-CoV-2. While the mechanisms of lymphopenia during COVID-19 remain elusive, it is especially pronounced in a specialized innate-like T cell population called Mucosal Associated Invariant T cells (MAITs). MAITs has been suggested to express Angiotensin-Converting Enzyme 2 (ACE2), which is the well-known cellular receptor for SARS-CoV-2. However, it is still unclear if SARS-CoV-2 can infect or affect MAIT cells directly. In this study, we performed multicolor flow cytometry on peripheral blood mononuclear cells obtained from COVID-19 patients to assess the frequencies of CD8+Vα7.2+CD161+ MAIT subsets at acute and convalescent disease phases. The susceptibility of MAITs and T cells to direct exposure by SARS-CoV-2 was analysed using cells isolated from healthy donor buffy coats by viability assays, virus-specific RT-PCR, and flow cytometry. In situ lung immunofluorescence was used to evaluate retention of T cells, especially MAIT cells, in lung tissues during acute COVID-19. Our study confirms previous reports indicating that circulating MAITs are activated, and their frequency is declined in patients with acute SARS-CoV-2 infection, whereas an accumulation of MAITs and T cells was seen in the lung tissue of individuals with fatal COVID-19. However, despite a fraction of MAITs found to express ACE2, no evidence for the susceptibility of MAITs for direct infection or activation by SARS-CoV-2 particles was observed. Thus, their activation and decline in the circulation is most likely explained by indirect mechanisms involving other immune cells and cytokine-induced pro-inflammatory environment but not by direct exposure to viral particles at the infection site.

The Plasticity of Immune Cell Response Complicates Dissecting the Underlying Pathology of Multiple Sclerosis.

Multiple sclerosis (MS) is a neurodegenerative autoimmune disease characterized by the destruction of the myelin sheath of the neuronal axon in the central nervous system. Many risk factors, including environmental, epigenetic, genetic, and lifestyle factors, are responsible for the development of MS. It has long been thought that only adaptive immune cells, especially autoreactive T cells, are responsible for the pathophysiology; however, recent evidence has indicated that innate immune cells are also highly involved in disease initiation and progression. Here, we compile the available data regarding the role immune cells play in MS, drawn from both human and animal research. While T and B lymphocytes, chiefly enhance MS pathology, regulatory T cells (Tregs) may serve a more protective role, as can B cells, depending on context and location. Cells chiefly involved in innate immunity, including macrophages, microglia, astrocytes, dendritic cells, natural killer (NK) cells, eosinophils, and mast cells, play varied roles. In addition, there is evidence regarding the involvement of innate-like immune cells, such as γδ T cells, NKT cells, MAIT cells, and innate-like B cells as crucial contributors to MS pathophysiology. It is unclear which of these cell subsets are involved in the onset or progression of disease or in protective mechanisms due to their plastic nature, which can change their properties and functions depending on microenvironmental exposure and the response of neural networks in damage control. This highlights the need for a multipronged approach, combining stringently designed clinical data with carefully controlled in vitro and in vivo research findings, to identify the underlying mechanisms so that more effective therapeutics can be developed.

A comprehensive battery of flow cytometric immunoassays for the in vitro testing of chemical effects in human blood cells.

There is a growing need for immunological assays to test toxic and modulatory effects of chemicals. The assays should be easy to use, reproducible and superior to cell line-based assays. We have therefore developed a comprehensive portfolio of assays based on primary human blood cells that are suitable for testing chemical effects. The flow cytometry-based assays were designed to target a wide range of human peripheral blood mononuclear cells and whole blood, including T cells, NK cells, B cells, basophils and innate-like T cells such as γδT, MAIT and NKT cells. We have selected a set of activation markers for each immune cell, e.g: CD154 (T cells), CD137, CD107a (NK cells), CD63 (basophils), CD69, CD83 (B cells), CD69, IFN-γ (MAIT cells) and we selected cell specific stimuli: aCD3 antibodies (T cells); E. coli and cytokines IL-12/15/18 (MAIT cells); CpG ODN2006, R848 or aCD40 antibodies (B cells), fMLP or aFcϵR1 (basophils) or K562 cells (NK cells). By selecting immune cell-specific markers and cell-specific stimuli, we were able to induce particular immune responses from the targeted immune cells. For example, the response to stimulation with anti-CD3 antibodies was in 36.8% of CD107a+CD8+ cells. Cytokine stimulation induced the production of IFN-γ in 30% of MAIT cells. After stimulation with E. coli, around 50% of MAIT cells produced TNF. About 40% of basophils responded to aFcƐR1 stimulation. Similar activation ranges were achieved in K562-stimulated NK cells. Our test portfolio covers the most relevant immune cells present in human blood, providing a solid basis for in vitro toxicity and immunomodulatory testing of chemicals. By using human blood, the natural composition of cells found in the blood can be determined and the effects of chemicals can be detected at the cellular level.

Thymic development of human natural killer T cells: recent advances and implications for immunotherapy.

Invariant natural killer T (iNKT) cells are a subset of lipid-reactive, unconventional T cells that have anti-tumor properties that make them a promising target for cancer immunotherapy. Recent studies have deciphered the developmental pathway of human MAIT and Vγ9Vδ2 γδ-T cells as well as murine iNKT cells, yet our understanding of human NKT cell development is limited. Here, we provide an update in our understanding of how NKT cells develop in the human body and how knowledge regarding their development could enhance human treatments by targeting these cells.