A Retrospective Analysis of Leadership, Awardees, and Member Gender Representation of the Canadian Society for Immunology.

The Canadian Society for Immunology (CSI) established a formal Equity, Diversity, and Inclusion (EDI) Committee with the goal of providing EDI advocacy and leadership within the CSI, as well as in the broader scientific community. A first task of this committee was to review the publicly available historical data on gender representation within the CSI's membership, leadership, award recipients, and conference chairs/presenters as a step in establishing a baseline reference point and monitoring the trajectory of future success in achieving true inclusion. We found that, except for overall membership and a specific subset of awards, all categories showed a historical bias toward men, particularly prior to 2010. Bias persists in various categories, evident even in recent years. However, we note an encouraging trend toward greater gender parity, particularly in the roles of President, symposium presenters, and workshop chairs, especially from 2017 onward. We present these findings as well as our recommendations to enhance inclusivity. These include a more comprehensive collection and secure storage of self-identification data, emphasis on EDI as an essential component of all annual meeting activities, and innovative measures of outreach, collaboration, and leadership with the aim of making the CSI a model for improving EDI in other professional research societies.

Fecal microbiota transplantation plus anti-PD-1 immunotherapy in advanced melanoma: a phase I trial.

Fecal microbiota transplantation (FMT) represents a potential strategy to overcome resistance to immune checkpoint inhibitors in patients with refractory melanoma; however, the role of FMT in first-line treatment settings has not been evaluated. We conducted a multicenter phase I trial combining healthy donor FMT with the PD-1 inhibitors nivolumab or pembrolizumab in 20 previously untreated patients with advanced melanoma. The primary end point was safety. No grade 3 adverse events were reported from FMT alone. Five patients (25%) experienced grade 3 immune-related adverse events from combination therapy. Key secondary end points were objective response rate, changes in gut microbiome composition and systemic immune and metabolomics analyses. The objective response rate was 65% (13 of 20), including four (20%) complete responses. Longitudinal microbiome profiling revealed that all patients engrafted strains from their respective donors; however, the acquired similarity between donor and patient microbiomes only increased over time in responders. Responders experienced an enrichment of immunogenic and a loss of deleterious bacteria following FMT. Avatar mouse models confirmed the role of healthy donor feces in increasing anti-PD-1 efficacy. Our results show that FMT from healthy donors is safe in the first-line setting and warrants further investigation in combination with immune checkpoint inhibitors. ClinicalTrials.gov identifier NCT03772899 .

Targeting the MR1-MAIT cell axis improves vaccine efficacy and affords protection against viral pathogens.

Mucosa-associated invariant T (MAIT) cells are MR1-restricted, innate-like T lymphocytes with tremendous antibacterial and immunomodulatory functions. Additionally, MAIT cells sense and respond to viral infections in an MR1-independent fashion. However, whether they can be directly targeted in immunization strategies against viral pathogens is unclear. We addressed this question in multiple wild-type and genetically altered but clinically relevant mouse strains using several vaccine platforms against influenza viruses, poxviruses and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We demonstrate that 5-(2-oxopropylideneamino)-6-D-ribitylaminouracil (5-OP-RU), a riboflavin-based MR1 ligand of bacterial origin, can synergize with viral vaccines to expand MAIT cells in multiple tissues, reprogram them towards a pro-inflammatory MAIT1 phenotype, license them to bolster virus-specific CD8+ T cell responses, and potentiate heterosubtypic anti-influenza protection. Repeated 5-OP-RU administration did not render MAIT cells anergic, thus allowing for its inclusion in prime-boost immunization protocols. Mechanistically, tissue MAIT cell accumulation was due to their robust proliferation, as opposed to altered migratory behavior, and required viral vaccine replication competency and Toll-like receptor 3 and type I interferon receptor signaling. The observed phenomenon was reproducible in female and male mice, and in both young and old animals. It could also be recapitulated in a human cell culture system in which peripheral blood mononuclear cells were exposed to replicating virions and 5-OP-RU. In conclusion, although viruses and virus-based vaccines are devoid of the riboflavin biosynthesis machinery that supplies MR1 ligands, targeting MR1 enhances the efficacy of vaccine-elicited antiviral immunity. We propose 5-OP-RU as a non-classic but potent and versatile vaccine adjuvant against respiratory viruses.

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.

Monovalent and trivalent VSV-based COVID-19 vaccines elicit neutralizing antibodies and CD8+ T cells against SARS-CoV-2 variants.

Recombinant vesicular stomatitis virus (rVSV) vaccines expressing spike proteins of Wuhan, Beta, and/or Delta variants of SARS-CoV-2 were generated and tested for induction of antibody and T cell immune responses following intramuscular delivery to mice. rVSV-Wuhan and rVSV-Delta vaccines and an rVSV-Trivalent (mixed rVSV-Wuhan, -Beta, -Delta) vaccine elicited potent neutralizing antibodies (nAbs) against live SARS-CoV-2 Wuhan (USAWA1), Beta (B.1.351), Delta (B.1.617.2), and Omicron (B.1.1.529) viruses. Prime-boost vaccination with rVSV-Beta was less effective in this capacity. Heterologous boosting of rVSV-Wuhan with rVSV-Delta induced strong nAb responses against Delta and Omicron viruses, with the rVSV-Trivalent vaccine consistently effective in inducing nAbs against all the SARS-CoV-2 variants tested. All vaccines, including rVSV-Beta, elicited a spike-specific immunodominant CD8+ T cell response. Collectively, rVSV vaccines targeting SARS-CoV-2 variants of concern may be considered in the global fight against COVID-19.

Improved MAIT cell functions following fecal microbiota transplantation for metastatic renal cell carcinoma.

Strategies to modify the gut microbiome in cancer patients using fecal microbiota transplantation (FMT) have gained momentum as a therapeutic intervention. However, how FMT impacts innate-like, antimicrobial T lymphocytes is unclear. In this study, we assessed peripheral blood (PB) mucosa-associated invariant T (MAIT) cell frequencies and functions in patients with metastatic renal cell carcinoma (mRCC) before and seven days after they received FMT as part of a clinical trial. We found comparable MAIT cell frequencies in healthy controls and mRCC patients. In contrast, γδ T cells exhibited a numerical decline in mRCC, which was partially reversed by FMT. We also found a significant increase in the PB CD4+ MAIT cell compartment of mRCC patients with or without FMT. Paired sample analyses revealed CD69 upregulation on MAIT cells accompanied by decreased PD-1 levels post-FMT. These changes were unique to MAIT cells as non-MAIT T lymphocytes showed either no trend or a trend in the opposite direction. Importantly, FMT did not render MAIT cells exhausted as also judged by their stable expression of TIM-3, LAG-3, BTLA, CTLA-4, TIGIT and VISTA. These findings were corroborated in functional assays in which MAIT cells were stimulated with MR1 ligands or with a combination of IL-12 and IL-18 to produce inflammatory cytokines and granzyme B. Indeed, when stimulated ex vivo with IL-12 and IL-18, MAIT cells mounted a more rigorous TNF-α response post-FMT. In conclusion, FMT improves MAIT cell functions, which should serve patients well in subsequent microbial challenges in the face of cancer-elicited immunosuppression. Trial Registration: https://clinicaltrials.gov/ Identifier: NCT04163289 (registration date: November 14, 2019).

Correction: A vesicular stomatitis virus-based prime-boost vaccination strategy induces potent and protective neutralizing antibodies against SARS-CoV-2.

[This corrects the article DOI: 10.1371/journal.ppat.1010092.].

B cell-T cell interplay in immune regulation: A focus on follicular regulatory T and regulatory B cell functions.

B cells are the core components of humoral immunity. A mature B cell can serve in multiple capacities, including antibody production, antigen presentation, and regulatory functions. Forkhead box P3 (FoxP3)-expressing regulatory T cells (Tregs) are key players in sustaining immune tolerance and keeping inflammation in check. Mounting evidence suggests complex communications between B cells and Tregs. In this review, we summarize the yin-yang regulatory relationships between B cells and Tregs mainly from the perspectives of T follicular regulatory (Tfr) cells and regulatory B cells (Bregs). We discuss the regulatory effects of Tfr cells on B cell proliferation and the germinal center response. Additionally, we review the indispensable role of B cells in ensuring homeostatic Treg survival and describe the function of Bregs in promoting Treg responses. Finally, we introduce a new subset of Tregs, termed Treg-of-B cells, which are induced by B cells, lake the expression of FoxP3 but still own immunomodulatory effects. In this article, we also enumerate a sequence of research from clinical patients and experimental models to clarify the role of Tfr cells in germinal centers and the role of convention B cells and Bregs to Tregs in the context of different diseases. This review offers an updated overview of immunoregulatory networks and unveils potential targets for therapeutic interventions against cancer, autoimmune diseases and allograft rejection.

MAIT cells accumulate in ovarian cancer-elicited ascites where they retain their capacity to respond to MR1 ligands and cytokine cues.

The low mutational burden of epithelial ovarian cancer (EOC) is an impediment to immunotherapies that rely on conventional MHC-restricted, neoantigen-reactive T lymphocytes. Mucosa-associated invariant T (MAIT) cells are MR1-restricted T cells with remarkable immunomodulatory properties. We sought to characterize intratumoral and ascitic MAIT cells in EOC. Single-cell RNA sequencing of six primary human tumor specimens demonstrated that MAIT cells were present at low frequencies within several tumors. When detectable, these cells highly expressed CD69 and VSIR, but otherwise exhibited a transcriptomic signature inconsistent with overt cellular activation and/or exhaustion. Unlike mainstream CD8+ T cells, CD8+ MAIT cells harbored high transcript levels of TNF, PRF1, GZMM and GNLY, suggesting their arming and cytotoxic potentials. In a congenic, MAIT cell-sufficient mouse model of EOC, MAIT and invariant natural killer T cells amassed in the peritoneal cavity where they showed robust IL-17A and IFN-γ production capacities, respectively. However, they gradually lost these functions with tumor progression. In a cohort of 23 EOC patients, MAIT cells were readily detectable in all ascitic fluids examined. In a sub-cohort in which we interrogated ascitic MAIT cells for functional impairments, several exhaustion markers, most notably VISTA, were present on the surface. However, ascitic MAIT cells were capable of producing IFN-γ, TNF-α and granzyme B, but neither IL-17A nor IL-10, in response to an MR1 ligand, bacterial lysates containing MR1 ligands, or a combination of IL-12 and IL-18. In conclusion, ascitic MAIT cells in EOC possess inducible effector functions that may be modified in future immunotherapeutic strategies.

A vesicular stomatitis virus-based prime-boost vaccination strategy induces potent and protective neutralizing antibodies against SARS-CoV-2.

The development of safe and effective vaccines to prevent SARS-CoV-2 infections remains an urgent priority worldwide. We have used a recombinant vesicular stomatitis virus (rVSV)-based prime-boost immunization strategy to develop an effective COVID-19 vaccine candidate. We have constructed VSV genomes carrying exogenous genes resulting in the production of avirulent rVSV carrying the full-length spike protein (SF), the S1 subunit, or the receptor-binding domain (RBD) plus envelope (E) protein of SARS-CoV-2. Adding the honeybee melittin signal peptide (msp) to the N-terminus enhanced the protein expression, and adding the VSV G protein transmembrane domain and the cytoplasmic tail (Gtc) enhanced protein incorporation into pseudotype VSV. All rVSVs expressed three different forms of SARS-CoV-2 spike proteins, but chimeras with VSV-Gtc demonstrated the highest rVSV-associated expression. In immunized mice, rVSV with chimeric S protein-Gtc derivatives induced the highest level of potent neutralizing antibodies and T cell responses, and rVSV harboring the full-length msp-SF-Gtc proved to be the superior immunogen. More importantly, rVSV-msp-SF-Gtc vaccinated animals were completely protected from a subsequent SARS-CoV-2 challenge. Overall, we have developed an efficient strategy to induce a protective response in SARS-CoV-2 challenged immunized mice. Vaccination with our rVSV-based vector may be an effective solution in the global fight against COVID-19.

Physical restraint mouse models to assess immune responses under stress with or without habituation.

Physical confinement, or restraint, is a psychological stressor used in rodent studies. A single restraint episode elevates blood corticosterone levels, a hallmark of stress responses. Repeated restraint results in habituation (or desensitization), whereas chronic exposure to unpredictable stressors fails to induce habituation. Here, we provide our protocols and guidelines in using three mouse restraint models, namely prolonged restraint stress, repeated restraint stress, and chronic variable stress, to examine immunological homeostasis/competence, or lack thereof, under stress with or without habituation. For complete information on the generation and use of these protocols, please refer to Rudak et al. (2021).

In Vivo Cytotoxicity by α-GalCer-transactivated NK Cells.

Invariant natural killer T (iNKT) cells are innate-like, lipid-reactive T lymphocytes known for their potent immunomodulatory properties. In addition to expressing and utilizing cytolytic effector molecules of their own against certain target cells, iNKT cells can be stimulated with α-galactosylceramide (α-GalCer) to augment the cytotoxic capacity of natural killer (NK) cells. Herein, we describe a flow cytometry-based in vivo killing assay that enables examination of α-GalCer-promoted cytotoxicity against ß2 microglobulin knockout (ß2M-/-) target cells, which mimic tumor and virus-infected cells displaying little to no MHC class I molecules on their surface. Using an anti-asialo GM1 antibody, which depletes NK cells but not iNKT cells, we confirmed that the increased clearance of ß2M-/- cells in α-GalCer-primed recipients was mediated by NK cells. The protocol detailed here can be leveraged to assess the functional fitness of iNKT cells and their crosstalk with NK cells and to further our understanding of α-GalCer-promoted cytotoxicity in preclinical immunotherapeutic applications.

The HIV-1 accessory protein Nef increases surface expression of the checkpoint receptor Tim-3 in infected CD4+ T cells.

Prolonged immune activation drives the upregulation of multiple checkpoint receptors on the surface of virus-specific T cells, inducing their exhaustion. Reversing HIV-1-induced T cell exhaustion is imperative for efficient virus clearance; however, viral mediators of checkpoint receptor upregulation remain largely unknown. The enrichment of checkpoint receptors on T cells upon HIV-1 infection severely constrains the generation of an efficient immune response. Herein, we examined the role of HIV-1 Nef in mediating the upregulation of checkpoint receptors on peripheral blood mononuclear cells. We demonstrate that the HIV-1 accessory protein Nef upregulates cell surface levels of the checkpoint receptor T-cell immunoglobulin mucin domain-3 (Tim-3) and that this is dependent on Nef's dileucine motif LL164/165. Furthermore, we used a bimolecular fluorescence complementation assay to demonstrate that Nef and Tim-3 form a complex within cells that is abrogated upon mutation of the Nef dileucine motif. We also provide evidence that Nef moderately promotes Tim-3 shedding from the cell surface in a dileucine motif-dependent manner. Treating HIV-1-infected CD4+ T cells with a matrix metalloprotease inhibitor enhanced cell surface Tim-3 levels and reduced Tim-3 shedding. Finally, Tim-3-expressing CD4+ T cells displayed a higher propensity to release the proinflammatory cytokine interferon-gamma. Collectively, our findings uncover a novel mechanism by which HIV-1 directly increases the levels of a checkpoint receptor on the surface of infected CD4+ T cells.

Chronic stress physically spares but functionally impairs innate-like invariant T cells.

The deleterious effects of psychological stress on mainstream T lymphocytes are well documented. However, how stress impacts innate-like T cells is unclear. We report that long-term stress surprisingly abrogates both T helper 1 (TH1)- and TH2-type responses orchestrated by invariant natural killer T (iNKT) cells. This is not due to iNKT cell death because these cells are unusually refractory to stress-inflicted apoptosis. Activated iNKT cells in stressed mice exhibit a "split" inflammatory signature and trigger sudden serum interleukin-10 (IL-10), IL-23, and IL-27 spikes. iNKT cell dysregulation is mediated by cell-autonomous glucocorticoid receptor signaling and corrected upon habituation to predictable stressors. Importantly, under stress, iNKT cells fail to potentiate cytotoxicity against lymphoma or to reduce the burden of metastatic melanoma. Finally, stress physically spares mouse mucosa-associated invariant T (MAIT) cells but hinders their TH1-/TH2-type responses. The above findings are corroborated in human peripheral blood and hepatic iNKT/MAIT cell cultures. Our work uncovers a mechanism of stress-induced immunosuppression.

Harnessing the Versatility of Invariant NKT Cells in a Stepwise Approach to Sepsis Immunotherapy.

Sepsis results from a heavy-handed response to infection that may culminate in organ failure and death. Many patients who survive acute sepsis become immunosuppressed and succumb to opportunistic infections. Therefore, to be successful, sepsis immunotherapies must target both the initial and the protracted phase of the syndrome to relieve early immunopathology and late immunosuppression, respectively. Invariant NKT (iNKT) cells are attractive therapeutic targets in sepsis. However, repeated treatments with α-galactosylceramide, the prototypic glycolipid ligand of iNKT cells, result in anergy. We designed a double-hit treatment that allows iNKT cells to escape anergy and exert beneficial effects in biphasic sepsis. We tested the efficacy of this approach in the sublethal cecal ligation and puncture mouse model, which mirrors polymicrobial sepsis with progression to an immunosuppressed state. Septic mice were treated with [(C2S, 3S, 4R)-1-O-(α-d-galactopyranosyl)-N-tetracosanoyl-2-amino-1,3,4-nonanetriol] (OCH), a TH2-polarizing iNKT cell agonist, before they received α-galactosylceramide. This regimen reduced the morbidity and mortality of cecal ligation and puncture, induced a transient but robust IFN-γ burst within a proinflammatory cytokine/chemokine landscape, transactivated NK cells, increased MHC class II expression on macrophages, and restored delayed-type hypersensitivity to a model hapten, consistent with recovery of immunocompetence in protracted sepsis. Structurally distinct TH2-polarizing agonists varied in their ability to replace OCH as the initial hit, with their lipid chain length being a determinant of efficacy. The proposed approach effectively exploits iNKT cells' versatility in biphasic sepsis and may have translational potentials in the development of new therapies.

Measles Virus Infects and Programs MAIT Cells for Apoptosis.

Measles virus (MeV) binds, infects, and kills CD150+ memory T cells, leading to immune amnesia. Whether MeV targets innate, memory-like T cells is unknown. We demonstrate that human peripheral blood and hepatic mucosa-associated invariant T (MAIT) cells and invariant natural killer T cells express surprisingly high levels of CD150, more than other lymphocyte subsets. Furthermore, exposing MAIT cells to MeV results in their efficient infection and rapid apoptosis. This constitutes the first report of direct MAIT cell infection by a viral pathogen. Given MAIT cells' antimicrobial properties, their elimination by MeV may contribute to measles-induced immunosuppression and heightened vulnerability to unrelated infections.