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MR1 is a conserved molecule that binds microbial vitamin B metabolites and presents them to unconventional T cells. Lim and colleagues (2022. J. Cell Biol.https://doi.org/10.1083/jcb.202110125) uncover the role of AP2 in ensuring MR1 surface presentation, which relies on an atypical motif within the MR1 cytoplasmic tail.

The antigen presenting molecule, MR1, presents microbial metabolites to MAIT cells, a population of innate-like, anti-microbial T cells. It also presents an unidentified ligand to MR-1 restricted T cells in the setting of cancer. The cellular co-factors that mediate MR1 antigen presentation have yet to be fully defined. We performed a mass spectrometry-based proteomics screen to identify MR1 interacting proteins and identified the selective autophagy receptor SQSTM1/p62. CRISPR-Cas9-mediated knock out of SQSTM1/p62 increased MAIT cell activation in the presence of E.coli but not the synthetic ligand 5-OP-RU whereas depletion of Atg5 and Atg7, key autophagy proteins, increased MAIT activation irrespective of the ligand used. This regulation appears to occur at an early step in the trafficking pathway. This data implicates distinct roles for autophagy associated proteins in the regulation of MR1 activity and highlights the autophagy pathway as a key regulator of cellular antigen presentation.

SummaryIt is unclear whether prior endemic coronavirus infections affect COVID-19 severity. Here, we show that in cases of fatal COVID-19, antibody responses to the SARS-COV-2 spike are directed against epitopes shared with endemic beta-coronaviruses in the S2 subunit of the SARS-CoV-2 spike protein. This immune response is associated with the compromised production of ade novoSARS-CoV-2 spike response among individuals with fatal COVID-19 outcomes.

It is unclear whether prior endemic coronavirus infections affect COVID-19 severity. Here, we show that in cases of fatal COVID-19, antibody responses to the SARS-COV-2 spike are directed against epitopes shared with endemic beta-coronaviruses in the S2 subunit of the SARS-CoV-2 spike protein. This immune response is associated with the compromised production of a de novo SARS-CoV-2 spike response among individuals with fatal COVID-19 outcomes. Funding: This work was supported by the Georg and Emily von Opel Foundation, the National Institute for Health Research (NIHR) [award CO-­‐CIN-­‐01], the Medical Research Council [grant MC_PC_19059], ME was supported by The Leona M. and Harry B. Helmsley Charitable Trust on May 31, 2021 for the project titled, "ICARUS –IBD: International study of COVID-­‐19 Antibody Response Under Sustained immune suppression in Inflammatory Bowel Disease. RP also supported by funds provided under Professor RW Snow’s Wellcome Trust Principal Fellowship (# 212176). Meso Scale Diagnostics (USA) provided loan of equipment, reagents and technical support. JSB was supported by funding from the Biotechnology and Biological Sciences Research Council (BBSRC) [grant number BB/M011224/1]. CPT was funded by an ERC research grant UNIFLUVAC’ and two MRC CiC grants (Ref: BR00140). ALM is funded by a NIHR Research Capability Funding grant. HJK is supported by The Future of Humanity Institute at the University of Oxford DPhil Scholarship program. DE is funded by the Robertson Foundation. The funders played no role in the design, execution or reporting of the study. Declaration of Interest: DE declares lecture fees from Gilead. CPT and SG hold funding from Blue Water Vaccines. All others have nothing to disclose. Ethical Approval: Ethical approval was obtained for the Scottish National Blood Transfusion Service (SNBTS) anonymous archive -­‐ IRAS project number 18005. SNBTS blood donors gave fully informed consent to virological testing, donation was made under the SNBTS Blood Establishment Authorisation and the study was approved by the SNBTS Research and Sample Governance Committee.

Item description: Chapter 7 in book 'MAIT Cells' (2020), ed H Kaipe and I Magalhaes. Methods in Molecular Biology, volume 2098. Mucosal-associated invariant T (MAIT) cells are an abundant innate-like T cell subset in humans, enriched in mucosal tissues and the liver. MAIT cells express a semi-invariant T cell receptor (TCR) and recognize microbial-derived riboflavin metabolites presented on the MHC Class I-like molecule MR1. In addition to activation via the TCR, MAIT cells can also be activated in response to cytokines such as IL-12 and IL-18, in contrast to conventional T cells. Here we describe TCR-dependent and -independent methods for MAIT cell activation. The TCR-dependent approaches include stimulation with microbead- or plate-bound anti-CD3/anti-CD28 antibodies, and with 5-OP-RU or paraformaldehyde (PFA)-fixed E. coli in the presence of antigen-presenting cells (APCs). The latter method includes a combination of TCR- and cytokine-mediated stimulation. The TCR-independent methods include direct stimulation with the recombinant cytokines IL-12 and IL-18, and indirect stimulation with TLR-4/TLR-8 agonists or influenza A virus in the presence of APCs. Finally, we outline a protocol to analyze activated MAIT cells using flow cytometry.

Human MAIT cells sit at the interface between innate and adaptive immunity, are polyfunctional and are capable of killing pathogen infected cells via recognition of the Class IB molecule MR1. MAIT cells have recently been shown to possess an antiviral protective role in vivo and we therefore sought to explore this in relation to HIV-1 infection. There was marked activation of MAIT cells in vivo in HIV-1-infected individuals, which decreased following ART. Stimulation of THP1 monocytes with R5 tropic HIVBAL potently activated MAIT cells in vitro. This activation was dependent on IL-12 and IL-18 but was independent of the TCR. Upon activation, MAIT cells were able to upregulate granzyme B, IFNγ and HIV-1 restriction factors CCL3, 4, and 5. Restriction factors produced by MAIT cells inhibited HIV-1 infection of primary PBMCs and immortalized target cells in vitro. These data reveal MAIT cells to be an additional T cell population responding to HIV-1, with a potentially important role in controlling viral replication at mucosal sites.

Objectives Antiretroviral therapy (ART) during acute HIV infection (AHI) restricts the HIV reservoir, but additional interventions are necessary to induce a cure. Intravenous immunoglobulin (IVIG) is not HIV-specific but is safe and temporarily reduces the HIV reservoir in chronic HIV infection. We present a randomized controlled trial to investigate whether IVIG plus ART in AHI reduces the HIV reservoir and immune activation compared with ART alone. Methods Ten men with AHI (Fiebig II-IV) initiated ART (tenofovir, entricitabine, ritonavir boosted darunavir and raltegravir) at HIV-1 diagnosis and were randomized to ART alone or ART plus 5 days of IVIG, once virally suppressed (week 19). Blood samples were evaluated for viral reservoir, immune activation, immune exhaustion and microbial translocation. Flexible sigmoidoscopy was performed at weeks 19, 24 and 48, and gut proviral DNA and cell numbers determined. Results IVIG was well tolerated and no viral blips (> 50 HIV-1 RNA copies/mL) occurred during IVIG therapy. From baseline to week 48, total HIV DNA in peripheral blood mononuclear cells (PBMCs) (cases: -3.7 log10 copies/106 CD4 cells; controls: -3.87 log10 copies/106 CD4 cells) declined with no differences observed between the groups (P = 0.49). Declines were observed in both groups from week 19 to week 48 in total HIV DNA in PBMCs (P = 0.38), serum low copy RNA (P = 0.57) and gut total HIV DNA (P = 0.55), but again there were no significant differences between arms. Biomarkers of immune activation, immune exhaustion and microbial translocation and the CD4:CD8 ratio were similar between arms for all comparisons. Conclusions Although safe, IVIG in AHI did not impact total HIV DNA, immune function or microbial translocation in peripheral blood or gut tissue.

We show that intensification of treatment with maraviroc in patients chronically infected with HIV-1 receiving successful long-term antiretroviral therapy was not associated with improvements in HIV-related morbidity, HIV reservoir, microbial translocation, immune activation, or immune exhaustion in either gut or peripheral blood. The measurement of reservoir in both gut and blood longitudinally contributes to a paucity of data in the area.

BACKGROUND: The frequency of protective antiviral memory B cells after hepatitis B virus (HBV) vaccination is unknown. METHODS: A novel 2-step immunomagnetic protocol to assess the ex vivo frequency of protective HBV surface antigen (HBsAg)-specific memory B cells was used. RESULTS: HBsAg-specific memory B cells were detected in vaccinated individuals, although at very low frequency (median, 0.2% of CD19(+) cells [range, 0%-4% of CD19(+) cells]). No correlation existed between the frequency of HBsAg-specific memory B cells and the corresponding serum antibody titer or B cell enzyme-linked immunosorbent spot findings. CONCLUSION: Our results indicate sustained B cell-mediated protection against HBV despite waning antibody titers, which is consistent with clinical observations.