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Although mucosal-associated invariant T (MAIT) cells provide rapid, innate-like responses, they are not pre-set, and memory-like responses have been described for MAIT cells following infections. The importance of metabolism for controlling these responses, however, is unknown. Here, following pulmonary immunization with a Salmonella vaccine strain, mouse MAIT cells expanded as separate CD127-Klrg1+ and CD127+Klrg1- antigen-adapted populations that differed in terms of their transcriptome, function and localization in lung tissue. These populations remained altered from steady state for months as stable, separate MAIT cell lineages with enhanced effector programmes and divergent metabolism. CD127+ MAIT cells engaged in an energetic, mitochondrial metabolic programme, which was critical for their maintenance and IL-17A synthesis. This programme was supported by high fatty acid uptake and mitochondrial oxidation and relied on highly polarized mitochondria and autophagy. After vaccination, CD127+ MAIT cells protected mice against Streptococcus pneumoniae infection. In contrast, Klrg1+ MAIT cells had dormant but ready-to-respond mitochondria and depended instead on Hif1a-driven glycolysis to survive and produce IFN-γ. They responded antigen independently and participated in protection from influenza virus. These metabolic dependencies may enable tuning of memory-like MAIT cell responses for vaccination and immunotherapies.

Conventional antiviral memory CD4 T cells typically arise during the first two weeks of acute infection. Unlike most viruses, cytomegalovirus (CMV) exhibits an extended persistent replication phase followed by lifelong latency accompanied with some gene expression. We show that during mouse CMV (MCMV) infection, CD4 T cells recognizing an epitope derived from the viral M09 protein only develop after conventional memory T cells have already peaked and contracted. Ablating these CD4 T cells by mutating the M09 genomic epitope in the MCMV Smith strain, or inducing them by introducing the epitope into the K181 strain, resulted in delayed or enhanced control of viral persistence, respectively. These cells were shown to be unique compared to their conventional memory counterparts; producing higher IFNγ and IL-2 and lower IL-10 levels. RNAseq analyses revealed them to express distinct subsets of effector genes as compared to classical CD4 T cells. Additionally, when M09 cells were induced by epitope vaccination they significantly enhanced protection when compared to conventional CD4 T cells alone. These data show that late-rising CD4 T cells are a unique memory subset with excellent protective capacities that display a development program strongly differing from the majority of memory T cells. Author summary: Functional memory T cells are critical to ultimately control chronic viral infection. We show that cytomegalovirus (CMV) induces a population of unique memory CD4 T cells that expand late during infection and resolve viral persistence much better than conventional T memory cells. Mutation of the genomic CMV epitope recognized by these T cells results in markedly enhanced persistent replication, and introduction of the epitope into a CMV strain that lacks it induces much quicker resolution of persistence. When induced via vaccination, we show these T cells provide significantly enhanced protection against acute viral challenge. Together our study identifies a novel population of CD4 T cells that utilize distinct effector function(s) to rapidly resolve persistent viral replication. [ABSTRACT FROM AUTHOR]

Background: Graft-vs-host disease (GVHD) is a major complication of allogenic bone marrow transplantation (BMT). Targeting costimulatory molecules with antagonist antibodies could dampen the excessive immune response that occurs, while preserving the beneficial graft vs leukemia (GVL) of the allogeneic response. Previous studies using a mouse model of GVHD have shown that targeting the T-cell Inducible COStimulator (ICOS, CD278) molecule is beneficial, but it is unclear whether the same applies to human cells. Methods: Here, we assessed whether a monoclonal antibody (mAb) to human ICOS was able to antagonize the costimulatory signal delivered in vivo to human T cells. To test this hypothesis, we used a xenogeneic model of GVHD where human peripheral blood mononuclear cells were adoptively transferred in immunocompromised NOD. SCID.gc-null mice (NSG). results: In this model, control mice invariably lost weight and died by day 50. In contrast, 65% of the mice receiving a single injection of the anti-hICOS mAb survived beyond 100 days. Moreover, a significant improvement in survival was obtained in a curative xeno-GVHD setting. Mechanistically, administration of the anti-hICOS mAb was associated with a strong reduction in perivascular infiltrates in liver and lungs and reduction in frequencies and numbers of human T cells in the spleen. In addition, the mAb prevented T-cell expansion in the blood during xeno-GVHD. Importantly, GVHD-protected mice retained the ability to control the P815 mastocytoma cell line, mimicking GVL in humans. conclusion: A mAb-targeting human ICOS alleviated GVHD without impairing GVL in a xenograft murine model. Thus, ICOS represents a promising target in the management of BMT, preventing GVHD while preserving GVL. [ABSTRACT FROM AUTHOR]

Simple Summary: Current immune checkpoint inhibitors have shown limitations for immunotherapy of prostate cancer. Thus, it is crucial to investigate other immune checkpoints to prevent disease progression in patients with prostate cancer. Here, we first show that the HVEM/BTLA immune checkpoint is associated with disease progression in patients. We then show that immunotherapy aimed at targeting HVEM reduced tumor growth twofold in vivo in a humanized mouse model of the pathology. The mode of action of the therapy was dependent on CD8+ T cells and is associated with improved T cell activation and reduced exhaustion. Finally, we demonstrated that HVEM expressed by the tumor negatively regulated the anti-tumor immune response. Our results indicate that targeting HVEM might be an attractive option for patients with prostate cancer. The herpes virus entry mediator (HVEM) delivers a negative signal to T cells mainly through the B and T lymphocyte attenuator (BTLA) molecule. Thus, HVEM/BTLA may represent a novel immune checkpoint during an anti-tumor immune response. However, a formal demonstration that HVEM can represent a target for cancer immunotherapy is still lacking. Here, we first showed that HVEM and BTLA mRNA expression levels were associated with a worse progression-free interval in patients with prostate adenocarcinomas, indicating a detrimental role for the HVEM/BTLA immune checkpoint during prostate cancer progression. We then showed that administration of a monoclonal antibody to human HVEM resulted in a twofold reduction in the growth of a prostate cancer cell line in NOD.SCID.gc-null mice reconstituted with human T cells. Using CRISPR/Cas9, we showed that the therapeutic effect of the mAb depended on HVEM expression by the tumor, with no effect on graft vs. host disease or activation of human T cells in the spleen. In contrast, the proliferation and number of tumor-infiltrating leukocytes increased following treatment, and depletion of CD8+ T cells partly alleviated treatment's efficacy. The expression of genes belonging to various T cell activation pathways was enriched in tumor-infiltrating leukocytes, whereas genes associated with immuno-suppressive pathways were decreased, possibly resulting in modifications of leukocyte adhesion and motility. Finally, we developed a simple in vivo assay in humanized mice to directly demonstrate that HVEM expressed by the tumor is an immune checkpoint for T cell-mediated tumor control. Our results show that targeting HVEM is a promising strategy for prostate cancer immunotherapy. [ABSTRACT FROM AUTHOR]

Human cytomegalovirus (HCMV) causes severe birth defects, lifelong health complications, and $4 billion in annual costs in the United States alone. A major challenge in vaccine design is the incomplete understanding of the diverse protein complexes the virus uses to infect cells. In Herpesviridae , the gH/gL glycoprotein heterodimer is expected to be a basal element of virion cell entry machinery. For HCMV, gH/gL forms a "trimer" with gO and a "pentamer" with UL128, UL130, and UL131A, with each complex binding distinct receptors to enter varied cell types. Here, we reveal a third glycoprotein complex, abundant in HCMV virions, which significantly enhances infection of endothelial cells. In this "3-mer" complex, gH, without gL, associates with UL116 and UL141, an immunoevasin previously known to function in an intracellular role. Cryo-EM reveals the virion-surface 3-mer is structurally unique among Herpesviridae gH complexes, with gH-only scaffolding, UL141-mediated dimerization and a heavily glycosylated UL116 cap. Given that antibodies directed at gH and UL141 each can restrict HCMV replication, our work highlights this virion surface complex as a new target for vaccines and antiviral therapies.

Atherosclerotic cardiovascular diseases are the major cause of death worldwide. CD4 T cells responding to Apolipoprotein B (ApoB), the core protein of most lipoproteins, have been identified as critical disease modulators. In healthy individuals, ApoB-reactive (ApoB + ) CD4 T cells are mostly regulatory T cells (T regs ), which exert anti-inflammatory effects. Yet, they may obtain pro-inflammatory features and thus become proatherogenic. Evidence from animal studies suggests that vaccination against certain major histocompatibility complex (MHC) II-binding ApoB peptides induces an expansion of ApoB + T regs and thus confers atheroprotection. To date, in-depth phenotyping of vaccine-expanded ApoB + T cells has not yet been performed. To this end, we vaccinated C57BL/6J mice with the ApoB-peptide P6 (ApoB 978-993 TGAYSNASSTESASY) and performed single-cell RNA sequencing of tetramer-sorted P6 + T cells. P6 + cells were clonally expanded (one major, two minor clones) and formed a transcriptional cluster distinct from clusters mainly containing non-expanded P6 + and P6 - cells. Transcriptomic profiling revealed that most expanded P6 + cells had a strong T reg signature and highly expressed genes mediating suppressive functions. Yet, some expanded P6 + cells only had a residual T reg signature and expressed genes related to T helper 1 (T H 1) cells, which are proatherogenic. Modeling the T cell receptor (TCR) and P6:MHC-II interaction showed that only three amino acid residues in the α and β chain contact the P6 peptide in the MHC-II groove and thus determine the specificity of this TCR to P6. Our data begin to reveal the vaccination-induced response to an ApoB epitope., Competing Interests: KL was founder and co-owner of Atherovax, Inc. He received no compensation from Atherovax. No Atherovax funds were used in this study. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Nettersheim, Ghosheh, Winkels, Kobiyama, Durant, Armstrong, Brunel, Roy, Dileepan, Jenkins, Zajonc and Ley.)

Background: Throughout the inflammatory response that accompanies atherosclerosis, autoreactive CD4 + T-helper cells accumulate in the atherosclerotic plaque. Apolipoprotein B 100 (apoB), the core protein of low-density lipoprotein, is an autoantigen that drives the generation of pathogenic T-helper type 1 (T H 1) cells with proinflammatory cytokine secretion. Clinical data suggest the existence of apoB-specific CD4 + T cells with an atheroprotective, regulatory T cell (T reg ) phenotype in healthy individuals. Yet, the function of apoB-reactive T regs and their relationship with pathogenic T H 1 cells remain unknown., Methods: To interrogate the function of autoreactive CD4 + T cells in atherosclerosis, we used a novel tetramer of major histocompatibility complex II to track T cells reactive to the mouse self-peptide apo B 978-993 (apoB + ) at the single-cell level., Results: We found that apoB + T cells build an oligoclonal population in lymph nodes of healthy mice that exhibit a T reg -like transcriptome, although only 21% of all apoB + T cells expressed the T reg transcription factor FoxP3 (Forkhead Box P3) protein as detected by flow cytometry. In single-cell RNA sequencing, apoB + T cells formed several clusters with mixed T H signatures that suggested overlapping multilineage phenotypes with pro- and anti-inflammatory transcripts of T H 1, T helper cell type 2 (T H 2), and T helper cell type 17 (T H 17), and of follicular-helper T cells. ApoB + T cells were increased in mice and humans with atherosclerosis and progressively converted into pathogenic T H 1/T H 17-like cells with proinflammatory properties and only a residual T reg transcriptome. Plaque T cells that expanded during progression of atherosclerosis consistently showed a mixed T H 1/T H 17 phenotype in single-cell RNA sequencing. In addition, we observed a loss of FoxP3 in a fraction of apoB + T regs in lineage tracing of hyperlipidemic Apoe -/- mice. In adoptive transfer experiments, converting apoB + T regs failed to protect from atherosclerosis., Conclusions: Our results demonstrate an unexpected mixed phenotype of apoB-reactive autoimmune T cells in atherosclerosis and suggest an initially protective autoimmune response against apoB with a progressive derangement in clinical disease. These findings identify apoB autoreactive T regs as a novel cellular target in atherosclerosis.