γδ T cells mediate robust anti-HIV functions during antiretroviral therapy regardless of immune checkpoint expression.

Objectives: Although antiretroviral therapy (ART) efficiently suppresses HIV viral load, immune dysregulation and dysfunction persist in people living with HIV (PLWH). γδ T cells are functionally impaired during untreated HIV infection, but the extent to which they are reconstituted upon ART is currently unclear. Methods: Utilising a cohort of ART-treated PLWH, we assessed the frequency and phenotype, characterised in vitro functional responses and defined the impact of immune checkpoint marker expression on effector functions of both Vδ1 and Vδ2 T cells. We additionally explore the in vitro expansion of Vδ2 T cells from PLWH on ART and the mechanisms by which such expanded cells may sense and kill HIV-infected targets. Results: A matured NK cell-like phenotype was observed for Vδ1 T cells among 25 ART-treated individuals (PLWH/ART) studied compared to 17 HIV-uninfected controls, with heightened expression of 2B4, CD160, TIGIT and Tim-3. Despite persistent phenotypic perturbations, Vδ1 T cells from PLWH/ART exhibited strong CD16-mediated activation and degranulation, which were suppressed upon Tim-3 and TIGIT crosslinking. Vδ2 T cell degranulation responses to the phosphoantigen (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate at concentrations up to 2 ng mL-1 were significantly impaired in an immune checkpoint-independent manner among ART-treated participants. Nonetheless, expanded Vδ2 T cells from PLWH/ART retained potent anti-HIV effector functions, with the NKG2D receptor contributing substantially to the elimination of infected cells. Conclusion: Our findings highlight that although significant perturbations remain within the γδ T cell compartment throughout ART-treated HIV, both subsets retain the capacity for robust anti-HIV effector functions.

Cytokines enhance human Vγ9Vδ2 T-cell TCR-dependent and TCR-independent effector functions.

Vγ9Vδ2 T cells can recognize various molecules associated with cellular stress or transformation, providing a unique avenue for the treatment of cancers or infectious diseases. Nonetheless, Vγ9Vδ2 T-cell-based immunotherapies frequently achieve suboptimal efficacies in vivo. Enhancing the cytotoxic effector function of Vγ9Vδ2 T cells is one potential avenue through which the immunotherapeutic potential of this subset may be improved. We compared the use of four pro-inflammatory cytokines on the effector phenotype and functions of in vitro expanded Vγ9Vδ2 T cells, and demonstrated TCR-independent cytotoxicity mediated through CD26, CD16, and NKG2D, which could be further enhanced by IL-23, IL-18, and IL-15 stimulation throughout expansion. This work defines promising culture conditions that could improve Vγ9Vδ2 T-cell-based immunotherapies and furthers our understanding of how this subset might recognize and target transformed or infected cells.

Establishment and recall of SARS-CoV-2 spike epitope-specific CD4+ T cell memory.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and vaccination elicit CD4+ T cell responses to the spike protein, including circulating follicular helper T (cTFH) cells that correlate with neutralizing antibodies. Using a novel HLA-DRB1*15:01/S751 tetramer to track spike-specific CD4+ T cells, we show that primary infection or vaccination induces robust S751-specific CXCR5- and cTFH cell memory responses. Secondary exposure induced recall of CD4+ T cells with a transitory CXCR3+ phenotype, and drove expansion of cTFH cells transiently expressing ICOS, CD38 and PD-1. In both contexts, cells exhibited a restricted T cell antigen receptor repertoire, including a highly public clonotype and considerable clonotypic overlap between CXCR5- and cTFH populations. Following a third vaccine dose, the rapid re-expansion of spike-specific CD4+ T cells contrasted with the comparatively delayed increase in antibody titers. Overall, we demonstrate that stable pools of cTFH and memory CD4+ T cells established by infection and/or vaccination are efficiently recalled upon antigen reexposure and may contribute to long-term protection against SARS-CoV-2.