The female genital tract (FGT) mucosa is a critically important site for immune defense against microbes. Mucosal-associated invariant T (MAIT) cells are an innate-like T-cell population that recognizes microbial riboflavin metabolite antigens in an MR1-dependent manner. The role of MAIT cells in the FGT mucosa is unknown. Here, we found that MAIT cells and MR1⁺ antigen-presenting cells were present in the upper and lower FGT, with distinct tissue localization of MAIT cells in endometrium vs. cervix. The MAIT cells from the FGT and blood displayed a distinct phenotype with expression of interleukin (IL)-18Rα, CD127, α4β7, PD-1, as well as the transcription factors promyelocytic leukemia zinc finger (PLZF), RORγt, Helios, Eomes, and T-bet. Their expression levels of PLZF and Eomes were lower in the FGT compared with blood. When stimulated with Escherichia coli, MAIT cells from the FGT displayed a bias towards IL-17 and IL-22 expression, whereas blood MAIT cells produced primarily IFN-γ, TNF, and Granzyme B. Furthermore, both FGT- and blood-derived MAIT cells were polyfunctional and contributed to the T-cell-mediated response to E. coli. Thus, MAIT cells in the genital mucosa have a distinct IL-17/IL-22 profile and may have an important role in the immunological homeostasis and control of microbes at this site.

Objective: To investigate whether exosomes derived from human breast milk or plasma confer protection against HIV-1 infection of monocyte-derived dendritic cells (MDDCs) and subsequent viral transfer to CD4⁺ T cells. Design: MDDCs were generated and milk and plasma-derived exosomes were isolated from healthy donors. To determine the capacity of exosomes to inhibit HIV-1 infection, MDDCs were preincubated with exosomes before exposure to HIV-1_BaL. To investigate transfer of HIV-1 from MDDCs to CD4⁺ T cells, MDDCs preincubated with exosomes and HIV-1_BaL were cocultured with allogeneic CD4⁺ T cells. To explore receptors used by MDDCs for binding of exosomes, blocking experiments were performed. Methods: Productive HIV-1 infection was analysed in MDDCs and CD4⁺ T cells by determining p24 expression by flow cytometry. Confocal microscopy and flow cytometry was used to investigate uptake of fluorescently labelled exosomes by MDDCs. Results: Milk exosomes, but not plasma exosomes, bind MDDCs via DC-SIGN inhibiting HIV-1 infection of MDDCs and subsequent viral transfer to CD4⁺ T cells. Conclusion: We propose that milk exosomes act as a novel protective factor against vertical transmission of HIV-1 by competing with HIV-1 for binding to DC-SIGN on MDDCs.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants stresses the continued need for next-generation vaccines that confer broad protection against coronavirus disease 2019. We developed and evaluated an adjuvanted SARS-CoV-2 spike ferritin nanoparticle (SpFN) vaccine in nonhuman primates. High-dose (50-μg) SpFN vaccine, given twice 28 days apart, induced a T helper cell 1 (T _H 1)–biased CD4 T _H response and elicited neutralizing antibodies against SARS-CoV-2 wild type and variants of concern, as well as against SARS-CoV-1. These potent humoral and cell-mediated immune responses translated into rapid elimination of replicating virus in the upper and lower airways and lung parenchyma of nonhuman primates after high-dose SARS-CoV-2 respiratory challenge. The immune response elicited by SpFN vaccination and resulting efficacy in nonhuman primates support the utility of SpFN as a vaccine candidate for SARS-causing betacoronaviruses.

Invariant NKT cells are important in the activation and regulation of immune responses. They can also function as CD1d‐restricted killer cells. However, the role of activating innate NK‐cell receptors expressed on NKT cells in triggering cytolytic function is poorly characterized. Here, we initially confirmed that the cellular stress‐ligand receptor NKG2D is expressed on CD4⁻ NKT cells, whereas most CD4⁺ NKT cells lack this receptor. Interestingly, NKG2D⁺ NKT cells frequently expressed perforin, and both NKG2D and perforin localized at the site of contact with NKG2D ligand‐expressing target cells. CD4⁻ NKT cells degranulated in response to NKG2D engagement in a redirected activation assay independent of stimulation via their invariant TCR. NKT cells killed P815 cells coated with anti‐NKG2D mAb and CD1d‐negative K562 tumor target cells in an NKG2D‐dependent manner. Furthermore, NKG2D engagement co‐stimulated TCR‐mediated NKT‐cell activation in response to endogenous CD1d‐presented ligands or suboptimal levels of anti‐CD3 triggering. These data indicate that the CD4⁻ subset of human NKT cells can mediate direct lysis of target cells via NKG2D engagement independent of CD1d, and that NKG2D also functions as a co‐stimulatory receptor in these cells. NKG2D thus plays both a direct and a co‐stimulatory role in the activation of NKT cells.

Prevention of viral escape and increased coverage against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern require therapeutic monoclonal antibodies (mAbs) targeting multiple sites of vulnerability on the coronavirus spike glycoprotein. Here we identify several potent neutralizing antibodies directed against either the N-terminal domain (NTD) or the receptor-binding domain (RBD) of the spike protein. Administered in combinations, these mAbs provided low-dose protection against SARS-CoV-2 infection in the K18-human angiotensin-converting enzyme 2 mouse model, using both neutralization and Fc effector antibody functions. The RBD mAb WRAIR-2125, which targets residue F486 through a unique heavy-chain and light-chain pairing, demonstrated potent neutralizing activity against all major SARS-CoV-2 variants of concern. In combination with NTD and other RBD mAbs, WRAIR-2125 also prevented viral escape. These data demonstrate that NTD/RBD mAb combinations confer potent protection, likely leveraging complementary mechanisms of viral inactivation and clearance.