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SARS-CoV-2 mRNA vaccines induce robust anti-spike (S) antibody and CD4+ T cell responses. It is not yet clear whether vaccine-induced follicular helper CD4+ T (TFH) cell responses contribute to this outstanding immunogenicity. Using fine needle aspiration of draining axillary lymph nodes from individuals who received the BNT162b2 mRNA vaccine, we evaluated the T cell receptor sequences and phenotype of lymph node TFH. Mining of the responding TFH T cell receptor repertoire revealed a strikingly immunodominant HLA-DPB1∗04-restricted response to S167-180 in individuals with this allele, which is among the most common HLA alleles in humans. Paired blood and lymph node specimens show that while circulating S-specific TFH cells peak one week after the second immunization, S-specific TFH persist at nearly constant frequencies for at least six months. Collectively, our results underscore the key role that robust TFH cell responses play in establishing long-term immunity by this efficacious human vaccine., Analysis of draining lymph nodes of individuals vaccinated BNT162b2 mRNA vaccine against SARS-CoV-2 identifies viral spike-specific follicular helper CD4+ T cells that persist for months and contribute to long-term immunity.

Regulatory T cells suppress via a variety of mechanisms, both contact-dependent and -independent mechanisms. These is some controversy as to which mechanisms play more dominant roles during various disease states as well as maintenance of immune homeostasis. Our laboratory has found that regulatory T cells secrete exosome-like vesicles that are 20 to 50 nm in diameter. Membrane vesicles have been shown to mediate communication amongst immune cells, but they also mediate communication between immune cells and cancer cells and between and immune cells and pathogens. Membrane vesicles mediate physiologic changes in recipient cells by initiating cellular signaling events following receptor binding, or via uptake and integration of vesicular cargo, which can include receptors, enzymes, cytokines, chemokines and genetic material. We have found that functional regulatory T cell membrane vesicles mediate suppression of conventional CD4+ T cells, whereas resting regulatory T cell and conventional T cell vesicles do not. Furthermore, we have found that 293F cells package overexpressed immunosuppressive cytokines into exosomes following transfection. Taken together these data suggest that exosome-like vesicles represent a bridge between contact dependent and independent regulatory T cell suppression.