This work was supported in whole, or in part, with federal funds from your Defense Health Program (HU00012020067, HU00012120094) and the Immunization Healthcare Branch (HU00012120104) of the Defense Health Agency, United States Department of Defense, and the National Institute of Allergy and Infectious Disease (HU00011920111), under Inter-Agency Agreement Y1-AI-5072, and. PBMCs were collected from all participants prior to any SARS-CoV-2 illness or vaccination. Spike-specific IgG antibodies were quantified at one and six months post-vaccination by microsphere-based multiplex immunoassay. NK cell frequencies and phenotypes were assessed on pre-vaccination PBMCs from all participants by multi-color circulation cytometry, and on a subset of participants at time points after the 1stand 2nddoses of BNT162b2. Inflammatory side effects were assessed by organized sign questionnaires, and baseline NK cell features was quantified by anin vitrokilling assay on participants that reported high or low post-vaccination sign scores. == Results == Important observations include: 1) circulating NK cells show evidence of activation in the week following vaccination, 2) individuals with high sign scores after 1stvaccination experienced higher pre-vaccination NK cytotoxicity indices, 3) high pre-vaccination NK cell figures were associated with lower TAK-063 spike-specific IgG levels six months after two BNT162b2 doses, and 4) manifestation of the inhibitory marker NKG2A on immature NK cells was associated with higher antibody reactions 1 and 6 months post-vaccination. == Conversation == These results suggest that NK cell activation by BNT162b2 vaccination may contribute to vaccine-induced inflammatory symptoms and reduce durability of vaccine-induced antibody reactions. Keywords:NK cells, mRNA vaccine, vaccine side effects, reactogenicity, antibody durability, SARS-CoV-2 vaccine, COVID == Intro == Although TAK-063 initial formulations of mRNA vaccines have been tested since 1995 (1), the Pfizer-BioNTech COVID-19 vaccine (BNT162b2) was the 1st United States Food and Drug Administration (FDA) authorized mRNA vaccine. Phase III clinical tests shown that BNT162b2 was safe, and highly efficacious in avoiding COVID-19 (2). Subsequent studies have shown that while safety against illness with novel variants can be variable, the vaccine still confers significant safety against development of severe disease (3). As of February 2023, over 400 million BNT162b2 vaccinations have been administered in the United States (4). While the fundamental tenets by which mRNA vaccines work are fairly well characterized, there remain many unknowns concerning the precise factors which travel immunogenicity and reactogenicity of mRNA vaccines. Reactogenicity to BNT162b2 vaccination is very common but does not occur in all individuals. According to the Centers for Disease Control and Prevention (CDC), 84.7% of 18-55 year olds reported at least one community injection site reaction, and 77.4% reported at least one systemic reaction within seven days of vaccination (5). In the Prospective Assessment of SARS-CoV-2 Seroconversion TAK-063 (PASS) cohort, generally healthy adults reported considerable heterogeneity with regards to both severity and period of local and systemic symptoms after BNT162b2 vaccination (6). In addition, while most individuals develop detectable IgG antibodies to SARS-CoV-2 spike protein after BNT162b2 vaccination, there is a wide range in the levels of maximum antibody titers (7,8). The part natural killer (NK) cells perform in influencing BNT162b2 reactogenicity or immunogenicity has not been fully explored. Additional studies have shown early activation of NK cells within days of mRNA vaccine uptake in both animal models and humans (912). NK cells make up 5-20% of peripheral blood lymphocytes and non-specifically identify pathogens and danger signals through activating and inhibitory receptors (13). NK cell activation results in cytotoxicity and the launch of inflammatory cytokines (13). These functions contribute to the inflammatory environment and may influence the adaptive immune response (13). NK cells are well recognized as having the ability to both amplify and diminish adaptive immune reactions elicited by vaccines (14). After vaccination NK cells can launch cytokines and stimulate antigen-presenting cells, which enhances the adaptive response (14). On the other hand, NK cell cytolytic activity can serve to contain adaptive immunity by reducing the number of responding T cells, which can consequently diminish T cell help to TAK-063 B cells and reduce the amount and quality of antibodies produced (1416). Additionally, the part of NK cell activation and pro-inflammatory molecule launch in local and systemic adverse symptoms after mRNA vaccination is not known. Moreover, there is substantial person-to-person variance in terms of Rabbit polyclonal to IL20RB rate of recurrence, phenotype, and function of NK cells at baseline (before vaccination) (17). Therefore,.