== TCR sequences of the top expanded clonotypes in pre-vaccinated samples were investigated in the Adaptive database. were established by vaccination from rare clonotypes. These results suggest that de novo acquisition of memory Tfh-like cells upon vaccination may contribute to the longevity of anti-S antibody titers. Research organism:Human == Introduction == The pandemic COVID-19, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has expanded worldwide (Hu Entrectinib et al., 2021). Many types of vaccines have been developed or in basic and clinical phases to combat infection and deterioration of COVID-19 (Creech et al., 2021;Krammer, 2020). Among them, messenger Entrectinib ribonucleic acid (mRNA) vaccines, BNT162b2/Comirnaty and mRNA-1273/Spikevax, have been approved with over 90% efficacy at 2 months post-2nd dose vaccination (Baden et al., 2021;Polack et al., 2020), and widely used. Pathogen-specific antibodies are one of the most efficient components to prevent infection. Yet, mRNA vaccine-induced serum antibody titer is known to be waning over 6 months (Levin et al., 2021;Pegu et al., 2021). Accordingly, the effectiveness of the vaccines decreases over time, and thus multiple doses and repeated boosters are necessary (Andrews et al., 2022). The production and sustainability of spike (S)-specific antibody could be related to multiple factors, especially in the case of humans (Collier et al., 2021;Levin et al., 2021). Among them, the characteristics of SARS-CoV-2-specific T cells are critically involved in the affinity and longevity of the antibodies (Crotty, 2019;Nelson et al., 2022;Terahara et al., 2022). Elucidation of the key factors of T cell responses that contribute to the durable immune responses induced by vaccination would provide valuable information for the vaccine development in Entrectinib the future. However, the relationship between antibody sustainability and the types of antigen-specific T cells has not been investigated in a clonotype Entrectinib resolution. Recent studies reported that S-reactive T cells pre-existed before exposure to SARS-CoV-2 (Grifoni et al., 2020;Le Bert et al., 2020;Mateus et al., 2020;Meckiff et al., 2020;Sekine et al., 2020). Common cold human coronaviruses (HCoVs) including strains 229E, NL63, OC43, and HKU1 are considered major cross-reactive antigens that primed these pre-existing T cells (Becerra-Artiles et al., 2022;Low et al., 2021;Loyal et al., 2021;Mateus et al., 2020), while bacterial cross-reactive antigens were also reported (Bartolo et al., 2022;Lu et al., 2021). However, the functional relevance of cross-reactive T cells during infection or vaccination is still in debate. In this study, both humoral and cellular immune responses were evaluated at 3, 6, and 24 weeks after BNT162b2/Comirnaty vaccination. S-specific T cells before and after vaccination were analyzed on clonotype level using single-cell-based T cell receptor (TCR) and RNA sequencing to determine their characteristics and epitopes in antibody sustainers and decliners. These analyses suggest the importance of early acquisition of S-specific Tfh cells in the longevity of antibodies. == Results == == SARS-CoV-2 mRNA vaccine elicits transient humoral immunity == Blood samples were collected from a total of GPC4 43 individuals (Table 1) who had no SARS-CoV-2 infection history when they received two doses of SARS-CoV-2 mRNA vaccine BNT162b2. Samples were taken before and after the vaccination (Figure 1A). Consistent with the previous report (Polack et al., 2020), most participants exhibited more severe side effects after 2nd dose of vaccination than 1st dose locally (Table 2) and systemically (Table 3). At 3 weeks, anti-S IgG antibody titer increased in most participants. At 6 weeks, anti-S antibody titer was at its peak. S antibody titer gradually decreased over 24 weeks (Figure 1B). The antibody titer was reduced by 56.8% on average. Donors of different sexes or age groups showed no significant difference in anti-S antibody titer (Figure 1figure supplement 1). The neutralization activity of the post-vaccinated sera showed similar tendency with the anti-S antibody titer during the study period (Figure 1C). The above results indicate that the mRNA vaccine effectively activated humoral immune responses in healthy individuals, but decreased by 24 weeks over time as reported (Levin et al., 2021;Pegu et al., 2021)..
== TCR sequences of the top expanded clonotypes in pre-vaccinated samples were investigated in the Adaptive database