Preprint
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| PREPRINT-BIORXIV | ID: ppbiorxiv-500554
Although BNT162b2 vaccination was shown to prevent infection and reduce COVID-19 severity, and the persistence of immunological memory generated by the vaccination has not been well elucidated. We evaluated memory B and T cell responses to the SARS-CoV-2 spike protein before and after the third BNT162b2 booster. Although the antibody titer against the spike receptor-binding domain (RBD) decreased significantly 8 months after the second vaccination, the number of memoryB cells continued to increase, while the number of memoryT cells decreased slowly. Memory B and T cells from unvaccinated infected patients showed similarkinetics. After the third vaccination, the antibody titer increased to the level of the second vaccination, and memoryB cells increased at significantly higher levels before the booster, while memoryT cells recovered close to the second vaccination levels. In memoryT cells, the frequency of CXCR5+CXCR3+CCR6- cTfh1 was positively correlated with RBD-specific antibody-secreting B cells. Furthermore, T cell-dependent antibody production from reactivated memoryB cellsin vitro was correlated to the Tfh-like cytokine levels. For the response to variant RBDs, although 60%-80% of memoryB cells could bind to the Omicron RBD, their binding affinity was low, while memoryT cells show an equal response to the Omicron spike. Thus, the persistent presence of memory B and T cellswill quickly upregulate antibody production and T cell responses after Omicron straininfection, which prevents severe illness and death due to COVID-19.