Thus, upon COVID-19 mRNA vaccination, THX mice mount a mature neutralizing antibody response to Spike S1 RBD, entailing SHM/CSR, huB cell select clonal expansion and intraclonal diversification, huPC differentiation, generation of huMBCs and blood incretion of antibody response-related human cytokines. The gene discussed is ELAVL2; the disease is COVID-19.