CD27 and COVID-19: THX mice vaccinated intramuscularly (i.m.)with Pfizer-BioNTech 162b2 coronavirus disease 2019 (COVID-19) mRNA, according to human vaccination schedule, made huIgM, huIgG and, to a moderate degree, huIgA to SARS-CoV-2 Spike S1 RBD (37 amino acid core peptide) as well as RBD-specific huASCs, huCD19+ B cells, memory huCD19+CD27+ B cells and huCD19+CD27+CD38+ PBs (Fig. 7a–c).