CD4 and infection: Finally, we analyzed a CD4+ restricted SARS-CoV-2 specificity (DPB4/S167) (18, –20) and found the ex vivo frequency increased following infection and was maintained for 12 mo (M1: P = 0.0003; M6: P = 0.0029; M12: P = 0.0061) (SI Appendix, Fig. S1F).