Patients treated with CD19-directed CAR T-cell therapy receiving mRNA vaccines are incapable of generating new anti–SARS-CoV-2 IgG and IgA antibodies. (A) Absolute levels of IgG, IgM, and IgA antibodies in our study participants were measured using a commercially available enzyme-linked immunosorbent assay (ELISA; Invitrogen, Waltham, MA). (B) IgG antibodies against full-length recombinant influenza A nucleoprotein (Flu), tetanus toxoid (TT), Epstein-Barr virus glycoprotein gp350 (EBV), cytomegalovirus (CMV), and herpes simplex virus type 1 (HSV) glycoprotein D were measured in an ELISA as positive controls. IgG (C) and IgA (E) antibody titers against different SARS-CoV-2 S proteins, including their delta variants (RBD [L452R, T478K] and S1 [T19R, G142D, EF156-157del, R158G, L452R, T478K, D614G, P681R]), and SARS-CoV-2 N proteins were also measured in an ELISA. Values calculated represent reciprocal end point titers, and groups were compared using the Mann-Whitney U test. (D) Correlations between anti-RBD IgG antibody titers and neutralizing activity in the same patient or control. ns, not significant.