B-cell and antibody levels following CD19-directed CAR T-cell treatment. (A) Immediately prior to and following CAR T-cell infusion, B cells were measured in the blood by flow cytometry. Levels of protective IgG (B), HLA IgG (C), and total immunoglobulins (D) were measured prior to and at indicated times following CAR T-cell infusion. Dotted lines represent protective antibody levels. HIB, Hinfluenzae type B; MFI, mean fluorescence intensity; PBMC, peripheral blood mononuclear cells; PCP, pneumococcal capsular polysaccharide.