CD19 and B-cell acute lymphoblastic leukemia: Although CD19-specific chimeric antigen receptor (CAR) T-cell therapy has achieved high complete remission (CR) rates in relapsed/refractory B-cell acute lymphoblastic leukemia (r/r B-ALL) [1–4], a minority of patients have no response and many patients relapse with either CD19 positivity or CD19 negativity.