To evade host-mediated immunity and deliver anti-leukemic effects without graft-versus-host disease in patients with relapsed or refractory B-cell malignancies, gene-disrupted allogeneic CD19-directed BBζ CAR–T cells (known as UCART019) are developed by combining the lentiviral delivery of CAR and CRISPR mRNA electroporation to disrupt both of the endogenous T-cell receptor (TCR) and beta-2 microglobulin (B2M) genes. The gene discussed is B2M; the disease is graft versus host disease.