CD19 and acute lymphoblastic leukemia: For instance, up to 30% of B-ALL (B cell acute lymphoblastic leukemia) patients receiving CART19 (anti-CD19 CAR-T cells) or blinatumomab (anti-CD19/CD3 antibodies) relapsed due to the loss of CD19 epitope in some tumor cells, imposing a major concern that challenges the efficacy of immunotherapies targeting CD19 (51, 59).