Recent follow-up data from relapsed and/or refractory ALL patients and multiple myeloma treated with CD19 CAR-T therapy or B-cell maturation antigens (BCMA) targeted CAR-T cells indicates that the incidence of resistance to therapy in a small percentage of patients is due to the loss of CD19 and BCMA [204,205,206,207,208]. Here, CD19 is linked to plasma cell myeloma.