The great clinical success of CAR T cells in early trials for relapsed or refractory hematological malignancies of the B cell lineage has already resulted in the approval of five CAR T cell products, targeting CD19-positive leukemia and lymphoma (Kymriah®, Yescarta®, Tecartus®, and Breyanzi®) or B cell maturation antigen (BCMA)-positive multiple myelomas (Abecma®) (6, 8–10). Here, CD19 is linked to leukemia.