CD19 and acute lymphoblastic leukemia: One of the best documented phenomenon is the conversion of B-ALL (B-acute lymphoblastic leukemia) to a myeloid phenotype or MPAL (Mixed Phenotype Acute Leukemia) after anti-CD19 immunotherapy, where recurrent lineage switch after CAR-T or bispecific antibody (BiTEs) therapy is associated with the loss of CD19 and appearance of myeloid features, which correlates with the attenuation of the PAX5 axis and the amplification of the PU.1/C-EBP axis [20,112,113,114,115,116].