CD19 and acute lymphoblastic leukemia: One of the most extensively used antigens for cancerimmunotherapy is the B cell-specific surface marker CD19, which wasinitially discovered as B4 antigen by using a B4 specific monoclonalantibody (mAb).1,2 Due to its highly defined expressionpattern, being restricted to the B cell lineage, it serves as an optimaltarget for B cell malignancies, including acute lymphoblastic leukemia(ALL) and lymphomas.