CD22 and precursor B-cell acute lymphoblastic leukemia: CD22 is a cell surface antigen found in the majority (60–90%) of B-cell acute lymphoblastic leukemia (B-ALL).166,167 And binding to CD22 activates a series of downstream processes of the ADC, including internalization, linker hydrolysis and payload release, in a similar manner as seen in gemtuzumab ozogamicin.