CD28 and acute myeloid leukemia: Interestingly, although we used healthy donor T-cells from one individual in our comparative analyses, the effects of the CD28 antibody varied considerably across the AML cell lines and the 12 primary AML specimens tested, suggesting that one or more currently unidentified cancer cell-related factor(s) can further modulate the interaction with the CD28-activated T-cells; this modulation will need further investigation in future studies.