Specific reactivity of in vitro–induced anti–HB-1H.B44 CTL clone donor 2 in comparison with in vivo–induced CTL MP1. Production of IFN-γ of CTL clone donor 2 and MP1 was determined on stimulation with (A) Raji cells transfected with HLA-B44 (B*4402 or B*4403) plus HB-1H or HB-1Y and EBV-transformed B-cell lines endogenously expressing HB-1, and (B) B-ALL cells of HLA-B44–positive patients. HB-1 typing for each stimulator cell is shown in parenthesis. HLA-B44 subtype of patients 1, 2, and 3 is B*4402 and of patient 4 is B*4403.