Specificity of the HLA-B44–restricted CTL clone 2A12. The cytolytic activity of CTL-2A12 was evaluated in a standard 4-hour ⁵¹Cr release assay at the indicated E/T ratios. (A) CTL-2A12 recognition of target cells derived from recipient (Rt) but not donor (Do) B-LCLs. NK-sensitive K562 cells were used to determine nonspecific lysis. (B) CTL-2A12 recognition of Rt PHA-stimulated T cells (PHA blasts) but not of Rt dermal fibroblasts and bone marrow (BM)-derived fibroblasts pretreated with 500 U/mL IFN-γ and 10 ng/mL TNF-α for 48 hours before ⁵¹Cr labeling. (C) CTL-2A12 recognition of an HLA-B*4403- and -B*4402-restricted mHA epitope. The following target cells were tested: Rt B-LCL, B-LCLs of 2 unrelated individuals (UR1 and UR2) sharing an HLA-A33, B44 haplotype with the recipient, and B-LCLs of an HLA class I-mismatched individual (UR3) that were transduced with either HLA-A*3303, B*4403, or B*4402 (E/T ratio, 30:1).