Characterization of HLA-DP–specific alloreactive CD4⁺ T cell clones. (A-B) T-cell clones 501 (A) and 538 (B) were used at different effector-target cell ratios in a standard 4-hour cytotoxicity assay. The following BLCLs were used as targets: donor (•); patient (○); patient transduced with retroviral vector LDPB9SΔN (▪); patient transduced with retroviral vector LDPB9ΔCYTSΔN (□); donor transduced with retroviral vector LDPB9ΔCYTSΔN (▴); and WT100BIS (▵). For complete HLA typing of target cells see Table 1. (C-D) T-cell clones 501 (C) and 538 (D) were used at a fixed effector-target cell ratio of 1:1 (clone 501) or 10:1 (clone 538) in mAb inhibition assays of donor BLCL lysis. The mAbs were B7/21 (anti–HLA-DP), L243 (anti–HLA-DR), or W6/32 (anti–HLA class I). All mAbs were used at 1 μg/mL (▪) and mAb B7/21 was also used at 0.3 μg/mL (▦) , 0.1 μg/mL (▨) , or 0.03 μg/mL (□). Specific lysis in the absence of mAbs was 46% and 40% for clones 501 and 538, respectively.