The male-specific minor H antigen recognized by HLA-B8–restricted CTL clones is detected in hematopoietic cells but not fibroblasts. Lytic activity of a representative HLA-B8–restricted male-specific CTL clone (MRR-23) against EBV-LCL (□), dermal fibroblasts (□), and IFN-γ–treated fibroblasts (500 U/mL for 48 hours; ▪) derived from four unrelated HLA-B8⁺ male donors. The effector to target ratio is 20:1.