Ex vivo detection of HLA-Cw*0501–specific CD8 T cells during onset of severe GVHD in patient 4. (A) Course of CD4 (-○-) and CD8 T cells (-•-) measured by flow cytometry analysis in peripheral blood. (B) Course of liver transaminases AST (-⋄-) and ALT (-♦-), and frequencies of HLA-Cw*0501 mismatch–specific T cells measured by IFN-γ ELISPOT assays. ELISPOT responders were purified CD8 blood lymphocytes. Targets were parental K562 cells (▪), and K562 transfectants expressing either the matched HLA-A*0301 (⊡) or the mismatched HLA-Cw*0501 (□) recipient alleles. Stars indicate significant HLA-Cw*0501 reactivity compared with controls (P < .05).