HLA restriction of peptide recognition by HM1.24-specific CTL line. CTL line specific for HM1.24-165 peptide was established from a healthy donor (HLA-A2⁺, A24^-). (A) HLA restriction of HM1.24-165–induced CTLs was determined by blocking HLA class I on target cells. ⁵¹Cr-labeled target ARH-77 cells were preincubated with either control MoAb or anti–HLA class I MoAb for 45 minutes at room temperature before addition of the CTLs. Cytotoxicity (%) was measured by ⁵¹Cr-release assay (E/T ratio = 20). (B) Peptide recognition by the CTLs was determined by cold target inhibition assay. CTLs (6 × 10⁴ cells) were incubated with ⁵¹Cr-labeled target ARH-77 cells (3 × 10³ cells) in the presence of either HM1.24-165 peptide-loaded or unloaded MDA-MB-231 cells (6 × 10⁴ cells). Cytotoxic activity was measured by ⁵¹Cr-release assay (E/T ratio = 20). Values indicate the mean ± SD of triplicate experiments.