Allele-restricted fine specificity of CTL directed at HIV-1 peptides. HIV-1 peptide-specific T cells were generated from an A0201 donor using predicted A0201-restricted HIV-1 peptides (Table 1 and Fig. 1). HIV-1 peptide-specific T cells killed the A0201 transfected 721–221 cell line in a peptide-specific manner by 51Cr release assay. To test possible cross-reactivity of A0201 restricted HIV-1 peptide-specific CTL to other A02 alleles, we utilized A0202, A0203 and A0204 transfected 721–221 cells as targets. A0201 restricted HIV-1 peptide specific CTLs killed HIV-1 peptide loaded A0201 transfected 721–221 targets at a 10:1 ratio. +pp indicates addition of peptide pool, with solid bar = lysis upon +pp and gray bar = lysis with no peptide pool addition.