Effects of blocking antibodies on the cytotoxic activity of P210 CD8+ T cell clones against K562 target cells in chromium release assays. The increase in cytotoxicity in response to IFN is partly abrogated by incubation with anti–HLA-A,B,C. Cytotoxicity is largely blocked by anti-CD8 but unaffected by anti-CD4. Cytotoxicity data represent the mean ± SD percent specific lysis in chromium release assays performed in triplicate at an E:T ratio of 10:1.