NK cells lacking CD158a, CD158b, and CD94 or CD159a kill autologous T-cell blasts infected with an HIV strain that decreases MHC class I molecules but not T-cell blasts infected with an HIV strain that does not alter MHC class I molecules. HIV-1_SF162-infected T-cell blasts (A-B), HIV-_SF33-infected T-cell blasts (C-D), and K562 cells (A-D) were used as target cells in a 4-hour cytotoxic assay. NK cells were depleted of CD158a⁺, CD158b⁺, and CD94⁺ or CD159a⁺ cells before their use as effector cells in the cytotoxic assay. Effector cell-target cell ratios of 1:1, 2.5:1, 5:1, and 10:1 were used. All samples were performed in triplicate.