HIV-specific cytotoxicity by PBMCs from a representative HIV-infected donor (no. 234; A) is below background (10%) for freshly isolated samples but rapidly develops after culture overnight or for 3 days in IL-2. Healthy donor PBMCs (B) have no HIV-specific cytotoxicity before or after culture but develop LAK-like activity in an IL-2–dependent manner (as evidenced by the lysis of control vaccinia infected autologous B-LCLs). Cytotoxicity is measured by 4-hour⁵¹Cr release assay at an effector:target ratio of 50:1 against autologous targets infected with vaccinia recombinant virus expressing HIV gp160 (vPE16), RT (vCF21), and gag (vDK1). The control vaccinia (vSC8) expresses the lacZ gene.