Cytotoxic T-cells (CTL) provide the basis of protective immunity in many viral infections by appearing early in the immune response and becoming involved with the elimination of virus by lysis of infected cells. A considerable amount of evidence suggests that CTL may be an especially important component of the host defense against HIV-1 (1 ,2 ) . Strong CTL activity is seen early during the course of infection (3 ,4 ), in nonprogressor individuals, some of whom have been infected for a decade or more with HIV-1 (5 ,6 ) and also in some HIV-1 exposed sex workers (7 ) and babies (8 ,9 ) who remain HIV-1-negative.