An HIV-1 p17 subunit vaccine, HGP-30, was evaluated in 38 HIV-1 seronegative individuals in phase I clinical trials in U.K. and U.S.A. The vaccine preparation induced cytotoxic T-cell (CTL) (11/25) and lymphocyte proliferation responses to KLH (19/20) and HGP-30/p17 (24/29) as well as antibody responses to HGP-30 (29/38) and KLH (38/38). The CTL activity was observed in a higher number of vaccine recipients (9/18) in the lower dose groups (10 and 25 micrograms/kg) than the vaccine recipients (2/7) in the 50 and 100 micrograms/kg dose group. These observations suggest that the 10-25 micrograms/kg vaccine dose may preferentially induce TH1 cell responses. TH1 cell responses have been suggested as important in inducing protective cell mediated immunity. The CTL response has been shown to be CD8+. In a pilot study in SCID mice, HIV-1 virus challenge studies in mice reconstituted with cells from an HGP-30 immunized individual showed protection against virus challenge as compared to SCID mice reconstituted with cells from a non-immunized subject. These studies suggest that HGP-30 is capable of inducing protective cellular immunity.