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To investigate whether immunization with recombinant HIV-1 envelope protein derived from a clinical isolate could protect macaques from infection with an in vivo passaged chimeric simian–human immunodeficiency virus (SHIV).A total of 16 animals were studied from which three groups of four animals were immunized with vaccine formulations of the CC-chemokine receptor-5-binding recombinant gp120 of HIV-1W6.1D. Four weeks after the last immunization, all 16 animals were intravenously challenged with in vivo passaged SHIV derived from the same HIV-1 group B clinical isolate (W6.1D) as the vaccines.Vaccine protection from infection was demonstrated in 10 out of 12 macaques immunized with recombinant gp120. Complete protection from infection was achieved with all of the animals that received the SBAS2–W6.1D formulation, a potent inducer of both T-cell and humoral immune responses. Partial protection was achieved with SBAS1–W6.1D, a formulation based on immunomodulators known to induce T-cell responses in humans. In vaccinated animals that were infected, virus load was reduced and infection was delayed.In a relatively large number of primates, vaccine efficacy was demonstrated with a clinically relevant HIV-1 vaccine. These results reveal that it is possible to induce sterilizing immunity sufficient to protect from infection with SHIV which was passaged multiple times in vivo. Our findings have implications for current HIV-1 clinical vaccine trials and ongoing efforts to develop safe prophylactic AIDS vaccines.