This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This year, we examined two issues pertinent to the discovery of a successful HIV-1 vaccine. With experiment 1, we addressed an important debate concerning the ability of an immunodeficiency virus to elicit a protective immune response. With experiment 2 we tested the ability of a multi-vectored (DNA, vaccinia virus, protein), multi-envelope HIV-1 vaccine to protect against a heterologous SHIV challenge. Methods: In experiment 1, two macaques received an inoculation with SHIV KU-1 and were rested for 10 months, after which animals were exposed to SHIV 89.6P. This experiment was conducted prior to 2008, but evaluation was completed this year. In experiment 2, groups of macaques received multi-vectored, multi-envelope vaccines. Some animals received vaccinia virus that had been inactivated by ultra-violet light. Test and control animals were challenged with SHIV 89.6P. Results: In experiment 1, we found that SHIV KU-1 infection elicited diverse neutralizing antibody activities that improved during the e10 month period. After exposure to SHIV 89.6P, all control animals were infected and most succumbed to disease. In contrast, among test animals, one showed no evidence of superinfection and the second showed virus at only one time point. Neither animal showed signs of disease. Experiment 2 showed that the multi-envelope vaccine protected against disease and that the vaccinia virus recombinant vector was immunogenic even after inactivation. Discussion: Experiment 1 clearly demonstrated that infected animals could mount a protective immune response against superinfection. We suggest that this protective state may serve as a 'gold-standard'for HIV-1 vaccine development, as a similar degree of protection against immunodeficiency virus infections in humans would be much desired. Experiment 2 demonstrated the potency of a multi-envelope vaccine, while validating a vector modification that might be used in future clinical trials to ensure HIV-1 vaccine safety.