DESCRIPTION (provided by applicant): Developing an effective preventative vaccine for HIV-1 has proved to be an enormous challenge. The classical vaccine approach has failed thus far or produced modest efficacy in dealing with a virus infects a key component of immune system and exhibits great antigenic diversity and mutates rapidly. Novel approaches and ideas are needed to develop a preventative vaccine to HIV-1. Edward Jenner developed the successful smallpox vaccine based on the natural immunity observed in milkmaids. Thus, the correlates of natural immunity to HIV-1 documented in highly exposed uninfected individuals may provide a vital clue for the development of a preventative vaccine to HIV-1. Learning from immunologic correlates of protection from HIV-1 infection in a group of highly exposed HIV resistant Nairobi female sex workers, we propose that an effective preventative vaccine to HIV-1 should target key sites of HIV-1 and a vaccine targeting the 12 protease cleavage sites of HIV-1 can prevent HIV-1 acquisition. HIV protease is a small 99-amino acid aspartic enzyme that mediates the cleavage of Gag, Gag-Pol and Nef precursor polyproteins. The process is highly specific, temporally regulated and essential for the production of infectious viral particles. A total of twelve proteolytic reactions are required to generate an infectious virion. Therefore, a vaccine generating immune responses to the 12 protease cleavage sites of HIV-1 would have several major advantages. First, the host immune response could destroy the virus before its permanent establishment in the host. Second, the vaccine could force the virus to accumulate mutations eliminating the normal function of the HIV protease thus eliminating infectious virions. Third, restricting the immune responses to these sites can avoid distracting immune responses that often generate unwanted inflammatory responses, excess immune activation, and attract more targets for HIV- 1 infection, establishment and spread. To test this hypothesis we will use Mauritian Cynomolgus macaques and pathogenic SIVmac251 as an experimental model and peptides overlapping the 12 protease cleavage sites of SIVmac239 as immunogens to compare with full Gag and full Env as immunogens. We will deliver these immunogens with a) a modified vesicular stomatitis virus (VSV) vector system capable of targeting dendritic cells and generating robust immune responses; b) a nanostructure mucosal delivery system. The protection from infection will be examined by the ability of the macaques to resist repeated low dose intravaginal pathogenic SIVmac251 challenges. Secondary outcome such as viral load set point and CD4+ T cell decline will also be compared. Viral fitness analysis will be conducted to validate that the focused immune responses can drive deleterious viral mutation and produce virus of attenuated fitness and transmissibility. Confirmation of this hypothesis and vaccine approach will shift the paradigm of HIV vaccine development and develop an effective preventative HIV vaccine.