The Vaccine Branch of CCR has been exploring several novel approaches to an HIV vaccine, including an adenovirus-based vaccine, a DNA vaccine, and mucosal vaccination to induce T cell responses at the site of infection. In addition, scientists in the Institute of Human Virology (IHV) in Baltimore have been exploring a recombinant human full-length single chain (rhFLSC) HIV vaccine that involves epitopes located in and around the co-receptor binding site of HIV-1 envelope protein that are exposed after binding to CD4. These epitopes comprise some of the most conserved and functionally important residues and there is evidence that this vaccine can elicit neutralizing antibodies against diverse primary isolates of HIV. In FY2009, a collaborative project was initiated within CCR to test several HIV vaccine strategies of Jay Berzofsky, George Pavlakis, Barbara Felber, and Marjorie Robert-Guroff in the Vaccine Branch, CCR in combination with the rhFLCS vaccine of IHV. In particular, macaques will be vaccinated with combinations of rhFLCS vaccine combined with a recombinant adenovirus encoding rhFLCS, a rhFLSC DNA vaccine, or a mucosal HIV vaccine. The macaques would subsequently be challenged with SIVmac251 to assess the utility of these approaches in comparison with appropriate controls. A number of immunologic, virologic, and clinical tests will be done to assess the safety of these vaccine approaches and their ability to yield immunologic responses and provide protection against viral challenge.