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. Objective: To evaluate the impact of AIDS virus evolution on the design of vaccines, we will determine whether mutations that facilitate AIDS virus escape from CD8 T-cell responses also affect viral fitness in vitro and in vivo. We are also attempting to determine the major factors that contribute to elite control of AIDS virus replication. We have recently developed an animal model of elite control in Mamu-B*08+ Indian rhesus macaques. Remarkably, 50% of Mamu-B*08+ Indian rhesus macaques control replication of SIV, and Mamu-B*08 and HLA-B*27 bind similar peptides. Thus, these Mamu-B*08+ macaques are ideal for modeling human ECs. Understanding why ECs suppress viral replication should facilitate the development of an effective HIV vaccine. Elite controllers of HIV and SIV are studied with the goal of understanding immunological mechanisms underlying successful control of immunodeficiency virus replication. Elite control is associated with particular MHC class I alleles, implicating CD8+ T cells as mediators of control. Since in vivo CD8+ cell depletion in two Mamu-B*08+ EC rhesus macaques results in an immediate increase in viral replication, CD8+ lymphocytes are likely important for control in these ECs. Interestingly, SIVmac239[unreadable]nef-vaccinated Mamu-B*08+ macaques exhibit almost complete control of a heterologous SIVsmE660 challenge. Additionally, HLA-B*27 and Mamu-B*08 bind the same peptides requiring an arginine at position 2, and antigen-specific Mamu-B*08-restricted CD8+ T cell responses dominate the acute phase in ECs. These results implicate MHC class I-bound peptide-specific memory CD8+ T lymphocytes in control of viral replication in Mamu-B*08+ rhesus macaques. We have begun testing the hypothesis that Mamu-B*08-epitope-specific T cell responses play a central role in control of SIV replication in macaque ECs. We engineered point mutations into eight CD8+ T cell epitopes restricted by Mamu-B*08. This virus, 8X-SIVmac239, did not have a detectable fitness defect in vitro. Ten Mamu-B*08+ macaques were infected with 8X-SIVmac239. The disease progression and immune responses in these animals are currently being compared to 10 Mamu-B*08+ macaques infected with SIVmac239 where it is known that 50% of these animals will control viral replication. Over the first four weeks of infection, 0 of 10 of the 8X-SIVmac239-infected macaques made the typically immunodominant Vif RL9 or Vif RL8 responses. Immune responses to the three next most immunodominant epitopes, in the Nef and Env proteins, were undetectable or severely impaired compared to responses in wild-type infected animals. Normally subdominant Mamu-B*08-restricted responses, which did not have point mutations introduced, were somewhat stronger in 8X-SIVmac239 infected animals as compared with wild-type infected Mamu-B*08+ animals. In terms of frequency these responses did not compensate for the "knocked out" T cell responses however. At week 14 post-infection the geometric mean viral load for ten Mamu-B*08+ animals infected with SIVmac239 was 5,500 vRNA copy Eq/ml plasma, whereas the group of ten animals infected with 8X-SIVmac239 had a geometric mean viral load of 101,000 vRNA copy Eq/ml plasma. We are also continuing on research on Mamu-B*17. One in five rhesus macaques that express the MHC class I allele Mamu-B*17 control SIVmac239 replication and becomes an elite controller. We showed that the chronic-phase Mamu-B*17-restricted repertoire is focused primarily against just five epitopes, Vif HW8, Env FW9, Nef IW9, Nef MW9, and a cryptic epitope (cRW9), in both ECs and progressors. Viral variation occurred in all targeted Mamu-B*17-restricted epitopes, and recognition of escape variant peptides was commonly observed in both ECs and progressors. Our data suggests that the narrowly focused Mamu-B*17-restricted repertoire suppresses virus replication and drives viral evolution. However, no consistent differences were detected between Mamu-B*17-positive ECs and progressors using standard assays to measure immune responses. Therefore, control of SIV replication in these animals is likely multifaceted. Such is the case with HLA-B57-positive HIV-infected humans. This research used WNPRC Animal Services, Genetics Services, and Immunology &Virology Services.