PROJECT SUMMARY Natural killer (NK) cells provide an immediate defense against viruses and tumors by virtue of their ability to respond to infected or malignant cells without prior antigenic stimulation. This is accomplished through the integration of signals from activating and inhibitory NK cell receptors (aNKRs & iNKRs). In humans and other primate species, these include C-type lectin receptors, such as CD94/NKG2A and CD94/NKG2C, and the highly polymorphic killer-cell immunoglobulin-like receptors (KIRs), both of which interact with MHC class I ligands. These receptor-ligand interactions are fundamental to the ability of NK cells to differentiate healthy cells from unhealthy cells and provide a potential mechanism of specificity for the development of “NK cell memory”. NK cells can have a significant impact on HIV-1 infection. KIR and HLA class I polymorphisms have been identified that are associated with lower viral loads and slower courses of disease progression and certain NK cell subsets can kill HIV-infected cells in culture. Thus, NK cell-based therapies represent a promising approach for targeting HIV-infected cells and reducing the size of viral reservoirs. We hypothesize that viral peptides bound by the MHC class I ligands of aNKRs are critical to NK cell recognition and killing of HIV/SIV-infected cells and that the adoptive transfer of ex vivo activated NK cells in combination with latency reversal can deplete viral reservoirs in SIV-infected macaques on suppressive antiretroviral therapy (ART). In Aim 1, we will determine the contribution of viral peptides bound by MHC class I ligands of aNKRs to NK cell recognition of HIV- and SIV-infected cells. These studies will utilize high-throughput cellular assays to rapidly screen viral peptides for MHC class I interactions with aNKRs and to identify substitutions that disrupt these interactions. The corresponding changes will be introduced into HIV-1 and SIV to assess their impact on NK cell responses to virus-infected cells. In Aim 2, we will assess the capacity of ex vivo expanded NK cells in combination with latency reversal to deplete viral reservoirs in SIV-infected, ART-suppressed rhesus macaques. This aim will take advantage of barcoded SIV and a potent new latency reversal agent to compare with maximal sensitivity the ability of autologous versus allogeneic NK cell transfer to reduce the rate of viral reactivation after discontinuing ART. In Aim 3, we will test the hypothesis that the depletion of viral reservoirs by adaptive NK cell transfer can be enhanced by an Env-specific antibody with antibody-dependent cellular cytotoxicity against SIV-infected cells. This aim will use a similar approach as Aim 2 to determine the extent to which coupling NK cell effector function to the unparalleled specificity of antibodies can maximize reservoir depletion. These unprecedented studies will provide a better understanding of the role of viral peptides in NK cell recognition of HIV- and SIV-i...