Inhibition of Delta vif HIV-1 by APOBEC3G (A3G) and APOBEC3F (A3F) requires their expression in the virus producer cells and incorporation into virions. A3G and A3F deaminate cytidines in minus-strand DNA, causing G-to-A hypermutation and inhibiting viral DNA synthesis. HIV-1 Vif (Vif1) overcomes these host defenses by targeting A3G and A3F for proteasomal degradation. The Vif1-A3G and Vif1-A3F interactions provide two potential targets for development of pharmacological agents that interfere with Vif1-mediated degradation of A3G and A3F. To identify such small-molecule inhibitors, we have developed cell-based high-throughput assays. We are collaborating with the NIH Chemical Genomics Center (NCGC) to perform a quantitative high-throughput screen (qHTS) of a 330,000 compound collection to identify molecules that specifically inhibit the Vif1-A3G and Vif1-A3F interactions. Vif1 binds to several host proteasomal proteins; we are collaborating with the NCGC and using the same cell-based assays to carry out a small-interfering-RNA (siRNA) screen to identify host factors that may be involved in Vif1-mediated degradation of A3G and A3F. Gene therapy for HIV-1-infected individuals has the potential to provide a one-time treatment that will reduce viral load, lessen the use of toxic antiviral drugs, and preserve or improve immune function. Our goal is to test the hypothesis that expression of Vif1-resistant A3G and A3F proteins in HIV-1 target cells will reduce viral loads and control HIV-1 replication. We are developing novel retroviral vectors that can efficiently deliver the Vif1-resistant A3G and A3F to hematopoietic stem cells, and using a humanized mouse model system to determine the effect of the gene therapy on HIV-1 viral load and preservation of CD4+ T cells. These studies will provide the proof of concept that gene therapy with Vif1-resistant A3G and A3F can provide an effective treatment for HIV-1 infection. [Corresponds to Pathak Project 1 in the October 2011 site visit report of the HIV Drug Resistance Program]