A Non-Human Primate Model To Study Anti-HIV Gene Therapy Strategies.

AIDS remains a significant health problem worldwide despite the advent of highly active antiretroviral therapy (HAART). Although substantial efforts have been made to develop a vaccine there is still no cure and alternative strategies are needed to treat HIV infection and to control its spread. Our goal is to evaluate lenti and foamy retroviral vectors that inhibit HIV replication by RNA interference (RNAi) in a non-human primate SHIV model to develop a hematopoietic stem cell (HSC) gene therapy for AIDS. SHIV is a chimeric virus comprised of an SIV genome that contains the tat, rev and env genes of HIV and infects both T lymphocytes and macrophages. Infection of non-human primates with SHIV results in significant decreases in CD4+ T cells as early as 4 weeks post infection, and is currently the best large animal model available to test gene therapy strategies for AIDS. We are developing methylguanine-DNA-methyltransferase (MGMT) selection strategies for HSCs in the primate model to allow for high level marking with vectors containing anti-SHIV/HIV transgenes. We have obtained marking levels over 90% in granulocytes and over 30% in lymphocytes. To determine the effectiveness of an anti tat/rev shRNA to inhibit SHIV in vitro, a human T cell/B cell hybrid cell line (CEMx174) was transduced with a lentiviral vector expressing a short-hairpin RNA (shRNA) targeted to both HIV tat and rev sequences that also contained either a GFP reporter gene or a MGMT(G156A) resistance gene. Polyclonal populations of CEMx174 cells transduced with the GFP and MGMT(G156A) vectors were challenged with a 2.15x10³ TCID50 dose of SHIV. Expression of both tat and rev transcripts was reduced 88% and 97% respectively in these cultures as measured by real-time PCR and replication of SHIV was inhibited as evidenced by inhibition of p27 production. Although others reported a block to transduction of M. mulatta CD34⁺ cells with an HIV-based lentiviral vector, we observed efficient transduction rates (~45%) of M. nemestrina CD34+ cells, comparable to transduction rates observed in human CD34+ cells (~55%). Thus M. nemestrina monkeys provide a powerful model to test lenti and foamy virus mediated anti-HIV gene therapy strategies.