The use of highly active antiretroviral therapy (HAART) in human immunodeficiency virus (HIV)-1 infected individuals has dramatically changed the clinical outcome in many patients and has led to a substantial decline in the incidence of acquired immunodeficiency syndrome (AIDS) and in AIDS-related mortality. However, it is now clear that prolonged suppression of plasma viremia by HAART is not likely to eradicate HIV in most infected individuals. In addition, long-term HAART may lead to drug-induced toxicities, difficulties in adhering to drug regimens, and potential to develop drug resistant virus. Taken together, development of alternative immunologic and virologic strategies aimed at efficient suppression of HIV in infected individuals is urgently needed. Over the past year, we have initiated three basic and clinical research projects to address the above goal. 1. Identification of CD8+ T cell-associated antiviral factors from HIV-infected long-term non-progressors. Studies of the immune responses generated in HIV-infected individuals suggest that CD8+ T cells play an important role in controlling viral replication. At least two types of CD8+ T cell-mediated antiviral activities have been described in HIV infection. The first is a suppressive activity against HIV involving lysis of infected cells in an antigen-specific, HLA-restricted fashion, while the second mechanism inhibits viral replication in the absence of cell killing. Previous studies have demonstrated that these factors include CC-chemokines. Whereas these CC-chemokines exert their antiviral activity on the binding and ultimate entry of HIV into CD4+ T cells and macrophages, another class of currently unidentified antiviral factor (s) has been shown to suppress post-entry viral replication by down-regulating transcription of HIV in infected cells and exerts maximal levels of viral suppression in the setting of co-culture between infected CD4+ T cells and CD8+ T cells. We have constructed a cDNA library from freshly isolated CD8+ T cells from three HIV-infected long-term non-progressors and have begun the screening process to identify genes involved in inhibition of HIV via cell-to-cell contact. Upon identification of such antiviral candidates, we plan to characterize biological properties of such molecules in vitro followed by design of a clinical strategy to utilize these CD8+ T cell-derived antiviral factors in vivo. 2. Role of an immunosuppressive drug in HIV replication. Despite the development of successful therapeutic strategies, it has not been possible to eradicate HIV in infected individuals, mainly due to the persistence of various viral reservoirs. In particular, the presence of replication-competent virus, HIV-1 proviral DNA, including 2 LTR circles, spliced and unspliced HIV-1 RNA in CD4+ T cells has been demonstrated in the majority of infected individuals in whom plasma viremia has fallen below the limit of detection. This persistent viral reservoir has emerged as the major obstacle in preventing eradication of HIV. In addition, our recent work has shown a statistically significant inverse correlation between the frequency of CD4+ T cells carrying HIV-1 proviral DNA and the CD4+/CD8+ T cell ratios in aviremic infected individuals receiving HAART and in whom plasma viremia had been suppressed below the limit of detection for prolonged periods of time (>2.5 years). The above observations suggest that strategies aimed at minimizing cellular activation may further diminish residual viral replication in patients receiving HAART. In order to address this question, we have begun a pilot clinical trial to examine the safety and tolerability of a mildly immunosuppressive agent, daclizumab. Daclizumab is a humanized IgG1 monoclonal antibody that binds specifically to the alpha subunit (p55 alpha, CD25, or Tac subunit) of the human high-affinity IL-2 receptor expressed on the surface of activated lymphocytes. Considering the existence of an intimate relationship between the degree of immune activation and HIV replication, we hope to demonstrate that daclizumab can normalize immunologic profiles as well as reduce plasma viremia in study subjects. 3. Use of anti-CCR5 monoclonal antibodies to treat SIV infection in rhesus monkeys. The success of current antiretroviral therapies has been hampered by the emergence of drug resistant HIV, the necessity of sustained adherence to complex therapeutic regimens, and the potential for drug-induced side effects. Therefore, there is a need to develop novel classes of safe and effective agents for the treatment of HIV/AIDS. Antiviral agents that target the entry of HIV into CD4+ T cells offer hope in this area. The first HIV entry inhibitor that was approved for treatment of HIV/AIDS is Enfuvirtide, a 36-amino acid peptide that interferes with the fusion of viral Envelope protein with cellular membrane. In addition, the chemokine receptor CCR5, a co-receptor for HIV entry for the majority of HIV strains, is a target for several small molecule inhibitors that are in clinical development. The development of a fully humanized monoclonal antibody against CCR5 that is safe, well tolerated, and has potent antiviral activity will further enhance therapeutic options. Such an inhibitor of HIV may provide additional advantages including reduced drug-drug interactions, improved resistance profile, and the convenience of infrequent administration in infected patients due to prolonged plasma half-life of antibody molecules. In order to examine the efficacy of such antiviral molecules, we initiated an animal study in which two types of anti-CCR5 monoclonal antibodies along with an isotype control were injected into 10 rhesus macaques. We hope to demonstrate that anti-CCR5 antibodies can effectively block viral replication for extended periods of time in infected animals and to explore such a strategy in HIV-infected individuals in the near future.
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