A hallmark of chronic human immunodeficiency virus (HIV) infection is the impairment of CD8 T cell survival and effector functions, which likely contributes to HIV pathogenesis. A number of factors could be attributed to this impairment, including the declining number of CD4 T cells, progressive destruction of secondary lymphoid tissues and an increasingly inhibitory environment. As highly active antiretroviral therapy shows limited efficacy in improving CD8 T cell functions, this thesis explores the therapeutic application of costimulatory molecules in directly stimulating non-functional HIV-specific CD8 T cells and ultimately their relevance to the control of chronic HIV infection. Costimulatory molecules are adjuvants for functional activation of T cells that act in concert with the antigen-specific signal. The Tumor Necrosis Factor (TNF) family member, 4-1BBL, emerges as the most effective costimulatory molecule in the antigen-specific expansion of human memory CD8 T cells as compared to the related TNF family members CD70 and LIGHT. As well, 4-1BBL improves the cytolytic function of T lymphocytes on a per cell basis. Furthermore, 4-1BBL is identified as a key component in the therapeutic rescue of CD8 T cell function and its effect is at least partially dependent on its signaling adaptor TNF receptor associated factor 1 (TRAF1), both in vitro and in vivo. This thesis also identifies the loss of TRAF1 as a new mechanism of immune dysregulation of HIV-specific CD8 T cells during the chronic phase of HIV infection and offers a means to correct it. The loss of TRAF1 has functional relevance in HIV suppression and HIV-specific CD8 T cell responses. Finally, a combination therapy involving agonistic anti-4-1BB antibody is shown to be successful in a proof of concept treatment of chronic lymphocytic chroriomeningitis virus (LCMV) infection in mice, resulting in sustained reduction in viral load. A new model of HIV-specific CD8 T cell dysfunction is constructed based on these findings.

A hallmark of chronic human immunodeficiency virus (HIV) infection is the impairment of CD8 T cell survival and effector functions, which likely contributes to HIV pathogenesis. A number of factors could be attributed to this impairment, including the declining number of CD4 T cells, progressive destruction of secondary lymphoid tissues and an increasingly inhibitory environment. As highly active antiretroviral therapy shows limited efficacy in improving CD8 T cell functions, this thesis explores the therapeutic application of costimulatory molecules in directly stimulating non-functional HIV-specific CD8 T cells and ultimately their relevance to the control of chronic HIV infection. Costimulatory molecules are adjuvants for functional activation of T cells that act in concert with the antigen-specific signal. The Tumor Necrosis Factor (TNF) family member, 4-1BBL, emerges as the most effective costimulatory molecule in the antigen-specific expansion of human memory CD8 T cells as compared to the related TNF family members CD70 and LIGHT. As well, 4-1BBL improves the cytolytic function of T lymphocytes on a per cell basis. Furthermore, 4-1BBL is identified as a key component in the therapeutic rescue of CD8 T cell function and its effect is at least partially dependent on its signaling adaptor TNF receptor associated factor 1 (TRAF1), both in vitro and in vivo. This thesis also identifies the loss of TRAF1 as a new mechanism of immune dysregulation of HIV-specific CD8 T cells during the chronic phase of HIV infection and offers a means to correct it. The loss of TRAF1 has functional relevance in HIV suppression and HIV-specific CD8 T cell responses. Finally, a combination therapy involving agonistic anti-4-1BB antibody is shown to be successful in a proof of concept treatment of chronic lymphocytic chroriomeningitis virus (LCMV) infection in mice, resulting in sustained reduction in viral load. A new model of HIV-specific CD8 T cell dysfunction is constructed based on these findings.