No description available.

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.

In 1989 the hepatitis C virus was identified as a significant cause of post-transfusion hepatitis. Nearly two decades later there is still no vaccine, inadequate treatment options, and limited understanding of how the virus establishes chronicity in the majority of the people it infects. Recent reports suggest that the interaction of a negative co-stimulatory pathway mediated by PD-1 and PDL-1 is associated with persistent viral infection. The role, if any, that PD-1/PDL-1 has in HCV infection is unknown. In this study we report that PD-1 is upregulated in T-cells from persons with chronic HCV infection when compared to healthy donors. In addition, PD-1 and PDL-1 are upregulated on T-cells from healthy donors when exposed to extracellular HCV core protein (a nucleocapsid protein that is immunosuppressive); upregulation of PD-1 is mediated by core's ability to bind to the complement receptor gC1q. We also report that the observed T-cell function can be restored by blocking the PD-1/PDL-1 interaction. Our results indicate that HCV core can upregulate an important negative T-cell signaling pathway that is associated with viral persistence. This upregulation of PD-1/PDL-1 represents a novel and perhaps shared mechanism that viral pathogens may use to subvert the human immune response. It also represents a potential new treatment option for the millions of people who suffer from chronic hepatitis C infection.

No description available.

CD4 T cell homeostasis and competency are critical for the effectiveness of antiviral immunity. However, CD4 T cells derived from people living with HIV (PLWH) and individuals with chronic HCV infection often exhibit an inflammaging phenotype, evidenced by persistent inflammation, immune activation, exhaustion, senescence, and cellular apoptosis. Despite intensive investigations, the molecular mechanisms underlying CD4 T cell dysfunction in antiretroviral therapy (ART)-controlled PLWH and HCV-infected patients remain poorly understood. By investigating the roles of non-coding (nc)RNA transcripts in regulating the functions of CD4 T cells derived from PLWH and HCV-infected patients, we demonstrated that long non-coding (lnc)RNA - growth arrest-specific transcript 5 (GAS5) - is downregulated and plays a crucial role in regulating CD4 T cell functions through and beyond the microRNA (miR)-21-mediated signaling network. Our data suggest that disrupting the GAS5-miR21 axis may restore CD4 T cell homeostasis and competency during latent HIV infection and prevent premature CD4 T cell aging or immune senescence. Moreover, our results also showed that TRF2, a component of the shelterin complex maintaining the integrity of telomeres, is post-transcriptionally inhibited, which is one of the major forces driving cellular dysregulation in CD4 T cells from PLWH and HCV patients. Importantly, our study identified miR-23a as the key regulator of TRF2 translational expression by targeting its 3’UTR in CD4 T cells and that targeting miR-23a may restore the TRF2 protein level, and thereby reconstitute CD4 T cell homeostasis and competency to rescue CD4 T cells from premature aging and immunosenescence during latent HIV infection. The findings from these studies improved our understanding and knowledge of how ncRNA-mediated networks regulate the functions of CD4 T cells during chronic viral (HIV and HCV) infections. Understanding such mechanisms is important for developing therapeutic approaches to reverse the inflammaging phenotype observed in CD4 T cells from ART-controlled PLWH and chronically HCV-infected patients to improve their immunological functions and quality of life.

The clearance of viruses is largely dependent upon the activation of T cells to generate a robust immune response. However, host responses are suppressed during chronic viral infections. In this thesis, we explored the role of Top2α in DNA topology in individuals with chronic HBV, HCV, and HIV infections. We found that Top2α protein expression and activity were low in T cells derived from chronically virus-infected individuals compared to healthy subjects. Using CD4+ T cells treated with Top2α inhibitor or poisoner as a model, we demonstrated that Top2α inhibition disrupts the DNA topology, suppresses DNA repair kinase (ATM), and telomere protein (TRF2) expression, and induces T cell dysfunction. These findings reveal that Top2α inhibition is a mechanism by which viruses evade the host responses and establish persistent infection, and thus, restoring Top2α levels could be a way of boosting immune responses during chronic viral infections.