CD8 T Lymphocyte Responses to Human Herpesvirus 8 Lytic and Latency Proteins
2013
Human herpesvirus 8 (HHV-8) is a lymphotropic gammaherpesvirus that causes Kaposi's sarcoma (KS), a vascular tumor of spindle-shaped endothelial cells. The importance of determining effective prevention and treatment for HHV-8 infection is evident in that KS continues to be the most common cancer among HIV-1 and AIDS patients. It is postulated that CD8+ T cell responses play an important role in controlling HHV-8 infection and preventing KS. However, there are minimal data supporting the role for T cell immunity in control of HHV-8 infection. Therefore, I investigated CD8+ T cell responses to HHV-8 lytic and latency proteins.
I used our dendritic cell-based system in an IFN-γ ELISPOT to identify novel epitopes in healthy, HHV-8 seropositive individuals, then further assessed new epitopes for immune mediators using polychromatic flow cytometry. I also used multimer complexes to directly detect HHV-8-specific CD8+ T cells in blood. I investigated the effect of regulatory T cells (Treg) on these anti-HHV-8 T cell responses by depleting samples of Treg. I then applied these assays to patients in the Multicenter AIDS Cohort Study to longitudinally investigate the role of these responses during the progression to KS.
Through these studies, I identified 10 novel HLA A*0201-restricted epitopes, which activated both monofunctional and polyfunctional CD8+ T cells producing various combinations of immune mediators. Responses were lower over many years prior to development of KS. Although CD8+ T cell IFN-γ responses were modest, a low but consistent percent of HHV-8-specific CD8+ T cells were present in blood, suggesting a functional down-regulation of this response. In support of this, removal of Treg enhanced CD8+ T cell responses to HHV-8 epitopes, and numbers of Treg increased prior to KS development.
Overall, these data support that T cell responses, in frequency, magnitude and quality, are essential for the control of HHV-8 infection to prevent disease development. They also indicate that these antiviral T cell responses are in part controlled by Treg. Involvement of CD8+ T cells and Treg in control of HHV-8 infection has public health significance through implications for understanding the immunopathogenesis of HHV-8 needed for prevention and treatment of KS.
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