Characterization of gamma herpesvirus viral DNA in peripheral blood of patients with virus-associated malignancies and analysis of CD8+ T cell responses to viral antigens in patients with Hodgkin's lymphoma

Human gamma herpesviruses include Epstein-Barr virus (EBV) and human herpesvirus 8 (KSHV/HHV8) both of which are associated with human malignancies. EBV has been linked to Hodgkin's lymphoma (HL), Burkitt's lymphoma and nasopharyngeal carcinoma etc. KSHV has been associated with Kaposi Sarcoma (KS) and primary effusion lymphoma etc.; DNA from EBV or KSHV has been frequently found in peripheral blood of patients with virus-associated malignancies. The first part of this work investigated the characteristics of circulating viral DNA in patients with virus-associated malignancies. Viral loads were measured with real-time PCR in peripheral blood mononuclear cells (PBMC) and plasma. Viral loads in plasma were found to be more closely related to the presence of viral DNA in tumor cells. In HL, EBV DNA in plasma is more likely to be detected in EBV(+) HL and it disappears with therapy. EBV DNA in plasma of EBV(+) HL is at least in part derived from tumor cells. In AIDS-associated non-Hodgkin's lymphoma (AIDS-NHL), viral DNA is more common in EBV(+) AIDS-NHL and the aberrant promoter methylation could be found in plasma. However, the characteristics of EBV DNA in plasma was consistent with mostly virion origin. The results suggest the combined contribution of both virion particles and naked viral DNA of tumor origin in plasma. KSHV DNA in plasma of patients with AIDS-NHL was found to be of virion origin and it disappeared during chemotherapy in parallel with the disappearance of B cells. The second part of this work investigated CD8+ T cell responses to EBV and CMV antigens in HL. The frequency of antigen-specific CTLs was measured with ELISPOT and tetramer assay. The results indicate that in EBV(+) HL there is a selective decrease in the CD8+ T cell response to an EBV antigen LMP2 which is expressed in tumor cells, whereas in EBV(-) HL there is a general blunting of CTL responses to EBV and CMV antigens. Understanding the underlying immune dysfunction in EBV(+) HL plays a crucial role in designing and optimizing immunotherapy for this disease.