EBV-Specific CD4+ T Cell Responses in Acute Infectious Mononucleosis: a Dissertation

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus that establishes a life-long latent infection of B cells. It is usually asymptomatic in healthy individuals; however, individuals with compromised immunity often develop EBV-induced lymphoma. EBV also encodes potential oncogenes that can contribute to tumorigenesis. Therefore, vaccine and immunotherapeutic strategies targeting EBV are desirable. Recent studies have shown that infusion of EBV-specific CD8+T cells can elicit remission of lymphomas arising after administration of immunosuppressive drugs during transplantation, suggesting an important role for T cells in the prevention of EBV-induced malignancy. A better understanding of the cellular immune components involved in the control of EBV will aid in the development of methods to prevent infection and/or treat EBV-associated disease. While EBV infection is usually acquired asymptomatically during childhood, primary infection of adolescents and young adults can result in an illness termed acute infectious mononucleosis (AIM). Because of the characteristic symptoms of the illness, individuals with AIM can be readily identified and diagnosed with acute EBV infection. Thus, primary CD4+ and CD8+ T cell responses against the virus can be evaluated. It has been previously found that there is a marked expansion of lytic EBV protein-specific CD8+ T cells early during AIM, with delayed detection of lower frequencies of latent EBV protein-specific CD8+ T cells. The magnitude and specificity of CD4+T cell responses during AIM has been less well characterized. This thesis dissertation presents data from both functional assays and direct staining experiments documenting the timing, magnitude, and antigen-specificity of CD4+ T cells over the course of primary EBV infection. Lytic and latent protein-specific CD4+ T cells were readily detected by intracellular IFN-γ production at presentation with AIM and declined rapidly thereafter. Blood EBV load was also quantitated and found to decrease over time following AIM. By contrast, CD8+T cell IFN-y responses remained high for several weeks following presentation with AIM. Direct staining of lytic epitope-specific CD4+ T cells during AIM revealed high frequencies of virus-specific cells with low proliferative and IFN-γ-producing potential. Blood EBV load in these patients was persistently high through 6 wk following AIM. These data suggest a relationship between high EBV load during acute infection and impaired EBV-specific CD4+ T cell responses, which are compatible with impaired CD4+ T cell responses reported during high viremia associated with other viral infections. This may represent a mechanism by which persistent viruses, such as EBV, are able to establish a life-long infection in their hosts