Background and purpose:
T cells play a crucial role in anti-viral immunity. Both cytotoxic T-lymphocytes (CTL) and T helper (Th) cells can recognize virus-derived peptides presented by MHC molecules. After primary infection with the Epstein-Barr virus (EBV), the virus persists for life in a latent form in the B-lymphocytes. Reactivation of these latently infected B-lymphocytes is controlled by specific CD8+ CTL. HIV-infected individuals have a highly increased incidence of (EBV-positive) B cell non-Hodgkin lymphomas (AIDS-NHL). This is generally considered to be due to uncontrolled EBV-driven B lymphoproliferation because of loss of EBV-specific CD8+ T cell immunity 1. In some other viral infections it has been shown that CD4+ T cells are essential for maintenance of CTL responses and chronic control of viremia. The aim of the present project is to study the role of EBV-specific CD4+ T cell help for EBV-specific CD8+ CTL activity in HIV-1 infected individuals developing AIDS-NHL.
Plan of investigation:
To document the CD4+ T helper cell response against EBV in AIDS-NHL patients both quantitatively and qualitatively, the following questions will be addressed:
1. What is the magnitude and specificity of EBV-specific CD4+ T helper cells in HIV-1 infected individuals compared to healthy EBV-seropositive individuals?
2. What are the kinetics of EBV-specific CD4+ T helper cell responses in the natural course of HIV-1 infection in individuals progressing towards AIDS-NHL in comparison with long-term asymptomatics and progressers to opportunistic infections?
3. In case EBV-specific CD4+ T cells are lost in the course of HIV-1 infection: is this a physical or functional loss of EBV-specific CD4+ T cells?
4. is EBV-specific T helper cell and CD8+ T cell immunity restored by anti-retroviral combination therapy?
These questions will be studied using recently developed technologies to enumerate antigen specific T cells in longitudinally obtained cryopreserved PBMC samples from HIV-infected individuals progressing to NHL and appropriately matched control groups from the Amsterdam Cohort Studies on AIDS. These immunodeficient patients offer the unique possibility to investigate the role of CD4+ T helper cells in immunosurveillance against cancer. Tetrameric HLA class II-EBV peptide complexes will be generated to determine the total number of EBV-specific CD4+ T cells. The functional properties of the EBV-peptide specific CD4+ T cells will be determined by measurement of antigen-specific cytokine (INF-gamma, IL-2) production using ELISPOT and intracellular FACS-staining assays. In addition, the quality of the EBV-specific CD4+ T helper cell response will be studied in the light of cross-priming and T cell receptor repertoire diversity.
Possible results:
Our work may reveal whether EBV-specific CD4+ T helper cell activity plays a major role in maintaining EBV-specific CD8+ T cell mediated immunity.
Relevance for cancer research:
EBV-associated NHL in patients with acquired immunodeficiencies are of increasing importance, notably in the setting of allogeneic hematopoietic stem cell transplantation. Our studies will contribute to our understanding of the role of CD4+ T helper cells in immunosurveillance of EBV-associated neoplasia in particular but indirectly also in development of other cancers. This knowledge is essential for (further) development of new therapeutical approaches for both AIDS-NHL and post-transplant NHL such as adoptive transfer of EBV-specific CD4+ helper T cells in conjunction with EBV-specific CTL. |
