Analysis and manipulation of autoreactive and tumor-specific T cell responses

Sammanfattning: The focus of this work has been on the analysis and manipulation of T cell responses. One emphasis has been on T cells involved in autoimmune diabetes and another on T cells in tumor immunity. Primary activation of T cells as well as the role of the proteasome in T cell responses has been overlapping themes. Non obese diabetic (NOD) mice represent a mouse model for human Type I diabetes. Diabetes at NOD mice starts at around two weeks of age, when naïve autoreactive T cells encounter beta cell-derived antigen, in the pancreatic lymph nodes (PLN). Activated T cells proliferate at this site and subsequently leave the PLN and infiltrate the pancreas. Lymphocytes first appear in the pancreas at 3 weeks of age and diabetes occurs around 12 weeks of age. In an attempt to identify disease-initiating T cells, we studied the length of the CDR3 region on T cells isolated from the PLN of very young NOD mice. Immunoscope analysis of lymph node RNA from different time points (10, 14, 18 and 22 days of age), revealed subtle and transient oligoclonal expansion of TCRVbeta5.1-Jbeta1.5, TCRVbeta5.1-Jbeta1.3, TCRVbeta5.2Jbeta1.5 and TCRVbeta5.2-Jbeta1.6 in the PLN in comparison to the inguinal lymph node (ILN). Targeting those specific TCR species may offer novel treatment strategies in autoimmune diabetes. The subtleness of the initiating events in the PLN suggested that variation in activation thresholds could affect rate-limiting steps in order for T cell activation to proceeds. One such threshold may be stimulation needed for individual T cells to initiate IFN-gamma secretion. We found that naïve CD8+ T cells are geared towards IFN-gamma production when stimulated with low amounts of peptide, suggesting that they may play a role in early phases of immune responses in peripheral lymphoid organs. Another important focus of this thesis has been attempts to manipulate T cell responses using, proteasome inhibitors. Proteasome inhibitors affect peptide presentation but also modulate cytokine production, proliferation and survival of T cells. Applying proteasome inhibitor MG132 in a diabetes transfer model reduced diabetes with 76% in inhibitor treated mice compared with control recipients. The calpain inhibitor z-LeuLeu-H was without protective effect suggesting that MG132 acted via inhibition of the proteasome. Leukocyte infiltration of the pancreatic islets was not dramatically altered. However, our analysis revealed a decrease in proliferation of the transferred T cells in the PLN of the recipient mice, suggesting that the link between PLN proliferation and islet infiltration may reflect qualitative rather than quantitative effects. The use of proteasome inhibitors in a tumor system revealed a role of the proteasome in the production of certain tumor antigens. When tumor cells were adapted to grow in the presence of proteasome inhibitors they became more efficient in avoiding immunological reaction and formed more tumors in vivo. This phenotype might be preferentially selected in tumors to allow immune escape. Together, the studies presented in this thesis contribute to the understanding of T cell activation in autoimmune diabetes and cancer and propose different possibilities of modulation activation, proliferation and effector function of T cells.