Immunohistochemical study of rats receiving peripheral immunization with IFNg transfected glioma cells

Malignant glioma is, with rare exceptions in younger adults, an uncurable brain tumor, as very few survive more than 1-2 years after diagnosis. Despite advances in recent years, current treatments such as surgery, radiotherapy and chemotherapy only prolongs the life of the patients. Because of the poor prognosis, several additional therapies have been investigated and are under development, such as different immunotherapeutic strategies. Experimental models have shown that by enhanced antigen presentation, support of various immune functions with the addition of, for example, cytokines as well as inhibition of immunosuppressive factors, it is possible to reject growing tumors in the brain. The aim of this thesis was to study the immune response in rats receiving therapeutic immunization with glioma cells genetically engineered to express IFNg. IFNg is a multifunctional cytokine that has been shown to affect different immune functions such as the stimulation of phagocytosis and antigen presentation, as well as trafficking of leukocytes and induction of Th1 immune responses. More specifically, in study I we refined an immunohistochemical method and a computerized image analysis method to systematically evaluate variations in leukocyte infiltration between different immunotherapies. These methods were used in study II-IV. In study II, we investigated the kinetics as well as the amount of different leukocyte subtypes that infiltrated brain tumors of rats receiving immunization with IFNg transfected glioma cells. In studies III and IV, we characterized the local immune response in rats receiving immunotherapy with IFNg. Taken together, the data presented in this thesis show that IFNg induced an increased infiltration of TCR+ cells, CD8+ cells and NK-cells in brain tumors of rats receiving immunotherapy, as compared to control animals. IFNg induced a specific infiltration of TCR+ cells, CD8+ cells and NK-cells at the immunization site. Tumor cells were engulfed by mononuclear phagocytes and were transported to draining lymph nodes. We believe that these specific mechanisms are responsible for the therapeutic effects seen in animals immunized with IFNg transfected glioma cells.