Immunotherapy for malignant glioma: preclinical models to improve efficacy of the immune attack

The prognosis of high grade glioma (HGG) is poor in spite of advanced neurosurgery, radio- and chemotherapy. Evidence appears that active specific immunotherapy with mature dendritic cells loaded with tumor lysate (DCm-HGG-L) might induce long term survival. In our preclinical GL261 model, we are now looking for strategies to improve the efficacy of the immune attack. For this, we are approaching two key molecules on the tumor cells. Galectin-1 is known to play a central role in T cell homeostasis and tolerance by inducing T cell apoptosis. Moreover, it induces chemoresistance in tumor cells. Increased expression is found in malignant glioma. We stably knocked down Galectin-1 expression using a lentiviral vector construct, and created KD clones. Current experiments demonstrate that the engraftment of KD GL261 cells is postponed as compared to WT or mock GL261. This is dependent on a spontaneous CD8 T cell-mediated protection, as the effect disappears upon CD8 T cell depletion. DC vaccination results in an improved survival of mice challenged with KD GL261 cells as compared to mice challenged with WT GL261 cells. We are studying currently differences in tumor infiltrating immune cells after tumor challenge with KD or WT GL261. Osteopontin is also an important molecule for chemoresistance, radioresistance, invasion, angiogenesis and immune modulation in malignant glioma. Osteopontin KD tumor cells were created with lentivirus-induced shRNA, and clones were generated. The in vitro responsiveness to irradiation and to doxorubicin was not changed. However, KD cells engrafted slightly slower, and DC vaccination again yielded improved survival as compared to WT cells. We conclude that targeting specific molecules on the malignant glioma cells might induce improved sensitivity to the immune attack after active specific immunotherapy.