OS09.3 Synergistic activity of NKG2D-based chimeric antigen receptor (CAR)-T cells and radiotherapy against glioma

摘要

>Introduction: Glioblastoma is the most common primary brain tumor in adults and virtually always lethal despite a multimodal treatment regimen including surgery, chemotherapy and radiotherapy. Therefore, novel treatment modalities are needed. Adoptive immunotherapy with genetically engineered T cells that express a chimeric antigen receptor (CAR) to recognize and eliminate tumors in a MHC-independent manner is an emerging strategy that has led to remarkable responses in hematologic malignancies. CARs that target the natural-killer group 2-member D (NKG2D) system elegantly use the promiscuous binding properties of the NKG2D receptor that binds to several tumor-associated ligands. NKG2D-based CAR T cells have never been investigated against glioma and it is unknown if this strategy can overcome the challenges of this tumor entity and if it could even be implemented in established conventional treatment regimens. >Material and Methods: CAR T cells were generated by retroviral transduction of splenocytes to express a NKG2D-based CAR (chNKG2D) or wildtype NKG2D (wtNKG2D). For in vitro studies, murine glioma cells (GL-261, SMA-560, SMA-540, SMA-407) were co-cultured with chNKG2D or wtNKG2D T cells and we assessed the cytolytic activity and cytokine production. For in vivo studies, we used GL-261 cells syngeneic to C57BL/6 mice and monitored tumor growth by magnetic resonance imaging. We tracked CAR T cells in vivo with fluorescence molecular tomography (FMT), flow cytometry and immunohistochemistry. To study the combination of radiotherapy with CAR T cells, mice received a single subtherapeutic dose of local irradiation. >Results: In all murine glioma cell lines, chNKG2D T cells had a significantly higher specific cytolytic activity compared to wtNKG2D T cells. Furthermore, chNKG2D T cells produced more IFN-γ. In vivo, intravenously injected chNKG2D T cells migrated to the orthotopic tumor site, were tolerated without toxicities, prolonged the survival and cured a fraction of tumor-bearing mice. This anti-tumor effect was even more pronounced in case of intratumoral CAR T cell administration. Survivors were long-term protected against tumor re-challenge. Mechanistically, this was not the result of a classical immune memory response, but rather due to local persistence of chNKG2D T cells. Radiotherapy augmented the effect of chNKG2D T cell therapy already after a single application of a subtherapeutic dose. It promoted migration of CAR T cells to the tumor site and the effector function of NKG2D-based CAR T cells. >Conclusion: We provide the first systematical preclinical assessment of NKG2D-based CAR T cells against glioma. This strategy was effective, tolerated without toxicities, conferred long-term protection and was synergistic with radiotherapy. These findings could provide a rationale to test this immunotherapeutic strategy also in human glioma patients.