NKG2D-Based CAR T Cells and Radiotherapy Exert Synergistic Efficacy in Glioblastoma

Chimeric antigen receptor (CAR) T-cell therapy is an emerging immunotherapy against several malignancies including glioblastoma, the most common and most aggressive malignant primary brain tumor in adults. The challenges in solid tumor immunotherapy comprise heterogenously expressed tumor target antigens and restricted trafficking of CAR T cells to and impaired long-term persistence at the tumor site, as well as the unaddressed integration of CAR T-cell therapy into conventional anticancer treatments. We addressed these questions using a NKG2D-based chimeric antigen receptor construct (chNKG2D) in fully immunocompetent orthotopic glioblastoma mouse models. ChNKG2D T cells demonstrated high IFN gamma production and cytolytic activity in vitro. Upon systemic administration in vivo, chNKG2D T cells migrated to the tumor site in the brain, did not induce adverse events, prolonged survival, and cured a fraction of glioma-bearing mice. Surviving mice were protected long-term against tumor rechallenge. Mechanistically, this was not solely the result of a classical immune memory response, but rather involved local persistence of chNKG2D T cells. A subtherapeutic dose of local radiotherapy in combination with chNKG2D T-cell treatment resulted in synergistic activity in two independent syngeneic mouse gliomamodels by promoting migration of CAR T cells to the tumor site and increased effector functions. We thus provide preclinical proof-of-concept of NKG2D CAR T-cell activity in mouse glioma models and demonstrate efficacy, long-term persistence, and synergistic activity in combination with radiotherapy, providing a rationale to translate this immunotherapeutic strategy to human glioma patients. Significance: These findings provide evidence for synergy of conventional anticancer therapy and CAR T cells and heralds future studies for other treatment combinations. (C) 2017 AACR.