Dose-dependent enhancement of T-lymphocyte priming and CTL lysis following ionizing radiation in an engineered model of oral cancer

•Ionizing radiation (IR) induces apoptosis in a dose-dependent fashion.•8 Gy IR induces release of tumor antigen to a greater degree than 2 Gy.•8 Gy IR induces T-cell priming in vitro to a greater degree than 2 Gy.•8 Gy IR induces T-cell priming in peripheral and tumor compartments in vivo.•Higher single doses of IR should be considered when combining IR and immunotherapy.

ObjectivesDetermine if direct tumor cell cytotoxicity, antigen release, and susceptibility to T-lymphocyte killing following radiation treatment is dose-dependent.Materials and methodsMouse oral cancer cells were engineered to express full-length ovalbumin as a model antigen. Tumor antigen release with uptake and cross presentation of antigen by antigen presenting cells with subsequent priming and expansion of antigen-specific T-lymphocytes following radiation was modeled in vitro and in vivo. T-lymphocyte mediated killing was measured following radiation treatment using a novel impedance-based cytotoxicity assay.ResultsRadiation treatment induced dose-dependent induction of executioner caspase activity and apoptosis in MOC1 cells. In vitro modeling of antigen release and T-lymphocyte priming demonstrated enhanced proliferation of OT-1 T-lymphocytes with 8 Gy treatment of MOC1ova cells compared to 2 Gy. This was validated in vivo following treatment of established MOC1ova tumors and adoptive transfer of antigen-specific T-lymphocytes. Using a novel impedance-based cytotoxicity assay, 8 Gy enhanced tumor cell susceptibility to T-lymphocyte killing to a greater degree than 2 Gy.ConclusionIn the context of using clinically-relevant doses of radiation treatment as an adjuvant for immunotherapy, 8 Gy is superior to 2 Gy for induction of antigen-specific immune responses and enhancing tumor cell susceptibility to T-lymphocyte killing. These findings have significant implications for the design of trials combining radiation and immunotherapy.