Abstract IA-012: Differential immunological effects of carbon-ion versus photon radiation therapy

Abstract

Abstract Radiation therapy (RT) exerts multiple effects on the immune system; in particular RT can serve as an in situ vaccine to either prime new anti-tumor T cell responses, or to induce new responses. We and many others showed that these propitious effects appear to counter-balanced to some degree by immunosuppressive effects, including the expansion of regulatory T cells (Treg), recruitment of myeloid derived suppressive cells (MDSC), and induction of Trex which mitigates the pro-inflammatory effects of STING pathway activation. Carbon-ion radiation therapy (CiRT) is an emerging therapeutic modality based on data showing that heavy ions may improve dosimetry and decrease toxicity to normal tissues. Currently, CiRT is performed at a limited number of centers, thus its immunological effects remain relatively understudied. To address this knowledge gap, we used an orthotopic, syngenic murine model to compare the relative immunological effects of CiRT to conventional photon radiation therapy (PhRT). At short follow-up times post RT, PhRT decreased the prevalence of T cells in the TME at all doses examined, whilst CiRT appeared to be relatively lymphocyte sparing. Higher doses of CiRT increased the secretion of multiple pro-inflammatory cytokines to a greater degree than did PhRT. Consistent with our prior results, both modalities increased Treg infiltration; although this was less apparent with CiRT. Although these are early studies with several caveats, the results support the hypothesis that CiRT may have differential immunological effects than those mediated by PhRT. Citation Format: Charles G. Drake. Differential immunological effects of carbon-ion versus photon radiation therapy [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr IA-012.