PP017 Dynamic alterations in PD-1/PD-L1 activity and immune cell profiles depending on radiation response status: A preclinical study

Regarding the immunologic effects of anti-cancer treatment and their therapeutic implications, we aimed to evaluate radiotherapy (RT)-induced dynamic alterations in programmed death-1 (PD-1)/ death ligand-1 (PD-L1) expression profiles. Local RT with 2 Gy × 5 or 7.5 1 was applied CT26 mouse model. Tumors were resected evaluated at predefined time points according radiation response status: baseline, early (immediately after RT), middle (beginning tumor shrinkage), late (stable status effect), progression (tumor regrowth). PD-1/PD-L1 activity related immune cell profiles quantitatively assessed. upregulated PD-L1 levels cells from phase, which subsequently declined a level comparable baseline phase. induced lesser degree regression than Gy, frequency PD-L1+ myeloid-derived suppressor maintained be higher fractionated regimen. The proportion PD-1+ interferon (IFN)-γ+CD8α T continued increase, but mean fluorescence intensity values IFN-γ began decrease splenic PD-1+CD8+ significantly elevated, sustained longer 5. In transcriptomic data, stimulated transcription overall immune-related genes, showing sequentially altered patterns. observed depending on time-course responses. sequential patterns dose-fractionation should considered determine appropriate strategies radioimmunotherapy.