Prior irradiation results in elevated programmed cell death protein 1 (PD-1) in T cells

Purpose: In this study we addressed the question whether radiation-induced adverse effects on T cell activation are associated with alterations of T cell checkpoint receptors. Materials and methods: Expression levels of checkpoint receptors on T cell subpopulations were analyzed at multiple post-radiation time points ranging from one to four weeks in mice receiving a single fraction of 1 or 4 Gy of c-ray. T cell activation associated metabolic changes were assessed. Results: Our results showed that prior irradiation resulted in significant elevated expression of programmed cell death protein 1 (PD-1) in both CD4+ and CD8+ populations, at all three post-radiation time points. T cells with elevated PD-1 mostly were either central memory or naive cells. In addition, the feedback induction of PD-1 expression in activated T cells declined after radiation. Conclusion: Taken together, the elevated PD-1 level observed at weeks after radiation exposure is connected to T cell dysfunction. Recent preclinical and clinical studies have showed that a combination of radiotherapy and T cell checkpoint blockade immunotherapy including targeting the programmed death-ligand 1 (PD-L1)/PD-1 axis may potentiate the antitumor response. Understanding the dynamic changes in PD-1 levels in T cells after radiation should help in the development of a more effective therapeutic strategy.