Effect of PD-1 Inhibitor Combined with X-Ray Irradiation on the Inflammatory Microenvironment and Lung Tissue Injury in Mice

Purpose: This study was designed to evaluate the effects of PD-1 inhibitor on lung tissue morphology and the immune system in a mouse model of radiation-induced lung injury (RILI) and to assess interactions between radiation therapy and PD-1 inhibition. Methods: Twenty C57BL/6 mice were divided randomly into four groups of five mice each. Mice were treated with an anti-mouse PD-1 monoclonal antibody, whole thorax irradiation, both or neither. Lung tissue morphology and pathological changes were assessed by hematoxylin-eosin staining; lung fibrosis was assessed by Masson staining and analysis of hydroxyproline; CD3+, CD4+, and CD8+ T lymphocytes in lung tissues were detected immunohistochemically; and the concentrations of transforming growth factor-beta 1 (TGF-beta 1) and interleukin-6 (IL-6) in lung tissue were evaluated by cytokine multiplex analysis. Results: Lung injury scores and indicators of pulmonary fibrosis were higher in mice administration whole thorax irradiation than in control mice. Inflammatory infiltrate scores, alveoli deformation scores, collagen volume fractions and hydroxyproline contents in lung tissues were all significantly higher in mice administered PD-1 inhibitor plus irradiation than in the other three groups. Similarly, the percentages of CD3+ and CD8+T cells and the concentrations of IL-6 and TGF-beta 1 in lung tissue were significantly higher in mice treated with radiation and PD-1 inhibitor than in the other groups. However, PD-1 inhibitor and irradiation interacted significantly only in the elevation of TGF-beta 1 level. Conclusion: Whole thorax X-ray irradiation in mice can cause pulmonary injury and fibrosis, which could be exacerbated by PD-1 inhibitors. Radiotherapy combined with PD-1 inhibitors may aggravate RILI by synergistically upregulating TGF-beta 1 expression, thereby affecting the immune-inflammatory microenvironment in the lungs.