Effect of PD-1 Inhibitor on Cardiac Inflammatory Microenvironment and Radiation Induced Heart Injury

Purpose/Objective(s)Thoracic radiotherapy combined with PD-1 inhibitor can promote the activation of T cell and improve the treatment outcomes of patients with chest cancer. However, it also increases the risk of myocardial injury. A mouse model was used to observe the effects of PD-1 inhibitors on myocardial immune microenvironment and radiation induced injury, and to explore the potential mechanism of PD-1 inhibitors aggravating myocardial injury using.Materials/MethodsTotally 20 C57BL/6 mice were randomly divided into 4 groups, including group A as normal control, group B receiving intraperitoneally injected with anti-PD-1 antibody, group C receiving full thoracic x-ray irradiation with 15 Gy in one fraction, D group receiving anti–PD1 as the same as B group and full thoracic x-ray irradiation as C group. At 1 months after irradiation, mice were killed under anesthesia. Hematoxylin-eosin staining and Mason staining were used to observe myocardial injury and fibrosis. The levels of CD3+, CD3+CD4+, CD3+CD8+ lymphocyte and cytokines (IL-4, IL-6, IL-17A, TNF-α, TGF-β1, INF-γ) in myocardium were detected by flow cytometry. The apoptosis rate of myocardial cells was detected by TUNEL assay.ResultsMason staining showed that no obvious myocardial fibrosis in group B, and collagen fibers were distributed in the myocardial interstitium in groups C and D. The results of semi-quantitative analysis showed that the myocardial collagen volume fraction (CVF) of each group A, B, C and D were (1.97 ± 0.36)%, (2.83 ± 1.03)%, (5.39 ± 0.77)% and (7.72 ± 1.43)%, respectively. The CVF of group A was similar to that of group B (P = 0.314). There were statistically significant differences in CVF among other groups (P < 0.05). Compared with group A, the absolute value and percentage of CD3+T lymphocytes in groups B, C and D were increased (P < 0.01), and those in group D were higher than those in group B and C (P < 0.01). The absolute value and percentage of CD3+CD4+T lymphocytes in groups A, C, B and D were similar (P > 0.05). The absolute value and percentage of CD3+CD8+T lymphocytes in group D were higher than those in groups A, B and C (P < 0.001). The levels of IL-6, IL-17A and TGF-β1 in group D were higher than those in groups A, B and C (P < 0.001). The apoptotic index of groups A, B, C and D increased gradually, and the difference of apoptotic index among all groups was statistically significant (P < 0.001).ConclusionPD-1 inhibitors can aggravate radiation-induced myocardial injury by promoting myocardial immunoinflammatory response. Thoracic radiotherapy combined with PD-1 inhibitor can promote the activation of T cell and improve the treatment outcomes of patients with chest cancer. However, it also increases the risk of myocardial injury. A mouse model was used to observe the effects of PD-1 inhibitors on myocardial immune microenvironment and radiation induced injury, and to explore the potential mechanism of PD-1 inhibitors aggravating myocardial injury using. Totally 20 C57BL/6 mice were randomly divided into 4 groups, including group A as normal control, group B receiving intraperitoneally injected with anti-PD-1 antibody, group C receiving full thoracic x-ray irradiation with 15 Gy in one fraction, D group receiving anti–PD1 as the same as B group and full thoracic x-ray irradiation as C group. At 1 months after irradiation, mice were killed under anesthesia. Hematoxylin-eosin staining and Mason staining were used to observe myocardial injury and fibrosis. The levels of CD3+, CD3+CD4+, CD3+CD8+ lymphocyte and cytokines (IL-4, IL-6, IL-17A, TNF-α, TGF-β1, INF-γ) in myocardium were detected by flow cytometry. The apoptosis rate of myocardial cells was detected by TUNEL assay. Mason staining showed that no obvious myocardial fibrosis in group B, and collagen fibers were distributed in the myocardial interstitium in groups C and D. The results of semi-quantitative analysis showed that the myocardial collagen volume fraction (CVF) of each group A, B, C and D were (1.97 ± 0.36)%, (2.83 ± 1.03)%, (5.39 ± 0.77)% and (7.72 ± 1.43)%, respectively. The CVF of group A was similar to that of group B (P = 0.314). There were statistically significant differences in CVF among other groups (P < 0.05). Compared with group A, the absolute value and percentage of CD3+T lymphocytes in groups B, C and D were increased (P < 0.01), and those in group D were higher than those in group B and C (P < 0.01). The absolute value and percentage of CD3+CD4+T lymphocytes in groups A, C, B and D were similar (P > 0.05). The absolute value and percentage of CD3+CD8+T lymphocytes in group D were higher than those in groups A, B and C (P < 0.001). The levels of IL-6, IL-17A and TGF-β1 in group D were higher than those in groups A, B and C (P < 0.001). The apoptotic index of groups A, B, C and D increased gradually, and the difference of apoptotic index among all groups was statistically significant (P < 0.001). PD-1 inhibitors can aggravate radiation-induced myocardial injury by promoting myocardial immunoinflammatory response.