For instance, inhibiting Arg1 with nor-NOHA or IDO with INCB023843 after RT effectively increased the number of CD8+ T cells and delayed tumor growth.141,142 The PDE5 inhibitor sildenafil was reported to reduce the proportion of PMN-MDSCs and the expression of Arg1 in MDSCs in the Lewis lung carcinoma (LLC) mouse model, indicating that a combination of sildenafil and RT might be a promising strategy to overcome radioresistance.142. Here, IDO1 is linked to neoplasm.