Figure 5.

Effect of radiation therapy (RT) on MDSCs. Treatment with conventional fractionated radiotherapy (CFRT) promotes the secretion of tumor cytokines and chemokines in response to activation of the STING signaling pathway and DNA damage. These secreted factors bind to the receptors on the membrane of MDSCs, which increases the number of MDSCs migrating to the TME, upregulates the expression of PD-L1 on MDSCs, and strengthens the ability to suppress T cells. Ablative hypofractionated radiotherapy (ABHRT) reduces the recruitment of MDSCs by destroying the hypoxic environment in the TME and induces tumor apoptosis, leading to reactivation of the antitumor response. CCL, CC chemokine ligand; STING, stimulator of interferon genes; VEGF, vascular endothelial growth factor.