Tiragolumab/Atezolizumab

Radiation can induce immunogenic cell death, local release of inflammatory cytokines, and damage associated molecular patterns (DAMPs) resulting in local effects on endothelial cell expression of adhesion receptors, increased immune cell trafficking, and immune cell activation. Dose, fractionation, and volume of radiation can influence immunologic effects in the tumor microenvironment. Nonclinical studies suggest that despite an initial local depletion of lymphocytes, hypofractionated regimens of radiation may be immune activating. Additionally, recent work suggests that standard fractionation and hypofractionation induce expansion of unique immune populations with standard fractionation favoring a myeloid response and hypofractionation driving a lymphoid response that may be more favorable to adaptive anti-tumor immunity. Compared to high doses of radiation, which induce immunogenic cell death, dose-dependent increases of MHC-I and death receptors, moderate fractional doses of 3-10 Gy may be optimal for activating a type I IFN response in tumor cells via a dose-dependent increase in the cytoplasmic leakage of DNA from micronuclei, which activates the cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING) pathway. Extensive experimental evidence indicates that radiotherapy can work in synergy with immunotherapy to generate T cells that reject not only the irradiated tumor but also the metastases outside of the field of irradiation, which offers a rationale for utilizing radiotherapy to enhance response to immunotherapy where tumors are unlikely to respond to immunotherapy alone.