Exploring the mythical abscopal effect: Radiation and programmed cell death protein 1 (PD-1) blockade for hepatocellular carcinoma

After transplanting Hepa 1-6 cells in both hind legs of immunocompetent C57BL/6 mice, they irradiated the tumors in primary sites and observed abscopal effects in the non-irradiated tumors, with or without anti-programmed cell death protein 1 (PD-1) antibodies. While conventional RT is mainly directed at inducing apoptosis due to DNA damage, SBRT induces necrotic tumor cell death, which is a prerequisite for inducing an antitumor immune response. [...]they reported that fractionated RT, not single-fraction RT, induced immune-mediated abscopal effect when combined with CTLA-4 blockade [11]. Abbreviations cGAS, cyclic GMP-AMP synthase; CTLA-4, cytotoxic T-lymphocyte-associated protein 4; DCs, dendritic cells; HCC, hepatocellular carcinoma; ICIs, immune checkpoint inhibitors; ICV, inferior vena cava; PD-1, programmed cell death protein 1; SBRT, stereotactic body radiotherapy; STING, stimulator of interferon genes; TDLNs, tumor-draining lymph nodes 1.