Comparison of gene expression changes in TSA tumors following different radiation regimens.

Radiotherapy is under investigation in the clinic for its ability to induce an in situ vaccine and enhance responses to immune checkpoint inhibitors and other immunotherapies. A variety of radiation doses and delivery schedules have been used to induce anti-tumor T cells in preclinical studies. However, the mechanisms bu which radiation induces anti-tumor T cells against poorly immunogenic tumors remain incompletely understood. In this study, we investigated changes in gene expression in mouse mammary carcinoma TSA tumors after a single dose (SD) of 20 Gy and a multi-fraction (MF) radiation regimen of 3x8Gy. To this end, TSA cells were injected into syngeneic BALB/c mice. When tumors became palpable, they were treated with local radiation therapy (RT) and harvested 4 or 24 hours later for gene expression analysis. The genome-wide microarray analysis showed key differences between SD and MF RT that may explain the differential ability of these two RT regimens to synergize with immune checkpoint inhibitors (Dewan et al., Clin Cancer Res 2009).