Radiation + α-OX40 promotes abscopal effects. Anti-PD1 resistant tumor cells were inoculated into 129Sv/Ev mice (n = 10 per group) bilaterally (right hind leg and left hind leg) 4 days apart. Primary tumors were irradiated 11 days after their inoculation whereas second tumors were left untreated. Intratumoral α-OX40 (total of 5 doses, 200 μg each) was administered to the primary tumor starting 2 days after last dose of XRT. A, Primary tumor measurements recorded upon XRT + α-OX40 treatment along with control groups as indicated. XRT vs. XRT + α-OX40 (two-way ANOVA, P< 0.0001). B, Secondary tumor measurements recorded as in A. XRT vs. XRT + α-OX40 (two-way ANOVA, P< 0.0001). C, Percent survivals of mice from A were recorded and graphed. XRT vs. XRT + α-OX40 (log rank test, P=0.0001); α-OX40 vs. XRT + α-OX40 (log rank test, P=0.0002). D, Lung metastases were enumerated upon sacrificing mice in their subsequent groups. XRT vs. XRT + α-OX40 (t-test, P=0.006).