Long-term surviving mice treated with radiation and R848 are protected against subsequent tumor rechallenge by the induction of tumor-specific memory CD8⁺ cells. (A) Survival curve for EG7 tumor-bearing mice after combination therapy with 10 Gy local RT and R848 dosed weekly. ***P < .001 (log-rank; Mantel-Cox test). (B-C) Splenocytes were isolated from treatment naive control mice and from long-term survivors originally treated with local RT and R848 dosed weekly and cocultured with either 25 Gy irradiated EG7 cells (B) or SIINFEKL peptide (C) before being restimulated with fresh 25 Gy irradiated EG7 cells. **P < .01 (2-tailed Student t test). Experimental groups contained at least 3 mice and are representative of 2 independent experiments. (D) At > 100 days after initial tumor inoculation, a cohort of long-term surviving mice were rechallenged contralaterally with EL4 cells. **P < .01 (Mann-Whitney test). Experimental groups contained at least 5 mice and are representative of at least 2 independent experiments.