Combination of R848 dosed weekly with an RT regimen composed of 5 fractions of 2 Gy leads to complete eradication of EL4 and A20 tumors. EL4 tumor growth (A) and survival curves (B) after combination therapy with R848 dosed weekly and either a single 10-Gy dose or 5 fractions of 2 Gy local RT. (C) At > 60 days after initial tumor inoculation, a cohort of long-term surviving mice originally treated with 5 fractions of 2 Gy and R848 dosed weekly were rechallenged contralaterally with EL4 cells. (D) Survival curve of mice bearing established A20 tumors after combination therapy with R848 dosed weekly and 5 fractions of 2 Gy local RT. Experimental groups contained at least 5 mice and are representative of at least 2 independent experiments. *P < .05, compared with control mice (log-rank; Mantel-Cox test). ⁺P < .05, compared with control mice (log-rank; Mantel-Cox test). **P < .01, compared with monotherapy (log-rank; Mantel-Cox test). ⁺⁺P < .01, compared with monotherapy (log-rank; Mantel-Cox test). ***P < .001, compared with monotherapy (log-rank; Mantel-Cox test).