Combination but not single-agent treatment results in long-term protection against lymphoma. (A-B) Groups of 5 age-matched CBA mice were inoculated with 106 A31 tumor cells intravenously on day 0 and were treated with either (A) external beam TBI (single dose of 2 to 8 Gy at a rate of 1.15 Gy/min) plus PBS or (B) TBI plus anti-CD40 monoclonal antibody (1 mg, intravenously, giving the mAb 4 hours after irradiation). Treatment was as indicated. (C) Groups of 5 age-matched BALB/c mice were inoculated with 106 BCL1 lymphoma cells on day 0 and were treated with 5 Gy TBI with or without anti-CD40 (100 μg, intravenously) on day 15. All animals were fed acidified water substituted with neomycin sulfate starting 3 days prior to irradiation and continuing for a further 2 weeks. Survival was recorded daily. There is a clear radiation dose–dependent increase in survival treating with combined TBI and anti-CD40, with 5 Gy plus mAb, but not single treatment regimens, providing long-term survival against both lymphoma lines. Similar results were obtained in at least 2 separate experiments.
