In vivo tracking reveals delayed tumor growth followed by regression after combination therapy. CBA mice were inoculated with 106 tumor cells and treated on day 10 with TBI and anti-CD40 mAb (1 mg intravenously) according to the standard protocol. Control animals received PBS. At sequential time points, 2 mice per group were killed and the number of splenic tumor cells was calculated by 2-color flow cytometry with PE-labeled anti-CD19 and FITC-labeled anti-idiotype (see “Materials and methods”). Shown is the mean number of tumor cells present in the spleen at each time point. TBI results in a radiation dose–dependent decrease in tumor burden, with less than 1% of the tumor volume present prior to treatment (day 10) remaining 12 days after combination but not single-agent treatment. Similar results were obtained in at least 2 separate experiments.
