Chemotherapy diminishes the effect of radiation-mediated eradication of metastases and T-cell priming. (A) A total of 2 × 105 B16-CCR7 cells were subcutaneously injected; and on days 14, 15, and 16, mice received 15 Gy. On days 7 and 14 after RT, 200 mg/kg dacarbazine (also for human melanoma) was administered intraperitoneally. The radiation group showed a significantly smaller tumor size (***P < .001 at day 13 after RT). Additional dacarbazine after RT led to significant regrowth (**P < .007 at day 26 after RT, *P = .015 day 32 after RT; n = 3-5). (B) Tumor growth curve: 105 4T1 tumor cells were injected; and on days 15, 16, and 17, mice received 15 Gy. On days 7 and 14 after RT, 20 mg/kg paclitaxel was administered intraperitoneally. The radiation group showed significantly smaller tumor size (**P = .008 at day 23; n = 4-9 per group). (C) Metastasis assay: 105 4T1 tumor cells were subcutaneously injected; and on days 12, 13, and 14, Balb/c mice received local RT of 15 Gy. The tumors were removed on day 21. On days 7 and 12 after RT, 20 mg/kg paclitaxel was administered intraperitoneally No colonies were detected after radiation, whereas addition of chemotherapy completely eliminated the effect of radiation (n = 4 or 5 per group). (D) A total of 5 × 105 B16-SIY melanoma cells were injected subcutaneously. On day 17, mice were transferred with 2 × 106 CFSE-labeled 2C cells and locally RT with 20 Gy. A total of 200 mg/kg dacarbazine intraperitoneally was given 2 days after adoptive transfer. DLN and spleen were harvested on day 21 for analysis. (E) A total of 5 × 105 B16-SIY melanoma cells were injected subcutaneously. Mice received local tumor RT of 20 Gy once or 5 Gy × 4. Single-treatment 200 μg/mouse of anti-CD8 antibody was administered on days 0, 4, 8, and 12 after RT. Repeated treatment of radiation showed significant regrowth of tumor mass (*P = .03 at day 25; n = 4-6). (F) A total of 8 × 106 human lung tumor A549 cells were subcutaneously injected into B6/Rag−/− mice; and 4 weeks later, the mice were adoptively transferred with 2 × 106 LN cells from OT-I transgenic mice. Three days later, mice received 20 Gy of local RT. RT (P = .48) or T cells (P = .3) alone showed no significant differences from the no treatment group, whereas the radiation + T-cell group showed significantly smaller tumor size (*P = .018 at day 60). Similar experiments were repeated at least twice (A-F).
