Triple therapy mediates tumor regression in a mouse model of spontaneous melanoma. Grm-1 Tg mice spontaneously develop melanoma tumors between 4–6 mo of age. After development of large tumor lesions (10–13 mo of age), mice were treated with 5 Gy of RT in combination with tumor-reactive CD4⁺Trp1⁺ T cells and anti–CTLA-4, as described in Materials and methods. Tumor progression was monitored weekly by gross morphological examination. The individual tumor lesions were measured with calipers weekly for each animal. The total tumor volume for each mouse was considered as 100% on the first day of treatment. (a) Representative images of treated mice and tumor regression. (b) Tumor volume after triple therapy. (c) One mouse with aggressive disease continued to grow tumor up to day 10 after therapy when tumor volume started to decrease, similar to what is observed in the transplantable B16/BL6 model. (d and e) Mice were also monitored for expansion of CD4⁺Trp1⁺ T cells in the blood (d) and cytokine levels in the serum (e) of treated mice. Data are representative of two independent experiments (n = 7–10 mice).