Effect of anti-CD137 mAb in the prevention of recurrence and metastases of murine B16-OVA melanoma. (A) A schematic of mouse models of melanoma recurrence and metastases and anti-CD137 mAb treatment protocol. (B) Effect of anti-CD137 mAb in the prevention of recurrence of B16-OVA tumor. Upon removal of primary tumors, mice were challenged with B16-OVA tumor cells subcutaneously, and the sizes of tumors were measured individually and recorded as the mean tumor diameter regularly. Results are 1 representative of 3 independent experiments. (C) Effect of anti-CD137 mAb in the prevention of metastases of B16-OVA tumor. Upon removal of primary tumors, mice were challenged with B16-OVA tumor cells intravenously, and the survival of mice was monitored daily up to 120 days. Results are 1 representative of 3 independent experiments. ***Significantly different from control mAb (rat Ig) treatment group, P < .001. (D) Presensitization of mice to primary tumors is required for the effect of anti-CD137 mAb. Mice were mock-treated by surgery, as in panel B but without primary tumor inoculation, and subsequently treated with anti-CD137 mAb. B16-OVA tumors were then inoculated, measured individually, and recorded as the mean tumor diameter regularly. Results are 1 representative of 3 independent experiments.