Dual α-CTLA-4/α-PD-L1 mAb treatment can elicit protective immunity towards metastatic osteosarcoma. To evaluate protective immune responses to tumor, cured α-CTLA-4/α-PD-L1 mAb mice (n = 12) were challenged with 106 K7M2 cells at day 100. Cured α-CTLA-4/α-PD-L1 mAb treated mice cleared disease and significantly survived longer than age-matched control mice, p = 0.0049 (A). Lung tissue was evaluated for the presence of memory CD8 cells, and approximately 87% of the tumor-reactive memory T cells were CCR7 + CD62L+ (B). These CCR7 + CD62L + CD8+ cells were specific towards K7M2 cells used to generate the tumor, and able to produce IFNy and TNF in response to re-exposure, p=0.002 (C). To evaluate if protective immune responses to tumor were in fact due to memory CD8 T cells. Cured α-CTLA-4/α-PD-L1 mice (n = 6) were depleted of CD8 T cells at day 80, and challenged with 106 K7M2 cells after depletion. Mice depleted of CD8 T cells prior to challenge all succumbed to metastatic osteosarcoma in the lung tissue, in comparison to 100% survival (n = 6) in cured immune competent mice challenged. A log-rank test gives a p = 0.0177 (D).