CD274 and osteosarcoma: To determine if T cell responses to osteosarcoma metastatses in α-PD-L1 mAb treated mice may have become tolerized through engagement of other inhibitory ligands, we evaluated expression of PD-L1, CD80, and CD86 on metastatic osteosarcoma cells, in both mock treated and α-PD-L1 mAb treated mice.