With the exception of B7-H2, all measured immune checkpoint proteins—CD48, TIMD-4, B7-H6, CD134, B7-H5, CD47, and S100A8/A9—were significantly elevated in osteosarcoma patients compared to healthy controls (Figure 1A, p < 0.05). This evidence concerns the gene TNFRSF4 and osteosarcoma.