Additionally, the SDF-1/CXCR4 axis in the osteosarcoma microenvironment was found to contribute to MDSCs accumulation, diminishing the effectiveness of PD-1 therapy, and resulting in MDSCs infiltration that impeded the proliferation of cytotoxic T cells, demonstrating MDSCs’ adverse role in osteosarcoma (Jiang et al., 2019). This evidence concerns the gene PDCD1 and osteosarcoma.