The Updated Status and Future Direction of Immunotherapy Targeting B7-H1/PD-1 in Osteosarcoma

Although the mortality rate of osteosarcoma (OS) patients has improved, there are still many unsolved problems concerning how to reduce recurrence and metastasis. In the tumor microenvironment, immune escape plays a more important role in tumor progression and development. Many costimulatory molecules of the B7 family have been reported to be involved in regulating immunological interactions between OS cells and immune cells. Among these molecules, B7-H1 and its receptor, programmed death-1 (PD-1), have been the focus of the fields of tumor immunology and have been recently applied in clinical trials of therapies for several solid tumors. These therapies, referred to as B7-H1/PD-1 checkpoint blockade therapies, are designed to block the interaction between the two molecules. Although the mechanism has been reported in some malignancies, the specific impact of B7-H1/PD-1 expression on OS has not been well defined. Here, we review the expression, function, and regulatory mechanism of the B7-H1/PD-1 axis in OS and introduce and compare the advantages and disadvantages of B7-H1/PD-1 immunotherapies in OS.