CD274 and osteosarcoma: To test whether PD-1 blockades can overcome T cell exhaustion related to treatment resistance, we combined anti-PD-1 (pembrolizumab) or anti-PD-L1 (atezolizumab) monoclonal antibody and GD2-EATs or HER2-EATs and evaluated their synergy in osteosarcoma cell line xenograft mouse model (Fig. 4a).