PDCD1LG2 and osteosarcoma: With NIH3T3 cells as the positive control, the western blot analysis indicated that the HOS, KHOS, 143B, MNNG, SAOS-2, and U2OS cell lines showed relatively higher levels of PD-L1 protein than the MG63 cell line, while all osteosarcoma cell lines showed high levels of PD-L2 expression (Fig. 4a).