CD81 and osteosarcoma: In addition, we used a CRISPR/Cas9 system to stably knock out CD81 expression in 143B cells, transplanted the cells into mice, and assessed tumor formation and lung metastasis in these mice compared to those in the control group.<h4>Results</h4>We found that CD81 was expressed in the human osteoblast cell line and in all osteosarcoma cell lines tested.