Targeting programmed cell death ligand 1 by CRISPR/Cas9 in osteosarcoma cells

// Yunfei Liao 1, 2 , Lulu Chen 1 , Yong Feng 2, 3 , Jacson Shen 2 , Yan Gao 2 , Gregory Cote 4 , Edwin Choy 4 , David Harmon 4 , Henry Mankin 2 , Francis Hornicek 2 , Zhenfeng Duan 2 1 Department of Endocrinology, Wuhan Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China 2 Sarcoma Biology Laboratory, Department of Orthopaedic Surgery, Massachusetts General Hospital and Harvard Medical School, Boston 02114, Massachusetts, USA 3 Department of Orthopaedic Surgery, Wuhan Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China 4 Division of Hematology and Oncology, Massachusetts General Hospital and Harvard Medical School, Boston 02114, Massachusetts, USA Correspondence to: Zhenfeng Duan, email: zduan@mgh.harvard.edu Keywords: programmed cell death ligand 1, osteosarcoma, CRISPR/Cas9, metastasis Received: January 04, 2017      Accepted: March 09, 2017      Published: March 17, 2017 ABSTRACT Programmed cell death ligand 1 (PD-L1) is a transmembrane protein that is expressed on tumor cells that suppresses the T cell-mediated immune response. Therapies targeting the PD-L1 pathway promote anti-tumor immunity and have shown promising results in some types of cancers. However, the functional and therapeutic roles of PD-L1 in osteosarcoma remain largely unknown. In this study, we found that PD-L1 protein was expressed in osteosarcoma cell lines and tissue microarray of patient tumors. Tissue microarray immunohistochemistry analysis showed that the overall and five-year survival rates of patients with high levels of PD-L1 expression were significantly shorter than patients with low levels. High levels of PD-L1 expression were also associated with metastasis in osteosarcoma patients. Furthermore, we applied the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 system to target PD-L1 gene at the DNA level in osteosarcoma cell lines. We found that the expression of PD-L1 could be efficiently disrupted by CRISPR/Cas9 system and PD-L1 knockdown increased drug sensitivities for doxorubicin and paclitaxel. These results suggest that PD-L1 is an independent prognostic factor in osteosarcoma and that PD-L1 knockout by CRISPR/Cas9 may be a therapeutic approach for the treatment of osteosarcoma.