T cells engineered with chimeric antigen receptor (CAR) have been successfully applied to treat advanced refractory B cell malignancy.However,many challenges remain in extending its application toward the treatment of solid tumors.The immunosuppressive nature of tumor microenvironment is considered one of the key factors limiting CAR-T efficacy.One negative regulator of T cell activity is lymphocyte activation gene-3 (LAG-3).We successfully generated LAG-3 knockout T and CAR-T cells with high efficiency using CRISPR-Cas9 mediated gene editing and found that the viability and immune phenotype were not dramatically changed during in vitro culture.LAG-3 knockout CAR-T cells displayed robust antigen-specific antitumor activity in cell culture and in murine xenograft model,which is comparable to standard CAR-T cells.Our study demonstrates an efficient approach to silence immune checkpoint in CAR-T cells via gene editing.