Ablation of Cbl-b in ROBO1 CAR-NK92 Cells Enhances Their Antitumor Efficacy

Emerging evidence suggests CAR-NK cell therapy shows great promise in cancer treatment. ROBO1 is highly expressed in various cancer types, including glioblastoma, hepatocellular carcinoma, lung cancer, breast cancer, and uterine cancer. Our and other laboratories' studies have shown that ROBO1 CAR-NK cells exhibit promising tumor therapeutic effects. However, the results still have some limitations. Cbl-b, an E3 ubiquitin ligase, has been reported to negatively regulate NK cell activation, homeostasis, and antitumor immunity.¹ Therefore, we attempted to further enhance the antitumor activity of ROBO1 CAR-NK92 cells by knocking out Cbl-b using CRISPR/Cas9 gene-editing technology. In this study, we conjugated Cbl-b sgRNA with Cas9 protein to form ribonucleoprotein complexes, which were then delivered into ROBO1 CAR-NK92 and NK-92 cells (control cells) via electroporation. Through fluorescence-activated cell sorting, limiting dilution, and sequencing, we obtained monoclonal Cbl-b-knock-out (KO) cell lines. Both in vitro cytotoxicity assays and in vivo tumor xenograft experiments were conducted to examine whether Cbl-b knockout enhances the target cell killing and tumor suppression capacities of ROBO1 CAR-NK92 cells. In this study, monoclonal cell lines of ROBO1 CAR-NK92-Cbl-b-KO and NK92-Cbl-b-KO were successfully established. In vitro, at an effector-to-target (E:T) ratio of 0.1:1, ROBO1 CAR-NK92-Cbl-b-KO (50.55%) cells exhibited significantly higher cytolytic activity against ROBO1-positive T47D target cells after 3 h of coculture than ROBO1 CAR-NK92 (34.10%), NK92-Cbl-b-KO (22.22%), and parental NK-92 cells (3.28%). In vivo, tumor volume and weight measurements demonstrated that mice treated with ROBO1 CAR-NK92-Cbl-b-KO cells developed significantly smaller tumors than all control groups, achieving a tumor growth inhibition (TGI) rate of 32.45%, indicating enhanced antitumor efficacy conferred by Cbl-b knockout. In vitro and in vivo data confirmed that Cbl-b knockout potentiates the antitumor efficacy of ROBO1 CAR-NK92 cells. The overall cytotoxic capability ranked as follows: ROBO1 CAR-NK92-Cbl-b-KO > ROBO1 CAR-NK92 > NK92-Cbl-b-KO > NK-92.