Abstract 2899: Small molecule inhibitor of ubiquitin ligase CBL-B enhanced anti-tumor response of CAR-T and CAR-NK cell therapies
Authors: Yang Cuiqing , Wang Yifang , Liu Tingting , Jiang Fuwei , Wang Chao , Wang Qingyang , Wang Qin , Li Zhengtao , Mai Wansun , Ye Gang , Tang Renhong , Cao Zhuoxiao 
Published: June 2023

Abstract
Introduction: Chimeric antigen receptor (CAR) T-cell therapy is an emerging therapeutic option for cancer treatment. However, its efficacy is limited, especially in solid tumors. This is partly because the CAR T cells become dysfunctional and exhausted in the tumor microenvironment. However, the key pathways responsible for impaired function of exhausted T cells remain unclear. Immunosuppressive cytokines or checkpoint proteins like TGF-β and PD-L1, are overproduced, which may lead to the downregulation of CD8+ T cell action and the promotion of T-reg maturation. E3 ligase Casitas B-Lineage Lymphoma Proto-Oncogene B (CBL-B) is a key negative modulator of T/NK-cell receptor and co-stimulatory regulation. CBL-B inhibition lowers the threshold of antigen-specific T/NK cell activation, even in absence of co-stimulatory signaling or the presence of an immune suppressive environment. Genetic ablation of CBL-B or functional inactivation of its E3 ligase activity in mice or primary human T cells enhances immune-mediated tumor growth control. Therefore, CBL-B inhibition may address the suboptimal response to current immunotherapies due to low inflammation, no/low co-stimulation signal or a high immune suppressive environment. Several groups demonstrated that deficiency of CBL-B overcomes endogenous CD8+ T-cell exhaustion, and deletion of CBL-B in CAR-T cells renders them resistant to exhaustion and deletion of CBL-B in CAR-NK cells provides greater resistance to TGF-β.
Methods: We tested the CAR expression, T/NK cell activation and in vitro cytotoxicity when ex vivo culture of CAR-T or CAR-NK cells with CBL-B inhibitors.
Results: We demonstrated that the combination of CBL-B inhibitor and CAR-NK cells elicited remarkable persistence in multiple runs of repeated cancer cell clearance assay, as compared to CAR-NK cells alone. Moreover, the combination of CAR-NK cells with both anti-PDL1-IL15 and CBL-B inhibitor showed further increased persistence in repeated cancer cell clearance assay.
Conclusions: preclinical data provided evidence of CBL-B inhibitors to enhance key parameters associated with T/NK cell activation and reduce susceptibility to immune suppression. Our results suggest the combination strategy of cell therapy and immune regulating small/large molecule therapy might achieve better anti-tumor efficacy in both hematological and solid tumors.
Citation Format: Cuiqing Yang, Yifang Wang, Tingting Liu, Fuwei Jiang, Chao Wang, Qingyang Wang, Qin Wang, Zhengtao Li, Wansun Mai, Gang Ye, Renhong Tang, Zhuoxiao Cao. Small molecule inhibitor of ubiquitin ligase CBL-B enhanced anti-tumor response of CAR-T and CAR-NK cell therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2899.