TY - JOUR T1 - Deletion of Cbl-b inhibits CD8<sup>+</sup> T-cell exhaustion and promotes CAR T-cell function JF - Journal for ImmunoTherapy of Cancer JO - J Immunother Cancer DO - 10.1136/jitc-2020-001688 VL - 9 IS - 1 SP - e001688 AU - Jitendra Kumar AU - Ritesh Kumar AU - Amir Kumar Singh AU - Elviche L Tsakem AU - Mahesh Kathania AU - Matthew J Riese AU - Arianne L Theiss AU - Marco L Davila AU - K Venuprasad Y1 - 2021/01/01 UR - http://jitc.bmj.com/content/9/1/e001688.abstract N2 - Background Chimeric antigen receptor (CAR) T-cell therapy is an emerging option for cancer treatment, but 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 cells remain unclear, which is essential to overcome CAR T-cell exhaustion.Methods Analysis of RNA-sequencing data from CD8+ tumor-infiltrating lymphocytes (TILs) led to identification of Cbl-b as a potential target. The sequencing data were validated using a syngeneic MC38 colon cancer model. To analyze the in vivo role of Cbl-b in T-cell exhaustion, tumor growth, % PD1+Tim3+ cells, and expression of effector cytokines were analyzed in cbl-b+/+ and cbl-b–/– mice. To evaluate the therapeutic potential of Cbl-b depletion, we generated a new CAR construct, hCEAscFv-CD28-CD3ζ.GFP, that recognizes human carcinoembryonic antigen (CEA). cbl-b+/+ and cbl-b–/– CEA-CAR T cells were generated by retroviral transduction. Rag–/– mice bearing MC38-CEA cells were injected with cbl-b+/+ and cbl-b–/–; CEA-CAR T cells, tumor growth, % PD1+Tim3+ cells and expression of effector cytokines were analyzed.Results Our results show that the E3 ubiquitin ligase Cbl-b is upregulated in exhausted (PD1+Tim3+) CD8+ TILs. CRISPR-Cas9-mediated inhibition of Cbl-b restores the effector function of exhausted CD8+ TILs. Importantly, the reduced growth of syngeneic MC38 tumors in cbl-b–/– mice was associated with a marked reduction of PD1+Tim3+ CD8+ TILs. Depletion of Cbl-b inhibited CAR T-cell exhaustion, resulting in reduced MC38-CEA tumor growth, reduced PD1+Tim3+ cells and increased expression of interferon gamma, tumor necrosis factor alpha, and increased tumor cell killing.Conclusion Our studies demonstrate 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. Our results could facilitate the development of efficient CAR T-cell therapy for solid tumors by targeting Cbl-b. ER -