Abstract CT097: First report of preliminary safety, efficacy, and pharmacokinetics of C-CAR031 (GPC3-specific TGFβRIIDN CAR-T) in patients with advanced HCC

Abstract Introduction: Chimeric antigen receptor (CAR) T cells can mediate deep and durable responses in hematologic malignancies, however, achieving success in solid tumors has been so far limited largely by lack of suitable solid tumor-associated antigens and the immunosuppressive tumor microenvironment (TME). GPC3 is a surface antigen overexpressed in hepatocellular cancer (HCC) and virtually absent on healthy tissues. In this first-in-human (FIH) study, we investigated the feasibility, safety and initial anti- HCC efficacy of C-CAR031. C-CAR031 is an autologous, GPC3-directed armored CAR-T with affinity-tuned scFv to enhance the safety profile, and a 4-1BB and CD3ζ signaling domain. The C-CAR031 transgene includes a T2A viral self-cleaving peptide and a dominant negative TGF-β receptor II (TGFβRIIDN). The expression of TGFβRIIDN protects the cells against the immunosuppressive HCC TME and the T2A peptide allows for equimolar expression of the two transgene products. Methods: This FIH, open-label dose escalation trial employs an accelerated titration plus i3+3 design. Histologically confirmed GPC3+ advanced HCC patients (pts) who failed systemic treatments received a single-dose i.v. infusion of C-CAR031 following standard lymphodepletion. The primary objective was to assess the safety and tolerability. Adverse events (AEs) were graded using CTCAE 5.0, and cytokine release syndrome (CRS)/immune effector cell-associated neurotoxicity syndrome (ICANS) were graded according to ASTCT 2019 criteria. Results: As of Dec. 31st 2022, 7 pts received two dose levels (DL1, n=1; DL2, n=6) of C-CAR031. The median number of prior lines of therapies was 4 (range 1-6). The median follow-up was 77 (40-213) days. Six pts with ≥28 days’ follow-up were eligible for safety evaluation. The only ≥Gr3 non-hematologic product-related AE observed was transient Gr3 AST elevation in two pts. Five of 6 pts experienced Gr1/2 CRS, with median time to onset and duration of 3 (range 2-7) and 4 (4-6) days. No DLT or ICANS was observed. Of the 5 pts evaluable for preliminary efficacy, 4 pts had unconfirmed PR, which are currently pending confirmation. AFP was also stabilized or reduced in all 4 patients with uPR. All 5 pts had reduction in tumor burden, with a median change of -31.2% (range -3.4- -60.6%)/-41.4% (-3.4- -56.6%) per RECIST1.1/mRECIST. C-CAR031showed a robust cellular kinetic profile. In DL2, the median Tmax, Cmax and AUC0-28Day were 15 days, 772,014 copies/μg gDNA and 7,747,054 days*copies/μg gDNA, respectively. CAR-T cells were detectable in blood of all pts in the last follow-up. Conclusions: In this FIH study, C-CAR031 is well tolerated and shows promising anti- tumor activity. Enrollment is ongoing to confirm initial results. Citation Format: Qi Zhang, Qihan Fu, Wanyue Cao, Xingyuan Xu, Ao Xia, Jiaqi Huang, Andy Zou, Judy Zhu, Fei Wang, Yi Hong, Hui Wan, Yihong Yao, Nina Chu, Ryan Gilbreth, Maria Letizia Giardino Torchia, John Stone, Attilio Bondanza, Benny Farsaci, Gordon Moody, Mark Cobbold, Tingbo Liang. First report of preliminary safety, efficacy, and pharmacokinetics of C-CAR031 (GPC3-specific TGFβRIIDN CAR-T) in patients with advanced HCC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT097.