Preclinical evaluation of antitumor activity and toxicity of TROP2-specific CAR-T cells for treatment of triple-negative breast cancer

BACKGROUND: Triple-negative breast cancer (TNBC) represents a subtype of breast cancer with poorest prognosis due to limited effective targeted therapies. Chimeric antigen receptor T cell (CAR-T) therapy has shown remarkable efficacy in treating hematological cancers, but its application in TNBC requires further development. One major obstacle is the lack of suitable tumor-specific target in TNBC. Inspired by recent success of trophoblast cell-surface antigen 2 (TROP2) antibody-drug conjugate in TNBC, we developed a second-generation CAR that specifically targets TROP2 and formally evaluated its antitumor activity and safety profile using in vitro and in vivo models. METHODS: A CAR molecule targeting TROP2 was constructed based on the clinically-validated humanized antibody Sacituzumab and expressed in primary human T cells using a retroviral vector. Tumor cytotoxicity, cytokine production and T-cell proliferation of TROP2 CAR-T cells were tested against multiple TNBC cell lines in vitro. Antitumor efficacy was evaluated using orthotopic and metastatic models of cell line-derived xenograft in NSG mice and in patient-derived xenograft (PDX) model. The safety profile of TROP2 CAR-T cells was assessed using TROP2-humanized immunocompetent mice and an "AND"-logic gated SynNotch CAR targeting B7-H3 and TROP2 was engineered to minimize off-tumor, on-target toxicity of TROP2 CAR-T cells. RESULTS: Human TROP2 CAR-T cells demonstrated robust antitumor activity in vitro and in orthotopic/metastatic/PDX xenograft mouse models. TROP2 CAR-T cells caused lethal on-target, off-tumor toxicity in TROP2-humanized immunocompetent mice, causing severe tissue damage in lungs and systemic inflammation. The B7-H3/TROP2 "AND"-logic gated SynNotch CAR-T cells showed comparable antitumor efficacy without causing apparent adverse effects as in TROP2 CAR-T cells. CONCLUSIONS: These data indicate that while CAR-T therapy targeting TROP2 possesses potent antitumor activity against TNBC cell lines and PDX, its potential side effects could be lethal due to TROP2 expression in vital organs such as the lung. Using an "AND"-logic gated CAR is a viable solution to overcome its in vivo toxicity. Our study lays the groundwork for future development of TROP2 CAR-T cell therapy for TNBC.