B7 homolog 3-targeted CAR-T cells secreting EGFR T-cell engagers for improved control of glioblastoma progression

Glioblastoma (GBM) is the most aggressive primary malignant brain tumor, and while chimeric antigen receptor-T (CAR-T) cell therapy has shown promise, its efficacy remains limited by antigen heterogeneity and immune escape. Here, we investigated the expression of B7 homolog 3 (B7-H3), epidermal growth factor receptor (EGFR), and interleukin-13 receptor alpha 2 (IL-13RA2) in GBM tissues and cell lines. Although all three antigens were highly expressed, sustained exposure to B7-H3 CAR-T cells led to significant B7-H3 downregulation but concurrent EGFR upregulation, revealing a potential immune escape mechanism. To address this heterogeneity, we engineered T cells to express an anti-B7-H3 CAR and secrete an EGFR-targeting bispecific T-cell engager (EGFR-BsTe). These B7-H3-CAR-T-EGFR-BsTe cells exerted dual functionality: direct B7-H3-dependent cytotoxicity and recruitment of unmodified T cells via secreted EGFR-BsTe to eliminate EGFR-expressing tumor cells. Notably, EGFR-BsTe secretion promoted CAR-T cell proliferation and effector differentiation. In orthotopic GBM xenograft models, including mixed tumors with heterogeneous antigen expression, B7-H3-CAR-T-EGFR-BsTe cells demonstrated superior antitumor activity and prolonged survival compared to conventional B7-H3 CAR-T cells. Quantitative analysis revealed that EGFR-BsTe secretion abrogated EGFR upregulation and enhanced B7-H3 downregulation in a target-dependent manner; however, efficacy was diminished when the CAR-Target (B7-H3) was absent on a substantial fraction of tumor cells. Our findings suggest that arming B7-H3 CAR-T cells with EGFR-targeting bispecific engagers represents a promising strategy to overcome antigen heterogeneity and improve therapeutic outcomes for GBM patients.