A Bi-Specific T Cell-Engaging Antibody Shows Potent Activity, Specificity, and Tumor Microenvironment Remodeling in Experimental Syngeneic and Genetically Engineered Models of GBM.

Background: Bispecific T cell-engagers (BTEs) are engineered antibodies that redirect T cells to target antigen-expressing tumors. BTEs targeting various tumor-specific antigens, like interleukin 13 receptor alpha 2 (IL13RA2) and EGFRvIII, have been developed for glioblastoma (GBM). However, limited knowledge of BTE actions derived from studies conducted in immunocompromised animal models impedes progress in the field. To close this gap, we investigated how BTE functions, engaging hosts' immune systems in the context of the immunosuppressive tumor microenvironment (TME) of the orthotopic and genetically engineered pre-clinical models of GBM.

Methods: We developed a BTE protein that bridges CD3 epsilon on murine T cells to IL13RA2-positive GBM cells. We then investigated the BTE therapeutic mechanism to promote anti-glioma activity in immunocompetent mouse models of GBM. To do so, we paired survival studies with multi-color flow cytometry, multiparametric magnetic resonance imaging (MRI), and single-cell RNA sequencing (RNA-Seq) in several orthotopic and genetically engineered mouse (GEM) models of GBM.

Results: BTE-mediated interaction of murine T cells and GBM cells potently activated T cells, resulting in antigen-dependent killing of GBM cells. BTE treatment significantly extended the survival of mice bearing IL13RA2-expressing orthotopic glioma and formed GBM in the GEM model. The quantification parametric MR imaging validated the survival data, showing a reduction in tumor volume and decreased tumor viability. Flow cytometric and scRNA-seq analyses of the tumor microenvironment (TME) revealed robust increases in activated and memory T cells and decreases in immunosuppressive myeloid cells in the brains of mice following BTE treatment.

Conclusions: Our data demonstrate that BTE's survival benefits in GBM are due to its ability to engage the host immune system in direct killing, boost immunological memory, and modulate the TME. These findings provide a deeper insight into the mechanism of BTE actions in GBM.