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

Abstract

BackgroundBispecific T cell-engagers (BTEs) are engineered antibodies that redirect T cells to target antigen-expressing tumors. BTEs targeting tumor-specific antigens such as interleukin 13 receptor alpha 2 (IL13R2) and EGFRvIII have been developed for glioblastoma (GBM). However, there is limited mechanistic understanding of the action of BTE since prior studies were mostly conducted in immunocompromised animal models. To close this gap, the function of BTEs was assessed in the immunosuppressive glioma microenvironment (TME) of orthotopic and genetically engineered mouse models (GEMM) with intact immune systems. MethodsA BTE that bridges CD3 epsilon on murine T cells to IL13R2-positive GBM cells was developed and the therapeutic mechanism investigated in immunocompetent mouse models of GBM. Multi-color flow cytometry, single-cell RNA sequencing (scRNA-Seq), multiplex immunofluorescence, and multiparametric magnetic resonance imaging (MRI) across multiple pre-clinical models of GBM were used to evaluate the mechanism and action and response. ResultsBTE-mediated interactions between murine T cells and GBM cells triggered T cell activation and antigen-dependent killing of GBM cells. BTE treatment significantly extended the survival of mice bearing IL13R2-expressing orthotopic glioma and de novo forming GBM in the GEMM. Quantified parametric MR imaging validated the survival data showing a reduction in glioma volume and decreased glioma viability. Flow cytometric and scRNA-seq analyses of the TME revealed robust increases in activated and memory T cells and decreases in immunosuppressive myeloid cells in the brains of mice following BTE treatment. ConclusionsOur data demonstrate that the survival benefits of BTEs in preclinical models of glioma are due to the ability to engage the host immune system in direct killing, induction of immunological memory, and modulation of the TME. These findings provide a deeper insight into the mechanism of BTE actions in GBM. WHAT IS ALREADY KNOWN ABOUT THIS TOPICBi-specific T cell engaging antibodies (BTEs) targeting IL13R2 and EGFRvIII have been developed and shown to activate T cells that mediate killing of glioma cells in vitro and in in vivo. WHAT THIS STUDY ADDSBy using immune competent preclinical models, this study reveals that BTEs trigger in situ tumor immune memory within the central nervous system. HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICYInsights into the mechanism of action of BTEs inform response biomarkers that should be considered for inclusion in window-of-opportunity clinical trial assessments and for the rational selection of future combinatorial strategies.