IMMU-39. CAR T CELLS TARGETING ICAM-1 SHOW A SURVIVAL BENEFIT IN BOTH SYNGENEIC AND XENOGRAFT GLIOMA MOUSE MODELS

Abstract BACKGROUND Chimeric antigen receptor (CAR) T-cell therapy, while effective against hematological malignancies, has faced significant hurdles in its application to solid tumors. Challenges in CAR T-cell therapy for glioblastoma include the immunosuppressive tumor microenvironment, the limited infiltration of CAR T-cells into the tumor, heterogeneous target expression and antigen escape. In this study, we focused on targeting Intracellular adhesion molecule-1 (ICAM-1), a protein expressed on both glioma cells and tumor-associated cells like macrophages and endothelial cells. METHODS Glioblastoma and normal brain tissue microarray sections (TMA) were immunohistochemically analyzed for ICAM-1 expression. Second-generation human and murine ICAM-1-targeting CAR T cells were generated by lentiviral or retroviral transduction of T cells from healthy human donors or murine splenocytes. Their efficacy was evaluated in co- culture assays with human and murine glioma and endothelial cell lines. Syngeneic and xenograft orthotopic glioma mouse models were used to assess the in vivo activity of CAR T cells. Ex vivo analysis of these tumors included examination of changes in the tumor microenvironment using high-dimensional flow cytometry. RESULTS Immunohistochemical staining of TMA revealed a significant upregulation of ICAM-1 in human glioblastoma tissue compared to normal brain tissue. Single-cell RNA sequencing data from glioblastoma specimens showed a high level of ICAM-1 expression in tumor- associated macrophages. Human and murine ICAM-1-targeting CAR T cells displayed strong lysis of ICAM-1-expressing glioma and endothelial cells in vitro. Intratumoral application of CAR T cells resulted in a survival benefit in both syngeneic and xenograft glioma mouse models. Ex vivo analysis of the tumor microenvironment revealed treatment-induced changes from our CAR T cell therapy and indicates potential for further enhancements. CONCLUSION Our study demonstrates that ICAM-1-targeting CAR T cells improve survival in human and murine glioma mouse models. Flow cytometry of the tumor microenvironment reveals therapy-induced changes, for future improvements of the CAR T cell therapy.