IMST-05. NOVEL CAR-T CELLS TARGETING THE EXTRACELLULAR MATRIX OF GLIOBLASTOMA INDUCE STRONG ANTI-TUMOR IMMUNE RESPONSE

Abstract

To address the poor prognosis and dismal survival of glioblastoma (GBM) patients, immunotherapy is increasingly being considered as a fourth arm of treatment in addition to surgical resection, radiotherapy, and adjuvant chemotherapy with temozolomide. Adoptive tumor immunotherapies using engineered T cells expressing chimeric antigen receptors (CAR-T cells) targeting cell surface antigens have shown promising outcomes in hematological malignancies. Although several CAR-T cell-based approaches have been tested in GBM, it has been difficult to translate the success of CAR-T cell therapy observed in liquid malignancies. Here we discuss the development of a first-in-kind CAR-T cell that does not target an antigen on the tumor cell surface but in the tumor extracellular matrix (ECM), specifically, the ECM protein fibulin-3 that is expressed by GBM tumor cells but is absent in the brain. In vitro experiments demonstrated that anti-fibulin-3 CAR-T cells (Fib3 CAR-T) are immunologically reactive to fibulin-3-expressing GBM tumor cells as evidenced by: 1) increased CAR-T cell proliferation; 2) overexpression of IFN-gamma, IL-2, perforin, and granzyme; and 3) enhanced cytotoxicity to the tumor cells. Control experiments using fibulin-3-lacking cells yielded no such results. Treatment of animals implanted with fibulin- 3-expressing GBM xenografts, using intratumoral fib3 CAR-T injections, resulted in statistically significant increase in median survival compared to animals treated with untransduced or non-specific T cells. Fib3 CAR-T is the first CAR-T developed to recognize a non-cell-surface target/antigen and raises interesting possibilities of novel immunotherapeutic targets in the tumor ECM. Fib3 CAR-T can help overcome a major deterrent for the success of CAR-T therapy that results from the reduced exposure of these engineered T cells to cell surface target/antigens in solid tumors like GBM.