Immunotherapy for HER2-positive medulloblastoma: Regression of experimental tumors by transfer of HER2-redirected T cells in vivo

Abstract

9008 Background: The long-term objective of this project is to develop an innovative HER2-targeted immunotherapeutic approach for medulloblastoma, the most common malignant brain tumor of childhood. HER2 is expressed in 40% of medulloblastomas and at present less than one third of patients with HER2-positive tumors are cured by conventional therapies. The aim of this study was to determine if T cells grafted with a HER2-specific chimeric antigen receptor (CAR) recognize and kill HER2-positive medulloblastomas. Methods: Mitogen-activated T cells from healthy donors and medulloblastoma patients were transduced with a retroviral vector encoding a HER2-specific CAR with a ζ-signaling domain (HER2T-cells). We analyzed the ability of HER2T-cells to 1) proliferate, 2) produce immunostimulatory cytokines (IFN-γ and IL-2), and 3) kill HER2-positive targets in cytoxicity assays upon exposure to HER2-positive primary medulloblastoma cells and cell lines. The in vivo function was tested in an orthotopic murine xenograft model of human medulloblastoma, which allows for serial imaging by bioluminescence. Results: HER2T-cells killed both HER2-positive primary medulloblastoma cells and cell lines in cytotoxicity assays, whereas HER2-negative tumor cells were not killed. Stimulation of HER2T-cells resulted in T-cell proliferation and secretion of IFN-γ and IL-2 in a HER2-dependent manner. No functional difference was observed between cells generated from medulloblastoma patients receiving dexamethasone and healthy donors. In vivo, the adoptive transfer of HER2T-cells resulted in sustained regression of established medulloblastomas in an orthotopic murine xenograft model as judged by bioluminescence imaging. In contrast, delivery of non-transduced T cells did not change tumor growth in comparison to untreated tumors. Conclusions: This study shows for the first time that HER2 is a target antigen for the immunotherapy of medulloblastoma. HER2-redirected T-cells not only recognized and killed HER2-positive medulloblastomas ex vivo, but also induced regression of experimental medulloblastoma in vivo. Hence, adoptive transfer of HER2-redirected T-cells may represent a promising immunotherapeutic approach for medulloblastoma. No significant financial relationships to disclose.