Abstract B38: Tetravalent bispecific antibodies specific for HER2 and disialoganglioside GD2 to engage polyclonal T cells for osteosarcoma therapy

Introduction: Osteosarcoma is the most common pediatric high-grade bone tumor. Although multimodal therapeutic approaches have significantly improved patient survival to more than 60%, the prognosis for patients with metastatic or relapsed disease remains dismal—an urgent unmet need. Its genomic complexity and higher mutational burden compared to other pediatric cancers should provide neoantigens as potential targets for T cell-based immunotherapy; however, these tumors are in general “cold,” with insufficient or inactive tumor-infiltrating lymphocytes. Ganglioside GD2 is a tumor-associated surface antigen expressed in a broad spectrum of pediatric malignancies, including neuroblastoma, brain tumors, Ewing’s sarcoma, rhabdomyosarcoma, and osteosarcoma, while being restricted in normal tissues. Another promising target, HER2 or ErbB2, is overexpressed in many aggressive malignancies, including pediatric medulloblastoma, nephroblastoma, osteosarcoma, and desmoplastic small round cell tumor (DSRT). Fully humanized tetravalent bispecific antibodies (BsAb) specific for human GD2 and CD3 (hu3F8-BsAb) or HER2 and CD3 (HER2-BsAb), built on an IgG(L)-scFv platform, have been developed (Oncoimmunology 2017; Can Immunol Res 2015). They induce rapid and quantitative T-cell homing to tumors, mediating potent T-cell dependent cytotoxicity (TDCC) against GD2 or HER2 expressing tumor cells, effecting cures of xenografts in SCID mice. In this study, we evaluated the in vitro and in vivo antitumor properties of these BsAbs in the treatment of osteosarcoma. Methods: Hu3F8-BsAb and HER2-BsAb were tested both in vitro and in vivo against a panel of osteosarcoma cell lines (RG143B, U2OS, CRL1427, HOS, and SaOS2). Using these cell lines, FACS analysis for surface antigen (GD2 and HER2) expression (MFI), sensitivity to TDCC (EC50), and antitumor activity in vivo were evaluated. Two in vivo tumor models with different effector routes were used to simulate different clinical situations: 1) subcutaneous (sc) tumor cells/sc effector peripheral blood mononuclear cells (PBMCs), and 2) sc tumor cells/intravenous (iv) PBMCs. In vivo tumor responses were measured by Peira TM900 imaging device or by bioluminescence. Results: The majority of osteosarcoma cell lines express GD2 and HER2 on their surface, and their in vitro sensitivity to TDCC (EC50) was inversely correlated with MFI of their respective antigen. Both hu3F8-BsAb and HER2-BsAb mediated potent TDCC against osteosarcoma cell lines. In vivo, both hu3F8-BsAb and HER2-BsAb exerted a significant antitumor effect compared to control BsAb (P=0.001). Conclusions: Hu3F8-BsAb and HER2-BsAb induced strong TDCC and had significant antitumor effect against osteosarcoma cell lines both in vitro and in vivo. Considering the limited therapeutic options currently available in advanced osteosarcomas, these results support their further clinical development as potential T cell-based immunotherapeutics. Citation Format: Jeong A. Park, Hong Xu, Irene Cheung, Nai-Kong V. Cheung. Tetravalent bispecific antibodies specific for HER2 and disialoganglioside GD2 to engage polyclonal T cells for osteosarcoma therapy [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr B38.