Canine osteosarcoma as a solid tumor model for evaluation of dual valent B7H3-CXCR2 CAR T cell therapy

Abstract To develop more effective solid tumor CAR T cell therapies, we utilized the spontaneous canine metastatic osteosarcoma (OS) animal model. Our studies evaluated the relative activity of single B7H3 and dual-valent B7H3-CXCR2 CAR constructs. Studies were also designed to determine if modifying the tumor microenvironment (TME) with oral immunotherapy improved CAR activity, based on recent studies of losartan and propranolol in dogs with OS and glioma. We evaluated B7H3 expression on canine OS cell lines using flow cytometry and OS biopsies using IHC. High levels of B7-H3 were observed on OS cell lines and OS biopsies, whereas normal canine tissues were negative or low. To assess the utility of the dual CAR we determined that canine OS cell lines secreted high IL8 spontaneously. To assess the functionality of canine B7-H3 CAR T cells, we generated canine CAR T cells from whole blood from dogs with cancer. We next determined that canine dual CAR T cells exerted specific killing and cytokine activity against B7H3+ canine OS cell lines. To further establish functionality, we evaluated the two CAR constructs in a mouse xenograft model of canine OS. We found that the dual CAR construct was significantly more active than the single CAR construct in slowing tumor growth. We found that losartan and propranolol blocked migration of mouse inflammatory monocytes to xenografted canine OS tumors. Future steps will be to evaluate the effectiveness of dual CAR T cells with TME modification in dogs with metastatic OS, to investigate the translational relevance in human patients. Results from these studies in dogs will likely give more clinically relevant results for evaluating new CAR T cell therapies and bridging results between mouse models and human clinical trials. The V Foundation, The Shipley Family Foundation, and NIH T32 training grant