(O18) Chimeric Antigen Receptor T Cells Can Be Tracked in vivo and Induce remission in Dogs

Abstract: Background Chimeric Antigen Receptor (CAR)-T cell therapy can be curative for human patients with hematologic malignancies and there is great interest in bringing this technology to companion animals with lymphoma. However, considerations in cost, lack of available pre-conditioning protocols, and potential side effects have limited its application in dogs. Objectives We describe the use of human T cells engineered with TRAC and B2M CRISPR knockouts, a canine CD20 targeting CAR with the Sodium Iodide Symporter (NIS), and a novel lymphodepletion protocol towards live cell imaging, tracking, and application of xenogeneic CAR-T cells to spontaneous B cell lymphoma. Animals Two client-owned companion dogs with Stage IV-a CD20+ B cell lymphoma completed this observational protocol. Methods Dogs received immunosuppressive chemotherapy of 0.5 mg/kg pentostatin for 3 days and, on the 3rd day, 300mg/m2 cyclophosphamide along with supportive IV fluid and concomitant medications. Three days later, 25M CAR-T cells were injected intranodally, and 10M/kg infused intravenously and later assessed by 18F-TFB PET 24, 72, and 164 hours after treatment. Results Both dogs reached complete remission during the observation period with resolution of internal and peripheral lymph node enlargement. Moreover, CAR-T cells are well-tolerated, and live imaging in dogs is feasible, demonstrating the application of 18F-TFB PET for future study of CAR-T dynamics in spontaneous disease. Conclusions and clinical importance Combination cyclophosphamide and pentostatin is a potent yet dose-limiting lymphodepletion protocol in companion dogs. However, lymphodepletion followed by dual-administered CAR-T cells for lymphoma is an effective protocol for both live imaging and clinical response.