Development of a Sensitive and Efficient Reporter Platform for the Detection of Chimeric Antigen Receptor T Cell Expansion, Trafficking, and Toxicity

Introduction Despite the success of chimeric antigen receptor T (CART) cell therapy, it is limited by lower rates of durable responses related to inadequate CART cell expansion and trafficking and life-threatening complications such as cytokine release syndrome (CRS). Development of a strategy to efficiently track CART cells would allow the in vivo characterization of T cell expansion and trafficking to tumor sites as well as the development of strategies to potentially overcome these limitations. The sodium iodide symporter (NIS) is a sensitive reporter system that has been used for cell imaging in the clinic. Objectives NIS would be an efficient way to assess CART cell expansion, trafficking, and toxicity. Methods In vitro functions of CART cells were assessed by antigen specific proliferation, cytotoxicity, and cytokine production. NIS activity in vitro was evaluated by 125I uptake assay. In vivo imaging was performed using TFB PET/CT. CART cell trafficking assay was tested with OPM2 multiple myeloma (MM) xenografts and treated with either BCMA CART or NIS+BCMA CART cells. For CRS model, NSG mice were engrafted with patient-derived CD19+ acute lymphoblastic leukemia blasts. After the engraftment, mice were treated with either NIS+CART19 cells (5 × 106) or control. Results We generated NIS+CART19 and NIS+BCMA CART cells through dual transduction (Fig A) and revealed the exclusive 125I uptake in vitro (Fig B). In vitro functions of NIS+CART cells were equivalent to CART19 (Fig C). This indicates the incorporation of NIS into CART cells does not impair their antitumor activity. In vivo sensitivity assay revealed NIS+CART cells were detectable when cells were subcutaneously injected to NSG mice at a dose of 1.25 × 106 cells (Fig D). For in vivo trafficking assay, bioluminescence imaging (BLI) showed MM cells mainly engrafted in bones (Fig E). TFB PET confirmed the trafficking of NIS+BCMA CART cells to the bones, corresponding to BLI (Fig E). Both BCMA CART and NIS+BCMA CART cells exhibited similar antitumor activity. Finally, we explored whether TFB PET can detect CART massive expansion in vivo and predict CRS. One week after mice were treated with high dose NIS+CART19 cells, mice developed muscle weakness, hunched bodies, and weight loss (Fig F), which correlate with CRS. TFB PET revealed a significant uptake in the bone marrow, spleen, liver, and lungs (Fig G) of the diseased mice but not control mice. Flow cytometry revealed extensive infiltration of CART cells in the liver and spleen. This demonstrates the ability of TFB PET to detect NIS+CART cell expansion in vivo, correlating with the development of CRS. Conclusion Our results robustly show NIS+CART cells provides a sensitive, clinically applicable platform to image CART cells and to assess their expansion, trafficking to tumor sites, and the development of CRS. These studies illuminate a novel way to noninvasively assess CART cell functions in vivo.