Development of a Clinically Relevant Reporter for Chimeric Antigen Receptor T-cell Expansion, Trafficking, and Toxicity

Abstract

Although chimeric antigen receptor T (CART)–cell therapy has been successful in treating certain hematologic malignancies, wider adoption of CART-cell therapy is limited because of minimal activity in solid tumors and development of life-threatening toxicities, including cytokine release syndrome (CRS). There is a lack of a robust, clinically relevant imaging platform to monitor in vivo expansion and trafficking to tumor sites. To address this, we utilized the sodium iodide symporter (NIS) as a platform to image and track CART cells. We engineered CD19-directed and B-cell maturation antigen (BCMA)–directed CART cells to express NIS (NIS+CART19 and NIS+BCMA-CART, respectively) and tested the sensitivity of 18F-TFB-PET to detect trafficking and expansion in systemic and localized tumor models and in a CART-cell toxicity model. NIS+CART19 and NIS+BCMA-CART cells were generated through dual transduction with two vectors and demonstrated exclusive 125I uptake in vitro. 18F-TFB-PET detected NIS+CART cells in vivo to a sensitivity level of 40,000 cells. 18F-TFB-PET confirmed NIS+BCMA-CART-cell trafficking to the tumor sites in localized and systemic tumor models. In a xenograft model for CART-cell toxicity, 18F-TFB-PET revealed significant systemic uptake, correlating with CART-cell in vivo expansion, cytokine production, and development of CRS-associated clinical symptoms. NIS provides a sensitive, clinically applicable platform for CART-cell imaging with PET scan. 18F-TFB-PET detected CART-cell trafficking to tumor sites and in vivo expansion, correlating with the development of clinical and laboratory markers of CRS. These studies demonstrate a noninvasive, clinically relevant method to assess CART-cell functions in vivo.

Applying a clinical lens to animal models of CAR-T cell therapies

“…Although immunodeficient mice lack chemokines and cytokines that might otherwise influence cellular trafficking patterns, murine xenografts have allowed proof-of-concept studies to demonstrate that CAR-T cells can be effectively labeled and imaged, which is necessary prior to conducting large mammal studies to ensure tracking methods are tolerated. The sodium iodide symporter (NIS) 127 , 128 and somatostatin receptor 2 (SSTR2) 129 are reporter molecules successfully employed for non-invasive imaging of CAR-T cells in murine xenografts.…”

CAR T cell therapy and the tumor microenvironment: Current challenges and opportunities

“…In parallel to development of technologies aimed to enhance CAR T cell trafficking, strategies to enable real-time imaging of CAR T cells in vivo are being developed in preclinical and early-phase clinical trials. 70,71 Such strategies would enable non-invasive assessment of CAR T cell trafficking into tumor cells and allow expedited testing of novel interventions to improve CAR T cell functions.…”

Prospective approaches to enhancing CAR T cell therapy for glioblastoma

“…Moreover, chemokine receptor-overexpressing CAR T cells can potentially be attracted to tumors that highly express chemokine receptors, such as CCR6, leading to effective tumor clearance ( 27 , 28 ). Additionally, in parallel, technologies to enable in vivo real-time imaging of CAR T cells are being generated and assessed in preclinical and early phase clinical trials ( 29 , 30 ). Such a strategy would enable the noninvasive and rapid examination to improve CAR T cell trafficking to tumor cells and antitumor function.…”