Visualizing CAR-T cell Immunotherapy Using 3 Tesla Fluorine-19 MRI

Abstract

Purpose Chimeric antigen receptor (CAR) T cell cancer immunotherapies have shown remarkable results in patients with hematological malignancies and represent the first approved genetically modified cellular therapies. However, not all blood cancer patients respond favorably, serious side effects have been reported, and the treatment of solid tumors has been a challenge. An imaging tool for visualizing the variety of CAR-T cell products in use and being explored could provide important patient-specific data on CAR-T cell location to inform on potential success or failure of treatment as well as off-target toxicities. Fluorine-19 (19F) magnetic resonance imaging (MRI) allows for the noninvasive detection of 19F perfluorocarbon (PFC) labeled cells. Our objective was to visualize PFC-labeled (PFC +) CAR-T cells in a mouse model of leukemia using clinical field strength (3 Tesla) 19F MRI and compare the cytotoxicity of PFC + versus unlabeled CAR-T cells. Procedures NSG mice (n = 17) received subcutaneous injections of CD19 + human B cell leukemia cells (NALM6) expressing firefly luciferase in their left hind flank (1 × 106). Twenty-one days later, each mouse received an intratumoral injection of 10 × 106 PFC + CD19-targeted CAR-T cells (n = 6), unlabeled CD19-targeted CAR-T cells (n = 3), PFC + untransduced T cells (n = 5), or an equivalent volume of saline (n = 3). 19F MRI was performed on mice treated with PFC + CAR-T cells days 1, 3, and 7 post-treatment. Bioluminescence imaging (BLI) was performed on all mice days − 1, 5, 10, and 14 post-treatment to monitor tumor response. Results PFC + CAR-T cells were successfully detected in tumors using 19F MRI on days 1, 3, and 7 post-injection. In vivo BLI data revealed that mice treated with PFC + or PFC − CAR-T cells had significantly lower tumor burden by day 14 compared to untreated mice and mice treated with PFC + untransduced T cells (p < 0.05). Importantly, mice treated with PFC + CAR-T cells showed equivalent cytotoxicity compared to mice receiving PFC − CAR-T cells. Conclusions Our studies demonstrate that clinical field strength 19F MRI can be used to visualize PFC + CAR-T cells for up to 7 days post–intratumoral injection. Importantly, PFC labeling did not significantly affect in vivo CAR-T cell cytotoxicity. These imaging tools may have broad applications for tracking emerging CAR-T cell therapies in preclinical models and may eventually be useful for the detection of CAR-T cells in patients where localized injection of CAR-T cells is being pursued.

Molecular MRI-Based Monitoring of Cancer Immunotherapy Treatment Response

“…Similar to the IONP reports presented in Section 3.3.1 , a rodent tumor study by Ahrens et al showed that F MRI can be used to monitor dendritic cell migration to the lymph node [ 123 ]. Dubois et al imaged perfluorocarbon labeled CAR T-cells in a mouse model of leukemia at a clinical 3T field strength [ 124 ]. The detection was enabled as early as 1 day post-injection, and the perfluorocarbon did not alter the cytotoxic profile.…”

Recent Advances in Perfluorocarbon-Based Delivery Systems for Cancer Theranostics

“…After labeling the CD19-targeted CAR-T cells in vitro with the PFC emulsion and the intratumoral injection into the NALM6 subcutaneous tumor-bearing mice, the location and persistence of the CAR-T cells after injection were detected successfully using the 19 F MRI and a 3 T clinical magnetic field strength scanner. In addition, PFC labeling exerted no significant influence on CAR-T cell therapy . Dewitte et al designed DC-containing antigen PFC particles for the single-step antigen and PFC loading of DCs to allow for the specific tracking of antigen-containing DCs using 19 F MRI.…”

“…175 In addition to direct intravenous injection of 19 F nanoparticles for detecting the 19 F accumulation at tumor inflammation sites, 19 F MRI is also widely used for the noninvasive assessment of the location and persistence of cell-based cancer vaccines and other cell-based therapies. 176 Therapeutic cells, such as CAR T-cells, 177 dendritic cells (DC), 174,176 and peripheral blood mononuclear cells (PBMC), 27 may be detected in vivo after labeling with 19 F perfluorocarbon nanoparticles, and the cell viability, proliferation, phenotype, and function of these cells are not altered after labeling. The in vivo 19 F MRI signal intensity is linearly proportional to the 19 F-atom concentration, which allows for an unbiased measurement of the apparent cell population in the images.…”

“…In addition, PFC labeling exerted no significant influence on CAR-T cell therapy. 177 Dewitte et al 101 designed DC-containing antigen PFC particles for the single-step antigen and PFC loading of DCs to allow for the specific tracking of antigen-containing DCs using 19 F MRI. After the addition of DCs in vitro, the antigencontaining PFC particles were efficiently internalized, resulting in the presence of up to 40 pmol of 19 F atoms per cell.…”

Editorial to the Special Issue Entitled “Imaging in Immunooncology”

“…Cell tracking technologies that utilize MRI for the in vivo tumour accumulation of adoptively transferred cell therapies could be more easily integrated in many currently established clinical workflows. Dubois et al report in this Special Issue on how to approach this using fluorine-19 MRI on a 3T scanner [28].…”