19F-MRI for monitoring human NK cells in vivo

The availability of clinical-grade cytokines and artificial antigen-presenting cells has accelerated interest in using natural killer (NK) cells as adoptive cellular therapy (ACT) for cancer. One of the technological shortcomings of translating therapies from animal models to clinical application is the inability to effectively and non-invasively track these cells after infusion in patients. We have optimized the nonradioactive isotope fluorine-19 (19F) as a means to label and track NK cells in preclinical models using magnetic resonance imaging (MRI). Human NK cells were expanded with interleukin (IL)-2 and labeled in vitro with increasing concentrations of 19F. Doses as low as 2 mg/mL 19F were detected by MRI. NK cell viability was only decreased at 8 mg/mL 19F. No effects on NK cell cytotoxicity against K562 leukemia cells were observed with 2, 4 or 8 mg/mL 19F. Higher doses of 19F, 4 mg/mL and 8 mg/mL, led to an improved 19F signal by MRI with 3 × 1011 19F atoms per NK cell. The 4 mg/mL 19F labeling had no effect on NK cell function via secretion of granzyme B or interferon gamma (IFNγ), compared to NK cells exposed to vehicle alone. 19F-labeled NK cells were detectable immediately by MRI after intratumoral injection in NSG mice and up to day 8. When 19F-labeled NK cells were injected subcutaneously, we observed a loss of signal through time at the site of injection suggesting NK cell migration to distant organs. The 19F perfluorocarbon is a safe and effective reagent for monitoring the persistence and trafficking of NK cell infusions in vivo, and may have potential for developing novel imaging techniques to monitor ACT for cancer