Labeling cells for in vivo tracking using 19F MRI

Noninvasive in vivo cell tracking is crucial to fully understand the function of mobile and/or transplanted cells, particularly immune cells and cellular therapeutics. 19F MRI for cell tracking has several advantages; chief among them are its noninvasive nature which allows longitudinal data acquisition, use of a stable, non-radioactive isotope permitting long-term tracking, the absence of confounding endogenous signal, and the ability to quantify cell numbers from image data. However, generation of sufficient signal i.e. 19F cell loading is a key challenge, particularly with non-phagocytic cells such as lymphocytes and stem cells. A range of 19F cell labels have been developed, including emulsions, particles, polymers, and agents for clinical use. Various animal and primary human cells, such as dendritic cells, lymphocytes and phagocytes have been successfully labeled and studied in models of autoimmune disease, inflammation and transplant rejection. Primary human cells, particularly dendritic cells as used in vaccine therapy have been tested for imminent clinical application. Here, we summarize current cell loading strategies and sensitivity of in vivo cell imaging with 19F MRI, and discuss the processing of image data for accurate quantification of cell numbers. This novel technology is uniquely applicable to the longitudinal and quantitative tracking of cells in vivo.