Essential Elements to Consider for MRI Cell Tracking Studies with Iron Oxide-based Labeling Agents

Personalized diagnosis and treatment with allogenic or autologous cells have been intensively investigated over the past decade. Despite the promising findings in preclinical studies, the clinical results to date have been largely disappointing. Some critical issues remain to be solved, such as how to monitor the migration, homing, survival, and function of the transplanted cells in vivo. In the past years, imaging techniques have been introduced to solve these issues based on a concept that cells can be transformed to a cellular imaging agent following labeling of the cells with an imaging agent. For this purpose, magnetic resonance imaging (MRI) is so far the first choice imaging modality and iron oxide-based nanoparticles are the most frequently applied labeling agents. However, most MRI cell tracking studies are currently still limited in in vivo visualization of the labeled cells, some critical elements for cell tracking studies are often incompletely characterized, which makes it difficult to validate and meta-analyze the data generated from different studies. Incomplete information on preclinical studies also slows the transition of the findings to clinical practice. A robust protocol of MRI cell tracking studies is apparently critical to deal with these issues. In this review, we first briefly discuss the limitations of MRI cell tracking based on iron oxide nanoparticles and then recommend a minimum set of essential elements that should be considered in MRI cell tracking studies at preclinical stage.