Whole-Body Imaging of Hematopoietic and Cancer Cells Using Near-Infrared Probes

Noninvasive in vivo monitoring of cell behavior presents a major challenge to imaging researchers. Cells labeled with fluorescent probes or expressing bioluminescent reporter genes offer opportunities for in vivo tracking. However, it is important to verify that labeling remains stable once it is in the cell, does not impair cell phenotype or influence engrafting behavior. Herein, we provide a brief outline of current approaches to whole-body fluorescence imaging of cancer and hematopoietic cells by means of near-infrared (NIR) fluorescence-emitting agents. Cell-labeling approaches will be reviewed, with particular focus on the use of NIR lipophilic membrane dyes, nontargeted NIR cyanine-based fluorescent markers, NIR esterase-activatable fluorescent probes, and MR Quantum Dots. Each approach features both advantages and limitations, typically related to ease of use, sensitivity, specificity, toxicity or stability. The beneficial aspects of NIR imaging are maximized when used in conjunction of complementary imaging modalities. Thus, the final section of this chapter is devoted to the use of NW imaging in the context of multimodal imaging.