Unique perfluorocarbon nanobeacons improve stem/progenitor cell tracking with MRI

Abstract

Conventional 1H Magnetic Resonance Imaging (MRI) has been employed to define the migratory behavior of stem/progenitor cells noninvasively in vivo. In contrast, we propose fluorine (19F) MRI of liquid perfluorocarbon nanoparticles (PFC NP: 200 nm) comprising a phospholipid/surfactant monolayer surrounding a PFC core could provide a unique and sensitive cell marker distinct from tissue background signal. To determine the utility for cell tracking, stem/progenitor cells were harvested by density gradient centrifugation from human umbilical cord blood, grown under proendothelial conditions, and labeled with fluorescent PFC NP. Internalization of NP alone, without aid of any additional agents, was confirmed with confocal microscopy showing abundant NP uptake and distribution throughout the cytosol. Flow cytometry indicated ≥68% of cells contained NP and stained positive for CD34, CD133, and CD31 markers. Labeled cells were readily imaged using the 19F nuclear NP signal at 1.5T in vitro; and at 12T after injection of 106 cells into mouse skeletal muscle in situ. PFC NP provide an unequivocal signal for stem/progenitor cells, do not require adjunctive procedures to achieve cellular uptake, enable spatial cell localization with 19F MR imaging, and provide opportunity for quantification via 19F MR spectroscopy. This molecular imaging and tracking approach should facilitate longitudinal investigation of cellular events in vivo such as stem/progenitor cell localization, implantation, and differentiation.