Tat peptide-derivatized magnetic nanoparticles allow in vivo tracking and recovery of progenitor cells

The ability to track the distribution and differentiation of progenitor and stem cells by high-resolution in vivo imaging techniques would have signif icant clinical and research implications. We have developed a cell labeling approach using short HIV-Tat peptides to derivatize superparamagnetic nano particles. The particles are efficiently internalized into hematopoietic an d neural progenitor cells in quantities up to 10-30 pg of superparamagnetic iron per cell. Iron incorporation did not affect cell viability, different iation, or proliferation of CD34(+) cells. Following intravenous injection into immunodeficient mice, 4% of magnetically CD34(+) cells homed to bone m arrow per gram of tissue, and single cells could be detected by magnetic re sonance (MR) imaging in tissue samples. In addition, magnetically labeled c ells that had homed to bone marrow could be recovered by magnetic separatio n columns. Localization and retrieval of cell populations in vivo enable de tailed analysis of specific stem cell and organ interactions critical for a dvancing the therapeutic use of stem cells.