Stem cell therapy has the potential to repair and regenerate damaged tissues. Unlocking this potential requires effective methods both for isolating and expanding stem cells and for tracking their ultimate fate when introduced into their host. A study has been published online in the high impact journal Nature Nanotechnology describes new methods for isolating, expanding, and labeling lung stem cells, that uses fluorescent nanodiamonds to track the fate of individual cells. This technology may offer insights into the factors that determine the acceptance of transplanted stem cells and their ability to regenerate within a host.

　　The labs, headed by John Yu, M.D., Ph.D., Distinguished Chair of Institute of Cellular & Organismic Biology, and Huan-Cheng Chang, Ph.D., Distinguished Research Fellow, Institute of Atomic and Molecular Sciences, Academia Sinica, collaborated on the work.

　　First, they developed a new stem cell isolation method for lung stem cells (LSCs), using cell surface glycoprotein markers discovered by specialized proteomic analysis. They demonstrate that cells isolated with this method possess not only the abilities to self-renew and differentiate into lung tissues, but also the in vivo homing and regenerative abilities expected of a LSC.  Next, they used fluorescent nanodiamonds (FNDs) to label these cells. FNDs are novel imaging probes which are not only chemically robust and fluorescently stable, but also biologically inert and nontoxic. These nanoparticles can be readily taken up by cells through endocytosis. When excited by green-yellow light, the built-in fluorophores emit stable far-red emission with a fluorescence lifetime of up to 15 ns, much longer than 1 ~ 4 ns of endogenous and exogenous fluorophores commonly used in cell biology. This property makes it possible to separate FND emission from strong autofluorescence backgrounds of host tissue, using special strategies described in this manuscript.

　　The authors successfully demonstrate the use of this system to isolate LSCs, engraft them in mouse models of lung injury, and track single cell fates. They illustrate that FND-labeled LSCs preferentially home to injured lungs more rapidly than to uninjured controls, enabling the lung epithelium to be restored more rapidly. In addition to demonstrating the therapeutic potential of such treatment, these results also support an “active homing” model in which transplanted LSCs proactively migrate to injured tissue, as opposed to non-specific/passive entrapment.

　　Yu and Chang suggest that this method has broad applicability to stem cell research, and that similar techniques could be used to monitor the uptake of different kinds of stem cells in other tissues.

This team includes PhD students Tsai-Jung Wu from Institute of Biochemistry and Molecular Biology, National Yang-Ming University, and Yan-Kai Tzeng at Department of Chemistry, National Taiwan University, Taiwan.

　　full article entitled "Tracking the engraftment and regenerative capabilities of transplanted lung stem cells using fluorescent nanodiamonds" is available at the Nature Nanotechnology website at: http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2013.147.html