Stem cell enrichment approaches.

Adult somatic tissue, and the tumours that arise therein, are maintained by a small population of stem cells. In addition to the self-renewal potential and pluripotency, these stem cells express several phenotypic traits that can be used in isolation and enrichment strategies. Since most of the traits are not exclusive to the stem cells however, the resultant populations are typically heterogeneous and variable from one isolation to another. In this article, we review the strategies for isolation of stem cells, and the limitations thereof, with emphasis on mesenchymal tissue and bone tumours. The emerging evidence suggests that stem cell is not a distinct entity, but rather an indefinite state along a spectrum, characterized by phenotypic traits, epigenetic factors and the microenvironment.