The potential of stem and progenitor cells slumbers in our blood vessels

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http://www.elpais.com/articulo/sociedad/The/potential/of/stem/and/progenitor/cells/slumbers/in/our/blood/vessels/elpepusoc/20120214elpepusoc_1/Tes

The extensive efforts to identify and characterize stem cells continue because there is great hope that stem cells can be used to heal currently incurable diseases. Great strides in scientific techniques have enabled us to establish any cell type from differentiated adult human cells. Many niches exist in our body that harbour stem cells; one of these niches is the wall of blood vessels.

Mammalian life begins in a one cell state. The zygote (totipotent) gives rise to all the cells of an organism. Through successive cell divisions and stepwise specialization, 220 different cell types finally arise. Cell specialization passes through different levels; pluripotent stem cells, multipotent stem/progenitor cells and unipotent progenitor cells. Increasing cell specialization is accompanied by a decline in developmental potential. To create new tissue and organs to replace defective tissue, cells with pluri- or multipotent development potential are needed. Do such cells exist in our body? In 1954, Stevens and Little described pluripotent stem cells in teratocarcinoma, an embryonic tumour in the adult body. Intensive work has lead to the identification of different niches in our body that contain multi- and unipotent stem and progenitor cells. Studies by Briggs and King in 1952, and Hochedlinger and Jaenisch in 2002, revealed that the cellular differentiation process is not related to permanent genetic changes. Finally in 2006, Takahashi and Yamanaka were the first to show the reprogramming of adult mouse cells back to the level of pluripotency - as embryonic stem cells - by introducing only a few factors controlling gene activity. Subsequently, they reprogrammed human adult cells to the pluripotent level. These so-called induced pluripotent stem cells (iPS) prompted a media circus and raised hopes. However, the major problems that prevent them from being used clinically are their propensity to form tumours and the fact that all genes needed for iPS generation promote tumour growth or induce cancer. Despite technological improvements, the tumorigenic potential of iPS cannot yet be excluded.