Considerable effort has recently been focused on methods to induce a pluripotent state by reprogramming somatic cells. However, current methods have relied on the introduction of exogenous genes to accomplish reprogramming with low conversion rates. Not surprisingly, the use of induced pluripotent stem cells (iPSCs) derived from such methods will be an unlikely source for any beneficial cell-based therapy due to concerns regarding genetic modifications or artifacts that remain after differentiation. One solution is to screen for small molecules that can mimic the action of those gene products required for reprogramming.
Recent work published by Kuroda, et al, have isolated a distinct type of stem cell from several tissue sources capable of generating, at the single cell level, cells representative of all three germ layer(1). Interestingly enough, the cells appeared indistinguishable in adherent tissue culture but behaved differently when cultured in suspension, forming clusters exhibiting pluripotency markers such as SSEA-3. Upon isolation and further characterization the group found the cells exhibited slower proliferation rates than typically seen with ES cell cultures. Even more intriguing is the finding that they did not form teratomas in the testes of immunodeficient mice suggesting fundamental differences in proliferative capacity not seen with iPSCs or ESCs.
There are two implications of these finding 1) the isolation of these cells will help to better understand their role in tissue repair and regeneration 2) they provide a more readily available source of multipotent stem cell devoid of exogenous genes for potential use for cell-based therapy.
1 Kuroda Y, et al. (2010) Unique multipotent cells in adult human mesenchymal cell populations. PNAS 107:8639-8643.