| Most of the adult stem cells not only generate those mature cell types corresponding to their tissue of origin, but also cross tissue (or germ layer) boundaries to generate cell types of different lineages, which was named as adult stem cell plasticity, however, the explanations of adult stem cell plasticity remain a point of discussion and controversy. One well accepted possible mechanism for observation of adult stem cell plasticity relates to the action of rare pluripotent stem cells (PSCs) present in the test cell population.In the first part, we have succeeded in isolating Sca-l+CD117-Lin- primitive pluripotent stem cells from the mouse embryonic fibroblast populaiton. This cell population possesses the main characteristics of primitive pluripotent stem cells, including expression of embryonic stem cells (ESCs) marker, ability of giving rise to multiple types of three germ layers and potential of immunoregulation. In vivo studies indicated that the cell population could prolong the survival of allogeneic skin grafts, and strikingly promote the skin burn would healing by differentiating into multiple types of cells in the dermal and epidermal tissues. Our study will help us better understand the properties of plasticity and may greatly contribute to the use of stem cells as a target for cell transplantation and gene therapy.The second part indicated that the Sca-1+CD117-Lin- pluripotent stem cells could be induced to differentiate into CD11bhigh IalowCD11clow dendritic cells (DCs) with strong regulatory functions capable of suppressing mixed lymphocyte reaction, allogeneic delayed type-hypersensitivity and rejection of allogeneic skin grafts. The immune regulatory functions of these dendritic cells were found to be mediated by Jagged-2. Our studies revealed that ESC-like pluripotent stem cells exist in freshly isolated mouse embryonic fibroblast population and they can differentiate into DCs with strong regulatory functions.
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