[Cell therapy using stem cells: trophic factor, differentiation, and cell transplantation].

Our research of stem cell transplantation using mouse embryonic stem (ES) cells and induced pluripotent (iPS) cells was carried out from the aspect of trophic factor, cell differentiation, and better survival of grafted cells. Pleiotrophin, an enhanced trophic factor in the dopamine (DA)-depleted striatum, increased the number of DAergic neurons from ES-derived neural stem cells (ES-NSCs), increased cell survival of cultured DAergic neurons, and affected cell survival of grafted DAergic cells in Parkinson model rats. It was shown that DAergic differentiation from ES-NSCs was mediated by hypoxia inducible factor 1-alpha. Our challenges of the transplantation of ES-NSCs and iPS-derived oligodendrocyte progenitor cells (iPS-OPCs) into periventricular leukomalasia (PVL) model rats are also presented. It was found that grafted ES-NSCs survived better in the corpus callosum without immunosuppressant and most of them differentiated into neurons near the grafted site. It was also revealed that only a few of the grafted iPS-OPCs induced by a stepwise culture method with no use of serum could survive in PVL model rats, indicating that trophic factor (s) and improvement of graft techniques will be needed for better survival of grafted iPS-OPCs.