Abstract
Stem cells posses both capabilities of self-renewal and differentiation into various tissue-specific cells. Traditionally, stem cells have been divided into two groups; embryonic stem (ES) and somatic stem cells. Although human ES cells have the potential to generate new tissues in regenerative medicine, the establishment of human ES cell lines requires ethically problematic destruction of a human embryo and it remains to be resolved more extensively, along with the problem of the teratoma formation after transplantation. Now all regenerative medicine has been performed using somatic stem cells. For pre-clinical study of regenerative medicine using somatic stem cells it is anxious to establish a novel model mouse in which human somatic stem cells are able to proliferate and differentiate into appropriate mature cells. Recently, we developed a new strain of immunodeficient mouse (NOG mouse), which carried various immunological abnormalities. Successful engraftment was achieved even if a small number of human somatic stem cell were transplanted into NOG mice without administration of human cytokines. When human hematopoietic stem cells (HSC) expanded ex vivo were transplanted into the mice, multi-lineage reconstitution including a large number of human myeloid, B, T, NK, NKT, DC, erythroid cells and megakaryocytes were confirmed in various hematopoietic organs.
Stem cell plasticity, safety and ethical issues underlying the regenerative medicine are also discussed in this review.
