Can exogenous stem cells be used in transplantation?

Today's most urgent problem in transplantation is the lack of suitable dono r organs and tissues and as the population ages, demands for organs and tis sue therapies will only increase. One alternative to organ transplantation is cell therapy whose aim is to replace, repair or enhance the biological f unction of damaged tissue or diseased organs. One goal of cellular transpla ntation thus has been to find a renewable source of cells that could be use d in humans. Embryonic stem (ES) cells have the potential to proliferate in vitro in an undifferentiated and pluripotent state. Theoretically, ES cell s are capable of unlimited proliferation in vitro. ES cells spontaneously d ifferentiate into derivatives of all three primary germ layers: endoderm, e ctoderm and mesoderm, hence providing cells in vitro which can theoreticall y be isolated and used for transplantation. Furthermore, these pluripotent stem cells can potentially be used to produce large numbers of cells that c an be genetically modified in vitro. Once available, this source of cells m ay obviate some of the critical needs for organ transplantation. Murine ES cells have been extensively studied and all available evidence indicates th at all aforementioned expectations are indeed fulfilled by ES cells. ES cel ls as well as embryonic germ cells have recently been isolated and maintain ed in culture. The recent descriptions of human ES cells portend the eventu al use of allogeneic in vitro differentiated cells for human therapy. This goal, however, is fraught with obstacles. Our aim is first to review the re cent advances made with murine ES cells and then to point out potentials an d difficulties associated with the use of human ES cells for transplantatio n. Copyright (C) 1999 S. Karger AG, Basel.