Embryonic stem cells: technical aspects and hurdles in organ transplantation

Abstract

Purpose of review The pluripotency of embryonic stem cells, combined with their low immunogenicity, has inspired hope that embryonic stem cells could become a major source of cells for the repair of diseased or damaged tissues, as well as a means for the induction of transplantation tolerance. Recently, enormous progress has been made toward the application of pluripotent embryonic stem cells in replacement therapy. Embryonic stem cells have been directed in vitro and in vivo to differentiate into specific tissues, including neurons, hematopoietic cells, pancreatic islets, and cardiac or vascular cell lineages. However, the potential use of embryonic stem cells in the induction of transplantation tolerance without the need for host preconditioning is tantalizing. The authors discuss here the hurdles and limitations of the possible application of embryonic stem cells in cellular therapy and in the induction of transplantation tolerance. Recent findings Published data suggest that embryonic stem cells are immune privileged in allogeneic combinations. Whereas the constitutional expression of FasL by embryonic stem cells is possibly one of the protective mechanisms against T cell–mediated rejection, it seems that several factors, including soluble cytokines and growth factors, contribute to this unique property, which could be exploited for the induction of transplantation tolerance. Summary Despite the obvious low immunogenicity of embryonic stem cells, a clear advantage over hematopoietic and mesenchymal stem cells, several hurdles remain before clear concepts can be worked out for the use of embryonic stem cells in clinical organ transplantation. In particular, very little is understood about the robustness of embryonic stem cells immune privilege and the underlying mechanisms.