Derivation and application of pluripotent stem cells for regenerative medicine

Pluripotent stem cells (PSCs) are cells that can differentiate into any type of cells in the body, therefore have valuable promise in regenerative medicine of cell replacement therapies and tissue/organ engineering. PSCs can be derived either from early embryos or directly from somatic cells by epigenetic reprogramming that result in customized cells from patients. Here we summarize the methods of deriving PSCs, the various types of PSCs generated with different status, and their versatile applications in both clinical and embryonic development studies. We also discuss an intriguing potential application of PSCs in constructing tissues/organs in large animals by interspecies chimerism. All these emerging findings are likely to contribute to the breakthroughs in biological research and the prosperous prospects of regenerative medicine.     

Active Suppression of the Allogeneic Histocompatibility Reactions During the Metamorphosis of the Clawed Toad Xenopus

Metamorphosis is a privileged period for the induction of tolerance to allografts. Transfers of lymphocytes from metamorphosing Xenopus into isogenic adults prevented the rejection of a skin graft differing from the adult host by minor histocompatibility antigens. This implies that active suppression is involved at one step of the induction of tolerance to the self-antigens that differentiate at the time of metamorphosis. The reciprocal experiments of preventing tolerance induction by transfer of normal adult cells into metamorphosing animals failed. However, passive transfer of anti-graft immunity in tolerant animals was partially observed, provided that a transfer of primed cells was done simultaneously with the challenging graft. Thus, memory cells are not as sensitive to the suppression as are the cells that respond in a first set reaction.