Embryonic stem cells, derived either after in vitro fertilization or nuclear transfer, prolong survival of semi-allogeneic heart transplants.

Tolerance induction toward allogeneic organ grafts represents one of the major aims of transplantation medicine. Stem cells are
promising candidates for promoting donor-specific tolerance. In this study, we investigated the immunomodulatory properties of
murine embryonic stem cells (ESCs), obtained either by in vitro fertilization (IVF-ESCs) or by nuclear transfer (NT-ESCs), in heart
transplant mouse models. IVF-ESCs did not prolong the survival of fully allogeneic cardiac transplants but significantly prolonged
the survival of semiallogeneic hearts from the same ESC donor strain for >100 d in 44% of the animals. However, 28% of
transplanted animals infused with IVF-ESCs experienced development of a teratoma. NT-ESCs similarly prolonged semiallogeneic heart graft survival (>100 d in 40% of the animals) but were less teratogenic. By in vitro studies, IVF-ESC and NT-ESC
immunoregulation was mediated both by cell contact-dependent mechanisms and by the release of soluble factors. By adding
specific inhibitors, we identified PGE2 as a soluble mediator of ESC immunoregulation. Expansion of regulatory T cells was found
in lymphoid organs and in the grafts of IVF-ESC– and NT-ESC–tolerized mice. Our study demonstrates that both IVF-ESCs and
NT-ESCs modulate recipient immune response toward tolerance to solid organ transplantation, and that NT-ESCs exhibit a lower
tendency for teratoma formation. Because NT-ESCs are obtained by NT of a somatic cell from living individuals into an enucleated oocyte, they could represent a source of donor-derived stem cells to induce tolerance to solid organ allograft.