Quick! Hide! Stem cells!
Researchers in France have used mouse embryonic stem cells (ESTs) to repair the heart muscle of sheep, and in doing so shown that the stem cells of one species of mammal may possibly be used in future stem cell therapy of another (i.e, us lot) with out incuring the usual immune response problems what have dogged xenotransplantation research since such things were first thought of, which was ages ago. I'm sure I seem to remember that in the 1600 some Russian used a bit of a dogs skull to repair the skull of an arisotcrat. Or some such. That doesn't really sound credible does it? Oh well.
Basically stem cells are cells that can differentiate into any, or almost any, of the cell types in the body and so are known as totipotent (if they can form any cell type), or pluripotent (for those that can form many many cell types). Only the cells of the first few divisions of a zygote are truley totipotent, so most ESTs are pluripotent. ESTs don't seem to elicite an immune response, possibly due to fewer cell surface signalling molecules or some such, and so were selected to see it they could cross the species barrier.
Some sheeps were taken, some of which were immuno-repressed, and heart attacks indues, thus leaving scaring on the heart muscle. Murine ESTs were cultured with bone morphogenetic protein 2 (BMP2, one of the curses of my life) to make turn towards a cardiac fate, before being grafted on to the scar tissue of the the sheeps hearts. And you know what, it only boody worked. Well, kinda. And they only had 9 experimental animals, so don't do rushing out to get mice to help repair your heart attacks...
Claudine Mnard, Albert A Hagge, Onnik Agbulut, Marietta Barro, Miguel Cortes Morichetti, Camille Brasselet, Alain Bel, Emmanuel Messas, Alvine Bissery, Patrick Bruneval et al., Transplantation of cardiac-committed mouse embryonic stem cells to infarcted sheep myocardium: a preclinical study, The Lancet, Volume 366, Issue 9490, 17 September 2005-23 September 2005, Pages 1005-1012.