Recent studies from the Children's hospital of Philadelphia, published in Nature Medicine report that human mesenchymal stem cells have been successfully transplanted into sheep, where they grew and matured and differentiated. After human mesenchymal cells were transplanted into fetal sheep, they were identified in sheep tissue as long as 13 months after the original transplantation procedure. They were also found to have matured into chondrocytes (cartilage forming cells), adipocytes (fat producers), myocytes (muscle makers) and cardiomyocytes (makers of heart muscle). Even when the mesenchymal cells were transplanted late enough so that the sheep immune systems might have been expected to reject them, the human mesenchymal cells were able to grow and flourish. The authors of the study concluded that not only do mesenchymal stem cells retain their multipotent status after transplant, but they also have some ability to withstand immune system rejection. The potential for use of these cells in tissue engineering, cell therapy and gene therapy is just beginning to be understood.