To produce embryonic stem cells unique to an individual, scientists can now take the nucleus of one of this individual's cells and transplant it into the oocyte of a sheep or mouse that has been enucleated. This oocyte grows to the blastocyst stage, when cells of the inner cell mass (ICM) are harvested for embryonic stem cells. Therefore, the individual can now be treated with ES cells containing his own genetic information. This may be a critical factor in ensuring that grafted tissue/cells are not rejected by the individual's immune system.

The embryonic stem cells' high capacity for proliferation makes them useful for repairing damaged tissue quickly and efficiently. From only a few cells, or even just one, of a lineage, a virtually unlimited number of descendant cells can be created.

Current research is working towards ES cell replacement therapies for a variety of diseases.