For some reason, this reminds me of a filk song...
Geneticists at the University of Nevada have spent the past seven calendar years working on producing viable chimaerae, hybrid organisms of human and nonhuman natures. The project's most remarkable success to date was announced yesterday: A sheep that is 15% human by cell count. That's right - one tenth of its cellular makeup is from an unknown specimen of homo sapiens sapiens. During gestation, cells from an adult human were injected into the peritoneum of a sheep fetus, which allowed the cells to be integrated through the course of foetal development.
The purpose behind these experiments are the eventual development of transplantable organs for people - rather than hunting to find a suitable donor, an animal could be bred and harvested for replacement internal organs. The key is making sure that the animal cells won't trigger an immune response, a problem which at this time has not been worked out.
Still, here's hoping.