Scientists put human cells in a sheep embryo. Here's what that means.
Researchers have successfully incorporated human cells into a sheep embryo — the first step in a process that they hope may one day allow them to grow replacement organs in other animals. The advance is one of several recent ones in a burgeoning field that is raising ethical questions.
The bottom line: Advances in the past year are important proofs-of-principle that this is even a plausible approach but an organ hasn't been grown in a large animal.