Some 75,000 Americans are waiting for an organ donation. Today, like every other, around 20 will die. But researchers this week at the AAAS, a big science conference, held forth a tantalising prospect: animal organ factories. Take, for example, the fertilised egg of a pig and cut out genes that promote the development of the animal’s heart. Now, this pig will grow up without a heart of its own. Then inject human stem cells taken from a patient who needs a new heart into the embryo and then place it into the womb of a sow. Wait nine months. The result would be an adult pig with a heart made of human cells which can be slaughtered and the organ transplanted into the patient who provided the stem cells—a perfect genetic match. The concept has already been proven with mice-rat “chimeras”. Pig-human ones are more challenging, but getting closer.

[Source: Reap from a sow: organ transplants Espresso]