The researchers collected and cultured human induced pluripotent stem (hiPS) cells from foreskin fibroblasts, a standard cell source (medical waste can be pretty useful)

Even though the experiments only went on for four weeks, and not many pig embryos picked up glowing human cells, it worked! Human cells will join pig embryos.

Getting those human cells into the pig embryos wasn’t simple. The researchers injected 3 to 10 human cells into each of 2,181 pig embryos and transferred 2,075 of the embryos in batches of 30 to 50 into 41 sows. From day 21 through 28, the 18 pregnant pigs had 186 embryos harvested, 67 of which fluoresced in a variety of places. But 50 of the 67 were puny. So it isn’t perfect – but a good start to growing human organs in pigs.