Two studies push the envelope on interspecies transplants, but also raises the ethical debate another octave 

Science can’t help sounding like science fiction sometimes. Twenty years ago, Scottish scientists cloned sheep from an adult stem cell proving that it was possible to take a cell from a specific adult animal, and then used that cell to make a genetic copy of the adult animal. It changed the world of molecular genetics forever. 

Today, researchers reported in the journal Cell they had grown an embryo that was part pig and part human, opening the door to the possibility of viable animal organs for human transplantation, but also elevating the already volatile debate over introducing human material into animals. The study follows by a day another study demonstrating that organs for transplant can be grown in chimera embryos that are part-mouse, part-rat, The Washington Post reports. 

Researchers have long thought of growing organs suitable for human transplantation in pigs, but concerns over organ rejection stymied efforts. Scientists have also tried growing organs in petri dishes but they aren’t identical to the original and therefore also raise the risk of rejection.

These realities led researchers from the Salk Institute to just to see what happens if they injected human induced pluripotent stem cells into blastocysts derived from pancreas-deficient animals and see what happens. “That’s where the rationale of this kind of experiment comes in,” Juan Carlos Izpisua Belmonte, a developmental biologist at the Salk Institute and the senior author on the study of the human-pig chimera told The Washington Post. “What if we let nature do the work for us? What if we just put human cells inside the embryo and the embryo knows what do to?”

The Post reported that in the rat study, researchers induced pluripotent stem cells from mice and injected them into rat embryos genetically modified so that they could no longer grow their own pancreas, “emptying a niche” for the mouse stem cells to fill.