The Rise of Chimeras: Scientists Successfully Created First Ever Human-Pig Embryo

A team of scientists from Salk Institute has successfully generated human cells and tissues in the embryo of pigs, making it the first ever human-pig embryo.

Their results, described in a paper published in the journal Cell, could served as the stepping stone in developing transplantable human organs, such as heart, lungs, liver and kidneys, within the bodies of animals.

"The ultimate goal is to grow functional and transplantable tissue or organs, but we are far away from that," said Juan Carlos Izpisua Belmonte, a professor in the Salk Institute of Biological Studies' Gene Expression Laboratory and lead investigator of the study, in a press release. "This is an important first step."

For the study, the researchers injected several forms of human stem cells into pig embryos. These stem cells include the so-called "naïve", "intermediate", and "primed. Naïve pluripotent stem cells are cells from an earlier developmental origin that have unlimited potential. Primed stem cells are a bit more developed than the naïve but still remain as pluripotent. Intermediate stem cells are somewhere in between of the naïve and primed.

Among the three types of stem cells, the researchers found that the intermediate stem cells survived the longest and showed most potential to develop further. The pig embryos that survived after being injected with human stem cells were then transplanted to sows and allowed to grow for between three and four weeks.

Belmonte and his team decided to stop the further development of the embryos to stay within the ethical line.

The researchers found that the level of contribution to the chimerized embryo was low. The researchers noted that the development of the pig embryo appeared to be delayed by the human tissues. Additionally, the researchers believe that human organs grown from hybrid embryos would likely to be rejected by humans because it would contain so much pig tissue.