You can call it a chimera. You can call it a human-pig hybrid. You can call it a pigman. The journal Cell is calling it “Interspecies Chimerism with Mammalian Pluripotent Stem Cells.” Whatever you call it, researchers at the Salk Institute in California announced this week that they have created an embryo which contains both human and pig cells. Whatever you decide to call it, call them with your ethical complaints.
This is the first time that human cells are seen growing inside a large animal.
Professor Juan Carlos Izpisua Belmonte from the Salk Institute described the significance of this achievement. The researchers used human induced pluripotent stem cells, which are adult cells that have been reprogrammed backwards to act like embryonic stem cells.
These human cells were inserted into pig embryos, which were then placed in sows. The sows carried the embryos for four weeks, at which time they were removed o prevent possible development of brain cells.
We have those concerns too. That's why in this study we chose to stop the pregnancy at three to four weeks.
To the relief of Jun Wu, a member of the team and author of the study published in Cell, the tiny amount of human cells developed into muscle and organ cells. That fits in with the ultimate goal of this program – to grow human organs is pigs and cows for eventual transplanting in humans. While the first human-pig chimera is revolutionary, there’s a long way to go to reaching the goal. Only a few human cells developed in just a fraction of the embryos – 186 out of the 2,075 implanted.
While we’re waiting for hearts-from-hogs (sounds like a brand name in the making), Belmonte says these early human-pig hybrids can be used for drug testing, studying human diseases and learning about early human embryo development. At the same time, the researchers will be attempting to guide the development of the human cells – which in the experiment were left to develop on their own - into specific human organs.
This will also give everyone time to discuss the ethics of these experiments in terms of where they are today, where they plan to go and where they could go if left unchecked or end up in unscrupulous labs.
Considering we can’t even agree on what to call it, this is destined to be a long discussion.