Growing human organs for transplant inside human-pig chimeras?

For the first time, American researchers are proposing growing human organs in half-human, half-animal hybrid embryos called chimeras to allow more transplants.

In order to overcome the organ donation shortage for transplants, researchers in California have developed a method for growing human organs inside pigs. The chimerical animal thus serves as a holding tank for the organs, a “biological incubator” where they can grow and develop. In order to achieve this result, they use a technique known as CRISPR-Cas9 which, among other functions, allows gene segments to be edited.

In the current study, the part of the DNA responsible for developing the pig’s pancreas is deleted and replaced by human stem cells. Thus, the pancreas will develop with human cells. The embryo is then implanted in the sow until gestation is interrupted on the 28th day. Pablo Ross, a reproductive biologist, explains that they hope “that this pig embryo will develop normally even though its pancreas is almost exclusively made out of human cells and is compatible with a patient for transplantation.”

However, this technique raises several ethical issues, both towards man as well as towards animals. In fact, implanting human stem cells in pig embryos requires the destruction of human embryos. There is also a risk, although minimal, of transmitting animal viruses to the receiver. From a medical point of view, the main difficulty concerns the risk of immune rejection by the individual receiving the transplanted organ.

One of the major worries remain that of seeing the animal’s brain develop human cells which could change its behavior. Stuart Newman warns: “If you have pigs with partly human brains, you could have animals that might actually have consciousness like a human.”

For these reasons the NIH (US National Institute of Health) imposed a moratorium on the research on these “chimeras” in September 2015, until there is a better understanding of its’ implications.

« One of the concerns lots of people have, is that there is something sacrosanct in man, expressed in his DNA,” says Jason Robert, a bioethicist at Arizona State University. “To insert a part of the DNA into other animals and to give those animals potentially some of the capacities of man could be a kind of violation, even playing God”