The X Files: Pig-Primate Chimeras Born and Dead in Chinese Experiment

December 14, 2019

by Andreea Sterea

For the first time in history, two pig-primate chimeras were born alive in a lab. The two piglets died, however, within a week. The result is “discouraging” in the eyes of scientists who want to grow human organs in animals for transplants. 

The Pig-Primate Chimeras Experiment

A science team at the State Key Laboratory of Stem Cell and Reproductive Biology in Beijing managed to inject primate stem cells into fertilized pig embryos. Surrogate sows received the embryos implants. Of all the 10 piglets born, two were live pig-primate chimeras.

Creating interspecies animals (chimeras) is not new cutting-edge technology. Nevertheless, this is the first time when full-term pig-monkey chimeras are brought to life. Featuring DNA from two distinct animals – a pig and a monkey in this case – the two chimeras looked like perfectly healthy piglets.

The novelty issue about them was that they had heart, liver, spleen, lung, and skin monkey cells. The monkey cells’ proportion in the piglets’ tissues was, however, small. According to the reports, the ratio was between 1:1000 and 1:10,000.

Why Are We Creating Pig-Primate Chimeras?

Because we have some ethical issues with the creation of half-human and half-pig creatures. In case you did not know, back in 2017, scientists in the United States experimented with pig-human chimeras to unspectacular results. Such cutting edge technology does not have the purpose to simulate an X Files episode or to breed mad scientists. The purpose of creating chimeras is to save humankind. 

The idea behind these experiments is to create human organs (inside healthy animals) that can take a safe and fast route to the organ transplant system.

Results Have to Wait

Unfortunately, we are still far away from such goals. While scientists managed to create mice with rat pancreases, the pig-primate chimeras died within the week. Tang Hai, the lead researcher, admits that they do not know exactly why the piglets couldn’t make it. However, the team suspects it was the in vitro fertilization rather than the chimerism itself. In pigs, IVF does not work as well as it does in humans. Since all the experimental piglets died (not only the chimeras), it is a fair assumption that the IVF is to blame.

The Chinese scientists don’t want to throw the towel just yet. They want to repeat the experiment by using a higher proportion of monkey cells. If they succeed and the piglets live, the next step would be to create pig-primate chimeras where the pigs have one organ composed almost entirely of monkey cells.

Not Impressive, But Rather Discouraging

Ethical issues aside, the scientific community wanted to see more significant results. It didn’t. Some experts think we will never be able to grow viable organs for transplantation by creating human-animal chimeras.

Biologist Paul Knoepfler at the University of California, Davis, told News Scientist

Given the extremely low chimeric efficiency and the deaths of all the animals, I actually see this as fairly discouraging.

How Far Are We from Human-Animal Chimeras?

Given the fact that human-monkey chimeras are currently a work in progress in China, we want to see the published results first. Nevertheless, the pig-primate chimeras failed experiment should not become an obstacle in scientific research, experts agree. Along with tissue engineering, reviving dead organs, and other cutting-edge medical technologies and experiments, the creation of chimeras could prolong and save human lives.

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