Monkey stem cells were injected into fertilized pig embryos to generate the pig–monkey chimera. These were subsequently implanted into surrogate sows. Chimeras were a result of these piglets, which means that they contained DNA from a pig and a monkey.
“This is the first report of full-term pig-monkey chimeras,” co-author Tang Hai, a researcher at the State Key Laboratory of Stem Cell and Reproductive Biology in Beijing, told New Scientist.
The main goal of Hai and his co-researchers were for the growth of human organs in animals for transplant procedures. The team has received ethical qualms related to the development of human–animal chimeras.
Mechanism on the Growth of the Pig–Monkey Chimera
The cells of cynomolgus monkeys (Macaca fascicularis) were grown in lab dishes. The DNA cells were provided steps to build a fluorescent protein that aimed to change the DNA. A bright green glow was a result of this protein. Embryonic stem cells resulted from these luminescent cells that were injected into prepared pig embryos. Monkey cells were tracked by the researchers through these luminescent spots.
A total of 4,000 embryos were recipients of the monkey cell injection and were subsequently implanted in surrogate pigs. Ten piglets were born out of these sows but only two grew both pig and monkey cells. The team used the luminescent protein to scan for the monkey cells through different organs. The hybrid chimeras were comprised of 99% pig as there is one in 1,000 monkey cells in each organ.
The low ratio of monkey to pig cells still is greater compared with the 2017 human–pig chimera that was grown by scientists. The said chimera was only permitted to develop for a month since there is a possibility that the brain might grow human cells and provide the animal with a human-like consciousness.
The pressure from the scientific ethics committee did not stop the team from creating human–monkey chimeras early this 2019. The results of the said experiment were not published, but the researchers only allowed the human–primate chimera a few weeks to develop.
Despite the success achieved by Hai and his co-authors, stem cell biologist Paul Knoepler of the University of California, Davis was not impressed with the results as it is discouraging because of the low ration of monkey-to-pig cells.
“The exact reason for the piglets’ death remains “unclear,” Hai told New Scientist, but he said that he suspects the deaths are linked to the in vitro fertilization (IVF) procedure rather than the injection of monkey DNA. Other scientists have also found that IVF doesn’t consistently work in pigs, according to a 2019 report in the journal Theriogenology,” as reported by Live Science.
Hai and his team aim to increase the ratio of monkey cells to pig cells in future chimeras. The researchers aim to be able to grow human organs in animals for organ transplant procedures and to help in the field of human health.