A team of Chinese scientists has successfully injected piglets with monkey stem cells, bringing researchers one step closer to being able to grow human organs inside animals.
Monkey-pig hybrids were born are the Beijing State Laboratory of Stem Cells and Reproductive Biology in China. They are an organism derived from two or more zygotes, or the eukaryotic cell formed during fertilisation that contains essential DNA.
These animals were born alive and survived for several days. However, despite their death, they mark a milestone in the race to grow organs in the laboratory.
Although the monkey-pig hybrids died within the first week of birth, the researchers discovered that they both had macaque monkey DNA in their heart, liver, spleen, lung and skin (specifically crab macaque -Macaca fascicularis-), but were not found in other organs, such as the testicles and ovaries, due to the low rate of hybridisation, the researchers said.
They were raised from more than 4,000 five-day-old embryos that were implanted in the uterus of a sow using the in vitro fertilisation (IVF) technique to gestate the pregnancy.
The team genetically modified the monkey cells to produce a fluorescent protein that allowed researchers to track the cells; these modified cells were injected into pig embryos five days after fertilisation.
Of all the embryos, only ten came to term and were born alive. Of these ten, only two of them had monkey cells, that were "real" hybrids.
However, as we have seen, the success rate was significantly low since 10 out of 4,000 embryos were born; a circumstance that some leading stem cell scientists have taken advantage of to describe the controversial experiment as "discouraging".
The scientists responsible for the experiment stated that it was unclear why the two hybrid piglets died, but since the remaining eight normal piglets that were implanted also died, they believe that this is a problem related to the IVF process rather than the fact of having created a laboratory miracle, since IVF is a notoriously complicated procedure in pigs.
Despite the research, some members of the scientific community have warned against the creation of these miracles due to ethical concerns, because many fear that when it comes to stem cells they could end up in other parts of the animal or even in its brain, with unintended consequences.
The research is part of an ongoing effort to develop animals, whether sheep or pigs, that can produce human organs that we can then harvest for transplantation.
Human stem cells can be renewed and regenerated, making them potentially capable of generating human organs in mammals for future transplantation through a process called xenogenesis.
Mouse trials have been relatively successful in the production of hybrid organisms, but the method is much more complex in humans for many reasons (biological, ethical...).
Scientists plan to try again, increasing the proportion of chimeric cells (if that works, they will try to create pigs that are born with a complete organ composed of primate cells).
They believe that their data can help other scientists working in the same field.
"We believe that this work will facilitate the development of xenogenic organogenesis by providing a better understanding of the processes of xenogenic recognition, fate determination and the proliferation and differentiation of primate stem cells during porcine development. Our findings could pave the way for overcoming obstacles in re-engineering heterogeneous organs and achieving the ultimate goal of rebuilding human organs into a large animal," the authors claimed.
Reference: Rui Fu, Dawei Yu, Jilong Ren and Chongyang Li have contributed equally to this work. Domesticated cynomolgus monkey embryonic stem cells allow the generation of neonatal interspecies chimeric pigs. Protein Cell 2019. First Online: 28 November 2019 DOI: https://doi.org/10.1007/s13238-019-00676-8