Chimeric monkey created from embryonic stem cell lines

Researchers from the Chinese Academy of Sciences have reported the live birth of a ‘chimeric’ monkey composed of cells that originate from two genetically distinct embryos of the same species of monkey. This has previously been demonstrated in rats and mice but, until now, has not been possible in other species, including primates. The breakthrough has been described in the journal Cell.

The monkeys used in the study were cynomolgus monkeys, also known as crab-eating or long-tailed macaques. The investigators established nine stem cell lines using cells removed from seven-day-old blastocyst embryos, which were placed in culture to give them enhanced ability to differentiate into different cell types.

The team performed a number of different tests on the cells to confirm that they were pluripotent — having the ability to differentiate into all the cell types needed to create a live animal. The stem cells were also labelled with green fluorescent protein so the researchers would be able to determine which tissues had grown out of the stem cells in any animals that developed and survived.

The team selected a particular subset of stem cells to inject into early monkey morula embryos (embryos that are 4–5 days old). The embryos were implanted into female macaques, resulting in 12 pregnancies and six live births.

Analysis confirmed that one monkey that was born alive and one foetus that was miscarried were substantially chimeric, containing cells that grew out of the stem cells throughout their bodies. The investigators used the green fluorescent protein label to determine which tissues contained cells derived from the injected stem cells. They also used gene sequencing and other tests to confirm the presence of stem-cell-derived tissue across organs including the brain, heart, kidney, liver and gastrointestinal tract.

In the live monkey, the contribution of the stem cells in the different tissue types ranged from 21% to 92%, with an average of 67% across the 26 different types of tissue that were tested; the numbers were lower in the monkey foetus. In both animals, the team confirmed the presence of stem-cell-derived cells in the testes and in cells that eventually develop into sperm cells.

“This work helps us to better understand naive pluripotency in primate cells,” said co-corresponding author Qiang Sun. “In the future, we will try to increase the efficiency of this method for generating chimeric monkeys by optimising the culture conditions for the stem cells, the cultures for the blastocysts where the stem cells are inserted, or both.”

The investigators also plan to further explore the mechanisms that underlie the survival of the embryos in the host animals, which they say will help improve the efficiency of chimera generation.

“This research not only has implications for understanding naive pluripotency in other primates, including humans, but it also has relevant practical implications for genetic engineering and species conservation,” said senior author Zhen Liu. “Specifically, this work could help us to generate more precise monkey models for studying neurological diseases as well as for other biomedicine studies.”

Images show the green fluorescence signals in different body parts of the live-birth chimeric monkey at the age of three days. Images courtesy of Cell/Cao et al under CC BY-SA 4.0.