Scientists at the Kunming University of Science and Technology in Yunnan, China, injected human stems cells into fertilised macaque monkey embryos which were then cultured for up to 19 days. The stem cells were labelled using a fluorescent protein, allowing the researchers to observe how they grew with the monkey cells.
Professor Juan Carlos Izpisua Belmote of The Salk Institute, California and corresponding author of the study published in Cell, told the Guardian: 'We demonstrated that the human stem cells survived and generated additional cells, as would happen normally as primate embryos develop and form the layers of cells that eventually lead to all of an animal's organs.'
Previous research has involved the merging of human stem cells with animal embryos such as pigs, mice, and cows to generate chimeras. However, the evolutionary distance between humans and these animals led scientists to wonder if chimeras between humans and other primates may be more successful and informative.
'Twenty-five human cells were injected and on average we observed around four percent of human cells in the monkey epiblast,' said co-author Dr Jun Wu of Kunming University, China.
The team were able to detect communication between the human and monkey cells which enabled some embryos to progress to the point at which different cell types begin to differentiate. They hope that their findings may lead to a greater understanding of the evolution of embryogenesis, and potentially aid progress in regenerative medicine and the growth of human organs for transplant.
'These chimeric approaches could be really very useful for advancing biomedical research not just at the very earliest stage of life, but also the latest stage of life', Professor Belmonte told the BBC.
While the chimeric embryos were terminated at 20 days of development, the work has raised ethical concerns, particularly regarding what the technology could lead to in the future.
Professor Julian Savulescu, director of the Oxford Uehiro Centre for Practical Ethics told the BBC that the work 'opens Pandora's box to human-nonhuman chimeras'.
Sarah Norcross, director of the Progress Educational Trust (the charity that publishes BioNews) commented: 'Substantial advances are being made in embryo and stem cell research, and these could bring equally substantial benefits. However, there is a clear need for public discussion and debate about the ethical and regulatory challenges raised.'