Investigators in China and the United States have injected human stem cells into primate embryos and were able to grow chimeric embryos for a significant period of time–up to 20 days. The research, despite its ethical concerns, has the potential to provide new insights into developmental biology and evolution. It also has implications for developing new models of human biology and disease. The work appears April 15 in the journal Cell.
“As we are unable to conduct certain types of experiments in humans, it is essential that we have better models to more accurately study and understand human biology and disease,” says senior author Juan Carlos Izpisua Belmonte, a professor in the Gene Expression Laboratory at the Salk Institute for Biological Sciences. “An important goal of experimental biology is the development of model systems that allow for the study of human diseases under in vivo conditions.”
Interspecies chimeras in mammals have been made since the 1970s, when they were generated in rodents and used to study early developmental processes. The advance that made the current study possible came last year when this study’s collaborating team–led by Weizhi Ji of Kunming University of Science and Technology in Yunnan, China–generated technology that allowed monkey embryos to stay alive and grow outside the body for an extended period of time.
In the current study, six days after the monkey embryos had been created, each one was injected with 25 human cells. The cells were from an induced pluripotent cell line known as extended pluripotent stem cells, which have the potential to contribute to both embryonic and extra-embryonic tissues. After one day, human cells were detected in 132 embryos. After 10 days, 103 of the chimeric embryos were still developing. Survival soon began declining, and by day 19, only three chimeras were still alive. Importantly, though, the percentage of human cells in the embryos remained high throughout the time they continued to grow.
“Historically, the generation of human-animal chimeras has suffered from low efficiency and integration of human cells into the host species,” Izpisua Belmonte says. “Generation of a chimera between human and non-human primate, a species more closely related to humans along the evolutionary timeline than all previously used species, will allow us to gain better insight into whether there are evolutionarily imposed barriers to chimera generation and if [ … ]