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. https://phys.org/news/2021-04-human-monkey-chimeric-embryos.html