Izpisúa Belmonte says manipulating some of those pathways may help human cells survive in embryos of species "more appropriate for regenerative medicine." The human cells seemed to integrate with the monkey cells and had begun to specialize into cell types that would develop into different organs.īy analyzing gene activity, the researchers identified molecular pathways that were switched on or turned up in the chimeras, possibly promoting integration between human and monkey cells. The team reports today in Cell that the human cells showed staying power: After 13 days, they were still present in about one-third of the chimeras. They inserted 25 human EPS cells into each of 132 monkey embryos and reared the chimeras in culture dishes for up to 20 days. In the new study, Izpisúa Belmonte, reproductive biologist Weizhi Ji of Kunming University of Science and Technology, and colleagues tested those more capable cells in a closer human relative-cynomolgus monkeys. But so-called extended pluripotent stem (EPS) cells, made by exposing stem cells to a certain molecular cocktail, can spawn a greater variety of tissues. The pig study used human skin cells that had been reprogrammed into stem cells. After the embryos had developed in surrogate mother pigs for 3 to 4 weeks, only about one in 100,000 of their cells were human. That same year, developmental biologist Juan Carlos Izpisúa Belmonte of the Salk Institute for Biological Studies and colleagues reported injecting human stem cells into pig embryos. But cells from more distantly related species, such as pigs and humans, haven't gotten along as well. Transplanting the organs into mice with diabetes eliminated the disease. In 2017, researchers reported growing pancreases from mouse stem cells inserted into rat embryos. The findings hint at mechanisms by which cells of one species can adjust to survive in the embryo of another, adds Daniel Garry, a stem cell biologist at the University of Minnesota (UM), Twin Cities. "The paper is a landmark in the stem cell and interspecies chimera fields," says stem cell biologist Alejandro De Los Angeles of Yale University. These chimeras could help scientists hone techniques for growing human tissue in species better suited for transplants, such as pigs. In a step toward that goal, researchers have created the first embryos with a mixture of human and monkey cells. By slipping human stem cells into the embryos of other animals, we might someday grow new organs for people with faltering hearts or kidneys.
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