Scientists have announced a successful attempt at growing sheep embryos that contain human cells. The achievement in growing the chimeras was made by researchers from Stanford University and the University of California. The researchers presented their work at the annual American Association for the Advancement of Science in Austin, Texas.
A chimera is an organism that has a mixture of genetically different tissues. A chimera is typically formed by embryo fusion, mutation or grafting. These hybrids were made by fusing human stem cells into sheep embryos. The scientists were able to grow the chimeras into fetal animals over 28 days. A similar breakthrough was made in 2017 with human-pig chimeras.
These modified sheep could one day supply organs for human transplants. If the scientists could use a recipient’s own cells to make organs that are compatible with their bodies, it could reduce the chance of immune system rejection.
The demand for organs far outstrips supply in the U.S., as there are approximately 115,000 people who currently need a lifesaving organ transplant. According to the U.S. Department of Health and Human Services, about 20 people in the United States die waiting for organ transplants each day. Every 10 minutes, someone is added to the national transplant waiting list. Researcher Dr. Pablo Ross of the University of California, Davis said, “We need to explore all possible alternatives to provide organs to ailing people.”
A replacement pancreas grown inside the sheep could be used to cure Type 1 diabetes. Type 1 diabetes occurs when the body fails to produce enough insulin from the pancreas to regulate blood sugar levels. In 2017, researchers showed that transplants using the pancreas could cure diabetes in diabetic mice.
The sheep embryos created were only 0.01 percent human by cell count, but still higher than the 0.001 percent of the human-pig embryos. The next step will be to size up and try this approach with human organs. Ross said that in order to grow human organs, the proportion needs to be closer to 1 percent.
Animal-grown human organs could a viable solution to the current lack of available transplants. However, there are numerous ethical questions surrounding this type of research and restrictions on what scientists are allowed to do. At present, researchers are only allowed to develop their embryos for up to 28 days at a time. They also face a lack of funding since the U.S. National Institutes of Health forbids public funding of human-animal hybrids.