Scientists have successfully created the first embryos containing both human and monkey cells, an important step in helping researchers find ways to produce organs for transplants. The

results of the groundbreaking experiment, published Thursday in the journal _Cell_, describe the first mixed-species embryos known as chimeras. The research team in China was led by Juan

Carlos Izpisua Belmonte, who has previously experimented with human and pig embryos. The team injected 25 human stem cells into the embryos of macaque monkeys. The researchers were able to

detect human cells growing in 132 of the embryos after one day. They were able to study the embryos for 20 days, giving researchers enough time to learn about how animal and human cells

trying to understand how cells from different organisms communicate with one another," added Belmonte. The study was done in part to find new ways to produce organs for people who need

transplants, as the "demand for that is much higher than the supply," Belmonte explained. Insoo Hyun, a bioethicist at Case Western Reserve University and Harvard University, told

NPR that thousands of people die every year in the United States waiting to receive an organ transplant. Though groundbreaking, the research also sparks ethical concerns among many

scientists. According to NPR, scientists said the biggest concern is that someone could use this research to attempt to make a baby out of an embryo in this way. _NEVER MISS A STORY — SIGN

UP FOR__ _PEOPLE_'S FREE WEEKLY NEWSLETTER__ TO GET THE BIGGEST NEWS OF THE WEEK DELIVERED TO YOUR INBOX EVERY FRIDAY._ Others are concerned that using human cells in this manner could

produce animals with human sperm or eggs. However, Belmonte said his team consulted with bioethicists and has no intentions of trying to create animals with hybrid monkey-human embryos.