Scientists created embryos with human and monkey cells, stoking ethical concerns

Scientists are locked in debate over the necessity of creating chimera embryos that contain both monkey and human cells.

A study released on Thursday showed that human cells can indeed grow when implanted inside macaque monkey embryos. The goal of the research is to find ways to develop human organs and tissue that can be used for transplants. But some scientists are urging caution and question the need for this type of research at all.

The study took 132 monkey embryos and injected them with human stem cells. Scientists used a process that allowed them to develop monkey embryos for up to 20 days in a lab. Only three of the embryos made it to day 19 before they collapsed. What was most exciting to the scientists involved is that the human and monkey cells were able to communicate with one another, allowing the human cells to survive.

Past research has shown that trying to grow human cells in pigs or sheep yields far less stunning results, though humans and macaques are much more closely related than humans and pigs. The study’s authors see this research as key to better understanding human development and primate evolution, and an opportunity to advance the use of chimeras for organ creation.

The need for organs is great. In the U.S. alone, over 100,000 people are registered on the national waiting list for a transplant. Approximately 17 people die every day because they were unable to secure a transplant, according to the U.S. Health Resources and Services Administration.

Still, some scientists are concerned about what this research could mean in the future. The loudest worry is about the potential for so-called “rogue scientists” to use this research to develop true human-monkey chimeras. Another is that such experiments may develop in unintended ways. Plus, there are ethical questions about creating chimeras purely for organ extraction. The rules around developing chimeric embryos are foggy. Scientists internationally abide by a limit that prevents the development of human embryos for research beyond 14 days, though there are efforts to extend that cutoff to as many as 28 days. It’s not clear, however, how a monkey embryo with human cells would be regulated.

There’s also a question as to whether such animal-human research is necessary, especially where organ development is concerned. Scientists have made huge strides in developing human tissue and organs (known as organoids) in a lab. If lab-grown organs succeed, it may obviate the need to use animals as vessels for human organ growth.