Apr 17, 2021 - Science

Scientists create embryos with human and monkey cells

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A time-lapse video of the chimeric embryo development. Credit: Weizhi Ji/Kunming University of Science and Technology

Researchers for the first time have created embryos in the lab that contain both human and monkey cells.

Why it matters: So-called chimeric embryos could help scientists produce organs for people desperately in need of transplants, but the very act of mixing human and animal cells raises major ethical questions.

What's new: In a study published Thursday, researchers in the U.S. and China injected 25 induced pluripotent stem cells from humans into embryos from macaque monkeys.

  • After a single day, the researchers could detect human cells growing in 132 of the embryos, known as chimeras because they are a mix of species.
  • The embryos survived for 19 days.
  • The work provided the scientists with insight into how the human and monkey cells communicated in the chimeric embryos, which in turn could help them learn to grow organs for human transplantation in animals.

Background: Scientists have tried injecting human stem cells into sheep and pig embryos in recent years in an effort to grow organs for transplant, but they've had little success — hence the turn to macaque monkeys, which are more genetically similar to humans.

The catch: If the idea of mixing human and monkey cells in an embryo makes you a little squeamish, many bioethicists share your concerns.

  • Some fear that a rogue scientist might use these tools to make a baby out of chimeric embryo, which could result in a nightmare scenario of a living monkey spiked with human cells — including in its brain.
  • Chimeric embryos could also potentially confound medical regulations that treat animal and human subjects very differently.
  • "I do think it's an appropriate time for us to start thinking about, 'Should we ever let these go beyond a petri dish?'" Hank Greely, a Stanford bioethicist, told NPR.

What to watch: Next month the International Society for Stem Cell Research will issue revised guidelines for the field, including for work on non-human primate and human chimeras.

  • Those new guidelines may lead the NIH to lift a ban on federal funding for chimera research.

The bottom line: This is not the hybrid future I was expecting.

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