Controversial Stem Cell Research Makes Human-Monkey Hybrids

A groundbreaking experiment blending human and monkey cells could pave the way to artificially-grown replacement organs – while raising new ethical questions about so-called chimeric hybrids. It's the latest expansion of stem cell research, which has simultaneously fascinated scientists hoping to unlock new disease treatments and more, while horrifying groups concerned about the ethics or misuse of the technology.

Stem cells are precursors to other cells in the body, able to develop into different types depending on requirements. That's made them a focus of research looking to do things like grow replacement organs to cater to the marked shortfall of donors for things like hearts, livers, and other parts.

One area that has long been considered promising is using hosts such as pigs, within which human cells could be grown into such replacement organs. That, though, has run into issues with compatibility, something scientists believe could be down to the evolutionary distance between humans and pigs. This new research looked instead to one of our – comparatively – closer relatives, macaque monkeys.

The team, led by Salk Professor Juan Carlos Izpisua Belmonte, took human pluripotent stem cells and inserted them into macaque embryos in petri dishes. By tagging the human cells with a fluorescent protein – meaning they'd be identifiable in the correct conditions later on – they were able to see that the human cells not only survived, but integrated with the monkey cells with better relative efficiency than they had with pig tissue.

All of the experiments were terminated after 19 days after stem cell injection.

The goal was not to create something based on these cells that could eventually be implanted into a human. However, the hope is that the novel molecular communication observed in the chimeric cells could better explain how the early stages of human development occur.

"These chimeric approaches could be really very useful for advancing biomedical research not just at the very earliest stage of life, but also the latest stage of life," Izpisua Belmonte says.

"Once this molecular communication is further understood, chimeric organisms could allow researchers an unprecedented glimpse into the earliest stages of human development," the Salk Institute said in a statement. "Chimeric organisms containing human cells could be used to generate cells and organs for transplantations in host species more evolutionarily distant to humans, like pigs, that might be more appropriate for various reasons (social, economic and ethical, among others). Additionally, these studies constitute a new platform to study how specific diseases arise."

Looming over the research are the current strict rules around stem cell experiments. Nonetheless, even with those limits in place, some are still unhappy with the idea of using stem cells and embryos in this manner, a challenge that future experiments will need to continue to take into account.

With that in mind, the team plans to look more closely next at the molecular pathways, to better pinpoint which are critical to the viability of the hybrids. The current research was published today.