Chimeric monkey sheds light on what can be done with embryonic stem cells

I was quoted in this article today regarding a newly published study in Cell that demonstrates, in the author’s words, that ‘mammalian pluripotent stem cells possess preimplantation embryonic cell-like (naive) pluripotency.’ As the summary notes, this discovery about embryonic stem cells can now be said to have been demonstrated experimentally through the generation of a chimeric animal — a monkey whose embryonic development has been ‘complemented’ by homologous embryonic stem cells derived from another ‘donated’ line of cells. The monkey, in short, has developed from a blastocyst that is a compound of two embryonic stem cell lines.

Unsurprisingly, news stories have been focusing on one of the eye-grabbing aspects of this experiment: that the monkey in question has fluorescent green fingers and eyes. Unfortunately, the monkey died after only 10 days — which is still the longest period of time for which such a chimeric organism has lived before.

The reason that the monkey has these features is because the researchers used green fluorescent protein (GFP) to ‘label’ the embryonic stem cells (ESCs) that were incorporated into the host embryo at the blastocyst stage. And so what one is looking at when one sees the monkey with green fingers and eyes (visible even to the naked eye) is visual evidence that the embryonic stem cells have survived the process of being ‘complemented’ into the blastocyst of the host monkey and have spread throughout its body. In other words, the cells have been incorporated into the monkey’s cellular DNA; the monkey has both its ‘natural’ DNA and a ‘foreign’ line of DNA. Indeed, as the images indicate, there is a proliferation of these complemented ESCs throughout the monkey’s organs, including plenty in the brain and ileum (small intestine).

As the ‘Highlights’ section of the article points out, when these embryonic stem cells (ESCs) in the body of the monkey were ‘characterised’ (assessed), it was revealed that they remained in a so-called pluripotent state. In other words, the ESCs seem to have been able to differentiate into the different kinds of cellular categories: glial (brain) cells, heart cells (myocytes), lung cells (epithelial cells), and so on. Indeed, they continue to be in this pluripotent state, even as they maintain a ‘functional’ presence in the monkey’s body.

The story quotes me as follows:

Sydney University lecturer in health law Dr Christopher Rudge told the medical experiment had been on the cards for a long time.

“This is another step along the journey,” he said.

“The advancement here is that scientists have never been able to show such a prolific survival / proliferation of donated (or ‘complemented’) embryonic cells through a single organism.

“You’ve got more of these donated or secondary cells throughout the organism in a mammal.”

But he cautioned whether it would lead to anything substantive.

“Regenerative medicine has been hyped since the late 1990s,” he said. “Unfortunately it has not borne fruit.”


Obviously this scientific study demonstrates that certain new techniques can be adopted to expand the capacity of scientists to create chimeras. Scientists have long had the capacity to infuse mouse and rat blastocysts with pluripotent stem cells to generate live chimeric animals that feature this high proliferation of homologous cells. What is new here is that this capacity now extends to non-human primates — a species of animal much closer, in evolutionary terms, to humans.

It is arguably another step along the way in discovering how stem cells, including pluripotent embryonic stem cells, can be used as technologies of biological inquiry (for diagnosis, and to study developmental mechanisms) and, ultimately, to biological treatments. Of course, there is still so much more to learn.

Whether an experiment of this nature would be approved in Australia is an interesting question. If nothing else, this finding indicates that discoveries in stem cell medicine are continuing apace. Of course, given that this involved the effective fusing of two monkey embryos (or embryonic cell lines), the more serious bioethical questions regarding human-monkey chimeras, which have been posed before, do not arise in this instance.