July 31, 2019

expert reaction to reported approval in Japan of research that aims to grow human pancreas cells in rat and mouse embryos

Comment on reports that research aiming to grow human pancreas cells in rat and mouse embryos has been approved in Japan.

Prof Martin Johnson, Professor of Reproductive Sciences, University of Cambridge, said:

“First of all these would not be hybrids but chimaeras.  A chimaera is a mixture of cells.  A hybrid is a mixture of chromosomes.

“Second, the chances are that the chimaeras will not survive, as we generated rat: mouse chimaeras and they didn’t survive on transfer to mouse uteri.

“Third, I don’t know how the scientist in charge can say that only a relatively smaller number of iPCs will be present.

“Finally, if the goal of such studies is to discover a therapeutic application for humans, experiments on rats and mice are unlikely to produce a useful result not only because the size of the organ will not be sufficient and the result will be a far cry from humans anatomically, but also because there is every chance the pancreases formed will also be chimaeric, something that also applies to sheep and pigs.”

Dr M. William Lensch, strategic advisor, Harvard Medical School, said:

“Despite how the proposed research is labeled by some, it will not actually create a “human-animal hybrid”.  Rather, the recently approved work in Japan involves generating a “human-animal chimera” to study the biology of the pancreas.  There’s a big difference between hybrids and chimeras.  Using the right terms is important as if a person simply looked up the word “hybrid” in a dictionary in order to better understand the proposed research, they might be inappropriately alarmed by what they read.  The only way to get a human-animal hybrid is for a human to mate, to reproduce, with an animal, which is not at all what the researchers in Japan propose to do.

“To be more specific, in a human-animal hybrid, half of the DNA in every cell would be human and the other half would be animal.  In contrast, a human-animal chimera contains a mixture of human cells and animal cells within the same organism.  Each human cell in the resulting animal is wholly human and each animal cell is wholly animal.  For example, transplanting a human cancer specimen into an animal in order to study its growth or to test anti-cancer drugs creates a type of human-animal chimera, not a hybrid.  The distinction between hybrids and chimeras is quite significant and could no doubt make a difference to the public and to policy makers alike when considering this sort of research.”

Declared interests

Prof Martin Johnson: “Nothing to declare.”

Dr M. William Lensch: “I am not at all connected to the work in Japan.  I am simply an interested observer.”