Human-animal hybrids

The potential payoff for such research is enormous

Japan has just cleared a controversial experiment, which could have major consequences for the future of genetics research. Hiromitsu Nakauchi of the University of Tokyo and Stanford University will be allowed to insert human stem cells into a mouse embryo and allow the resulting hybrid embryo to develop till term. While such experiments have been conducted before, there is normally a time limit of 14 days before the embryo is destroyed. Indeed, many nations have a blanket ban on such experiments.

It is hoped that this experiment will result in insights that allow for entirely new medical transplant techniques. Variations on this theme, such as the insertion of animal stem cells into human embryos, could also yield very positive outcomes. But this experiment also opens a Pandora’s Box in terms of other, potentially nightmarish possibilities.

Pluripotent stem cells can grow into many types of organs. One possible outcome of such experiments could be the development of technologies where human organs are grown in donor animals. Current transplant procedures can be carried out only by the donation of organs from somebody who is genetically compatible with the recipient. 

There are high rejection rates and immuno suppression drugs that prevent rejection have undesirable side effects.

However, it may be eventually possible to insert the recipient’s own stem cells into a pig embryo (or sheep) and, thus, grow a replacement organ that is completely compatible. This particular experiment will start with trying to grow human pancreas cells in rodents and, if that works, attempting the same procedure in pigs. The mouse embryo has been treated to remove information about rodent pancreas cells so there should not be a genetic barrier to growing human pancreas cells. 

Growing a human pancreas or liver, or even a new heart, in a surrogate animal could be a game changer. There are over a million people waiting for liver and pancreas transplants. Many lives could be saved if such a process could be developed and standardised.

The inverse process, which is not on the cards, would be even more of a conceptual and ethical reach. Various animals have unusual genetics, which make them resistant or immune to various diseases. Sharks, for example, are immune to cancer. Some animals have unusual abilities — salamanders can regrow lost limbs. Elephants regrow entire sets of teeth through their lives. If it is possible to isolate the responsible genes and insert these, it could alter the human race. 

While Nakauchi and his team intend to proceed with caution, there are obvious ethical concerns. If human DNA proliferates in an animal embryo, the resulting creature would be a new hybrid species. This could be of really special concern if the brain is affected.

The researchers say they would set a cut-off point in terms of proliferation, destroying the hybrid if the proportion of human cells in the brain exceeds 30 per cent. In practice, no experiment had ever resulted in much more than one in 100,000 cells being of human origin. But bringing an embryo to term is new territory. The hybrid will be monitored for two years before the next experiment, which could involve pigs or sheep.

The potential payoff for such research is obviously enormous. But the risks are also high. Japan is a responsible nation, which has pondered the pros and cons of genetic engineering for years before giving the go ahead. However, this could set a precedent where less responsible governments or private researchers decide to accelerate research processes, throwing caution to the wind. 

There is little practical chance of something going seriously wrong at this stage. There are very few labs with the requisite facilities and, perhaps, even fewer scientists with the necessary skills to work in this field. But as a body of work builds up, more research in this domain is inevitable. One can only hope researchers will heed the maxim “with great power comes great responsibility”.