The chimera was a zoological monstrosity of Greek myth: a fire-breathing beast with the head of a lion, the body of a goat and a serpent for a tail. It was vanquished by Bellerophon, who dropped lead into the creature’s mouth, inducing molten suffocation.
Scientists are now breathing life into the concept of chimeras by creating organisms containing the cells of humans and animals. Several teams in the US are inserting human tissue into early pig and sheep embryos. The journal MIT Technology Review estimates that 20 such hybrid embryos have been produced, an early proof-of-principle step towards growing human organs inside animal tissue. The hybrid embryos have been observed in early development but, crucially, are never brought to term. The Salk Institute in California, together with the universities of Stanford and Minnesota, are among the institutions pioneering the as-yet-unpublished research.
The idea of mixing animal and human tissue is controversial — so much so that the US’s National Institutes of Health, which controls federal spending on medical research, has refused to fund it. It is notable, then, that scientists have sought private money to carry on. The biomedical fraternity are frustrated that fundamental science is being slowed down by conservative attitudes and outlandish fears. NIH’s stance has been labelled a “threat to progress”.
The purpose of chimera research is not to bring “manimals” to life, as Dr Moreau did on the island imagined by HG Wells. Instead, non-human embryos can be thought of as Petri dishes in which the development of human tissue can be observed. They may also allow the cultivation of human tissue, such as hearts, livers and kidneys. Nurturing human organs inside pigs and sheep is one possible solution to the worldwide shortage of organs available for transplantation. Growing them from a patient’s own cells may also mean a lower risk of rejection.
In fact, chimera research has a long history. For decades, newborn mice have been “humanised” by the insertion of human liver cells and immune cells to render them more biologically analogous to humans during drug testing. Now “pluripotent” human cells are being inserted into early animal embryos: these are cells feted for their ability to blossom into virtually any cell, and very early animal embryos are able to integrate them more easily.
When the NIH stopped funding such research, citing concerns that those human cells could flower into neurons and reproductive tissue, its stance was underpinned by the spectre of cross-species horrors: first, a non-human animal with human consciousness (possibly motivated by a 2014 paper suggesting mice become smarter when human cells are put inside their brains); second, the chance of a human embryo gestating inside another species.
These are scenarios that exist only in science fiction, according to academics. Private funds have enabled American research to continue legally (chimera research is also legal in the UK, provided labs have a licence and embryos are destroyed after 14 days). One source is the private California Institute for Regenerative Medicine, set up by the state to enable controversial biological research to continue whatever the political climate.
And this climate, in fact, may be the key to the conservatism displayed by the NIH, which echoes restrictions placed on stem cell research in the US during the last Bush administration. Fusing human and animal cells to make human organs may be seen by some on the religious right as an affront to human dignity. There are also animal welfare considerations.
On the other hand, some 123,000 Americans are waiting for organ transplants, a shortage that costs lives and fuels the sordid business of transplant tourism. Neither of which does much for human dignity, either.