US agency lifts ban on funding human–animal hybrids

Since September 2015, researchers have been banned from receiving funding from the US National Institutes of Health (NIH) for adding human stem cells to animal embryos, creating blends called chimaeras. 

But a proposal by the NIH released on 4 August would lift the funding moratorium, except for certain situations. It would also set up a panel to review the ethics and oversight of grant applications.

The new rules shorten the developmental window during which human cells can be introduced into non-human primate embryos, disallowing it before the stage of development in which the central nervous system begins to form. This is intended to limit the number of human cells that would make up the chimaera’s brain. They also prohibit breeding animals that contain human cells, so as to prevent a human-like embryo from growing in a non-human womb or the birth of an animal that is more humanized than its parents.

Any grant applications that fall into a grey area would undergo a panel review. “It would be an extra set of eyes to make sure we’re not triggering any animal-welfare issues,” says Carrie Wolinetz, associate director for science policy at the NIH in Washington DC. The panel will pay particular attention to applications involving primates, mammals at very early stages of development or those in which human cells could affect an animal's brain.

Chimaeras are a growing area of research. Currently, researchers use them to study early embryonic development and to create animal models of human diseases. But one major goal is to engineer animals to grow human organs. The organs could later be harvested from the adult animal and used for transplantation into a patient.