Scientists have grown human cells inside pig embryos, a very early step toward the goal of growing livers and other human organs inside animals to transplant into people.
The cells made up just a tiny part of each embryo, and the embryos were grown for only a few weeks, researchers reported Thursday.
Such human-animal research has raised ethical concerns. The U.S. government suspended taxpayer funding of experiments in 2015. The new work, done in California and Spain, was paid for by private foundations.
Any growing of human organs in pigs is “far away,” said Juan Carlos Izpisua Belmonte of the Salk Institute in La Jolla, Calif., an author of the paper in the journal Cell.
He said the new research is “just a very early step toward the goal.”
Even before that is achieved, he said, putting human cells in animals could pay off for studies of how genetic diseases develop and for screening potential drugs.
Animals with cells from different species are called chimeras.