DAVIS, CALIFORNIA — A team of scientists from the University of California, Davis are attempting to produce human-pig embryos in order to grow human organs in pigs.

To grow a human organ such as a pancreas in a pig, one must first remove the DNA that is responsible for growing a pig pancreas from a fertilized pig embryo using a technique known as CRISPR gene editing.

A void is created after the gene editing, and human induced pluripotent stem cells are then injected into the embryo to fill up the void. Human induced pluripotent stem cells are adult cells that have been reprogrammed into stem cells. They can develop into any tissue in the human body, including corneas, lungs, hearts, livers and kidneys

The human-pig embryo, known as a chimera, is then implanted into a sow and is allowed to develop for 28 days. Then the pregnancy is terminated and the tissue removed for analysis.

“Our hope is that this pig embryo will develop normally but the pancreas will be made almost exclusively out of human cells and could be compatible with a patient for transplantation,” Pablo Ross, lead researcher on the project and assistant professor at the Department of Animal Science at UC Davis told the BBC.

However, the idea of growing human-pig embryos remains highly controversial, with the U.S. National Institutes of Health imposing a moratorium on funding such experiments.

Ross told the BBC that the main concern is that the human stem cells might migrant to develop in the pig embryo's brain, which would make the pig somewhat human-like.

Others are worried that growing human organs in pigs may lead to a new source of animal abuse, despite the fact that it may help to ease the shortage in organ donations in the U.S.