Scientists have succeeded in growing human stem cells in pig embryos. The approach involves generating stem cells from a patient’s skin, growing the desired new organ in a large animal like a pig, and then harvesting it for transplant into the patient’s body.
Since the organ would be made of a patient’s own cells, there would be little risk of immune rejection.
The human-organ-growing pigs would be examples of chimeras, animals composed of two different genomes. They would be generated by implanting human stem cells into an early pig embryo, resulting in an animal composed of mixed pig and human cells.
One team of biologists, led by Jun Wu and Juan Carlos Izpisua Belmonte at the Salk Institute, has shown for the first time that human stem cells can contribute to forming the tissues of a pig, despite the 90 million years of evolution between the two species.
Another group, headed by Tomoyuki Yamaguchi and Hideyuki Sato of the University of Tokyo, and Hiromitsu Nakauchi of Stanford, has reversed diabetes in mice by inserting pancreas glands composed of mouse cells that were grown in a rat.
Many technical and ethical barriers have yet to be overcome, but the research is advancing alongside the acute need for organs.
Scientists expressed confidence that ethical concerns about chimera research could be addressed.
Chimeras are typically mosaics in which each organ is a mixture of the host and donor cells. But new techniques like the Crispr-Cas gene editing system should allow the human cells in a pig embryo both to be channelled into organs of interest and to be excluded from tissues of concern like the brain and reproductive tissues.