The experiment, described Thursday in the journal Cell, involves injecting human stem cells into the embryo of a pig, then implanting the embryo in the uterus of a sow and allowing it to grow. After four weeks, the stem cells had developed into the precursors of various tissue types, including heart, liver and neurons, and a small fraction of the developing pig was made up of human cells.
The human-pig hybrid -- dubbed a "chimera" for the mythical creature with a lion's head, a goat's body and a serpent's tail -- was "highly inefficient," the researchers cautioned. But it's the most successful human-animal chimera and a significant step toward the development of animal embryos with functioning human organs.
In a study published a day earlier, an international team of researchers demonstrated that organs for transplant can be grown in chimera embryos that are part-mouse, part-rat. Writing in Nature, the researchers reported Wednesday that they were able to grow a mouse pancreas inside a rat embryo, then transfer insulin-secreting tissue from that organ into diabetic mice, alleviating their illness without triggering an immune response.
It was the first demonstration that such an interspecies organ transplant is possible. Researchers hope that one day doctors may be able to grow human tissue using chimera embryos in farm animals, making organs available for sick humans who might otherwise wait years for a transplant.
'If you are not concerned about this development, you should be.'
~ Charles Krauthammer