By Rob Ludacer and Jessica Orwig From Business Insider

After years of trial and error, scientists have finally done something incredible: They have successfully grown human stem cells in a pig embryo. Why would anyone do this?

Turns out, many scientists have been working on growing the organs of one animal inside of a different type of animal. For example, scientists recently reported the successful growth of mouse pancreases inside of rats.

The ultimate goal of this type of work is to grow human organs inside of other animals as a means to ending the organ shortage that is costing thousands of Americans — who need a transplant — their lives each year.

Now, using similar methods as the mouse-rat hybrid, scientists have produced the first human-pig hybrid embryo, which is more difficult than you might think. Getting cells from one species to survive in an entirely different species is extremely tricky and has eluded scientists for years.

Even now, this breakthrough is preliminary. Only about one out of every 100,000 cells in the hybrid embryos was human. If the scientists had grown the embryos to maturity (which they did not), the organs would probably not have enough human cells in them for a human body to recognize — resulting in the human body rejecting the organ and potentially killing the patient.

This is why more research is critical to improving the techniques, and hopefully, one day, paving the way for the first human transplant with a human-pig hybrid organ. But that day is years, possibly decades, off.

The group of scientists published their work on Thursday, Jan. 26, in the prestigious science journal Cell.

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