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We’re another step closer to made-to-order human kidneys

There’s a chronic shortage of available transplant organs, which leads to the unnecessary death of thousands of people each year. To help alleviate this situation, medical researchers and scientists are working hard to find other ways of sourcing human-compatible organs, whether by bio-printing them in a lab or figuring out ways to repurpose organs from other animals.

While there is still a ways to go for both these approaches, researchers from Japan’s National Institute for Physiological Sciences recently made a breakthrough, which could have enormous implications for future kidney transplants. In a pioneering study, they demonstrated that it is possible to grow functional mouse kidneys inside rats using donor stem cells. Initial attempts to do this had failed, since rat stem cells don’t differentiate into the two main cell types required for forming kidneys. However, the researchers got around this by injecting mouse stem cells into rat blastocysts, the cell clusters formed after an egg is fertilized. When these were implanted into developing rats, they grew into normal fetuses, but containing a pair of mouse-derived kidneys. All of these kidneys were intact and more than half were capable of producing urine.

As with other transplant organs, kidney shortage is a big problem. In the U.S. alone, 95,000 patients are on the waiting list for a donor kidney. In the case of patients with end-stage renal disease, this is their only hope of once again regaining quality of life. Could this study be potentially applicable to these people? According to Masumi Hirabayashi, one of the researchers on the project, it could. He suggests that it might be possible one day to grow human stem cell-derived organs in other animals, and then transplant them into patients.

Hirabayashi said that pigs would be the most likely host animal species for human organ regeneration — although differences in the gestation period of a pig and a human could conceivably pose challenges for the creation of fully functioning human kidneys.

“Theoretically I can expect blastocyst complementation strategy to work as well in a combination of human pluripotent stem cells (PSCs) and domestic animal blastocysts,” Hirabayashi told Digital Trends. “However, there are serious technical barriers and complex ethical issues that must be discussed and solved before producing human organs in animals.”

A paper describing the work is published in the journal Nature Communications.

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