Brain and Body

Stem-Cell-Grown Kidneys May End Need for Organ Donation

September 29, 2015 | Sarah Tse

Urine excretion from a bladder grown after a cloacal transplant.
Photo credit: Shinya Yokote, Hitomi Matsunari, Satomi Iwai, Shuichiro Yamanaka, Ayuko Uchikura, Eisuke Fujimoto, Kei Matsumoto, Hiroshi Nagashima, Eiji Kobayashi, and Takashi Yokoo

Scientists have finally succeeded in using stem cells to grow fully functioning miniature kidneys in rat and pig subjects. This marks a significant step towards providing lab-grown replacements for human patients in need of kidney transplants.

Many labs have successfully grown kidneys, which is quite an accomplishment in itself — the kidney needs an intricate network of blood vessels and tubes to properly filter urine and maintain the balance of dissolved substances in the blood. But even if the organs grow into the right structure, they also have to correctly perform their duties and cooperate with other bodily systems.

Several groups of scientists had already used the stem cell method to grow kidneys de novo, or from the beginning, but they ran into problems with getting the organs to function properly. The synthetic kidneys were able to filter body fluids and process urine, but something went wrong with the plumbing; instead of draining urine out through the collecting duct the way normal kidneys do, the lab-grown specimens just kept ballooning with fluid and eventually burst from the pressure in a condition called hydronephrosis.

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To overcome this problem, Dr. Takashi Yokoo’s team at Jikei University School of Medicine grew extra plumbing alongside the kidney, in a technique called a “stepwise peristaltic ureter” system. They transplanted embryonic kidneys along with bladders into host rats, where the fledgling tissues could incubate. Once the kidney, a special drainage tube, and a preliminary bladder were fully grown, the scientists hooked up the synthesized bladder with the host rat’s existing ureter, and everything flowed properly. The transplanted kidney successfully produced and excreted urine into the transplanted bladder, and finally into the rat’s original bladder. Eight weeks later, the transplants still functioned perfectly.

Then the researchers set about testing their new technique on a larger scale. The lab-generated kidneys worked just as well in cloned pigs, without any issues of hydronephrosis. Amazingly, these findings overcome the problems previously encountered when growing kidneys from stem cells.

Although the technique works in rats and pigs, employing it in human systems will require extensive testing before clinical trials can even begin. The eventual goal is to inject human stem cells into incubator pigs that have been modified to suppress their natural kidney development, leaving room for the transplants. Once the kidneys are partially grown, they can be transplanted into the human recipient to complete development. This way, the complex system of tubes and vessels will grow exactly as it should, with proper integration between transplant and host tissues.

There’s still a long road ahead for humans in need of kidney transplants. But once the technology is ready, we might finally meet the escalating global demand for replacement kidneys and save millions of lives.

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