The number of people requiring kidney transplants has been growing worldwide, with demand for donated kidneys far outstripping the supply. Around 2% of all adults experience kidney disease, and which results in tens of thousands of deaths each year. Only 25% of those on the wait list for a donor kidney will ever receive the lifesaving call. The kidney is actually one of the most complicated organs to grow. This is due to its highly delicate and complex tissue structure, crammed with networks of vessels carrying both blood and urine. Some have been experimenting with 3D printing organs, while others are looking at using stem cells to grow neo-kidneys. But the new study focuses on growing them de novo, or from the beginning. The main problem with growing kidneys from embryonic stem cells has been getting them to excrete the urine they produce. This causes a problem known as hydronephrosis, where the organs balloon and swell as the urine builds-up inside them.
A team led by investigators at the Jikei University School of Medicine in Tokyo has shown that mini kidneys grown in vitro from human stem cells can be connected to the excretory systems of rats and pigs. When transplanted into pigs and rats, the kidneys worked, passing urine just like natural ones. Getting the urine out has been a problem for earlier prototypes, causing them to balloon under the pressure. Although still years off human trials, the research helps guide the way towards the end goal of making organs for people.