Researchers in Japan have found a way to overcome a major obstacle to using stem-cell grown kidneys in animals.
Previous attempts at generating fully functional kidneys in the laboratory have failed because the kidneys produced were unable to excrete urine. This leads to a state called hydronephrosis in which the kidney swells, stretches, and ultimately fails, due to a build up of urine.
A research team, led by Dr Takashi Yokoo at the Jikei University School of Medicine in Tokyo, got around this obstacle by developing a new transplant technique that connects the transplanted kidney to the excretion system of the host animal.
Implementing this new technique, which they call the 'stepwise peristaltic ureter (SWPU)', the scientists transplanted embryonic cells that give rise to the kidneys into adult rats. Importantly, these were taken from cells within the embryo that are also able to develop bladders.
Four weeks later, the researchers connected one of the ureters of the transplanted kidney to the newly developed bladder. Within a few weeks, they found that this allowed urine to pass from the transplanted kidneys into the transplant-grown bladder and, subsequently, into the rat's bladder ready for excretion.
The researchers found that this prevented hydronephrosis and, eight weeks after transplant, the kidneys show signs of maturity and were excreting waste products into the urine. They also found that the transplant system was successful in pigs.
'We have demonstrated that the SWPU system may provide the means to construct a urinary excretion pathway for stem cell-generated embryonic kidneys,' the authors write in PNAS. 'The creation of such a pathway is one of the most important problems to be overcome in the de novo generation of whole kidneys, and the solution of this problem represents a significant advance in the field.'
Professor Chris Mason, an expert in stem cells and regenerative medicine at University College London, told the BBC: 'This is an interesting step forward. The science looks strong and they have good data in animals. But that's not to say this will work in humans. We are still years off that.'
Dr Yokoo said he is optimistic about the prospects of the new transplant system. 'We already started the next stage to show that this system can be used in primates, using marmosets for the application to human,' he told Healthline.