Growing functional organs in the lab is something of a medical holy grail. In some impressive new research, scientists have been able to transplant lab-grown kidneys into animals that could then pass urine. Though this research, published in PNAS, is encouraging, human trials are still likely to be years away.
The number of people requiring kidney transplants has been growing worldwide, with demand for donated kidneys far outstripping the supply. In the U.K., for example, the average waiting time for a kidney transplantation is three years. 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.
This has led researchers to look for other ways to source this organ. 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.
To get around this problem, the researchers effectively grew extra plumbing and another bladder in host animals. They were then able to demonstrate that, when transplanted into rats and pigs and connected to the animals' existing bladder, the system functioned effectively. The urine was created in the new kidney, passed into the new bladder, and then into the original bladder.
“This is an interesting step forward,” Professor Chris Mason, from University College London who was not involved with the study, told BBC News. “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. It's very much mechanistic. It moves us closer to understanding how the plumbing might work.”
But human trials is where the researchers want things to go. Previous studies have shown that it’s possible to take stem cells from rats and inject them into mouse embryos that have been genetically engineered not to develop specific organs. When growing, the mice instead go on to develop rat organs. The only problem with this is that if the organs are left to develop fully, although the organ is made of rat tissue, the connecting blood vessels are made of mouse tissue.
So the researchers want to take human stem cells and inject them into pig embryos that have been genetically modified not to grow kidneys, and then transplant the newly grown kidneys back – before they’ve fully grown – into humans. This should mean that the blood vessels that permeate the kidney will also be human, and won’t be rejected. Unfortunately, while this is exciting, this research is likely to take years to develop.