Submitted on December 4, 2025
Every year, thousands of viable kidneys are discarded before they can reach recipients in need. When a kidney is prepared for donation, it is flushed, put on ice and viable for about 24 hours. Due to challenges with logistics and delivery, about 10 percent of donated kidneys end up thrown away. UCSF Professor of Urology Marshall Stoller, MD, is working to change those odds.
Working with Heiko Yang, PhD from the University of Colorado and Jake Elmer, PhD from Villanova University, Dr. Stoller is developing a normothermic kidney perfusion system to keep kidneys metabolically active for days instead of hours. The team has already demonstrated promising results in more than 30 pig kidneys and several human kidneys deemed unsuitable for transplant, maintaining healthy function well beyond 24 hours.
“Once we can reliably keep a kidney alive outside the body, the possibilities multiply,” Stoller said. “We can test drug toxicity, accelerate discovery of new therapeutics, even transfect organs to correct monogenic diseases before re-implantation.”
“If a patient has a disease like cystinuria with a known genetic defect, we could potentially edit the DNA outside the body, reimplant the kidney, and cure the disease but that depends on keeping the kidney viable for several days.”
To extend the viability of donated kidneys, Stoller’s team designed Prototype C, a refined perfusion model capable of maintaining longer periods of kidney function. The system includes an infusion drip to replenish nutrients and heparin, and a pinch valve that acts as an adjustable flow resistor to fine-tune perfusion pressure.
A sterile containment bag, fashioned from a 3-liter fluid bag, stabilizes the kidney using small neodymium magnets and allows for collection and recycling of venous outflow. The team also customized a simple reservoir system using neonatal suction canisters and tissue culture flasks, which maintains temperature by circulating warm water through the oxygenator’s heating ports. This cost-effective, modular design makes the system accessible to a wide range of researchers and could ultimately extend to other organs such as the pancreas and spleen. One of the project’s most novel elements is its oxygen-delivery solution, which is inspired by earthworms.
In collaboration with Dr. Elmer, the team is testing erythrocruorin, a non-cellular oxygen carrier that can transport 144 oxygen molecules per protein (compared with one in human hemoglobin) and remain stable at room temperature for months. This natural molecule could have applications far beyond transplantation. “Imagine a system that delivers oxygen without needing refrigeration or cross-matched blood,” Stoller said. “It could help trauma victims in the field, patients who decline transfusions, or people in countries where blood supplies are limited.”
While the molecule is not a blood substitute, it serves as an oxygen delivery system that could transform emergency medicine, global health and transplantation. Though still in its early stages, the research is laying the groundwork for a future where organ preservation, oxygen delivery and therapeutic innovation may look entirely different. “We’re setting the stage now for discoveries that could one day become everyday medicine,” Dr. Stoller said.