Keeping an organ able to work

Transplantation depends on more than a suitable organ and a skilled team. The organ must remain usable while decisions, transportation, preparation and surgery take place. Extending that interval could change how transplantation is organized. The important word is usable: an organ that looks intact but cannot sustain its recipient has not been successfully preserved.

Between donation and implantation, the usual supply of oxygen and nutrients is interrupted. Cooling reduces the demand for energy, but does not make the tissue invulnerable. Injury can accumulate during storage and when blood flow returns. This is why preservation is a distinct frontier. It does not require an organ to become younger. It requires useful function to survive a process that would otherwise damage it. [1] [4]

Static cold storage places the organ in a protective solution at low temperature. Machine perfusion circulates fluid through its blood vessels. Some systems work cold; others maintain conditions nearer body temperature. Oxygen delivery, temperature, timing and the composition of the circulating fluid differ among systems. A result from one configuration cannot automatically be assigned to every machine carrying the same general label. [1] [2] [3]

Perfusion can also create a window for assessment. A liver that is metabolically active can reveal information that an organ sitting quietly in cold storage cannot. Reconditioning goes a step further: the aim is to improve an injured organ before transplantation. Demonstrating that a test selects usable organs is different from demonstrating that the machine repaired them. That distinction matters when a discarded organ is described as rescued. [4]

Cryopreservation asks a more ambitious storage question. Could an organ be cooled into a stable state, kept for much longer, and recovered with its complex structure and function intact? A rat kidney experiment offers a striking proof of principle. Human perfusion studies and that animal experiment belong in the same story of buying time, but on different levels of evidence. [6]

The kidney test: function after transplant

A useful preservation study follows the organ beyond the machine. Does the graft function after transplantation? Does the recipient need additional treatment? How often does the graft fail? These questions move the evidence from technical performance to consequences that patients experience.

A 2009 randomized trial used a particularly informative comparison. From each of 336 deceased donors, one kidney was assigned to hypothermic machine perfusion and the other to static cold storage. The 672 recipients were followed for a year. Pairing kidneys from the same donor helped the investigators compare preservation methods without relying entirely on differences between unrelated donors. [1]

The primary outcome was delayed graft function, defined as requiring dialysis during the first week after transplantation. It occurred in 70 recipients in the machine-perfusion group and 89 in the cold-storage group. Those counts correspond to approximately 21% and 26%, respectively. The reported adjusted odds ratio was 0.57, with P=0.01. The adjusted odds ratio and the simple percentages summarize the data differently; they should not be treated as interchangeable measures. [1]

One-year graft survival was 94% with machine perfusion and 90% with cold storage. The investigators found no significant differences in several other secondary outcomes, and reported no serious adverse events directly attributable to perfusion. This was meaningful clinical evidence for the studied method and setting. It was not a demonstration that kidneys could be stored indefinitely, or that every future perfusion protocol would produce the same benefit. [1]

The endpoint also needs careful language. Delayed graft function is an early complication, not a synonym for permanent graft failure. A method may improve early recovery without eliminating the other causes of transplant failure. For a reader following new preservation claims, the practical habit is to ask for both clocks: how long the organ was preserved, and how long the recipient was followed. An impressive storage interval needs a convincing recovery story.

What liver trials actually showed

The liver makes the distinction between a promising marker and a patient outcome especially clear. In a 2018 randomized trial involving 220 liver transplantations, normothermic preservation was associated with roughly half the graft injury measured by release of liver-cell enzymes, compared with conventional static cold storage. The trial also reported a 50% lower organ-discard rate and a 54% longer mean preservation time. [2]

Those are important findings, but the same report found no significant difference in bile-duct complications, graft survival or patient survival. Lower enzyme release is not itself proof that recipients live longer. A lower discard rate could expand access to transplantation, but the consequences for waiting-list mortality require their own evidence. The study supports a particular set of claims, rather than a blanket declaration that warmer preservation is better in every respect. [2]

A different randomized trial, published in 2021, tested hypothermic oxygenated machine perfusion for livers donated after circulatory death. Of 160 enrolled patients, 156 received a study transplant: 78 in each group. The primary outcome was nonanastomotic biliary strictures within six months, a form of bile-duct narrowing away from the surgical connection that can cause serious complications. [3]

These strictures occurred in 6% of the machine-perfusion group and 18% of the static-cold-storage group. The reported risk ratio was 0.36, with a 95% confidence interval of 0.14 to 0.94. Early graft dysfunction also occurred less often, while the incidence of adverse events was similar between groups. Here the benefit included a defined clinical complication, not only a laboratory marker. [3]

The two trials should not be turned into a head-to-head contest. They studied different approaches and circumstances. Their shared lesson is more useful: preservation has several jobs, and success should be named precisely. Preventing a bile-duct complication, reducing tissue injury, extending transport time and increasing the number of organs used are related goals. None is a substitute for measuring the others.

A second look at a declined organ

An organ may be declined because clinicians cannot confidently judge how it will perform. Machine perfusion offers an opportunity to observe function before committing a recipient to surgery. Its value can therefore come from better information as well as better preservation.

The VITTAL study, published in 2020, assessed 31 selected livers that had been discarded for clinical use. Twenty-two met the study's viability criteria and were transplanted after a median total preservation time of about 18 hours. Patient and graft survival were both 100% at 90 days. These findings show that assessment enabled transplantation of some organs that otherwise would not have been used in that setting. [4]

The longer view was less simple. During a median follow-up of 542 days, four patients developed biliary strictures requiring another transplant. The trial was a single-center, nonrandomized study with selected organs and lower-risk recipients. The 71% utilization figure applies to its 31 enrolled livers, not to all discarded livers everywhere. Nor can its design cleanly separate selection of organs that were already viable from repair caused by perfusion. [4]

Lung research provides another example of this assessment window. In a prospective, nonrandomized 2011 study, lungs from 23 high-risk donors underwent four hours of ex vivo lung perfusion. Twenty remained physiologically stable and were transplanted. The comparison group comprised 116 conventionally selected transplants. Primary graft dysfunction at 72 hours was 15% versus 30%, but that difference was not statistically significant (P=0.11). The study supported feasibility; it did not establish that perfusion halved the risk. [5]

Both examples encourage a more careful use of the word rescue. A machine can help clinicians reconsider an organ, measure its behavior and sometimes treat it. Showing which of those steps produced the benefit takes additional study. The goal is not to maximize acceptance at any cost. It is to expand the usable donor pool while protecting recipients from avoidable failure, including complications that emerge after an initially reassuring recovery.

Cooling is only half the problem

Long-term organ banking would require more than extending today's transport window. Vitrification aims to turn the organ and its protective solution into an ice-free, glass-like state. Avoiding damaging ice during cooling is only part of the task. Ice can form during rewarming, while uneven heating can create physical stress and cracking. The return from storage is as important as entry into it. [6]

In a 2023 study, researchers used nanowarming to address that return journey. Magnetic nanoparticles were distributed through rat-kidney blood vessels, then heated using an alternating magnetic field. The approach was designed to warm tissue rapidly and uniformly. Protective chemicals and nanoparticles were subsequently unloaded by perfusion before transplantation. [6]

The investigators reported that vitrified rat kidneys stored for up to 100 days could be recovered, transplanted and sustain life in recipients whose own kidneys had been removed. This goes beyond demonstrating an intact-looking organ or activity in isolated cells. The graft had to perform essential work inside a living recipient. It is a substantial proof of principle in that model. [6]

The limitations belong beside that achievement. The study used male rats, with small experimental groups, and followed transplant recipients for 30 days. The recovered kidneys had an initial period of dysfunction lasting roughly two to three weeks before renal function normalized. Storage for 100 days and follow-up for 30 days are separate measurements. Neither number establishes durable human graft function. [6]

Scale changes the challenge. Human-sized organs have different distances for heat and protective chemicals to travel, and their vascular distribution must be reliable throughout the tissue. Residual materials, chemical toxicity, reproducibility and the immune response also require attention. The authors identified translation to human-sized kidneys and clinical-grade processes as future work. The result supports continued organ-banking research, not a claim that human organs can already be routinely banked for months. It also offers no evidence for preserving or reviving an entire person. [6]

More time, with a reason to trust it

A bank of transplantable organs could make matching less hurried, allow more deliberate preparation and create more flexible scheduling. Wider geographic access is another possible benefit. These are plausible goals, not demonstrated outcomes of the rat experiment. Making time available would not by itself determine who receives an organ or whether access becomes fairer.

The next convincing result should answer a chain of questions. What organ, donor population and preservation method were studied? How long was storage, and what happened during recovery? Was the organ transplanted? How did the recipient fare, for how long, and compared with what alternative? A headline about duration is incomplete until the rest of that chain is visible.

For clinical perfusion, the question is increasingly which approach is useful for which organ and circumstance. The kidney, liver and lung studies in this issue show why an umbrella phrase such as machine perfusion is too broad to carry a single promise. Temperature, oxygenation, timing, donor injury and the purpose of assessment all affect what a result can reasonably mean. [1] [2] [3] [4] [5]

For cryopreservation, the bridge to patients still needs evidence at a larger scale, reproducible recovery and longer observation after transplantation. A kidney that eventually recovers after an early period of dysfunction may still have clinically important consequences. Measuring those consequences is part of development, not a distraction from the storage achievement. [6]

Delivery matters too. Equipment, trained teams, transport, monitoring and reliable backup plans all shape whether a method can serve patients beyond a research center. A future comparison should account for those demands alongside graft outcomes. Better preservation may buy time, but that time has value only when it can be used safely.

The field is compelling because its aim is tangible: keep a donated organ able to do its work, and give a transplant team a better chance to use it well. The strongest progress combines an ambitious technical goal with modest, specific claims. Ask how long preservation lasted. Then ask how the recovered organ performed.

Sources & reading

[1] Cyril Moers, Jacqueline M Smits, Mark-Hugo J Maathuis, et al. Machine perfusion or cold storage in deceased-donor kidney transplantation. The New England journal of medicine. 2009 Jan 01;360(1):7-19. doi:10.1056/NEJMoa0802289. PMID:19118301.

[2] David Nasralla, Constantin C Coussios, Hynek Mergental, et al. A randomized trial of normothermic preservation in liver transplantation. Nature. 2018 May;557(7703):50-56. doi:10.1038/s41586-018-0047-9. PMID:29670285.

[3] Rianne van Rijn, Ivo J Schurink, Yvonne de Vries, et al. Hypothermic Machine Perfusion in Liver Transplantation - A Randomized Trial. The New England journal of medicine. 2021 Apr 15;384(15):1391-1401. doi:10.1056/NEJMoa2031532. PMID:33626248.

[4] Hynek Mergental, Richard W Laing, Amanda J Kirkham, et al. Transplantation of discarded livers following viability testing with normothermic machine perfusion. Nature communications. 2020 Jun 16;11(1):2939. doi:10.1038/s41467-020-16251-3. PMID:32546694.

[5] Marcelo Cypel, Jonathan C Yeung, Mingyao Liu, et al. Normothermic ex vivo lung perfusion in clinical lung transplantation. The New England journal of medicine. 2011 Apr 14;364(15):1431-40. doi:10.1056/NEJMoa1014597. PMID:21488765.

[6] Zonghu Han, Joseph Sushil Rao, Lakshya Gangwar, et al. Vitrification and nanowarming enable long-term organ cryopreservation and life-sustaining kidney transplantation in a rat model. Nature communications. 2023 Jun 09;14(1):3407. doi:10.1038/s41467-023-38824-8. PMID:37296144.