In This Issue

Can we really freeze and unfreeze people?

🧊  The pitch: Until Labs wants to run four fluids and a load of magnetic nanoparticles through an organ's own blood vessels, so a kidney can be cooled to -196°C and then rewarmed from the inside out.

⚠️  The catch: The current evidence of success is a rat kidney. A human one is roughly a hundred times the volume, and everything that makes vitrification hard gets worse with size.

💰  Follow the money: Until Labs is past US$100M led by Founders Fund. X-Therma, the nearest chemistry competitor, has raised about a third of that in its lifetime.

📄  The paperwork: Beyond the feasibility questions, the claims start to bleed into gene editing which opens a totally new and complicated approval process.

The Freeze Button

The words reversible cryopreservation in this patent's title was enough to freeze me in my tracks! So, is the startup Until Labs (who raised more than US$100 million) actually freezing people?

The company answers that question three paragraphs into the patent. It says that reversible cryopreservation of whole mammals and whole organisms would allow sick patients with no current treatment to be preserved until a cure for their disease arrives.

That is the far end of their ambition. And the patent even mentions preserving astronauts during long-distance spaceflight!

But the patent also talks about uses that are closer to execution today. A kidney that currently has to reach a recipient inside a day and a half could instead remain frozen until the right patient is found. How about ovarian tissue taken from a girl before cancer treatment, banked with a better chance of restoring her fertility later? Or human brain tissue held in a functional state so neuroscientists can reduce animal testing?

Freezing is the easier part, and the hard problem is bringing it back. Ice forms on the way down and again on the way up, and warming an organ unevenly cracks it like a windscreen in a cold snap.

Until Labs has the answer! And investors are buying in.

Until Labs is based in South San Francisco and was previously called Cradle. It develops organ-scale reversible cryopreservation as the first product and whole-body preservation as the stated long-term goal. Sixteen inventors are named on this patent. The system in the filing is a cooling chamber plus a set of pumps, and it works by running four different fluids through the organ's own blood vessels in sequence.

First comes the cryoprotective fluid, the antifreeze. The patent names trimethylamine-N-oxide as one option, a compound deep-sea fish use to survive pressure and cold, alongside a more conventional mix of ethylene glycol, DMSO, formamide and polyglycerol.

Second, a thicker inert fluid is pushed in behind it. This one does not mix with the antifreeze, so it sweeps the cryoprotectant out of the vasculature while leaving it inside the tissue where it is needed.

Third, a thinner inert fluid replaces the thick one, because you cannot move heat quickly through treacle.

Fourth, the pumps push magnetic nanoparticles through the vessels. The patent describes core shell particles with a cobalt iron core and a manganese shell, at least 20 nanometres across, coated so they stay suspended in the fluorous fluid carrying them.

Then the organ is cooled, from somewhere between 10°C and minus 20°C down to as low as minus 196°C.

The nanoparticles are the heater. Put the vitrified organ inside a magnetic coil, run an alternating field through it at somewhere between 100 kHz and 10 MHz, and the particles warm from magnetic losses. A vitrified organ is one that has been cooled into a glass, without ice crystallisation. Because the nanoparticles are distributed through the vasculature, the heat starts everywhere at once instead of creeping in from the surface. The patent describes warming rates as high as 2,000°C per minute. Afterwards, the particles and the antifreeze get flushed back out.

One of the claims is quite strange. Claim 11 covers antifreeze proteins produced inside the cells themselves, via transient transfection, gene editing or viral infection. Read literally, that is an organ modified to manufacture its own frost protection before you ever chill it.

Right now a donated organ involves an immensely stressful courier job. Hearts, lungs and livers have to reach a recipient within roughly 4 to 12 hours of procurement (and kidneys stretch to about 24 to 36).

Everything downstream bends around that window. Matching gets compromised for proximity, patients sit in hospitals waiting for a call, surgical teams work at 3am because the organ decided the schedule. Thousands of usable organs are discarded every year for reasons that are logistical rather than medical.

The field splits into two philosophies. One camp keeps the organ alive and working outside the body. The other stops it entirely and tries to restart it.

The closest technical match to this patent is John Bischof and Erik Finger's group at the University of Minnesota published nanowarming work in Nature Communications in 2023, vitrifying rat kidneys, rewarming them with magnetic nanoparticles in the vasculature, then transplanting them successfully. Bischof's name appears repeatedly in this patent's cited references, which is the polite way a filing acknowledges whose shoulders it is standing on.

21st Century Medicine, the lab behind much of the modern vitrification chemistry, shows up in those citations too. Unfreezing things has been their unsolved half.

X-Therma takes a different bet, designing synthetic peptoid molecules that shape ice crystals and stop them growing, aiming to hold organs at around -5°C without freezing at all. It is a more conservative product with a clearer near-term regulatory path.

Then there are the incumbents, TransMedics, XVIVO, Getinge and Terumo, who sell machine perfusion systems that keep organs warm and metabolising in transit. They dominate the hospital relationships, the regulatory experience and the sales channel.

Which is the real question hanging over Until Labs. The company has raised more than the entire disclosed venture funding of its nearest chemistry competitor, on the strength of a system whose core rewarming principle was demonstrated by a university lab three years ago.

The organ preservation market is worth around US$368.65 million in 2026, heading to US$684.06 million by 2034 on Fortune Business Insights figures.

It is also arguable that this should currently sit in a small market for a reason. Preserving an organ today means a few hours in a cooler with a bag of University of Wisconsin solution, and you cannot charge much for a few hours. If organs can be banked, the value moves from the solution in the bag to the inventory system around it, and that gets priced against the cost of a failed match, a wasted retrieval flight and a discarded kidney.

There were 109,817 men, women and children on the US national transplant waiting list as of July 2026, and 95,492 of them were waiting for a kidney, per organdonor.gov. Another name joins that list every seven minutes. Twelve of the people already on it die each day. The US performed a record 48,149 transplants in 2024 from 16,988 deceased donors and 7,030 living donors, according to the OPTN.

The waste figure is important, because it is the part a freezer directly addresses. In 2023, 27.9% of deceased donor kidneys that were recovered for transplant were never transplanted, up from 26.6% the year before, per the OPTN/SRTR 2023 Annual Data Report. For kidneys that were biopsied first, nonuse hit 41.4%. For donors aged 65 or older it reached 72.2%. Globally those numbers are worse. Solid organ transplants rose 76% between 2008 and 2023, from 101,990 to 179,091, and kidneys accounted for 65% of the 2023 total.

A lot of the market numbers talk to the dire state of the problem Until Labs aims to address. How do you think the valuation of organ donation technology could change if the time-window expands as a result of improved reversible cryopreservation?

Until Labs is the outlier. The company raised US$48 million in seed funding, then closed a US$58 million Series A led by Founders Fund with Lux Capital and Field Ventures, taking it past US$100 million total (longevity.technology & HIT Consultant). Founders Fund leading a cryobiology round is an interesting signal, as that firm underwrites long-horizon physical science bets, and its presence reframes the category from fringe to fundable.

We can compare that with X-Therma, the nearest chemistry competitor. It closed a US$13 million Series A in 2021 led by LOREA AG, then US$22.4 million in Series B in 2024 to push its preservation devices toward FDA clearance (Medical Device Network). Until Labs has raised roughly three times X-Therma's lifetime funding.

Sylvatica Biotech has funded its liver banking work largely through NIH SBIR grants rather than venture rounds, which is the pattern you see when a technology is real but the commercial timeline is longer than a fund's life.

Machine perfusion companies have built real revenue by extending organ viability from hours to slightly more hours, which is a much easier sell to a hospital than a freezer full of glassy kidneys. This is where the money in organ preservation currently sits.

Read together, the pattern is a category with one well-funded moonshot, a handful of grant-funded labs, a modestly funded chemistry challenger and a profitable incumbent layer solving the same problem badly but reliably.

The hard risk here is that the science may not clear the gap between a rat and a human.

The published art is evidenced with a rat kidney. A human kidney is roughly a hundred times the volume, and everything that makes vitrification difficult gets worse with size. Heat has further to travel, thermal stress gradients grow, and cracking becomes more likely. There doesn't appear to be any published success on a human scale…

Toxicity is the second problem. The concentrations of DMSO, formamide and ethylene glycol needed to vitrify a whole organ are high enough to damage the tissue they are protecting.

Then there is the big, bold claim 11. Producing antifreeze proteins inside the cells using gene editing or viral vectors turns a preserved organ into a genetically modified one, and no regulator has a settled framework for a transplant that arrives pre-edited.

"Reversible" in the title is a claim about capability, and it sits next to a cryonics industry that has sold reversibility for fifty years without demonstrating it.

So is this startup freezing and unfreezing people? Maybe one day. But that is a distant future that overshoots many positive implementations on a smaller scale.

Getting there involves proving that a system built around nanoparticle heating scales from a gram of rat tissue to a 150 gram human kidney without cracking, and that the antifreeze can be washed out of something that size. Neither has been shown publicly.

This week's patent is US 12,616,191 B2, titled "Systems and Methods for Reversible Cryopreservation", published by Until Labs, Inc.

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•  Rat kidneys, vitrified and brought back with Nature Communications: Read the 2023 paper that made nanowarming credible, and the one this patent's citation list keeps pointing back to.

•  Five decades of trying to freeze organs properly with Karger / PMC: Explore a review by Michael Taylor and colleagues covering supercooling, vitrification, pressure and the other approaches competing with this one.

•  The company's own account of scaling rewarming with Until Labs: See how the team describes engineering an alternating magnetic field system big enough for a whole organ, including the question they say everyone asks them first.

•  Where the preservation money actually is with Fortune Business Insights: Zoom out on a market still dominated by cold storage solutions and perfusion hardware, and see how small the freezing segment remains.

•  The round that put a cryonics-adjacent startup on the map with longevity.technology: Discover how Until positioned an organ transplant product as the first step toward whole-body preservation, and who wrote the cheque.