More than anything, Peter Thiel, the billionaire technology investor and Donald Trump supporter, wants to find a way to escape death. He's channeled millions of dollars into startups working on anti-aging medicine, spends considerable time and money researching therapies for his personal use, and believes society ought to open its mind to life-extension methods that sound weird or unsavory.

Speaking of weird and unsavory, if there's one thing that really excites Thiel, it's the prospect of having younger people's blood transfused into his own veins.

That practice is known as parabiosis, and, according to Thiel, it's a potential biological Fountain of Youth--the closest thing science has discovered to an anti-aging panacea. Research into parabiosis began in the 1950s with crude experiments that involved cutting rats open and stitching their circulatory systems together. After decades languishing on the fringes, it's recently started getting attention from mainstream researchers, with multiple  clinical  trials underway in humans in the U.S. and even more advanced studies in  China and  Korea.

Considering the science-fiction promise of parabiosis, the studies have received notably little fanfare. But Thiel has been watching closely.

Thiel and Ambrosia.

In Monterey, California, about 120 miles from San Francisco, a company called Ambrosia recently commenced one of the trials. Titled "Young Donor Plasma Transfusion and Age-Related Biomarkers," it has a simple protocol: Healthy participants aged 35 and older get a transfusion of blood plasma from donors under 25, and researchers monitor their blood over the next two years for molecular indicators of health and aging. The study is patient-funded; participants, who range in age from late 30s through 80s, must pay $8,000 to take part, and live in or travel to Monterey for treatments and follow-up assessments.

Ambrosia's founder, the Stanford-trained physician Jesse Karmazin, has been studying aging for more than a decade. He became interested in launching a company around parabiosis after seeing impressive data from animals and studies conducted abroad in humans: In one trial after another, subjects experience a reversal of aging symptoms across every major organ system. While the mechanisms at play aren't totally understood, he said, young organisms' blood not only contains all sorts of proteins that improve cell function; somehow it also prompts the recipients' body to increase its production of those proteins.

"The effects seem to be almost permanent," he says. "It's almost like there's a resetting of gene expression."

While Ambrosia advertised the study to attract participants, it didn't seek broader coverage. So Karmazin was somewhat surprised to get a message from Jason Camm, chief medical officer at Thiel Capital, who expressed interest in what the company was doing. (Karmazin said he hasn't reached out to any investors: "I'd really want to talk about what the business model would be.")

Although his LinkedIn profile identifies him as an angel investor, that's not Camm's primary job. An osteopath with a background in treating elite athletes, Camm is "Personal Health Director to Peter Thiel ... and a number of other prominent Silicon Valley business leaders and investors," according to his professional profile. "He enables his clients to make radical breakthroughs in their immediate day-to-day health, cognitive functioning and physical performance -- all of which increase their prospects for Optimal Health and significant Lifespan Extension."

Among his duties at Thiel Capital is this: "Communicates with a number of the World's best physicians, health care professionals, and researchers in the USA, Europe and the Middle East on Life Extension, optimizing blood markers and novel techniques to improve health." 

"We're a little too biased."

When I interviewed Thiel a year ago about his investments in biotech and life-extension medicine, I asked him what health interventions he found compelling enough to incorporate in his own life.

"There are all these things I've looked into doing. I haven't quite, quite, quite started yet," he told me, adding that he is "always really uncomfortable giving general advice on this stuff."

"I suspect we're a little too biased against all these things in society," he told me.

After briefly discussing the pros and cons of caloric restriction, human growth hormone, and the diabetes drug metformin, Thiel said this:

I'm not convinced yet we've found a single panacea that works. It's possible there exist single-point things that could work. I'm looking into parabiosis stuff, which I think is really interesting. This is where they did the young blood into older mice and they found that had a massive rejuvenating effect. And so that's ... that is one that ... again, it's one of these very odd things where people had done these studies in the 1950s and then it got dropped altogether. I think there are a lot of these things that have been strangely underexplored.

I followed up to ask if he meant parabiosis was "really interesting" as a business opportunity or a personal-health treatment.

He made it clear he was talking about the latter. "That would be one where it's more just, do we think the science works? Some of these it's not clear there's actually a great company to start around it. It may just be it's not necessarily patentable. The parabiosis would not require -- there's no FDA approval needed because it's just blood transfusions."

There are widespread rumors in Silicon Valley, where life-extension science is a popular obsession, that various wealthy individuals from the tech world have already begun practicing parabiosis, spending tens of thousands of dollars for the procedures and young-person-blood, and repeating the exercise several times a year. In our April 2015 interview, Thiel was seemingly explicit that parabiosis was something he hadn't "quite, quite, quite started yet." A Thiel Capital spokesman said nothing had changed since then.

Off-label blood and the FDA.

Anyone seeking to practice parabiosis privately would quickly encounter the question of where to obtain sufficient quantities of young people's blood. But human blood isn't available for purchase to just anybody.

A spokeswoman for the Food and Drug Administration says the agency "regulates the collection and manufacture of blood and blood components to help protect the health of the blood donor and to ensure the safety, purity and potency of the blood product." While it's not approved specifically for anti-aging treatments, like other drugs, it can be prescribed for so-called off-label uses as long as there is no advertising or efficacy claims involved. 

Clinical trials like Ambrosia's can get blood from blood banks fairly easily for that purpose, but Ambrosia is a for-profit company. For it to begin selling transfusions as a service to patient clients like Thiel, it would presumably need to figure out a source other than non-profit blood banks.

Karmazin acknowledges the potential supply issue, but notes that plasma is relatively abundant and has a two-year shelf life. He speculates that a surge of popular attention for parabiosis might inspire more blood donations by young donors, whose blood tends to provide greater benefit when administered in more conventional therapeutic transfusions.

For Thiel, the day when technologies like parabiosis are not only clinically proven but socially accepted can't come soon enough.

After all, he's not getting any younger.