We heard a great deal about T cells during the Covid pandemic. They are crucial to resisting infection, and they are manufactured in your thymus, a small organ behind your breastbone. Unfortunately, the thymus starts to deteriorate when you are young, which is why the elderly were particularly susceptible to Covid. Greg Fahy was already a successful and noted cryobiologist when he embarked on a series of experiments to regenerate the thymus. He wants to remind our bodies how to be young.

Wanting to be President

When Greg Fahy was small he wanted to be President. This was simply because he wanted to be remembered, but then he noticed that something bad was happening to the older people in his family and beyond: they were getting old and dying. He decided this was a Bad Thing, and rather than being President, he would like be remembered for doing something about aging.

So at the age of 12, he resolved to be an excellent student in order to tackle aging. He was awarded a Ph.D. in pharmacology by the Medical College of Georgia in 1977, and became a cryobiologist, working on novel approaches to the vitrification (flash-freezing) of large biological systems.


In 2002, his company, Twenty-First Century Medicine, successfully cryopreserved (preserved by freezing) a kidney from one rabbit, and transplanted it into a second rabbit after re-warming. The second rabbit lived on with the re-warmed organ as its only kidney.

Fahy has been awarded more than 30 patents for discoveries related to cryopreservation and related techniques. He is the 2021-2022 President of the Society for Cryobiology. Back in 1991 he edited “The Future of Aging”, a compilation of essays by 40 eminent authors on the causes of aging and possible ways to prevent it. Thirty years later, he remains optimistic about the prospects for stopping and reversing aging, and believes that we now have solid evidence that it is possible, although the timing is unpredictable.

The thymus: your immune system’s master gland

One of the most profoundly seminal moments in Fahy’s career happened in 1986, five years before the publication of that book. A paper was published in a prestigious journal – PNAS, the Proceedings of the National Academy of Sciences – describing how the thymus of a rat could be regenerated by being injected with growth hormones.
The thymus is the master gland of your immune system. It is located in your upper chest, in front of your heart and behind your sternum, or breastbone. Using stem cells from your bone marrow, it manufactures T cells – white blood cells which fight off infections.

The thymus starts to deteriorate from an early age, and by the time you are 50 it has almost entirely converted to fat. Fortunately for those of us older than 50, T cells survive a decade or two, so we don’t all drop dead in middle age. But in your mid-60s, your T cell population declines rapidly, and your immune system is increasingly compromised, as we saw very clearly during the Covid epidemic.


The 1986 rat research suggested that the thymus can be converted back from fat to functional tissue. Excited by this idea, Fahy tried to raise awareness of the paper, but despite a couple of follow-up studies, there was little interest in the research. Fahy remained intrigued, and a decade later, he secured the help of his personal physician to undertake a self-experiment based on the research. He started injecting himself with recombinant human growth hormone (rhGH). After a week his insulin had risen by 50%, so he added DHEA, or Dehydroepiandrosterone, a steroid that acts as a hormone, and his insulin levels fell back to normal.

He recorded positive effects and published the results, but again they received scant attention. He tried a number of variations on the treatment, but nothing else worked as well. He thought about how to launch a scientific trial of his approach to thymus regeneration, but he lacked the resources – both money and time – until he persuaded a hedge fund manager, Bobby Brook, of the project’s potential. The result of this collaboration was the TRIIM trial (Thymus Regeneration, Immunorestoration, and Insulin Mitigation).

The TRIIM trial

Between 2015 and 2017, the TRIIM trial tracked the results of growth hormone and steroid injections in ten men between the ages of 51 and 65. The result was a two-to-three year reduction in the men’s apparent ages. In most cases, their kidney functions improved, and some of the men’s hair became darker too. Fahy admits to having no conclusive proof that these effects were due to thymus regeneration, but there were no indications of any alternative explanations. In his 2019 paper on the study, he described the test as the “first known proof of extended human lifespan from a currently available therapy.”

Buoyed by the success of the first TRIIM trial, Fahy moved to broaden its scope. TRIIM-X started in November 2020, and its 26 members include women, and members of ethnic minorities. It also broadened the age range to between 40 and 80. Final results are expected later this year, but so far, the indications are similar to the original trial. Members of the trial are excited by the observable impact on their health and well-being.

Showing his continued confidence in the thymus regeneration project, Fahy is enrolled in the trial himself. As he puts it, he eats his own dogfood. He reports that his apparent age is five years less than his calendar age, and he certainly looks young.

Despite all the positive findings, the TRIIM trial is generating only modest levels of interest from the longevity community, and still less from the wider pharmaceutical and healthcare communities. Fahy is both surprised and unsurprised by this. Professionally, he is known for his work on cryobiology, not longevity, and the original TRIIM trial was a small one. Perhaps the results of the larger TRIIM-X trial will win a wider audience.

Don’t try this at home, folks

Although the professionals are failing to beat a path to Fahy’s door, he does get requests from members of the public who would like to enrol in the programme. His strong advice, to coin a phrase, is not to try this at home. It is imperative for subjects to be monitored closely and regularly, which is neither straightforward nor cheap. At the moment the study is limited to the USA, but Fahy is interested in expanding it abroad, perhaps initially to Canada, and then to Europe.

If thymus regeneration does turn out to be reliably achievable with growth hormones, it would not be necessary to keep taking the treatment forever. Because T cells live a dozen years or so, patients would only need to take a course that often. Thymus regeneration is not a comprehensive cure for aging, but it should allow us to fend off many of the diseases which currently shorten our lives. It would be a bridge to longer lifespans as well as improved healthspans.

Reminding our bodies how to be young

It is a striking and curious feature of longevity science that we don’t really know why we age and die. One popular theory is that our brain and body are simply subject to wear and tear, like a car driving along bumpy roads. Parts degrade and fail, and sometimes actually fall off. An alternative explanation is that aging is built into us, just as cynics think that manufacturers build obsolescence into their products, so that we have to buy replacement models every now and then. In this explanation, aging is regulated, and all we have to do is figure out the regulation mechanism, and how to stop it and then reverse it. The gradual conversion of the thymus from functional tissue to fat could be a significant part of that regulated aging process. By reversing that degradation we would, in effect, simply be reminding our bodies how to be young.


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