An Interview with Greg Fahy on Thymus Rejuvenation

Greg Fahy is currently wrapping up a trial of one of the simpler methods that might produce some degree of rejuvenation in the the thymus, turning back a little of the process of thymic involution, the withering of functional tissue in this organ. The thymus atrophies quite early in adult life, and further with later aging. As the thymus provides an environment for processes that are necessary in the creation of the immune cells called T cells, this decline limits the immune system. A faster pace of creation for T cells should help with some of the age-related deterioration of the immune system, which arises in part because too many of the existing cells become dysfunctional, and because the pace of replacement is too slow to keep up.

I think that this trial is unlikely to be enormously effective at addressing the problem, and will probably only produce modest effects, but the point of the exercise is to prove in humans that any degree of thymic restoration can produce a commensurate level of benefits. If that can be accomplished via this approach, then hopefully funds can be found to bring one of the more effective methods demonstrated in mice into human medicine: FOXN1 gene therapy, tissue engineering and transplant of replacement thymic tissue, some form of cell therapy to spur regeneration of new thymus tissue, and so forth.

So from around age 20 (or younger) the thymus begins to shrink and loses the ability to produce T cells, why does this happen?

Nobody knows why thymic atrophy, or involution, occurs, but it happens in all vertebrates, starting really at the age of puberty. Some have suggested that it happens to save energy, since the production of properly qualified T cells is very energy intensive and inefficient, and of course, at puberty, the body begins to devote more energy to reproduction, which might require a tradeoff against using energy for immune maintenance. This could be adaptive since, in nature, humans would not have lived long enough for immune system collapse to set in, even though today, the situation is different. Regardless of the evolutionary reason for it, the most immediate biochemical cause of involution seems to be mostly a drop in thymic FOXN1 expression, although some have pointed to a decline in intra-thymic IL-7 and the negative influence of circulating sex hormones, for example.

You recently ran a human clinical trial to regrow the thymus gland. Can you please tell us what is the main goal of the project and what is the progress?

The trial was conducted under an FDA-approved IND and with review from multiple scientific and ethics committees. It consisted of a 12-month treatment course for 9 men divided into two cohorts, with the first cohort starting in October of 2015 and the second ending in April of this year. Our goal was to gather preliminary evidence indicating that it is possible to safely regenerate the normal aging human thymus and restore its functions, essentially reversing the process of age-related immunological deterioration. We chose to work with healthy men in part because this was a small trial, which required a reasonably uniform population, and in part because more information was available for men than for women. We chose an age range of 50 to 65 years because this range extends from several years before to a few years after the threshold age at which the immune system tends to collapse. Success would therefore suggest the possibility of preventing or even reversing the early stages of immune collapse. In future trials, we intend to enroll both women and older men.

The outcome measures included MRI evaluation of thymic density before and after treatment, simple and sophisticated assessment of T cell population distributions, measurements of many serum factors related to immune system function and general health, lymphocyte telomere length distributions and telomerase activity, and biological age based on the Horvath epigenetic clock. Regarding our results, first of all, when you're working with human beings, safety has to be the top priority, so I'm glad to be able to say that we met or exceeded all of our safety targets. Regarding thymic imaging results, preliminary analyses indicate that there was a consistent and substantial increase in thymic density, which indicates replacement of thymic fat with more water-rich material, and in previous studies on human immunodeficiency patients, this coincided with improved thymic function. Superficial tests of immune system aging showed improvements in 8 out of 9 men, and we were able to identify a possible correctable reason for the failure of the 9th volunteer. Men of all ages were able to respond positively and to avoid side effects. However, the most definitive endpoints of our study are still being analyzed at four different locations around the world, so we won't really know the final results of our study for probably another month or two.

Are we going to see a publication anytime soon?

I'm not sure about soon, but certainly, as soon as we can. This will be a complicated paper with lots of authors and lots of data to present, but also with top-tier academic co-authors who can help us go through the scientific review process quickly. In any case, we certainly want to make sure that any novel results are shared with the broader medical and scientific communities.



melatonin in high doses shown to regrow thymus in mice. Interesting if somebody tried to replicate this in humans

Posted by: Andey at October 6th, 2017 8:31 AM

I am a little more than surprised that Greg Fahy used FOX1N to rejuvenate the thymus? Dixit and others have been using Fibroblast Growth Factor FGFR21 to rejuvenate the thymus in mice, and have succeeded in extending the life of mice 40% by injecting FGFR21 deficient mice with it. I guess different research teams are trying different methods for thymus rejuvenation. Hope something works as this would be an incredible anti-aging advance.

Posted by: Biotechy at October 6th, 2017 9:29 AM

I referred to the miracle thymus hormone above as FGFR21 and it should be FGF21 instead. Sorry.

Posted by: Biotechy at October 6th, 2017 9:37 AM

Andey: thanks for info on melatonin.

Posted by: CD at October 6th, 2017 11:47 AM

@biotechy - Reason's link to a conference blog piece indicates Greg Fahy probably used human growth hormone injections into the thymus, not FOX1N gene therapy.

Posted by: Jim at October 6th, 2017 3:01 PM

@Andey: melatonin has never been shown to regrow the thymus in mice. I think you're remembering somewhat questionable work by Walter Pierpaoli finding that aging mice engrafted with young animals' pineal glands at their thymuses showed greatly reduced thymic involution.

@Biotechy: If Dixit succeeded in extending the life of mice 40% by injecting FGF21 deficient mice with it, that wouldn't imply anything about its benefits to mice (or humans) with their FGF21 production intact. I suspect you're thinking of PMID: 23066506, which both the popular press and even the abstract of the paper claimed showed that transgenic overdose of FGF21 extended the life of mice by 30% without concomitant CR. However, despite this assertion, the FGF21-Tg mice did, in fact, reduce their food intake - by about 30%, meaning that the lifespan extension was in line with what you'd expect from CR.

This is somewhat buried in the paper. Food intake is reported in grams of food per gram of mouse per 3 day period, and is unchanged or possibly slightly increased in Tg vs WT mice -- but body weight was reduced by ~1/3 in males and by even more in females, so actual food intake was also cut by >30%. (Despite the widespread misunderstanding, long-term CR does not reduce food intake per unit of metabolic mass). So this is "crypto-CR" is sufficient to account for a lifespan increase of ~30%.

Posted by: Michael at October 6th, 2017 10:30 PM

@Michael I mean this study (and previous one by the same author)
Our results show that melatonin distinctly reversed the age-related thymic involution as revealed by the notable increase of thymus weight, total number of thymocytes and percentage of thymocytes at G2+S phases. More strikingly, spleen weight, total number of splenocytes and some peripheral immune capacity such as mitogen responsiveness and NK cell activity were also significantly recovered by 60 days of melatonin application in aged mice.
and one study in rats by other authors that rather shows clear connection between pineal and thymus

Posted by: Andey at October 7th, 2017 7:34 AM

I am not an MD of any sort but injecting anything directly in the thymus could be problematic as it located behind the breastbone. Its possible as injecting trough sternum have some use in emergency medicine but to do it on a regular basis....

Posted by: Andey at October 7th, 2017 9:45 AM

In the March 2017 Life Extension Foundation Update, they said that thymic regeneration has been demonstrated in animals, HIV-infected people, and, for the first time, in a healthy older person in an ongoing trial in collaboration with Stanford researchers. Indicators show reversal of markers related to inflammation and immune senescence in this 9-person cohort proof-of-concept study. We may be close to a major application of Thymus Regeneration Technology.

Posted by: Biotechy at October 9th, 2017 1:29 PM

"...Are we going to see a publication anytime soon?
I'm not sure about soon, but certainly, as soon as we can..."

Does someone know about a publication on this?

Posted by: albedo at February 28th, 2018 11:54 AM

I am not an MD.
26 years ago at age 65 I began taking DHEA. Shortly thereafter, by sheer coincidence, I met the late Dr Phillip White, Vice President of the Canadian Longevity and Anti-Aging Academy. On his advice I reduced my daily intake to 25 mg.firmly convinced that I was taking HGH. But a recent press report on the work of Greg Fahy says that HGH is rhGH. I would welcome some enlightenment.

NB. I am regularly complimented on being a very young 91 years old.

Posted by: James Wood at September 8th, 2019 1:25 PM


I have seen several credible vet studies that experiments with dogs using the mamalian growth hormone Colostrum with a catalytic thymic astracted product known as Kyosenex has strengthen immune deficiency linked diseases in dogs, quite convincingly. But so far I found no credible scientific study that Colostrum or human equivalent of Kyosenex have been done as
pre-clinical with negative or positive results. Why Not ???

Internet search result today: "Thymus Theraphy 2013: A Forgotten Gland and Is Inluence in the Body" , published March 8, 2019 by P.J. Broadfoot, DVM, Van Buren , AR.

Posted by: Avi Dey at April 14th, 2020 9:50 PM
Comment Submission

Post a comment; thoughtful, considered opinions are valued. New comments can be edited for a few minutes following submission. Comments incorporating ad hominem attacks, advertising, and other forms of inappropriate behavior are likely to be deleted.

Note that there is a comment feed for those who like to keep up with conversations.