Earlier this week, Life Biosciences, a biotech company focused on reversing age-related diseases, announced that it had dosed its first volunteer. A person with glaucoma has had an experimental treatment injected straight into their eyeball.

The idea is to try to treat the disease—which can cause vision loss—by regenerating healthy nerves in the eye. But David Sinclair, the chairman and cofounder of the company behind the trial, hopes to go further. If the treatment can reverse glaucoma, perhaps similar treatments can reverse other diseases of aging. Maybe, just maybe, they can reverse aging altogether.

Aging is complicated. As we get older, we experience so many changes across pretty much all our biological systems. Scientists have tried to categorize these effects. In 2013, one team published a seminal paper describing nine “hallmarks of aging.” That list features many of the processes scientists have attempted to target. But some of those targets have fallen in and out of fashion over the years.

Take telomere attrition, for example. Telomeres are DNA sequences at the ends of our chromosomes, often likened to the plastic caps that stop the ends of our shoelaces from fraying. When cells divide, telomeres shorten until, eventually, the DNA is vulnerable to damage.

When I started reporting on aging, telomere shortening was all the rage. Shrinking telomeres had been linked to age-related diseases of the heart and brain. Shortened telomeres were considered a sign of premature aging. In 2015 Liz Parrish, CEO of the biotech company BioViva, injected herself with an experimental gene therapy that she hoped might lengthen her telomeres.

Then it suddenly seemed to go out of style. Research continued, but all the excitement within the aging and longevity community seemed to move on to another hallmark. (Parrish also continued with self-experimentation; she calls herself “the most genetically modified person on Earth.”)

That hallmark was cellular senescence. This happens when cells stop dividing but don’t die, instead entering a “zombie” state in which they churn out chemicals that can cause harmful inflammation.

Again, that doesn’t mean senolytic drugs that target “zombie cells” won’t work. But it feels as if many in the field have moved on. These days, the buzz is all about ✨reprogramming✨.

The idea here is to essentially return cells to a young state. It’s based on the Nobel Prize–winning discovery that four genetic factors can turn an adult cell into a stem cell, which can be encouraged to develop into pretty much any other cell type.

Some promising studies in mice suggest that this approach might help wind back the clock. It seems to improve tissue healing, restore vision, and even improve learning and memory.

Running parallel to all this research are repeated injections of hundreds of millions of dollars in funding. In 2021, my colleague Antonio Regalado reported on the founding of the biotech company Altos Labs to pursue reprogramming for rejuvenation.

Altos was funded by the billionaire Yuri Milner—reportedly along with Jeff Bezos, among others—to the tune of $3 billion, a previously unheard-of figure for a biotech startup. Other well-funded companies have since sprung up in this space.

There’s Retro Biosciences, for instance, which is pursuing reprogramming (among other approaches) in an effort to add 10 years of healthy life to human lifespans. Retro’s launch was supported by $180 million from OpenAI’s Sam Altman. Last month, the company announced a valuation of $1.8 billion.

NewLimit, another billionaire-backed biotech exploring reprogramming, says it has promising results from research in mice. It plans to trial a drug designed to rejuvenate the liver in people next year. Last week, the company announced it had raised $435 million toward reaching that goal, among others.

Life Biosciences, which was founded by the Harvard biologist David Sinclair, most recently secured $80 million to support its research. The eye trial is now officially underway, but Sinclair also has plans for whole-body rejuvenation. Earlier this week, he told my colleague Antonio that he plans to test a “highly, highly confidential” oral reprogramming drug as part of a $101 million competition organized by the XPrize Foundation. 

Reprogramming has certainly caught the attention of scientists, biotech companies, and investors. Studies in mice are hugely promising. Human trials are launching. And research in the field has billions of dollars’ worth of support.A lot of people in the field are really excited about reprogramming. But it comes with risks. And we still don’t know if it will work. The question now is: Do we finally have a rejuvenation drug within reach? And if not, what will the next research trend look like?

This article first appeared in The Checkup, MIT Technology Review’s weekly biotech newsletter. To receive it in your inbox every Thursday, and read articles like this first, sign up here.

Correction: This article has been updated to reflect that Liz Parrish claimed to have undergone her first experimental gene therapy in 2015, not 2017.