Getting old can be painful. Stick around long enough, and you're bound to weather some kind of age-related decline, like creaky joints, clogged arteries, or vision loss.

Silicon Valley billionaires, including Jeff Bezos, Peter Thiel, Yuri Milner, and Sam Altman, who want to skip all that mess and reprogram their cells back to a more youthful state, have invested in startups working on the hottest trend in longevity science: cellular reprogramming.

The technique has rejuvenated lots of mice and monkeys, but it had never been tried in humans — until this year. The first human trial of cellular reprogramming is underway at Life Biosciences, where patients are being dosed with a first-of-its-kind rejuvenation therapy for glaucoma, an eye disease that can cause vision loss.

On Thursday, Life Biosciences released its first safety data. So far, three patients received the experimental therapy: an eye injection, coupled with eight weeks of daily antibiotics that turn on the rejuvenation factors inside their cells. The company said none of the patients reported major side effects and that it was "well-tolerated."

The goal of the treatment is to essentially turn back time at the cellular level, making old eyes young again by delivering genetic programming instructions, similar to those that rejuvenate stem cells and embryos.

Cellular reprogramming as a 'master key' for age-related health issues

There are some early signals that the technique might be working. Two of the three patients showed significant vision improvements on a standard eye exam, suggesting that the new drug might be restoring sight, or at least improving it.

Dr. James Tsai, president of New York Eye and Ear Infirmary of Mount Sinai, told Business Insider the news is "exciting," but very preliminary. Tsai, a glaucoma specialist who was not involved in this trial, said it's possible the therapy did not fully regenerate the eyeball but merely improved existing electrical signals in patients who still had some vision.

"I need a lot more information to say, 'Hey, we're truly at the holy grail of really reversing vision [loss],'" he said. "The exciting thing is they've done it in humans."

Based on the positive results, an independent safety monitoring board has approved a threefold increase in dose for the next group of patients in the study, which could improve the therapy's effectiveness.

If Life Biosciences's initial trial of this technology proves successful, it could be applied to other diseases next. Its chief operating officer, Michael Ringel, points to successful animal trials of cellular reprogramming for various age-related conditions, including arthritis, high blood pressure, fatty liver disease, and even brain diseases like Alzheimer's.

"We believe it has the potential to really be a master key to address a broad range of age-related diseases," Ringel said. "But of course, that's something that will have to be shown clinically. We have to prove it, not just think it."

Silicon Valley is racing toward human trials for longevity

Life Biosciences is the first company to try this longevity technique in humans, but several Silicon Valley biotech startups are gunning to get into the race next. Jeff Bezos-backed Altos Labs hired clinical trial expert Joan Mannick last year, appointing her as head of product development.

"You only bring in Joan if you have something that's getting ready for trial," longevity scientist and XPRIZE Healthspan director Jaime Justice said.

Then there is New Limit, which recently raised $435 million in a Series C round led by Peter Thiel's Founders Fund. The company has been bullish about its ambitions to begin its first human trials of a liver-cell reprogramming therapy in 2027. And Sam Altman-backed Retro Biosciences is also researching the idea.