This piece is part of our first-annual Health Care Heroes series, where we spotlight people doing amazing things in the health care and medical fields. Read the rest of the stories here.
IT’S BEEN ALMOST 50 years—yep, five-zero—since the HIV epidemic began, yet it remains an ongoing public health crisis as more than a million people globally continue to become infected with the virus each year. And while the U.S. has an ambitious goal to end HIV by 2030, which includes preventing new HIV infections and reducing HIV-related disparities and equities, it doesn’t come without its challenges. Helping to meet that challenge are people like Tomas Cihlar, PhD, senior vice president of virology at Gilead, who oversees antiviral drug discovery and preclinical research at the pharmaceutical company.
Cihlar started working at Gilead more than three decades ago, where he’s dedicated his career to fighting viral infections from HIV to hepatitis to COVID-19. But perhaps his most significant accomplishment yet is the role he played in pioneering lenacapavir (sold under the brand names Sunlenca and Yeztugo)—twice-yearly injections that are used to prevent and treat HIV. “It started with an idea to explore what we call a new mechanism of action based on some early groundbreaking science done at the University of Utah by my close friend Wes Sundquist,” he explains. “We had the vision to interfere with the virus infection, the virus growth, and the replication in the people who have the infection.”
Developed over the course of two decades, lenacapavir is a molecule created by the Gilead research team that blocks multiple critical steps in the HIV replication cycle, including the movement and disassembly of the viral capsid. The capsid is essentially a “shell” made of viral proteins that protects the genetic material of the virus and delivers it into a specific location in the cell, which is key for the HIV infection to take hold. If that shell doesn’t function correctly, then the virus isn’t infectious and stops multiplying. After it received FDA approval in 2025, the drug now belongs to a group of HIV prevention medications known as pre-exposure prophylaxis (PrEP), which are available to anyone who’s at high risk of exposure.
For Men’s Health’s first-annual Health Care Heroes series, we spoke with Cihlar—who proposed and oversaw the program that created one of the most potent drugs against HIV to date—about his groundbreaking work in HIV research, what we still don’t understand about the virus, the future of a once-yearly PrEP medication, and whether he believes we’ll one day have a cure for HIV.
Men’s Health: Can you talk to us about lenacapavir’s development after its discovery?
Tomas Cihlar: The first phase is the initial short-term testing. You start with a single dose and then you expand to one week or two weeks of dosing. People who are taking the drug are closely monitored to make sure that the drug is safe and doesn't cause any significant side effects. Then towards the end of phase one, you start establishing the clinical efficacy in the short-term trials to figure out what dose might be needed and how long the drug actually lasts in people's bodies.
Phase two was focused on a small population of people who urgently needed a new type of treatment because there’s a population of people living with HIV who have so-called multi-drug resistant virus. The virus is resistant to most of the existing HIV drugs. So they need the new drugs to keep the virus suppressed in their bodies—and lenacapavir was one of them. This was quickly tested in these patients and was approved by the FDA in 2022 under the brand name Sunlenca. That was the initial pillar of the program. But then the program, of course, expanded much more into the prophylactic or the PrEP studies. This was the program with the 10,000 participants across the world with two large phase-three clinical studies. Those were completed in 2024.
In 2025, lenacapavir was approved in the U.S., Europe, and then in many other countries under the brand name Yeztugo for HIV prevention. And that's the once-every-six-months subcutaneous injection. That’s a really significant breakthrough for the field because not only can it be given very infrequently, but also the efficacy is very high for preventing HIV infection.
MH: Would you say it’s essentially as effective as a vaccine?
TC: I would say so. It’s not a vaccine because a vaccine stimulates your own body to generate immune responses against the virus and then you are protected by your own immune system. The prevention in general with HIV drugs is so-called chemoprophylaxis. That’s a different approach where the people need to keep taking the drug and keep certain levels of the drug in the body so it actually protects them. It's not the immune response of your own body. But the problem in the past was that these prevention strategies for HIV mostly relied on the daily pills and people had to take them rigorously to be protected. And in many circumstances, this turned out to be very difficult.
The compliance is an even bigger problem in different parts of the world. For example, among the young women in Sub-Saharan Africa where it's very difficult for them to keep the bottle of the pills with them all the time and take them every day. With this, you get the injection and you are protected for six months. So, in principle, it’s approaching the impact of the vaccines. We now actually have a late-stage program that’s exploring the development of a new composition of lenacapavir that can be given only once a year. And I think that would be fantastic because people can get an injection and then basically forget about the virus that they might be at risk or exposed to because they would be protected for the whole year.
MH: Would that mean just giving a higher dose of the drug or is there a different mechanism involved?
TC: You need a higher dose so it lasts longer, but with the higher dose you also need to change the composition of the drug product that’s being injected. It’s also an intramuscular injection instead of subcutaneous, which allows for a little bit larger amount of the drug to be administered. The composition of the additives is a little bit different, but the actual molecule that acts on the virus and protects people from the virus is the same between the six months and once a year. It’s in the late-stage, phase-three clinical trials. The data hopefully will be coming in the foreseeable future.
MH: Access and affordability are major concerns for HIV treatments. How is the company thinking about that equitable global distribution of the drug?
TC: We have had multiple strategies that were built over the years to make sure that our HIV drugs are globally accessible. And one of them is the mechanism Gilead has pioneered called voluntary license, where we basically give the patents to several well-selected generic companies that can produce the drug at low cost with high quality. That’s primarily for the supply to low- and middle-income countries. And we also very closely collaborate with many institutions and agencies like the Gates Foundation, The Global Fund, and the Clinton Health Access Initiative that help with the funding of the access to this low-cost product. We started this program long before lenacapavir was approved by the FDA, which was also very unique. That allowed us to have a quite a bit headstart to build a globally inclusive access program.
MH: If the drug becomes widely adopted globally, what impact do you hope to see it have on the HIV epidemic?
TC: Well, I think for all of us who were involved with lenacapavir, the big dream is to see a significant change in the course of the global HIV epidemic in terms of the number of the cases of infections. Because when you look at the statistics, nowadays there’s still about a 1.3 to 1.4 million new infections annually around the world, and many of those infections happen to people who have no protection. Often they don't have the knowledge of the HIV risk. But if this drug that can be easily administered allows for broader protection—particularly in the parts of the world where HIV is a critical problem and for the people who are most vulnerable—it may help to not only stop the HIV epidemic, but eventually also eliminate the HIV.
MH: What do we still not fully understand about HIV when it comes to treatment?
TC: For prevention, lenacapavir is enough to protect people from HIV, but the treatment requires two or three different drugs that need to be combined together to make sure that the virus is fully suppressed in people who live with the virus. So we do have lenacapavir as the pillar, but we need several other similar drugs that can be combined for the treatment. That’s our big goal in the space of HIV research and development—to actually come up with the molecules that are similar to lenacapavir and can be given on the same treatment schedule once every six months or once a week or once a month orally. That’s what we are focused on right now and I think that there is still quite a bit of potential to actually make the treatment of HIV more straightforward, more accessible, and easier to be compliant.
MH: And what about the virus itself? Do scientists and researchers have a pretty good understanding of the virus or are there still some gaps in knowledge?
TC: In terms of what the virus is doing to the body—what it’s doing to the immune system, how the virus replicates, and where the virus grows and hides—that's all understood. But the one big area where the research is probably most focused and active is to understand better this so-called reservoir. The long-lasting reservoir of HIV is the reason why HIV cannot be cured by antiviral drugs. You can stop the evolution of the disease and progression of the disease if you take the drugs regularly, but that doesn't cure people of HIV. So they need to stay on the drugs for their lifetime.
I’ve been working with my colleagues over the past 15 years or so asking the question, what would it take to actually cure HIV completely so people don't need to keep taking the drugs for the rest of their life? And for that, you need to really understand why the reservoir of HIV is surviving for so long in the human body and how you can potentially target it with new mechanisms. That’s the biggest unknown yet in our field of HIV research.
MH: Do you have hope that one day we'll have a cure for HIV?
TC: Yeah, hope is the foundation. You have to have it first in order to be able to work for years on the program. This is one of most challenging problems of modern medicine—how to cure HIV. How far we get in the next three or five years…it’s very hard to say. It's quite unpredictable. But the more we try, the higher likelihood of the success. We take it very seriously as our mission to keep trying to achieve the cure for HIV.
This interview has been edited for length and clarity.
Rachel Epstein is the features director at Men's Health and Women's Health, where she leads the brands' most ambitious storytelling across platforms from reported narratives, profiles, and investigations to buzzy, expert-backed service packages. Her work has been nominated for two National Magazine Awards. Offline, she's likely watching a Heat game or finding a new coffee shop.
