About 38 million people worldwide take antiretroviral pills every day to keep HIV under control. Two antibodies that only need to be injected once could one day make that daily therapy unnecessary. Early results from the RIO trial suggest the virus can be suppressed long-term in a majority of patients, without daily medication.
What the Trial Showed
At the centre of the research are two broadly neutralizing antibodies: teropavimab (scientifically 3BNC117-LS) and zinlirvimab (10-1074-LS). Both have been modified to remain in the body unusually long. A single injection is enough to work for several months.
In the phase 1 stage of the RIO trial, led by Imperial College London, 68 participants received either the antibody combination or a placebo. After 20 weeks, 75 percent of treated participants had kept their viral load below the detection threshold. In the placebo group, only 11 percent had. Particularly notable: two trial participants have now gone more than a year without any antiretroviral therapy while still controlling their viral load.
At CROI 2026, the leading international HIV conference, extended data were presented. More than half of the 34 participants from the placebo group who subsequently received the antibodies achieved sustained viral suppression for over 20 weeks. No serious adverse events were attributed to the antibodies.
What a Functional Cure Means
The term functional cure does not describe a state in which HIV has been fully eliminated from the body. The virus remains latent in so-called reservoirs. A functional cure means the immune system or a treatment keeps the virus under control long enough that no damage occurs and no transmission is possible, without daily medication.
Antiretroviral therapy, the standard since the mid-1990s, has dramatically reduced AIDS mortality. But it does not prevent latent infection and must be continued for life. If a patient interrupts therapy, the viral load typically rebounds within weeks.
How the Antibodies Work
Broadly neutralizing antibodies attack parts of HIV that have barely changed over evolution because they are indispensable for the virus. Teropavimab binds to the CD4 binding site on the envelope protein gp120; zinlirvimab targets the V3 loop. This combination makes it hard for the virus to escape through a single mutation.
The long-acting variants used rely on modifications to the Fc region of the antibodies, which substantially extend their half-life in the body. In the RIO trial, the antibodies were given intravenously; researchers are working on subcutaneous formulations that would enable self-injection.
What Comes Next
Phase 3 of the RIO trial is being planned and will examine, among other things, whether controlled viral rebounds can stimulate the immune system to control HIV long-term on its own. This concept of immune-system priming could be the key to truly durable control.
The results are still far from approval. Phase 3 clinical trials typically take several years, and the question of manufacturing costs for antibody therapy remains open. But for millions of people who take daily medication, these early signals are one of the most hopeful developments since antiretroviral therapy arrived 30 years ago.