A landmark HIV cure trial has produced results that researchers are describing as extraordinary. The RIO trial, presented at the Conference on Retroviruses and Opportunistic Infections (**CROI 2026**) in March, showed that a single course of broadly neutralising antibodies kept **65% of participants off all HIV medication for at least 20 weeks** — with one person remaining completely virus-free and drug-free for four years.
For context: without antiretroviral therapy (ART), **95% of people living with HIV typically experience viral rebound within six weeks** of stopping medication. The RIO trial didn't just beat that number — it obliterated it in a significant proportion of participants.
**What Is the RIO Trial?**
The Reaching for an Immunological Outcome (RIO) trial, run by **Imperial College London** and the **Rockefeller University**, investigates whether broadly neutralising antibodies (bNAbs) — engineered proteins that can neutralise HIV across a wide range of viral variants — can reprogram the immune system to control HIV without daily drugs.
The study enrolled people living with HIV who had started antiretroviral therapy early after infection and maintained sustained viral suppression. They received two long-acting bNAbs — known as 3BNC117-LS and 10-1074-LS (teropavimab and zinlirvimab) — and then stopped their ART to see what happened.
**Phase One: The Numbers**
In the first phase of the RIO trial, 68 participants were randomised to receive either the bNAbs or a placebo. After stopping ART, the results diverged dramatically:
- **65%** of bNAb recipients had not reached the viral load threshold requiring ART restart by week 20 - Only **two individuals** in the placebo group achieved the same - bNAb recipients were **91% less likely to rebound** compared to placebo - At 72 weeks, **39%** of the bNAb group maintained viral suppression vs 5% in placebo - One participant has remained **completely undetectable for four years** without any medication
That final figure — a person living with HIV, drug-free, undetectable for four years — is something researchers have been working toward for decades.
**Phase Two: Even Better**
The second phase of RIO, presented at CROI 2026, enrolled participants who had previously received placebo and rebounded rapidly. These were, in a sense, the harder cases.
Of 28 participants in this phase, **15 (54%) had not rebounded 20 weeks after stopping ART**. Six had not rebounded by week 39. Five maintained low or undetectable viral loads for a year — with two still completely off ART.
Crucially, the antibodies had cleared the body before the treatment interruption, meaning any sustained viral suppression came from **lasting changes to the immune system** — not the antibodies still being active.
**Shrinking the Reservoir**
Perhaps the most scientifically significant finding: for the first time in a clinical trial, long-acting bNAbs were shown to **significantly reduce the size of the HIV reservoir** — the pools of dormant infected cells that make HIV impossible to fully eliminate with standard ART. Some participants reached undetectable reservoir levels.
Reducing the reservoir while retraining the immune system is what researchers have long theorised might be possible. The RIO trial is showing it happening in humans.
**What This Means**
The RIO results are not yet an announcement of an HIV cure. Ongoing ART remains essential for the vast majority of people living with HIV, and a third phase of the trial has already been announced to test further refinements.
But this is clinical evidence that the human immune system can, in a significant proportion of people, be **retrained to control HIV without daily medication** — with a single course of treatment.
Globally, approximately **39 million people** are living with HIV. The daily burden of antiretroviral therapy — adherence, access, cost in lower-income settings — is real. A treatment offering months or years of drug-free viral control would change millions of lives.
Four years undetectable, zero drugs. That's not a statistic. That's a person living a life that looked impossible not long ago. 💉❤️
*Sources: Imperial College London · Rockefeller University · aidsmap.com · medRxiv (preprint) · CROI 2026 conference proceedings · EATG · MedPage Today*
