HIV became undetectable in the anonymous “London patient” after a bone marrow transplant, even though he was not taking antiretroviral drugs to control his illness. Scientists are officially calling the condition long-term remission, but some experts are describing him as cured. Their results will be published Tuesday in the journal Nature and presented at the Conference on Retroviruses and Opportunistic Infections in Seattle.

The first successful use of this method came over a decade ago with the “Berlin patient“, identified as Timothy Ray Brown, who received bone marrow transplants in 2007 and 2008 and has been in remission since. In both successful cases, patients were given bone marrow transplants as a treatment for cancer when they stopped responding to chemotherapy. Because both men were HIV-positive, doctors sought bone marrow from donors who have a genetic mutation that makes some people resistant to HIV.

This breakthrough doesn’t mean there is a cure for HIV, however, as doctors warn that bone marrow transplants are too dangerous for healthy people living with HIV to undergo. Meanwhile, in the decade between the successful cure of Brown and the London patient, none of the other attempts to use the same method have worked.

Even Brown nearly died of the treatment in the months after his transplant. He suffered complications for months and at one point was put in an induced coma.

Despite this, the success of the London patient remains a step in the right direction. Professor Graham Cooke of Imperial College London told the BBC it could help doctors to identify why the treatment works in some patients and not others, which could ultimately help them develop a cure for HIV.

Still, no one is arguing this will be a practical way to treat HIV in the millions of people around the world who are living with it.