The patients had received a treatment regimen similar to that given to Timothy Ray Brown, known as the ‘Berlin patient’, who doctors said in 2009 had been cured of the virus by a bone-marrow transplant with cells that were resistant to HIV infection.

Unlike Brown, however, the two ‘Boston patients’ — nicknamed for the Massachusetts city where they were treated — received bone-marrow transplants with cells that were not resistant to HIV. Still, both of them seemed to be free of the virus for months after stopping treatment with antiretroviral medications. But at a meeting on HIV persistence this week in Miami, Florida, researchers reported that the virus has rebounded in both of the Boston patients.

“It’s disappointing and very sobering,” says virologist Deborah Persaud of the Johns Hopkins Children's Center in Baltimore, Maryland, who reported in March that her team seemed to have cured an infant of HIV through treatment with antiretroviral medication.