Brown's doctors used a donor who had a rare genetic mutation that provides resistance against HIV. So far, no one has observed similar results using ordinary donor cells such as those given to the two patients by the Harvard researchers.
The researchers, Timothy Henrich and Daniel Kuritzkes of the Harvard-affiliated Brigham and Women's Hospital in Boston, announced last year that blood samples taken from the men - who both had blood cancers - showed no traces of HIV eight months after they received bone marrow transplants to replace cancerous blood cells with healthy donor cells. The men were still on anti-HIV drugs at the time.
The men have both since stopped antiretroviral therapy - one 15 weeks ago and the other seven weeks ago - and show no signs of the virus, Henrich told an international AIDS conference in Malaysia on Wednesday.
"They are doing very well," Henrich said. "While these results are exciting, they do not yet indicate that the men have been cured. Only time will tell."
The virus may be hiding in other organs such as the liver, spleen, or brain and could return months later, he warned.
Further testing of the men's cells, plasma, and tissue for at least a year will help give a clearer picture on the full impact of the transplant on HIV persistence, he said.
Kuritzkes said the patients would be put back on the drugs if there was a viral rebound.