Two men with HIV seem to have been cleared of the virus after receiving stem-cell transplants to treat their lymphoma, scientists announced Wednesday at an International AIDS Society conference in Kuala Lumpur. One of the men has now been off off antiretroviral therapy for 15 weeks; the other stopped taking HIV-suppressing drugs seven weeks ago.

Doctors have been unable to detect HIV infection in the two men since they received the stem-cell therapy, though it is too early to be certain that the virus has completely disappeared from their bodies, according to Timothy Henrich, a physician and researcher at Harvard Medical School and Brigham and Women's Hospital in Boston.

The cases of these two men differ from that of Timothy Ray Brown, the first person to be cured of HIV, in a significant way: The so-called Berlin patient received a bone-marrow transplant to treat leukemia in 2007, using stem cells from a donor with a rare genetic mutation that makes people resistant to HIV, Reuters reports. The stem cells transplanted into the two Boston patients did not have that genetic mutation.