Super sensitive tests have not been able to detect any virus in two HIV-positive men after each received reduced-intensity chemotherapy followed by stem cell transplants to treat lymphoma. A third man in the study died of recurrent lymphoma, although researchers did observe a reduction in his HIV reservoir.

When researchers reported their findings in July, one of the men had gone 15 weeks without a viral rebound since stopping his antiretrovirals, and the other had gone seven weeks.

Qualifying his study results as “exciting and encouraging,” Timothy Henrich, MD, of Harvard Medical School, says, “It may take a year, or up to a year and a half before we're able to say that the chances of HIV returning are very, very low.” At that point, Henrich says, he would define the men as “in remission off therapy.”

Unlike Timothy Brown, a.k.a the Berlin Patient, who was functionally cured of HIV and leukemia following two bone marrow transplants from a donor with a rare genetic resistance to HIV, these men did not receive such genetically resistant cells. The researchers theorize the treatment succeeded at least in part because of what's known as graft-versus-host disease in which newly transplanted cells attack the old, HIV-infected ones, which have been weakened by chemotherapy. The disease can be fatal if left unchecked, so both men received rounds of immunosuppressive therapies and steroids.

Henrich stresses that it would be unethical to provide such a treatment, which has a 15 to 20 percent mortality rate, to anyone who does not already need it as a cancer therapy.