Two HIV-positive patients have shown no sign of their infection after receiving bone marrow transplants.(Credit: Getty Images/Cultura RF)

Two HIV-positive patients who underwent bone marrow transplants have shown no sign of their HIV infection despite being off HIV drugs for months.

Harvard Medical School researcher Dr. Timothy Henrich announced Wednesday that he has been unable to detect HIV in two of his patients who purposefully went off antiretroviral therapy for 15 and seven weeks, respectively. Although it's not clear whether their HIV will return, the findings may represent another step toward a cure.

"Both patients have been very involved in the research," Henrich said at the International AIDS Society conference in Kuala Lampur. "They've been very interested in what we are doing. And they've been very excited to participate in the studies that are ongoing."

Read about the HIV-positive Mississippi baby's supposed "fundamental cure."

The two patients had been on long-term antiretroviral therapy, which suppresses HIV and stops its progression into full-blown AIDS, but they both developed lymphoma several years ago. To treat the cancer, Henrich treated these men with chemotherapy and a bone marrow transplant, but they continued antiretroviral therapy during and after transplant.

This year, Henrich conducted a clinical study in which he instructed the patients to stop taking antiretrovirals to see what would happen. So far, the virus has not rebounded, as it normally would have without continued antiretroviral therapy.

"It's possible the virus could come back next week. It's possible the virus could come back months from now, and it's even possible that it could take one or two years for this virus to return to these patients," Henrich said. ""We still do not know the full impact of the findings that we have."

Although more research is needed, Henrich said it's possible the patients were able to suppress the HIV without drugs because of a bone marrow transplant complication called "graft-versus-host." Although this complication usually has a negative connotation, it could mean that the donor stem cells in the bone marrow attacked the HIV patients' remaining HIV-positive cells and replaced them with healthy ones.

Perhaps the most famous HIV-positive patient to receive a bone marrow transplant is known as "the Berlin patient," a man who stopped taking antiretrovirals the day of his transplant in 2006 and says he hasn't needed them since. This man, however, accepted a bone marrow transplant from a donor with a mutation called CCR5, which makes patients immune to HIV.

Henrich said his patients received bone marrow from donors who did not have this mutation, meaning their cells were susceptible to HIV infection.

Read about the "Berlin patient" and his announcement six years after transplant.

Earlier this year, doctors announced that they'd "fundamentally cured" a rural Mississippi baby by introducing high doses of antiretrovirals just hours after the little girl was born to an HIV-positive mother. Less than two weeks later, French researchers claimed they had 14 HIV-positive patients who'd experienced remission after stopping antiretroviral therapy because it was "fashionable at the time."

Read about the 14 patients in HIV remission.