Two new cases involving HIV-positive cancer patients that exhibited undetectable levels of HIV after receiving bone marrow transplants fuel optimism that scientists may be on the cusp of finding a cure for HIV. The patients, both Australian men, were treated for blood cancers while on anti-retroviral therapy (ART) for their HIV infections. Afterwards, their HIV levels fell below the lowest limit of detection.

Human Immunodeficiency Virus, or HIV, is a viral infection that attacks the immune system and when not managed with ART most often leads to Acquired Immune Deficiency Syndrome, or AIDS. There is currently no cure for AIDS, a degenerative and deadly disease.

The patients are still on ART as a precaution, according to David Cooper, director of the Kirby Institute at the University of New South Wales in Sydney. Cooper led the recent discovery and presented details of the two cases on Monday in Melbourne in anticipation of next week’s 20^th International AIDS Conference. Cooper’s presentation came a day after the downing of Malaysia Airlines flight MH17 over Ukraine, a plane that was carrying several HIV/AIDS researchers destined for the conference.

Last year, a team of U.S. researchers reported that two HIV-positive patients who had received stem cell transplants were subsequently virus-free. Cooper, who was in attendance of the conference in which the cases were reported, began searching for similar cases. He and his colleagues reviewed archives of St. Vincent’s hospital in Sydney.

“We went back and looked whether we had transplanted [on] any HIV-positive patients, and found these two,” said Cooper.

One patient received a bone marrow transplant in 2011 during treatment for non-Hodgkin’s lymphoma. The other received a transplant in 2012 during treatment for leukemia. Both remain on ART as a precaution, and Cooper and colleagues are not ready to say the patients are completely free of HIV.