Scientists have uncovered two new cases of HIV patients in whom the virus has become undetectable.

The two patients, both Australian men, became apparently HIV-free after receiving stem cells to treat cancer. They are still on antiretroviral therapy (ART) “as a precaution”, but those drugs alone could not be responsible for bringing the virus to such low levels, says David Cooper, director of the Kirby Institute at the University of New South Wales in Sydney, who led the discovery. A year ago, a different group of researchers had reported cases with a similar outcome.