Treating HIV with an antibody can reduce the levels of the virus in people's bodies — at least temporarily. The approach, called passive immunization, involves infusing antibodies into a person's blood. Several trials are under way in humans, and researchers hope that the approach could help to prevent, treat or even cure HIV. The work is a milestone towards those goals, says Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases in Bethesda, Maryland. “This is an early study, but it’s a study with some impressive results,” he says.