For the first time, an HIV-like infection has been cleared from an animal without the use of antiviral drugs. The infection was eliminated from mice using a human protein that peps up immune cells.

Marc Pellegrini from the Walter and Eliza Hall Institute of Medical Research in Melbourne, Australia, and colleagues infected mice with lymphocytic choriomeningitis virus (LCMV), which causes a chronic infection that spreads throughout the body. “The virus overwhelms mice, mimicking the massive viral loads associated with HIV infection in humans,” says Pellegrini.

Eight days after infection, some of the mice were injected with human interleukin-7 (IL-7) – a chemical messenger that plays a role in the development of immune cells – once a day for three weeks. The others received a placebo instead.

“Usually mice never clear this virus,” says Pellegrini. But 30 days later, those given treatment had cleared most of the infection and removed all of it by 60 days.