The journal Nature reports infected animals survived almost twice as long after a single treatment to raise immune response to the virus.
An independent expert said multiple doses were possible, and might eliminate the virus.
Current antiretroviral drugs must be taken for life, giving HIV the opportunity to build up resistance.
Scientists are constantly looking for alternative ways to keep the virus in check.
One option is being tested in the US on macaque monkeys infected with "simian immunodeficiency virus" - their equivalent of HIV.
One of the features of HIV is its ability to shut down or impede the body's own methods for clearing viral infections.
In particular, it manages to activate a signalling system in the body's immune cells - which then actually holds back the body's immune response.
The latest treatment works by blocking that signalling system, which has the effect of boosting the function of "killer" immune cells.
The blocking antibody was injected once into nine animals who had developed AIDS after SIV infection, all of whom lived on average almost twice as long as other monkeys who did not receive the treatment.
The treated monkeys had clear signs of more active immune systems and reduction of the amount of virus circulating in their blood, both signs that they were tackling the disease more efficiently.
While the virus was not fully controlled in any of the monkeys, the scientists said that more than one dose was possible, and that it could be used in combination with antiretroviral drugs.
