Medical researchers have discovered specifically how the immune system makes a powerful antibody that blocks HIV infection of cells, in a breakthrough that brings the possibility of an HIV vaccine one step closer.

The natural antibody blocks HIV infection by targeting a site on the virus called V1V2. Researchers now believe that if a vaccine could elicit potent antibodies to a key site in the V1V2 region, then the vaccine could protect people from HIV infection.

V1V2 is one of a handful of sites that remains constant on the fast-mutating virus.

An experimental HIV vaccine has been in the works for some time, but analyses to date to have shown success only in patients whose antibodies at sites within V1V2 were protective.

The new findings point the way toward a potentially more effective vaccine that would generate genuine V1V2-directed HIV neutralising antibodies.

The most recent research was undertaken by experts from US and South African institutions.

They began by identifying an HIV-infected volunteer in the who naturally developed V1V2-directed HIV neutralising antibodies, named CAP256-VRC26, after several months of infection.

Using techniques similar to those employed in an earlier study of HIV-antibody co-evolution, the researchers analysed blood samples donated by the volunteer between 15 weeks and 4 years after becoming infected.

This enabled them to determine the genetic make-up of the original form of the antibody; identifying and defining the structure of a number of the intermediate forms that the antibody takes as it mutates toward its fullest breadth and potency; and to describe the interplay between virus and antibody that fostered the maturation of CAP256-VRC26 to its final, most powerful HIV-fighting form.

The study revealed that after relatively few mutations, even the early intermediates of CAP256-VRC26 can neutralise a significant proportion of known HIV strains.

Buoyed by their positive results, the researchers have begun work on a set of vaccine components designed to elicit V1V2 neutralizing antibodies and guide their maturation.

The results will be published in a report titled ‘Developmental pathway for potent V1V2-directed HIV-neutralizing antibodies’ in the upcoming edition of the journal Nature.