Scientists in the US have isolated two novel antibodies capable of neutralising more than 90% of HIV strains; they've also unpicked out how one of the antibodies works, bringing the prospect of a vaccine a significant step closer.
NIH researchers John Mascola and Peter Kwong, in a pair of papers in Science, set out how the antibodies, called VC01 and VC02, were discovered and then how they work. The respective teams actually isolated the antibodies from the blood of an HIV-infected patient. By building a molecular "probe" resembling the crucial part of the surface of the HIV particle that binds to a structure called CD4 on white blood cells, the team were able to identify individual blood cells capable of making antibodies to this part of the virus.
They then copied the genes coding for the antibody sequences from these cells and inserted them into new cells that were geared up to make large amounts of the antibody. Tests showed that these antibodies could block infectivity of 90% of HIV strains circulating around the world, suggesting that, if a vaccine could be designed to elicit their production in suspectible individuals, these people could be protected from infection.
But to do this, it's first necessary to understand how exactly these antibodies are working. To find out, Peter Kwong's team then produced and studied crystals of the antibodies bound to the target region of the virus. This revealed exactly what part of the virus the antibodies were recognising, and how, providing the team with vital clues as to how to construct a vaccine, which they are now developing.
So if an HIV-infected individual already makes these antibodies, why should they still have the infection? The answer is that once the virus has infected a person it inserts copies of its genetic material into the DNA of the host, and can also spread by triggering an infected cell to partially fuse with an uninfected cell, enabling the virus to pass covertly between cells, beneath the immunological radar.
But if antibodies were present when a person is first exposed to HIV they would be able to mop up the viral particles before they could infect and cause harm...