Prof Jonathan Weber, from Imperial College London, said those on the 48-week regime "end up with much higher CD4 cell count and a much lower viral load".

BBC: Early HIV drugs 'slow virus down'

The researchers used a sophisticated statistical modeling technique to assess viral load and CD4 cell loss in more than 2, 800 patients with HIV who were not receiving treatment.

BBC: Cell infected with HIV

But gp120's innards are exposed for 30 minutes or so while the protein is hooked to its human receptor, called CD4, in preparation to invade a cell.

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Two specific types of immune system cell that attack invaders - CD4 T-cells and natural killer cells - increased in number with age, with a higher rate of increase in women than in men.

BBC: Biological clue to why women live longer than men

Eventually, he began to study an antibody called Ibalizumab that was designed to block HIV from attaching to CD4, the primary receptor used by the virus to infect a cell.

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