The researchers note that their approach was based on a long-held hypothesis that conventional vaccines – that rely on stimulating an immune response to a microbe in advance of exposure to it – could not work in HIV, as this virus uses the very cells that proliferate in an immune response (primarily CD4 T-cells) as the ones it chooses to reproduce in. The trick with an HIV vaccine would therefore be to induce the body to recognise HIV but not mount a proliferative response to it. This could work if the body is induced to respond to HIV as if it was harmless – to induce so-called immune tolerance to it.