Scientists have discovered an antibody that can neutralise 98 percent of HIV strains.
The strength and dynamism of the antibody - known as N6 - means it could be developed and re-purposed to treat and prevent HIV infections.
Remarkably, the research team at the US National Institutes of Health have found N6 can neutralise 16 of the 20 strains which have so far resisted all kinds of medication.
It is the most promising discovery to date after decades of failed attempts to neutralise the virus, which rapidly changes its surface proteins to evade recognition.
The last time HIV researchers made such a strong leap in the field was in 2010, with the discovery of an antibody called VRC01.