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.
VRCO1 can stop up to 90 percent of HIV strains from infecting human cells.
It works in the same way as N6: both block the virus by binding to a part of the HIV enveloped called the CD4 binding site.
This prevents the virus from attaching itself to immune cells.
However, N6 can better tolerate changes in the HIV envelope.
For example, one of the key ways HIV evades the immune system is by gathering and attaching sugars, which tend to loosen the antibody's grip. N6, however, is not affected by this change.
The findings, revealed in a report on Wednesday, have emerged as scientists continue to test N6 as an intravenous infusion in clinical trials to see if it can safely prevent HIV infection in humans.
Due to its potency, N6 may offer stronger and more durable prevention and treatment benefits, and researchers may be able to administer it subcutaneously (into the fat under the skin) rather than intravenously.
In addition, its ability to neutralise nearly all HIV strains would be advantageous for both prevention and treatment strategies.