Researchers into HIV said they had identified 17 potent antibodies whose discovery opened up valuable pathways in the search for an AIDS vaccine.
Antibodies are the foot soldiers in the immune system, latching onto viral or microbial intruders and tagging them for destruction by specialised "killer" cells.
Priming antibodies to recognise pathogens is a textbook method in vaccines, although it has proven agonisingly hard in the case of the human immunodeficiency virus (HIV) which causes AIDS.
The new "broadly neutralising" antibodies are the biggest single haul so far and also many times more potent than those found previously, the scientists report in Thursday's issue of the British journal Nature.
"Most antiviral vaccines depend on stimulating the antibody response to work effectively," said Dennis Burton of the Scripps Research Institute in La Jolla, California.
"Because of HIV's remarkable variability, an effective HIV vaccine will probably have to elicit broadly neutralizing antibodies. This is why we expect that these new antibodies will prove to be valuable assets to the field of AIDS vaccine research."
The International AIDS Vaccine Initiative (IAVI), a US NGO that sponsored the search, said the quest for HIV-neutralising antibodies was "perhaps the greatest challenge" facing vaccine engineers.
The 17 antibodies were isolated from four individuals with HIV, an achievement similar to looking for a needle in a haystack as only a very small number of people produce these powerful molecules.
AIDS has claimed some 30 million lives since the disease came to public notice in 1981. Around 34 million people today are infected with HIV, according to UN estimates.