Plans are under way to try the so-called trispecific antibody in initial human trials before the end of 2018, potentially adding a new weapon in the fight against AIDS, assuming the product proves safe and effective.

If all goes well, the three-in-one antibody could be used either as a long-acting treatment or a vaccine, according to Sanofi Chief Scientific Officer Gary Nabel.

"There is certainly urgency for a vaccine and this could help fill that void," he said in an interview. "But we need to do the clinical studies and let nature tell us what works."

Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, whose experts collaborated on the project, described the new approach as "intriguing".

Unlike naturally occurring antibodies, the laboratory-made ones hit multiple biological targets in a single product - a feature that is particularly valuable in fighting HIV, given the huge genetic diversity of viruses around the world.

After exposing 24 monkeys to two strains of a monkey form of HIV, researchers found the majority of those given a traditional antibody developed infection compared with none of those receiving the trispecific one.

The results were published in the journal Science on Wednesday.

Other experiments showed the novel antibodies were active against 99 percent of more than 200 diverse strains of HIV tested.

The ability of trispecific antibodies to hit three targets at once might also make them useful in fighting cancer, other infectious diseases and autoimmune diseases. A number of drug companies are already working with bispecific antibodies but a three-pronged approach takes things to the next level.

"This is the beginning of a technology platform that we could adapt to other diseases, so we will look carefully at that," Nabel said.

(Editing by Louise Heavens)

By Ben Hirschler