Llama antibodies may hold key to broad-coverage flu vaccine

Flu season is well underway but researchers continue to look for ways to improve vaccines against flu viruses, and llamas may hold the key.

A new report from the Scripps Research Institute, published in Science, suggests that llama antibodies can be developed into a mega-protein that can protect against a multitude of flu viruses. The protective antibodies found in llamas were used to create a nasal spray that researchers gave to mice that were then injected with 60 fatal doses of various flu strains. The nasal vaccine provided protection against 59 strains of both influenza A and B in the mice, according to the study. The only flu strain for which the vaccine was not effective in this trial was an avian flu-one that is not known to infect humans.

Researchers attribute the success of llama antibodies to their size. The antibodies are so small, according to the report, they can bind to recessed binding sites on flu viruses and keep them from replicating. The vaccine was given as a nasal spray rather than an injection to provide the most potent contact in the respiratory tract where infection originates, therefore concentrating the antibodies where infection may be most rampant.

Joost A. Kolkman, PhD, a project director with Janssen Pharmaceuticals who collaborated on the study, said the study is the first to find an antibody that can neutralize activity against both influenza A and B viruses.

“None of the broadly neutralizing HA antibodies (bnAbs) discovered to date are capable of directly neutralizing both influenza A and B. In addition, almost all bnAbs show a large variability in neutralization titers and fail to neutralize one or more influenza strains that have been circulating in humans,” Kolkman said. “The unique neutralization profile of the multi-domain antibody opens up the possibility of a passive immunization strategy that protects against all seasonal and pandemic influenza strains.”

Llama antibodies have been studied for some time due to unique properties that make them ideal for drug development, Kolkman said.

“They can bind to epitopes that are not accessible to conventional antibodies because of their small size and shape. In addition, they can be easily linked together to create multi-specific antibodies binding to different epitopes on the same or different targets,” Kolkman said. “Multi-specificity is key to obtain broad coverage of highly variable pathogens like influenza.”

While the research is promising, Kolkman said it is too to map a future for this vaccine. Researchers are now working to determine what additional studies will be needed to progress to trials for prophylactic use.