HIV's genius is variability: its envelope protein mutates so fast that antibodies raised against one strain usually fail against the next. Researchers at Karolinska Institutet, with colleagues at Scripps Research and Emory University, report in Nature a vaccine strategy that steers the immune system towards one of the virus's few stable weak points, the apex at the tip of the envelope spike, which changes little between strains.
Rhesus macaques received liposomes carrying a selected HIV envelope protein, followed by booster immunisations in which the protein was progressively altered to guide antibody maturation towards breadth. The result was remarkable consistency: every vaccinated macaque developed broadly neutralising antibodies, which also neutralised highly divergent strains the animals had never been exposed to. Structural analysis showed the vaccine-induced antibodies bind the apex in a manner resembling PG9, a well-characterised broadly neutralising antibody originally isolated from a person living with HIV.
The authors are clear about what the study is and is not: an animal experiment offering proof that the immune system can be deliberately guided to a protected viral site, not an imminent human vaccine. Even so, after decades in which broadly neutralising responses seemed almost impossible to vaccinate into existence, achieving them in every animal marks genuine progress.