SOUTH African scientists have discovered how some people can make potent antibodies capable of neutralising strains of HIV, taking researchers a step closer to developing a vaccine.
A vaccine that prevents HIV infection has proven elusive for decades, partly because there are many different varieties of the rapidly evolving virus. One of the strategies scientists are exploring is how to produce a vaccine that prompts the body to make "broadly acting antibodies" that combat multiple strains of HIV.
Scientists have known for some time that about one in five people infected with HIV is capable of making these powerful antibodies after they have been infected for several years, but exactly how they arise has been a mystery.
But now a team of South African scientists has discovered that when the virus evolves to evade its host’s immune system by adding a sugar molecule to its surface, the host’s antibodies adapt to recognise the sugar in such a way they can kill nine of 10 known strains of HIV.
"We’re hoping we can use this information to develop a vaccine that prompts the body’s immune system to make broadly neutralising antibodies," said Penny Moore, lead author of a paper describing the discovery, published in the journal Nature Medicine on Sunday, and a senior scientist at the National Institute for Communicable Diseases (NICD).
The study is based on blood samples taken at regular intervals over several years from two women infected with HIV, enabling scientists to study how both the virus and the women’s antibodies have changed over time, she said.
The scientists found that a sugar molecule called a glycan, located at a specific point on the virus’s outer protein coating labelled 332, prompted the immune systems of these women to make antibodies that killed 88% of HIV strains.
Unfortunately these broadly acting antibodies do not cure HIV, but they do stop it from infecting healthy cells, said Dr Moore. "They don’t help the people who develop them at all, because the virus is already established," she said.
The scientists found that the glycan at position 332 was present in about two thirds of HIV-C, the subtype circulating in Southern Africa.
This means a vaccine that targets just this glycan would be only partially effective, and suggests a vaccine would need to take aim at multiple weak points in the virus, said Dr Moore.
The study was conducted by a consortium from the Centre for Aids Programme of Research in South Africa (Caprisa), the NICD, the universities of Cape Town and KwaZulu-Natal, and the US universities of North Carolina and Harvard.
"Like all science, this study now needs to be replicated by other researchers," said consortium leader Prof Salim Abdool Karim, president of the Medical Research Council and co-director of Caprisa.
The discovery was welcomed by John Mascola, deputy director of Vaccine Research Center. He said: "Once we can see how (broadly neutralising antibodies) arise naturally, during infection, it becomes much more realistic to think that we can design vaccine strategies to induce similar neutralising antibodies."
Funding came from the Department of Science and Technology, the NIH, and the Bill and Melinda Gates Foundation. Prof Abdool Karim said the consortium would not patent its findings. "The knowledge we generate belongs to the world," he said.
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