HIV superinfection key to vaccine, say experts

Saturday April 7 2012

By Christabel Ligami

Women infected by two different strains of HIV — a condition known as HIV superinfection — have more potent antibody responses that block the replication of the virus compared with women who have only been infected once, according to a study in the PLoS publication.

Researchers from the University of Nairobi, University of Washington and Fred Hutchinson Cancer Research Center’s Institutional Review Boards found that women who had been infected twice not only had more potent antibody responses, but some of these women had “elite” antibody activity.

“This means that they have a broad and potent ability to neutralise a wide variety of strains of HIV over a sustained period time,” said Julie Overbaugh, a researcher at the Hutchinson Center’s Human Biology Division.

The researchers tracked the immune activity of 12 superinfected women from Mombasa in Kenya, over a five-year period and compared each to a control group of three women infected with only one strain.

They assessed the ability of antibodies present in the superinfected and singly infected women to neutralise a spectrum of circulating HIV-1 variants.

This enabled them determine whether the presence of two viruses compared with one made a difference in immune response.

The researchers then controlled for variables such as antibody response prior to super infection and biomarkers of immunity such as CD4+ T cell count and viral load.

“From our study we found that superinfected women had, on average, 1.68 times more neutralising antibodies than non-superinfected women, and they scored much higher in their ability to neutralise the virus and also superinfected women had 1.46 times greater potency than the singly infected women,” said Dr Overbaugh.

It is estimated that only about 1 per cent of people with HIV are so-called “elite neutralisers” who are able to potently neutralise multiple subtypes of the virus.

“Individuals who become superinfected with a second virus from a different partner represent a unique opportunity for studying the antibody response and may provide insights into the process of developing broad neutralising antibodies that could inform HIV vaccine design,” she said.

The study suggests that harbouring a mixture of different viral strains may be one way to promote a robust antibody response.

“The findings also suggest that being infected with two different HIV strains not only leads to a strong response, but also a more rapid response that is capable of recognising many other HIV strains,” said Dr Overbaugh.

An HIV vaccine is considered the best approach to long-term protection from HIV infection, but attempts to develop such a vaccine so far have meet with limited success.

“The holy grail of an HIV vaccine is to elicit antibodies to the virus because antibodies have been shown to block virus infection. But there has been little progress in determining how to elicit such antibodies with a vaccine,” said Dr Overbaugh.

“The study of HIV infected individuals who have developed strong antibody responses to the virus may shed light on the best approach to design a vaccine that will induce an effective immune response.”