by Keiron Audain

Created on: October 13, 2009

Given the general pessimism that has engulfed HIV vaccine research, and the dismal outcome of the last major vaccine trial in 2007, there is little doubt that recent results of a combined vaccine that can cut infection rates, warrants a significant amount of praise.

In a statement released by the U.S. Military HIV Research Program and the Thailand Government, a combination of two HIV vaccine candidates has demonstrated approximately 31% effectiveness in a phase III trial conducted in Thailand.

The hope for this regimen is that once the mechanism of how the vaccine actually works is fully understood, scientists can then begin to improve on its design and eventually create a more effective vaccine.

The two vaccine candidates combined in this trial are a neutralizing vaccine, which induces antibodies specific to HIV virus particles, and a cell mediated vaccine, which targets cells already infected with HIV. The significance of these two candidates is that both have performed poorly when tested individually.

The neutralising vaccine applies the concept that an isolated HIV protein (usually a derivative of gp120 - the HIV surface protein that binds to CD4 cells) can induce neutralising antibodies that may deactivate HIV virus particles. The problem with this has been that no HIV protein derivative has thus far been immunogenic enough, meaning they don't induce the right amount or the right type of antibodies. Also, whilst some antibodies may be effective against a particular HIV strain, being the remarkably clever virus that HIV is, its mutation leaves the antibodies futile against the emergent strains.

Scientists have been relentlessly on the lookout for new broadly neutralising antibodies, which are antibodies that target a particular section of the HIV surface protein that has been observed to remain constant during the many mutations of HIV. Only four broadly neutralising antibodies had been identified, none of which were in the past decade. However, two such antibodies may have been found according to researchers from the Scripps Institute in California, the International Aids Vaccine Initiative and biotech companies Theraclone Sciences and Monogram Biosciences. Not only are these antibodies broadly neutralising, but they are also more potent that those previously identified, after having been observed to neutralise close to three quarters of 160 different strains of HIV, isolated from infected donors across the world. Investigations are currently ongoing

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