20100712
allafrica

Researchers have discovered a protein that can protect against a wide range of HIV, and said they may now be able to finally design a vaccine against the fatal and incurable virus.

The proteins called antibodies are used by the body's defence system to identify and neutralise foreign objects, such as bacteria and viruses.

"I am more optimistic about an Aids vaccine at this point than I have been probably in the last 10 years," Dr Gary Nabel of the US National Institute of Allergy and Infectious Diseases, who led the study, said in a telephone interview.

Two of the antibodies can attach to and neutralise 90 per cent of the various mutations of the human immuno-deficiency virus that causes Aids, Nabel said.

There are two main types of the virus: HIV-1 and HIV-2 with the most prevalent in Kenya being the former. HIV-1 is classified into four groups which further fall into several sub-types.

These different strains make it difficult to produce a vaccine that could protect an individual from the virus, mainly because of what is called super infection or co-infection.

This means that a person already carrying the virus can be infected with a different strain. This indicates that a vaccinated person against one strain is not protected against all other strains.

Current approaches also mean researchers have to spend a lot of time and resources testing vaccine for various strains in trials tested in many different localities where differing strains are found.

Theoretically, the new find is the proverbial "hitting many birds with one stone". Using one vaccine candidate, tested in only one location could mean offering a blanket cover against the virus.

The virus is difficult to fight in part because it attacks immune system cells and in part because it mutates constantly, making it a moving, ever shifting target for drugs or the immune system.

It has been almost impossible to make a vaccine that will affect the virus.

Last September, researchers reported their biggest success yet with a vaccine that appeared to slow down the rate of infection by about 30 per cent among Thai volunteers, but the trial left many questions unanswered.

Researchers have been looking for parts of the virus that do not mutate, so they can design a vaccine that will protect against these constantly changing versions.

Nabel's team found two of the antibodies in the blood of a patient infected with HIV who had not become ill despite the infection.

Such people are called non-progressors, and researchers study their immune systems to find out why they control the virus better than most patients. They then found the immune system cells called B-cells that made these particular antibodies, using a new molecular device that they invented.

In yet another experiment, they managed to freeze one of the antibodies in the process of attaching to and neutralising the virus, getting an atomic-level image in a process called x-ray crystallography.

Being able to "see" what the structure looks like could enable researchers to design a vaccine using a process called rational vaccine design, akin to an established technique for making drugs called rational drug design, Nabel said.

It may also be possible to design gene therapy to help patients make these antibodies themselves, or use an older technique that transfuses the antibodies directly.

One of the antibodies, called VRC01, partially mimics the way an immune cell called a CD4 T-cell attaches to a piece of the Aids virus called gp120, the researchers said.

"The antibodies attach to a virtually unchanging part of the virus, and this explains why they can neutralise such an extraordinary range of HIV strains," Dr John Mascola, who worked on the study, said in a statement.

"The discovery of these exceptionally broadly neutralising antibodies to HIV and the structural analysis that explains how they work are exciting advances that will accelerate our efforts to find a preventive HIV vaccine for global use," NIAID director Anthony Fauci added in a statement.

"In addition, the technique the teams used to find the new antibodies represents a novel strategy that could be applied to vaccine design for many other infectious diseases."