Human trials of AIDS vaccine to begin in Africa

A special report from Rick MacInnes-Rae "AIDS in Zimbabwe"

DURBAN, SOUTH AFRICA — At the World AIDS Conference in Durban, there's word that the first AIDS vaccine designed specifically for Africa will enter human trials this summer.

It's hoped the experimental vaccine will prevent infection by a particular strain of HIV.

Across Africa, more than 25 million people are believed to be infected. A vaccine could prevent others from getting the virus.

But even if the vaccine is effective it will not be widely available for many years.

There are many AIDS vaccines under development in laboratories around the world, but this one is different. It's designed to prevent infection by the A-strain of HIV-1, the virus found in many parts of Africa.

The experimental vaccine has just received approval for phase one tests in humans.

"The point of this phase one study will be to confirm the safety of the vaccine and look at the immune responses that it stimulates," said Dr. Andrew McMichael of Oxford University, who was involved in its development.

The vaccine is a so-called DNA vaccine, meaning that it's based on genetic material taken from the virus. The material is not infectious, so the volunteers who will be injected with it do not run a risk of contracting HIV.

The inspiration for this vaccine comes from a study involving Canadian researchers. Dr. Frank Plummer of the University of Manitoba has been following a small group of Kenyan prostitutes for several years. The women are remarkable because they appear to have a natural immunity to HIV infection.

Dr. McMichael says their bodies produce a type of microbial hunter called killer T cells, that find and destroy HIV.

"These are exactly the T cell responses, the immune responses, that the highly exposed sex workers in Nairobi make. And these women are resistant to HIV infection," he said. "This is a tiny minority of the sex workers, but those who are resistant make this type of immune response that we're after.

"So this is what we're trying to mimic with the vaccine," he said.

With 25 million people infected on the African continent the vaccine trials are coming not a moment too soon. But the road from trials to an effective vaccine is very long and full of unknowns.

Even if the vaccine works by preventing HIV infection, researchers say it will be another five to 10 years before it can be available for widespread use.

Chances are millions more will become infected before then, and many will die.

Faced with the sobering knowledge that a vaccine is still far away researchers are trying to make the most of the drugs they have for AIDS. Dr. Mauro Schechter is with the B.C. centre for excellence in HIV/AIDS in Vancouver. He says doctors face serious choices.

"The thing what we have to rethink is how best to use them and should we be using them for persons who are less immuno-compromised, who have less risk of developing any disease in the near future," he said.

One treatment strategy being considered is called 'structured intermittent therapy.' Rather than a continuous course of treatment this method keeps those treated on a cocktail of drugs for a specific period, after which they get a break for several weeks, when no drugs are taken.

Another variation is one week on, the next week off. The effect of this, according to U.S. researcher Anthony Fauci, is a dramatic lowering of the amount of virus in a person's body.

"This brought us to the conclusion that we really need to divert our attention from eradication to what I call the long term rational control of HIV disease."

Fauci says much more research is needed on the benefits of interrupted therapy. Yet it holds promise for developing countries in Africa which cannot afford the life-prolonging, but highly expensive drugs now available in the developed world.