Is an HIV vaccine on the horizon

Dewi Anggraeni, Contributor, Melbourne

No one in Indonesia, or in the region for that matter, can pretend that HIV/AIDS is an insignificant problem as available data shows that the illness has affected at least one in every 1000 in the population.

Since an effective medication has not been found, physicians explored measures to reduce its effects and prevention programs during the recent International Congress on AIDS in Asia Pacific (ICAAP) held in Melbourne, Australia, from Oct. 5 to Oct. 10.

Dr Margaret Johnston, a vaccine expert from the National Institute of Health in the U.S., believes that vaccination is the most cost effective way of preventing the spread of HIV/AIDS. How far then, have the efforts to find an effective HIV/AIDS vaccine progressed?

The following are excerpts from an interview conducted by Dewi Anggraeni with Johnston during the ICAAP.

Question: Why is the vaccine crucial in preventing the disease? How does it work?

Answer: We believe that finding a safe and effective vaccine is the best solution in stopping the spread of HIV. A preventive vaccine would be given to people at risk, so if they subsequently become exposed to the virus, that they either don't become infected at all or if they do become infected, their immune systems are able to handle the virus more efficiently. And they can control the virus and remain healthy, and not spread the virus to other people.

In your presentation you mentioned that a very promising vaccine was coming to the end of its testing period. Could you please explain what this vaccine will be able to do?

There has been optimism from the developed vaccines which have been tested on animals, that it has been able to protect the animals from the disease. So we are optimistic that such a vaccine can be obtained. But we still have to determine which vaccines would work in humans. And this will take time.

Are there trials currently conducted on humans?

The first efficacy trial is currently under way in Thailand, and a separate trial of the same kind of design, in the United States. The results from the North America trial may be available as early as next month. The results from the trial in Thailand will be available half a year later. So by the end of 2002 or the beginning of 2003 we'll have the results from the trial in Thailand.

We don't expect, however, that the first vaccine that shows efficacy will be a hundred percent effective. What we'd like to do is to find something that has some level of efficacy so we can identify why that vaccine works and improve on it.

Are there other vaccines still being developed?

There are many other vaccines that are in earlier stages of development. Another source of our optimism is that this pipeline of potential products is really quite vibrant. Each time we test a vaccine we learn something new, and become smarter about how to design a vaccine. There have been clinical testings of HIV vaccines since 1989. Only one so far has advanced to the final stages of testing.

You mentioned in your presentation that the most difficult problem was to teach our antibodies to recognize the virus.

There are several types of immune responses that we're interested in seeing the vaccine induce. And in particular we want those immune responses to be broadly reactive against the various types of HIV that are circulating in the world. And with respect to the antibody responses, the virus is extremely smart.

It has found ways to trick the immune system into looking at the parts of the virus that are highly variable. But recent research in the laboratory has deciphered more information about the structure of the virus. How the structure changes when the virus binds to the target cell, and enters it.

What have you found?

What we've seen in this laboratory studies is that there are parts of the virus that are highly conserved. These are normally hidden, but become exposed during the infection process. So now researchers are very hard at work in trying to find a vaccine that mimics those conserved regions. That way the vaccine can be used to induce immune responses that specifically recognize those conserved regions. If we can do this, our optimism will be even greater.

The other part of the immune system is the cellular one.

Antibodies bind to free virus particles to prevent them from going into other cells and spreading. There is also a special kind of killer cell that the immune system has, that can recognize cells that are already infected by the virus and eliminate them. So instead of killing the viruses, it stops the viruses producing factories. That type of immune system tends to recognize the portion of HIV that get expressed on the surface of these cells as the virus particles are being formed. And those immune responses are broadly cross-reactive.

It can recognize and kill cells infected by different viruses, not just the one on which the vaccine was based.

HIV around the world is genetically diverse. We classify them by sub-types based on the genetic sequence. There are nine different classes of virus. They circulate in different parts of the world. Ideally we'd like to get a vaccine against HIV that recognizes all of them.

What are the next steps after getting the results?

Once those results are available it'll probably take some time before the vaccine is manufactured in large enough amounts to be made available. We need a manufacturing plant built, a regulatory agency to review all the data and determine whether it is worthy of being licensed to sell. All this might take three or four years.