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New Front in AIDS War

By Sean Henahan, Access Excellence

Bethesda (12/01/02)- Some 20 years after HIV first appeared, AIDS has reached pandemic proportions with dire long-term socioeconomic and political implications for both the developed and developing world. An effective vaccine remains the elusive but essential goal of biological researchers around the world. A new generation of vaccines now entering clinical trials could represent an important new front in the battle against AIDS.

HIV, the virus that causes AIDS, poses a particularly difficult challenge to vaccine developers. For one thing, there are several strains of the virus circulating in the world, and an effective vaccine would need to immunize the public against all of the major strains. Second, the virus is constantly mutating as part of its strategy to elude the immune system, so an effective vaccine would need to disable the virus in spite of these mutations. Early candidate vaccines targeted one strain of the virus, and tended to attack or block the virus on one front only. The new generation of vaccines are designed to block the virus on several fronts.

Most HIV vaccine candidates that have been developed so far have been designed to generate antibodies to a protein called gp120 that is found on the surface of the AIDS virus. While some of the vaccines have elicited immune responses to some forms of gp120, researchers have a had a hard time developing a vaccine that can generate antibodies against the many forms of gp120 that occur naturally.

In November of this year, clinical trials began with a new vaccine that targets the three most globally important HIV subtypes, or clades. The vaccine incorporates genetic material from the A, B and C clades of HIV, which together are associated with some 90 percent of all HIV infections worldwide.

"This is the first multigene, multiclade HIV vaccine to enter human trials. It marks an important milestone in our search for a single vaccine that targets US subtypes of HIV as well as clades causing the global epidemic," said Anthony S. Fauci, M.D, Director of the National Institute of Allergic and Infectious Diseases.

The novel vaccine incorporates modified elements of four HIV genes known as gag, pol, nef and env. Previous clinical trials have shown that this type of DNA vaccine is very safe and cannot induce HIV infection. Each of the HIV genes play an important role in infection. For example, the env gene codes for a protein on the outer coat of the virus that allows it to recognize and attach to human cells. The current candidate vaccine includes env components from several HIV subtypes.

The researchers say that the current trial represents an important step in an ongoing process of HIV vaccine development. If an when the multicalde vaccine is shown to be safe and to elicit an effective immune response, the researchers would then add additional HIV protein components in an attempt to increase the immune response even further.

"Ultimately, we aim to build a potent vaccine designed to prevent HIV infection. Any HIV vaccine must hit a constantly moving target. Essentially, we are trying to enlarge that target through a multiclade vaccine," notes Gary Nabel, M.D., Ph.D., director of the Dale and Betty Bumpers Vaccine Research Center where the vaccine was developed.

The initial stage of the trial is being conducted at the National Institutes of Health in Bethesda, MD. The Phase I trial will enroll 50 volunteers who are not infected with HIV and is designed solely to confirm the safety of the vaccine. Volunteers between the ages of 18 and 40 years old will be vaccinated with either the test vaccine or an inactive placebo solution in a series of increasing doses. The trial is a double-blind design, meaning neither the volunteers nor the doctors will know which group receives the active compound. The researchers will check the volunteers regularly for one year to look for immune responses and adverse effects. Once the safety of the vaccine has been established, the trial will be expanded to include volunteers in the US, Haiti and South Africa

"We want the community to understand and support the process of vaccine development so that together we can attain the goal of stopping or slowing the AIDS pandemic. Although thousands have already volunteered to take part in HIV vaccine trials, many more are needed. The importance of community participation cannot be overemphasized," notes Barney Graham, M.D., Ph.D., lead investigator in the multiclade vaccine trial.

Clinical trials are ongoing around the world with both therapeutic and prophylactic HIV vaccine candidates. Prophylactic vaccines are the more familiar kind that are designed to prevent infection with a virus, e.g. the small pox, influenza and varicella vaccines. Therapeutic vaccines are those which might prove useful in bolstering the immune response of those already infected with HIV. There have been more than 50 HIV vaccine clinical trials since 1988, involving more than 26 different vaccine candidates. More than two dozen clinical trials are now underway, although only one has reached the final Phase III stage.

There is a growing consensus among researchers that an effective vaccine against HIV infection will be developed within the next ten years. Public health authorities will then face a new set of logistic and political challenges as they determine how to get the vaccine to where it is needed most in a long-term global effort both in the the developed world and in areas of the developing world already decimated by the effects of the pandemic.

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