HIV/AIDS- How far are we from getting a vaccine against the virus?

May 31, 2009

MAY 18 was World AIDS Vaccine Day. The day serves to raise awareness on the need for a vaccine to stop the spread of HIV/AIDS. It is also an occasion to recognise efforts geared towards finding an AIDS vaccine.

By Halima Shaban

MAY 18 was World AIDS Vaccine Day. The day serves to raise awareness on the need for a vaccine to stop the spread of HIV/AIDS. It is also an occasion to recognise efforts geared towards finding an AIDS vaccine.

Disease prevention through immunisation is not a new concept; vaccines have been around for years. The International AIDS Vaccine Initiative (IAVI) is speeding up the search for an AIDS vaccine, the best hope to end the spread of the disease.

Dr. Pontiano Kaleebu, the principal investigator of the vaccine trials, says there is need for a full package of HIV prevention and treatment tools, including a vaccine.

“History shows that no health intervention is more effective at combating viral epidemics than a vaccine,” he says. Currently over 20 potentially fatal diseases can be prevented by vaccines.

Increased access to treatment and prevention has saved about two million lives in low and middle-income countries since 2002, yet the number of people living with HIV increased in the world over the past two years.

“As we do everything possible to treat and care for those who are infected, we must pursue the development of new prevention tools, such as vaccines and microbicides that hold the most promise of halting the spread of AIDS,” he says.

According to Kaleebu, the World AIDs Vaccine Day is meant to help people understand why a vaccine is the best way to stop the spread of HIV, what it will take to develop an effective vaccine and how ordinary people can be part of the international effort to find one.

The development of the vaccine will take time, but there is evidence that it is feasible, so we must persevere, he adds.

A preventive vaccine would be given to people to shield them from infection. “In Africa, most new HIV infections occur among women; a vaccine would protect those who are coerced into unsafe sex.

Vaccines have eradicated smallpox and polio from most countries. We must add AIDS to this list, Kaleebu says.

He explains that 23 years since AIDS was first diagnosed, there are 14,000 new HIV infections everyday.

Magnitude of HIV infection
Each day, almost 12,000 children, women and men become infected with HIV, 95% of them in developing countries.

Last year, AIDS claimed 2.9 million lives. Globally, HIV infection rates among women are increasing and account for nearly half of all new cases.

Among young people aged 15 to 24 in sub-Saharan Africa, HIV-infected young women outnumber their male counterparts four to one.

Hope for a vaccine
Kaleebu says preventing HIV is a challenge, but scientists believe an AIDS vaccine is possible.

To date, there have been several milestones in AIDS vaccine development, marking progress in understanding of HIV and ways to design an effective vaccine against it.

Research has shown that a small number of individuals remain uninfected despite repeated exposure to HIV and that the immune systems of some individuals have the ability to suppress HIV to undetectable levels.

Kaleebu says the biggest challenge in the development of the vaccine is that experiments are carried out in animals before they are tested on human beings. The vaccine may be effective on the animals but fail in humans.

“Developing an AIDS vaccine remains one of the greatest scientific challenges of our time. Developing a new vaccine is a long-term process; it took 47 years to develop the polio vaccine,” he says.

Since robust AIDS vaccine efforts only began in the mid-1990s, there is still a lot of work ahead.

Scientists turn to new methods to fight HIV virus
Unsuccessful at developing vaccines that cause the body’s natural immune system to battle the virus, researchers are testing inserting a gene into the muscle that can cause it to produce protective antibodies against HIV.

The new method worked in mice and has proved successful in monkeys, they reported recently in the journal Nature Medicine.

The team is led by Dr Philip Johnson of the Children’s Hospital of Philadelphia.

That does not mean an AIDS vaccine is in the wings, Johnson said. Years of work may lie ahead before a product is ready for human use.

Dr Beatrice Hahn, an AIDS researcher at the University of Alabama said of the new method: “It shows there is light at the end of the tunnel and that thinking outside the box can yield results.”

Most efforts at blocking AIDS have sought to stimulate the body’s immune system to produce antibodies that fight the disease.

This model has worked for diseases such as measles and smallpox. It has not done as well with HIV/AIDS.

“We used a leapfrog strategy, bypassing the natural immune system response that was the target of all previous HIV and Simian virus (SIV) vaccine candidates,” Johnson said. SIV affects monkeys.

He said the researchers knew there were proteins that could neutralise the HIV virus. They developed immunoadhesins, antibody-like proteins designed to attach to SIV and block it from infecting cells.

They used the adeno-associated virus (AAV) to get the immunoadhesins into the cells. The virus was injected into the muscles and they began producing the protective proteins.

Scientists tested the idea in monkeys because SIV is closely related to HIV and would be a good test model.

A month after administering the AAV, nine immunised monkeys and six which were not, were injected with SIV.

None of the immunised monkeys developed AIDS and only three showed any indication of SIV infection. All six unimmunised monkeys became infected.

The next step is moving toward human trials, Johnson said. He said he is working with the International AIDS Vaccine Initiative to carry out tests in humans in the next few years.
AP

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