06 July 2004
After more than two decades and hundreds of millions of dollars in investments, a cure for AIDS or vaccine to prevent it remain elusive. Scientists say further research is needed to develop powerful weapons against the wily virus that has sickened and killed millions of people around the world.
The news is disappointing. Some 20 years into the epidemic, scientists still know little about the way HIV - the virus that causes AIDS - and the human immune system interact.
Dr. Sean Emery of Australia's National Center in HIV Epidemiology & Clinical Research is heading a team developing a potential AIDS vaccine. "We don't know what bits of the immune system prevent HIV from infecting a person," he says. "We don't know which bits to try and induce through a vaccine and until we get a clearer understanding of that relationship, the approaches that are currently being tested really are best guesses."
The human immune system fights infection by releasing germ-killing antibodies. But HIV is different in that it specifically attacks the antibodies tasked to destroy it. Traditionally, vaccines mimic human immune response. But with a dearth of superior antibodies to work with, scientists are finding it difficult to outsmart HIV.
Dennis Burton, director of the Scripps Research Institute at the University of California, told a recent HIV conference that new approaches are needed. "We really don't have something particularly good to mimic and what we have argued - in the antibody case - is what we need to do is dissect successful neutralizing antibody responses understand them, and turn them to our advantage," he said.
HIV is transmitted from person to person through blood, sexual intercourse and through breast milk from an infected mother.
The United Nations says more than 20 million people have died of the disease since it was identified in the early 1980s. Millions more are infected with the virus, most of them living in developing nations in Africa and Asia.
More than 20 vaccine candidates are currently under various stages of testing around the world. But last year, the most advanced human vaccine trial failed - dashing hopes that a vaccine is only a few years away.
Others say even a partially effective vaccine - one that may not totally prevent infection but reduces HIV transmission or boosts the immune system - would still be a breakthrough.
"We shouldn't really be aiming at something that's never going to be available," says Dr. Emery. "Certainly not in the short term, at the expense of throwing out things that could really have quite a profound and beneficial impact in a number of different settings around the world where all we're doing is watching many, many thousands new infections every year and not being able to prevent that from happening."
With no vaccine, the best hope for HIV infected people are antiretroviral drugs. First developed in the late 1980s, antiretrovirals, or ARVs, slow the speed at which the virus replicates inside the human body. Foiling HIV viral replication slows down the onset of AIDS - making it a manageable, chronic illness.
Current drugs intervene in the HIV replication process after the virus has already attached itself to cells. Researchers are now developing drugs - called inhibitors - that would block HIV from penetrating cells. But the drugs are expensive, cause some serious side effects and have to be taken in certain time-sensitive combinations. Drug companies though are working on reducing the number of pills in the regimen with less toxicity.
But there is a new worry on the horizon: that HIV could become resistant to antiretrovirals.
Dr. Kiat Ruxrungtham, deputy director of the HIV-NAT Thai Red Cross AIDS Research Center in Thailand, says resistance to a single pill alone will make the whole ARV regimen impotent. "When a patient fails in one class, if you leave that failure last too long, you are going to see a high level resistance, so the resistance issue is a problem," he says. "Most of the new drugs in the pipeline will try to solve the resistance issue, but it's not completely solved."
Dr. Emilio Emini, head of vaccine development at the International AIDS Vaccine Initiative in New York says AIDS researchers have to push harder. "What we do as a collective scientific community over the years will determine quite frankly whether or not a vaccine becomes available in the next 10 years or so," he says. "If we don't seize the moment - then the goal - we're gonna have to leave to the next generation."
Dr. Emini's group estimates that while funds for AIDS vaccine development have increased over the years, it remains less than one percent of total spending on health and pharmaceutical related research and development.
Some scientists are hoping that institutions investing in AIDS would look beyond short-term gains and fund further basic research on the virus itself. Unless the mysteries of the virus are discovered, they say, they will not be able to find the right weapon against it.