|HIV Fighters Hit 'Superinfection' Roadblock|
Just when they thought an effective anti-HIV vaccine could be at hand, government-funded researchers discovered a person suffering from a second strain of HIV despite having undergone effective drug treatment for the first.
"For the first time, we've shown it is possible for an individual to become infected with two closely related strains of HIV," says Bruce D. Walker, M.D., a grantee of the National Institute of Allergy and Infectious Diseases (NIAID) and a researcher at Massachusetts General Hospital and Harvard Medical School.
HIV 'Superinfections' challenge researchers
The discovery of this patient underscores the complex challenge of developing a broadly effective vaccine against HIV, said Dr. Walker. Rather than completely preventing infection, Walker suspects that currently available vaccines may keep HIV from leading to AIDS by limiting the virus' ability to reproduce. Unfortunately, the appearance of a second, or "superinfection" shows that a vaccine effective against one strain of HIV my offer the patient no protection at all against other, closely related strains.
"The implications of superinfection for an individual with HIV/AIDS are not yet clear," says Anthony S. Fauci, M.D., NIAID's director. "However, there is little doubt what these new data mean in terms of public health: It is imperative that safer sex be practiced during each encounter, even when both partners are HIV-infected."
Dr. Walker's team had held under control for several months using a technique called "structured treatment interruption," or STI. In STI, medications are applied frequently during early stages of HIV infection, but are reduced or even halted once the patient's immune system stabilizes. In some cases, the patient's immune system is strengthened enough to fight off the HIV infection by itself. "This patient's immune response against HIV was really quite robust," said Dr. Walker. After successfully suppressing the patient's HIV for over a year, the researchers were understandably puzzled when symptoms of the virus returned. The patient subsequently failed to respond to continued STI therapy.
Amino acids point to second HIV strain
To find out why their treatment had failed, Dr. Walker and his co-investigators, "dissected the immune system" of the patient. They found that the amino acids produced by the HIV virus during the successful STI treatment differed from those produced after STI had failed. The difference in amino acids, the researchers determined, had resulted from infection by a second strain of HIV appearing well after the first had been controlled.
While previous cases of superinfection had been reported, they had all involved simultaneous infections by different subtypes of the HIV virus. The case found by Walker's team is the first published report of infections by two strains from the same HIV subtype. "We were stunned," said Dr. Walker. "Essentially, the [patient's] immune system was encountering two markedly different viruses."
A little good among the bad
On the positive side, the researcher's study of the superinfected patient revealed an expanded ability of the body's own HIV-fighting cells, called "T cells," to battle the virus. According to Dr. Walker, the patient's immune system produced new T cells (CD8+ T) that responded correctly to the attack of the second HIV strain, even under conditions of chronic infection. As a result, researchers expressed cautious optimism that vaccines effective in treating persons with chronic HIV infection remained a possibility.
- The report on this research, titled "AIDS: Double Infection" is published in the Nov. 28, 2002 edition of Nature magazine.
NIAID is a component of the National Institutes of Health (NIH), which is an agency of the Department of Health and Human Services. NIAID supports basic and applied research to prevent, diagnose, and treat infectious and immune-mediated illnesses, including HIV/AIDS and other sexually transmitted diseases, illness from potential agents of bioterrorism, tuberculosis, malaria, autoimmune disorders, asthma and allergies.
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