Q&A: HIV Vaccine
Q: HIV has been around for a while now. Why isn’t there a vaccine yet?
A: Good question, not an easy answer. First of all, in the scheme of things, HIV has not been around a while. Both French and American research teams isolated HIV as the causative agent in AIDS in 1983. The American team named it Human T-cell Lymphotrophic Virus-3 (HTLV-3) and the French team named it Lymphadenopathy Associated Virus (LAV). In comparison, smallpox virus has been well described in historical sources for millennia and vaccines were developed in the late 60’s. We have vaccines against influenza but not against the common cold virus. We have a vaccine against hepatitis B virus but not hepatitis C virus.
In less than thirty years, we developed more than thirty drugs against HIV. This is a most phenomenal accomplishment in medical history because prior to HIV, we didn’t have very many drugs that selectively controlled viral infections.
So why not a vaccine? It’s not because we haven’t tried. One important challenge is understanding how the immune system controls the virus. The immune system has two basic lines of attack against infections. The humoral response involves the production of antibodies. Antibodies bind to bacteria, viruses, or fungi and block their ability to infect cells as well as helping clear the pathogen from blood and tissue. The cell-mediated response uses special cells in the immune system to destroy infected cells in the body. For viral infection, killing the infected cell also kills the viruses and keeps them from using that cell to reproduce, hence halting an infection. Better to sacrifice the few infected cells than to risk an infection spreading.
To develop a vaccine, we must know how the body most effectively fights the infection. We know that the immune system does indeed control HIV, at least for awhile before the virus gets the upper hand. But we’re still not sure the best way to launch an attack against HIV with a vaccine.
There’s another big problem. In order to develop a vaccine, the vaccine must be designed to target a critical region in the structure of the virus. This is precisely what the immune system does. It recognizes specific regions of the pathogen to launch an attack against it. But HIV has a trick. It is constantly changing the structure of these regions by generating genetic mutations. These changes allow the virus to escape recognition and attack by the immune system. Similarly, it become difficult to design a vaccine directed against a moving target. Some research strategies have involved identifying important regions of the viruses structure that don’t mutate as rapidly. Also, instead of targeting proteins, vaccines are being studied that target the HIV genetic code directly (DNA vaccines). These are some of the challenges for developing a vaccine to prevent HIV infection.
For many years, there has also been intensive research on therapeutic vaccine. These vaccines are used in people who are already infected. The goal is to boost the immune response against the virus while protecting the immune system with HIV drugs. Success has been limited but researchers are constantly studying way to improve this.