Antibodies fight back against HIV
But hope for a therapeutic vaccine against AIDS is limited.
AIDS is notorious for its ability to deceive and destroy the human immune system. Now researchers have shown that part of that system can fight back: certain antibodies can deliver a short-lived blow against the virus.
The result comes with good and bad news. It lends support to the idea that therapeutic vaccines, which are designed to be taken after someone is infected, might work against AIDS. But the effect is so limited, the authors say, that a simple dose of antibodies alone will not do a patient much good.
The current best treatment for AIDS involves drug therapy with antiretroviral compounds: medicines that attempt to stop HIV replicating in the body. But these can produce unpleasant side-effects. Some people develop gastrointestinal problems and chronic nausea, for example.
To give HIV patients more options, researchers have studied the use of antibodies, the proteins in the body that naturally hunt down and destroy infections. But this has proved a difficult strategy. HIV is very good at dodging antibodies by undergoing rapid genetic mutations that make it unrecognizable.
Researchers have had to hunt down special varieties of antibodies that can recognize a broad range of viral targets, but it is uncertain whether even these will work in a vaccine. They do seem to work against HIV in test tubes and in animal models, says Huldrych Günthard of the University Hospital in Zurich. And some people with HIV who produce such antibodies naturally seem not to develop AIDS, but such evidence of the worth of these antibodies for humans is considered circumstantial.
To pin down how well such antibodies work, Günthard and his colleagues gave regular doses of three promising varieties (called 2G12, 2F5 and 4E10) to HIV patients who had recently been taken off antiretroviral treatments. The researchers then monitored levels of virus in the blood, to see if the antibodies could hold back viral replication.
In patients who received antibody doses, it took about 8 weeks for the virus to reach levels of 10 copies per millimetre of blood. In contrast, this increase took only 3.5 weeks in a control group.
The increase means the antibodies aren't nearly as effective as antiretrovirals. But the delay in viral replication provides direct proof of the immune proteins' ability to fight against HIV, says Günthard. His results appear this week in Nature Medicine1.
However, the limited response means that a dose of antibodies is unlikely to prove a useful treatment on its own. And there are still problems in sourcing antibodies, because proteins from one patient need to be able to act against the virus in another patient.
Researchers continue to look for vaccines based on both antibodies and cell-mediated parts of the immune system. No promising vaccines have yet made it through clinical trials.
- Trkola A., et al. Nature Medicine, Advanced Online Publication (2005). Doi: 10.1038/nm1244 (2005).