LONDON, ENGLAND -- November 28, 1997 -- Although developing a vaccine against the human immunodeficiency virus (HIV) is likely to prove to difficult, there is hope that it can be done, write two researchers in this week's a The Lancet.

The main obstacle to vaccine development is HIV's high replication and mutation rate, said professor Charles Bangham of the Imperial College School of Medicine in London and Rodney Phillips of John Radcliffe Hospital in Oxford, England. Like other RNA viruses, HIV replicates very quickly -- and very sloppily. As a result it frequently makes mistakes when it makes copies of its genetic code.

These mistakes can be harmful to the virus, but they can also turn out to be advantageous mutations that allow the virus to evade the immune system and resist antiviral drugs. In fact, HIV mutation rate is so high that not only is there significant genetic variation in viruses found in different populations, there are often significant genetic variations between strains found in a single individual. Therefore, to be effective, any HIV vaccine will have to protect against more than one strain of virus.

Another major obstacle to HIV vaccine development is the virus' ability to make a DNA copy of its genome which then hides within a person's chromosomes. The presence of these silent DNA copies of the virus cannot be detected by the immune system. As a result, even if it were possible to wipe out all the actively replicating RNA forms of the virus, the infection could still re-emerge when, for whatever reason, the hidden viral DNA becomes reactivated.

The reason for hope that despite these problems an HIV vaccine can be made, Bangham and Phillips said, is the fact that the human immune system does seem to be able to suppress HIV at least early in the infection. There are also evidence from animal and human studies that infection with a weakened -- and possibly harmless -- version of the virus may protect against infection by more virulent disease-causing strains.

The challenge facing vaccine researchers today, said the authors, is to find out exactly which components of the immune response to HIV a vaccine must stimulate if it is to be able to prevent, or at least, contain the infection.

Thanks to The Doctor's Guide to the Internet™ for the article