Map of life expectancy at birth from Global Education Project.

Monday, December 08, 2008

The argument from authority

The CBS News web site is headlining the story that Luc Montagnier, who is about to receive a Nobel prize as co-discoverer of HIV, thinks there will be a therapeutic vaccine within 4 to 5 years. The reporter at least has the wit to add "He did not elaborate as to why he believed scientists were close."

Indeed, that is a puzzle. Montagnier is certainly outside of the consensus of scientific opinion on this question. It is puzzling and a bit unsettling that he would say this, since any statement by him on this subject is bound to become a major news story. Montagnier's current work does focus on approaches to an HIV vaccine, but this doesn't necessarily constitute an endorsement of his views. It is an occupational hazard for scientists to be overly optimistic about the prospects for their own work.

A balanced, in-depth view of the current state of the quest is given by Anthony Fauci in this interview with Scientific American's Nikhil Swaminathan. When Motagnier first discovered HIV, people assumed it would be only a matter of a few years before a vaccine could be developed. Bill Clinton set a goal of developing a vaccine by this year; but in fact we're nowhere close. As Fauci puts it, in a nutshell, vaccines work by mobilizing the body's natural defenses against a pathogen; but humans do not mount an effective immune response against HIV in the first place. You can't boost what doesn't exist.

Actually it's more complicated than that. The immune system does keep HIV in check for quite a while. Untreated people do not develop AIDS for several years, typically a decade. But their immune systems do not prevent the virus from replicating or eliminate it from the body. Rather, the cells that HIV preferentially destroys, immune system cells called helper T-cells, continue to reproduce as fast as HIV destroys them; but eventually, the virus wins the race.

The two major reasons why HIV defeats the immune system are a) its envelope proteins hide, they aren't readily recognized by the cells that normally produce antibodies against viruses; and b) HIV mutates rapidly, so that a vaccine that might be effective against a given strain will not be effective against the multitude of strains that infect any single individual. Another big problem is that there are long-term reservoirs of HIV in infected people that are completely inaccessible to the immune system, or to antiretroviral drugs, from which the virus can continually re-emerge. (By the way, it has been shown that people are initially infected by only one or two viral particles, and early in the course of infection have homogeneous virus; but the virus quickly mutates into multiple varieties.)

Unfortunately, there is no solution to these problems on the horizon. It would be unfortunate if Dr. Montagnier's optimism deflects our attention from what we already know how to do: prevent transmission of HIV by encouraging safe behavior. In this field, many of the most important principles of public health are highly salient. More to come on that subject.

1 comment:

roger said...

nice use of the title for this post.

too many of us seem to want a pill to solve all health problems or complaints. sometimes a change in behavior is more effective and less dangerous than medicine.