Wodarz D, Levy DN. Human immunodeficiency virus evolution towards reduced replicative fitness in vivo and the development of AIDS. Proc Biol Sci. 2007 Jul; 31:2481-2490.
Scientists are hopeful that new research on how HIV infection progresses to AIDS will shed light on new treatments in the future. Using a complex, mathematical model of viral replication and immune cell death, investigators theorize that AIDS begins when a fast-killing strain of HIV dominates over a less-lethal, but more prolific, strain.
For years, scientists believed that various strains of HIV battle amongst themselves until the strongest strain (the one that reproduces itself the most) emerges to overwhelm the body's immune cells and destroys the host's defenses against disease.
In this study, researchers constructed a model that accounted for two factors about HIV: 1. how fast various strains replicate and 2. how fast they kill cells. The model also took into account human immune system responses to HIV.
The results of this study were contrary to popular belief: AIDS begins when a less fit strain of HIV kills immune system cells widely and quickly, but limits the number of copies of itself it can produce. AIDS emerges because this form of HIV is capable of killing large numbers of immune cells quickly. Many times, two or more strains can co-infect the same immune system cell. If a fast-killing HIV strain is one of them, it will kill the immune cell before the slower, better replicating HIV strain can make millions of new viral particles. The authors note that without "ganging up" on the same immune cell, the killer virus that leads to AIDS would go extinct because evolution would select against it. This means that, according to the model, one way of keeping AIDS at bay might be to make sure that only one type of HIV invades a cell at any given time.
Experts are quick to point out that though an interesting concept, the model will need to be tested in a laboratory setting to verify the results.