If the immune system could respond to quickly mutating viruses like HIV as fast as the viruses mutate, it could defeat them, suggests a mathematical model of viral and immune evolution. Photo by Ezume Images/Shutterstock
PHILADELPHIA, July 22 (UPI) -- Scientists have been unable to create a vaccine against or cure for HIV because the virus changes so rapidly, with many different strains in a patient's body because the immune system cannot react fast enough -- but given enough time, it might be able to, according to a new study.
Researchers at the University of Pennsylvania created a mathematical model to study the potential for the immune system to evolve fast enough to effectively battle the virus at the same speed it changes, though they note the idea remains entirely theoretical.
During an infection, the immune system produces antibodies that proliferate based on their success rate against the cause of the infection. While broadly neutralizing antibodies are capable of attacking HIV, its mutation rate outpaces antibody production, so eventually the immune system loses.
In the new study, however, the researchers propose finding a way to train the immune system by exposing it to a wider set of viral antigens so the broadly neutralizing antibodies are better armed against invaders that mutate during infection. The theory may even extend to diseases with multiple strains, such as the constantly evolving influenza virus, they say.
"The model that we built was able to show that, if viral diversity is very large, the chance that these broadly neutralizing antibodies outcompete more specifically targeted antibodies and proliferate goes up," Dr. Armita Nourmohammad, a researcher at Princeton University who worked with University of Pennsylvania researchers on the study, said in a press release.
For the study, published in the journal PLOS ONE, researchers designed a model to look at how mutations affect the binding of antibodies to viruses. The model calculates the average binding between entire populations of viral strains and antibodies over time, allowing the researchers to see patterns of how they evolve.
The model revealed an S-shaped curve suggesting the speed of mutation is key to whether a viral invader can survive the onslaught of the immune system.
To verify the model, the researchers compared its results to data from two HIV patients showing how antibodies competed against viruses at different times during their HIV infection. They saw that, at times, the immune system begins to get the upper hand against the virus, but when the virus mutates, antibodies cannot evolve fast enough to match the new mutation.
If a method were found to train the body, through a vaccine or otherwise, however, the researchers say the potential is there for a virus such as HIV or influenza to be beaten using the immune system itself.
"This isn't a prescription for how to design an HIV vaccine," said Dr. Joshua Plotkin, a professor at the University of Pennsylvania. "But our work provides some quantitative guidance for how to prompt the immune system to elicit broadly neutralizing antibodies."