Lab scientists say estimates of HIV progression fell short
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Discovery on disease's spread suggests it will be tougher to combat
4/13/2008 - 4/10/08
When it comes to understanding HIV, looking at the big picture sometimes isn't enough.
What's really needed to understand how truly prolific the virus is, is to look at the big movie.
That's what Los Alamos National Laboratories researcher Alan Perelson did when he was trying to figure out how fast the disease replicates throughout the human body.
And it turns out the big movie — a lifetime history of how the disease spreads from a single cell — shows that HIV spreads a lot more quickly than anybody previously thought.
"Previous estimates, which just looked at a cell at a single point in time, suggested that 100 to 200 viruses might be made in each infected cell," Perelson said. "That estimate was later raised to 1,000 to 2,000. But when we looked at a cell over its life span, we found each cell was making approximately 50,000 viruses — and it looks like that's the minimum."
Perelson and other researchers analyzed how much virus was produced in cells of rhesus monkeys, which were infected with a version of simian immunodeficiency virus, or SIV, the simian version of HIV. The two diseases act similarly, so it's reasonable to think that HIV could behave the same way, Perelson said.
In the past, scientists only looked at how much virus was produced from a cell at one specific time — like taking a snapshot. But in the rhesus study, scientists could determine how much virus was produced from a cell over its life span.
"The other method is like looking at a General Motors manufacturing plant and seeing 100 cars on the line and saying, 'Oh, that plant makes 100 cars,' " Perelson said. "But we know it makes a lot more than that over time."
The SIV strain the scientists engineered could infect one cell and produce offspring, but the offspring were defective and couldn't infect any other cells. After the experiment, the researchers searched the body and counted the virus reproduced from the one cell.
A similar test isn't easy to do in humans, because the subject has to be dead before scientists can count how much the virus has reproduced.
But the conclusions are similar for both diseases, he said.
"Overall, though, this tells us the infection is a lot tougher to combat," Perelson said. "Early in the infection, sharing needles, blood, if a small number of cells are transferred, the disease has a larger chance of spreading through the body quickly."
Bette Korber, a LANL fellow and expert on HIV, said the results are helpful as a means to study HIV, although the knowledge can't be directly applied in the creation of a vaccine, which is something she's working on.
"This lets us know more what we're up against," Korber said. "Maybe it tells us something about the efficacy of a vaccine. Maybe you can't protect against infection, but you could try to find a way to stop the progression of HIV."
Now that his study is finished, Perelson will continue his work trying to model HIV and Hepatitis C, incorporating the new information, he said.
Los Alamos has a group dedicated to working on HIV and other diseases, which sprang out of the lab's work mapping the genome, he added.
"A number of scientists at LANL have been aggressive and gotten funding for some very important problems like this, to help the nation and the world," Perelson said.
And this step, while not a cure, at least reveals another piece of the puzzle that could one day help scientists find a cure, he said.
"You have to know your enemy before you can fight it," Perelson said.
Contact Sue Vorenberg at 986-3072 or svorenberg@sfnewmexican.com.
