LANL: HIV's complexities make work on vaccine difficult
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11/21/2008 - 11/22/08
It's not easy to talk to the human immune system.It doesn't speak English, for one thing. And, so far as we know, it also doesn't see or hear.
Instead it communicates in the chemical and biological dialects of medical science, which to some degree, experts can now actually speak.
Scientists learned that dialect by watching the immune system work, modeling it with computers and then creating vaccines or medicines that help it more quickly understand how to fight off infection.
But when it comes to creating an HIV vaccine, there are no language courses available — because scientists can't find the Rosetta Stone of the disease, which would be to view the body as it successfully fights off an HIV attack, said Ruy Ribeiro, a scientist at Los Alamos National Laboratory's Theoretical Biology and Biophysics Group.
"Usually we see how nature does things with the immune system, and then we try to imitate that — that's how it's been done for other vaccines," Ribeiro said. "But with HIV we don't know what a successful response by the immune system is. We've never seen it. So it's very hard to find a way to replicate it."
Ribeiro spoke about the difficulty in creating an HIV vaccine Tuesday night at the Center for Nonlinear Studies in Santa Fe, as part of a ongoing science public lecture series there.
LANL is heavily involved in HIV research through the lab's efforts to model on supercomputers how the disease works and how vaccines or other strategies would fight it, said Alan Perelson, a scientist, colleague and former supervisor of Ribeiro at the lab.
"Scientists at Los Alamos have been interested in how the immune system functions for the past 30 years, in part because of the computers we've had," Perelson said. "People think of us as just a nuclear weapons lab, but we do a lot more than that."
Perelson, who works for the lab's theoretical biology group, called Ribeiro "one of the talented, young, up-and-coming scientists" at the lab working on the problem of HIV.
And that problem requires a lot of effort by many different scientists around the world, Ribeiro said, because there are so many factors that make finding a cure or a vaccine difficult.
HIV is a retrovirus, which is a type of virus that works in reverse order compared with other viruses. It has an RNA genome and replicates using a host cell's DNA, he said. Usually, a virus uses its DNA genome to make copies of itself using a host's RNA.
Another problem is that the only animals that have a version of HIV that scientists can study are monkeys. And studying a disease in monkeys, as opposed to mice or rats, is a lot more expensive "and it raises ethical issues," Ribeiro said.
Beyond that, the disease replicates very quickly in the human body, and as it replicates, it makes mistakes. Each mistake creates a new strain of the virus, which has caused a huge amount of variability in the types of HIV that exist, even in one person, he said.
"If you compare that with the flu, with flu vaccines, and you think about how you get a new shot each year to protect from the latest strain of the virus, it can give you some idea of what we're looking at," Ribeiro said. "HIV has a huge diversity compared with the flu, which means you need a really good singular vaccine or many, many individual types of vaccine."
In general, it often takes a long time to create a vaccine for any disease, he said.
For example, the cause of pertussus, or whooping cough, was identified in 1906, but a vaccine wasn't available until 1948.
The cause of chicken pox was identified in 1953, but a vaccine wasn't available until 1995.
Meningitis was identified in 1889, but a vaccine wasn't available until 1981.
A vaccine for cervical cancer was developed relatively fast, coming out in 2006, only 25 years after the cause of the disease was identified in 1981.
So considering that the mechanism behind HIV was discovered in 1983, there's probably still some time to wait before the science, clinical testing and other factors come together to create a successful vaccine, Ribeiro said.
"I think there is hope that we can do it, but it's not going to be in the next five years," Ribeiro said. "Maybe in the next 10 to 20 years, though."
And there are some optimistic signs that a vaccine could work.
For one thing, some people have lived with HIV infections for 25 years or more, and the disease has remained at very low levels in their blood streams, indicating that their immune systems are doing at least something to hold the disease in check, Ribeiro said.
Another optimistic sign is that a study of some prostitutes in Africa showed that they were not infected after repeated exposure, he said.
"That's a hopeful sign, but some of these women eventually do get infected," Ribeiro said. "It's not perfect."
Also, people missing a protein in their bodies called CCR5 tend to be resistant to the disease, he said.
"They're very hard to get infected," he said. "But we're not sure what would happen if we blocked the protein in normal people."
Considering that more than 33 million people in the world are infected with HIV, though, and that it kills
2.1 million people each year, it's certainly worth the time, money and effort to create a vaccine, he said.
"This epidemic is still growing," Ribeiro said. "It's slowing, but it's still growing. In some African countries, 20 percent of the people are infected. Think about your family, and how many people you would know with the disease if you lived there."
Contact Sue Vorenberg at svorenberg@sfnewmexican.com.
