HARVARD GAZETTE ARCHIVES

David Knipe (from left), Judy Lieberman, and Deborah Palliser have found a way to protect mice from a genital herpes virus that infects millions of humans and is important for the transmission of AIDS. They hope to use their results to develop an inexpensive medicine to protect people from getting and infecting others with the AIDS virus. (Staff photo T.J. Kirkpatrick/Harvard News Office)

"In the United States, approximately 20 percent of the population are infected with HSV-2 (herpes simplex virus 2)," says Deborah Palliser of Harvard Medical School. "Each year around 1 million more cases occur. In sub-Saharan Africa, the infection rate is about 80 percent. For all these people, there is a threefold increased risk of also becoming infected with HIV [the virus that causes AIDS]." In 2005, some 5 million people developed AIDS, bringing the total number of people living with the disease to more than 40 million worldwide.

At Harvard's CBR Institute for Biomedical Research, Palliser and her colleagues put small amounts of genetic material known as small interfering RNA (siRNA) into the vaginas of mice. Such molecules can suppress the activity of disease-causing genes.

Mice given siRNAs that block the genital herpes survived after being challenged with lethal doses of the virus. Those given siRNA not active against the virus did not.

The herpes virus is not fatal in humans, but it causes chronic infection and genital ulcers that dramatically increase the risk of infection by HIV and other viruses. In humans, the siRNA would be applied to inside and outside genital surfaces.

"The siRNA could either be administered to a person already infected to reduce viral shedding, pain, and transmission to a sexual partner, or it could be administered to those who are not infected to protect them," says Judy Lieberman, professor of pediatrics at Harvard Medical School and director of the Division of AIDS at the CBR Institute for Biomedical Research.

The story of this research was first told on the Web site of the journal Nature on Nov. 23, and it will be printed in a later edition of that scientific magazine. Authors of the report include David Knipe, Higgins Professor of Microbiology and Molecular Genetics at Harvard Medical School, who first identified the genes necessary for the herpes virus to reproduce, the genes silenced by the siRNAs.

Lieberman notes that very little siRNA was required to protect the mice. The manufacturing cost of a single application for humans is "crudely estimated to be $8," she says. "Given the devastating global epidemic and the unlikelihood of there being an effective HIV vaccine soon, we feel that further investigating siRNAs is a sensible approach."

What's next

These investigations are going ahead. According to Palliser, siRNA can be given rectally to prevent genital herpes, a big problem among gay men. However, she cautions, "this route has yet to be tested."

For both sexes, the path from herpes to HIV involves many factors. When herpes simplex virus 2 gets involved, it causes inflammation and erosion of the layers of skin surfacing the inside and outside of genital areas. Without such wear and tear, these layers would act as a tight barrier to the AIDS virus. When this barrier is weakened or partly shredded, it is much easier to get infected by HIV or other sexually transmitted diseases. The siRNAs provide a new line of defense.

"We will now work to extend our results to produce a microbicide that directly targets HIV genes," explains Lieberman. Such a protective compound would also knock out the human genes required for the AIDS virus to enter and infect body cells, thus preventing AIDS transmission to sexual partners.

In addition, Lieberman continues, "We want to determine whether chemical modification of the siRNAs will enhance their effectiveness, what dose is optimal, and how to put siRNAs into a gel that can be retained in the vagina," especially after menstruation.

Before using the microbicide on humans, tests will be done on monkeys. Lieberman and Palliser speculate that further studies on animals with different doses of siRNA could lead to better protection with lower doses. Although hopes are high, they warn that, "a lot more work needs to be done."

Other targets

If siRNAs can block herpes and AIDS viruses, they should also provide protection against other types of viruses and parasites. Different research groups are studying their use against flu and hepatitis, as well as for treating nervous system diseases like ALS (Lou Gehrig's disease). Other medical investigators plan to use siRNAs to target parasites that cause malaria.

The target list also includes lung infections. Small siRNA molecules can be taken up by cells lining the lungs. Here they would interfere with influenza and other respiratory viruses that cause a significant number of deaths in newborn children.

"You can aim treatments against either the genes of an invader or those of its host that are important for the invading pathogen's survival," Palliser points out. She and Lieberman agree that, "A lot more research is needed before siRNA molecules become an active part of microbicides used against AIDS or other diseases, but we think that work will be well worthwhile."