Herpesvirus may boost AIDS expression.

Herpesvirus may boost AIDS expression

A type of herpesvirus may accelerate the development of AIDS in people infected with human immunodeficiency virus (HIV), new laboratory studies suggest. The finding may help explain why some HIV-positive people remain relatively healthy for long periods while others sicken and die within months.

For years, scientists have been searching for a cofactor that increases an HIV-infected person's likelihood of getting full-blown AIDS (SN: 4/4/87, p.220). A team led by Paolo Lusso of the Bionetics Research Inc. in Rockville, Md., and Robert C. Gallo of the National Cancer Institute in Bethesda, Md., focused on herpesvirus-6 because it attacks the same T-cells that are depleted in AIDS patients and because most AIDS patients have active herpesvirus-6 infections. Herpesvirus-6 is a recently identified member of the herpes family (SN: 11/8/86, p.302).

Lusso and Gallo studied cultured human T-lymphocytes infected with herpesvirus-6 and/or HIV. In the Jan. 26 NATURE, they report finding more dead T-cells in cultures infected with both viruses than in cultures infected with either agent alone. The data suggest the two viruses act synergistically, attacking the immune system's T-cells in an accelerated fashion. By the sixth day of infection, the observed death of T-cells was up to three times greater than what would have been predicted by a simple additive effect.

Lusso and Gallo's work suggests herpesvirus-6 starts a lethal cycle for T-cells by "turning on" the gene that triggers the HIV replicative cycle. The researchers hypothesize that HIV, in turn, can stimulate herpesvirus-6 to replicate.

More work is needed to prove that the in vitro results extend to the human body, Gallo says. The National Cancer institute plans a trial comparing the progression of AIDS in HIV-infected people with and without herpesvirus-6 infection. But that may be difficult, LUSSO says, because most people have been infected by herpesvirus-6 in childhood. Researchers believe herpesvirus-6 is contracted via close contact, but in most cases it lies dormant and does not cause disease.

If herpesvirus-6 is shown to be an HIV cofactor, scientists may be able to slow--but not prevent--the progression to full-blown AIDS by finding a drug that halts herpesvirus-6 replication, Lusso says. Acyclovir, a drug used to treat some herpes infections, does not seem effective against herpesvirus-6, he adds.

Other researchers warn against too much optimism. HIV alone kills T-cells and causes full-blown AIDS in time, says Robert R. Redfield at the Walter Reed Army Research Institute in Washington, D.C.