By Sean Henahan, Access Excellence

BOSTON- A less virulent strain of HIV (HIV-2) appears to offer natural protection from the virus that causes AIDS, report researchers from Harvard University. The finding offers encouragement to scientists attempting to develop AIDS vaccines.

Researchers from Harvard and Senegal's Cheikh Anta Diop University have been monitoring HIV infection and disease over the past nine years in a group Senegalese sex workers. They found that women with HIV-2 failed to develop AIDS symptoms for prolonged periods of time and that the women were significantly less likely to subsequently become infected with HIV-1.

The 756 participants in the study underwent regular testing for HIV-1, HIV-2 and various sexually transmitted diseases. Serum samples were evaluated using immunoblotting for antibody reactivity to the viral antigens of both forms of HIV. Serum samples showing dual reactivity were tested again using recombinant peptides from the envelope protein regions HIV-1 and HIV-2. Dual infection was confirmed using PCR.

The protective effect of HIV-2 was consistent throughout the study. The HIV-2 infected women were far less likely to become infected with HIV-1 than women who were not infected with HIV-2. The researchers were uncertain whether initial infection with HIV-1 would block infection with HIV-2.

While the cross-protective mechanisms aren't known, the results may point to new avenues for HIV-1 vaccine development. The protection provided by HIV-2 may be a result of cross-reactive immunity to epitopes found in both forms of the virus. Receptor blockage, HIV-1 replication suppression, and inhibition of HIV-1 gene expression are all being evaluated as potential explanations for the cross-protection observed in this study.

HIV-2, found almost exclusively in West Africa, was discovered shortly after HIV-1. HIV-2 shares substantial genetic features with HIV-1, demonstrated by common cellular receptors and partial antigenic cross-reactivity. However, patients infected with HIV-2 can remain symptom-free for decades without getting sick. Even after HIV-2 disease manifests, it is not as severe as the sudden immune collapse seen in AIDS.

"Our data suggest that HIV-2 infection provides approximately 70% protection from subsequent HIV-1 protection. Despite the demonstrated protection potential and the lower virulence of HIV-2, the risks involved in any live attenuated vaccine may far outweigh the potential benefits. There fore we would rather suggest that the immune effector mechanisms identified in HIV-2 seropositive individuals may be targeted to cross-reactive epitopes that could be useful in HIV-1 vaccine development," said Dr. Phyllis Kanki, Harvard AIDS Institute.

For more information on this study, see Science, Vol. 268, 6/16/95, Travers et al., pp. 1612-1615. In addition, a search of 'Science Update' using a keyword such as HIV will provide texts of related articles.

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