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Vaccine Improves Survival in Monkey Tests

By John S. James

June 29, 2006

Summary: A vaccine tested at the U.S. NIAID clearly improved the survival of monkeys, a benefit not predicted by T-cell and viral load tests. It was predicted by measurements of memory T cells in the first few months of infection -- giving important insights into how HIV disease develops, and how to test HIV vaccines early so that only the best candidates will go into large human trials.

Researchers at the U.S. National Institute of Allergy and Infectious Diseases (NIAID) reported that an experimental vaccine clearly improved the survival of monkeys after infection by SIV (simian immunodeficiency virus), a virus similar to HIV -- even though it did not prevent infection, and did not much improve viral load or total T-cell count.

While the viral load and T-cell count did not predict the greater survival, something else did -- measurement of memory cells (one kind of T-cells) in the first few months of infection. Memory cells make up more than half of T-cells in adults, and early in HIV disease many of these cells are infected and eventually lost. In the monkey test, three to five times fewer of the memory cells were infected in vaccinated animals than in unvaccinated animals.

The vaccine used in this study was a simplified version of an HIV vaccine now in phase II human trials in the U.S. and some other countries.

Besides the possibility of a survival benefit in humans even if a vaccine fails to prevent infection, this is important for additional reasons:

For More Information

NIAID published a press release, "Monkeys Vaccinated Against SIV Survive Longer After Infection" on June 9.

This press release includes references to the two articles, one in Science, and the other in Journal of Experimental Medicine.

Copyright 2006 by John S. James. See "Permission to Copy" at:

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