Reports for NATAP

AIDS Vaccine 2001 Conference

September 6, 2001 Philadelphia, PA

Merck Vaccine: AIDS vaccine appears effective in early simian test
   Steve Sternberg
   04/02/2001
   USA Today

An AIDS vaccine tested in monkeys provokes an immune response potent enough to suppress blood-borne virus at barely detectable levels, research out Sunday shows.

The vaccine could not prevent infection, but it did hold the amount of virus at 500 copies per cubic centimeter, 100 to 1,000 times less than the amount of the virus seen in monkeys given two other vaccine prototypes, says John Shiver, director of vaccine research for Merck & Co.

The new vaccine appeared so effective at least in this early test that it puts the activated immune system on par with many of the most effective anti-AIDS drugs now used to combat the virus.

"The vaccine controlled the virus at levels comparable to what many of the anti-retrovirals are able to do," Shiver said.

Shiver presented the results to many of the world's leading HIV vaccine researchers at a weekend conference in Keystone, Colo. Other primate studies, presented by researchers from Targeted Genetics and Epimmune Inc., also appeared to reflect progress toward an HIV vaccine , though all of the work is preliminary and no one knows whether the vaccines will work in humans.

Researchers at Merck used prototype vaccines made with a structural gene from Simian Immunodeficiency Virus (SIV), the monkey version of the AIDS virus. The gene, called gag, was dissolved in saltwater or inserted into three types of envelopes capable of carrying it into cells: the crippled shell of a cold virus, a similarly damaged cowpox virus and a plasmid, a ring of DNA found in bacteria.

Twenty-one monkeys were used in the trial; six served as controls. All of the monkeys were infected with an especially nasty combination of both SIV and HIV, the human AIDS virus. The virus is so virulent that it quickly generated a hundred million copies of itself in every cubic centimeter of blood.

Shiver says the cold virus vaccine turned out to be much stronger than the other approaches, dramatically reducing viral replication and preserving the immune system cells that are usually wiped out by AIDS. It may eventually be used with the second best vaccine, using the same gene coupled with a special immune booster called CRL10-5, Shiver says.

Five of the six control monkeys have developed AIDS-like illnesses and four have died, he says. All of the vaccinated monkeys are still living. None of the monkeys given the two best prototypes developed any AIDS-like illnesses. "All of the studies are very early," he notes. "It's impossible to predict whether any of these approaches will work in humans."

Shiver says Merck plans to continue studying the effects in monkeys "to learn all we can about the nature of immunization and the best types of immune responses to block infection. We want to incorporate what we learn into clinical trials in humans."

A year ago, Merck launched a preliminary human trial of a vaccine made with the gag gene. The firm has just started its first human trial to test the sa fety of its cold-virus-based vaccine.

The website for the Vaccine Conference is:
http://www.AIDSvaccine2001.org