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Researchers are excited about a vaccine they have developed that protects rhesus monkeys from infection with a primate version of the AIDS virus. They hope to use what they've learned to develop an agent that prevents HIV infection in humans.

With more than 2.6 million new HIV infections every year, and almost two million deaths from the sexually transmitted virus, an AIDS vaccine remains an urgent, but elusive, goal for AIDS researchers.

Now, scientists at the Oregon Health and Science University's Vaccine and Gene Therapy Institute, or VGTI, think they may finally be on to something. Louis Picker, the head of VGTI's vaccine program, says researchers have developed an agent that protects rhesus macaque monkeys from simian immunodeficiency virus, or SIV.

He compares the vaccine to an army on alert, springing into action at the first sign of infection, before the virus has had a chance to gain a foothold in the body.

"It keeps armed troops at the borders that are able to intercept the incoming HIV or SIV right from the beginning," says Picker. "There's no delay that requires the recruitment of effector cells that other vaccines require."

Effector cells are immune system cells that are mobilized against bacterial or viral invaders.

Currently, vaccine developers try to prime the body's immune system to recognize and destroy HIV by attaching genetic material from the virus to a harmless cold virus. But so far, Picker says, the strategy hasn't worked well because the cold virus doesn't survive very long in the body.

Picker's team of investigators used cytomegalovirus instead. CMV infects most of the world's population, rarely causes disease, and remains alive - but dormant - indefinitely.

In the monkey experiments, researchers gave the primates a genetically-modified cytomegalovirus SIV vaccine or the CMV vaccine plus a modified cold virus vaccine. A third group of rhesus got a standard SIV cold virus vaccine alone and a fourth group was not vaccinated.

Researchers then infected the primates with SIV. While the untreated monkeys and those that got the adenovirus vaccine eventually got sick and developed AIDS, Picker says half of the 24 rhesus macaques that received either the CMV vaccine alone or the CMV plus the cold virus vaccine showed no sign of infection.

"And in fact, when we tried to find the virus after a year or so it was very difficult to find by a variety of techniques," says Picker, "raising the possibility of whether the infection had actually been cleared from these monkeys which would be unprecedented for an SIV vaccine."

Picker's goal now is to formulate a more effective CMV vaccine that is safe enough to begin clinical trials in humans against HIV infection.