Study shows how some AIDS vaccines may harm

Study shows how some AIDS vaccines may harm
A Chinese woman checks her mobile phone while passing an anti-AIDS poster in Beijing November 28, 2004. Some viruses being used in experimental AIDS vaccines may damage the immune system by exhausting key cells, researchers reported on Thursday in a finding that may further cloud the field of HIV vaccines. (Claro Cortes/Reuters)WASHINGTON (Reuters) - Some viruses being used inexperimental AIDS vaccines may damage the immune system byexhausting key cells, researchers reported on Thursday in afinding that may further cloud the field of HIV vaccines.
They said vaccines using the viruses should not be testedon people until more studies are done. But other vaccineexperts said the findings, while scientifically interesting,were not a cause for immediate alarm.
The usually harmless viruses are used as so-called vectorsto carry genetic material from the AIDS virus into the body sothat the immune system can recognize and rally against it.
But the viruses, called adeno-associated viruses, maythemselves be doing harm, said Dr. Hildegund Ertl, director ofthe Wistar Institute Vaccine Center in Philadelphia.
In mice, the adeno-associated virus, or AAV vaccines,directly interfered with immune cells called CD8 T-cells,Ertl's team reported in the Journal of Clinical Investigation.These are the "killer" T-cells that a vaccine is supposed tomuster to fight HIV.
"The immune cells become exhausted," Ertl said in atelephone interview.
"It is simply a defense mechanism of T-cells -- if there istoo much antigen for too long a time they simply turnthemselves off."
Antigens are the proteins the immune system uses torecognize enemies such as bacteria and viruses. In the case ofHIV, turned-off T-cells could leave a person more vulnerablethan usual to infection.
"AAVs do not cause disease," Ertl's team wrote. They cannoteven replicate on their own, instead piggybacking ontoadenoviruses, which cause colds, or herpes viruses.
But they do persist in the body.
VULNERABLE TO HIV
Ertl said it was unclear whether her findings might castlight on the troubling developments in a trial of an AIDSvaccine that used another virus, an adenovirus.
Vaccine maker Merck & Co stopped that trial in Septemberand said last week it appeared that the adenovirus used in thevaccine may have somehow made patients more vulnerable to HIVinfections.
The International AIDS Vaccine Initiative or IAVI used anadeno-associated virus in a trial of an AIDS vaccine thatwrapped up in January in Belgium, Germany and India, andanother in South Africa, Uganda and Zambia.
IAVI's Pat Fast said the group was not testing AAV vaccinesany more.
"While we find the AAV study by Dr. Ertl and her group ...very interesting and we'll consider whether it can inform ourfuture studies, their study was conducted in mice and there arefundamental differences between mice and humans in theirrespective immune responses, particularly with regard to theimmune response against HIV," Fast said in a statement.
"The dose given to these mice was equivalent, on the basisof body weight, to 3,000 to 4,000 times the highest dose givento humans in the ... study in India."
Dr. Anthony Fauci, director of the National Institute ofAllergy and Infectious Diseases, said the study should be taken"with a very heavy dose of caution."He noted that adenoviruses and adeno-associated viruses arevery different microbes, despite the similarity of their names."We may be dealing with apples and oranges," Fauci said ina telephone interview.(Editing by Mohammad Zargham)