AIDS vaccines may weaken immune system

20 November, 2007

Some viruses being used in experimental vaccines for the acquired immunodeficiency syndrome (AIDS) may actually weaken the body’s immune defense against the AIDS virus by exhausting key cells.

In a new study that might delay further the search for a vaccine for the human immunodeficiency virus (HIV), researchers have said that vaccines using the viruses should not be tested on people until more studies are done.

The study is the latest in a series that may force scientists to rethink methods they have used to develop a vaccine against AIDS.

Around 40 million people worldwide are affected by AIDS.

The harmless viruses usually used to carry genetic material from the AIDS virus into the body so that the immune system can defend against it.

In the new study, conducted by Dr Hildegund Ertl, director of the Wistar Institute Vaccine Center in Philadelphia, the United States, and colleagues,
found that the so-called adeno-associated viruses might themselves be doing harm.

In mice, the adeno-associated virus, or AAV vaccines, directly interfered with immune cells called CD8 T-cells, the researchers reported in the Journal of Clinical Investigation. These are the “killer” T-cells that a vaccine is supposed to gather to fight HIV.

Dr Hildegund Ertl said the immune cells become exhausted and that “it is simply a defense mechanism of T-cells – if there is too much antigen for too long a time, they simply turn themselves off.”

Dr Hildegund Ertl said it was unclear whether her findings might shed light on the disturbing developments in a trial of an AIDS vaccine that used another virus, an adenovirus: Merck & Company, manufacturer of vaccines, had stopped trial on an HIV vaccine in September 2007. The company said it seemed that the adenovirus used in the vaccine might have somehow made patients more vulnerable to HIV infections.

The International AIDS Vaccine Initiative (IAVI) had used an adeno-associated virus in a trial of an AIDS vaccine that was completed in January 2007 in Belgium, Germany and India, and another trial conducted in South Africa, Uganda and Zambia. The IAVI has said the group was not testing AAV vaccines any more.