Common cold may explain HIV vaccine trial’s failure

Associated Press / November 17, 2009

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WASHINGTON - The failure of an experimental AIDS vaccine trial two years ago may have been caused by the common cold virus.

The vaccine was intended to block the spread of HIV, or human immunodeficiency virus, which causes AIDS. But the test was canceled after volunteers who got the shots were more likely to become infected with acquired immune deficiency syndrome than those who got a dummy shot.

The problem, which could hamper efforts to stifle the spread of HIV in developing countries, may have been that the vaccine used the common adenovirus to carry HIV material around the body to help the immune system recognize the invader. The conclusion comes from researchers reporting in today’s edition of Proceedings of the National Academy of Sciences.

The test vaccine itself did not spread the illness, the team of researchers said.

However, adenovirus - which causes the common cold - is so widespread that many people have been exposed to it.

The researchers said that prior exposure resulted in mucus membranes producing large numbers of immune cells called CD4 T-cells to fight off the adenovirus. But those are also the cells that HIV infects, providing a ready place for the AIDS virus to grow in people who had received the vaccine and were later exposed to HIV, the researchers said.

Adenovirus is also used in vaccines for tuberculosis and malaria that are under development, said Steven Patterson, lead author of the study. This raises a problem in many areas of the world with a high rate of HIV, and high rates of TB and malaria that will be targeted by vaccines for those diseases, he said.

“If our hypothesis is correct, then the use of an adenovirus vaccine against any disease in an area of high HIV prevalence may increase the risk of HIV infection,’’ he said.

However, Patterson noted, “there are scientists in the HIV vaccine field who do not believe that the adenovirus was the reason for increased number of infections in the vaccinated group.’’