Larger trial of adenovirus AIDS vaccine begins

A Phase II trial of an AIDS vaccine candidate developed by the US-based company Merck began enrolling 1,500 volunteers in December at sites in the US and Canada. Enrollment will continue in the coming months in Peru, the Dominican Republic, Haiti, Puerto Rico, and Australia.

The vaccine candidate uses an adenovirus called Ad5. In its natural form adenovirus can cause severe colds but a weakened version is used to make the vaccine. The adenovirus vector delivers three different HIV genes to the immune system. None of the vaccine components can cause HIV infection. For more about the use of this viral vector see the Primer in this issue.

Scientists are hopeful that the vaccine will cause the immune system to raise a strong response against HIV by producing killer T cells to attack HIV-infected cells. The trial is the first large-scale study to test the ability of this vaccine candidate to protect people from infection with HIV. The study will also follow volunteers who later become infected with HIV during the trial follow-up period (four and a half years) to see if the vaccine can help control disease progression.