April 11 (HealthDay News) -- A new HIV/AIDS vaccine designed to overcome the problem of preexisting immunity to common vaccine vectors is being tested in an early clinical trial at Brigham and Women's Hospital in Boston.

Preexisting immunity is believed to be a major problem in developing nations.

There will be 48 healthy volunteers taking part in the trial of the vaccine, which consists of a replication-incompetent, recombinant adenovirus serotype 26 (rAd26) vector encoding an HIV-1 envelope gene.

Each volunteer will receive either two or three immunizations, and then be monitored to assess the safety of the vaccine and its ability to trigger an immune response.

The rAd26 vaccine was developed by the Integrated Preclinical/Clinical AIDS Vaccine Development (IPCAVD) program, sponsored by the U.S. National Institute of Allergy and Infectious Diseases. The program brings together academic and industry researchers to accelerate development of promising HIV/AIDS vaccine candidates.

The vaccine, the first HIV-1 vaccine candidate to emerge from the IPCAVD program, is made by Dutch biotechnology company Crucell Holland B.V.

The approach used in developing the rAd26 vaccine enables researchers to circumvent preexisting immunity to serotype 5, the virus responsible for the common cold. This virus has recently shown limitations as an HIV-1 vaccine vector.

"The rAd26 vector does not regularly occur in the human population, and human antibodies to this vector are rare. The rAd26 vector therefore is efficacious in eliciting good T and B (immune) cell responses," Jaap Goudsmit, chief scientific officer at Crucell, said in a prepared statement.

About 33.2 million people worldwide are living with HIV/AIDS, and there were 2.7 million new infections reported in 2007.

SOURCE: Brigham and Women's Hospital, news release, April 3, 2008