Vical Incorporated announced that a "prime-boost" vaccine regimen tested in 40 HIV-uninfected subjects in a National Institutes of Health (NIH) sponsored phase 1 clinical trial was safe and well-tolerated, and was highly effective in inducing T-cell immune responses with multiple functions that may be important for controlling HIV infection.

The trial involved priming an immune response with three doses of a plasmid DNA vaccine, based on Vical's proprietary DNA delivery technology, and boosting the response with a single dose of adenoviral vector vaccine given at a later date.

"We are encouraged that the prime-boost vaccine regimen in this trial was highly effective in generating multiple types of HIV-specific T-cell immune responses, representing another logical step toward development of an effective HIV vaccine," said Vijay B. Samant, Vical's president and chief executive officer.

The vaccine was developed by scientists at the Dale and Betty Bumpers Vaccine Research Center (VRC) of the National Institute of Allergy and Infectious Diseases (NIAID), part of the NIH, and was manufactured by Vical. The vaccine incorporates HIV genetic material from the three most globally important HIV subtypes, clades A, B and C, which are involved in about 85 percent of all HIV infections around the world. The same prime-boost vaccine combination is being tested in 480 HIV-uninfected subjects through a multinational Phase 2 trial initiated in October 2005. The combination also is being tested in 15 HIV-infected subjects receiving highly active antiretroviral therapy (HAART) through a Phase 1 trial initiated in August 2006. A larger multinational Phase 2 trial in several thousand HIV-uninfected subjects is expected to begin in early 2007.

The vaccine used in the Phase 1 trial incorporates parts of four HIV genes. Three of these vaccine components are modified versions of HIV genes called gag, pol and nef, synthetically made based on sequence from clade B, the subtype that predominates in Europe and North America. The fourth vaccine component is a modified version of the HIV gene named env. The env gene codes for a protein on the outer coat of the virus that allows it to recognize and attach to human cells. VRC scientists were the first to combine modified env from clades A and C, which are the most common in Africa and parts of Asia, with the modified env gene from clade B. The study was conducted at the NIH Clinical Center.