Following the recent failure of a Merck HIV vaccine, the NIH has still not decided whether to continue with planned clinical trials of a similar HIV vaccine.

Yesterday (December 12), the AIDS Vaccine Research Committee of the National Institute of Allergy and Infectious Diseases met to discuss the PAVE100 study, which was suspended after data from the Merck trials came back. Both vaccines use an adenovirus vector to deliver HIV genes and replicate their proteins. The data from the Merck trials suggested that the vaccine might have actually made people with pre-existing immunity to adenovirus more susceptible to HIV infection, leading to the halting of the PAVE100 trials.

The sentiment at yesterday's meeting seemed to be that the vaccines are different enough to warrant going ahead with the PAVE100 study, Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases told The Scientist. The PAVE100 vaccine also includes a plasma DNA prime with several additional HIV genes, including envelopes.

"The immune response seems to be higher with that strategy and the quality of the immune response seems to be enhanced," Eric Hunter of Emory University, who chairs the AIDS Vaccine Research Committee, told The Scientist. The response to the PAVE100 vaccine includes a greater percentage of multifunctional cd4 and cd8 lymphocytes, Hunter said.

The committee suggested that researchers running the PAVE study only test the vaccine in people with no pre-existing immunity to adenovirus, Hunter said. In the Merck trials, that group did not have an increased rate of infection.

Whereas the Merck trials got to phase 3, the PAVE study has gone through immunologic trials only, and the clinical studies were slated to begin in late 2007. Fauci said he expects a final decision about the trial to be made at the working group's next meeting in January.