Merck Reenters AIDS Vaccine Field

Merck & Co., a pharmaceutical powerhouse that dropped out of the HIV vaccine field in the early 1990s, is aggressively reentering the arena. The company has plans to launch tests of two different vaccines before the end of the year, ScienceNOW has learned.

In the 1980s, Merck had a high-profile AIDS vaccine program with Repligen, a Cambridge, Massachusetts, biotechnology company. That project aimed to make a vaccine that stimulated production of HIV antibodies, preventing the virus from entering cells. But the strategy proved unpromising, and the effort died in 1994. Now Merck is focusing on the other arm of the immune system: cell-mediated immunity, which rids the body of cells that the virus has already managed to infect.

Emilio Emini, a virologist who heads Merck's vaccine program, is sketchy about plans but says the company is putting much effort into developing a so-called DNA vaccine. In this approach, HIV genes are stitched into a stretch of DNA called a plasmid, which can infect cells and produce viral proteins. Merck also is developing a live, but defective, viral vector that Emini declines to discuss publicly. "One of the reasons we've kept a low profile is we don't want to raise expectations," he says. "The likelihood for failure is pretty high." Then again, he says, Merck is putting a lot of resources into the project. "It's a big program for us." In its preliminary, Phase I, vaccine trials the company plans to rely on its own clinical trial system rather than on the extensive AIDS vaccine trial network run by the National Institute of Allergy and Infectious Diseases.

AIDS vaccine researchers are much heartened by news of Merck's involvement, as few major pharmaceutical companies have shown any interest in pursuing this daunting scientific challenge. "The more [players] we can get in with good ideas, the more the whole field benefits," says Donald Burke, who heads AIDS vaccine clinical trials at Johns Hopkins University. "The momentum right now is less than optimal."