Uncommon ICAM blocks common cold virus.

Uncommon ICAM blocks common cold virus

When the space shuttle Atlantis finally blasted off last week, a full week behind schedule, NASA estimated the delay had cost the agency a whopping $2.7 million. Several factors contributed to the five launch postponements, but the first and perhaps most frustrating among them was the common cold that left crew commander John Creighton too congested to fly.

Most colds don't have such dire consequences. But virologists Steven D. Marlin, Vincent J. Merluzzi and their colleagues couldn't have asked for a more timely backdrop as they published their latest research in the March 1 NATURE describing a way to block infection by cold-causing viruses.

Working at Boehringer Ingelheim Pharmaceuticals Inc. in Ridgefield, Conn., the researchers mass-produced slightly altered versions of a protein receptor that normally serves as the nasal-passage docking site for rhinoviruses -- the kind of virus that causes about 50 percent of common colds. Using cultured human cells that bear the rhinoviruses receptor, called ICAM-1 (SN: 3/18/89, p. 165), the researchers showed that when they flooded the cells with synthetic ICAM-1s, the decoy receptors sopped up more than 90 percent of the rhinoviruses before the viruses had a chance to infect the cultured cells. This level of protection, if achieved in people, could feasibly prevent the onset of some colds, the researchers suggest.

In theory, the approach has several benefits over those employed by other antiviral drugs, Marlin and others note. Most important, since the virus absolutely requires the ICAM-1 receptor to initiate infection, researchers need not fear the virus will mutate into a form that lacks an affinity for the synthetic decoys. "The virus has no other way of binding to cells," Marlin says. "If they mutate such that they don't bind to ICAM-1, they're dead viruses."

But several hurdles remain. For one, scientists remain uncertain what kind of ill effects may follow if they repeatedly flood the nasal passages with large quantities of the synthetic receptor, which in its natural form has important duties beyond serving as a welcome mat for rhinoviruses. For example, ICAM-1 plays a key role in both triggering immune responses and in shepherding immune-system cells from the circulatory system into surrounding tissues.

Marlin says there are reasons to believe that extra copies of ICAM-1 may not cause serious problems in the body. However, he adds, "The only way to find out is to try it." Since no other animal suffers from this common human ailment, that means trying it on people. But clinical trials are probably still a few years away, Marlin says.