A flurry of reports and congressional hearings, sparked by the death of a volunteer in a study at Penn, are due in the next few weeks. The Penn episode points up a central problem: The field still lacks an ideal vector

Dusty Miller, a veteran gene therapy researcher, wants to test a new idea for treating cystic fibrosis. He has engineered a strain of virus to create a new “vector” to inject useful genes into cells. He has tested it in his lab at the Fred Hutchinson Cancer Research Center in Seattle, getting “wonderful” results in mice. Although he can't guarantee that it's safe for human use, he's confident that it is. Yet he's hesitating about testing it in patients, stretching out preliminary research while using an established but, he thinks, less efficient vector in volunteers. He's being supercautious, he says, because the “climate for gene therapy” has turned cold.