T  hese days, there are lots of things you can do with a strand of DNA. You could sequence
       the genetic code of a particular organism, then reconstruct it in the lab. Or you could transfer a gene from one species to another—to make a strain of corn that’s resistant to herbicides, say, or to produce bacteria that digest oil spills. You could “knock out” genes in laboratory mice, rendering the animals less prone to a particular disease. Or, if you’re a bioterrorist bent on mass destruction, you could try to engineer a virus so contagious and so deadly that it could quickly lay waste to entire populations.

It’s that last possibility, synthetic biology, that worries such people as Michael G. Kurilla, director of the Office for Biodefense Research Affairs at the National Institute for Allergy and Infectious Diseases. Whereas many experts think the real bioterror threat involves well-known agents—smallpox, pneumonic plague and, of course, anthrax, which infected 22 people and killed five in the attacks of fall 2001—Kurilla and others are more frightened by the specter of diseases that don’t yet exist. They envision designer pathogens that could be created in the bioweapons laboratories of rogue states or terrorist camps, and whose spread we would be powerless to stop. To these people, the risks posed by engineered germs and emerging infections mean that our strategies must change. “It has become abundantly clear that the one-bug, one-drug approach is not sustainable,” says Kurilla. “Nature throws potential threats at us much faster than we can deal with them, and terrorists don’t have to contend with the FDA.”

Kurilla points out that the traditional tools—vaccines and antibiotics—have obvious shortcomings. Vaccines are an inherently limited solution to disease threats because they’re difficult to develop and deploy. Drug companies don’t make money on them; many people, both in Africa and the West, don’t want to take them; and many vaccines need to be kept in cold storage or they spoil. What’s more, you can’t develop a vaccine for a disease that doesn’t yet exist. Antibiotics are problematic because germs so often develop resistance to them and because, of course, they work only against bacteria, not viruses.

For Kurilla and others, the solution is to develop whole new ways of treating disease, approaches that fundamentally modify not germs, but our response to them. They want to try something radically new—to enhance innate, or nonspecific, immunity, which kicks in as soon as a host is exposed to an unfamiliar germ. They’re convinced that nonspecific immunity could be boosted sufficiently to treat any disease, new or old, natural or designed.