In 1989 when scientists discovered the defective gene that causes cystic fibrosis, a serious hereditary disorder that primarily strikes children of European descent, it seemed as though a long-hoped-for cure might soon follow. After all, tests in many laboratories showed that providing normal copies of the gene should enable patients to make healthy copies of the protein specified by the gene. If successful, that feat would go a long way toward restoring health in the tens of thousands of people around the world who suffered from cystic fibrosis and typically died in their late 20s. (Half of all patients now live to their late 30s or beyond.) The question was whether researchers would be able to reliably insert the correct gene into the proper tissues in patients’ bodies to rid them of the illness forever.

That task proved harder than anyone had believed. Although scientists successfully engineered viruses to ferry copies of the correct gene into patients’ cells, the viruses did not do the job well. By the late 1990s additional unexpected complications made it increasingly obvious that another approach to addressing the fundamental problem in cystic fibrosis would need to be found.

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