The field then suffered a major setback when an Arizona teenager died in a gene therapy experiment in 1999 and two French boys with SCID developed leukemia in 2002.
The idea suffered major setbacks in 1999 when a U.S. teenager died in a gene-therapy trial and again soon after when several children in Europe developed leukemia after receiving gene therapy.
One notorious example came when just about every major drug company in the mid-1990s rushed to develop drugs to block a cancer-causing gene called ras.