WASHINGTON - Researchers and administrators at St. Jude Children's Research Hospital knew for months about procedural errors in a gene therapy trial that could have compromised patient safety. But they did not inform regulators because they judged the risk to be small, according to scientists and administrators involved in the study and a senior FDA official.

As disclosed on Friday, juvenile neuroblastoma patients in a gene therapy trial at St. Jude received treatment with advenoviral vector material derived from seed stock that may have been contaminated with HIV and hepatitis C virus (see BioCentury Extra, Feb. 11). The St. Jude material also was the source of a tumor vaccine developed at Baylor College of Medicine, which last week said it had suspended use of the vector even though it had been "re-derived and retested" to assure the absence of any contaminants including HIV.