BETHESDA, Md. - New data presented at an NIH symposium last week suggest possible reasons why administration of an experimental adenoviral gene therapy killed Jesse Gelsinger, who was being treated at the University of Pennsylvania for ornithine transcarbamylase deficiency (OTC).

The data also raise broader issues about the safety of adenovirus vectors. But the discussion failed to pinpoint the exact cause of the widely publicized death, and did not provide evidence that the Pennsylvania researchers seriously violated the approved protocols governing the study.