The March 2008 issue of Molecular Therapy contains an excellent article by ethicist Nancy King and gene transfer researcher Odile Cohen-Haguenauer that attempts to answer this question. They argue that gene transfer is subject to high degrees of uncertainty, and that a trial's knowledge environment can change rapidly. Though the authors shy from branding gene transfer as "unique" or "distinctive," they also seem to suggest that scientific uncertainty, and a number of other considerations, call out for a different model for thinking about translational research ethics.
I couldn't agree more. (photo credit: his noodly appendage 2005, Alberto Boccioni 1913)