In addition, our studies demonstrated the potential to use an orally administered prodrug instead of the intravenous infusion.  This was a key advancement since it greatly decreased the morbidity of the study to the patients (a few pills a day, versus two or three one hour intra-venous infusions a day for fourteen days per course of treatment) and greatly reduced the cost per patient in the trial. With the advent of the oral prodrug, we were able to design clinical gene therapy studies that involved only simple outpatient procedures.