Gene therapy for cystic fibrosis with aerosolized adenovirus-CFTR: Characterization of the aerosol and scintigraphic determination of lung depositionin baboons

For cystic fibrosis (CF) gene therapy using an aerosolized adenovirus expre ssing the CFTR gene, optimization of the inhalation conditions is a prerequ isite to obtain sufficient amount of CFTR protein expression in the target areas of the respiratory tract. For such a purpose, in vivo radioisotopic i maging of the radiolabeled virus is a unique strategy for a quantitative as sessment of the actual deposition. In the present study, an adenovirus CFTR (AdCFTR) was labeled with 99m Technetium gamma emitting isotope in such co nditions that its bioactivity was preserved. The Tc-99m-AdCFTR aerosol was characterized using both laser diffraction and cascade impaction for sizing with further determination of nebulized and inhalable fractions. After adm inistration to baboons, scintigraphic quantitation of the regional lung dis tribution was performed and the actual dose deposited in the target area wa s estimated and expressed as an equivalent viral titer. Since a virus scint igraphy is not realistic in a hospital setting, we have developed an approa ch using Tc-99m-DTPA (diethylene triamino pentaacetic acid) that could be u sed to predict the virus deposition. Indeed, similarities observed between Tc-99m-DTPA and Tc-99m-adenovirus aerosol imaging patterns validates the us e of the 99mTc-DTPA scintigraphy that we propose as a pretherapeutic test f or each patient prior to gene transfer.