Gene therapy for cystic fibrosis with aerosolized adenovirus-CFTR: characterization of the aerosol and scintigraphic determination of lung deposition in baboons.
For cystic fibrosis (CF) gene therapy using an aerosolized adenovirus expressing the CFTR gene, optimization of the inhalation conditions is a prerequisite to obtain sufficient amount of CFTR protein expression in the target areas of the respiratory tract. For such a purpose, in vivo radioisotopic imaging of the radiolabeled virus is a unique strategy for a quantitative assessment of the actual deposition. In the present study, an adenovirus CFTR (AdCFTR) was labeled with 99m Technetium gamma emitting isotope in such conditions that its bioactivity was preserved. The 99mTc-AdCFTR aerosol was characterized using both laser diffraction and cascade impaction for sizing with further determination of nebulized and inhalable fractions. After administration to baboons, scintigraphic quantitation of the regional lung distribution was performed and the actual dose deposited in the target area was estimated and expressed as an equivalent viral titer. Since a virus scintigraphy is not realistic in a hospital setting, we have developed an approach using 99mTc-DTPA (diethylene triamino pentaacetic acid) that could be used to predict the virus deposition. Indeed, similarities observed between 99mTc-DTPA and 99mTc-adenovirus aerosol imaging patterns validates the use of the 99mTc-DTPA scintigraphy that we propose as a pretherapeutic test for each patient prior to gene transfer.