Towards fetal gene therapy for cystic fibrosis: ultrasound guided delivery of recombinant adenoviral vectors to the fetal sheep trachea results in efficient marker gene expression in the airway epithelia

Abstract

Fetal gene therapy for cystic fibrosis may have advantages over adult treatment. We aimed (1) to develop a percutaneous ultrasound guided technique to inject adenoviral vectors into the fetal sheep trachea and (2) to improve transgene expression with transduction enhancing agents. Adenoviral vectors containing the β-galactosidase gene (2.0×10¹¹–8.3×10¹¹ particles/kg) and transduction enhancing agents were delivered to the trachea via a needle inserted through the thorax of late (n = 3) or mid gestation (n = 15) fetal sheep using ultrasound guidance. Tissues were analysed 48 hours after injection (n = 17) or 12 hours after birth (n = 1) for transgene expression. Transthoracic injection of the trachea was successful in 16 fetuses with 100% survival. Expression of β-galactosidase, as measured by ELISA, was low after delivery of adenoviral vector alone, but increased 10-fold when the vector was complexed with the polycation DEAE dextran. Pretreatment of the fetal airways with sodium caprate, which opens tight junctions to reach the basolateral surface of lung epithelia, resulted in a 90-fold increase in expression. A synergistic effect of the two agents resulted in widespread staining of the trachea, main bronchi and all airways, confirmed by immunohistochemistry for β-galactosidase. Instillation of perflubron following sodium caprate and vector/DEAE dextran complex injection increased transduction of the peripheral small airways at the expense of tracheal and large airways transduction.