RK Scheule, RG Bagley, AL Erickson, KX Wang, SL Fang, C Vaccaro, CR O'Riordan, SH Cheng and AE Smith
Genzyme Corporation, Framingham, Massachusetts 01701-9322, USA.

To assess the feasibility of protein replacement as a potential therapy for cystic fibrosis, we have evaluated the ability of influenza hemagglutinin (HA) to mediate the delivery of purified cystic fibrosis transmembrane conductance regulator (CFTR) to recipient cells in vitro. CFTR was purified from both CHO cells and Sf9 cells and reconstituted into two different types of vesicular delivery vehicles. In one, CFTR and HA were co-reconstituted into the same lipid vesicle. After binding to the cell surface, delivery of CFTR to the recipient cell was achieved by a transient, low-pH activation of the fusion activity of HA. A second delivery strategy used HA virosomes together with purified CFTR that had been reconstituted into vesicles containing gangliosides, a receptor for HA. After binding of the HA virosomes and CFTR- containing vesicles to the recipient cells, delivery to the plasma membrane again was achieved by a transient pH drop. Delivery of functional CFTR was assessed using the SPQ fluorescence assay. Functional CFTR was detected in a fraction (> 20%) of the recipient cells using this assay. Quantitative binding and fusion assays using radiolabeled virosomes and lipid vesicles showed that on the order of 1,000 of the added CFTR-containing vesicles bound to each C127 cell under the conditions of our delivery protocols. However, only a fraction of these vesicles fused and delivered CFTR to the cell plasma membrane. The two delivery strategies were found to be approximately equivalent in their ability to deliver active CFTR, and there were no significant differences between deliveries using purified CFTR from either cell source. These feasibility studies suggest that purified CFTR can be delivered to a recipient cell in a functional form and therefore represent a significant step in establishing the concept of protein replacement as a therapy for cystic fibrosis.