IVjV.2.b. Expression of CFTR- phenotypic correction of CF epithelia 
IVA.2.b.(i) Correction of retrovirally transduced CFTR cDNAs 
of immortalized CF airway epithelia: 
The CFT1 cell line is a cell line derived from a patient who was homozygous 
for the AF508 mutation (85). The cells were transformed with HPV-18 E6/E7 
genes. The important feature of this cell line is that it differentiates well into a 
polarized ion-transporting epithelium when pleuripotent cells are placed on 
collagen matrices that permit feeding of both sides of the epithelial cell by growth 
media that contains raised calcium and 3T3 cell conditioned medium. Using a a 
murine-derived retroviral vector, functional correction of non-differentiated CFT1 
cells exposed to retrovirus (LCFSN) was detected by patch clamp techniques (37). 
Importantly, when CFT1 cells were differentiating into polarized, ion transporting 
epithelial cells, correction was maintained. Thus, it appears that the CFTR protein 
not only can be expressed in airway epithelia but targets functionally to the apical 
membrane of differentiated airway epithelia. Finally, because CFT1 cells are a 
continuous cell line, persistence of the expression of the CFTR cDNA could be 
measured. It was found that after 6 months of continuous culture, CFT1 cells still 
express correction. However, the level of correction had diminished from the level 
of correction at one month. Analyses of cells indicated that all cells were still 
expressing the CFTR proviral cDNA, but that the level of transcription had been 
reduced. 
IV.A.2.b.(ii) Efficiency of correction as a function of cells in a 
defined surface area of the airway wall: 
As described above, we quantitated the fraction of CF cells that must be 
corrected by the transduction of the wild type CFTR cDNA to restore function to 
the overall epithelium (49). As shown in Figure 12 below and in the manuscript in 
Appendix B, partial restoration of function is observed when 3-6% of the cells in the 
epithelium are corrected, and full restoration of function is effected by correction of 
10% of the cells in the epithelium. 
[466] 
Recombinant DNA Research, Volume 17 
