It is also not known whether all airway epithelial cells are involved in 
the pathogenesis of the airway disease, or only a subset. For example, if 
the "external electrolyte milieu" hypothesis is correct, it is likely that 
most, if not all of the epithelium is involved, consistent with the wide- 
spread (albeit low) expression of the CFTR gene in the surface airway 
epithelium. Alternatively, if the "internal milieu" hypothesis holds, a 
subset of cells, such as mucus producing cells, may play a dominant role. 
Independent of the mechanisms leading to the abnormal mucus, bacterial 
colonization and inflammation, there is general agreement that the intense 
neutrophil -dominated inflammation deranges the airway epithelium (Doring, 
1989; McElvaney et al., 1991). While a variety of mediators are likely 
involved, injury to the epithelium is mediated to a large extent by neutro- 
phil elastase and neutrophil -generated oxidants (McElvaney et al., 1991; 
McElvaney et al . , 1992; Roum et al., 1990). 
1.12 Rationale for Using a Replication Deficient Adenovirus Containing the 
Human CFTR cDNA to Treat the Respiratory Manifestations of Cystic 
Fibrosis . 
Although the pathogenic processes causing the pulmonary manifestations of 
CF are not exactly identified, the available evidence presents an over- 
whelming case for the fundamental abnormality in the lung of CF patients to 
be an abnormality in expression of the CFTR gene in the airway epithelium. 
This strongly supports the concept that it is rational to use gene transfer 
directly to airway epithelial cells to correct the CF defect that ultimate- 
ly causes the major clinical manifestation of the disease. 
One strategy to accomplish this is to utilize a replication deficient 
recombinant adenovirus that contains an active promoter and a normal CFTR 
cDNA (Rosenfeld et al., 1992). In addition to the ability to accommodate a 
large (up to 7.5 kb) exogenous cDNA, the adenovirus has the advantage of 
being tropic for respiratory epithelium and capable of transferring recom- 
binant genes into non-proliferating cells. The recombinant adenoviral 
approach has been successful in transferring the human al- antitrypsin gene 
to the respiratory epithelium of experimental animals in vivo (Rosenfeld et 
al., 1991) and directly relevant to this protocol, a recombinant adenovirus 
containing a normal CFTR cDNA has been successful in mediating iji vivo 
transfer and expression of the human CFTR gene to the respiratory epitheli- 
um of the lungs of experimental animals (Appendix 1). Further, a recombi- 
nant adenovirus containing the human CFTR cDNA will correct the Cl" secre- 
tory abnormality of epithelial cells of individuals with CF in vitro . 
Details of the vector are presented in Section 2 and details of the experi- 
mental evidence supporting the use of a replication deficient recombinant 
adenovirus containing the human CFTR cDNA to treat the respiratory manifes- 
tations of cystic fibrosis are presented in Section 3. 
In contrast to the adenovirus, there is currently no other vector system 
capable of transferring the CFTR cDNA to the airway epithelium in vivo with 
efficacy and efficiency necessary to treat the disease. The only other 
vector system that has been shown to mediate in vivo transfer of the human 
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