life of epithelial cells is 80-100 days) making retroviral strategies unlikely to succeed since 
replicating cell targets are extremely rare in the adult lung. Although it would be preferable to 
permanently transfer the CFTR to the lung, present strategies must consider vectors that 
efficiently transfer genes to the epithelial cells of the lung and do not pose risks of insertional 
mutagenesis. To date, lipofection and retroviral methods have not been efficient vectors for gene 
delivery to the lung in vivo. 
1.8.3 Animals for the Study of Cystic Fibrosis: Unfortunately, there are no animal models 
with phenotypic and biochemical features identical to those of human cystic fibrosis. Recently, 
several groups have produced cystic fibrosis mice (CFTR(-)) by homologous recombination 
(Snouwaert et.al., 1992, Dorin et.al., 1992). These animals have features consistent with a CF 
phenotype but, at present, homozygous CF(-) mice generally succumb at an early age from to 
GI dysfunction and do not develop significant lung pathology. There are no other known animal 
models with the CF defect with or without pulmonary pathology consistent with cystic fibrosis. 
The respiratory epithelium of rodents contains cell types virtually identical to those in the human 
respiratory tract. However, the location and relative abundance of these cells is quite distinct 
in rodents compared to human lung, and the pathology related to CFTR deficiency in the mouse 
may be quite distinct from that in human cystic fibrosis. Thus at present there are no animal 
models with the CF defect that can be utilized to demonstrate amelioration of lung disease by 
gene transfer of the CFTR. Because of the severe morbidity and mortality associated with CF, 
and the availability of a technology with the potential for therapeutic benefit, we believe it is 
appropriate that somatic cell gene therapy in human patients should be considered in spite of the 
lack of appropriate animal models. 
1.8.4 Consideration of Single vs. Repetitive Treatment with AvlCF2: The presently 
approved protocols for use of adenovirus for delivery of hCFTR (Wilson et.al., RAC proposal, 
1992, Welsh et.al., RAC proposal, 1992, and Crystal et.al., RAC proposal, 1992) will test the 
efficacy of gene transfer with single exposure to virus. Published animal studies have not 
demonstrated the effectiveness or immunological responses to repeated exposure to the 
adenoviral-CFTR vectors in test animals. Therefore at present it is unclear whether significant 
systemic and local humoral, as well as cell mediated responses may be evoked by the virus. 
Such immunological issues will have to be addressed with all gene transfer strategies, whether 
viral, plasmid or liposomal. In our protocol we will administer the virus a second time at the 
same dose given initially. The present application seeks to test whether a second treatment with 
AvlCF2 will be effective in transferring the CFTR and whether it will initiate a significant 
humoral or clinical response. The detection of inflammatory cells or a significant clinically 
detectable inflammatory response in the airway would provide information critical to assessing 
the likelihood of success in the repeated viral exposure that is expected to be required for lung 
from therapy of cystic fibrosis. Quantitation of hCFTR mRNA after the first infection (prior 
to reinfection) will provide information critical to assessment of the length of AvlCF2 direction 
of hCFTR mRNA in our cystic fibrosis patients. 
Recombinant DNA Research, Volume 17 
J367] 
