M.J. Welsh and A.E. Smith, RAC Application 
c. Another potential problem with the administration of a live, though disabled virus, is the 
possibility of virus replication. If replication were to occur in the patient, virus could 
spread to other persons and to the environment. Replication in the patient could occur, by a 
variety of means. The adenovirus vector itself, though disabled, may have some low level 
ability to replicate. The missing El functions could be provided by coinfection with 
another adenovirus; by coinfection with another virus able to provide El -like functions; by 
expression of El resulting from an earlier perhaps now latent infection (100); or by host 
cell proteins, which though not directly related to the El -encoded proteins, nevertheless 
were able to mimic their activity (101,102). In addition to complementation of viral 
activity, a further possibility is that the defective virus could recombine with a related virus 
either by homologous recombination or by illegitimate means so as to create a new viral 
entity with novel biological properties. 
d. The adenovirus vector will require repeated administration, since we do not expect to 
target a progenitor cell and we expect vector expression to decrease with time. Such 
repeated administration will likely be necessary for almost all approaches to gene therapy 
for CF. 
In Section 8.0 (the NIH Points to Consider), we address these issues of inflammation and 
replication and describe animal and tissue culture safety experiments. Those results lead us 
to believe that the potential risk posed by these factors is small and that our protocol both 
minimizes such risks and allows their assessment. 
5.0 USE OF NASAL EPITHELIUM FOR STUDIES OF GENE THERAPY 
For our first studies of gene therapy, we propose to use the nasal epithelium for several 
important reasons. 
5.1 Nasal and Pulmonary Epithelia Have Similar Morphology and Function. 
As indicated above, disease of the pulmonary airways is the major cause of morbidity and 
mortality in CF. However, the upper airway epithelium that lines the nasal cavity is similar 
in morphology and function to the airway epithelium that lines the lower pulmonary 
airways. 
Most importantly for our studies, CF causes similar abnormalities of electrolyte transport in 
both. Both manifest the lack of CFTR chloride channel function. In fact, the first evidence 
to suggest that CF airway epithelia have defective electrolyte transport, was a study of nasal 
airway epithelium (103). Since then, many in vitro and in vivo studies have used the nasal 
epithelium as a model of the lower respiratory tract epithelium. 
5.2 Use of Nasal Epithelium Provides Advantages for Safety. 
a. Use of the nasal epithelium will allow us to use a very small total amount of virus 
because we can apply it to a limited area. As a result, we will be able to obtain a great deal 
of useful information, but at the same time, use of a small amount of virus will minimize 
the risk. 
b. Use of the nasal epithelium for our first studies of the recombinant virus has the 
advantage that the epithelium is more readily accessible than that in the lower airway for 
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