M.J. Welsh and A.E. Smith, RAC Application 
the frequent studies required to test safety and efficacy. Because it is more accessible, there 
will be less patient discomfort and risk. 
c. Use of the nasal epithelium will allow us to obtain a biopsy of the precise area to which 
the recombinant virus was applied. This will allow an assessment of cytopathic effects and 
the inflammatory response. 
d. If significant inflammation or cytotoxicity should develop as a result of administration of 
the recombinant virus, the consequences to the patient will be much less severe if they 
occur in the nasal epithelium than if they occur more generally in the lung. 
5.3 Use of Nasal Epithelium Provides Advantages for Assessing Efficacy. 
Measurement of the transepithelial electrical potential difference across the nasal 
epithelium provides an easy and reliable measure of the chloride transport function of the 
epithelium (103,104). The test is noninvasive; it only involves the use of a small 
polyethylene tube to probe the voltage generated across the nasal mucosa. Moreover, the 
test can be repeated frequently and there is little discomfort to the patient. Use of the nasal 
epithelium will also allow us to assess the presence of mRNA and protein. Thus, the 
functional and biochemical evaluation of recombinant virus application can be more readily 
performed with less risk to the patient in the nasal epithelium then in the pulmonary 
epithelium. 
6.0 IS THE USE OF AN ADENOVIRUS VECTOR SAFE? 
Although live adenovirus has been used for vaccine purposes and an E3 replacement 
recombinant adenovirus has been tested in limited clinical trials (93), there is clearly 
concern as to whether the use of an El replacement vector will be safe. These issues are 
dealt with in detail in Section 8.0, the NIH Points to Consider. Here we highlight what we 
believe to be novel aspects of using adenovirus in human gene therapy. 
6.1 Will the Virus Cause Immediate Damage? 
Replication of wild-type Ad2 is usually associated with only minor respiratory ailments; 
the vector to be used here is disabled for replication. Doses in excess of 10 4 times the 
proposed human dose (on a mass/kg basis) have been tested in monkeys and hamsters with 
only a minor transient inflammatory response. 
6.2 Will the Virus Cause Tumors? 
Although some adenoviruses can cause tumors in newborn animals, no naturally occurring 
tumor in animals or humans has ever been associated with any adenovirus strain (80,98,99). 
The adenovirus genes associated with cellular transformation in tissue culture are deleted. 
Although adenovirus DNA can integrate, this is not part of the normal viral replication 
cycle and there is no evidence for insertional mutagenesis. 
6.3 Will the Virus Replicate? 
The vector proposed here is doubly defective: it lacks a crucial early viral gene, El, 
required for viral replication and it contains a genome of 104.5% normal size which renders 
it difficult to package. Although we present data for limited viral DNA synthesis, we have 
no evidence for replication of the adenovirus vector in tissue culture cells, in monkeys, or 
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