M.J. Welsh and A.E. Smith, RAC Application 
know the mechanism whereby DNA loss eventually occurs, but assume the unintegrated 
DNA is degraded by cellular nucleases. 
Complementation and DNA stability 
We assume that the limited viral DNA synthesis reported in B.2.a.(3) results from a small 
amount of residual viral gene expression, even in the absence of El a and Elb gene 
functions. In addition, the absence of these proteins could be complemented by provision 
of El by a wild-type virus coinfecting the host cell. Under these circumstances, we expect 
the wild-type virus to overgrow the defective virus. Figure 8 shows an experiment which 
mimics such a possibility under the most favorable conditions for growth of the defective 
virus, i.e., in 293 cells. When the ratio of added Ad2/CFTR-1 to wild -type Ad2 was 100:1, 
within 2 passages the amount of wild-type virus exceeded Ad2/CFTR-1 by a ratio of 2:1. 
In conditions where wild-type virus outgrows defective virus in a patient, we would expect 
such infection to eventually become self-limiting. Complementation of the defective virus 
might also occur by provision of El gene function as a result of an earlier, perhaps now 
latent adenovirus infection (100), (as a result of proteins encoded by another virus that can 
mimic the activity of El (119,127-129), or as a result of cellular proteins with El-like 
activity (101,102). We have not detected growth of defective virus even in hamsters 
treated with adenovirus at 100 times the maximum proposed human dose or in primates 
treated with 2000 times the maximum proposed human dose (see below). Nevertheless, 
such a possibility remains. If such virus replication did occur in the patient, we would 
expect it to be reduced (compared to wild- type) and eventually self-limiting. As 
safeguards, we will test nasal cells from patients for the presence of Ad2/Ad5 El sequences 
using PCR methods prior to treatment, and will only treat patients who are seropositive for 
Ad2. 
[ 886 ] 
Recombinant DNA Research, Volume 16 
