Recombinant DNA Advisory Committee - 12/3-4/92 
Are there risks associated with the repeat administration of the vector? Dr. Crystal 
noted that no evidence of untoward effects was observed in either the cotton rat or non- 
human primate models. Does shedding occur? Shedding is infrequent and transient in 
both the cotton rats and non-human primates. The vector is often present in the stool 
for several days, but then disappears. Is recombination possible? Although 
recombination is possible, the risks are very minimal with the precautions that will be 
taken. Is there a risk of malignancy? There is no evidence of malignancy associated 
with this virus serotype. The possibility of genome integration is very remote. In 
response to concerns regarding cDNA regulation and CFTR overexpression. Dr. Crystal 
said that no clinical signs or symptoms have been observed in 250 cotton rats for as long 
as 14 months or in the 16 rhesus monkeys out to 240 days. 
Dr. Crystal discussed the E3 region in further detail. The region deleted from the 
proposed vector is approximately 3.5 kilobases and codes for 6 proteins. The most 
important of these proteins, gp 19, blocks the Class I MHC antigens from being 
expressed on the epithelial surfaces. There are two other proteins coded by this region 
which down-regulate the EGF receptor. E3 was removed from the vector for the 
purpose of reducing the size of the vector and to increase the stability of the vector. 
Although there is a greater inflammatory response when El is present and E3 is deleted, 
if there is a recombinational event, this vector is safer because it would be recognized 
and eliminated by CTL. Data suggests that E3 minus mutants shed less than E3 positive 
mutants. 
Dr. Crystal responded to Dr. Parkman's question regarding the theoretical possibility that 
a patient who is no longer shedding the vector becomes infected with adenovirus. 
Experiments were described in which cotton rats received either El minus or E3 minus 
mutants. When animals received the replication-deficient virus, no shedding was 
observed. When these animals were rechallenged with the wild-type vector 7 days later, 
no shedding was observed. The same results were obtained in the rhesus model. In 
response to Dr. D. Miller's question regarding other viruses present in the 293 cells, Dr. 
Crystal said that the 293 cells will be assayed for many adventitious viruses, including 
AAV. 
Dr. Crystal stated that 20 ml was chosen as the administration dosage because this is the 
volume that is required to reach the entire airway. Can any predictions be made 
regarding efficacy? Efficacy is expected at the higher titers, although it will probably be 
transient over a period of months. In vivo animal data suggests that immunity will not 
be a problem in terms of repeat administration. 
Dr. Crystal agreed with Dr. Walter's suggested change in the title of the protocol and 
suggested the addition of the word lung after the words conductance regulator. Dr. 
Crystal agreed to move the clinical benefit section to the beginning of the informed 
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Recombinant DNA Research, Volume 16 
