The question regarding the safety of deleting the E3 genes is related to 
the function of their products relevant to subverting the inflammato- 
ry/iimnune system in recognizing the virus i.e., does the deletion of gpl9K, 
10. 4K and 14. 5K genes in AdCFTR and AvlCFl have relevance from a safety 
view point? 
The gpl9K product is a transmembrane protein with two N-linked glyco- 
sylation sites. It is localized in the endoplasmic reticulum of Ad-infectec^ 
cells where it forms non-covalent complexes with newly synthesized class I 
MHC antigens , blocking the transport of these antigens to the cell surface 
(Kvist et al., 1978; Wold and Gooding, 1991). This has the effect of sup- 
pressing cytotoxic T-cell responses. Studies in cotton rats have demon- 
strated that nasal administration of a replication competent adenovirus 
type 2 with a deletion of the gene coding for the gpl9K protein was associ- 
ated with increased lymphocyte/macrophage inflammatory response in the lung 
compared to infectious, replication competent Ad2 (Ginsberg et al . , 1989). 
The 10. 4K and 14. 5K products are integral cytoplasmic membrane proteins co- 
translated from the same mRNA (Tollefson et al . , 1990a; Tollefson et al., 
1990b; Wold and Gooding, 1991). Both function to down regulate the epi- 
dermal growth factor receptor (EGF-R) in human Ad- infected cells (complexes 
of these proteins induce endosome-mediated degradation of EGF-R) (Carlin et 
al., 1989; Tollefson et al . , 1991). In the context that this mimics the 
normal function of EGF, it has been suggested that this activates the 
target cell, and may help the virus to replicate. Both proteins block the 
effects of tumor necrosis factor of mouse cell lines (Gooding et al., 1988; 
Gooding et al., 1991). 
The advantages of deleting the middle portion of the E3 region are as 
follows : 
(1) If recombination should occur (for example a cross over to pro- 
duce a infectious, replication competent E3 _ adenovirus), it is 
desirable to have the immune/inflammatory system recognize the 
infected cells and suppress the infection. Since E3 products 
subvert the ability of the immune/inflammatory system to recog- 
nize adenovirus, the inclusion of E3 may subvert the ability of 
the immune/inflammatory system to clear a replication competent 
recombinant adenovirus. In this context, if a replication compe- 
tent recombinant adenovirus should emerge, it is an advantage to 
have the immune/inflammatory system recognize this and respond to 
it appropriately to clear the infection. 
(2) If complementation should occur, the result would be more AdCFTR, 
a virus identical to the vector used for therapy. 
(3) The CF airways are constantly exposed to an intense inflammatory 
process, likely outweighing any process induced by emergence of 
an E3 _ replication competent adenovirus (see Section 4.4 and 
Table 4 . 4-A) . 
(4) Human studies with enteric administration of a wild type E3 _ type 
Recombinant DNA Research, Volume 16 
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