Galpin/DA/N2 IIIBenv 
detection of replication-competent retroviruses (RCR) are described in more detail in 
Section 2.3.5(d), below. 
2.3.5 Safety Features of the Producer Cell Line 
Risks of gene transfer using retroviral vectors have been comprehensively 
addressed by others in animal models and most recently in human subjects 38 . As 
discussed below, a significant effort in the selection and development of the HIV- 
IT(V) has been made to minimize the potential risks associated with this technology. 
(a) Canine Cells as Producer Lines: 
To increase the safety profile of producer cell lines, Viagene's PCL has been 
generated from a canine cell line. Southern hybridization analysis has been performed 
which shows that parental D-17 cells lack genomic sequences homologous to 
MoMLV. In addition, no reports have been found of authentic endogenous canine 
retroviruses. Thus, the PCL background genome contains no known sequences 
homologous with the vector or the vector particle structural genes. 
Murine cell lines have been widely used to develop PCLs for use in gene transfer. 
It is possible to generate RCR from the very large number of homologous, defective, 
endogenous proviruses found in murine cells 39 - 40 ’ 41 . In addition, murine cell lines can 
produce endogenously encoded xenotropic retrovirus either spontaneously, or after 
induction 42 - 43 ’ 44 . Furthermore, many defective endogenous proviruses (retrovirus-like 
genomes such as VL30 sequences) in the murine genome are expressed and the RNA 
can be recognized by the retroviral structural gene products of murine PCLs. These 
RNA genomes can be incorporated into retroviral vectors, and can be delivered to 
38 Cornetta, et al., Human Gene Therapy, 2:5-14, (1991). 
39 Steffen and Weinberg, Cell, 15:1003-1010, (1978). 
40 Canaani and Aaronson, Proc. Natl. Acad. Sci., U.S.A., 76:1677-1681, (1979). 
41 Stoye and Coffin, J. Virol, 61:2659-2669, (1987). 
42 Aaronson and Dunn, J. Virol., 13:181-185, (1974). 
43 Stephenson and Aaronson, Proc. Natl. Acad. Sci., USA., 71:4925-4929, (1974). 
44 Aaronson and Stephenson, Biochim. Biophys. Ada., 458:323-354, (1976). 
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