yet carry little risk of malignant transformation, or will attempts to increase 
expression always Increase the incidence of malignancy? 
What will be the incidence of malignancy of patients undergoing gene 
therapy? We do not know. If a helper free system is utilized, the incidence 
should be lower. Difficulties in making such a determination are related to 
the following factors. (1) The number of proto-oncogenes and the number of 
Integration sites that will result in their activation is not known. (2) 
While retroviruses integrate throughout the genome their integration may not be 
totally random. The frequency of integration into regions required for 
malignant transformation is not known. (3) The tropism that the Moloney MuLV 
has for various human tissues and the malignant potential that might result are 
unknown. 
Studies are being conducted in our laboratory to determine the safety of 
the SAX vector. We are injecting a large dose of S3A RSV as well as a large 
dose of the wild type amphotropic virus 4070A into primates under P3 
containment conditions. The protocol is attached in Appendix A. We will 
follow the Infected monkeys for viremia. antibody response to the injected 
retrovirus, evidence for recombination with endogeneous or exogenous sequences, 
as well as for pathological and/or malignant sequel lae. 
4) Safety measures 
1. Producer Cell Line 
a) The history of development of the S3 A producer cell line is known in 
detail. In addition, accurate records of the tissue culture medium used have 
been kept. 
b) S3A was made using equipment where no other cells or supernatants were 
present. Once the clone met the criteria for selection (G418 resistance, human 
ADA expression, intact structure by Southern analysis, high viral titer) and 
sufficient cells were present, a Master Cell Bank was formed. Only one 
ffioi Recombinant DNA Research, Volume 12 
