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such a vector system, there still remains the possibility of induction of harmful mutations 
by integration of the vector into an essential gene in the patient’s cells and the possible ef- 
fects of the mutant vector molecules that arise as a result of genetic variation during the 
replication of the vector, that is, the formation of the vector virus and infection forming a 
pro virus. 
C. Risk Assessment 
The general populace reacts to risks not simply in terms of the probability that 
they are harmful, but in terms of more complex considerations. For example, in the sum- 
mer of 1986, travel to Europe and the Middle East from the US decreased about 50% in 
some countries as a result of fear of terrorism (Bames,1986). However, only a very small 
number of Americans, few of them tourists, were killed (23 in 1985) or hurt by terrorists 
compared to 43,500 deaths from automobiles in the US in 1985 (Bames,1986). Studies 
of risk perception indicate that the public underestimates familiar risks and overestimates 
those that are unfamiliar, involuntary, invisible, and potentially catastrophic (Fischoff et 
al. 1981). Somatic gene therapy of human disease with retrovirus vectors is certainly un- 
familiar, invisible, and in the eyes of some, potentially catastrophic, especially in terms of 
the possibility of a new virus being formed by recombination of the vector with 
endogenous or helper cell sequences. Therefore, it is the responsibility of scientists in- 
volved in this work to explain fully to the public the details of this technology, so they 
can determine if the benefits outweigh the risks. 
D. Appropriate Models For Comparison Of Risks 
In considering the safety of somatic gene therapy of human disease with 
retrovirus vectors, we can look at reactions to other therapies. Kidney transplantation and 
cancer chemotherapy of children may be relevant. In both cases there is a life-threatening 
illness, and the therapy can result in negative effects on the patient. Kidney transplant 
Recombinant DNA Research, Volume 12 
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