virus, which also produces tutors in animals, which are the 
primary objects of recombinant DNA research in animal 
viruses. 
5. The virulence of influenza virus, and the sponta- 
neous occurrence in nature at certain times of devastating 
flu epidemics (such as the one of 1918) is apparently 
controlled by the reassortment in nature of the 12 sub- 
units of the viral RNA-^ Yet the genetic basis and the 
mechanism by which these viruses are rendered highly 
virulent is not understood. Again, therefore, any 
recombinant DNA procedure involving any animal virus 
or cells containing such a virus must be considered 
to pose the risk of creating highly virulent or 
infectious strains. 
6. The expression of any foreign gene, however seemingly 
innocuous it may be in the cells of a human or other 
mammal, whether inserted by viral infection or some 
other mechanism, poses the risk that a protein will 
be produced in the infected cells which has never been 
seen by the host's immune system. Thus the possibility 
of an auto immune disease exists (as in rheumatic fever 
or degenerative kidney disease) in which the body produces 
antibodies against proteins within or produced by its 
own cells, ultimately destroying the cells themselves. 
The NIH guidelines discuss "harmful" genes in the sense 
of DNA specifying antibiotic resistance factors or protein toxins. 
1/ Davis, et al., supra at 1318. RNA = ribonucleic acid. Some 
viruses contain RNA rather than DNA. 
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