- 3 - 
(p38455) , experiments testing marker rescue by normal strains from such vectors 
have yet to be performed. Even such experiments ignore the potential recombi- 
nation by mechanisms such as I have detailed above. The transducing phage we 
have found in a very common enteropathogenic ^ coli would easily repair, at 
high efficiency, one or more of the defects in an ^ coli K-12 vector, and un- 
doubtedly there are very many other such phages, and plasmids, in other common 
gut coliforms. It is true that the requirement for a separate recombination 
event for each of several markers drastically reduces the probability of repair- 
ing all defects. However, complete repair of all mutant markers might not be 
necessary to permit subsequent transfer of the recombinant DNA fragment to a 
non-K-12 host. 
All permissible recombinant experiments, including the most potentially 
hazardous (shotgun experiments from primate DNA) are permissible with EK2 hosts, 
providing containment is stringent enough. In my opinion, the probability of 
marker rescue conferred by the above mechanisms is high enough to make the EK2 
systems described in the Guidelines unsuitable for such use. 
III. Dangers Inherent in the Use of Mammalian Viruses of Oncogenic Potential 
I will comment less on this problem because of less familiarity with the 
field, but certain points are apparent. At first blush, polyoma, which cannot 
transform primate cells, and SV 40, made defective so that it has lost essential 
functions, seems relatively safe because of the low probability of their survi- 
val ^ vivo . But, as for ^ coli , the safety may well be only apparent because 
recombinational events in vivo , as yet unassayed, may occur, especially if, as is 
likely, a large number of as yet unidentified viruses. Including defective ones, 
exist in normal tissues. 
I view the situation as precisely analogous to the ^ coli one, but more 
dangerous, because our ability to assay the many unknown viruses that might 
rescue markers is very primitive, and our ability to design experiments to test 
this rescue is very limited. For this reason, I believe that animal virus 
vectors should be limited to non-mammalian viruses, with no oncogenic potential 
in mammalian hosts or tissue culture systems. 
IV . Containment Measures 
I believe that stringent containment procedures, while necessary and commend- 
able, will reduce only slightly (perhaps by a factor of 10“2 or so), the risk of 
vector spread. My belief is based on observing the efficacy of radioactive 
isotope control in biomedical research. As any laboratory worker can attest 
from personal knowledge (especially if promised anonymity.'), there have been 
innumerable instances of careless handling of isotopes. Even though isotopic 
contamination is readily detectible, the vast majority of these escape the 
attention of enforcing agents. This problem does not reflect any especial 
wickedness or irresponsibility on the part of scientists: scientists are human, 
and some are more human than others. Whether from error, the excitement of the 
"scientific chase," underestimating the risks involved, or, only very rarely, 
deliberate flouting of rules, such accidents will occur. 
Appendix K — 121 
