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The other thing — other than survival — which we have to be particularly 
concerned with in talking about biological containment is to limit transmis- 
sion of vectors which carry recombinant DNA to other organisms. That is, 
it doesn't do us much good if the host has died if the vector carrying the 
recombinant has already been transmitted to a new host which is able to 
survive outside the laboratory. In this respect we concern ourselves, for 
instance, with host-dependent mutations, for instance amber mutations and 
the bacteriophage lambda, so that it can only grow in particular hosts 
which carry suppressor mutations. These are the two aspects of biological 
containment which will come up again as I discuss the particular categories 
which we are proposing for the revised Guidelines. 
I would also like you to keep in mind that in the last year there has 
been significant progress in the application of the concept of biological 
containment to recombinant DNA technology. As of a year ago, there were 
not any certified EK2 host-vector systems, and now there are a variety of 
them both, hosts and vectors — plasmid vectors and bacteriophage vectors. 
Our experience with certifying these and looking at the test data on these 
plays some part in the revision of the Guidelines, which I will be talking 
about . 
The major change which you may all notice in the proposed revised 
Guidelines is a new nomenclature, HV1 , HV2, HV3. This stands for host-vec- 
tor systems. This is a generalization of the concept that was used in the 
original Guidelines, EK1 for E. coli K-12. And we have put it in as a 
beginning framework to start considering hosts other than E. coli K-12. 
Within the HV1, HV2, and HV3 nomenclature, EK1 , EK2, and EK3 are particular 
examples, and really the ones which are almost exclusively in use at the 
moment . 
To begin with, then, we have generalized EK1 to an HV1 possibility, and 
we have changed a little bit the requirements for host-vector systems other 
than E. coli . I think in the initial Guidelines my impression is that hosts 
other than E. coli were mostly considered in terms of their safety relative 
to E. coli K-12. That is, the relevant paragraphs in the 1976 Guidelines 
suggest that any new host-vector systems should offer some advantage over 
E. coli K-12 in terms of safety and containment. 
What we are proposing for the revised Guide-lines is somewhat different 
criteria. That is, I think it has become obvious that in some cases one 
wants to use a different host-vector system not because it is necessarily 
better than E. coli K-12, but if it is as good, one would like to use it 
because one wants to study that particular bacteria for instance. There 
are scientific considerations that suggest that one should generalize the 
use of different hosts and vectors. 
So therefore, we have built some flexibility into the possibility of 
certification of other host-vector systems. But I want to emphasize that 
we are not suggesting that these new host-vector systems be taken as whole- 
sale replacements for E. coli K-12. What we are suggesting is that if a 
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