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host-vector system is proposed for certification as HV1 , it be considered by 
an expert group in terms of (1) its degree of containment with respect to 
E. coli K-12, and it should be at least as good as that system; (2) it is a 
necessity in scientific terms for use as a host-vector system. If it is 
approved in that condition, we suggest approval only for P2 cloning, P2 
level physical containment cloning into that HV1 organism of nonpathogenic 
prokaryotes. So we have not suggested levels for any other classes of clon- 
ing, and what we have said is that any further experiments to be put into 
that HV1 system would require explicit approval by the Recombinant Advisory 
Committee. So in other words, an HV1 system which is approved by the Recom- 
binant Advisory Committee after careful consideration of its containment 
potential would only be approved for nonpathogenic prokaryote cloning, 
and would not be available for use, for instance, for cloning eukaryote DNA 
unless that were specifically considered by the Committee on its merits. 
Okay, that covers essentially the changes in HV1 . 
The HV2 is at the moment only EK2 . That is, there is no other system, 
I don't think, which has been proposed or is close to being proposed as an 
HV2 system, a moderate-containment, biological- containment system. The EK2 
requirements are essentially unchanged from those in the original Guidelines 
— that is, that less than one in 10 8 organisms should be able to escape from 
the laboratory if one assumes total failure of physical containment. 
I think the major change in EK2 is not in the precise wording of the 
Guidelines, but in the interpretation which has been applied to that wording 
over the last year, and I would like to just review briefly what has happened 
in the past year in terms of certification of EK2 so that you will have a 
clear understanding of how we come to approve EK2's. 
An expert working group of people working with bacteriophage and a 
separate group with expertise in plasmid vectors met, and each put together 
something which they called instructions to investigators, indicating the 
kinds of tests that they considered essential for careful testing of the 
survival and transmission characteristics of EK2 systems. The basic princi- 
ples which apply are that any numbers that we get should be most stringently 
interpreted that if we are looking, for instance, at transfer of plasmids 
from one host to another, those should be done under the most permissive 
possible conditions, and that those numbers should be submitted to the 
Committee who can then consider what the meaning of those numbers might be 
actually jji vivo , that in considering the degree of biological containment 
we should assume total failure of physical containment. That is, we know 
that all of these experiments also are to be done with particular levels of 
physical containment, but that should not be considered when we calculate 
how biologically contained an organism is. 
Following the instructions to investigators, we have received data on a 
number of EK2 systems, and particularly in the early cases I think we have 
had a great deal of discussion on them. We have asked experimenters to go 
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