Proc. Nat. Acad. Sci. USA 72 (1975) 
Conference on Recombinant DNA Molecules 1983 
can be performed in minimal risk containment facilities. 
Where such experiments pose a potential hazard, more 
stringent containment may be warranted. 
Experiments involving the creation and propagation of 
recombinant DNA molecules from DNAs of species that 
ordinarily do not exchange genetic information, generate 
novel biotypes. Because such experiments may pose bio- 
hazards greater than those associated with the original organ- 
isms, they should be performed, at least, in low risk contain- 
ment facilities. If the experiments involve either pathogenic 
organisms or genetic determinants that may increase the 
pathogenicity of the recipient species, or if the transferred 
DNA can confer upon the recipient organisms new metabolic 
activities not native to these species and thereby modify its 
relationship with the environment, then moderate or high 
risk containment should be used. 
Experiments extending the range of resistance of established 
human pathogens to therapeutically useful antibiotics or dis- 
infectants should be undertaken only under moderate or high 
risk containment, depending upon the virulence of the 
organism involved. 
2. Animal Viruses. Experiments involving linkage of viral 
genomes or genome segments to prokaryotic vectors and their 
propagation in prokaryotic cells should be performed only 
with vector-host systems having demonstrably restricted 
growth capabilities outside the laboratory and with moderate 
risk containment facilities. Rigorously purified and character- 
ized segments of non-oncogenic viral genomes or of the de- 
monstrably non-transforming regions of oncogenic viral DNAs 
can be attached to presently existing vectors and propagated 
in moderate risk containment facilities; as safer vector-host 
systems become available such experiments may be performed 
in low risk facilities. 
Experiments designed to introduce or propagate DNA from 
non-viral or other low risk agents in animal cells should use 
only low risk animal DNAs as vectors (e.g., viral, mitochon- 
drial) and manipulations should be confined to moderate risk 
containment facilities. 
3. Eukaryotes. The risks associated with joining random 
fragments of eukaryote DNA to prokaryotic DNA vectors 
and the propagation of these recombinant DNAs in pro- 
karyotic hosts are the most difficult to assess. 
A priori, the DNA from warm-blooded vertebrates is more 
likely to contain cryptic viral genomes potentially pathogenic 
for man than is the DNA from other eukaryotes. Conse- 
quently, attempts to clone segments of DNA from such 
animal and particularly primate genomes should be performed 
only with vector-host systems having demonstrably re- 
stricted growth capabilities outside the laboratory and in a 
moderate risk containment facility. Until cloned segments of 
warm-blooded vertebrate DNA are completely characterized, 
they should continue to be maintained in the most restricted 
vector-host system in moderate risk containment laboratories ; 
when such cloned segments are characterized, they may be 
propagated as suggested above for purified segments of 
virus genomes. 
Unless the organism makes a product known to be danger- 
ous (e.g., toxin, virus), recombinant DNAs from cold-blooded 
vertebrates and all other lower eukaryotes can be constructed 
and propagated with the safest vector-host system available 
in low risk containment facilities. 
Purified DNA from any source that performs known func- 
tions and can be judged to be non-toxic, may be cloned with 
currently available vectors in low risk containment facilities. 
(Toxic here includes potentially oncogenic products or sub- 
stances that might perturb normal metabolism if produced 
in an animal or plant by a resident microorganism.) 
Experiments to be Deferred. There are feasible experi- 
ments which present such serious dangers that their perform- 
ance should not be undertaken at this time with the currently 
available vector-host systems and the presently available 
containment capability. These include the cloning of re- 
combinant DNAs derived from highly pathogenic organisms 
(i.e., Class III, IV, and V etiologic agents as classified by the 
United States Department of Health, Education and Welfare), 
DNA containing toxin genes, and large scale experiments 
(more than 10 liters of culture) using recombinant I )NAs that 
are able to make products potentially harmful to man, 
animals, or plants. 
IV. IMPLEMENTATION 
In many countries steps are already being taken by national 
bodies to formulate codes of practice for the conduct of ex- 
periments with known or potential biohazard. ft,tt Until 
these are established, we urge individual scientists to use the 
proposals in this document as a guide. In addition, there are 
some recommendations which could be immediately and 
directly implemented by the scientific community. 
A. Development of safer vectors and hosts 
An important and encouraging accomplishment of the meeting 
was the realization that special bacteria and vectors which 
have a restricted capacity to multiply outside the laboratory 
can be constructed genetically, and that the use of these 
organisms could enhance the safety of recombinant DNA 
experiments by many orders of magnitude. Experiments 
along these lines are presently in progress and in the near 
future, variants of X bacteriophage, non-transmissible plas- 
mids, and special strains of Escherichia coli will become 
available. All of these vectors could reduce the potential bio- 
hazards by very large factors and improve the methodology as 
well. Other vector-host systems, particularly modified strains 
of Bacillus subtilis and their relevant bacteriophages and 
plasmids, may also be useful for particular purposes. Quite 
possibly safe and suitable vectors may be found for eukaryotic 
hosts such as yeast and readily cultured plant and animal 
cells. There is likely to be a continuous development in this 
area and the participants at the meeting agreed that improved 
vector-host systems which reduce the biohazards of recom- 
binant DNA research will be made freely available to all 
interested investigators. 
B. Laboratory procedures 
It is the clear responsibility of the principal investigator to 
inform the staff of the laboratory of the potential hazards of 
ft Advisory Board for the Research Councils, “Report of the 
Working Party on the Experimental Manipulation of the Genetic 
Composition of Micro-Organisms. Presented to Parliament by 
the Secretary of State for Education and Science by Command 
of Her Majesty, January 1975.’’ London: Her Majesty’s Sta- 
tionery Office, 1975, 23pp. 
National Institutes of Health Recombinant DNA Molecule 
Program Advisory Committee. 
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