Soon after the discovery in 1970 of the first restriction enzyme by American microbiologist Hamilton Smith, it became possible to combine DNA from different sources into one molecule, producing recombinant DNA. Concern by scientists and lay people that some of this recombinant technology DNA might be harmful to humans—either by unintentional or deliberate release or recombinant DNA into the environment—prompted the research to stop until scientists could evaluate its risks.
In February 1975, over 100 internationally respected molecular biologists met at the Asilomar conference center in California. There, they decided upon a set of guidelines to be followed by all scientists doing recombinant DNA research. They considered each class of experiments, and assigned it a level of risk: minimal, low, moderate, or high. Each level of risk required a corresponding set of containment procedures designed to minimize the chance of vectors (carriers) containing recombinant DNA molecules from escaping into the environment where they could potentially harm humans or other parts of the ecosystem. Because these projected experiments had never been done, assignment to a risk category was, of course, somewhat speculative and subjective. Accordingly, the potential risks were arrived at by estimate.
At all risk levels, the guidelines called for the use of biological barriers. Bacterial host cells should be from strains unable to survive in natural environments (outside the test tube). Vectors carrying recombinant DNA, including plasmids, bacteriophages, and other viruses, were to be nontransmissible and also unable to survive in natural environments.
For experiments having minimal risk, the guidelines recommended that scientists follow general microbiology safety procedures. These included not eating, drinking, or smoking in the lab; wearing laboratory coats in the work area; and promptly disinfecting contaminated materials.
Low risk procedures required a bit more caution. For example, procedures producing aerosols, such as using a blender, were to be performed under an enclosed ventilation hood to eliminate the risk of the recombinant DNA being liberated into the air.
Moderate risk experiments required the use of a laminar flow hood, the wearing of gloves, and the maintenance of negative air pressure in the laboratory. This would ensure that air currents did not carry recombinant DNA out of the laboratory.
Finally, in high risk experiments, maximum precautions were specified. These included isolation of the laboratory from other areas by air locks, having researchers shower and change their clothing upon leaving the work area, and the incineration of exhaust air from the hoods.
Certain types of experiments were not to be done at all. These most potentially dangerous experiments included the cloning of recombinant DNA from highly pathogenic organisms or DNA containing toxin genes. Also forbidden were experiments involved the production of more than 10 liters of culture using recombinant DNA molecules that might render the products potentially harmful to humans, animals, or plants.
The scientists at the Asilomar conference also resolved to meet annually to re-evaluate the guidelines. As new procedures were developed and safer vectors and bacterial cells became available, it became possible to reevaluate and relax some of the initially stringent and restrictive safety standards.
█ FURTHER READING:
Barinaga, Marcia, "Asilomar Revisted: Lessons for Today?" Science 287 (2000).