Recombinant DNA Advisory Committee - 09/14-15/92 
researchers. Approximately how many laboratories have used this expression system? 
What level of physical containment has been employed? Dr. Temple introduced his co- 
investigator, Dr. Liljestrom, to respond to Dr. Doi's question. Dr. Liljestrom said that 
the system has only been used in about ten laboratories because of safety concerns. All 
of these laboratories have a great deal of expertise working with SFV. 
Dr. Krogstad spoke in regard to the earlier question about transmission. Just because no 
data exists regarding the issue of mosquito transmission, one should not rule out 
transmission by mosquito vectors. It is appropriate for the RAC to make their decisions 
based on the nature of the virus and on the appropriate containment for protecting it 
from exposure to the outside. There is inadequate evidence regarding the vector 
population in the U.S. and its competence. 
As a point of clarification, Dr. D. Miller asked Dr. Liljestrom if the term "leakiness" 
referred to the ability to infect cells, but not necessarily to replicate. Dr. Liljestrom 
agreed to the interpretation of the term "leakiness". Dr. D. Miller noted that the data 
presented earlier suggested that the SQL mutant could convert to a pathogenic virus at a 
relatively high frequency, i.e., 1 in 10 7 particles. It is conceivable that an investigator 
may be working with as much as 10 9 particles using this kit. Therefore, there is a high 
probability that replication competent helper virus will be generated using this system. 
Dr. Liljestrom disagreed with Dr. D. Miller's statement, noting that the recombination 
frequency would have to be combined with the reversion frequency to estimate the 
frequency of replication competent particles. Dr. Schaechter stated that the data is not 
convincing. It represents the actual conditions of the experiment to be performed; 
therefore, the data does not accurately reflect the likelihood of detecting recombinant 
particles. One experiment does not reflect the degree of variability that would be 
observed from multiple tests. The data reflects imprecise measurements. Dr. Temple 
agreed that they have not performed strict reconstruction experiments. Instead, they are 
only able to conclude that they can detect a single or several recombinational events 
when equal number of cells to viral particles are used. 
Dr. D. Miller said if helper virus is detected occasionally, what is the persistence of this 
virus on cell surfaces? How stable are these viruses in the laboratory environment? Dr. 
Temple responded that there is no data regarding the persistence of the viruses on open 
surfaces. Dr. D. Miller asked if inactivation experiments were performed. Dr. 
Liljestrom stated that SFV is a membrane virus; therefore, it is probably very labile. 
Virus particles would probably be dead in one to two days since detergents or 1% 
hypochlorite inactivate animal membrane viruses in seconds; contamination of membrane 
viruses could be cleaned up readily. 
Dr. Temple responded to the question regarding the physical containment classification 
of BL3. The classification was based on the one reported death attributed to contact 
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