Recombinant DMA Advisory Committee - 3/3-4/94 
infectious organisms or more. The introduction of the chloramphenicol resistance gene 
will eliminate one of the two antibiotics (chloramphenicol and tetracycline) known to be 
effective in the treatment of a human infection, louse-bome typhus. Dr. Straus stated 
that if there are known deletions of the virulence genes, the organism cannot revert to a 
virulent form, or the organism is crippled in some other way, he would recommend 
approval of this request; however, considering the significant safety concerns, the RAC 
should not set a precedent by approving this proposal even for a one-time experiment 
under BL3 containment. 
Other Comments 
Dr. Parkman suggested an alternative to disapproving this request. The RAC could 
recommend approval with the stipulation that any residual bacterial stocks be destroyed 
once the transformation experiment has been conducted. 
Dr. Straus said that there is no absolute scientific reason for inserting the 
chloramphenicol resistance gene. Although the investigator has stated that 
chloramphenicol resistance is the selectable marker of choice, other options are 
available. Dr. Straus said that he would recommend approval of this experiment only in 
a Biosafety Level 4 containment facility and contingent on the destruction of any residual 
bacterial stocks once the experiment is performed. The RAC should not set a precedent 
for this type of experiment. 
Dr. Motulsky inquired about the scientific merit of this experiment. Dr. Straus explained 
that the biology of Rickettsia organisms is not well understood. These bacterial 
pathogens cause serious human disease, e.g.. Rocky Mountain Spotted Fever and typhus- 
like syndromes. This organism has been known to cause devastating illness (typhus) in 
wartime. Currently, there is no vaccine for typhus. Dr. Straus stated that the objective 
of such research is extremely valuable; however, a selectable marker other than 
chloramphenicol resistance would be preferable. 
Dr. Post said that in consideration of the serious safety concerns raised by Dr. Straus, 
this request should be deferred until the investigator proposes an alternative request, 
e.g., use of a Biosafety Level 4 facility, alternative selectable marker, etc. 
Dr. DeLeon asked whether the investigator submitted additional data since the previous 
review. Dr. Post answered that additional data was not provided, only a more detailed 
description of the proposed experiment. 
Dr. Walters asked whether there is any genetically modified Rickettsia that would be less 
virulent. Dr. Straus said that for many bacteria the virulence genes are not well-defined. 
He cited a recently published document showing that it is possible to create an 
experimental environment in which the organism has reduced virulence. Under this 
condition, experiments using virulent organisms can be performed. It might be 
worthwhile to attempt to produce avirulence in culture and then transfer the organism to 
animals where there is the possibility of upregulating certain genes that will restore 
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