Recombinant DNA Advisory Committee - 03/1-2/93 
Dr. Hirano said that there is no evidence that the third treatment is necessary. How 
long does GCV persist in the body? Is there data to demonstrate that the proposed 
concentration of GCV will not kill the VPC before the HS-tk gene has been integrated 
into the patient's brain tumor cells? Regarding the safety of the VPC, what is the 
minimum concentration of VPC per ml that will be produced per production lot? Will 
all of the proposed safety studies be performed on only a portion of each production lot? 
Are the assays employed for the detection of replication-competent retroviruses (RCR) 
sensitive enough to detect less than one RCR particle per volume, i.e., 200 ml? Are the 
VPC cryopreserved? If not, are these cells stable after several weeks in culture? What 
is the timetable from the production of the VPC to the time that they are administered 
to the patient? She noted that the investigators did not include the possibility of a third 
treatment in the informed consent document. She requested that the investigators 
provide an update regarding Dr. Oldfield's approved glioblastoma protocol, on which Dr. 
Culver is a co-investigator. 
Review-Dr. Geiduschek 
Dr. Geiduschek stated that the investigators had provided adequate responses to his 
concerns regarding the preclinical summary and the informed consent document; 
however, their response regarding the safety of the PA317 packaging cell line was 
inadequate. Dr. Culver stated in his written response that no breakout of RCR has 
occurred with PA317, and that there is no alternative packaging cell line that can be 
used for this protocol. Dr. Geiduschek said that although breakout of RCR in PA317 
occurs at a relatively low frequency, it is possible. In addition, there are alternative 
packaging cells lines that could be used for this protocol. 
Dr. Geiduschek suggested that the problems associated with RCR breakout in PA317 
might be minimized by implementing the following procedures: (1) limit the period of 
time that the PA317 cells are expanded in culture, (2) cryopreserve the PA317 cells 
while a portion of these cells is grown in culture for a defined period of time to monitor 
for RCR breakout, or (3) use a new generation of packaging cells, i.e., Y-CRIP producer 
cells. 
Other Comments 
Dr. Miller stated that new packaging cell lines are being developed with split genomes in 
which the gag and env portions are separated. A canine packaging cell line is currently 
being developed that would eliminate the problems associated with murine helper virus 
production. However, the developer of this canine cell line recently reported an incident 
of helper virus production. Therefore, using a split genome packaging cell line does not 
necessarily guarantee safety. Since there is no method available to determine whether 
helper virus will be produced in the patient's brain, the RAC must determine that the 
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Recombinant DNA Research, Volume 17 
