Recombinant DNA Advisory Committee - 6/9-10/94 
should be used for the human experiments in order to avoid possible complications due 
to immunogenicity of HSV-TIC 
Dr. Parkman said that the HSV-TK gene is used for two purposes in this experiment: 
(1) to eliminate the transduced cells in the event of severe local reaction, and (2) as a 
surrogate marker to monitor transgene expression. Dr. Miller said that if the HSV-TK 
gene is to be used in the human study, the same vector construct should be tested in 
rabbit experiments. Dr. Miller asked the investigators to clarify whether the proposed 
MFG vector has the frame shift mutation that prevents viral gene expression or is it 
the original vector that expresses gag. 
Dr. Walters remarked that the proposed study does not involve a life threatening disease. 
Dr. Parkman said that this protocol involves the first autoimmune disease study reviewed 
by the RAC. 
Investigator Responses-Drs. Evans and Robbins 
Dr. Evans said that the investigators are well aware that the proposed trial is for a 
chronic non-fatal disease; therefore, the safety issues are an overriding concern. For this 
reason, the HSV-TK gene was included as a means to eliminate the transduced cells 
(particularly for later trials that will last more than 1 week) in the event that the cells 
escape from the synovial space or cause an unexpected adverse effect. If the RAC 
considers inclusion of the HSV-TK gene unnecessary, the IRAP alone construct will be 
used for the human study. He noted that the IRAP construct was used for the 
preclinical rabbit experiments that demonstrated efficacy. 
Dr. Evans presented expression data using the IRAP alone construct versus the 
IRAP/HSV-TK construct. A preliminary experiment with human synovial fibroblasts 
(passages 2 and 4) demonstrated between 20 and 50 ng of IRAP/1 x 10*^ cells/24 hours. 
This level of expression can be further boosted by multiple rounds of transduction. The 
current expression level exceeds the minimal level of 10 ng/1 x 10*^ cells/24 hours that 
resulted in a measurable response in rabbits. Dr. Parkman inquired about the amount 
required for maximum protection and whether the response is measured biochemically, 
i.e., glycosaminoglycan (GAG) release from the cartilaginous matrix (the presence of 
IRAP strongly protects the cartilage from breakdown). Dr. Evans responded that 
maximal protection is observed at 100 ng/1 x 10*^ cells/24 hours, and the response 
monitored is GAG production. 
Dr. Evans presented additional data on GCV sensitivity of HSV-TK transduced cells. 
Responding to the question of immunogenicity of HSV-TK, he said that HSV-TK is 
expressed as a intracellular protein and should not be immunogenic. GCV 
administration is included as a precaution against toxicity from the treatment. GCV 
administration has been considered for every patient upon completion of the experiment. 
Dr. Straus was concerned about the rationale regarding the use of GCV, and he said that 
GCV can cause bone marrow toxicity, particularly in subjects who have bone marrow 
suppression. Dr. Bill Macaulay of the University of Pittsburgh (Dr. Evans' colleague) 
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Recombinant DNA Research, Volume 19 
