Human Gene Therapy Subcommittee - July 29-30, 1991 
with respect to oncogenesis are largely unknown. 
Dr. Wilson said there is genotype-specific variation in the level of residual LDL 
receptor activity amongst FH patients. If a patient has a deletion of both alleles, the 
level of residual activity is zero. If there is a simple point mutation in which a 
defective receptor is formed, there may be some residual function. There is a 
continuum in the patient population because of this genetic heterogeneity, and the 
hypothesis is that the level of residual LDL receptor function correlates with severity of 
disease. There are plans to evaluate the receptor status of FH homozygotes who are 
symptomatic with coronary artery disease as defined by angina pectoris and/or a history 
of myocardial infarction. If these patients are receptor-negative, which is defined as 
having less than 2% residual activity, they would undergo a noninvasive evaluation to 
identify any contraindications to the surgical procedure. Patients with no contradictions 
would be evaluated by the consult service, and appropriate support for their procedure 
would be provided. The percentage of the receptor-defective patients meeting these 
inclusion criteria is unknown. 
Dr. Wilson discussed the vectors and viruses to be used in the treatment. He noted his 
extensive experience with recombinant retroviruses, vectors, and packaging cell lines. 
He said the packaging cell line, T-CRIP, is theoretically safer than the existing 
packaging cell line that has been previously approved for use in human gene transfer 
protocols. Two key functions that are necessary to make a recombinant retrovirus are 
located on separate DNA fragments, and they are sequentially transfected into a 
packaging cell line. In animal experiments, gene expression persisted for at least six 
weeks, and there were no untoward effects. A 15% decrease in patients' cholesterol 
would be considered a success. Dr. Wilson also stated that valuable information about 
FH would be derived from this protocol. 
Dr. Neiman asked about the sensitivity level for detecting infectious virus particles in 
the supernatant of the packaging cell line. Dr. Wilson said he could probably detect a 
single replication-competent virus per 10 ml. Dr. Neiman said this is the same 
detection level seen with another packaging cell line, PA317. 
Dr. D. Miller asked what viruses the investigators were capable of detecting. Dr. 
Wilson said he had assayed for ecotropic and amphotropic viruses, but not xenotropic 
viruses. 
Dr. D. Miller asked if the packaging cell line had been tested for other adventitious 
agents. Dr. Wilson said they were currently in the process of screening for these 
agents. 
Mr. Capron asked how long it would take to complete these studies. Dr. Wilson said 
that FDA was the rate-limiting step. The information will take approximately three 
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Recombinant DNA Research, Volume 14 
