Recombinant DNA Advisory Committee - 10/7-8/91 
patients in the United States. This homozygous group has on average elevated 
cholesterol levels of around 700 mg/dl. There is no therapeutic treatment of choice for 
homozygous FH at this time. One approach is to purge the blood of LDL by bringing 
the patient in every other week for plasmapheresis. The level of LDL goes down 
temporarily and then returns to baseline. This is done for the life of the patient. There 
is also orthotopic liver transplantation. There is significant morbidity associated with this 
procedure although some decrease in cholesterol levels has been obtained. These 
conditions suggested a model for gene therapy in that selective reconstitution of LDL 
receptor expression in the liver could produce some level of metabolic correction. 
Dr. Wilson described the experimental strategy. A portion of the liver from a FH 
patient would be removed and cultures of the hepatocytes established. The recombinant 
retrovirus able to efficiently transduce these cells would be generated, the cells 
transduced, and transplanted back into the patient. He cautioned that normal levels of 
LDL receptor activity cannot be reconstituted in the patient. However, the procedure 
should provide some level of correction. He described the preclinical animal 
experiments. In the animal model for FH, the Watanabe rabbit, a portion of the liver 
was removed, the hepatocytes were transfused with a recombinant retrovirus that 
expresses the rabbit LDL receptor gene, and introduced back into the rabbit. LDL 
receptor expression was reconstituted in about 20%, or as many as 50%, of the 
transduced hepatocytes as shown in RNAse protection analysis. The level of correction 
varied between a 175 mg/dl to a 450 mg/dl decrease in cholesterol levels. It seemed to 
be proportional to the level of baseline cholesterol in the rabbits, which averages 
approximately 600 mg/dl. 
Dr. Wilson then described experiments using human hepatocytes. Interestingly, 
hepatocytes obtained from the youngest patient yielded the highest level of gene transfer. 
As to the issue of the age of the patients used in the study, his observation in virtually 
every animal experiment, as well as in the limited human cell experiments, is that the 
hepatocytes isolated from a younger specimens are more capable of incorporating the 
retrovirus. He noted that the entire vector to be used in the study is being sequenced in 
an appropriate FDA-approved laboratory. The packaging cell line is Y-CRIP. It differs 
from the packaging cell lines used by others in that both functions necessary to form a 
virus are contained on separate DNA molecules. This would make it less likely that a 
recombinant replication competent virus would be formed. 
Dr. Wilson noted that the real risks of the procedure are not related to recombinant 
DNA but are related to the surgical procedures and manipulations. The patient is only 
subjected to one operative procedure. During the liver resection, a catheter that exits 
percutaneously will be placed in the inferior mesenteric vein which leads into the portal 
circulation. The cells will be infused into the catheter which will be subsequently 
removed; this can be done at the bedside. After a dialogue with the referring physician, 
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Recombinant DNA Research, Volume 15 
