SOMATIC GENE TRANSFER IN THE STUDY AND TREATMENT OF METABOLIC DISEASES 
James M. Wilson, M.D., Ph.D., Assistant Investigator 
Research in Dr. Wilson's laboratory focused on 
the use of somatic cell gene transfer in the study 
and treatment of metabolic diseases. A variety of so- 
matic cells were used as targets for gene transfer, 
including hepatocytes, vascular endothelial cells, 
and hematopoietic stem cells. 
I. Liver-directed Gene Transfer. 
Familial hypercholesterolemia (FH) is an autoso- 
mal dominant disorder in humans caused by defi- 
ciency of the receptor for low-density lipoproteins 
(LDL) that Dr. Wilson has used as a model for de- 
veloping liver-directed gene therapies. This genetic 
disease is a useful model because 1) biochemical, 
pathophysiological, and clinical aspects of FH have 
been well described, and the corresponding normal 
gene is available; 2) phenotypic correction of the 
metabolic abnormalities associated with FH will 
probably require gene transfer into the hepatocyte, 
because the liver is the primary organ responsible 
for degradation of LDL and the only organ capable 
of excreting cholesterol; 3) an authentic animal mod- 
el for FH exists, the Watanabe heritable hyperlipid- 
emic (WHHL) rabbit; and 4) no effective conven- 
tional therapy exists for homozygous deficient FH, 
other than combined liver heart transplantation. 
One approach to the genetic treatment of FH is 
similar in concept to the well-described bone mar- 
row gene therapies. This method involves isolating 
hepatocytes from a genetically deficient animal, 
transferring a functional LDL receptor gene to he- 
patocytes in vitro, and transplanting the genetically 
modified cells back into the affected animal. Hepa- 
tocytes were harvested from WHHL rabbits, plated 
in primary cultures, and exposed to recombinant 
retroviruses capable of efficiently transferring a 
functional LDL receptor gene. The genetically mod- 
ified cells were harvested and infused into the por- 
tal vein of WHHL recipients; serial measurements of 
serum cholesterol were performed. Similar trans- 
plantation experiments were performed with the 
hepatocytes derived from an allogeneic strain of 
rabbits that expresses normal levels of LDL recep- 
tor. In each case, transplantation of hepatocytes 
that express LDL receptor into WHHL rabbits con- 
sistently led to substantial decreases in total serum 
cholesterol for up to 14 days; fractionation of lipo- 
proteins indicated that this is largely due to dimin- 
ished LDL cholesterol. 
A potentially more effective and less morbid ap- 
proach to the genetic treatment of FH is to target 
the delivery of a functional LDL receptor gene to 
hepatocytes in vivo. Dr. Wilson is collaborating 
with Drs. George and Cathy Wu (University of Con- 
necticut) to develop methods for targeting recombi- 
nant genes to hepatocytes that are based on inter- 
actions with the hepatocyte-specific receptor, the 
asialoglycoprotein receptor. The most encouraging 
results have been obtained with a synthetic DNA- 
protein complex. A high-affinity ligand for the asia- 
loglycoprotein receptor (asialoorosomucoid) is co- 
valently linked to polylysine, and this protein 
conjugate is coupled with DNA of an expression 
vector. When injected into the venous circulation of 
rats, the protein-DNA complex is specifically inter- 
nalized by hepatocytes via the asialoglycoprotein 
receptor, and the reporter gene of the vector is 
expressed for —2-3 days. Expression has been 
demonstrated in rat liver in vivo with vectors that 
contain constitutive as well as liver-specific tran- 
scriptional elements. In an attempt to achieve long- 
term expression of the recombinant gene, rats were 
subjected to partial hepatectomy immediately after 
the administration of DNA-protein complex. High- 
level expression of the reporter gene has been de- 
tected in livers of these animals for at least 4 
months. The mechanisms responsible for this per- 
sistent transgene expression have not been defined. 
Similar approaches will be used to target the deliv- 
ery of functional LDL receptor genes to the livers of 
WHHL rabbits. 
II. Recombinant Gene Expression in Vascular Endo- 
thelial Cells. 
The endothelial cell is an important component 
of blood vessels that is involved in the maintenance 
of vascular homeostasis. Dr. Wilson, in collabo- 
ration with Dr. Richard Mulligan (Whitehead 
Institute), has explored the possibility of using 
the vascular endothelial cells to target for gene 
transfer. 
Replication-defective retroviruses were used to 
transduce recombinant genes efficiently into pri- 
mary cultures of endothelial cells established from 
human, canine, and bovine vascular tissues. A vari- 
ety of recombinant genes have been expressed in 
endothelial cells using this system, including those 
that encode for platelet-derived growth factor re- 
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