Somatic Cell Gene Transfer 
James M. Wilson, M.D., Ph.D. — Assistant Investigator 
Dr. Wilson is also Assistant Professor of Internal Medicine and Biological Chemistry at the University of 
Michigan Medical School. He received his undergraduate degree in chemistry from Albion College and his 
Ph.D. (biological chemistry) and M.D. degrees from the University of Michigan. He completed a residency 
and clinical fellowship at Massachusetts General Hospital and conducted postdoctoral research at the 
Massachusetts Institute of Technology, Whitehead Institute, with Richard Mulligan. His laboratory is in- 
vestigating ways to treat genetic diseases by correcting the relevant genetic defects. 
GENE replacement therapy is being consid- 
ered for the treatment of a variety of ac- 
quired and inherited diseases. These novel thera- 
peutic modalities involve the transfer of genetic 
material into somatic tissues of affected individ- 
uals. A major focus of my laboratory is the devel- 
opment of new therapies for the treatment of car- 
diopulmonary diseases based on gene transfer 
into hepatocytes and airway epithelial cells. 
Familial hypercholesterolemia (FH) is an auto- 
somal dominant disorder in humans that is an ex- 
cellent model for developing gene replacement 
therapies of hyperlipidemic states. Patients with 
the homozygous-deficient form of FH have severe 
hypercholesterolemia and suffer life-threatening 
coronary artery disease in childhood that is refrac- 
tory to conventional medical therapies. The mo- 
lecular basis of this disorder is a systemic defi- 
ciency in the receptor that degrades low-density 
lipoprotein (LDL), the primary carrier of plasma 
cholesterol. Hepatocytes are the appropriate tar- 
get for gene transfer in this disease, because the 
liver is the primary organ responsible for LDL me- 
tabolism and cholesterol excretion. 
We have used an animal model for FH — the 
Watanabe heritable hyperlipidemic (WHHL) rab- 
bit — to develop different types of liver-directed 
gene replacement therapies for this disease. One 
approach is similar in concept to the well- 
described bone marrow-directed gene therapies. 
This ex vivo method involves isolating hepato- 
cytes from a genetically deficient animal, trans- 
ferring functional genetic material into the hepa- 
tocyte in vitro, and transplanting the genetically 
modified hepatocytes back into the affected re- 
cipient. We have used recombinant retroviruses 
to transfer a functional human LDL receptor gene 
stably into hepatocytes derived from WHHL rab- 
bits. Transplantation of these cells into WHHL 
rabbits leads to substantial decreases in serum 
cholesterol for over six months. 
An alternative and less-invasive approach is to 
deliver a functional LDL receptor gene into the 
hepatocytes in vivo. We have collaborated with 
George and Cathy Wu (University of Connecti- 
cut) to develop an in vivo gene delivery system 
that is based on interactions with hepatocyte- 
specific receptors. Using this approach we can 
deliver reporter genes specifically to hepatocytes 
in vivo and obtain high-level expression in the 
liver for at least four months following gene 
transfer. Administration of a gene transfer sub- 
strate capable of expressing LDL receptor into the 
circulation of WHHL rabbits led to significant re- 
ductions in the level of serum cholesterol. He- 
patic overexpression of LDL receptor by gene 
transfer can potentially prevent atherosclerotic 
disease in FH and other hyperlipidemic states. 
Cystic fibrosis (CF), another inherited disease, 
is characterized by abnormal salt and water trans- 
port that leads to pathology within the pancreas 
and lungs. CF is the most common congenital dis- 
ease among Caucasians, with a prevalence of 1 in 
2,000 births. The recent discovery of the gene 
that causes CF suggests a new therapeutic strategy 
in which normal functioning CF genes are di- 
rectly introduced into pancreatic or respiratory 
cells of affected patients. 
As a first step in the development of a genetic 
cure for CF, we have attempted to correct the 
physiological abnormality in cells from a patient 
with CF by introducing into them a normal CF 
gene. Replication-defective viruses were used to 
shuttle a normal CF gene into pancreatic cells of a 
patient with CF. Prior to gene transfer, the cells 
manifested the typical abnormalities associated 
with this disease (i.e., decreased transport of salt 
across the membrane). Following gene transfer, 
the cells regained normal regulation of salt trans- 
port. This demonstrates the feasibility of gene 
therapy of CF at a cellular level. 
We have now entered the second and more dif- 
ficult phase of the development of CF gene thera- 
pies, in which we are attempting to deliver nor- 
mal CF genes to the relevant somatic cells of the 
body, the cells that line the airways of the lung. 
The overall strategy is to develop a gene transfer 
substrate capable of delivering a functional CF 
gene to airway cells in vivo. Direct inhalation of 
the gene transfer substrate could provide a nonin- 
vasive way for delivering the genes to the appro- 
priate cell. 
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