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DAVID
G. HWANG, M.D., F.A.C.S.
Professor
Co-Director, Cornea Service
Director, Refractive Surgery Service
Director, Laser Vision Center
Medical Director, MTF Tissue Services, California
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Research
Summary
Corneal
Transplantation
My research efforts have focused on developing novel cell transplant
and gene therapy strategies to address two current problems in corneal
transplantation: the worldwide shortage of donor corneal tissue and
the risk of corneal transplant rejection. Of particular interest is
a technique called corneal endothelial cell transplantation (pioneered
by Drs. Jorge Alvarado, Denis Gospodarowicz
and colleagues at UCSF, who successfully transplanted corneal endothelial
cells cultured from cow eyes into the eyes of rabbits and cats). |
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This
investigational technique promises to complement or supplant conventional
corneal transplantation. A sample of corneal cells is harvested, multiplied
in culture, and surgically implanted into the eye. We have improved
methods for culturing human corneal endothelial cells and have demonstrated
successful results from experimental transplants of these human corneal
cells into animal eyes. This technique could allow healthy cells from
a patient's eye to be cloned and transplanted back to the patient,
without the threat of rejection. Alternatively, cells from a single
donor could provide enough cells for hundreds of recipients, thereby
alleviating shortages of donor corneal tissue.
Growing Corneal Endothelial Cells.
Coaxing human cells to grow in culture is a much more difficult task
than prodding cow cells to grow in culture. After birth, human corneal
endothelial cells no longer are capable of dividing. However, by placing
cells on dishes coated with a specially formulated matrix and exposing
the cells to specific growth factors, the cells can be triggered into
remembering a long-inactive program that instructs them how to divide.
In collaboration with Drs. Ge Ming Lui and Jorge Alvarado, we have
reported success in growing corneal endothelial cells from donors
of all ages, and we have induced these cells to divide as many as
20 to 40 times without slowdown, which translates into an amplification
factor of over a million-fold. Unlike native corneal endothelium,
which must be used within days of harvesting, cultured corneal endothelium
can be readily frozen and thawed when desired for later use.
Immunomodulation and Gene Therapy.
We have demonstrated that cultured corneal endothelial cells can be
pharmacologically treated or genetically modified to enhance their
characteristics prior to transplantation. Certain compounds, when
added to cultured endothelial cells, can reduce their "foreignness"
(antigenicity), which may make them less prone to rejection. We have
reported that nicotinamide (a drug currently used for the treatment
of elevated cholesterol) can suppress the expression of histocompatibility
antigens in cultured human corneal endothelial cells. We have also
synthesized a small fragment of DNA that blocks activation of transplantation
antigen genes. This novel strategy, called donor tissue immunomodulation,
could improve the odds of rejection-free graft survival and reduce
the long-term need for immunosuppressive medications.
We have also introduced genes into cultured human corneal endothelial
cells using a variety of techniques and shown that these cells retain
their genetic modification after being transplanted yet continue to
function normally. With these techniques, patients suffering from
corneal disease might some day have their cells harvested, treated
with gene therapy, then re-introduced into the eye. In work with Dr.
Fen Zhang, we have also designed special vectors, which when injected
are capable of transferring genes directly into eye tissues. |
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