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Abstract from the SRS 2001 Annual Meeting
M. Darryl Antonacci, M.D.
Manu Nothias
Catherine Humphreys
Richard Frisch
Marion Murray, Ph.D. Philadelphia, PA, USA INTRODUCTION: In a recent publication
from our institution (J. Neuroscience, June, 1999), regeneration of the rubrospinal
tract was demonstrated in an adult rat cervical spinal cord injury model with
recovery of forelimb function. This was achieved through transplantation of cell
cultures of fibroblasts genetically modified to secrete NT3 (neurotrophin-3) and
BDNF (brain derived neurotrophic factor), using ex-vivo gene therapy, into a hemi-section
model. The purpose of the current study was to achieve regeneration across a complete
cord transection defect. METHODS: 21 adult rats underwent mid-thoracic laminectomy
and complete spinal cord transection, creating an approximately 3 mm defect. The
defect was filled with a carefully titrated number of genetically modified fibroblasts
which were engineered using retroviral vectors to secrete neurotrophic factors
(NT-3, and BDNF), which are known to enhance axonal regeneration. Animals received
modified fibroblasts suspended in Vitrogen (a collagen based carrier); powdered
gelfoam, platelet gel, and without matrix. Post-operatively, rats were functionally
tested using the BBB test for locomotion. Rats also received cyclosporin A immunosuppression
post-operatively. At two months rats were sacrificed. Graft site and adjacent
spinal cord tissue was harvested and serially sectioned for histologic analysis.
Immunofluorescent mouse antibody labeling for neurofiliment protein (RT97) and
serotonin was also carried out. RESULTS: Data for a complete spinal cord transection
model supports prior published data for cervical hemisections. Robust regeneration
of adult CNS axons was observed traversing the spinal cord defect and for several
segments distal to the injury. Overall transplanted fibroblast survival was high
in each group. A trend towards more axonal regeneration was noted in groups which
received a higher titrated number of modified fibroblasts. Some functional recovery
was noted in rats receiving transplants versus controls by increases in BBB score
by 2-3 grades. SUMMARY: By providing specific nerve growth factors using gene
therapy, regeneration of CNS axons in adult rats across a complete spinal cord
transection was achieved. Regeneration using ex-vivo gene therapy is a significant
step in the development of treatments for spinal cord injury in humans. Future
studies will focus on combining ex-vivo gene therapy with pharmacological and
rehabilitative treatments to produce the greatest possible behavioral recovery,
first in experimental models, and later clinically.
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