Background: Genetically modified cells have been used in several animal models for the in vivo delivery of therapeutic proteins. One of the problems encountered is early cell death after the implantation of cells.
Materials and methods: To improve the survival of implanted cells, we have developed a system in which transfected fibroblasts are seeded onto biodegradable collagen matrices and transplanted into animals after several days of in vitro culture. Since G-CSF is widely used clinically to accelerate reconstitution of hematopoiesis after cancer chemotherapy, it was chosen to investigate in vivo delivery by transfected fibroblasts.
Results: Expression of the human G-CSF gene is maintained by transfected cells when grown on collagen scaffolds in vitro. After the i.p. implantation of collagen matrices seeded with G-CSF gene transfected fibroblasts, G-CSF serum levels could be detected for more than 2 weeks. Histological analysis of matrices explanted on day 31 and demonstration of in vitro G-CSF production reveals that genetically modified cells can survive on these implants in vivo. Large areas of the collagen are degraded and substituted with a network of endogenous argyrophilic fibers. Also ingrowth of blood vessels into the matrices is observed leading to the formation of "neo-organ' like structures.
Conclusions: Biodegradable collagen matrices can serve as scaffolds for survival of transfected fibroblasts in vivo.