A localizable, biological-based system for the delivery of bioactive IGF-1 utilizing microencapsulated genetically modified human fibroblasts

Control of the timing and dosage of IGF-I delivery from encapsulated cells

We report here on the development and characterization of a cell-based system for the regulated delivery of bioactive insulin-like growth factor I (IGF-I). A stable mammalian cell line, CHO-K1 Tet-IGFI, was genetically modified to have tetracycline-induced transcription of the human IGF-I gene. Cells were activated to express IGF-I in the presence of doxycycline (DOX), a tetracycline derivative, while expression was inactivated in the absence of DOX. Temporal, or on-off, release of IGF-I from cells encapsulated within Ca²⁺-alginate hydrogels was demonstrated in a pilot study over the course of 10 days in culture. Released growth factor was bioactive, exhibiting a proliferative effect comparable to recombinant purified IGF-I protein. The dosage levels and temporal control of IGF-I release from encapsulated cells meet the requirements of orthopedic wound repair, making this approach an attractive means for the controlled synthesis and delivery of growth factors in situ for wound healing.

Clinical potential and challenges of using genetically modified cells for articular cartilage repair

Articular cartilage defects do not regenerate. Transplantation of autologous articular chondrocytes, which is clinically being performed since several decades, laid the foundation for the transplantation of genetically modified cells, which may serve the dual role of providing a cell population capable of chondrogenesis and an additional stimulus for targeted articular cartilage repair. Experimental data generated so far have shown that genetically modified articular chondrocytes and mesenchymal stem cells (MSC) allow for sustained transgene expression when transplanted into articular cartilage defects in vivo. Overexpression of therapeutic factors enhances the structural features of the cartilaginous repair tissue. Combined overexpression of genes with complementary mechanisms of action is also feasible, holding promises for further enhancement of articular cartilage repair. Significant benefits have been also observed in preclinical animal models that are, in principle, more appropriate to the clinical situation. Finally, there is convincing proof of concept based on a phase I clinical gene therapy study in which transduced fibroblasts were injected into the metacarpophalangeal joints of patients without adverse events. To realize the full clinical potential of this approach, issues that need to be addressed include its safety, the choice of the ideal gene vector system allowing for a long-term transgene expression, the identification of the optimal therapeutic gene(s), the transplantation without or with supportive biomaterials, and the establishment of the optimal dose of modified cells. As safe techniques for generating genetically engineered articular chondrocytes and MSCs are available, they may eventually represent new avenues for improved cell-based therapies for articular cartilage repair. This, in turn, may provide an important step toward the unanswered question of articular cartilage regeneration.