681. Hydrogel Encapsulation of Adenovirus-Transduced Cells Expressing BMP2 for Local Osteoinduction

Abstract

The use of gene therapy as an alternative to autogenous bone grafting techniques commonly utilized to promote regeneration and healing have been very promising due to recent advances in recombinant adenoviral vectors encoding bone morphogenetic protein 2 (BMP2), which have been shown to induce bone formation via ex vivo cell transduction. However, major limitations to the delivery of transduced cells include targeted immune reactions towards the cells that result in increased clearance and a lack of immobilization of the cells within a specific tissue that can lead to spatially uncontrolled gene expression. One alternative is the encapsulation of ex vivo transduced BMP2 expressing cells within immunoprotective hydrogels. The poly(ethylene glycol)-based hydrogels used in these studies have permeability sufficient to allow diffusion of BMP2 out of the hydrogels but are impermeable to antibodies and immune cells. Thus, we have encapsulated human diploid lung fibroblasts (MRC-5) transduced with a chimeric adenovirus type 5 (Ad5) with a fiber gene of adenovirus type 35 encoding BMP2 (Ad5F35-BMP2) within PEG diacrylate (PEGDA) hydrogels to form tissue engineered scaffolds that offer immuno-protection. PEGDA hydrogels were polymerized in a 1:1 ratio of polymer:cell suspension into circular disks having diameter of |[sim]|11.5mm and thickness of |[sim]|0.5mm and maintained in culture for 14d. The conditioned media from the cultured disks were then assayed for BMP2 protein with an ELISA assay, which showed continued BMP2 production for the 14d period with peak protein levels occurring on day 5 that were comparable to control transduced plated cells at the same time interval (p>0.05). Cell viability was determined using Molecular Probes Live/Dead Staining Kit 24 h post encapsulation, which showed viabilities of |[sim]|74% and |[sim]|66% for encapsulated MRC-5 and transduced MRC-5 (tMRC-5) cells, respectively. The mechanical strength of the PEGDA hydrogels with encapsulated cells was investigated on an Instron 3342 mechanical tester at a crosshead speed of 1 mm/min, which showed that there was no significant difference in compressive modulus, 277kPa for hydrogel only and 270kPa for hydrogel with cells (p>0.05).