846. Copolymer-Protected Vector Mediated BMP-2 Gene Delivery to Articular Chondrocytes in a 3-Dimensional Injectable Fibrin Matrix for Tissue Engineering

We have previously demonstrated the superiority of copolymer-protected gene vectors (COPROGs) over naked DNA and standard nonviral vectors in matrix-mediated gene delivery (Scherer et al. 2002, J. Gene Med. 4:634-643). Here we present a novel carrier formulation based on lyophilized fibrinogen-vector compositions. Upon rehydration and local mixing with thrombin, these preparations can be used as fibrin glues for the local in situ delivery of genes and nucleic acids, particularly of growth factor genes for tissue engineering. As fibrin is an excellent matrix for cell growth, the preparations can be formulated with cells to fill tissue defects such as cavities in cartilage or bone or to cover skin defects. Naked DNA is readily released from fibrin clots (70 % within 5 days) while COPROGs remain tightly immobilized in the fibrin matrix over extended periods of time with a linear release of 0.29 % per day. Naked DNA was essentially inactive in mediating gene delivery to primary cells including chondrocytes and keratinocytes incorporated in vector-loaded fibrin clots. COPROGs mediated efficient and sustained transfection resulting in transgene expression over at least three weeks. The transfection of the BMP-2 gene in chondrocytes enclosed in COPROG-loaded fibrin clots in vitro led to sustained BMP-2 expression and to the induction of alkaline phosphatase as well as to increased production of extracellular matrix. Sustained reporter gene expression was achieved in critical cartilage defects in rabbit knee joints filled with autologous chondrocyte-COPROG-fibrin glue composites. In conclusion, COPROG-loaded fibrinogen preparations used as gene-activated fibrin glue display a strong potential as injectable implants for tissue repair and also as growth factor producing matrices for tissue engineering.