They have proposed engineering tissues by the incorporation and sustained release of plasmids encoding tissue-inductive proteins from polymer matrices. Matrices of poly(lactide-co-glycolide) (PLG) were loaded with plasmid, which was subsequently released over a period ranging from days to a month in vitro. Sustained delivery of plasmid DNA from matrices led to the transfection of large numbers of cells. Furthermore, in vivo delivery of a plasmid encoding platelet-derived growth factor enhanced matrix deposition and blood vessel formation in the developing tissue. This contrasts with direct injection of the plasmid, which did not significantly affect tissue formation. This method of DNA delivery may find utility in tissue engineering and gene therapy applications.
Lost or deficient tissue function leads to millions of surgical procedures each year and a loss to the US economy of hundreds of billions of dollars1. Tissue engineering has emerged as a potential means of growing new tissues and organs to treat these patients, and several approaches are currently under investigation to engineer structural tissues. One approach involves transplanting cells on biodegradable polymer matrices. Matrices serve to deliver cells to a specific anatomic site, create and maintain a space for tissue development, and guide tissue formation before being degraded2. Limitations of this approach include the need to isolate and expand cells in vitro, and poor survival of many cell types following transplantation3. A separate strategy involves the delivery of tissue-inductive proteins (e.g., bone morphogenic proteins, platelet-derived growth factor [PDGF])4. One important drawback of this approach is decreased protein stability in the delivery system5. Recently, delivery of plasmid DNA encoding for inductive factors has been proposed as a replacement to direct delivery of the protein6,7. However, the delivery of plasmid DNA in vivo is typically associated with low levels of gene transfer and cellular expression, perhaps due to a limited exposure of cells to the plasmid8.
We propose that incorporation of plasmid DNA into tissue engineering matrices and its subsequent sustained release in vivo may provide an optimal means to engineer tissues. Sustained delivery of plasmid DNA from the polymer matrix may transfect large numbers of cells at a localized site leading to production of a therapeutic protein to enhance tissue development. Delivery of a plasmid encoding PDGF, a potent factor in tissue repair, has now been used to demonstrate that the composition and structure of engineered tissue can be controlled with this approach. Localized PDGF delivery may allow for tissue regeneration in a variety of situations (e.g., periodontal disease9). In addition, this gene delivery approach may find use in other applications, including DNA vaccines and correction of metabolic deficiencies.1
Shea, L., Smiley, E., Bonadio, J. et al. DNA delivery from polymer matrices for tissue engineering. Nat Biotechnol17, 551–554 (1999). https://doi.org/10.1038/9853