Leena-Stiina Kontturi, 2014
"Cell therapy is defined as cell transplantation into the patient to treat a certain disease state. Therapies utilizing cells can be divided into two main categories, (1) tissue regeneration or engineering and (2) drug delivery. In tissue engineering, the transplanted cells are used to regenerate the functions of a diseased tissue. In drug delivery, the transplanted cells are used as biological factories that produce therapeutic molecules inside the body. For successful cell therapy applications, cells usually must be combined with biomaterials and bioactive factors to mimic the growth environment in vivo. The properties of these scaffolds are important for outcomes of the treatments, because the local environment determines the functionality of the cells. Thus, research on cell-biomaterial interactions is essential for the progress of cell based therapies. Hydrogels are promising cell therapy materials, because their structure resembles the natural tissue environment; they consist of long polymer chains with high water content and elastic properties, thereby enabling cellular functionality.
The aim of this study was to investigate hydrogels for cell therapy applications. Firstly, we encapsulated human retinal pigment epithelial cell line (ARPE-19) genetically engineered to secrete an anti-angiogenic protein (1) into alginate-poly-L-lysine-alginate (APA) microcapsules and (2) into a composite hydrogel of cross-linked collagen and interpenetrating hyaluronic acid (HA). A custom-made cell encapsulation device was designed, built and optimized, and pharmacokinetic/pharmacodynamic (PK/PD) model was developed to investigate the intravitreal drug delivery of the anti-angiogenic protein by the encapsulated cells. Secondly, chondrocytes were encapsulated into the cross-linked collagen/HA hydrogel supplemented with transforming growth factor β1 (TGFβ1).
Using the cell encapsulation device, cell microcapsules of symmetrical shape and narrow size distribution were produced. The encapsulated ARPE-19 cells remained viable and functional for at least five months. The cross-linked collagen-HA hydrogel was shown to be a suitable encapsulation matrix for ARPE-19 cells; the cells maintained viability and secreted the anti-angiogenic protein at a constant rate for at least 50 days. Moreover, the hydrogel composition could be modified to adjust the properties of the gel structure without compromising cell viability. This approach is suggested to have potential in the treatment of retinal neovascularization. The developed PK/PD model could be used to predict drug levels and therapeutic responses after intravitreal anti-angiogenic drug delivery. The simulations may augment the design of in vivo experiments. The collagen/HA matrix with TGFβ1 was suitable for chondrocyte encapsulation. The hydrogel supported viability and phenotypic cell stability. This hydrogel is strong, stable and biodegradable, and it can be delivered non-invasively as injection. Overall, it is potentially a useful delivery vehicle of chondrocytes for cartilage tissue engineering.
In conclusion, ARPE-19 cells maintain viability in different hydrogels for prolonged periods and secrete the therapeutic transgene product constantly, supporting the suitability of ARPE-19 cells for cell therapy. The cross-linked collagen/HA hydrogel appears to be a potential matrix for cell therapy. It is an injectable system that supports functionality of cells, and it is applicable in drug delivery and tissue engineering."
Leena-Stiina Kontturi, Cell encapsulation in hydrogels for long-term protein delivery and tissue engineering applications, University of Helsinki, Finland, 2014.