Alginate-based microencapsulation and lyophilization of human retinal pigment epithelial cell line (ARPE-19) for cell therapy

Cells have multiple functions in the body, including maintenance of the tissue structure and physiological homeostasis. The cells express and secrete proteins and other factors that exert actions in other cells. These principles form the underlying basis for cell therapy and cell transplantations. Transplanted cells can be used to regenerate tissue structures and homeostasis or they can be used as platform for secretion of therapeutic molecules. Biomaterials can be used to augment the cell growth, differentiation and viability in cell therapy. In addition, the biomaterial matrix may help the surgical placement of the cells into the target site. Importantly, the biomaterial may protect the cell from the immunological and inflammatory reactions after transplantation. The immunological protection of the transplanted therapeutic cells is based to selectively permeable artificial membrane. The membrane prevents the passage of high-molecular weight substances such as large antibodies and cytotoxic immune cells, but permits the passage of smaller molecules, like the secreted therapeutic molecules, nutrients, waste products and oxygen. Lately the interest in cell encapsulation and biomaterial cell interactions has increased due to the emerging techniques of cellular engineering and stem cell differentiation. Storage of microencapsulated cells in freeze-dried form would improve the logistics of the cell therapies (e.g. shipment to the hospitals for reconstitution and use). Otherwise, the microencapsulated cells should be kept viable in continuous culture conditions. The goal of this work was to evaluate alginate based microencapsulation of retinal pigment epithelial cell line (ARPE-19) for cell therapy. Cell viability was evaluated with stably expressed secreted alkaline phosphatase (SEAP), live/dead imaging and oxygen consumption. An empirical kinetic model was built based on FITC-dextran release and protein secretion to describe, release and potential accumulation of therapeutic proteins in the cell microcapsules. Primary animal experiments were done to evaluate the protein release and functionality in the cell microcapsules. Alginate based cell microcapsules were frozen and freeze-dried in order to evaluate the possibility for cell microcapsule preservation in dry powder form. In conclusion, ARPE-19 is a potential cell line for long-term cell therapy based on the expression of transgenes. ARPE-19 cells remain vital in the alginate microcapsules, and they are able to express stably transfected transgene over long periods (at least 20 months). The best cell viability was obtained with alginate microcapsules with calcium and barium cross-linking. This method results in adequate pore sizes that allowed secretion of SEAP. The same microcapsules showed biocompatibility after intraperitoneal administration in preliminary animal experiments. Empirical kinetic simulation model was able to predict the possibility of accumulation inside the alginate microcapsules and demonstrated that the accumulation potential depends on the microcapsule structure. Lyophilization of the cell microcapsules showed that the cells were able to retain some viability during freeze-drying and reconstitution when lyoprotectants were used.