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BDNF, brain-derived neurotrofic factor; BHK cells, baby hamster kidney cells; BMP, bone morphogenetic protein; EPO, erythropoietin; GDNF, glial-cell derived neurotrofic factor; MPS, mucopolysaccharidosis; VE, vascular endothelium; VEGF, vascular endothelial growth factor.

BDNF, brain-derived neurotrofic factor; BHK cells, baby hamster kidney cells; BMP, bone morphogenetic protein; EPO, erythropoietin; GDNF, glial-cell derived neurotrofic factor; MPS, mucopolysaccharidosis; VE, vascular endothelium; VEGF, vascular endothelial growth factor.

new applications based on cell microencapsulation technology. For example, immobilized cells secreting granulocyte macrophage-colony-stimulating factor (GM-CSF) are being studied for immunomodulating or adjuvant activity in the context of immunization in humans and animals. These live vaccines might be suited for both cancer immunotherapy and vaccination against infectious diseases.

Another application consists on the immobilization of engineered cells secreting therapeutic antibodies. Several cell types have been used for this approach, including hybridomas, skin fibroblasts, keratinocytes, myogenic cells, and hepa-tocytes. Interestingly, in some cases the antibodies produced both in vitro and in vivo, retain the specificity and the affinity of the parenteral antibody and no anti-idiotypic response is detected in animals producing ectopic antibodies (48). Similarly, as repeated delivery of a vector is necessary to ensure adequate transfer of the therapeutic gene, encapsulated cells producing retroviral vectors have been evaluated for long-term in vivo gene transfer (49).

Scientists are making great efforts in the development of a bioartificial pancreas by immobilizing pancreatic islets in polymer microcapsules. Some research groups have concentrated on creating a neovascularized site where the encapsulated islets can be implanted. Although not fully supported by all experts, this approach will, in theory, facilitate the contact between the blood-stream and the immobilized cells and this could be beneficial for their long-term performance and functionality (50,51). Such a strategy can be easily performed by coencapsulating angiogenic factor-secreting cells or using basic fibroblast growth factor (bFGF) or vascular endothelial growth factor-impregnated gelatin microspheres (52).

6. Conclusions and Perspectives

Cell microencapsulation is gaining attention as an alternative strategy to conventional therapeutic treatments. However, numerous challenges remain in this technology including developing biomaterials with higher biocompatibility and purity, fabricating microencapsulated systems with higher reproducibility and biosafety, and testing novel cell lines with improved functionality once immobilized. The ability to address all these challenges will potentiate this technology and extend its therapeutic applications.

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