Cell microencapsulation is a fundamental technique in cell-based therapy allowing continuous delivery of biologic drugs. In the prestigious journal, Nature Biotechnology (2001), we reported an alginate-encapsulation cells system, designed to deliver anti-angiogenic biologic drugs, which led to significant inhibition of glioblastoma tumors. Since then, we mainly focus on the development of new encapsulation platforms which will facilitate the prospective clinical application of this cell-based therapy approach. These include polymeric system comprising alginate and chitosan, exhibiting superior mechanical properties and biocompatibility a system which releases anti-inflammatory drugs along with the therapeutic protein and a system for encapsulation of transfected mesenchymal stem cells secreting antiangiogenic proteins for the treatment of solid tumors. In addition, we developed a process to create microcapsules from solubilized decellularized extracellular matrix (ECM), from different origins. These microcapsules provide the cells with a more natural and supportive microenvironment than conventional alginate microcapsules, which dramatically improve cell function.
Mesenchymal stem cells entrapped in microcapsules made of pancreatic extracellular matrix:
This work assessed the effect of local delivery of the angiogenesis inhibitor endostatin on human glioma cell line (U-87MG) xenografts. Baby hamster kidney (BHK) cells were stably transfected with a human endostatin (hES) expression vector and were encapsulated in alginate-poly L-lysine (PLL) microcapsules for long-term delivery of hES. The release of biologically active endostatin was confirmed using various in vitro studies. In vivo, a single local injection of encapsulated endostatin-secreting cells in a nude mouse model resulted in a 72.3% reduction in subcutaneous U87 tumor weight 21 days post treatment. This inhibition was achieved by only 150.8 ng/ml human endostatin secreted from 2 x 105 encapsulated cells. Encapsulated endostatin-secreting cells are effective for the treatment of human glioblastoma xenografts. Continuous local delivery ofendostatin may offer an effective therapeutic approach to the treatment of a variety of tumor types.
The use of chitosan in complexation with alginate appears to be a promising strategy for cell microencapsulation, due to the biocompatibility of both polymers and the high mechanical properties attributed by the use of chitosan. The present work focuses on the optimization and characterization of the alginate-chitosan system to achieve long-term cell encapsulation. Microcapsules were prepared from four types of chitosan using one- and two-stage encapsulation procedures. The effect of reaction time and pH on long-term cell viability and mechanical properties of the microcapsules was evaluated. Using the single-stage encapsulation procedure led to increase of at least fourfold in viability compared with the two-stage procedure. Among the four types of chitosan, the use of high molecular weight (MW) chitosan glutamate and low MW chitosan chloride provided high viabilitylevels as well as good mechanical properties, i.e., more than 93% intact capsules. The high viability levels were found to be independent of the reaction conditions when using high MW chitosan. However, when using low MW chitosan, better viability levels (195%) were obtained when using a pH of 6 and a reaction time of 30 min. An alginate-chitosan cell encapsulation system was devised to achieve high cell viability levels as well as to improve mechanical properties, thus holding great potential for future clinical application.
We hypothesized that encapsulation system, which incorporates polymeric particles releasing anti-inflammatory drug in addition to the encapsulated cells, will result in improved biocompatibility, thus improving therapeutic efficacy. In this work, we have developed, optimized and studied a combined microencapsulation system in which Ibuprofen loaded PLGA microspheres (MS) are co-entrapped with cells. The combined system was optimized in terms of Ibuprofen release profile, and the survival and proliferation of the co-encapsulated cells. The system was shown to release Ibuprofen within two weeks, and support long-term cell viability. It had improved the biocompatibility within the release period of Ibuprofen. Altogether, the co-encapsulation of anti-inflammatory loaded MS along with cells offers a clear advantage in the development of effective, long lasting cell based drug delivery systems.
A novel artificial pancreas encapsulation platform was developed for the treatment of diabetes that is based on solubilized whole porcine pancreatic ECM. This unique system was used to entrap human liver cells and mesenchymal stem cells that were induced to differentiate into glucose-regulated insulin-producing cells. The ECM-microcapsule platform provides a natural fibrous 3D niche, supporting cell viability and differentiation, while significantly improving cell-insulin secretion.
This work presents the design of alginate-PLL microcapsules that can encapsulate human mesenchymal stem cells (hMSCs) for extended periods. The encapsulated hMSCs maintained their mesenchymal surface markers and differentiated to all the typical mesoderm lineages. In vitro and in vivo immunogenicity studies revealed that encapsulated hMSCs were significantly hypoimmunogenic, leading to a 3-fold decrease in cytokine expression compared to entrapped cell lines. The efficacy of the system is demonstrated by genetically modifying the cells to express PEX, an inhibitor of angiogenesis. Encapsulated hMSC-PEX injected adjacent to glioblastoma tumors in nude mice led to a significant reduction in tumor volume and weight. We clearly demonstrate that hMSCs are the cell of choice for microencapsulation cell based-therapy, thus bringing this technology closer to clinical application.