Encapsulated human primary myoblasts deliver functional hFIX in hemophilic mice

Cell Encapsulation Within Alginate Microcapsules: Immunological Challenges and Outlook

Cell encapsulation is a bioengineering technology that provides live allogeneic or xenogeneic cells packaged in a semipermeable immune-isolating membrane for therapeutic applications. The concept of cell encapsulation was first proposed almost nine decades ago, however, and despite its potential, the technology has yet to deliver its promise. The few clinical trials based on cell encapsulation have not led to any licensed therapies. Progress in the field has been slow, in part due to the complexity of the technology, but also because of the difficulties encountered when trying to prevent the immune responses generated by the various microcapsule components, namely the polymer, the encapsulated cells, the therapeutic transgenes and the DNA vectors used to genetically engineer encapsulated cells. While the immune responses induced by polymers such as alginate can be minimized using highly purified materials, the need to cope with the immunogenicity of encapsulated cells is increasingly seen as key in preventing the immune rejection of microcapsules. The encapsulated cells are recognized by the host immune cells through a bidirectional exchange of immune mediators, which induce both the adaptive and innate immune responses against the engrafted capsules. The potential strategies to cope with the immunogenicity of encapsulated cells include the selective diffusion restriction of immune mediators through capsule pores and more recently inclusion in microcapsules of immune modulators such as CXCL12. Combining these strategies with the use of well-characterized cell lines harboring the immunomodulatory properties of stem cells should encourage the incorporation of cell encapsulation technology in state-of-the-art drug development.

Fibronectin-Alginate microcapsules improve cell viability and protein secretion of encapsulated Factor IX-engineered human mesenchymal stromal cells

Continuous delivery of proteins by engineered cells encapsu-lated in biocompatible polymeric microcapsules is of considerable therapeutic potential. However, this technology has not lived up to expectations due to inadequate cell--matrix interactions and subsequent cell death. In this study we hypoth-esize that the presence of fibronectin in an alginate matrix may enhance the viability and functionality of encapsulated human cord blood-derived mesenchymal stromal cells (MSCs) expressing the human Factor IX (FIX) gene. MSCs were encapsulated in alginate-PLL microcapsules containing 10, 100, or 500 μg/ml fibronectin to ameliorate cell survival. MSCs in microcapsules with 100 and 500 μg/ml fibronectin demonstrated improved cell viability and proliferation and higher FIX secretion compared to MSCs in non-supplemented microcapsules. In contrast, 10 μg/ml fibronectin did not significantly affect the viability and protein secretion from the encapsulated cells. Differentiation studies demonstrated osteogenic (but not chondrogenic or adipogenic) differentiation capability and efficient FIX secretion of the enclosed MSCs in the fibronectin-alginate suspension culture. Thus, the use of recombinant MSCs encapsulated in fibronectin-alginate microcapsules in basal or osteogenic cultures may be of practical use in the treatment of hemophilia B.

Multifunctional hydrogel-based scaffold for improving the functionality of encapsulated therapeutic cells and reducing inflammatory response

Since the introduction of cell immunoisolation as an alternative to protect transplanted cells from host immune attack, much effort has been made to develop this technology into a realistic clinical proposal. Several promising approaches have been investigated to resolve the biotechnological and biosafety challenges related to cell microencapsulation. Here, a multifunctional hydrogel-based scaffold consisting of cell-loaded alginate-poly-l-lysine-alginate (APA) microcapsules and dexamethasone (DXM)-loaded poly(lactic-co-glycolic) acid (PLGA) microspheres embedded in alginate hydrogel is developed and evaluated. Initially, the feasibility of using an alginate hydrogel for enclosing APA microcapsules was studied in a xenogeneic approach. In addition, the performance of the local release of DXM was addressed. The in vitro studies confirmed the correct adaptation of the enclosed cells to the scaffolds in terms of metabolic activity and viability. The posterior implantation of the hydrogel-based scaffolds containing cell-loaded microcapsules revealed that the hematocrit levels were maintained high and constant, and the pericapsular overgrowth was reduced in the DXM-treated rats for at least 2months. This multifunctional scaffold might have a synergistic effect: (1) providing a physical support for APA microcapsules, facilitating administration, ensuring retention and recuperation and preventing dissemination; and (2) reducing post-transplantation inflammation and foreign body reaction, thus prolonging the lifetime of the implant by the continuous and localized release of DXM.

Therapeutic applications of encapsulated cells

The synergy of some promising advances in the fields of cell therapy and biomaterials together with improvements in the fabrication of more refined and tailored microcapsules for drug delivery have triggered the progress of cell encapsulation technology. Cell microencapsulation involves immobilizing the transplanted cells within a biocompatible scaffold surrounded by a membrane in attempt to isolate the cells from the host immune attack and enhance or prolong their function in vivo. This technology represents one strategy which aims to overcome the present difficulties related to local and systemic controlled release of drugs and growth factors as well as to organ graft rejection and thus the requirements for use of immunomodulatory protocols or immunosuppressive drugs. This chapter gives an overview of the current situation of cell encapsulation technology as a controlled drug delivery system, and the essential requirements of the technology, some of the therapeutic applications, the challenges, and the future directions under investigation are highlighted.

Encapsulation of factor IX-engineered mesenchymal stem cells in fibrinogen-alginate microcapsules enhances their viability and transgene secretion

Cell microencapsulation holds significant promise as a strategy for cellular therapies; however, inadequate survival and functionality of the enclosed cells limit its application in hemophilia treatment. Here, we evaluated the use of alginate-based microcapsules to enhance the viability and transgene secretion of human cord blood–derived mesenchymal stem cells in three-dimensional cultures. Given the positive effects of extracellular matrix molecules on mesenchymal stem cell growth, we tested whether fibrinogen-supplemented alginate microcapsules can improve the efficiency of encapsulated factor IX–engineered mesenchymal stem cells as a treatment of hemophilia B. We found that fibrinogen-supplemented alginate microcapsules (a) significantly enhanced the viability and proliferation of factor IX–engineered mesenchymal stem cells and (b) increased factor IX secretion by mesenchymal stem cells compared to mesenchymal stem cells in nonsupplemented microcapsules. Moreover, we observed the osteogenic, but not chondrogenic or adipogenic, differentiation capability of factor IX–engineered cord blood mesenchymal stem cells and their efficient factor IX secretion while encapsulated in fibrinogen-supplemented alginate microcapsules. Thus, the use of engineered mesenchymal stem cells encapsulated in fibrinogen-modified microcapsules may have potential application in the treatment of hemophilia or other protein deficiency diseases.

Animal models of hemophilia

The X-linked bleeding disorder hemophilia is caused by mutations in coagulation factor VIII (hemophilia A) or factor IX (hemophilia B). Unless prophylactic treatment is provided, patients with severe disease (less than 1% clotting activity) typically experience frequent spontaneous bleeds. Current treatment is largely based on intravenous infusion of recombinant or plasma-derived coagulation factor concentrate. More effective factor products are being developed. Moreover, gene therapies for sustained correction of hemophilia are showing much promise in preclinical studies and in clinical trials. These advances in molecular medicine heavily depend on availability of well-characterized small and large animal models of hemophilia, primarily hemophilia mice and dogs. Experiments in these animals represent important early and intermediate steps of translational research aimed at development of better and safer treatments for hemophilia, such a protein and gene therapies or immune tolerance protocols. While murine models are excellent for studies of large groups of animals using genetically defined strains, canine models are important for testing scale-up and for long-term follow-up as well as for studies that require larger blood volumes.

Hierarchical scaffold design for mesenchymal stem cell-based gene therapy of hemophilia B

Gene therapy for hemophilia B and other hereditary plasma protein deficiencies showed great promise in pre-clinical and early clinical trials. However, safety concerns about in vivo delivery of viral vectors and poor post-transplant survival of ex vivo modified cells remain key hurdles for clinical translation of gene therapy. We here describe a 3D scaffold system based on porous hydroxyapatite-PLGA composites coated with biomineralized collagen 1. When combined with autologous gene-engineered factor IX (hFIX) positive mesenchymal stem cells (MSCs) and implanted in hemophilic mice, these scaffolds supported long-term engraftment and systemic protein delivery by MSCs in vivo. Optimization of the scaffolds at the macro-, micro- and nanoscales provided efficient cell delivery capacity, MSC self-renewal and osteogenesis respectively, concurrent with sustained delivery of hFIX. In conclusion, the use of gene-enhanced MSC-seeded scaffolds may be of practical use for treatment of hemophilia B and other plasma protein deficiencies.

Efficacy of engineered FVIII-producing skeletal muscle enhanced by growth factor-releasing co-axial electrospun fibers

Co-axial electrospun fibers can offer both topographical and biochemical cues for tissue engineering applications. In this study, we demonstrate the sustained treatment of hemophilia through a non-viral, tissue engineering approach facilitated by growth factor-releasing co-axial electrospun fibers. FVIII-producing skeletal myotubes were first engineered on aligned electrospun fibers in vitro, followed by implantation in hemophilic mice with or without a layer of core-shell electrospun fibers designed to provide sustained delivery of angiogenic or lymphangiogenic growth factors, which serves to stimulate the lymphatic or vascular systems to enhance the FVIII transport from the implant site into systemic circulation. Upon subcutaneous implantation into hemophilic mice, the construct seamlessly integrated with the host tissue within one month, and specifically induced either vascular or lymphatic network infiltration in accordance with the growth factors released from the electrospun fibers. Engineered constructs that induced angiogenesis resulted in sustained elevation of plasma FVIII and significantly reduced blood coagulation time for at least 2-months. Biomaterials-assisted functional tissue engineering was shown in this study to offer protein replacement therapy for a genetic disorder such as hemophilia.

Characterization of viability and proliferation of alginate-poly-L-lysine-alginate encapsulated myoblasts using flow cytometry

Genetically modified cells encapsulated in alginate-poly-L-lysine-alginate (APA) are being developed to deliver therapeutic products to treat a variety of diseases. The characterization of the encapsulated cells thus becomes paramount. This study reports a novel method to assess the viability, granularity and proliferation of encapsulated cells based on flow cytometry. The in vitro viability of encapsulated G8 murine myoblasts secreting canine FVIII (cFVIII) measured by flow cytometry was comparable to the traditional trypan blue exclusion method and both correlated with cFVIII secretion levels. In contrast, after implantation into mice, only viability measured by flow cytometry correlated with cFVIII secretion. Further, flow cytometry analysis of encapsulated cells maintained in vitro and in vivo revealed a greater fraction of granular cells compared to free cells, suggesting that encapsulation influences the morphology (cytoplasmic composition) of cells within APA microcapsules. Interestingly, the proliferation study showed that encapsulated cells proliferate faster, on average, and were more heterogeneous in vivo compared to in vitro culture conditions, suggesting that encapsulated cell proliferation is complex and environment-dependent. In conclusion, we show that flow cytometry analysis allows for a more consistent and comprehensive examination of encapsulated cells to aid in the development of cell therapy protocols.