Sustained and therapeutic delivery of factor IX in nude haemophilia B mice by encapsulated C2C12 myoblasts: concurrent tumourigenesis

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.

Microencapsulation of Engineered Cells to Deliver Sustained High Circulating Levels of Interleukin-6 to Study Hepatocellular Carcinoma Progression

Interlukin-6 (IL-6) is a pleitropic cytokine that plays a central role in normal and abnormal hepatic function and response. The aims of the current study were to determine the viability of using cell encapsulation technology to introduce a genetically modified xenogeneic (CHO) cell population to elevate circulating levels of rhIL-6 in a rat model and determine the effects of sustained high rhIL-6 levels on hepatocellular carcinoma (HCC) progression in vivo. An alginate matrix was combined with transfected CHO cells, selected for their ability to synthesize rhIL-6, and used to generate uniform alginate–cell beads. Once encapsulated transfected cells continued to undergo replication, formed colonies within the bead, and synthesized/released large quantities of rhIL-6 into culture medium in vitro. Intraperitoneal implantation of beads into rats resulted in significantly increased circulating and intrahepatic levels of rhIL-6 up to 4 days postimplantation. Prolonged implantation led to the escape of CHO cells from the bead, resulting in a host response and CHO cell death within the bead. Subsequently CHO-IL-6 encapsulated cells were implanted into rats previously inoculated intrahepatically with the H4IIE HCC cell line. These studies demonstrated the maintenance of high circulating/intrahepatic rhIL-6 levels in this model. Despite significantly increased rhIL-6, this technique did not significantly alter the rate of net tumor progression. However, Stat3 activity was significantly increased in both normal liver and HCC tissue resected from animals implanted with CHO-IL-6 cells. Collectively these data demonstrate the short-term viability of using cell encapsulation technology to generate high levels of active circulating and intrahepatic cytokines and raise the possibility of modifying specific signal transduction cascades identified to be important during tumor progression.

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.

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.

Cell encapsulation technology as a novel strategy for human anti-tumor immunotherapy

Granulocyte-macrophage colony-stimulating factor (GM-CSF) as an adjuvant in autologous cell-based anti-tumor immunotherapy has recently been approved for clinical application. To avoid the need for individualized processing of autologous cells, we developed a novel strategy based on the encapsulation of GM-CSF-secreting human allogeneic cells. GM-CSF-producing K562 cells showed high, stable and reproducible cytokine secretion when enclosed into macrocapsules. For clinical development, the cryopreservation of these devices is critical. Thawing of capsules frozen at different time points displayed differences in GM-CSF release shortly after thawing. However, similar secretion values to those of non-frozen control capsules were obtained 8 days after thawing at a rate of >1000 ng GM-CSF per capsule every 24 h. For future human application, longer and reinforced capsules were designed. After irradiation and cryopreservation, these capsules produced >300 ng GM-CSF per capsule every 24 h 1 week after thawing. The in vivo implantation of encapsulated K562 cells was evaluated in mice and showed preserved cell survival. Finally, as a proof of principle of biological activity, capsules containing B16-GM-CSF allogeneic cells implanted in mice induced a prompt inflammatory reaction. The ability to reliably achieve high adjuvant release using a standardized procedure may lead to a new clinical application of GM-CSF in cell-based cancer immunization.

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.

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.

Sustained baculovirus-mediated expression in myogenic cells

BACKGROUND

Baculovirus has emerged as a promising gene delivery vector due to its low cytotoxicity and nonreplication nature in mammalian cells. However, baculovirus-mediated expression is transient and generally lasts less than 14 days, which could restrict its application in the treatment of diseases requiring stable transgene expression.

METHODS

We transduced myoblast cell lines C2C12, Sol 8 and primary myoblasts with a baculovirus expressing the enhanced green fluorescent protein (EGFP) under the control of cytomegalovirus immediate-early promoter and measured the transduction efficiency by flow cytometry. Myogenic differentiation was induced after transduction and the longevity of EGFP expression was monitored by fluorescence microscopy. The myogenic differentiation was confirmed by reverse transcription-polymerase chain reaction (RT-PCR). The persistence of the egfp DNA and transcripts was monitored by real-time PCR and quantitative real-time RT-PCR.

RESULTS

Baculovirus efficiently transduced C2C12, Sol 8 and the primary myoblasts. The transgene expression persisted for a prolonged period of time (at least 63 days) in the cells differentiating into myotubes, but was transient in HeLa cells (<7 days). The sustained expression paralleled the myogenic differentiation and stemmed from the intracellular persistence of egfp DNA and mRNA.

CONCLUSIONS

The transgene delivered by baculovirus persists in the myotubes and endows sustained expression, which is distinct from its rapid degradation and transient expression in other cell types. These findings justify the future use of baculovirus for muscle-based gene therapy.

Isolation of human foetal myoblasts and its application for microencapsulation

Foetal cells secrete more growth factors, generate less immune response, grow and proliferate better than adult cells. These characteristics make them desirable for recombinant modification and use in microencapsulated cellular gene therapeutics. We have established a system in vitro to obtain a pure population of primary human foetal myoblasts under several rounds of selection with non-collagen coated plates and identified by desmin staining. These primary myoblasts presented good proliferation ability and better differentiation characteristics in monolayer and after microencapsulation compared to murine myoblast C2C12 cells based on creatine phosphokinase (CPK), major histocompatibility complex (MHC) and multi-nucleated myotubule determination. The lifespan of primary myoblasts was 70 population doublings before entering into senescent state, with a population time of 18–24 hrs. Hence, we have developed a protocol for isolating human foetal primary myoblasts with excellent differentiation potential and robust growth and longevity. They should be useful for cell-based therapy in human clinical applications with microencapsulation technology.

Encapsulated human primary myoblasts deliver functional hFIX in hemophilic mice

BACKGROUND

Hemophilia B is a bleeding disorder caused by defective factor IX (FIX), currently treated by regular infusions of plasma-derived or recombinant FIX. We propose a gene therapy strategy based on the implantation of cells secreting FIX enclosed in alginate microcapsules as a highly desirable alternative treatment. We have reported sustained delivery of human factor IX (hFIX) in immunocompetent mice implanted with encapsulated primary mouse myoblasts engineered to secrete hFIX. As a step towards the treatment of human patients, in this study we report the implantation of encapsulated human primary myoblasts secreting hFIX in hemophilia B mice.

METHODS

Human primary myoblasts were transfected with plasmids pKL4M-hFIX, pLNM-betaIXL, pMFG-hFIX, and transduced with retrovirus MFG-hFIX. Two human primary myoblast clones secreting approximately 1 microg hFIX/10(6) cells/day were enclosed in biocompatible alginate microcapsules and implanted intraperitoneally into SCID and hemophilic mice.

RESULTS

Circulating hFIX (peak of approximately 120 ng/ml) was detected in hemophilia B mice on day 1 after implantation. Human FIX delivery was transient, however, becoming undetectable on day 14. Concurrently, anti-hFIX antibodies were detected. At the same time, activated partial thromboplastin time (APTT) was reduced from 94 s before treatment to 78-80 s. Tail bleeding time decreased from 15 min to 1.5-7 min after treatment, some mice being normalised. These findings indicate that the delivered hFIX is biologically active. Similarly treated NOD/SCID mice had circulating hFIX levels of 170 ng/ml on day 1 that remained detectable for 1 month, albeit at low levels. Cell viability of microcapsules retrieved on day 60 was below 5%.

CONCLUSIONS

Our findings indicate that encapsulated human primary myoblasts secrete functional hFIX. Furthermore, implantation of encapsulated human primary myoblasts can partially correct the phenotype of hemophilia B mice, supporting the feasibility of this gene therapy approach for hemophilia B. However, the long-term viability of the encapsulated human myoblasts must first be improved.

Genetic engineering for haemophilia A

At first sight, haemophilia A would appear to be an ideal candidate for treatment by gene therapy. There is a single gene defect; cells in different parts of the body, but especially the liver, produce Factor VIII, and only 5% of normal levels of Factor VIII are necessary to prevent the serious symptoms of bleeding. This review attempts to outline the status of gene therapy at present and efforts that have been made to overcome the difficulties and remaining problems that require solving. Undoubtedly, success will be achieved, but it is likely that considerably more work will be necessary before experimental models can be introduced into the clinic with any likelihood of success. The most successful results in animals that may have clinical application were from introducing the Factor VIII gene to newborn animals before antibodies are produced, presumably inducing a state of tolerance.

Angiogenesis Enhances Factor IX Delivery and Persistence from Retrievable Human Bioengineered Muscle Implants

Human muscle progenitor cells transduced with lentiviral vectors secreted high levels of blood clotting factor IX (FIX). When bioengineered into postmitotic myofibers as human bioartificial muscles (HBAMs) and subcutaneously implanted into immunodeficient mice, they secreted FIX into the circulation for >3 months. The HBAM-derived FIX was biologically active, consistent with the cells' ability to conduct the necessary posttranslational modifications. These bioengineered muscle implants are retrievable, an inherent safety feature that distinguishes this "reversible" gene therapy approach from most other gene therapy strategies. When myofibers were bioengineered from human myoblasts expressing FIX and vascular endothelial growth factor, circulating FIX levels were increased and maintained long term within the therapeutic range, consistent with the generation of a vascular network around the HBAM. The present study implicates an important role for angiogenesis in the efficient delivery of therapeutic proteins using tissue engineered stem cell-based gene therapies.

Sustained and therapeutic levels of human factor IX in hemophilia B mice implanted with microcapsules: key role of encapsulated cells

BACKGROUND

A gene therapy delivery system based on microcapsules enclosing recombinant cells engineered to secrete a therapeutic protein was explored in this study. In order to prevent immune rejection of the delivered cells, they were enclosed in non-antigenic biocompatible alginate microcapsules prior to being implanted intraperitoneally into mice. We have shown that encapsulated C2C12 myoblasts can temporarily deliver therapeutic levels of factor IX (FIX) in mice, but the C2C12 myoblasts elicited an immune response to FIX. In this study we report the use of mouse fetal G8 myoblasts secreting hFIX in hemophilia mice.

METHODS

Mouse G8 myoblasts were transduced with MFG-FIX vector. A pool of recombinant G8 myoblasts secreting approximately 1500 ng hFIX/10(6) cells/24 h in vitro were enclosed in biocompatible alginate microcapsules and implanted intraperitoneally into immunocompetent C57BL/6 and hemophilic mice.

RESULTS

Circulating levels of hFIX in treated mice reached approximately 400 ng/ml for at least 120 days (end of experiment). Interestingly, mice treated with encapsulated G8 myoblasts did not develop anti-hFIX antibodies. Activated partial thromboplastin time (APTT) of plasmas obtained from treated hemophilic mice was reduced from 107 to 82 sec on day 60 post-treatment, and whole blood clotting time (WBCT) was also corrected from 7-9 min before treatment to 3-5 min following microcapsule implantation. Further, mice were protected against bleeding following major trauma. Thus, the FIX delivery in vivo was biologically active.

CONCLUSIONS

Our findings suggest that the type of cells encapsulated play a key role in the generation of immune responses against the transgene. Further, a judicious selection of encapsulated cells is critical for achieving sustained gene expression. Our findings support the feasibility of encapsulated G8 myoblasts as a gene therapy approach for hemophilia B.

Effects of genetic fusion of factor IX to albumin on in vivo clearance in mice and rabbits

Individuals with haemophilia B require replacement therapy with recombinant or plasma-derived coagulation factor IX (fIX). More benefit per injected dose might be obtained if fIX clearance could be slowed. The contribution of overall size to fIX clearance was explored, using genetic fusion to albumin. Recombinant murine fIX (MIX), and three proteins with C-terminal epitope tags were expressed in HEK 293 cells: tagged MIX (MIXT), tagged mouse serum albumin (MSAT) and MFUST, in which MIX and MSAT were fused in a single polypeptide chain. Proteins MFUST and MIXT were two- to threefold less active in clotting assays than MIX. In mice, the area under the clearance curve (AUC) was reduced for MFUST compared with MSAT or plasma-derived MSA (pd-MSA); the terminal catabolic half-life (t(0.5)) did not differ amongst the three proteins. Two minutes after injection, >40% of the injected MFUST was found in the liver, compared with <10% of either MSAT or pd-MSA. In rabbits, the AUC for MFUST was reduced compared to MIXT, MSAT, or pd-MSA, while the t(0.5) of the fusion protein fell between that of MIXT and MSAT or pd-MSA. Similar results were obtained with non-radioactive fused or non-fused recombinant human fIX in fIX knockout mice. The clearance behaviour of the fusion protein thus more closely resembled that of fIX than that of albumin despite a modest increase in terminal half-life, suggesting that fIX-specific interactions that are important in determining clearance were maintained in spite of the increased size of the fusion protein.

In vivo calcium deposition on polyvinyl alcohol matrix used in hollow fiber cell macroencapsulation devices

The encapsulation of genetically modified cells represents a promising approach for the delivery of therapeutic proteins. The functionality of the device is dependent on the characteristics of the biomaterials, the procedures used in its confection and the adaptability of the encapsulated cells in the host. We report conditions leading to the development of calcifications on the polyvinyl alcohol (PVA) matrix introduced in hollow fiber devices for the encapsulation of primary human fibroblasts implanted in mice. The manufacturing procedures, batches of PVA matrix and cell lineages were assessed for their respective role in the development of the phenomenon. The results showed that the calcification is totally prevented by substituting phosphate-buffer saline with ultra-pure sterile water in the rinsing procedure of the matrix. Moreover, a positive correlation was found, when comparing two fibroblast cell lineages, between the level of lactate dehydrogenase (LDH) activity measured in the cells and the degree of calcium deposition. Higher LDH activity may decrease calcium depositions because it generates in the device a more acidic microenvironment inhibiting calcium precipitation. The present study defines optimized conditions for the encapsulation of primary human fibroblasts in order to avoid potentially detrimental calcifications and to allow long-term survival of encapsulated cells.

Tetracycline-regulated secretion of human insulin in transfected primary myoblasts

A mechanism for safely regulating transgene expression will be necessary for gene therapy approaches to endocrine disorders. In this study, a two-plasmid tetracycline-inducible system was used to regulate expression of human proinsulin (hppI1) and a mutated proinsulin construct (hppI4, allowing cleavage by furin) in primary rat soleus myoblasts. In hppI1 and hppI4 transient transfections, the presence of 0.01 and 0.1 microg/ml tetracycline for 48 h inhibited pro/insulin secretion to 19-27% and 7-12%, respectively, compared to tetracycline untreated myoblasts. Following a 48 h tetracycline incubation (1.0 microg/ml), pro/insulin secretion in hppI1 and hppI4 transfected myoblasts was reduced to <4% of that in cells incubated without tetracycline. Pro/insulin secretion equivalent to that of untreated cells was restored following tetracycline withdrawal and incubation for a further 72 h. Conversion of proinsulin to insulin in transfected myoblasts was <1% for hppI1 and >45% for hppI4. In conclusion, regulated insulin secretion has been achieved in a dose-dependent and reversible manner in primary myoblasts.

Complete and sustained phenotypic correction of hemophilia B in mice following hepatic gene transfer of a high-expressing human factor IX plasmid

Therapeutic correction of hemophilia B was achieved by rapid infusion of a large-volume solution containing a high-expressing human factor IX (hFIX) plasmid into the tail vein of hemophilia B mice. hFIX circulated at therapeutic levels (1-5 micro g mL-1) in all animals for more than 1 year as determined by both species-specific antigen assay and an activated partial thromboplastin time (APTT)-based clotting assay. There was acute, transient hepatic tissue damage by the infusion procedure and no significant inhibitory anti-hFIX antibodies developed. No bleeding episode was observed during or after treatment. Immunohistochemical studies indicated that the hFIX gene was exclusively expressed in hepatocytes, and that transduced cells had readily detectable hFIX protein at 4 h postinfusion, and stainable protein persisted for up to 1 year. Repeated infusions of hFIX plasmids boosted the hFIX expression to higher levels. These results demonstrate that hemophilia B can be treated by gene transfer of naked hFIX plasmids.

Hemophilia gene therapy: update

Gene transfer is an exciting and potentially important treatment approach for hemophilia A and B. Four phase I clinical trials of the safety of gene transfer in hemophilia A or B have been completed and two more trials are currently underway. The results of these trials indicate that gene transfer in hemophilia with the vectors and doses used is safe and well tolerated. Efforts continue to understand the basic biology and improve the efficiency of gene transfer.

Therapeutic levels of human factor VIII in mice implanted with encapsulated cells: potential for gene therapy of haemophilia A

BACKGROUND

A gene therapy delivery system based on microcapsules enclosing recombinant cells engineered to secrete a therapeutic protein has been evaluated. The microcapsules are implanted intraperitoneally. In order to prevent cell immune rejection, cells are enclosed in non-antigenic biocompatible alginate microcapsules prior to their implantation into mice. It has been shown that encapsulated myoblasts can deliver therapeutic levels of Factor IX (FIX) in mice. The delivery of human Factor VIII (hFVIII) in mice using microcapsules was evaluated in this study.

METHODS

Mouse C2C12 myoblasts and canine MDCK epithelial kidney cells were transduced with MFG-FVIII (B-domain deleted) vector. Selected recombinant clones were enclosed in alginate microcapsules. Encapsulated recombinant clones were subsequently implanted intraperitoneally into C57BL/6 and immunodeficient SCID mice.

RESULTS

Plasma of mice receiving C2C12 and encapsulated MDCK cells had transient therapeutic levels of FVIII in immunocompetent C57BL/6 mice (up to 20% and 7% of physiological levels, respectively). In addition, FVIII delivery in SCID mice was also transient, suggesting that a non-immune mechanism must have contributed to the decline of hFVIII in plasma. Quantitative RT-PCR analysis confirmed directly that the decline of hFVIII is due to a reduction in steady-state hFVIII mRNA, consistent with transcriptional repression. Furthermore, encapsulated cells retrieved from implanted mice were viable, but secreted FVIII ex vivo at three-fold lower levels than the pre-implantation levels. In addition, antibodies to hFVIII were detected in immunocompetent C57BL/6 mice.

CONCLUSIONS

Implantable microcapsules can deliver therapeutic levels of FVIII in mice, suggesting the potential of this gene therapy approach for haemophilia A. The findings suggest vector down-regulation in vivo.