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

Sustained Delivery of a Monoclonal Antibody against SARS-CoV-2 by Microencapsulated Cells: A Proof-of-Concept Study

BACKGROUND

Monoclonal antibody (mAb) therapy is a promising antiviral intervention for Coronovirus disease (COVID-19) with a potential for both treatment and prophylaxis. However, a major barrier to implementing mAb therapies in clinical practice is the intricate nature of mAb preparation and delivery. Therefore, here, in a pre-clinical model, we explored the possibility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mAb delivery using a mAb-expressing encapsulated cell system.

METHODS

Murine G-8 myoblasts were transfected with plasmids coding for the heavy and light chains of CR3022, a well-characterized SARS-CoV-2 mAb that targets the Spike receptor binding domain (RBD), and then encapsulated into alginate microcapsules. The microcapsules were then intraperitoneally implanted into immunocompetent (C57/BL6J) mice and changes in circulating CR3022 titres were assessed. The in vitro and ex vivo characterization of the mAb was performed using western blotting, RBD ELISA, and microscopy.

RESULTS

Transfected G-8 myoblasts expressed intact CR3022 IgG at levels comparable to transfected HEK-293 cells. Cell encapsulation yielded microcapsules harbouring approximately 1000 cells/capsule and sustainably secreting CR3022 mAb. Subsequent peritoneal G-8 microcapsule implantation into mice resulted in a gradual increase of CR3022 concentration in blood, which by day 7 peaked at 1923 [1656-2190] ng/mL and then gradually decreased ~4-fold by day 40 post-implantation. Concurrently, we detected an increase in mouse anti-CR3022 IgG titers, while microcapsules recovered by day 40 post-implantation showed a reduced per-microcapsule mAb production.

SUMMARY

We demonstrate here that cell microencapsulation is a viable approach to systemic delivery of intact SARS-CoV-2 mAb, with potential therapeutic applications that warrant further exploration.

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.

In Vitro Culture Duration does Not Impact the Ability of Encapsulated Choroid Plexus Transplants to Prevent Neurological Deficits in an Excitotoxin-Lesioned Rat Model of Huntington's Disease

Delivery of neurotrophic molecules to the CNS is a potential treatment strategy for preventing the neuronal loss accompanying many neurological disorders. Choroid plexus (CP) epithelial cells secrete a cocktail of neurotrophic factors, and encapsulated CP transplants are neuroprotective in animal models of stroke and Huntington's disease (HD). Prior to clinical use, it is essential to identify and optimize parameters such as the length of time that transplant products such as encapsulated CP can be maintained. In the present study, neonatal porcine CP was encapsulated within alginate microcapsules and maintained in vitro for 1, 2, or 7 months. The encapsulated cells remained viable (>80%) at all time points and were transplanted unilaterally into the rat striatum. Seven days later, the same animals received unilateral injections of quinolinic acid (QA; 225 nmol) adjacent to the implant site. Separate groups of animals served as controls and received QA alone. After surgery, animals were periodically evaluated for weight loss and were tested for motor function 14 days post-QA. In controls, QA lesions produced a significant loss of body weight and impaired function of the contralateral forelimb. In contrast, implants of CP were potently neuroprotective as rats receiving CP transplants did not lose body weight and were not significantly impaired when tested for motor function. These benefits were independent of the length of time that the cells were held in vitro and demonstrate that the potential potency of alginate encapsulated CP cells can be retained for extremely long periods of time in vitro.

In utero stem cell transplantation and gene therapy: rationale, history, and recent advances toward clinical application

Recent advances in high-throughput molecular testing have made it possible to diagnose most genetic disorders relatively early in gestation with minimal risk to the fetus. These advances should soon allow widespread prenatal screening for the majority of human genetic diseases, opening the door to the possibility of treatment/correction prior to birth. In addition to the obvious psychological and financial benefits of curing a disease in utero, and thereby enabling the birth of a healthy infant, there are multiple biological advantages unique to fetal development, which provide compelling rationale for performing potentially curative treatments, such as stem cell transplantation or gene therapy, prior to birth. Herein, we briefly review the fields of in utero transplantation (IUTx) and in utero gene therapy and discuss the biological hurdles that have thus far restricted success of IUTx to patients with immunodeficiencies. We then highlight several recent experimental breakthroughs in immunology, hematopoietic/marrow ontogeny, and in utero cell delivery, which have collectively provided means of overcoming these barriers, thus setting the stage for clinical application of these highly promising therapies in the near future.

Hemophilia A: an ideal disease to correct in utero

Hemophilia A (HA) is the most frequent inheritable defect of the coagulation proteins. The current standard of care for patients with HA is prophylactic factor infusion, which is comprised of regular (2-3 times per week) intravenous infusions of recombinant or plasma-derived FVIII to maintain hemostasis. While this treatment has greatly increased the quality of life and lengthened the life expectancy for many HA patients, its high cost, the need for lifelong infusions, and the fact that it is unavailable to roughly 75% of the world's HA patients make this type of treatment far from ideal. In addition, this lifesaving therapy suffers from a high risk of treatment failure due to immune response to the infused FVIII. There is thus a need for novel treatments, such as those using stem cells and/or gene therapy, which have the potential to mediate long-term correction or permanent cure following a single intervention. In the present review, we discuss the clinical feasibility and unique advantages that an in utero approach to treating HA could offer, placing special emphasis on a new sheep model of HA we have developed and on the use of mesenchymal stromal cells (MSC) as cellular vehicles for delivering the FVIII gene.

Treatment of Hemophilia A in Utero and Postnatally using Sheep as a Model for Cell and Gene Delivery

Hemophilia A represents the most common inheritable deficiency of the coagulation proteins. Current state-of- the-art treatment consists of frequent prophylactic infusions of plasma-derived or recombinant FVIII protein to maintain hemostasis, and has greatly increased life expectancy and quality of life for many hemophilia A patients. This treatment approach is, however, far from ideal, due to the need for lifelong intravenous infusions, the high treatment cost, and the fact that it is unavailable to a large percentage of the world's hemophiliacs. There is thus a need for novel treatments that can promise long-term or permanent correction. In contrast to existing protein based therapeutics, gene therapy offers to provide a permanent cure following few, or even a single, treatment. In the present paper, we review ongoing work towards this end, focusing on studies we have performed in a large animal model. Some of the key topics covered in this review include the unique opportunities sheep offer as a model system, the re-establishment and clinical and molecular characterization of a line of sheep with severe hemophilia A, the advantages and feasibility of treating a disease like hemophilia A in utero, and the use of Mesenchymal Stem Cells (MSC) as cellular delivery vehicles for the FVIII gene. The review finishes with a brief discussion of our recent success correcting ovine hemophilia A with a postnatal transplant with gene-modified MSC, and the limitations of this approach that remain to be overcome.

Intravascular recovery of VWF and FVIII following intraperitoneal injection and differences from intravenous and subcutaneous injection in mice

Intravenous infusion studies in humans suggest that both von Willebrand factor (VWF) and factor VIII (FVIII) remain intravascular in contrast to other coagulation proteins. We explored whether infusion of VWF and FVIII by either intraperitoneal (i.p.) or subcutaneous (s.c.) injection would result in efficient absorption of these large proteins into the vascular circulation. FVIII(null) or VWF(null) mice were infused with plasma-derived or recombinant VWF and/or FVIII by i.p., s.c., or intravenous (i.v.) injection. Both VWF and FVIII were absorbed into the blood circulation after i.p. injection with a peak between 2 and 4 h at levels similar to those observed in mice infused intravenously. In contrast, neither VWF nor FVIII was detected in the plasma following s.c. injection. Although i.v. injection achieved peak plasma levels quickly, both human VWF and FVIII rapidly decreased during the first 2 h following i.v. injection. Following both i.v. and i.p. infusion of VWF, the multimeric structure of circulating VWF was similar to that observed in the infusate. These results demonstrate that both VWF and FVIII can be efficiently absorbed into the blood circulation following i.p., but not s.c. injection, indicating that i.p. administration could be an alternative route for VWF or FVIII infusion.

Ectopic platelet-delivered factor (F) VIII for the treatment of Hemophilia A: Plasma and platelet FVIII, is it all the same?

Hemophilia A is the most common inherited bleeding diathesis and is due to a deficiency of functional coagulation factor (F) VIII. Most patients have a severe deficiency and require a program of prophylactic plus acute infusions of recombinant FVIII to prevent significant joint and other target organ damage. One of the greatest challenges remaining in the care of these patients is that one fifth to third of the patients develop inhibitors to the infused proteins. While a significant portion of such inhibitors can be either overcome or the inhibitors eliminated, some patients with persistent and significant titers of inhibitors need to rely on second tier therapies that are not as effective at preventing significant bleeding morbidity or mortality. A number of groups have been developing therapeutic strategies for FVIII gene therapy for this disorder. Virtually all of these therapies have in common a rise in the plasma level of FVIII, and interpretation of their efficacy is straightforward related to levels achieved. However, several groups have also shown that FVIII can be ectopically expressed in developing megakaryocytes, where although plasma FVIII levels remain undetectable, this FVIII can be released and be effective at sites of platelet activation. Moreover, it is clear that this platelet (p) FVIII is protected to a degree from inhibitors, making pFVIII a particularly attractive strategy for gene therapy for hemophilia A. Yet at the same time, we have shown that pFVIII has a different availability and distribution in a growing thrombus than plasma FVIII. The clinical implications and challenges of these findings as murine and canine hemophilia A preclinical studies go forward with pFVIII are discussed.

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.

Repeated oral administration of chitosan/DNA nanoparticles delivers functional FVIII with the absence of antibodies in hemophilia A mice

BACKGROUND

Current treatment of hemophilia A is expensive and involves regular infusions of factor (F)VIII concentrates. The supply of functional FVIII is further compromised by the generation of neutralizing antibodies. Thus, the development of an alternative safe, cost effective, non-invasive treatment that circumvents immune response induction is desirable.

OBJECTIVES

To evaluate the feasibility of oral administration of chitosan nanoparticles containing FVIII DNA to provide sustainable FVIII activity in hemophilia A mice.

METHODS

Nanoparticles were characterized for morphology, DNA protection and transfection efficiency. Oral administration of nanoparticles containing canine FVIII in C57Bl/6 FVIII(-/-) hemophilia A mice was evaluated for biodistribution, plasma FVIII activity and phenotypic correction. Sustainable FVIII expression was elucidated after repeated nanoparticle administration. Immune responses to repeated oral nanoparticle administration were also investigated.

RESULTS

Chitosan nanoparticles had a particle size range of 200-400 nm and protected DNA from endonuclease and pH degradation. In addition, nanoparticles transfected HEK 293 cells resulted in expression of eGFP, luciferase and FVIII. Hemophilia A mice that ingested chitosan nanoparticles demonstrated transient canine FVIII expression reaching > 100 mU 1 day after treatment, together with partial phenotypic correction. The delivered FVIII plasmid DNA was detected in the intestine and, to a lesser extent, in the liver. Importantly, repeated weekly administrations restored FVIII activity. Furthermore, inhibitors and non-neutralizing FVIII antibodies were not detectable.

CONCLUSIONS

Repeat oral administration of FVIII DNA formulated in chitosan nanoparticles resulted in sustained FVIII activity in hemophilic mice, and thus may provide a non-invasive alternative treatment for hemophilia A.

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.

The treatment of hemophilia A: from protein replacement to AAV-mediated gene therapy

Factor VIII (FVIII) is an essential component in blood coagulation, a deficiency of which causes the serious bleeding disorder hemophilia A. Recently, with the development of purification level and recombinant techniques, protein replacement treatment to hemophiliacs is relatively safe and can prolong their life expectancy. However, because of the possibility of unknown contaminants in plasma-derived FVIII and recombinant FVIII, and high cost for hemophiliacs to use these products, gene therapy for hemophilia A is an attractive alternative to protein replacement therapy. Thus far, the adeno-associated virus (AAV) is a promising vector for gene therapy. Further improvement of the virus for clinical application depends on better understanding of the molecular structure and fate of the vector genome. It is likely that hemophilia will be the first genetic disease to be cured by somatic cell gene therapy.

Aging reduces the neuroprotective capacity, VEGF secretion, and metabolic activity of rat choroid plexus epithelial cells

Delivery of neurotrophic molecules to the brain has potential for preventing neuronal loss in neurodegenerative disorders. Choroid plexus (CP) epithelial cells secrete numerous neurotrophic factors, and encapsulated CP transplants are neuroprotective in models of stroke and Huntington's disease (HD). To date, all studies examining the neuroprotective potential of CP transplants have used cells isolated from young donor animals. Because the aging process significantly impacts the cytoarchitecture and function of the CP the following studies determined whether age-related impairments occur in its neuroprotective capacity. CP was isolated from either young (3-4 months) or aged (24 months) rats. In vitro, young CP epithelial cells secreted more VEGF and were metabolically more active than aged CP epithelial cells. Additionally, conditioned medium from cultured aged CP was less potent than young CP at enhancing the survival of serum-deprived neurons. Finally, encapsulated CP was tested in an animal model of HD. Cell-loaded or empty alginate capsules (control group) were transplanted unilaterally into the rat striatum. Seven days later, the animals received an injection of quinolinic acid (QA; 225 nmol) adjacent to the implant site. Animals were tested for motor function 28 days later. In the control group, QA lesions severely impaired function of the contralateral forelimb. Implants of young CP were potently neuroprotective as rats receiving CP transplants were not significantly impaired when tested for motor function. In contrast, implants of CP from aged rats were only modestly effective and were much less potent than young CP transplants. These data are the first to directly link aging with diminished neuroprotective capacity of CP epithelial cells.

Stability of alginate-polyornithine microcapsules is profoundly dependent on the site of transplantation

Alginate encapsulation is a form of cell-based therapy with numerous preclinical successes but recalcitrant complications related to stability and reproducibility. Understanding how alginate stability varies across different transplant sites will help identify indications that might benefit most from this approach. Alginate stability has been quantified in the peritoneum, but there are no systematic studies comparing its relative stability across transplant sites. This study compares the stability of alginate-polycation microcapsules implanted in the peritoneum to those implanted in the brain and subcutaneous space at 14, 28, 60, 90, 120, and 180 days in-life. Using Fourier-Transform Infrared Spectroscopy (FTIR), the surface of explanted capsules was analyzed for the relative proportion of alginate (outer coat) and the polycationic polyornithine (middle coat). Using a mathematic relationship between FTIR peaks related to these two material components, an index was generated to compare the stability of four different alginates. A notable difference was observed with rapid breakdown in the peritoneum. Conversely, identical alginate capsules transplanted into the brain or subcutaneous space were stable for the 6 month study. These data suggest that (1) successful intraperitoneal transplantation requires modifications of the capsule configuration, the host environment, or both and (2) that sites such as the brain and subcutaneous space are inherently less hostile to conventional alginate capsule configurations.

Prolonged bleeding-free period following prophylactic infusion of recombinant factor VIII reconstituted with pegylated liposomes

Prophylactic treatment for hemophilia A involves infusion of factor VIII (FVIII) concentrates every 2 to 3 days. Liposomes can be efficacious vehicles for medicines, and surface modification by PEGylation can prolong liposome circulation time. When reconstituted with PEGylated liposomes (PEGLip's), recombinant FVIII binds noncovalently but with high affinity to the external liposome surface. This preparation showed prolongation of FVIII half-life and increased protection from bleeding in preclinical models. Here we report a blinded, controlled, crossover, multicenter clinical study that evaluated the time free from bleeding episodes in patients with hemophilia A during prophylaxis with standard rFVIII (no liposomes) or PEGLip rFVIII (PEGLip reconstituted) at 25 and 35 IU/kg doses. Of 24 enrolled patients, 23 were eligible for efficacy analysis. Mean number of days without bleeds was 7.2 ± 1.7 with standard rFVIII compared with 13.3 ± 4.8 with PEGLip rFVIII at the 35 IU/kg dose and 5.9 ± 1.7 with standard rFVIII versus 10.9 ± 2.9 with PEGLip rFVIII at the 25 IU/kg dose (P < .05 between treatment groups for each dose). PEGLip rFVIII was well tolerated. These data suggest that reconstitution of rFVIII with PEGLip's may reduce the frequency of treatment during prophylaxis.

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.

Extensive neuroprotection by choroid plexus transplants in excitotoxin lesioned monkeys

Huntington's disease (HD) results from degeneration of striatal neurons. Choroid plexus (CP) cells secrete neurotrophic factors, and CP transplants are neuroprotective in rat models of HD. To determine if similar neuroprotective effects could be obtained in primates, porcine CP was encapsulated in alginate capsules. PCR confirmed that the CP cells expressed transthyretin and immunocytochemistry demonstrated typical ZO-1 and tubulin staining. In vitro, CP conditioned media enhanced the survival and preserved neurite number and length on serum deprived neurons. Cynomolgus primates were transplanted with CP-loaded capsules into the caudate and putamen followed by quinolinic acid (QA) lesions 1 week later. Control monkeys received empty capsules plus QA. Choroid plexus transplants significantly protected striatal neurons as revealed by stereological counts of NeuN-positive neurons (8% loss vs. 43% in controls) and striatum volume (10% decrease vs. 40% in controls). These data indicate that CP transplants might be useful for preventing the degeneration of neurons in HD.

Expression of Human Calcitonin by Microencapsulated Recombinant Myoblasts

A novel approach to treat post-menopausal osteoporosis is proposed by engineering cell lines for the secretion of human calcitonin (hCT) and which would then be suitable for implantation in different allogeneic hosts. Mouse myoblast were transfected with the cDNA for hCT using the liposome-based gene delivery technique and clones secreting of human calcitonin were isolated. Human calcitonin expression was detected by ELISA. Western blot and immunohistochemical analyses also confirmed the plasmid, pcDNA3-hCT, had been transfected into the cells. Upon enclosure in microcapsules, which are biocompatible membranes that permit exit of therapeutic proteins but not entry of immune mediators, the myoblasts continued to secrete human calcitonin into the culture medium. These results demonstrate the feasibility of using these encapsulated recombinant myoblasts to deliver human calcitonin and the potential of allergenic gene therapy for postmenopausal osteoporosis.

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.

Regional intravascular delivery of AAV-2-F.IX to skeletal muscle achieves long-term correction of hemophilia B in a large animal model

In earlier work, we showed that adeno-associated virus-mediated delivery of a Factor IX gene to skeletal muscle by direct intramuscular injection resulted in therapeutic levels of circulating Factor IX in mice. However, achievement of target doses in humans proved impractical because of the large number of injections required. We used a novel intravascular delivery technique to achieve successful transduction of extensive areas of skeletal muscle in a large animal with hemophilia. We provide here the first report of long-term (> 3 years, with observation ongoing), robust Factor IX expression (circulating levels of 4%-14%) by muscle-directed gene transfer in a large animal, resulting in essentially complete correction of the bleeding disorder in hemophilic dogs. The results of this translational study establish an experimental basis for clinical studies of this delivery method in humans with hemophilia B. These findings also have immediate relevance for gene transfer in patients with muscular dystrophy.

Sustained Expansion and Transgene Expression of Coagulation Factor VIII–Transduced Cord Blood–Derived Endothelial Progenitor Cells

Objective— Although hemophilia A seems particularly suitable for gene therapy because even low amounts of plasma coagulation factor VIII (FVIII) provide a significant clinical benefit to the patients, the ideal target cell for recombinant FVIII expression and gene therapy approaches remains to be identified. In this study, we tested the capacity of cord blood–derived endothelial progenitor cells (CBECs) for FVIII expression on stable lentiviral transduction.

Methods and Results— CD34 + endothelial progenitor cells (EPCs) from cord blood were differentiated into CBECs. Endothelial phenotype was characterized, and lentiviral transduction of early-passage CBECs with a vector encoding FVIII and EGFP did not alter their functional properties and proliferative potential. CBEC could be expanded by 5 to 9 orders of magnitude, thus allowing the expansion of up to 10 15 FVIII-secreting CBECs, starting from as little as 10 6 CD34 + cells. CBECs proved to be highly suitable for FVIII secretion, with 0.35 to 0.39 IU FVIII:C/5×10 4 cells per 48 hours (7.0 to 7.8 IU FVIII:C/10 6 cells per 48 hours), which remained stable over the expansion period.

Conclusions— Our data indicate that CBECs are attractive target cells for inherited coagulation disorders such as hemophilia A, which on lentiviral transduction can be readily expanded to large numbers of transplantable gene-modified cells in vitro.

Prospects for Delivery of Recombinant Angiostatin by Cell-Encapsulation Therapy

Implantation of encapsulated nonautologous cells that have been genetically modified to secrete proteins with tumor suppressor properties represents an alternative nonviral strategy to cancer gene therapy. We report an approach to raise the yield of recombinant proteins from encapsulated cells substantially. We hypothesized that by optimizing the encapsulation procedure, the production efficacy from the encapsulated cells could be increased. HEK 293 EBNA cells were genetically engineered to produce angiostatin. Encapsulation was performed by varying bead size, cellular density, homogeneity, and ion composition of the gel. The morphology and viability of the cells and the release of angiostatin were studied. Computer software was developed for three-dimensional imaging and quantification of cell viability. Angiostatin production was assessed at 3, 6, and 11 weeks using enzyme-linked immunosorbent assay (ELISA). Inhomogeneous gels facilitated cell growth and viability. The most efficient inhomogeneous microcapsules were generated by reducing the size and cellular density of the beads. The viability and the production of angiostatin were 3 to 5 times higher than in the homogeneous capsules. Significant amounts of viable cells were present in both homogeneous and inhomogeneous beads after 6 months of culture. The stability of the alginate matrix was greatly enhanced by gelling in the presence of barium. In conclusion, the viability and production efficacy of recombinant angiostatin from alginate-encapsulated cells can be increased considerably by optimizing the encapsulation procedure. The development of such optimized microcapsules brings cell-encapsulation therapy further towards clinical use in cancer therapy.

Bone marrow mesenchymal cells for haemophilia A gene therapy using retroviral vectors with modified long-terminal repeats

Bone marrow (BM) cells are attractive target cells for ex vivo gene therapy of genetic diseases, including haemophilia A. However, BM-derived haematopoietic stem/progenitor cells (HSCs) transduced with factor VIII (FVIII) retroviral vectors, failed to express FVIII in vivo. To overcome the limitations of HSCs for haemophilia gene therapy, BM-derived mesenchymal cells were explored as alternative target cells. The BM mesenchymal cell population contains self-renewing mesenchymal stem/progenitor cells that give rise to different mesenchymal lineages and have been used safely in phase I gene-marking trials. Human BM mesenchymal cells were transduced in vitro with an improved retroviral vector encoding a human B-domain deleted FVIII (hFVIIIdeltaB) cDNA (MND-MFG-hFVIIIdeltaB). This vector contains multiple modifications in the cis-acting elements within the MoMLV long-terminal repeats (LTR) that prevent the binding of repressive transcription factors. These modifications were previously shown to increase and prolong gene expression in embryonic stem (ES) cells and HSCs. Transduction of BM mesenchymal cells with the MND-MFG-hFVIIIdeltaB retroviral vector resulted in high levels of functional human FVIII in vitro, ranging between 300 +/- 50 SD and 700 +/- 100 SD mU per 106 cells per 24 h. Following xenografting of the transduced human BM cells into immunodeficient NOD-SCID mice, therapeutic hFVIII levels of 12 +/- 10 ng mL-1 were detected in the plasma. Polymerase chain reaction analysis demonstrated long-term engraftment (>3 months) of the human BM mesenchymal cells. The long-term persistence of BM mesenchymal cells in the absence of myelo-ablative conditioning and the therapeutic FVIII levels in vivo underscore the potential usefulness of BM-derived mesenchymal cells for haemophilia gene therapy, as opposed to BM-derived HSCs. Despite the modifications of the MoMLV LTR, FVIII expression declined, which coincided with a decrease in FVIII mRNA transcription levels, indicating that the salutary effect of the LTR modification on transgene expression is not universally applicable to all cell types.