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

Potential long-term treatment of hemophilia A by neonatal co-transplantation of cord blood-derived endothelial colony-forming cells and placental mesenchymal stromal cells

Background

Hemophilia A (HA) is an X-linked recessive disorder caused by mutations in the Factor VIII (FVIII) gene leading to deficient blood coagulation. As a monogenic disorder, HA is an ideal target for cell-based gene therapy, but successful treatment has been hampered by insufficient engraftment of potential therapeutic cells.

Methods

In this study, we sought to determine whether co-transplantation of endothelial colony-forming cells (ECFCs) and placenta-derived mesenchymal stromal cells (PMSCs) can achieve long-term engraftment and FVIII expression. ECFCs and PMSCs were transduced with a B domain deleted factor VIII (BDD-FVIII) expressing lentiviral vector and luciferase, green fluorescent protein or Td-Tomato containing lentiviral tracking vectors. They were transplanted intramuscularly into neonatal or adult immunodeficient mice.

Results

In vivo bioluminescence imaging showed that the ECFC only and the co-transplantation groups but not the PMSCs only group achieved long-term engraftment for at least 26 weeks, and the co-transplantation group showed a higher engraftment than the ECFC only group at 16 and 20 weeks post-transplantation. In addition, cell transplantation at the neonatal age achieved higher engraftment than at the adult age. Immunohistochemical analyses further showed that the engrafted ECFCs expressed FVIII, maintained endothelial phenotype, and generated functional vasculature. Next, co-transplantation of ECFCs and PMSCs into F8 knock-out HA mice reduced the blood loss volume from 562.13 ± 19.84 μl to 155.78 ± 44.93 μl in a tail-clip assay.

Conclusions

This work demonstrated that co-transplantation of ECFCs with PMSCs at the neonatal age is a potential strategy to achieve stable, long-term engraftment, and thus holds great promise for cell-based treatment of HA.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1138-8) contains supplementary material, which is available to authorized users.

An effective ex-vivo approach for inducing endothelial progenitor cells from umbilical cord blood CD34+ cells

Background

Transplantation of endothelial progenitor cells (EPCs)/endothelial cells (ECs) has been used for the treatment of ischemic diseases and hemophilia A, due to their great capacity for producing factor VIII and for repairing vascular damage. We established an effective approach to stimulate the expansion and differentiation of EPCs for potential therapeutic applications.

Methods

CD34⁺ cells isolated from human cord blood were cultured in a two-step system for 21 days. The generated adherent cells were characterized via flow cytometry and immunofluorescent staining. Moreover, single-cell clonogenic and tube-forming assays were carried out to evaluate their potential to proliferate and form vessel networks. Furthermore, these cells were transplanted into a mouse model of hepatic sinusoidal endothelium injury by hepatic portal vein injection to investigate their in-vivo behavior.

Results

The two-step culture protocol promoted the expansion and differentiation of human cord blood CD34⁺ cells efficiently, resulting in a large number of adherent cells within 3 weeks. The generated adherent cells were identified as EPCs/ECs based on the expression of CD31, CD144, vWF, and FVIII, and cell numbers showed a 1400-fold increase compared with the initial number. Moreover, these EPCs/ECs were capable of proliferating and establishing colonies as individual cells, and forming tube-like structures. More significantly, tissue examination of mice after transplantation revealed that the injected EPCs/ECs migrated and integrated into the liver, reconstituting the sinusoidal endothelial compartment.

Conclusions

We developed an approach for the generation of cord blood-derived EPCs/ECs on a large scale, characterized them phenotypically, and demonstrated their in-vivo functional capacity. Our approach provides an excellent source of healthy EPCs/ECs for use in cell therapy in a clinical setting.

Gene therapy for hemophilia

Hemophilia is an X-linked inherited bleeding disorder consisting of two classifications, hemophilia A and hemophilia B, depending on the underlying mutation. Although the disease is currently treatable with intravenous delivery of replacement recombinant clotting factor, this approach represents a significant cost both monetarily and in terms of quality of life. Gene therapy is an attractive alternative approach to the treatment of hemophilia that would ideally provide life-long correction of clotting activity with a single injection. In this review, we will discuss the multitude of approaches that have been explored for the treatment of both hemophilia A and B, including both in vivo and ex vivo approaches with viral and nonviral delivery vectors.

A systematic approach to the establishment and characterization of endothelial progenitor cells for gene therapy

It has been recently demonstrated that endothelial progenitor cells (EPCs) have increasing potential for gene therapy or regenerative cell therapy for cardiovascular diseases and cancer. However, current therapies involving EPCs are inefficient because of the very low level of EPCs in the available sources, for example, in blood. One solution is to derive in vitro an expanded population of EPCs from circulation. In addition, EPCs like other progenitor cells have an intrinsic predisposition of differentiating into mature cell types, for example, mature endothelial cells; therefore, establishing a sufficient amount of EPCs alongside maintaining the EPC characteristic phenotype during genetic modification and long-term culture presents a significant challenge to the field of gene and cell therapies. In this study, we have systematically investigated EPCs from different sources and used multiple parameters, including cell surface markers and a tubule formation assay to identify factors that influence the establishment, characteristics, and vector transduction capability of EPCs. Our results show the considerable promise, as well as certain limitations in the establishment and manipulation of genetically modified EPCs for gene therapy. While obtaining high transduction efficiency and robust in vitro tubule formation of EPCs using lentiviral vectors, we also observed that lentiviral vector transduction significantly altered EPC phenotype as demonstrated by an increased percentage of CD34(+) progenitor cells and increased expression of adhesion molecule CD144 (VE-cadherin). Taking account of the increased expression of CD144 reported in cancer patients, the altered expression of EPC-related markers, for example, VE-cadherin and the enrichment of CD34(+) cells, after vector transduction indicates the importance of extensive characterization and vigorous safety control of genetically modified EPCs before they are accepted for clinical use.

Transient transfection of serum-free suspension HEK 293 cell culture for efficient production of human rFVIII

Background

Hemophilia A is a bleeding disorder caused by deficiency in coagulation factor VIII. Recombinant factor VIII (rFVIII) is an alternative to plasma-derived FVIII for the treatment of hemophilia A. However, commercial manufacturing of rFVIII products is inefficient and costly and is associated to high prices and product shortage, even in economically privileged countries. This situation may be solved by adopting more efficient production methods. Here, we evaluated the potential of transient transfection in producing rFVIII in serum-free suspension HEK 293 cell cultures and investigated the effects of different DNA concentration (0.4, 0.6 and 0.8 μg/10⁶ cells) and repeated transfections done at 34° and 37°C.

Results

We observed a decrease in cell growth when high DNA concentrations were used, but no significant differences in transfection efficiency and in the biological activity of the rFVIII were noticed. The best condition for rFVIII production was obtained with repeated transfections at 34°C using 0.4 μg DNA/10⁶ cells through which almost 50 IU of active rFVIII was produced six days post-transfection.

Conclusion

Serum-free suspension transient transfection is thus a viable option for high-yield-rFVIII production. Work is in progress to further optimize the process and validate its scalability.

Pluripotent reprogramming of fibroblasts by lentiviral mediated insertion of SOX2, C-MYC, and TCL-1A

Reprogramming of somatic cells to pluripotency promises to boost cellular therapy. Most instances of direct reprogramming have been achieved by forced expression of defined exogenous factors using multiple viral vectors. The most used 4 transcription factors, octamer-binding transcription factor 4 (OCT4), (sex determining region Y)-box 2 (SOX2), Kruppel-like factor 4 (KLF4), and v-myc myelocytomatosis viral oncogene homolog (C-MYC), can induce pluripotency in mouse and human fibroblasts. Here, we report that forced expression of a new combination of transcription factors (T-cell leukemia/lymphoma protein 1A [TCL-1A], C-MYC, and SOX2) is sufficient to promote the reprogramming of human fibroblasts into pluripotent cells. These 3-factor pluripotent cells are similar to human embryonic stem cells in morphology, in the ability to differentiate into cells of the 3 embryonic layers, and at the level of global gene expression. Induced pluripotent human cells generated by a combination of other factors will be of great help for the understanding of reprogramming pathways. This, in turn, will allow us to better control cell-fate and apply this knowledge to cell therapy.

Calcitonin gene-related peptide inhibits angiotensin II-induced endothelial progenitor cells senescence through up-regulation of klotho expression

BACKGROUND

It has been shown that angiotensin II (Ang II) is able to accelerate endothelial progenitor cells (EPCs) senescence through induction of oxidative stress. Calcitonin gene-related peptide (CGRP), a major neurotransmitter of the capsaicin-sensitive sensory nerves, protects endothelial function. Whether CGRP protects against EPCs senescence is unknown.

METHODS AND RESULTS

In cord-derived EPCs, the effects of CGRP on Ang II-induced cell senescence were evaluated by exogenous application of CGRP and rutaecarpine (to stimulate the endogenous CGRP production) or by over-expression of CGRP. The anti-senescence mechanisms of CGRP on EPCs were investigated either by applying CGRP antagonist or by silence of klotho, an anti-aging protein. The results showed that both CGRP and klotho mRNA expression were reduced in Ang II-induced senescent EPCs. Exogenous application of CGRP inhibited Ang II-induced EPCs senescence by down-regulating the expression of NADPH oxidase and reactive oxygen species production. Similarly, rutaecarpine or CGRP I over-expression also inhibited Ang II-induced EPCs senescence. The effects of CGRP and rutaecarpine were reversed by CGRP(8-37), a select antagonist of CGRP receptor and capsazepine, a selective antagonist of transient receptor potential vanilloid 1, respectively. Furthermore, gene silence of klotho markedly attenuated the anti-senescence effect of CGRP on EPCs.

CONCLUSIONS

The results suggest that CGRP can counteract Ang II-induced EPCs senescence through down-regulating the expression of NADPH oxidase and reactive oxygen species production and increasing the production of klotho.

Altered adhesive properties of cord blood endothelial outgrowth cells expressing IL-1ra

The aim of this study was to examine the potential of endothelial outgrowth cells (EOCs) expanded from CD34(+) cord blood-derived cells (CB-EOCs) for overexpression of therapeutic transgenes. As proof of principle, we overexpressed icIL-1ra in CB-EOCs. Proinflammatory activation of CB-EOCs in response to cytokine stimulation (IL-1beta and tumor necrosis factor (TNF)) and during coculture with monocytes showed that icIL-1ra-expressing CB-EOCs express significantly reduced levels of ICAM-1, MCP-1 and thrombin receptor expression. Moreover, overexpression of icIL-1ra attenuated the IL-1beta-mediated proinflammatory activation by diminishing the expression of ICAM-1, SELE, MCP-1 and IL-1beta. Interestingly, overexpression of icIL-1ra also inhibited TNF-induced upregulation of ICAM-1. Expression of ICAM-1, VCAM-1, tissue factor and IL-1beta was also decreased on direct contact with monocytes. These changes in gene expression were accompanied by functional reduction in leukocyte rolling, adhesion of monocytes to CB-EOCs, as well as by a reduction in transendothelial migration of monocytes. Our findings show that CB-EOCs stably expressing transgenic icIL-1ra are protected against activation by not only IL-1beta but also TNFalpha-mediated proinflammatory stimuli and inhibit decisive pathomechanisms of inflammatory processes such as rolling, adhesion and transmigration of monocytes. Therefore, icIL-ra transgenic CB-EOCs may prove to be beneficial in the treatment of IL-1beta- and TNFalpha-mediated inflammatory vasculopathies.

Combined reporter gene PET and iron oxide MRI for monitoring survival and localization of transplanted cells in the rat heart

There is a need for in vivo monitoring of cell engraftment and survival after cardiac cell transplantation therapy. This study assessed the feasibility and usefulness of combined PET and MRI for monitoring cell engraftment and survival after cell transplantation.

METHODS

Human endothelial progenitor cells (HEPCs), derived from CD34+ mononuclear cells of umbilical cord blood, were retrovirally transduced with the sodium iodide symporter (NIS) gene for reporter gene imaging by (124)I-PET and labeled with iron oxides for visualization by MRI. Imaging and histologic analysis were performed on 3 groups of nude rats on days 1, 3, and 7 after intramyocardial injection of 4 million HEPCs.

RESULTS

In vitro studies demonstrated stable expression of functional NIS protein and normal viability of HEPCs after transduction. On day 1, after intramyocardial transplantation, iron- and NIS-labeled HEPCs were visualized successfully on MRI as a regional signal void in the healthy myocardium and on PET as (124)I accumulation. The (124)I uptake decreased on day 3 and was undetectable on day 7, and the MRI signal remained unchanged throughout the follow-up period. Histologic analysis with CD31 and CD68 antibodies confirmed the presence of either labeled or nonlabeled control transplanted HEPCs at the site of injection on day 1 but not on day 7, when only iron-loaded macrophages were seen. Furthermore, deoxyuride-5'-triphosphate biotin nick end labeling showed extensive apoptosis at the site of transplantation.

CONCLUSION

The combination of MRI and PET allows imaging of localization and survival of transplanted HEPCs together with morphologic information about the heart. Although iron labeling rapidly loses specificity for cell viability because of phagocytosis of iron particles released from dead cells, reporter gene expression provided specific information on the number of surviving cells. This multimodality approach allows complementary analysis of cell localization and viability.

Storage and regulated secretion of factor VIII in blood outgrowth endothelial cells

BACKGROUND

Gene therapy provides an attractive alternative for protein replacement therapy in hemophilia A patients. Recent studies have shown the potential benefit of directing factor (F)VIII gene delivery to cells that also express its natural carrier protein von Willebrand factor (VWF). In this study, we explored the feasibility of blood outgrowth endothelial cells as a cellular FVIII delivery device with particular reference to long-term production levels, intracellular storage in Weibel-Palade bodies and agonist-induced regulated secretion.

DESIGN AND METHODS

Human blood outgrowth endothelial cells were isolated from peripheral blood collected from healthy donors, transduced at passage 5 using a lentiviral vector encoding human B-domain deleted FVIII-GFP and characterized by flow cytometry and confocal microscopy.

RESULTS

Blood outgrowth endothelial cells displayed typical endothelial morphology and expressed the endothelial-specific marker VWF. Following transduction with a lentivirus encoding FVIII-GFP, 80% of transduced blood outgrowth endothelial cells expressed FVIII-GFP. Levels of FVIII-GFP positive cells declined slowly upon prolonged culturing. Transduced blood outgrowth endothelial cells expressed 1.6+/-1.0 pmol/1 x 10(6) cells/24h FVIII. Morphological analysis demonstrated that FVIII-GFP was stored in Weibel-Palade bodies together with VWF and P-selectin. FVIII levels were only slightly increased following agonist-induced stimulation, whereas a 6- to 8-fold increase of VWF levels was observed. Subcellular fractionation revealed that 15-22% of FVIII antigen was present within the dense fraction containing Weibel-Palade bodies.

CONCLUSIONS

We conclude that blood outgrowth endothelial cells, by virtue of their ability to store a significant portion of synthesized FVIII-GFP in Weibel-Palade bodies, provide an attractive cellular on-demand delivery device for gene therapy of hemophilia A.

Directed engineering of a high-expression chimeric transgene as a strategy for gene therapy of hemophilia A

Human coagulation factor VIII (fVIII) is inefficiently biosynthesized in vitro and has proven difficult to express at therapeutic levels using available clinical gene-transfer technologies. Recently, we showed that a porcine and certain hybrid human/porcine fVIII transgenes demonstrate up to 100-fold greater expression than human fVIII. In this study, we extend these results to describe the use of a humanized, high-expression, hybrid human/porcine fVIII transgene that is 89% identical to human fVIII and was delivered by lentiviral vectors (LVs) to hematopoietic stem cells for gene therapy of hemophilia A. Recombinant human immunodeficiency virus-based vectors encoding the fVIII chimera efficiently transduced human embryonic kidney (HEK)-293T cells. Cells transduced with hybrid human/porcine fVIII encoding vectors expressed fVIII at levels 6- to 100-fold greater than cells transduced with vectors encoding human fVIII. Transplantation of transduced hematopoietic stem and progenitor cells into hemophilia A mice resulted in long-term fVIII expression at therapeutic levels despite <5% genetically modified blood mononuclear cells. Furthermore, the simian immunodeficiency virus (SIV) -derived vector effectively transduced the human hematopoietic cell lines K562, EU1, U.937, and Jurkat as well as the nonhematopoietic cell lines, HEK-293T and HeLa. All cell lines expressed hybrid human/porcine fVIII, albeit at varying levels with the K562 cells expressing the highest level of the hematopoietic cell lines. From these studies, we conclude that humanized high-expression hybrid fVIII transgenes can be utilized in gene therapy applications for hemophilia A to significantly increase fVIII expression levels compared to what has been previously achieved.

Angiogenesis by transplantation of HIF-1 alpha modified EPCs into ischemic limbs

Hypoxia inducible factor-1 alpha (HIF-1 alpha) is a key determinant of oxygen-dependent gene regulation in angiogenesis. HIF-1 alpha overexpression may be beneficial in cell therapy of hypoxia-induced pathophysiological processes, such as ischemic heart disease. To address this issue, human peripheral blood mononuclear cells (PBMNCs) were induced to differentiate into endothelial progenitor cells (EPCs), and then were transfected with either an HIF-1 alpha-expressing or a control vector and cultured under normoxia or hypoxia. Hypoxia-induced HIF-1 alpha mRNA and protein expression was increased after HIF-1 alpha transfection. This was accompanied by VEGF mRNA induction and increased VEGF secretion. Hypoxia-stimulated VEGF mRNA induction was significantly abrogated by HIF-1 alpha-specific siRNA. Functional studies showed that HIF-1 alpha overexpression further promoted hypoxia-induced EPC differentiation, proliferation and migration. The expressions of endothelial cell markers CD31, VEGFR2 (Flk-1) and eNOS as well as VEGF and NO secretions were also increased. Furthermore, in an in vivo model of hindlimb ischemia, HIF-1 alpha-transfected EPCs homed to the site of ischemia. A higher revascularization potential was also demonstrated by increased capillary density at the injury site. Our results revealed that endothelial progenitor cells ex vivo modification by hypoxia inducible factor-1 alpha gene transfection is feasible and may offer significant advantages in terms of EPC expansion and treatment efficacy.

Recombinant expression of coagulation factor VIII in hepatic and non-hepatic cell lines stably transduced with third generation lentiviral vectors comprising the minimal factor VIII promoter

BACKGROUND

Lentiviral vectors have the capacity to transduce stably non-dividing, differentiated and undifferentiated cells of various tissues, including liver. To obtain high-level expression of transgenes, vectors often rely on viral promoters. However, recent data suggest that the supraphysiologic expression from ubiquitous viral promoters may not be beneficial and harbor the risk of oncogene activation. Therefore this study explored the lentiviral-mediated expression of human coagulation factor VIII (FVIII) driven by the physiologic FVIII gene promoter (FVIII-p), the liver-specific human alpha-1-antitrypsin gene promoter (hAAT-p), the ubiquitous but non-viral EF1alpha promoter (EF1alpha-p) and the viral CMV promoter.

METHODS

Hepatic and non-hepatic cell lines were stably transduced with lentiviral vectors encoding FVIIIdelB and EGFP. To compare the different promoters, lentiviral vectors were cloned to drive FVIII expression from FVIII-p, EF1alpha-p, hAAT-p and CMV-p.

RESULTS

As expected, the strong viral CMV-p and the ubiquitous EF1alpha-p resulted in the highest FVIII expression in all cell lines tested (CMV-p 1.85 IU/mL/10(6) cells for 293T, 3.15 for HepG2, 5.03 for SK-Hep, 0.91 for Hepa1-6; EF1-alpha promoter 0.30 IU/mL/10(6) cells for 293T, 0.04 for HepG2, 2.75 for SK-Hep, 0.46 for Hepa1-6). While the hAAT-p resulted in low FVIII levels (0.10 IU/mL/10(6)cells in HepG2 and 0.04 in Hepa1-6), the FVIII promoter gave reasonable expression levels in hepatic cells (0.47 IU/mL/10(6)cells in Hepa1-6 and 0.44 in SK-Hep).

DISCUSSION

These results indicate the potential usefulness of the FVIII-p for hemophilia A gene therapy.

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.

Cardiovascular gene delivery: The good road is awaiting

Atherosclerotic cardiovascular disease is a leading cause of death worldwide. Despite recent improvements in medical, operative, and endovascular treatments, the number of interventions performed annually continues to increase. Unfortunately, the durability of these interventions is limited acutely by thrombotic complications and later by myointimal hyperplasia followed by progression of atherosclerotic disease over time. Despite improving medical management of patients with atherosclerotic disease, these complications appear to be persisting. Cardiovascular gene therapy has the potential to make significant clinical inroads to limit these complications. This article will review the technical aspects of cardiovascular gene therapy; its application for promoting a functional endothelium, smooth muscle cell growth inhibition, therapeutic angiogenesis, tissue engineered vascular conduits, and discuss the current status of various applicable clinical trials.

Phenotypic correction of von Willebrand disease type 3 blood-derived endothelial cells with lentiviral vectors expressing von Willebrand factor

Von Willebrand disease (VWD) is an inherited bleeding disorder, caused by quantitative (type 1 and 3) or qualitative (type 2) defects in von Willebrand factor (VWF). Gene therapy is an appealing strategy for treatment of VWD because it is caused by a single gene defect and because VWF is secreted into the circulation, obviating the need for targeting specific organs or tissues. However, development of gene therapy for VWD has been hampered by the considerable length of the VWF cDNA (8.4 kb [kilobase]) and the inherent complexity of the VWF protein that requires extensive posttranslational processing. In this study, a gene-based approach for VWD was developed using lentiviral transduction of blood-outgrowth endothelial cells (BOECs) to express functional VWF. A lentiviral vector encoding complete human VWF was used to transduce BOECs isolated from type 3 VWD dogs resulting in high-transduction efficiencies (95.6% +/- 2.2%). Transduced VWD BOECs efficiently expressed functional vector-encoded VWF (4.6 +/- 0.4 U/24 hour per 10(6) cells), with normal binding to GPIbalpha and collagen and synthesis of a broad range of multimers resulting in phenotypic correction of these cells. These results indicate for the first time that gene therapy of type 3 VWD is feasible and that BOECs are attractive target cells for this purpose.

Promoter Dependence of Transgene Expression by Lentivirus-Transduced Human Blood-Derived Endothelial Progenitor Cells

Peripheral blood- derived endothelial progenitor cells (EPCs) have considerable potential for the autologous therapy of vascular lesions or ischemic tissues. By introducing stable genetic modifications into these cells, this potential might be further enhanced. We investigated to what extent transgene expression can be controlled by using different transgene promoters. This was investigated in early- or late-outgrowth human EPCs obtained by culturing blood mononuclear cells for 1 or 4 weeks on type 1 collagen in medium containing endothelial growth supplements. A large fraction of these cells were stably transduced using lentiviral vectors for expression of the enhanced green fluorescent protein (EGFP). Transgene expression in vitro or in vivo after injection into nude mice was highest when under the control of the cytomegalovirus (CMV) promoter, intermediate with the EF1alpha promoter, and lowest with the phosphoglycerate kinase promoter. When blood mononuclear cells were cultured for 1 week in the absence of endothelial growth supplements, CMV promoter- driven expression of EGFP was two orders of magnitude lower than in similarly transduced EPCs. Our results show that lentiviral vectors are useful tools for the stable introduction of exogenous genes into EPCs and for their expression at desired levels using the appropriate gene promoter.

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.

Endothelial-like cells expanded from CD34+ blood cells improve left ventricular function after experimental myocardial infarction

Mobilization and recruitment of endothelial progenitor cells (EPC) contributes to vasculogenesis in vivo. So far, applications for cell therapy are limited by the number of available cells. Expansion of EPC or their progeny may, therefore, facilitate its therapeutic use in ischemic disease. The aim of this study was to expand CD34+ EPC-derived progeny from different sources, characterize them, and investigate their potential for use in therapeutic vasculogenesis. CD34+ cells from G-CSF-mobilized peripheral blood (PB) and cord blood (CB) were isolated using immunomagnetic beads and cultured in endothelial cell medium. Cells were expanded up to 16 (PB) and up to 46 (CB) population doublings, respectively. Immunophenotypic and mRNA expression analyses showed a high degree of similarity between the cultured cells and human umbilical vein endothelial cells (HUVEC). By day 14 after transplantation, transplanted human CD31-positive EPC-derived cells were detected. These cells expressed the proliferation marker Ki67 and formed vessel-like structures in ischemic myocardium. Most strikingly, transplantation of EPC-derived cells improved left ventricular function after experimental ischemia, as shown by echocardiography. In conclusion, cells cultured from CD34+ EPC can be expanded in vitro to clinically relevant numbers. In vivo, these cells proliferate, form vascular structures, and improve left ventricular function after experimental myocardial infarction. Therefore, in vitro expanded EPC-derived endothelial cells may be beneficial in the treatment of ischemic disease.

Endothelium-Targeted Gene and Cell-Based Therapies for Cardiovascular Disease

Most common cardiovascular diseases are accompanied by endothelial dysfunction. Because of its predominant role in the pathogenesis of cardiovascular disease, the vascular endothelium is an attractive therapeutic target. The identification of promoter sequences capable of rendering endothelial-specific transgene expression together with the recent development of vectors with enhanced tropism for endothelium may offer opportunities for the design of new strategies for modulation of endothelial function. Such strategies may be useful in the treatment of chronic diseases such as hypertension, atherosclerosis, and ischemic artery disease, as well as in acute myocardial infarction and during open heart surgery for prevention of ischemia and reperfusion (I/R)-induced injury. The recent identification of putative endothelial progenitor cells in peripheral blood may allow the design of autologous cell-based strategies for neovascularization of ischemic tissues and for the repair of injured blood vessels and bioengineering of vascular prosthesis. "Proof-of-concept" for some of these strategies has been established in animal models of cardiovascular disease. However the successful translation of these novel strategies into clinical application will require further developments in vector and delivery technologies. Further characterization of the processes involved in mobilization, migration, homing, and incorporation of endothelial progenitor cells into the target tissues is necessary, and the optimal conditions for therapeutic application of these cells need to be defined and standardized.