Capture and expansion of bone marrow-derived mesenchymal progenitor cells with a transforming growth factor-beta1-von Willebrand's factor fusion protein for retrovirus-mediated delivery of coagulation factor IX

The advent of a pan-collagenous CLOVIS POINT for pathotropic targeting and cancer gene therapy, a retrospective

The 'Clovis Point'-an enabling prehistoric gain-of-function in stone-age tool technologies which empowered the Paleoindian-Americans to hunt, to strike-deep, and to kill designated target megafauna more efficiently-was created biochemically by molecular-genetic bio-engineering. This Biomedical "Clovis Point" was crafted by adapting a broad-spectrum Pan-Collagen Binding Domain (Pan-Coll/CBD) found within the immature pre-pro-peptide segment of Von Willebrand Factor into a constructive series of advanced medical applications. Developed experimentally, preclinically, and clinically into a cutting-edge Biotechnology Platform, the Clovis Point is suitable for 1) solid-state binding of growth factors on collagenous scaffolds for improved orthopedic wound healing, 2) promoting regeneration of injured/diseased tissues; and 3) autologous stem cell capture, expansion, and gene-based therapies. Subsequent adaptations of the high-affinity Pan-Coll/CBD (exposed-collagen-seeking/surveillance function) for intravenous administration in humans, enabled the physiological delivery, aka Pathotropic Targeting to diseased tissues via the modified envelopes of gene vectors; enabling 4) precision tumor-targeting for cancer gene therapy and 5) adoptive/localized immunotherapies, demonstrating improved long-term survival value-thus pioneering a proximal and accessible cell cycle control point for cancer management-empowering modern medical oncologists to address persistent problems of chemotherapy resistance, recurrence, and occult progression of metastatic disease. Recent engineering adaptations have advanced the clinical utility to include the targeted delivery of small molecule APIs: including taxanes, mAbs, and RNA-based therapeutics.

Tumor bioengineering using a transglutaminase crosslinked hydrogel

Development of a physiologically relevant 3D model system for cancer research and drug development is a current challenge. We have adopted a 3D culture system based on a transglutaminase-crosslinked gelatin gel (Col-Tgel) to mimic the tumor 3D microenvironment. The system has several unique advantages over other alternatives including presenting cell-matrix interaction sites from collagen-derived peptides, geometry-initiated multicellular tumor spheroids, and metabolic gradients in the tumor microenvironment. Also it provides a controllable wide spectrum of gel stiffness for mechanical signals, and technical compatibility with imaging based screening due to its transparent properties. In addition, the Col-Tgel provides a cure-in-situ delivery vehicle for tumor xenograft formation in animals enhancing tumor cell uptake rate. Overall, this distinctive 3D system could offer a platform to more accurately mimic in vivo situations to study tumor formation and progression both in vitro and in vivo.

A novel human TGF-β1 fusion protein in combination with rhBMP-2 increases chondro-osteogenic differentiation of bone marrow mesenchymal stem cells

Transforming growth factor-beta (TGF-β) is involved in processes related to the differentiation and maturation of osteoprogenitor cells into osteoblasts. Rat bone marrow (BM) cells were cultured in a collagen-gel containing 0.5% fetal bovine serum (FBS) for 10 days in the presence of rhTGF (recombinant human TGF)-β1-F2, a fusion protein engineered to include a high-affinity collagen-binding decapeptide derived from von Willebrand factor. Subsequently, cells were moderately expanded in medium with 10% FBS for 4 days and treated with a short pulse of rhBMP (recombinant human bone morphogenetic protein)-2 for 4 h. During the last 2 days, dexamethasone and β-glycerophosphate were added to potentiate osteoinduction. Concomitant with an up-regulation of cell proliferation, DNA synthesis levels were determined. Polymerase chain reaction was performed to reveal the possible stemness of these cells. Osteogenic differentiation was evaluated in terms of alkaline phosphatase activity and mineralized matrix formation as well as by mRNA expression of osteogenic marker genes. Moreover, cells were placed inside diffusion chambers and implanted subcutaneously into the backs of adult rats for 4 weeks. Histological study provided evidence of cartilage and bone-like tissue formation. This experimental procedure is capable of selecting cell populations from BM that, in the presence of rhTGF-β1-F2 and rhBMP-2, achieve skeletogenic potential in vitro and in vivo.

Bone marrow-derived mesenchymal stem cells

Human mesenchymal stem cells (MSCs) contribute to the regeneration of mesenchymal tissues, and are essential in providing support for the growth and differentiation of primitive hemopoietic cells within the bone marrow microenvironment. Techniques are now available to isolate human MSCs and manipulate their expansion in vitro under defined culture conditions without change of phenotype or loss of function. Mesenchymal stem cells have generated a great deal of interest in many clinical settings, including that of regenerative medicine, immune modulation and tissue engineering. Studies have already demonstrated the feasibility of transplanted MSCs providing crucial new cellular therapy. In this review, many aspects of the MSC will be discussed, with the main focus being on clinical studies that describe the potential of MSCs to treat patients with hematological malignancies who are undergoing chemotherapy and/or radiotherapy.

Regeneration of meniscus cartilage in a knee treated with percutaneously implanted autologous mesenchymal stem cells

Mesenchymal stem cells are pluripotent cells found in multiple human tissues including bone marrow, synovial tissues, and adipose tissues. They have been shown to differentiate into bone, cartilage, muscle, and adipose tissue and represent a possible promising new therapy in regenerative medicine. Because of their multi-potent capabilities, mesenchymal stem cell (MSC) lineages have been used successfully in animal models to regenerate articular cartilage and in human models to regenerate bone. The regeneration of articular cartilage via percutaneous introduction of mesenchymal stem cells (MSC's) is a topic of significant scientific and therapeutic interest. Current treatment for cartilage damage in osteoarthritis focuses on surgical interventions such as arthroscopic debridement, microfracture, and cartilage grafting/transplant. These procedures have proven to be less effective than hoped, are invasive, and often entail a prolonged recovery time. We hypothesize that autologous mesenchymal stem cells can be harvested from the iliac crest, expanded using the patient's own growth factors from platelet lysate, then successfully implanted to increase cartilage volume in an adult human knee. We present a review highlighting the developments in cellular and regenerative medicine in the arena mesenchymal stem cell therapy, as well as a case of successful harvest, expansion, and transplant of autologous mesenchymal stem cells into an adult human knee that resulted in an increase in meniscal cartilage volume.

Potential of mesenchymal stem cells in gene therapy approaches for inherited and acquired diseases

The intriguing biology of stem cells and their vast clinical potential is emerging rapidly for gene therapy. Bone marrow stem cells, including the pluripotent haematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs) and possibly the multipotent adherent progenitor cells (MAPCs), are being considered as potential targets for cell and gene therapy-based approaches against a variety of different diseases. The MSCs from bone marrow are a promising target population as they are capable of differentiating along multiple lineages and, at least in vitro, have significant expansion capability. The apparently high self-renewal potential makes them strong candidates for delivering genes and restoring organ systems function. However, the high proliferative potential of MSCs, now presumed to be self-renewal, may be more apparent than real. Although expanded MSCs have great proliferation and differentiation potential in vitro, there are limitations with the biology of these cells in vivo. So far, expanded MSCs have failed to induce durable therapeutic effects expected from a true self-renewing stem cell population. The loss of in vivo self-renewal may be due to the extensive expansion of MSCs in existing in vitro expansion systems, suggesting that the original stem cell population and/or properties may no longer exist. Rather, the expanded population may indeed be heterogeneous and represents several generations of different types of mesenchymal cell progeny that have retained a limited proliferation potential and responsiveness for terminal differentiation and maturation along mesenchymal and non-mesenchymal lineages. Novel technology that allows MSCs to maintain their stem cell function in vivo is critical for distinguishing the elusive stem cell from its progenitor cell populations. The ultimate dream is to use MSCs in various forms of cellular therapies, as well as genetic tools that can be used to better understand the mechanisms leading to repair and regeneration of damaged or diseased tissues and organs.

Autologous human-derived bone marrow cells exposed to a novel TGF-β1 fusion protein for the treatment of critically sized tibial defect

We report the first clinical case of transplantation of autologous bone marrow-derived cells in vitro exposed to a novel recombinant human transforming growth factor (rhTGF)-β1 fusion protein bearing a collagen-binding domain (rhTGF-β1-F2), dexamethasone (DEX) and β-glycerophosphate (β-GP). When such culture-expanded cells were loaded into porous ceramic scaffolds and transplanted into the bone defect of a 69-year-old man, they differentiated into bone tissue. Marrow cells were obtained from the iliac crest and cultured in collagen gels impregnated with rhTGF-β1-F2. Cells were selected under serum-restricted conditions in rhTGF-β1-F2-containing medium for 10 days, expanded in 20% serum for 22 days and osteoinduced for 3 additional days in DEX/β-GP-supplemented medium. We found that the cell number harvested from rhTGF-β1-F2-treated cultures was significantly higher (2.3- to 3-fold) than that from untreated cultures. rhTGF-β1-F2 treatment also significantly increased alkaline phosphatase activity (2.2- to 5-fold) and osteocalcin synthesis, while calcium was only detected in rhTGF-β1-F2-treated cells. Eight weeks after transplantation, most of the scaffold pores were filled with bone and marrow tissue. When we tested the same human cells treated in vitro in a rat model using diffusion chambers, there was subsequent development of cartilage and bone following the subcutaneous transplantation of rhTGF-β1-F2-treated cells. This supports the suggestion that such cells were marrow-derived cells, with chondrogenic and osteogenic potential, whereas the untreated cells were not under the same conditions. The ability for differentiation into cartilage and bone tissues, combined with an extensive proliferation capacity, makes such a marrow-derived stem cell population valuable to induce bone regeneration at skeletal defect sites.

Transfer and Stable Transgene Expression of a Mammalian Artificial Chromosome into Bone Marrow-Derived Human Mesenchymal Stem Cells

Mammalian artificial chromosomes (ACEs) transferred to autologous adult stem cells (SCs) provide a novel strategy for the ex vivo gene therapy of a variety of clinical indications. Unlike retroviral vectors, ACEs are stably maintained, autonomous, and nonintegrating. In this report we assessed the delivery efficiency of ACEs and evaluated the subsequent differentiation potential of ACE-transfected bone marrow-derived human mesenchymal stem cells (hMSCs). For this, an ACE carrying multiple copies of the red fluorescent protein (RFP) reporter gene was transferred under optimized conditions into hMSCs using standard cationic transfection reagents. RFP expression was detectable in 11% of the cells 4-5 days post-transfection. The RFP-expressing hMSCs were enriched by high-speed flow cytometry and maintained their potential to differentiate along adipogenic or osteogenic lineages. Fluorescent in situ hybridization and fluorescent microscopy demonstrated that the ACEs were stably maintained as single chromosomes and expressed the RFP transgenes in both differentiated cultures. These findings demonstrate the potential utility of ACEs for human adult SC ex vivo gene therapy.

Transduction of bone-marrow-derived mesenchymal stem cells by using lentivirus vectors pseudotyped with modified RD114 envelope glycoproteins

Bone-marrow-derived mesenchymal stem cells (MSCs) have attracted considerable attention as tools for the systemic delivery of therapeutic proteins in vivo, and the ability to efficiently transfer genes of interest into such cells would create a number of therapeutic opportunities. We have designed and tested a series of human immunodeficiency virus type 1 (HIV-1)-based vectors and vectors based on the oncogenic murine stem cell virus to deliver and express transgenes in human MSCs. These vectors were pseudotyped with either the vesicular stomatitis virus G (VSV-G) glycoprotein (GP) or the feline endogenous virus RD114 envelope GP. Transduction efficiencies and transgene expression levels in MSCs were analyzed by quantitative flow cytometry and quantitative real-time PCR. While transduction efficiencies with virus particles pseudotyped with the VSV-G GP were found to be high, RD114 pseudotypes revealed transduction efficiencies that were 1 to 2 orders of magnitude below those observed with VSV-G pseudotypes. However, chimeric RD114 GPs, with the transmembrane and extracellular domains fused to the cytoplasmic domain derived from the amphotropic Moloney murine leukemia virus 4070A GP, revealed about 15-fold higher titers relative to the unmodified RD114 GP. The transduction efficiencies in human MSCs of HIV-1-based vectors pseudotyped with the chimeric RD114 GP were similar to those obtained with HIV-1 vectors pseudotyped with the VSV-G GP. Our results also indicate that RD114 pseudotypes were less toxic than VSV-G pseudotypes in human MSC progenitor assays. Taken together, these results suggest that lentivirus pseudotypes bearing alternative Env GPs provide efficient tools for ex vivo modification of human MSCs.

Regulation of proliferation and migration in retinoic acid treated C3H10T1/2 cells by TGF-? isoforms

Proliferation of mesenchymal precursors of osteogenic and chondrogenic cells and migration of these precursors to repair sites are important early steps in bone repair. Transforming growth factor-beta (TGF-beta) has been implicated in the promotion of bone repair and may have a role in these processes. Three isoforms of TGF-beta, TGF-beta1, -beta2, and -beta3, are expressed in fracture healing, however, their specific roles in the repair process are unknown. Differential actions of the TGF-beta isoforms on early events of bone repair were explored in the multipotent mesenchymal precursor cell line, C3H10T1/2. Cell migration was determined using a modified Boyden chamber in response to concentrations of each isoform ranging from 10(-12) to 10(-9) g/ml. All three isoforms demonstrated a dose-dependent chemotactic stimulation of untreated C3H10T1/2 cells. Checkerboard assays indicated that all three isoforms also stimulated chemokinesis of the untreated cells. C3H10T1/2 cells treated with all-trans-retinoic acid (ATRA) and expressing relatively higher levels of osteoblastic gene markers such as alkaline phosphatase and collagen type I, lower levels of chondrocytic gene markers collagen type II and aggrecan, and unchanged levels of the adipose marker adipsin did not demonstrate significant chemokinesis or chemotaxis in response to TGF-beta1 or -beta3 at concentrations ranging from 10(-12) to 10(-9) g/ml. In the ATRA-treated cells, TGF-beta2 stimulated a significant increase in chemotaxis only at the highest concentration tested. Cell proliferation was assessed by mitochondrial dehydrogenase activity and cell counts at TGF-beta concentrations from 10(-11) to 10(-8) g/ml. None of the TGF-beta isoforms stimulated cell proliferation in untreated or ATRA-treated C3H10T1/2 cells. Analysis of TGF-beta receptors (TGF-betaR1, -betaR2, and -betaR3) showed a 1.6- to 2.8-fold decrease in mRNA expression of these receptors in ATRA-treated cells.

IN CONCLUSION

(1) while all three TGF-beta isoforms stimulate chemotaxis/chemokinesis of multipotent C3H10T1/2 cells, TGF-beta1 and -beta3 do not stimulate chemotaxis in C3H10T1/2 cells treated with ATRA while TGF-beta2 stimulated chemotaxis only at the highest concentration tested. (2) TGF-beta isoforms do not appear to stimulate cell proliferation in C3H10T1/2 cells in either a multipotent state or after ATRA treatment when expressing higher levels of alkaline phosphatase and collagen type I gene markers. (3) Decrease in mRNA expression for TGF-betaR1, -betaR2, and -betaR3 upon ATRA treatment could potentially explain the lack of chemotaxis/chemokinesis in these cells expressing higher levels of alkaline phosphatase and collagen type I.

Targeting cytokines to inflammation sites

To increase the half-life of a cytokine and target its activation specifically to disease sites, we have engineered a latent cytokine using the latency-associated protein (LAP) of transforming growth factor-beta 1 (TGF-beta 1) fused via a matrix metalloproteinase (MMP) cleavage site to interferon (IFN)-beta at either its N or C terminus. The configuration LAP-MMP-IFN-beta resembles native TGF-beta and lacks biological activity until cleaved by MMPs, whereas the configuration IFN-beta-MMP-LAP is active. LAP provides for a disulfide-linked shell hindering interaction of the cytokine with its cellular receptors, conferring a very long half-life of 55 h in vivo. Mutations of the disulfide bonds in LAP abolish this latency. Samples of cerebrospinal fluid (CSF) or synovial fluid from patients with inflammatory diseases specifically activate the latent cytokine, whereas serum samples do not. Intramuscular injection in arthritic mice of plasmid DNA encoding these constructs demonstrated a greater therapeutic effect of the latent as compared to the active forms.

Glass needle-mediated microinjection of macromolecules and transgenes into primary human mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) are multipotent cells that can differentiate into various tissue types, including bone, cartilage, tendon, adipocytes, and marrow stroma, making them potentially useful for human cell and gene therapies. Our objective was to demonstrate the utility of glass needle-mediated microinjection as a method to deliver macromolecules (e.g. dextrans, DNA) to hMSCs for cell and molecular biological studies. hMSCs were isolated and cultured using a specific fetal bovine serum, prescreened for its ability to promote cell adherence, proliferation, and osteogenic differentiation. Successful delivery of Oregon Green-dextran via intranuclear microinjection was achieved, yielding a postinjection viability of 76 +/- 13%. Excellent short-term gene expression (63 +/- 11%) was achieved following microinjection of GFP-containing vectors into hMSCs. Higher efficiencies of short-term gene expression ( approximately 5-fold) were observed when injecting supercoiled DNA, pYA721, as compared with the same DNA construct in a linearized form, YA721. Approximately 0.05% of hMSCs injected with pYA721 containing both the GFP and neomycin resistance genes formed GFP-positive, drug-resistant colonies that survived >120 days. Injection of linearized YA721 resulted in 3.6% of injected hMSC forming drug-resistant colonies, none of which expressed GFP that survived 60-120 days. These studies demonstrate that glass needle-mediated microinjection can be used as a method of delivering macromolecules to hMSCs and may prove to be a useful technique for molecular and cell biological mechanistic studies and future genetic modification of hMSCs.

Bone marrow stromal cells as a genetic platform for systemic delivery of therapeutic proteins in vivo: human factor IX model

BACKGROUND

Hemophilia B is an X-linked bleeding disorder that results from a deficiency in functional coagulation factor IX (hFIX). In patients lacking FIX, the intrinsic coagulation pathway is disrupted leading to a lifelong, debilitating and sometimes fatal disease.

METHODS

We have developed an ex vivo gene therapy system using genetically modified bone marrow stromal cells (BMSCs) as a platform for sustained delivery of therapeutic proteins into the general circulation. This model exploits the ability of BMSCs to form localized ectopic ossicles when transplanted in vivo. BMSCs were transduced with MFG-hFIX, a retroviral construct directing the expression of hFIX. The biological activity of hFIX expressed by these cells was assessed in vitro and in vivo.

RESULTS

Transduced cells produced biologically active hFIX in vitro with a specific activity of 90% and expressed hFIX at levels of approximately 497 ng/10(6) cells/24 h and 322 ng/10(6) cells/24 h for human and porcine cells, respectively. The secretion of hFIX was confirmed by Western blot analysis of the conditioned medium using a hFIX-specific antibody. Transduced BMSCs (8 x 10(6) cells per animal) were transplanted within scaffolds into subcutaneous sites in immunocompromised mice. At 1 week post-implantation, serum samples contained hFIX at levels greater than 25 ng/ml. Circulating levels of hFIX gradually decreased to 11.5 ng/ml at 1 month post-implantation and declined to a stable level at 6.1 ng/ml at 4 months.

CONCLUSIONS

These findings demonstrate that genetically modified BMSCs can continuously secrete biologically active hFIX from self-contained ectopic ossicles in vivo, and thus represent a novel delivery system for releasing therapeutic proteins into the circulation.

Multilineage cells from adipose tissue as gene delivery vehicles

We have characterized a population of mesenchymal progenitor cells from adipose tissue, termed processed lipoaspirate (PLA) cells, which have multilineage potential similar to bone marrow-derived mesenchymal stem cells and are also easily expanded in culture. The primary benefit of using adipose tissue as a source of multilineage progenitor cells is its relative abundance and ease of procurement. We examined the infection of PLA cells with adenoviral, oncoretroviral, and lentiviral vectors. We demonstrate that PLA cells can be transduced with lentiviral vectors at high efficiency. PLA cells maintain transgene expression after differentiation into adipogenic and osteogenic lineages after lentiviral transduction. Therefore, PLA cells and lentiviral vectors may be an efficient combination for use as a therapeutic gene delivery vehicle.

Lentiviral vectors for sustained transgene expression in human bone marrow-derived stromal cells

Bone marrow-derived mesenchymal stromal cells (MSCs) have attracted attention as potential platforms for the systemic delivery of therapeutic proteins in vivo following gene transfer using oncogenic retroviruses. However, the major limitations of this strategy include low levels of gene transfer and a general lack of long-term transgene expression. We have investigated the expression of several transgenes in MSCs following HIV-1 lentiviral vector-mediated gene transfer. Vectors containing a variety of strong promoters driving enhanced green fluorescence protein (EGFP) and coral (Discosoma sp.)-derived red fluorescent protein (DsRed) reporter genes pseudotyped with the vesicular stomatitis virus-G (VSV-G) glycoprotein were able to transduce cultured MSCs with high efficiency. Transduction efficiencies and transgene expression levels in MSCs were found to be higher with lentiviral vectors than with a vector based on the murine stem cell virus pseudotyped with VSV-G. Transgene expression was maintained in culture for at least 5 months. HIV-1-based lentiviral vectors were able to transduce clonogenic mesenchymal progenitor cells, which were capable of maintaining transgene expression by their MSC progeny, over several cell divisions and during differentiation into adipocytes, indicating that terminal adipocyte cell differentiation was unaffected by lentivirus-mediated reporter gene transfer. Collectively these results suggest that lentivirus-mediated gene transfer strategies provide an efficient tool for ex vivo modification of MSCs that does not interfere with differentiation.

Phenotypic differentiation of TGF-beta1-responsive pluripotent premesenchymal prehematopoietic progenitor (P4 stem) cells from murine bone marrow

On the horizon of modern molecular medicine is the requisite technology to capture multipotent human stem cells that are capable of self-renewal and to direct these stem cells along defined lineages for therapeutic purposes. In this article, we describe the hematopoietic and mesenchymal differentiation potential of a unique population of transforming growth factor-beta1 (TGF-beta1)-responsive stem cells derived from murine bone marrow. Stringent selection of the stem cells was accomplished under low serum conditions by virtue of an inherent survival response to a TGF-beta1-vWF fusion protein that was bound to collagen matrices. The TGF-beta1-responsive stem cells initially exhibited a non-adherent and uniformly blastoid morphology, underwent expansion into colonies upon serum reconstitution, and were capable of overt cytodifferentiation along fibrogenic, osteogenic, chondrogenic, or adipogenic lineages upon growth factor stimulation. Remarkably, these stem cells also underwent rapid expansion in the presence of either hematopoietic stem cell factor (SCF) or interleukin3 (IL-3), and differentiated into myeloid and lymphoid phenotypes upon exposure to the latter. Taken together, these results support the hypothesis that pluripotent premesenchymal prehematopoietic progenitor cells, designated P4 stem cells, are present postnatally in murine bone marrow and, thus, may be summarily isolated for various cell-based experimental therapies.

Bone marrow stromal stem cells: nature, biology, and potential applications

Bone marrow stromal cells are progenitors of skeletal tissue components such as bone, cartilage, the hematopoiesis-supporting stroma, and adipocytes. In addition, they may be experimentally induced to undergo unorthodox differentiation, possibly forming neural and myogenic cells. As such, they represent an important paradigm of post-natal nonhematopoietic stem cells, and an easy source for potential therapeutic use. Along with an overview of the basics of their biology, we discuss here their potential nature as components of the vascular wall, and the prospects for their use in local and systemic transplantation and gene therapy.

Human mesenchymal stem cells maintain transgene expression during expansion and differentiation

Human adult bone marrow contains both hematopoietic stem cells that generate cells of all hematopoietic lineages and human mesenchymal stem cells (hMSCs), which support hematopoiesis and contribute to the regeneration of multiple connective tissues. The goal of the current study was to demonstrate that transduced hMSCs maintain transgene expression after stem cell differentiation in vitro and in vivo. We have introduced genes into cultured hMSCs by retroviral vector transfer and demonstrated long-term in vitro and in vivo expression of human interleukin 3 (hIL-3) and green fluorescent protein (GFP). Protocols were developed to achieve transduction efficiencies of 80-90% in these stem cells. In vitro expression of hIL-3 averaged 350 ng/10(6)cells/24 h over 17 passages (> 6 months) and GFP expression was stable over the same time period. Transduced hMSCs were able to differentiate into osteogenic, adipogenic, and chondrogenic lineages and maintained transgene expression after differentiation. Parallel studies were performed in vivo using NOD/SCID mice. Human MSCs expressing hIL-3 were cultured on several matrices and then delivered by subcutaneous, intravenous, and intraperitoneal routes. Sampling of peripheral blood demonstrated that systemic hIL-3 expression was maintained in the range of 100-800 pg/ml over a period of 3 months. These results illustrate the ability of hMSCs to express genes of therapeutic potential and demonstrate their potential clinical utility as cellular vehicles for systemic gene delivery.

Engineered human mesenchymal stem cells: a novel platform for skeletal cell mediated gene therapy

BACKGROUND

Human mesenchymal stem cells (hMSCs) are pluripotent cells that can differentiate to various mesenchymal cell types. Recently, a method to isolate hMSCs from bone marrow and expand them in culture was described. Here we report on the use of hMSCs as a platform for gene therapy aimed at bone lesions.

METHODS

Bone marrow derived hMSCs were expanded in culture and infected with recombinant adenoviral vector encoding the osteogenic factor, human BMP-2. The osteogenic potential of genetically engineered hMSCs was assessed in vitro and in vivo.

RESULTS

Genetically engineered hMSCs displayed enhanced proliferation and osteogenic differentiation in culture. In vivo, transplanted genetically engineered hMSCs were able to engraft and form bone and cartilage in ectopic sites, and regenerate bone defects (non-union fractures) in mice radius bone. Importantly, the same results were obtained with hMSCs isolated from a patient suffering from osteoporosis.

CONCLUSIONS

hMSCs represent a novel platform for skeletal gene therapy and the present results suggest that they can be genetically engineered to express desired therapeutic proteins inducing specific differentiation pathways. Moreover, hMSCs obtained from osteoporotic patients can restore their osteogenic activity following human BMP-2 gene transduction, an important finding in the future planning of gene therapy treatment for osteoporosis.

Mesenchymal stem cells are capable of homing to the bone marrow of non-human primates following systemic infusion

OBJECTIVE

The human bone marrow contains mesenchymal stem cells capable of differentiating along multiple mesenchymal cell lineages. Using a non-human primate model, we sought to determine whether the systemic infusion of baboon-derived mesenchymal stem cells was associated with toxicity and whether these cells were capable of homing to and persisting within the bone marrow.

MATERIALS AND METHODS

Five baboons (Papio anubis) were administered lethal irradiation followed by intravenous autologous hematopoietic progenitor cells combined with either autologous (n = 3) or allogeneic (n = 2) mesenchymal stem cells that had been expanded in culture. In four of these baboons, the mesenchymal stem cells were genetically modified with a retroviral vector encoding either the enhanced green fluorescent protein gene (n = 3) or the human placental alkaline phosphatase gene (n = 1) for tracking purposes. A sixth animal received only intravenous gene marked autologous mesenchymal stem cells but no hematopoietic stem cells or conditioning irradiation.

RESULTS

Following culture, baboon mesenchymal stem cells appeared morphologically as a homogeneous population of spindle-shaped cells that were identified by the monoclonal antibodies SH-3 and SH-4. These cells did not express the hematopoietic markers CD34 or CD45. Baboon mesenchymal stem cells isolated from primary culture were capable of differentiating along both adipogenic and osteogenic lineages. There was no acute or chronic toxicity associated with the intravenous infusion of mesenchymal stem cells. In all five recipients of gene marked mesenchymal stem cells, transgene was detected in post-transplant bone marrow biopsies. In two animals receiving autologous mesenchymal stem cells, including the one non-conditioned recipient, transgene could be detected over 1 year following infusion. In one recipient of allogeneic gene marked mesenchymal stem cells, transgene was detected in the bone marrow at 76 days following infusion.

CONCLUSION

These data demonstrate that baboon mesenchymal stem cells: 1) are not associated with significant toxicity when administered intravenously, 2) are capable of homing to the bone marrow following intravenous infusion, and 3) have the capacity to establish residence within the bone marrow for an extended duration following systemic administration.

Engineering, expression, and renaturation of a collagen-targeted human bFGF fusion protein

Basic fibroblast growth factor (bFGF) is a potent in vitro mitogen for capillary endothelial cells, stimulates angiogenesis in vivo, and may participate in tissue repair. Basic FGF is found in abundance in tissues such as brain, kidney and cartilage. This study reports the expression, purification, and renaturation of a biologically active human basic fibroblast growth factor fusion protein (hbFGF-F1) from Escherichia coli. A prokaryotic expression vector was engineered to produce a tripartite fusion protein consisting of (i) a purification tag, (ii) a protease-sensitive linker/collagen-binding domain, and (iii) cDNA sequence encoding the active fragment of hbFGF. The expressed hbFGF-F1 and hbFGF-F2 (it contains a collagen-binding domain), located in inclusion bodies, were solubilized with 6 M guanidine-HCl and renatured using a glutathione redox system and protracted dialysis under various experimental conditions. The purification of the recombinant proteins was achieved by binding the His-tag of the fusion protein on a Ni-NTA metal chelate column. The biological activity of the recombinant growth factors was demonstrated by their ability to stimulate proliferation of human vein endothelial cells (HVEC), monitored by [3H]-thymidine incorporation, where commercial recombinant human bFGF (rhbFGF) served as a positive control. Purified rhbFGF-F1 and rhbFGF-F2 constructs exhibited proliferative activity comparable to commercial rhbFGF. Binding of the renatured hbFGF-F2 fusion protein to collagen was demonstrated by stable binding on a collagen-conjugated Sephadex-G15 column. The high affinity binding was also demonstrated by the binding of [3H]-collagen to the rhbFGF-F2 protein immobilized on a Ni-NTA column. The rhbFGF-F2 fusion protein bound to collagen coated surfaces with high affinity but exhibited comparatively lower biological activity than the fusion protein in solution, suggesting a potentially latent configuration. Taken together, these results demonstrate that biologically active rhbFGF fusion proteins can be recovered from transformed bacteria by oxidative refolding; thus, providing a means for its high-yield production, purification, and renaturation from microorganisms. Furthermore, we demonstrate that the auxiliary collagen-binding domain effectively targets the recombinant growth factor to type I collagen. The clinical effect of rhbFGF-F2 on wound healing is also studied in streptozotocin-induced diabetic rats and evaluated by histological examination comparing with rhbFGF-F1 and commercial bFGF effects. The highly beneficial effects of rhbFGF-F2 on wound healing is suggested to be due to its extremely potent angiogenesis and granulation tissue formation activities, leading to a rapid reepithelialization of the wound. Topical application of rhbFGF-F2 mixed with type I collagen is a more effective method in accelerating closure of full-thickness excisional skin-wound in diabetic rats when compared with the fusion protein alone or commercial hbFGF at the same doses. These studies advance the technology necessary to generate large quantities of targeted bFGF fusion proteins as well as to develop new strategies for specific biomedical applications.

Mesenchymal stem cells: biology and potential clinical uses

There has been an increasing interest in recent years in the stromal cell system functioning in the support of hematopoiesis. The stromal cell system has been proposed to consist of marrow mesenchymal stem cells that are capable of self-renewal and differentiation into various connective tissue lineages. Recent efforts demonstrated that the multiple mesenchymal lineages can be clonally derived from a single mesenchymal stem cell, supporting the proposed paradigm. Dexter demonstrated in 1982 that an adherent stromal-like culture was able to support maintenance of hematopoietic stem as well as early B lymphopoeisis. Recent data from in vitro models demonstrating the essential role of stromal support in hematopoiesis shaped the view that cell-cell interactions in the marrow microenvironment are critical for normal hematopoietic function and differentiation. Maintenance of the hematopoietic stem cell population has been used to increase the efficiency of hematopoietic stem cell gene transfer. High-dose chemotherapy and frequently cause stromal damage with resulting hematopoietic defects. Data from preclinical transplantation studies suggested that stromal cell infusions not only prevent the occurrence of graft failure, but they have an immunomodulatory effect. Preclinical and early clinical safety studies are paving the way for further applications of mesenchymal stem cells in the field of transplantation with respect to hematopoietic support, immunoregulation, and graft facilitation.

Targeted Inactivation of the Coagulation Factor IX Gene Causes Hemophilia B in Mice

Hemophilia B is a leading target for gene therapy because current therapy is not optimal. Hence, a murine model of factor IX (F. IX) deficiency was generated to develop gene therapy strategies for hemophilia B. A targeting vector was created by replacing a 3.2-kb segment of the gene encompassing the catalytic domain with a phosphoglycerokinase promoter-driven neomycin resistant (neor) gene cassette. The transfected embryonic stem cell clones generated chimeric male mice, and germ line transmission of the inactivated F. IX gene was observed in their offsprings. Southern analysis confirmed the mutant genotype in hemizygous male and carrier female mice. F. IX transcripts were not detected in liver RNA isolated from hemizygous mice, and lower levels of F. IX mRNA were noted in carrier female mice when compared with those of normal litter mates. As expected, the mean F. IX coagulant titer of affected male mice was 2.8 U/dL (n = 10), while the mean F. IX titer of carrier female mice was 35 U/dL (n = 14), compared with 69 U/dL (n = 9) for the normal female mice and 92 U/dL (n = 22) for normal male and female litter mates. Further, the tail bleeding time of hemizygous mice was markedly prolonged (>3 hours) compared with those of normal and carrier female litter mates (15 to 20 minutes). Seven of 19 affected male mice died of exsanguination after tail snipping, and two affected mice died of umbilical cord bleeding. Currently, there are 10 affected mice surviving at 4 months of age. Aside from the factor IX defect, the carrier female and hemizygous male mice had no liver pathology by histologic examination, were fertile, and transmitted the F. IX gene mutation in the expected Mendelian frequency. Taken together, we have generated a F. IX knockout mouse for evaluation of novel gene therapy strategies for hemophilia B.