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

Trends in Hybrid Cultured Meat Manufacturing Technology to Improve Sensory Characteristics

The projected growth of global meat production over the next decade is attributed to rising income levels and population expansion. One potentially more pragmatic approach to mitigating the adverse externalities associated with meat production involves implementing alterations to the production process, such as transitioning to cultured meat, hybrid cultured meat, and meat alternatives. Cultured meat (CM) is derived from animal stem cells and undergoes a growth and division process that closely resembles the natural in vivo cellular development. CM is emerging as a widely embraced substitute for traditional protein sources, with the potential to alleviate the future strain on animal-derived meat production. To date, the primary emphasis of cultured meat research and production has predominantly been around the ecological advantages and ethical considerations pertaining to animal welfare. However, there exists substantial study potential in exploring consumer preferences with respect to the texture, color, cuts, and sustainable methodologies associated with cultured meat. The potential augmentation of cultured meat's acceptance could be facilitated through the advancement of a wider range of cuts to mimic real muscle fibers. This review examines the prospective commercial trends of hybrid cultured meat. Subsequently, the present state of research pertaining to the advancement of scaffolding, coloration, and muscle fiber development in hybrid cultured meat, encompassing plant-based alternatives designed to emulate authentic meat, has been deliberated. However, this discussion highlights the obstacles that have arisen in current procedures and proposes future research directions for the development of sustainable cultured meat and meat alternatives, such as plant-based meat production.

Sensorial and Nutritional Aspects of Cultured Meat in Comparison to Traditional Meat: Much to Be Inferred

Cultured meat aspires to be biologically equivalent to traditional meat. If cultured meat is to be consumed, sensorial (texture, color, flavor) and nutritional characteristics are of utmost importance. This paper compares cultured meat to traditional meat from a tissue engineering and meat technological point of view, focusing on several molecular, technological and sensorial attributes. We outline the challenges and future steps to be taken for cultured meat to mimic traditional meat as closely as possible.

Vascularization of tissue-engineered skeletal muscle constructs

Skeletal muscle tissue can be created in vitro by tissue engineering approaches, based on differentiation of muscle stem cells. Several approaches exist and generally result in three dimensional constructs composed of multinucleated myofibers to which we refer as myooids. Engineering methods date back to 3 decades ago and meanwhile a wide range of cell types and scaffold types have been evaluated. Nevertheless, in most approaches, myooids remain very small to allow for diffusion-mediated nutrient supply and waste product removal, typically less than 1 mm thick. One of the shortcomings of current in vitro skeletal muscle organoid development is the lack of a functional vascular structure, thus limiting the size of myooids. This is a challenge which is nowadays applicable to almost all organoid systems. Several approaches to obtain a vascular structure within myooids have been proposed. The purpose of this review is to give a concise overview of these approaches.

Coculture Method to Obtain Endothelial Networks Within Human Tissue-Engineered Skeletal Muscle

Skeletal muscle tissue engineering aims at creating functional skeletal muscle in vitro. Human muscle organoids can be used for potential applications in regenerative medicine, but also as an in vitro model for myogenesis or myopathology. However, the thickness of constructs is limited due to passive diffusion of nutrients and oxygen. Introduction of a vascular network in vitro may solve this limitation. Here, we describe tissue engineering of in vitro skeletal muscle consisting of human aligned myofibers with interspersed endothelial networks. To create bio-artificial muscle (BAM), human muscle progenitor cells are cocultured with human umbilical vein endothelial cells (HUVECs) in a fibrin hydrogel. The cell-gel mix is cast into silicone molds with end attachment sites and cultured in endothelial growth medium (EGM-2) for 1 week. The passive forces generated in the contracted hydrogel align the myogenic cells parallel to the long axis of the contracted gel such that they fuse into aligned multinucleated myofibers. This results in the formation of a 2 cm long and ~1.5 mm tick human BAM construct with endothelial networks.

Engineering of Human Skeletal Muscle With an Autologous Deposited Extracellular Matrix

Adult skeletal muscle progenitor cells can be embedded in an extracellular matrix (ECM) and tissue-engineered to form bio-artificial muscles (BAMs), composed of aligned post-mitotic myofibers. The ECM proteins which have been used most commonly are collagen type I and fibrin. Fibrin allows for in vitro vasculogenesis, however, high concentrations of fibrinolysis inhibitors are needed to inhibit degradation of the ECM and subsequent loss of BAM tissue structure. For in vivo implantation, fibrinolysis inhibition may prove difficult or even harmful to the host. Therefore, we adapted in vitro culture conditions to enhance the deposition of de novo synthesized collagen type I gradually replacing the degrading fibrin ECM. The in vitro viscoelastic properties of the fibrin BAMs and deposition of collagen were characterized. BAMs engineered with the addition of proline, hydroxyproline, and ascorbic acid in the tissue culture medium had a twofold increase in Young’s Modulus, a 2.5-fold decrease in maximum strain, and a 1.6-fold increase in collagen deposition. Lowering the fibrin content of the BAMs also increased Young’s Modulus, decreased maximum strain, and increased collagen deposition. Tissue engineering of BAMs with autologous ECM may allow for prolonged in vivo survival.

Human tissue-engineered skeletal muscle: a novel 3D in vitro model for drug disposition and toxicity after intramuscular injection

The development of laboratory-grown tissues, referred to as organoids, bio-artificial tissue or tissue-engineered constructs, is clearly expanding. We describe for the first time how engineered human muscles can be applied as a pre- or non-clinical model for intramuscular drug injection to further decrease and complement the use of in vivo animal studies. The human bio-artificial muscle (BAM) is formed in a seven day tissue engineering procedure during which human myoblasts fuse and differentiate to aligned myofibers in an extracellular matrix. The dimensions of the BAM constructs allow for injection and follow-up during several days after injection. A stereotactic setup allows controllable injection at multiple sites in the BAM. We injected several compounds; a dye, a hydrolysable compound, a reducible substrate and a wasp venom toxin. Afterwards, direct reflux, release and metabolism were assessed in the BAM constructs in comparison to 2D cell culture and isolated human muscle strips. Spectrophotometry and luminescence allowed to measure the release of the injected compounds and their metabolites over time. A release profile over 40 hours was observed in the BAM model in contrast to 2D cell culture, showing the capacity of the BAM model to function as a drug depot. We also determined compound toxicity on the BAMs by measuring creatine kinase release in the medium, which increased with increasing toxic insult. Taken together, we show that the BAM is an injectable human 3D cell culture model that can be used to measure release and metabolism of injected compounds in vitro.

Elderly Patient-Derived Endothelial Cells for Vascularization of Engineered Muscle

In vitro prevascularization of engineered tissue constructs promises to enhance their clinical applicability. We hypothesize that adult endothelial cells (ECs), isolated from limb veins of elderly patients, bear the vasculogenic properties required to form vascular networks in vitro that can later integrate with the host vasculature upon implantation. Here, we show that adult ECs formed vessel networks that were more developed and complex than those formed by human umbilical vein endothelial cells (HUVECs) seeded with various supporting cells on three-dimensional (3D) biodegradable polymer scaffolds. In parallel, secreted levels of key proangiogenic cytokines were significantly higher in adult EC-bearing scaffolds as compared to HUVEC scaffolds. As a proof of concept for applicability of this model, adult ECs were co-seeded with human myoblasts as well as supporting cells and successfully formed a branched network, which was surrounded by aligned human myotubes. The vascularized engineered muscle tissue implanted into a full-thickness defect in immunodeficient mice remained viable and anastomosed with the host vasculature within 9 days of implantation. Functional "chimeric" blood vessels and various types of anastomosis were observed. These findings provide strong evidence of the applicability of adult ECs in construction of clinically relevant autologous vascularized tissue.

Insight on stem cell preconditioning and instructive biomaterials to enhance cell adhesion, retention, and engraftment for tissue repair

Stem cells are a promising solution for the treatment of a variety of diseases. However, the limited survival and engraftment of transplanted cells due to a hostile ischemic environment is a bottleneck for effective utilization and commercialization. Within this environment, the majority of transplanted cells undergo apoptosis prior to participating in lineage differentiation and cellular integration. Therefore, in order to maximize the clinical utility of stem/progenitor cells, strategies must be employed to increase their adhesion, retention, and engraftment in vivo. Here, we reviewed key strategies that are being adopted to enhance the survival, retention, and engraftment of transplanted stem cells through the manipulation of both the stem cells and the surrounding environment. We describe how preconditioning of cells or cell manipulations strategies can enhance stem cell survival and engraftment after transplantation. We also discuss how biomaterials can enhance the function of stem cells for effective tissue regeneration. Biomaterials can incorporate or mimic extracellular function (ECM) function and enhance survival or differentiation of transplanted cells in vivo. Biomaterials can also promote angiogenesis, enhance engraftment and differentiation, and accelerate electromechanical integration of transplanted stem cells. Insight gained from this review may direct the development of future investigations and clinical trials.

Endothelial Network Formation Within Human Tissue-Engineered Skeletal Muscle

The size of in vitro engineered skeletal muscle tissue is limited due to the lack of a vascular network in vitro. In this article, we report tissue-engineered skeletal muscle consisting of human aligned myofibers with interspersed endothelial networks. We extend our bioartificial muscle (BAM) model by coculturing human muscle progenitor cells with human umbilical vein endothelial cells (HUVECs) in a fibrin extracellular matrix (ECM). First, the optimal medium conditions for coculturing myoblasts with HUVECs were determined in a fusion assay. Endothelial growth medium proved to be the best compromise for the coculture, without affecting the myoblast fusion index. Second, both cell types were cocultured in a BAM maintained under tension to stimulate myofiber alignment. We then tested different total cell numbers containing 50% HUVECs and found that BAMs with a total cell number of 2 × 10(6) resulted in well-aligned and densely packed myofibers while allowing for improved interspersed endothelial network formation. Third, we compared different myoblast-HUVEC ratios. Including higher numbers of myoblasts improved endothelial network formation at lower total cell density; however, improvement of network characteristics reached a plateau when 1 × 10(6) or more myoblasts were present. Finally, addition of Matrigel to the fibrin ECM did not enhance overall myofiber and endothelial network formation. Therefore, in our BAM model, we suggest the use of a fibrin extracellular matrix containing 2 × 10(6) cells of which 50-70% are muscle cells. Optimizing these coculture conditions allows for a physiologically more relevant muscle model and paves the way toward engineering of larger in vitro muscle constructs.

Mechanical cues in orofacial tissue engineering and regenerative medicine

Cleft lip and palate patients suffer from functional, aesthetical, and psychosocial problems due to suboptimal regeneration of skin, mucosa, and skeletal muscle after restorative cleft surgery. The field of tissue engineering and regenerative medicine (TE/RM) aims to restore the normal physiology of tissues and organs in conditions such as birth defects or after injury. A crucial factor in cell differentiation, tissue formation, and tissue function is mechanical strain. Regardless of this, mechanical cues are not yet widely used in TE/RM. The effects of mechanical stimulation on cells are not straight-forward in vitro as cellular responses may differ with cell type and loading regime, complicating the translation to a therapeutic protocol. We here give an overview of the different types of mechanical strain that act on cells and tissues and discuss the effects on muscle, and skin and mucosa. We conclude that presently, sufficient knowledge is lacking to reproducibly implement external mechanical loading in TE/RM approaches. Mechanical cues can be applied in TE/RM by fine-tuning the stiffness and architecture of the constructs to guide the differentiation of the seeded cells or the invading surrounding cells. This may already improve the treatment of orofacial clefts and other disorders affecting soft tissues.

Tissue clearing for confocal imaging of native and bio-artificial skeletal muscle

Novel clearing techniques have revolutionized three-dimensional confocal imaging of the brain without the need for physical tissue sectioning. We evaluated three clearing methods, ScaleA2, Clear(T2), and 3DISCO for visualizing native and tissue engineered muscle by confocal microscopy. We found that Clear(T2) treatment improved the depth of visualization of immunohistochemical staining slightly, but did not improve depth of visualization of endogenous green fluorescent protein (GFP). ScaleA2 preserved endogenous GFP signal better and permitted significantly deeper GFP imaging, but it was incompatible with tropomyosin immunohistochemical staining. 3DISCO treatment preserved both endogenous GFP and immunohistochemical staining, and permitted significantly deeper imaging. Clearing time for the 3DISCO procedure is short compared to ScaleA2 and Clear(T2). We suggest that 3DISCO is the preferable clearing method for native and tissue engineered skeletal muscle tissue.

Engineering muscle constructs for the creation of functional engineered musculoskeletal tissue

Volumetric muscle loss (VML) is a disabling condition in which current clinical procedures are suboptimal. The field of tissue engineering has many promising strategies for the creation of functional skeletal muscle in vitro. However, there are still two key limitations that prevent it from becoming a solution for treating VML. First, engineered muscle tissue must be biocompatible to facilitate muscle tissue regrowth without generating an immune response. Second, engineered muscle constructs must be scaled up to facilitate replacement of clinically relevant volumes of tissue (centimeters in diameter). There are currently no tissue engineering strategies to produce tissue constructs that are both biocompatible and large enough to facilitate clinical repair. However, recent advances in tissue engineering using synthetic scaffolds, native scaffolds, or scaffold-free approaches may lead to a solution for repair of VML injuries.

Minimally invasive approach to the repair of injured skeletal muscle with a shape-memory scaffold

Repair of injured skeletal muscle by cell therapies has been limited by poor survival of injected cells. Use of a carrier scaffold delivering cells locally, may enhance in vivo cell survival, and promote skeletal muscle regeneration. Biomaterial scaffolds are often implanted into muscle tissue through invasive surgeries, which can result in trauma that delays healing. Minimally invasive approaches to scaffold implantation are thought to minimize these adverse effects. This hypothesis was addressed in the context of a severe mouse skeletal muscle injury model. A degradable, shape-memory alginate scaffold that was highly porous and compressible was delivered by minimally invasive surgical techniques to injured tibialis anterior muscle. The scaffold controlled was quickly rehydrated in situ with autologous myoblasts and growth factors (either insulin-like growth factor-1 (IGF-1) alone or IGF-1 with vascular endothelial growth factor (VEGF)). The implanted scaffolds delivering myoblasts and IGF-1 significantly reduced scar formation, enhanced cell engraftment, and improved muscle contractile function. The addition of VEGF to the scaffold further improved functional recovery likely through increased angiogenesis. Thus, the delivery of myoblasts and dual local release of VEGF and IGF-1 from degradable scaffolds implanted through a minimally invasive procedure effectively promoted the functional regeneration of injured skeletal muscle.

Biomimetic engineered muscle with capacity for vascular integration and functional maturation in vivo

Tissue-engineered skeletal muscle can serve as a physiological model of natural muscle and a potential therapeutic vehicle for rapid repair of severe muscle loss and injury. Here, we describe a platform for engineering and testing highly functional biomimetic muscle tissues with a resident satellite cell niche and capacity for robust myogenesis and self-regeneration in vitro. Using a mouse dorsal window implantation model and transduction with fluorescent intracellular calcium indicator, GCaMP3, we nondestructively monitored, in real time, vascular integration and the functional state of engineered muscle in vivo. During a 2-wk period, implanted engineered muscle exhibited a steady ingrowth of blood-perfused microvasculature along with an increase in amplitude of calcium transients and force of contraction. We also demonstrated superior structural organization, vascularization, and contractile function of fully differentiated vs. undifferentiated engineered muscle implants. The described in vitro and in vivo models of biomimetic engineered muscle represent enabling technology for novel studies of skeletal muscle function and regeneration.

Gene therapy for hemophilia

Hemophilia A and B are X-linked monogenic disorders resulting from deficiencies of factor VIII and FIX, respectively. Purified clotting factor concentrates are currently intravenously administered to treat hemophilia, but this treatment is non-curative. Therefore, gene-based therapies for hemophilia have been developed to achieve sustained high levels of clotting factor expression to correct the clinical phenotype. Over the past two decades, different types of viral and non-viral gene delivery systems have been explored for hemophilia gene therapy research with a variety of target cells, particularly hepatocytes, hematopoietic stem cells, skeletal muscle cells, and endothelial cells. Lentiviral and adeno-associated virus (AAV)-based vectors are among the most promising vectors for hemophilia gene therapy. In preclinical hemophilia A and B animal models, the bleeding phenotype was corrected with these vectors. Some of these promising preclinical results prompted clinical translation to patients suffering from a severe hemophilic phenotype. These patients receiving gene therapy with AAV vectors showed long-term expression of therapeutic FIX levels, which is a major step forwards in this field. Nevertheless, the levels were insufficient to prevent trauma or injury-induced bleeding episodes. Another challenge that remains is the possible immune destruction of gene-modified cells by effector T cells, which are directed against the AAV vector antigens. It is therefore important to continuously improve the current gene therapy approaches to ultimately establish a real cure for hemophilia.

Induced formation and maturation of acetylcholine receptor clusters in a defined 3D bio-artificial muscle

Dysfunction of the neuromuscular junction is involved in a wide range of muscular diseases. The development of neuromuscular junction through which skeletal muscle is innervated requires the functional modulation of acetylcholine receptor (AchR) clustering on myofibers. However, studies on AchR clustering in vitro are mostly done on monolayer muscle cell culture, which lacks a three-dimensional (3D) structure, a prominent limitation of the two-dimensional (2D) system. To enable a better understanding on the structure-function correlation underlying skeletal muscle innervation, a muscle system with a well-defined geometry mimicking the in vivo muscular setting is needed. Here, we report a 3D bio-artificial muscle (BAM) bioengineered from green fluorescent protein-transduced C3H murine myoblasts as a novel in vitro tissue-based model for muscle innervation studies. Our cell biological and molecular analysis showed that this BAM is structurally similar to in vivo muscle tissue and can reach the perinatal differentiation stage, higher than does 2D culture. Effective clustering and morphological maturation of AchRs on BAMs induced by agrin and laminin indicate the functional activity and plasticity of this BAM system toward innervation. Taken together, our results show that the BAM provides a favorable 3D environment that at least partially recapitulates real physiological skeletal muscle with regard to innervation. With a convenience of fabrication and manipulation, this 3D in vitro system offers a novel model for studying mechanisms underlying skeletal muscle innervation and testing therapeutic strategies for relevant nervous and muscular diseases.

Myogenic differentiation of mesenchymal stem cells co-cultured with primary myoblasts

TE (tissue engineering) of skeletal muscle is a promising method to reconstruct loss of muscle tissue. This study evaluates MSCs (mesenchymal stem cells) as new cell source for this application. As a new approach to differentiate the MSCs towards the myogenic lineage, co-cultivation with primary myoblasts has been developed and the myogenic potential of GFP (green fluorescent protein)-transduced rat MSC co-cultured with primary rat myoblasts was assessed by ICC (immunocytochemistry). Myogenic potential of MSC was analysed by ICC, FACS and qPCR (quantitative PCR). MSC-myoblast fusion phenomena leading to hybrid myotubes were evaluated using a novel method to evaluate myotube fusion ratios based on phase contrast and fluorescence microscopy. Furthermore, MSC constitutively expressed the myogenic markers MEF2 (myogenic enhancer factor 2) and α-sarcomeric actin, and MEF2 expression was up-regulated upon co-cultivation with primary myoblasts and the addition of myogenic medium supplements. Significantly higher numbers of MSC nuclei were involved in myotube formations when bFGF (basic fibroblast growth factor) and dexamethasone were added to co-cultures. In summary, we have determined optimal co-culture conditions for MSC myogenic differentiation up to myotube formations as a promising step towards applicability of MSC as a cell source for skeletal muscle TE as well as other muscle cell-based therapies.

Gene therapy strategies for hemophilia: benefits versus risks

Hemophilia is an inherited bleeding disorder caused by a deficiency of functional clotting factors VIII or IX in the blood plasma. The drawbacks of the classical protein substitution therapy fueled interest in alternative treatments by gene therapy. Hemophilia has been recognized as an ideal target disease for gene therapy because a relatively modest increase in clotting factor levels can result in a significant therapeutic benefit. Consequently, introducing a functional FVIII or FIX gene copy into the appropriate target cells could ultimately provide a cure for hemophilic patients. Several cell types have been explored for hemophilia gene therapy, including hepatocytes, muscle, endothelial and hematopoietic cells. Both nonviral and viral vectors have been considered for the development of hemophilia gene therapy, including transposons, γ-retroviral, lentiviral, adenoviral and adeno-associated viral vectors. Several of these strategies have resulted in stable correction of the bleeding diathesis in hemophilia A and B murine as well as canine models, paving the way towards clinical trials. Although clotting factor expression has been detected in hemophilic patients treated by gene therapy, the challenge now lies in obtaining prolonged therapeutic FVIII or FIX levels in these patients. This review highlights the benefits and potential risks of the different gene therapy strategies for hemophilia that have been developed.

Novel hyperactive transposons for genetic modification of induced pluripotent and adult stem cells: a nonviral paradigm for coaxed differentiation

Adult stem cells and induced pluripotent stem cells (iPS) hold great promise for regenerative medicine. The development of robust nonviral approaches for stem cell gene transfer would facilitate functional studies and potential clinical applications. We have previously generated hyperactive transposases derived from Sleeping Beauty, using an in vitro molecular evolution and selection paradigm. We now demonstrate that these hyperactive transposases resulted in superior gene transfer efficiencies and expression in mesenchymal and muscle stem/progenitor cells, consistent with higher expression levels of therapeutically relevant proteins including coagulation factor IX. Their differentiation potential and karyotype was not affected. Moreover, stable transposition could also be achieved in iPS, which retained their ability to differentiate along neuronal, cardiac, and hepatic lineages without causing cytogenetic abnormalities. Most importantly, transposon-mediated delivery of the myogenic PAX3 transcription factor into iPS coaxed their differentiation into MYOD(+) myogenic progenitors and multinucleated myofibers, suggesting that PAX3 may serve as a myogenic "molecular switch" in iPS. Hence, this hyperactive transposon system represents an attractive nonviral gene transfer platform with broad implications for regenerative medicine, cell and gene therapy.

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

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

Erythroid-specific human factor IX delivery from in vivo selected hematopoietic stem cells following nonmyeloablative conditioning in hemophilia B mice

We have developed a lentiviral vector system for human factor IX (hFIX) gene transfer in hematopoietic stem cells (HSCs) that provides erythroid cell-derived systemic protein delivery following nonmyeloablative conditioning and in vivo methylguanine methyltransferase (MGMT) drug selection. After bone marrow transplantation under moderate Busulfan conditioning, the initial hFIX expression in the chimeras was minimally detectable. However, the hFIX levels rose sharply following in vivo MGMT-drug selection and eventually reached a level that is considered curative in hemophilia B therapy (>500 ng/ml). The rise of hFIX levels was proportional to the increase in vector copy (VC) number in peripheral blood cells. High levels of hFIX expression were maintained in serially engrafted mice chimeras for 18 months. Importantly, high-level hFIX expression by erythroid cells did not result in anemia or adversely affect red blood cell counts. The prospect of combining reduced intensity conditioning, a presumably lowered risk of insertional mutagenesis due to low VC number requirement and erythroid-restricted transgene expression, as well as long-term protein expression at high level, strongly supports the potential applicability of adult stem cell-based gene therapy in nonlethal blood or metabolic disorders, as demonstrated here for hemophilia.

Cell delivery mechanisms for tissue repair

Many cell populations, derived from both adult tissues and embryonic stem cells, show promise for the treatment of a variety of diseases. Although the major effort in stem cell therapies in the past has been identifying potentially therapeutic cells, it is now clear that developing systems to deliver these cells and promote their efficient engraftment will provide an equally challenging task. More sophisticated pretransplantation manipulations and material carriers may dramatically improve the survival, engraftment, and fate control of transplanted stem cells and their ultimate clinical utility.

Growth, differentiation, transplantation and survival of human skeletal myofibers on biodegradable scaffolds

Skeletal muscle transplantation strategies for muscle repair or gene therapy involve either the injection of proliferating myoblasts followed by fusion with host myofibers or implantation of ex vivo differentiated myofibers; however, both implant procedures are associated with significant cell loss. Biodegradable porous, gas-foamed poly-lactide-co-glycolide (PLG) scaffolds have desirable characteristics for cell transfer and were used to study attachment, growth, differentiation and survival of human myogenic cells. Primary human myoblasts suspended in clinical grade extracellular matrixes (ECMs) and adhered to PLG scaffolds differentiated in vitro into high-density tropomyosin positive myofibers. An immunodeficient non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mouse implant model was used to study the transfer and in vivo survival of differentiated human myofibers on these scaffolds. Scaffold rigidity allowed the myofibers to be maintained under tension in vitro and following subcutaneous transplantation in vivo. Following implantation, myofiber density on the PLG scaffolds decreased linearly by 78% over a 4-week period. ECM composed of either Tisseel fibrin or Zyderm collagen type I did not significantly affect in vivo cell viability over the 4-week period. Varying PLG scaffold microsphere content (10-100%) also had little effect on cell survival in vivo. In contrast, when the residual NK cell population in the immunodeficient NOD/SCID mouse model was depleted with anti-asialo GM1 (ASGM1) antiserum, in vivo cell survival significantly increased from 22% to 34% after 4 weeks. With further improvements in cell survival, PLG scaffolds may prove useful for the implantation of primary human myofibers in future clinical applications.

Cell-based drug delivery

Drug delivery has been greatly improved over the years by means of chemical and physical agents that increase bioavailability, improve pharmacokinetic and reduce toxicities. At the same time, cell based delivery systems have also been developed. These possesses a number of advantages including prolonged delivery times, targeting of drugs to specialized cell compartments and biocompatibility. Here we'll focus on erythrocyte-based drug delivery. These systems are especially efficient in releasing drugs in circulations for weeks, have a large capacity, can be easily processed and could accommodate traditional and biologic drugs. These carriers have also been used for delivering antigens and/or contrasting agents. Carrier erythrocytes have been evaluated in thousands of drug administration in humans proving safety and efficacy of the treatments. Erythrocyte-based delivery of new and conventional drugs is thus experiencing increasing interests in drug delivery and in managing complex pathologies especially when side effects could become serious issues.

Gene therapy, bioengineered clotting factors and novel technologies for hemophilia treatment

The World Federation of Hemophilia estimates that of the 400,000 individuals worldwide with hemophilia, 300,000 receive either no, or very sporadic, treatment. Thus, considerable innovation will be required to provide cost-effective therapies/cures for all affected individuals. The high cost of prophylactic regimens hampers their widespread use, which further justifies the search for novel cost-effective therapies and ultimately a cure. Five gene transfer phase I clinical trials have been conducted using either direct in vivo gene delivery with viral vectors or ex vivo plasmid transfections and reimplantation of gene-engineered cells. Although there was evidence of gene transfer and therapeutic effects in some of these trials, stable expression of therapeutic factor VIII or FIX levels has not yet been obtained. Further improvements of the vectors and a better understanding of the immune consequences of gene transfer is warranted, as new trials are being initiated. Bioengineered clotting factors with increased stability and/or activity are being validated further in preclinical studies. Novel clotting factor formulations based on PEGylated liposomes with prolonged activities are being tested in the clinic, and are yielding encouraging results.