Hydrogels to modulate lentivirus delivery in vivo from microporous tissue engineering scaffolds

IL-10 lentivirus-laden hydrogel tubes increase spinal progenitor survival and neuronal differentiation after spinal cord injury

A complex cellular cascade characterizes the pathophysiological response following spinal cord injury (SCI) limiting regeneration. Biomaterial and stem cell combination therapies together have shown synergistic effects, compared to the independent benefits of each intervention, and represent a promising approach towards regaining function after injury. In this study, we combine our polyethylene glycol (PEG) cell delivery platform with lentiviral-mediated overexpression of the anti-inflammatory cytokine interleukin (IL)-10 to improve mouse embryonic Day 14 (E14) spinal progenitor transplant survival. Immediately following injury in a mouse SCI hemisection model, five PEG tubes were implanted followed by direct injection into the tubes of lentivirus encoding for IL-10. Two weeks after tube implantation, mouse E14 spinal progenitors were injected directly into the integrated tubes, which served as a soft substrate for cell transplantation. Together, the tubes with the IL-10 encoding lentivirus improved E14 spinal progenitor survival, assessed at 2 weeks posttransplantation (4 weeks postinjury). On average, 8.1% of E14 spinal progenitors survived in mice receiving IL-10 lentivirus-laden tubes compared with 0.7% in mice receiving transplants without tubes, an 11.5-fold difference. Surviving E14 spinal progenitors gave rise to neurons when injected into tubes. Axon elongation and remyelination were observed, in addition to a significant increase in functional recovery in mice receiving IL-10 lentivirus-laden tubes with E14 spinal progenitor delivery compared to the injury only control by 4 weeks postinjury. All other conditions did not exhibit increased stepping until 8 or 12 weeks postinjury. This system affords increased control over the transplantation microenvironment, offering the potential to improve stem cell-mediated tissue regeneration.

Efficient in situ gene delivery via PEG diacrylate matrices

For diseases related to genetic disorders or cancer, many cellular therapies rely on the ex vivo modification of cells for attaining a desired therapeutic effect. The efficacy of such therapies involving the genetic modification of cells relies on the extent of gene expression and subsequent persistence of modified cells when infused into the patient's body. In situ gene delivery implies the manipulation of cells in their in vivo niche such that the effectiveness can be improved by minimizing post manipulation effects like cell death, lack of persistence, etc. Furthermore, material-based in situ localized gene delivery can reduce the undesired side effects caused by systemic modifications. Here, we have used polyethylene (glycol) diacrylate (PEGDA) based cryogels to genetically modify cells in vivo with a focus on immunotherapy. PEGDA cryogels were either blended with gelatin methacrylate (GELMA) or surface modified with poly-l-lysine (PLL) in order to improve cell adhesion and/or retain viruses for localized gene delivery. On using the lentiviruses encoding gene for green fluorescent protein (GFP) in in vitro experiments, we found higher transduction efficiency in HEK 293FT cells via PEGDA modified with poly-l-lysine (PEGDA-PLL) and PEGDA-GELMA cryogels compared to PEGDA cryogels. In vitro release experiments showed improved retention of GFP lentiviruses in PEGDA-PLL cryogels, which were then employed for in vivo gene delivery and were demonstrated to perform better than the corresponding bolus delivery of lentiviruses through an injection. Both physical and biological characterization studies of these cryogels show that this material platform can be used for gene delivery as well as other tissue engineering applications.

Biofunctionalized self-assembly of peptide amphiphile induces the differentiation of bone marrow mesenchymal stem cells into neural cells

Bone marrow mesenchymal stem cells (BMSCs) are multipotential differentiation cells which can differentiate into different cell types such as osteoblasts, chondrocytes, adipocytes, cardiomyocytes, hepatocytes, endothelial cells, and neuronal cells. Such multipotential differentiation makes them attractive for stem cell-based therapy aimed at treating previously incurable disorders. In the present work, we encapsulated BMSCs into a hydrogel with a three-dimensional (3D) network of nanofibers, formed from self-assembling of peptide amphiphile. The self-assembling of peptide amphiphile into hydrogel was triggered by mixing cell suspensions with dilute aqueous solutions of amphipathic peptide. Moreover, this hydrogel was designed to present cells the neurite-promoting laminin epitope IKVAV at nearly van der Waals density, which induced the successful differentiation of BMSCs into neural cells.

Biomaterial-Guided Gene Delivery for Musculoskeletal Tissue Repair

Gene therapy is a promising strategy for musculoskeletal tissue repair and regeneration where local and sustained expression of proteins and/or therapeutic nucleic acids can be achieved. However, the musculoskeletal tissues present unique engineering and biological challenges as recipients of genetic vectors. Targeting specific cell populations, regulating expression in vivo, and overcoming the harsh environment of damaged tissue accompany the general concerns of safety and efficacy common to all applications of gene therapy. In this review, we will first summarize these challenges and then discuss how biomaterial carriers for genetic vectors can address these issues. Second, we will review how limitations specific to given vectors further motivate the utility of biomaterial carriers. Finally, we will discuss how these concepts have been combined with tissue engineering strategies and approaches to improve the delivery of these vectors for musculoskeletal tissue regeneration.

Injectable Hydrogels for Spinal Cord Repair: A Focus on Swelling and Intraspinal Pressure

Spinal cord injury (SCI) is a devastating condition that leaves patients with limited motor and sensory function at and below the injury site, with little to no hope of a meaningful recovery. Because of their ability to mimic multiple features of central nervous system (CNS) tissues, injectable hydrogels are being developed that can participate as therapeutic agents in reducing secondary injury and in the regeneration of spinal cord tissue. Injectable biomaterials can provide a supportive substrate for tissue regeneration, deliver therapeutic factors, and regulate local tissue physiology. Recent reports of increasing intraspinal pressure after SCI suggest that this physiological change can contribute to injury expansion, also known as secondary injury. Hydrogels contain high water content similar to native tissue, and many hydrogels absorb water and swell after formation. In the case of injectable hydrogels for the spinal cord, this process often occurs in or around the spinal cord tissue, and thus may affect intraspinal pressure. In the future, predictable swelling properties of hydrogels may be leveraged to control intraspinal pressure after injury. Here, we review the physiology of SCI, with special attention to the current clinical and experimental literature, underscoring the importance of controlling intraspinal pressure after SCI. We then discuss how hydrogel fabrication, injection, and swelling can impact intraspinal pressure in the context of developing injectable biomaterials for SCI treatment.

Gene delivery strategies to promote spinal cord repair

Gene therapies hold great promise for the treatment of many neurodegenerative disorders and traumatic injuries in the central nervous system. However, development of effective methods to deliver such therapies in a controlled manner to the spinal cord is a necessity for their translation to the clinic. Although essential progress has been made to improve efficiency of transgene delivery and reduce the immunogenicity of genetic vectors, there is still much work to be done to achieve clinical strategies capable of reversing neurodegeneration and mediating tissue regeneration. In particular, strategies to achieve localized, robust expression of therapeutic transgenes by target cell types, at controlled levels over defined time periods, will be necessary to fully regenerate functional spinal cord tissues. This review summarizes the progress over the last decade toward the development of effective gene therapies in the spinal cord, including identification of appropriate target genes, improvements to design of genetic vectors, advances in delivery methods, and strategies for delivery of multiple transgenes with synergistic actions. The potential of biomaterials to mediate gene delivery while simultaneously providing inductive scaffolding to facilitate tissue regeneration is also discussed.

Modulation of leukocyte infiltration and phenotype in microporous tissue engineering scaffolds via vector induced IL-10 expression

Biomaterial scaffolds are central to many tissue engineering strategies as they create a space for tissue growth and provide a support for cell adhesion and migration. However, biomaterial implantation results in unavoidable injury resulting in an inflammatory response, which can impair integration with the host and tissue regeneration. Toward the goal of reducing inflammation, we investigated the hypothesis that a lentiviral gene therapy-based approach to localized and sustained IL-10 expression at a scaffold could modulate the number, relative proportions, and cytokine production of infiltrating leukocyte populations. Flow cytometry was used to quantify infiltration of six leukocyte populations for 21 days following implantation of PLG scaffolds into intraperitoneal fat. Leukocytes with innate immune functions (i.e., macrophages, dendritic cells, neutrophils) were most prevalent at early time points, while T lymphocytes became prevalent by day 14. Reporter gene delivery indicated that transgene expression persisted at the scaffold for up to 28 days and macrophages were the most common leukocyte transduced, while transduced dendritic cells expressed the greatest levels of transgene. IL-10 delivery decreased leukocyte infiltration by 50% relative to controls, increased macrophage IL-10 expression, and decreased macrophage, dendritic cell, and CD4 T cell IFN-γ expression. Thus, IL-10 gene delivery significantly decreased inflammation following scaffold implant into the intraperitoneal fat, in part by modulating cytokine expression of infiltrating leukocytes.

Enhanced adenovirus transduction of hMSCs using 3D hydrogel cell carriers

Hydrogels are increasingly being investigated as a means to implant cells for tissue engineering. One way to further enhance the repair response would be to combine the hydrogel cell carrier with gene transfer. Gene therapy, using adenoviral vectors, is an effective way to provide transient delivery of bioactive factors. However, current protocols require further optimization, especially if they are to be transferred into the clinic. This study opted to compare the efficiency of protocols for standard two-dimensional (2D) versus three-dimensional (3D), adenoviral-mediated, transduction of human mesenchymal stem cells. Two different multiplicities of infection were tested. After encapsulation in fibrin, alginate or agarose, cells were cultured for 28 days. Transduction in 3D showed a much higher efficiency, compared to standard 2D transduction protocols. In 3D, the amount of transgene produced was significantly higher, for every condition investigated. Furthermore, transduction in 3D does not require a cell culture step and can be conducted within the operating theatre. In conclusion, it was demonstrated that 3D transduction, using adenoviral vectors, is superior to standard transduction protocols in 2D. It therefore, might help increasing its administration in tissue engineering and clinical applications.

Polysaccharide-modified scaffolds for controlled lentivirus delivery in vitro and after spinal cord injury

Gene delivering biomaterials have increasingly been employed to modulate the cellular microenvironment to promote tissue regeneration, yet low transduction efficiency has been a persistent challenge for in vivo applications. In this report, we investigated the surface modification of poly(lactide-co-glycolide) (PLG) scaffolds with polysaccharides, which have been implicated in binding lentivirus but have not been used for delivery. Chitosan was directly conjugated onto PLG scaffolds, whereas heparin and hyaluronan were indirectly conjugated onto PLG scaffolds with multi-amine crosslinkers. The addition of chitosan and heparin onto PLG promoted the association of lentivirus to these scaffolds and enhanced their transduction efficiency in vitro relative to hyaluronan-conjugated and control scaffolds that had limited lentivirus association and transduction. Transduction efficiency in vitro was increased partly due to an enhanced retention of virus on the scaffold as well as an extended half-life of viral activity. Transduction efficiency was also evaluated in vivo using porous, multiple channel PLG bridges that delivered lentivirus to the injured mouse spinal cord. Transgene expression persisted for weeks after implantation, and was able to enhance axon growth and myelination. These studies support gene-delivering PLG scaffolds for in vivo regenerative medicine applications.

A PLG/HAp composite scaffold for lentivirus delivery

Gene delivery from tissue engineering scaffolds provides the opportunity to control the microenvironment by inducing expression of regenerative factors. Hydroxyapatite (HAp) nanoparticles can bind lentivirus, and we investigated the incorporation of HAp into poly(lactide-co-glycolide) (PLG) scaffolds in order to retain lentivirus added to the scaffold. PLG/HAp scaffolds loaded with lentivirus enhanced transgene expression over 10-fold in vitro relative to scaffolds without HAp. Following in vivo implantation, PLG/HAp scaffolds promoted transgene expression for more than 100 days, with the level and duration enhanced relative to control scaffolds with lentivirus/HAp complexes added to PLG scaffolds. The extent of HAp incorporated into the scaffold influenced transgene expression, in part through its impact on porous architecture. Expression in vivo was localized to PLG/HAp scaffolds, with macrophages the primary cell type transduced at day 3, yet transduction of neutrophils and dendritic cells was also observed. At day 21 in PLG/HAp scaffolds, non-immune cells were transduced to a greater extent than immune cells, a trend that was opposite results from PLG scaffolds. Thus, in addition to retaining the virus, PLG/HAp influenced cell infiltration and preferentially transduced non-immune cells.

Hydrogels for lentiviral gene delivery

INTRODUCTION

Gene delivery from hydrogel biomaterials provides a fundamental tool for a variety of clinical applications including regenerative medicine, gene therapy for inherited disorders and drug delivery. The high water content and mild gelation conditions of hydrogels support their use for gene delivery by preserving activity of lentiviral vectors and acting to shield vectors from any host immune response.

AREAS COVERED

Strategies to control lentiviral entrapment within and retention/release from hydrogels are reviewed. The authors discuss the ability of hydrogel design parameters to control the transgene expression profile and the capacity of hydrogels to protect vectors from (and even modulate) the host immune response.

EXPERT OPINION

Delivery of genetic vectors from scaffolds provides a unique opportunity to capitalize on the potential synergy between the biomaterial design for cell processes and gene delivery. Hydrogel properties can be tuned to directly control the events that determine the tissue response to controlled gene delivery, which include the extent of cell infiltration, preservation of vector activity and vector retention. While some design parameters have been identified, numerous opportunities for investigation are available in order to develop a complete model relating the biomaterial properties and host response to gene delivery.

Sustained, localized transgene expression mediated from lentivirus-loaded biodegradable polyester elastomers

The study of biomaterials for gene delivery in tissue engineering and regenerative medicine is a growing area, necessitating the investigation of new biomaterials and gene delivery vectors. Poly(1,8-octanediol citrate) (POC) and poly(glycerol-sebacate) (PGS) are biodegradable, biocompatible elastomers that have tunable mechanical properties, surface characteristics, and degradation rate. The objective of this work was to investigate whether POC and PGS would support the immobilization and release of lentivirus to allow sustained and localized transgene expression. Porous biomaterials were prepared using salt as a porogen, and in vitro and in vivo transgene expression from immobilized and released lentiviruses were assessed. Cells seeded onto biomaterials loaded with lentiviruses yielded titer-dependent transgene expression in vitro. Lentivirus activity on both biomaterials was maintained for at least 5 days. When implanted subcutaneously in rats, POC and PGS with immobilized lentivirus exhibited sustained and localized transgene expression for at least 5 weeks. This research demonstrates that lentivirus immobilization on POC and PGS is feasible and potentially useful for a variety of tissue engineering and regenerative medicine applications.

Hydrogel macroporosity and the prolongation of transgene expression and the enhancement of angiogenesis

The utility of hydrogels for regenerative medicine can be improved through localized gene delivery to enhance their bioactivity. However, current systems typically lead to low-level transgene expression located in host tissue surrounding the implant. Herein, we investigated the inclusion of macropores into hydrogels to facilitate cell ingrowth and enhance gene delivery within the macropores in vivo. Macropores were created within PEG hydrogels by gelation around gelatin microspheres, with gelatin subsequently dissolved by incubation at 37 °C. The macropores were interconnected, as evidenced by homogeneous cell seeding in vitro and complete cell infiltration in vivo. Lentivirus loaded within hydrogels following gelation retained its activity relative to the unencapsulated control virus. In vivo, macroporous PEG demonstrated sustained, elevated levels of transgene expression for 6 weeks, while hydrogels without macropores had transient expression. Transduced cells were located throughout the macroporous structure, while non-macroporous PEG hydrogels had transduction only in the adjacent host tissue. Delivery of lentivirus encoding for VEGF increased vascularization relative to the control, with vessels throughout the macropores of the hydrogel. The inclusion of macropores within the hydrogel to enhance cell infiltration enhances transduction and influences tissue development, which has implications for multiple regenerative medicine applications.

Extrahepatic islet transplantation with microporous polymer scaffolds in syngeneic mouse and allogeneic porcine models

Intraportal transplantation of islets has successfully treated select patients with type 1 diabetes. However, intravascular infusion and the intrahepatic site contribute to significant early and late islet loss, yet a clinical alternative has remained elusive. We investigated non-encapsulating, porous, biodegradable polymer scaffolds as a vehicle for islet transplantation into extrahepatic sites, using syngeneic mouse and allogeneic porcine models. Scaffold architecture was modified to enhance cell infiltration leading to revascularization of the islets with minimal inflammatory response. In the diabetic mouse model, 125 islets seeded on scaffolds implanted into the epididymal fat pad restored normoglycemia within an average of 1.95 days and transplantation of only 75 islets required 12.1 days. Increasing the pore size to increase islet-islet interactions did not significantly impact islet function. The porcine model was used to investigate early islet engraftment. Increasing the islet seeding density led to a greater mass of engrafted islets, though the efficiency of islet survival decreased. Transplantation into the porcine omentum provided greater islet engraftment than the gastric submucosa. These results demonstrate scaffolds support murine islet transplantation with high efficiency, and feasibility studies in large animals support continued pre-clinical studies with scaffolds as a platform to control the transplant microenvironment.