3-D Scaffold Platform for Optimized Non-viral Transfection of Multipotent Stem Cells

Mineral coated microparticles doped with fluoride and complexed with mRNA prolong transfection in fracture healing

Introduction: Impaired fracture healing, specifically non-union, has been found to occur up to 14% in tibial shaft fractures. The current standard of care to treat non-union often requires additional surgeries which can result in long recovery times. Injectable-based therapies to accelerate fracture healing have the potential to mitigate the need for additional surgeries. Gene therapies have recently undergone significant advancements due to developments in nanotechnology, which improve mRNA stability while reducing immunogenicity. Methods: In this study, we tested the efficacy of mineral coated microparticles (MCM) and fluoride-doped MCM (FMCM) to effectively deliver firefly luciferase (FLuc) mRNA lipoplexes (LPX) to the fracture site. Here, adult mice underwent a tibia fracture and stabilization method and all treatments were locally injected into the fracture. Level of osteogenesis and amount of bone formation were assessed using gene expression and histomorphometry respectively. Localized and systemic inflammation were measured through gene expression, histopathology scoring and measuring C-reactive protein (CRP) in the serum. Lastly, daily IVIS images were taken to track and measure transfection over time. Results: MCM-LPX-FLuc and FMCM-LPX-FLuc were not found to cause any cytotoxic effects when tested in vitro. When measuring the osteogenic potential of each mineral composition, FMCM-LPX-FLuc trended higher in osteogenic markers through qRT-PCR than the other groups tested in a murine fracture and stabilization model. Despite FMCM-LPX-FLuc showing slightly elevated il-1β and il-4 levels in the fracture callus, inflammation scoring of the fracture callus did not result in any differences. Additionally, an acute systemic inflammatory response was not observed in any of the samples tested. The concentration of MCM-LPX-FLuc and FMCM-LPX-FLuc that was used in the murine fracture model did not stimulate bone when analyzed through stereological principles. Transfection efficacy and kinetics of delivery platforms revealed that FMCM-LPX-FLuc prolongs the luciferase signal both in vitro and in vivo. Discussion: These data together reveal that FMCM-LPX-FLuc could serve as a promising mRNA delivery platform for fracture healing applications.

KERS-Inspired Nanostructured Mineral Coatings Boost IFN-γ mRNA Therapeutic Index for Antitumor Immunotherapy

Tumor-associated macrophage (TAM) reprogramming is a promising therapeutic approach for cancer immunotherapy; however, its efficacy remains modest due to the low bioactivity of the recombinant cytokines used for TAM reprogramming. mRNA therapeutics are capable of generating fully functional proteins for various therapeutic purposes but accused for its poor sustainability. Inspired by kinetic energy recovery systems (KERS) in hybrid vehicles, a cytokine efficacy recovery system (CERS) is designed to substantially augment the therapeutic index of mRNA-based tumor immunotherapy via a "capture and stabilize" mechanism exerted by a nanostructured mineral coating carrying therapeutic cytokine mRNA. CERS remarkably recycles nearly 40% expressed cytokines by capturing them onto the mineral coating to extend its therapeutic timeframe, further polarizing the macrophages to strengthen their tumoricidal activity and activate adaptive immunity against tumors. Notably, interferon-γ (IFN-γ) produced by CERS exhibits ≈42-fold higher biological activity than recombinant IFN-γ, remarkably decreasing the required IFN-γ dosage for TAM reprogramming. In tumor-bearing mice, IFN-γ cmRNA@CERS effectively polarizes TAMs to inhibit osteosarcoma progression. When combined with the PD-L1 monoclonal antibody, IFN-γ cmRNA@CERS significantly boosts antitumor immune responses, and substantially prevents malignant lung metastases. Thus, CERS-mediated mRNA delivery represents a promising strategy to boost antitumor immunity for tumor treatment.

Materiomically Designed Polymeric Vehicles for Nucleic Acids: Quo Vadis?

Despite rapid advances in molecular biology, particularly in site-specific genome editing technologies, such as CRISPR/Cas9 and base editing, financial and logistical challenges hinder a broad population from accessing and benefiting from gene therapy. To improve the affordability and scalability of gene therapy, we need to deploy chemically defined, economical, and scalable materials, such as synthetic polymers. For polymers to deliver nucleic acids efficaciously to targeted cells, they must optimally combine design attributes, such as architecture, length, composition, spatial distribution of monomers, basicity, hydrophilic-hydrophobic phase balance, or protonation degree. Designing polymeric vectors for specific nucleic acid payloads is a multivariate optimization problem wherein even minuscule deviations from the optimum are poorly tolerated. To explore the multivariate polymer design space rapidly, efficiently, and fruitfully, we must integrate parallelized polymer synthesis, high-throughput biological screening, and statistical modeling. Although materiomics approaches promise to streamline polymeric vector development, several methodological ambiguities must be resolved. For instance, establishing a flexible polymer ontology that accommodates recent synthetic advances, enforcing uniform polymer characterization and data reporting standards, and implementing multiplexed in vitro and in vivo screening studies require considerable planning, coordination, and effort. This contribution will acquaint readers with the challenges associated with materiomics approaches to polymeric gene delivery and offers guidelines for overcoming these challenges. Here, we summarize recent developments in combinatorial polymer synthesis, high-throughput screening of polymeric vectors, omics-based approaches to polymer design, barcoding schemes for pooled in vitro and in vivo screening, and identify materiomics-inspired research directions that will realize the long-unfulfilled clinical potential of polymeric carriers in gene therapy.

A microparticle approach for non-viral gene delivery within 3D human mesenchymal stromal cell aggregates

Three-dimensional (3D) multicellular aggregates, in comparison to two-dimensional monolayer culture, can provide tissue culture models that better recapitulate the abundant cell-cell and cell-matrix interactions found in vivo. In addition, aggregates are potentially useful building blocks for tissue engineering. However, control over the interior aggregate microenvironment is challenging due to inherent barriers for diffusion of biological mediators (e.g. growth factors) throughout the multicellular aggregates. Previous studies have shown that incorporation of biomaterials into multicellular aggregates can support cell survival and control differentiation of stem cell aggregates by delivering morphogens from within the 3D construct. In this study, we developed a highly efficient microparticle-based gene delivery approach to uniformly transfect human mesenchymal stromal cells (hMSC) within multicellular aggregates and cell sheets. We hypothesized that release of plasmid DNA (pDNA) lipoplexes from mineral-coated microparticles (MCMs) within 3D hMSC constructs would improve transfection in comparison to standard free pDNA lipoplex delivery in the media. Our approach increased transfection efficiency 5-fold over delivery of free pDNA lipoplexes in the media and resulted in homogenous distribution of transfected cells throughout the 3D constructs. Additionally, we found that MCMs improved hMSC transfection by specifically increasing macropinocytosis-mediated uptake of pDNA. Finally, we showed up to a three-fold increase of bone morphogenetic protein-2 (BMP-2) expression and enhanced calcium deposition within 3D hMSC constructs following MCM-mediated delivery of a BMP-2 encoding plasmid and culture in osteogenic medium. The technology described here provides a valuable tool for achieving efficient and homogenous transfection of 3D cell constructs and is therefore of particular value in tissue engineering and regenerative medicine applications. STATEMENT OF SIGNIFICANCE: This original research describes a materials-based approach, whereby use of mineral-coated microparticles improves the efficiency of non-viral gene delivery in three-dimensional human mesenchymal stromal cell constructs. Specifically, it demonstrates the use of mineral-coated microparticles to enable highly efficient transfection of human mesenchymal stromal cells in large, 3D culture formats. The manuscript also identifies specific endocytosis pathways that interact with the mineral coating to afford the improved transfection efficiency, as well as demonstrates the utility of this approach toward improving differentiation of large cell constructs. We feel that this manuscript will impact the current understanding and near-term development of materials for non-viral gene delivery in broad tissue engineering and biofabrication applications, and therefore be of interest to a diverse biomaterials audience.

Dual non-viral gene delivery from microparticles within 3D high-density stem cell constructs for enhanced bone tissue engineering

High-density mesenchymal stem cell (MSC) aggregates can be guided to form bone-like tissue via endochondral ossification in vitro when culture media is supplemented with proteins, such as growth factors (GFs), to first guide the formation of a cartilage template, followed by culture with hypertrophic factors. Recent reports have recapitulated these results through the controlled spatiotemporal delivery of chondrogenic transforming growth factor-β1 (TGF-β1) and chondrogenic and osteogenic bone morphogenetic protein-2 (BMP-2) from microparticles embedded within human MSC aggregates to avoid diffusion limitations and the lengthy, costly in vitro culture necessary with repeat exogenous supplementation. However, since GFs have limited stability, localized gene delivery is a promising alternative to the use of proteins. Here, mineral-coated hydroxyapatite microparticles (MCM) capable of localized delivery of Lipofectamine-plasmid DNA (pDNA) nanocomplexes encoding for TGF-β1 (pTGF-β1) and BMP-2 (pBMP-2) were incorporated, alone or in combination, within MSC aggregates from three healthy porcine donors to induce sustained production of these transgenes. Three donor populations were investigated in this work due to the noted MSC donor-to-donor variability in differentiation capacity documented in the literature. Delivery of pBMP-2 within Donor 1 aggregates promoted chondrogenesis at week 2, followed by an enhanced osteogenic phenotype at week 4. Donor 2 and 3 aggregates did not promote robust glycosaminoglycan (GAG) production at week 2, but by week 4, Donor 2 aggregates with pTGF-β1/pBMP-2 and Donor 3 aggregates with both unloaded MCM and pBMP-2 enhanced osteogenesis compared to controls. These results demonstrate the ability to promote osteogenesis in stem cell aggregates through controlled, non-viral gene delivery within the cell masses. These findings also indicate the need to screen donor MSC regenerative potential in response to gene transfer prior to clinical application. Taken together, this work demonstrates a promising gene therapy approach to control stem cell fate in biomimetic 3D condensations for treatment of bone defects.

Functionalization of microparticles with mineral coatings enhances non-viral transfection of primary human cells

Gene delivery to primary human cells is a technology of critical interest to both life science research and therapeutic applications. However, poor efficiencies in gene transfer and undesirable safety profiles remain key limitations in advancing this technology. Here, we describe a materials-based approach whereby application of a bioresorbable mineral coating improves microparticle-based transfection of plasmid DNA lipoplexes in several primary human cell types. In the presence of these mineral-coated microparticles (MCMs), we observed up to 4-fold increases in transfection efficiency with simultaneous reductions in cytotoxicity. We identified mechanisms by which MCMs improve transfection, as well as coating compositions that improve transfection in three-dimensional cell constructs. The approach afforded efficient transfection in primary human fibroblasts as well as mesenchymal and embryonic stem cells for both two- and three-dimensional transfection strategies. This MCM-based transfection is an advancement in gene delivery technology, as it represents a non-viral approach that enables highly efficient, localized transfection and allows for transfection of three-dimensional cell constructs.

Emerging potential of gene silencing approaches targeting anti-chondrogenic factors for cell-based cartilage repair

The field of cartilage repair has exponentially been growing over the past decade. Here, we discuss the possibility to achieve satisfactory regeneration of articular cartilage by means of human mesenchymal stem cells (hMSCs) depleted of anti-chondrogenic factors and implanted in the site of injury. Different types of molecules including transcription factors, transcriptional co-regulators, secreted proteins, and microRNAs have recently been identified as negative modulators of chondroprogenitor differentiation and chondrocyte function. We review the current knowledge about these molecules as potential targets for gene knockdown strategies using RNA interference (RNAi) tools that allow the specific suppression of gene function. The critical issues regarding the optimization of the gene silencing approach as well as the delivery strategies are discussed. We anticipate that further development of these techniques will lead to the generation of implantable hMSCs with enhanced potential to regenerate articular cartilage damaged by injury, disease, or aging.

Engineering a Cell Home for Stem Cell Homing and Accommodation

Distilling complexity to advance regenerative medicine from laboratory animals to humans, in situ regeneration will continue to evolve using biomaterial strategies to drive endogenous cells within the human body for therapeutic purposes; this approach avoids the need for delivering ex vivo-expanded cellular materials. Ensuring the recruitment of a significant number of reparative cells from an endogenous source to the site of interest is the first step toward achieving success. Subsequently, making the "cell home" cell-friendly by recapitulating the natural extracellular matrix (ECM) in terms of its chemistry, structure, dynamics, and function, and targeting specific aspects of the native stem cell niche (e.g., cell-ECM and cell-cell interactions) to program and steer the fates of those recruited stem cells play equally crucial roles in yielding a therapeutically regenerative solution. This review addresses the key aspects of material-guided cell homing and the engineering of novel biomaterials with desirable ECM composition, surface topography, biochemistry, and mechanical properties that can present both biochemical and physical cues required for in situ tissue regeneration. This growing body of knowledge will likely become a design basis for the development of regenerative biomaterials for, but not limited to, future in situ tissue engineering and regeneration.

Immune modulation with primed mesenchymal stem cells delivered via biodegradable scaffold to repair an Achilles tendon segmental defect

Tendon healing is a complex coordinated series of events resulting in protracted recovery, limited regeneration, and scar formation. Mesenchymal stem cell (MSC) therapy has shown promise as a new technology to enhance soft tissue and bone healing. A challenge with MSC therapy involves the ability to consistently control the inflammatory response and subsequent healing. Previous studies suggest that preconditioning MSCs with inflammatory cytokines, such as IFN-γ, TNF-α, and IL-1β may accelerate cutaneous wound closure. The objective of this study was to therefore elucidate these effects in tendon. That is, the in vivo healing effects of TNF-α primed MSCs were studied using a rat Achilles segmental defect model. Rat Achilles tendons were subjected to a unilateral 3 mm segmental defect and repaired with either a PLG scaffold alone, MSC-seeded PLG scaffold, or TNF-α-primed MSC-seeded PLG scaffold. Achilles tendons were analyzed at 2 and 4 weeks post-injury. In vivo, MSCs, regardless of priming, increased IL-10 production and reduced the inflammatory factor, IL-1α. Primed MSCs reduced IL-12 production and the number of M1 macrophages, as well as increased the percent of M2 macrophages, and synthesis of the anti-inflammatory factor IL-4. Primed MSC treatment also increased the concentration of type I procollagen in the healing tissue and increased failure stress of the tendon 4 weeks post-injury. Taken together delivery of TNF-α primed MSCs via 3D PLG scaffold modulated macrophage polarization and cytokine production to further accentuate the more regenerative MSC-induced healing response. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:269-280, 2017.

Mineral particles modulate osteo-chondrogenic differentiation of embryonic stem cell aggregates

Pluripotent stem cell aggregates offer an attractive approach to emulate embryonic morphogenesis and skeletal development. Calcium phosphate (CaP) based biomaterials have been shown to promote bone healing due to their osteoconductive and potential osteoinductive properties. In this study, we hypothesized that incorporation of CaP-coated hydroxyapatite mineral particles (MPs) within murine embryonic stem cell (ESC) aggregates could promote osteo-chondrogenic differentiation. Our results demonstrated that MP alone dose-dependently promoted the gene expression of chondrogenic and early osteogenic markers. In combination with soluble osteoinductive cues, MPs enhanced the hypertrophic and osteogenic phenotype, and mineralization of ESC aggregates. Additionally, MPs dose-dependently reduced ESC pluripotency and thereby decreased the size of teratomas derived from MP-incorporated ESC aggregates in vivo. Our data suggested a novel yet simple means of using mineral particles to control stem cell fate and create an osteochondral niche for skeletal tissue engineering applications.

STATEMENT OF SIGNIFICANCE

Directing stem cell differentiation and morphogenesis via biomaterials represents a novel strategy to promote cell fates and tissue formation. Our study demonstrates the ability of calcium phosphate-based mineral particles to promote osteochondrogenic differentiation of embryonic stem cell aggregates as well as modulate teratoma formation in vivo. This hybrid biomaterial-ESC aggregate approach serves as an enabling platform to evaluate the ability of biomaterials to regulate stem cell fate and regenerate functional skeletal tissues for clinical applications.