Mechanically enhanced microcapsules for cellular gene therapy

Probing of New Polymer-Based Microcapsules for Islet Cell Immunoisolation

Islet allotransplantation offers a promising cell therapy for type 1 diabetes, but challenges such as limited donor availability and immunosuppression persist. Microencapsulation of islets in polymer-coated alginate microcapsules is a favored strategy for immune protection and maintaining islet viability. This study introduces Poly [2-(methacryloyloxy)ethyl]trimethylammonium chloride (PMETAC) as an innovative coating material for microcapsules. PMETAC enhances biocompatibility and durability, marking a significant advancement in islet encapsulation. Our approach combines alginate with PMETAC to create Langerhans islet microcapsules, simplifying material composition and preparation and ultimately lowering costs and increasing clinical applicability. Our comprehensive evaluation of the stability (including osmotic stability, thermal stability, and culture condition stability) and cytotoxicity of a novel microencapsulation system based on alginate-PMETAC-alginate offers insights into its potential application in islet immunoisolation strategies. Microcapsules with PMETAC content ranging from 0.01 to 1% are explored in the current work. The results indicate that the coatings made with 0.4% PMETAC show the most promising outcomes, remaining stable in the mentioned tests and exhibiting the required permeability. It was shown that the islets encapsulated in this manner retain viability and functional activity. Thus, alginate microcapsules coated with 0.4% PMETAC are suitable for further animal trials. While our findings are promising, further studies, including animal testing, will be necessary to evaluate the clinical applicability of our encapsulation method.

Type 1 Diabetes Mellitus reversal via implantation of magnetically purified microencapsulated pseudoislets

Microencapsulation of pancreatic islets for the treatment of Type I Diabetes Mellitus (T1DM) generates a high quantity of empty microcapsules, resulting in high therapeutic graft volumes that can enhance the host's immune response. We report a 3D printed microfluidic magnetic sorting device for microcapsules purification with the objective to reduce the number of empty microcapsules prior transplantation. In this study, INS1E pseudoislets were microencapsulated within alginate (A) and alginate-poly-L-lysine-alginate (APA) microcapsules and purified through the microfluidic device. APA microcapsules demonstrated higher mechanical integrity and stability than A microcapsules, showing better pseudoislets viability and biological function. Importantly, we obtained a reduction of the graft volume of 77.5% for A microcapsules and 78.6% for APA microcapsules. After subcutaneous implantation of induced diabetic Wistar rats with magnetically purified APA microencapsulated pseudoislets, blood glucose levels were restored into normoglycemia (<200 mg/dL) for almost 17 weeks. In conclusion, our described microfluidic magnetic sorting device represents a great alternative approach for the graft volume reduction of microencapsulated pseudoislets and its application in T1DM disease.

Auxotrophy to Xeno-DNA: an exploration of combinatorial mechanisms for a high-fidelity biosafety system for synthetic biology applications

BACKGROUND

Biosafety is a key aspect in the international Genetically Engineered Machine (iGEM) competition, which offers student teams an amazing opportunity to pursue their own research projects in the field of Synthetic Biology. iGEM projects often involve the creation of genetically engineered bacterial strains. To minimize the risks associated with bacterial release, a variety of biosafety systems were constructed, either to prevent survival of bacteria outside the lab or to hinder horizontal or vertical gene transfer.

MAIN BODY

Physical containment methods such as bioreactors or microencapsulation are considered the first safety level. Additionally, various systems involving auxotrophies for both natural and synthetic compounds have been utilized by iGEM teams in recent years. Combinatorial systems comprising multiple auxotrophies have been shown to reduced escape frequencies below the detection limit. Furthermore, a number of natural toxin-antitoxin systems can be deployed to kill cells under certain conditions. Additionally, parts of naturally occurring toxin-antitoxin systems can be used for the construction of 'kill switches' controlled by synthetic regulatory modules, allowing control of cell survival. Kill switches prevent cell survival but do not completely degrade nucleic acids. To avoid horizontal gene transfer, multiple mechanisms to cleave nucleic acids can be employed, resulting in 'self-destruction' of cells. Changes in light or temperature conditions are powerful regulators of gene expression and could serve as triggers for kill switches or self-destruction systems. Xenobiology-based containment uses applications of Xeno-DNA, recoded codons and non-canonical amino acids to nullify the genetic information of constructed cells for wild type organisms. A 'minimal genome' approach brings the opportunity to reduce the genome of a cell to only genes necessary for survival under lab conditions. Such cells are unlikely to survive in the natural environment and are thus considered safe hosts. If suitable for the desired application, a shift to cell-free systems based on Xeno-DNA may represent the ultimate biosafety system.

CONCLUSION

Here we describe different containment approaches in synthetic biology, ranging from auxotrophies to minimal genomes, which can be combined to significantly improve reliability. Since the iGEM competition greatly increases the number of people involved in synthetic biology, we will focus especially on biosafety systems developed and applied in the context of the iGEM competition.

Structural changes in alginate-based microspheres exposed to in vivo environment as revealed by confocal Raman microscopy

A next-generation cure for type 1 diabetes relies on immunoprotection of insulin-producing cells, which can be achieved by their encapsulation in microspheres made of non-covalently crosslinked hydrogels. Treatment success is directly related to the microsphere structure that is characterized by the localization of the polymers constituting the hydrogel material. However, due to the lack of a suitable analytical method, it is presently unknown how the microsphere structure changes in vivo, which complicates evaluation of different encapsulation approaches. Here, confocal Raman microscopy (CRM) imaging was tailored to serve as a powerful new tool for tracking structural changes in two major encapsulation designs, alginate-based microbeads and multi-component microcapsules. CRM analyses before implantation and after explantation from a mouse model revealed complete loss of the original heterogeneous structure in the alginate microbeads, making the intentionally high initial heterogeneity a questionable design choice. On the other hand, the structural heterogeneity was conserved in the microcapsules, which indicates that this design will better retain its immunoprotective properties in vivo. In another application, CRM was used for quantitative mapping of the alginate concentration throughout the microbead volume. Such data provide invaluable information about the microenvironment cells would encounter upon their encapsulation in alginate microbeads.

Layer-by-layer assembled biopolymer microcapsule with separate layer cavities generated by gas-liquid microfluidic approach

In this work, a layer-by-layer (LbL) assembled biopolymer microcapsule with separate layer cavities is generated by a novel and convenient gas-liquid microfluidic approach. This approach exhibits combined advantages of microfluidic approach and LbL assembly method, and it can straightforwardly build LbL-assembled capsules in mild aqueous environments at room temperature. In particular, using this approach we can build the polyelectrolyte multilayer capsule with favorable cavities in each layer, and without the need for organic solvent, emulsifying agent, or sacrificial template. Various components (e.g., drugs, proteins, fluorescent dyes, and nanoparticles) can be respectively encapsulated in the separate layer cavities of the LbL-assembled capsules. Moreover, the encapsulated capsules present the ability as colorimetric sensors, and they also exhibit the interesting release behavior. Therefore, the LbL-assembled biopolymer capsule is a promising candidate for biomedical applications in targeted delivery, controlled release, and bio-detection.

Alginate encapsulation of human embryonic stem cells to enhance directed differentiation to pancreatic islet-like cells

The pluripotent property of human embryonic stem cells (hESCs) makes them attractive for treatment of degenerative diseases such as diabetes. We have developed a stage-wise directed differentiation protocol to produce alginate-encapsulated islet-like cells derived from hESCs, which can be directly implanted for diabetes therapy. The advantage of alginate encapsulation lies in its capability to immunoisolate, along with the added possibility of scalable culture. We have evaluated the possibility of encapsulating hESCs at different stages of differentiation. Encapsulation of predifferentiated cells resulted in insufficient cellular yield and differentiation. On the other hand, encapsulation of undifferentiated hESCs followed by differentiation induction upon encapsulation resulted in the highest viability and differentiation. More striking was that alginate encapsulation resulted in a much stronger differentiation compared to parallel two-dimensional cultures, resulting in 20-fold increase in c-peptide protein synthesis. To elucidate the mechanism contributing to encapsulation-mediated enhancement in hESC maturation, investigation of the signaling pathways revealed interesting insight. While the phospho-protein levels of all the tested signaling molecules were lower under encapsulation, the ratio of pSMAD/pAKT was significantly higher, indicating a more efficient signal transduction under encapsulation. These results clearly demonstrate that alginate encapsulation of hESCs and differentiation to islet-cell types provides a potentially translatable treatment option for type 1 diabetes.

Inflammatory bowel disease: clinical aspects and treatments

Inflammatory bowel disease (IBD) is defined as a chronic intestinal inflammation that results from host-microbial interactions in a genetically susceptible individual. IBDs are a group of autoimmune diseases that are characterized by inflammation of both the small and large intestine, in which elements of the digestive system are attacked by the body’s own immune system. This inflammatory condition encompasses two major forms, known as Crohn’s disease and ulcerative colitis. Patients affected by these diseases experience abdominal symptoms, including diarrhea, abdominal pain, bloody stools, and vomiting. Moreover, defects in intestinal epithelial barrier function have been observed in a number of patients affected by IBD. In this review, we first describe the types and symptoms of IBD and investigate the role that the epithelial barrier plays in the pathophysiology of IBD as well as the major cytokines involved. We then discuss steps used to diagnose this disease and the treatment options available, and finally provide an overview of the recent research that aims to develop new therapies for such chronic disorders.

Bio-Encapsulation for the Immune-Protection of Therapeutic Cells

The design of new technologies for treatment of human disorders is a complex and difficult task. The aim of this article is to explore state of art discussion of various techniques and materials involve in cell encapsulations. Encapsulation of cells within semi-permeable polymer shells or beads is a potentially powerful tool, and has long been explored as a promising approach for the treatment of several human diseases such as lysosomal storage disease (LSD), neurological disorders, Parkinsons disease, dwarfism, hemophilia, cancer and diabetes using immune-isolation gene therapy.

Systematic study of alginate-based microcapsules by micropipette aspiration and confocal fluorescence microscopy

Micropipette aspiration and confocal fluorescence microscopy were used to study the structure and mechanical properties of calcium alginate hydrogel beads (A beads), as well as A beads that were additionally coated with poly-L-lysine (P) and sodium alginate (A) to form, respectively, AP and APA hydrogels. A beads were found to continue curing for up to 500 h during storage in saline, due to residual calcium chloride carried over from the gelling bath. In subsequent saline washes, micropipette aspiration proved to be a sensitive indicator of gel weakening and calcium loss. Aspiration tests were used to compare capsule stiffness before and after citrate extraction of calcium. They showed that the initial gel strength is largely due to the calcium alginate gel cores, while the long term strength is solely due to the poly-L-lysine-alginate polyelectrolyte complex (PEC) shells. Confocal fluorescence microscopy showed that calcium chloride exposure after PLL deposition led to PLL redistribution into the hydrogel bead, resulting in thicker but more diffuse and weaker PEC shells. Adding a final alginate coating to form APA capsules did not significantly change the PEC membrane thickness and stiffness, but did speed the loss of calcium from the bead core.

Improving covalent cell encapsulation with temporarily reactive polyelectrolytes

Calcium alginate/poly-L-lysine beads were coated with either 50% hydrolyzed poly(methyl vinyl ether-alt-maleic anhydride) (PMM(50)), or with poly(vinyl dimethyl azlactone-co-methacrylic acid) (50:50, PMV(50)), to form covalently shell-crosslinked capsules, and compared with analogous capsules coated with sodium alginate. All capsule types were prepared with and without C2C12 murine myoblast cells, and implanted into mice for up to 6 weeks. Cell viability, capsule integrity, fibrotic overgrowth, and mechanical strength of the capsules were assessed, and correlated with inflammatory cytokine marker levels in tail vein blood samples taken at different time points. AP-PMM(50) capsules displayed the least amount of fibrotic overgrowth, were found to be the strongest, and showed the lowest levels of TNF-α in tail vein serum samples taken at 4 h, 24 h, 1 and 6 weeks post transplantation. The results for APA and AP-PMV(50) capsules were more variable and depended on the presence or absence of encapsulated cells.