Extracellular matrix protein-coated scaffolds promote the reversal of diabetes after extrahepatic islet transplantation

Stem cell and gene therapies for diabetes mellitus

In this Perspectives article, we comment on the progress in experimental stem cell and gene therapies that might one day become a clinical reality for the treatment of patients with diabetes mellitus. Research on the ability of human embryonic stem cells to differentiate into islet cells has defined the developmental stages and transcription factors involved in this process. However, the clinical applications of human embryonic stem cells are limited by ethical concerns, as well as the potential for teratoma formation. As a consequence, alternative forms of stem cell therapies, such as induced pluripotent stem cells and bone marrow-derived mesenchymal stem cells, have become an area of intense study. Finally, gene therapy shows some promise for the generation of insulin-producing cells. Here, we discuss two of the most frequently used approaches: in vitro gene delivery into cells which are then transplanted into the recipient and direct delivery of genes in vivo.

Prosaposin in the secretome of marrow stroma-derived neural progenitor cells protects neural cells from apoptotic death

Functionally, adult stem cells not only participate in replication and differentiation to various cell lineages, but also may be involved in rescuing cells from apoptosis. Identifying functional factors secreted by stem cells, as well as their target cells, may advance our understanding of stem cells' multifaceted physiologic functions. Here, we report that mouse bone marrow stromal cell-derived neuroprogenitor cells (mMSC-NPC) provide a protective function by secreting a key factor, prosaposin (PSAP), capable of rescuing mature neurons from apoptotic death. This factor is identified as the lead protein in the secretome of mMSC-NPC cultures by tandem mass spectroscopic profiling, and further validated by western blotting and immunocytochemistry. The secretome of MSC-NPC reduces toxin-induced cell death in cultures of rat pheochromocytoma neuronal cells, human ReNcell CX neurons, and rat cortical primary neurons; removal of PSAP by immunodepletion annuls this protective effect. This neuronal protection against toxin treatment was validated further by the recombinant PSAP peptide. Interestingly, the secretome of neuronal culture does not possess such a self-protective action. We suggest that upon injury, a subgroup of MSCs differentiates into neural/neuronal progenitor cells, and remains in this intermediate stem cell-like stage, defending injured neighboring mature neurons from apoptosis by secreting PSAP.

Pig-to-nonhuman primate islet xenotransplantation

Type 1 diabetes continues to present a therapeutic challenge. The restoration of normoglycemia and insulin independence in immunosuppressed type 1 diabetic recipients of human islet allografts has highlighted the potential of cell-based diabetes therapy. The unlimited and on-demand availability of pig islets from healthy, young, living, designated pathogen-free, and potentially genetically modified donors presents unique opportunities for improving the availability and outcomes of islet replacement therapies in diabetes. One of the fundamental prerequisites for initiating clinical research is a favorable benefit-over-harm determination in the stringent preclinical transplant model in nonhuman primates. To date, xenotransplants of pig islet cell therapy products have been reported by 15 institutions in 181 NHPs, including xenotransplants in 72 non-diabetic and 109 diabetic recipients. These studies have demonstrated the feasibility of successful preclinical islet xenotransplantation and have provided insights into the critical events operative in the immune recognition and destruction of islet xenografts in nonhuman primates. Particularly promising is the recent achievement of prolonged insulin independence in this model by means of several distinct islet xenotransplantation products, implantation sites, and immunotherapeutic strategies. Further progress appears likely and the development of suitable source pigs will position the scientific community to translate these findings safely to the clinic.

Local gene delivery from ECM-coated poly(lactide-co-glycolide) multiple channel bridges after spinal cord injury

Tissue engineering scaffolds with complex geometries can provide an architecture that directs tissue formation. Drug delivery from these scaffolds to promote regeneration is often challenging due to the complex fabrication processes. Surface-mediated DNA delivery from multiple channel bridges was applied to deliver lipoplexes in vivo to the injured spinal cord. The surface properties of the polymer, DNA deposition with or without drying, and the presence of ECM components were investigated. In vitro studies revealed that fibronectin produced greater expression levels and immobilization efficiencies compared with collagen, laminin, and no coating. In addition, lipoplex incubation on ECM-coated PLG increased expression relative to either of the drying methods. Additionally, the incubation method had more homogeneously distributed lipoplexes and a higher number of transfected cells relative to the dried conditions. Translation to three-dimensional bridges led to high levels of transgene expression in vitro. In vivo, lipoplexes immobilized to the bridge produced transgene expression levels in a rat spinal cord hemisection model that were 2-fold greater than naked plasmid. Additionally, expression with lipoplexes persisted for at least three weeks. Surface-mediated delivery can be applied to scaffolds with complex geometries to promote transgene expression in vivo.

Islet cell transplantation

PURPOSE OF REVIEW

The transplantation of human islets has come a long way since the first diabetic person became insulin independent in 1989. The advent of a steroid-free immunosuppressive protocol in 2000 resulted in most recipients becoming insulin independent and remaining so for a year. However, beta-cell function declines thereafter. Strategies to enhance the islet mass transplanted and preserve beta-cell function are necessary.

RECENT FINDINGS

This review covers recent advances in determining the selection of appropriate enzymes for islet isolation, use of pancreases from heart-dead donors and techniques for predicting the functional capacity of isolated islets prior to transplantation. Changing the transplantation site away from the liver, where many islets are destroyed by an inflammatory process, is reviewed, and the possibility of seeding islets onto three-dimensional biodegradable scaffolds discussed. A method of preventing apoptosis of the beta cells prior to transplantation is detailed, as is the beneficial effect of using exenatide, after transplantation. Novel techniques to image islets are discussed, and this requires the labelling of the islets prior to implantation. Enhancing the vascularization of islets is shown to enhance functional outcomes. Encapsulation of the islets should obviate the need for using antirejection drugs, and it may be possible to expand beta cells in vitro.

SUMMARY

The above strategies are likely to enhance the outcomes of clinical islet transplants.