The reduction in immunogenicity of neurotrophin overexpressing stem cells after intra-striatal transplantation by encapsulation in an in situ gelling collagen hydrogel.

Delivery of neurotrophic factors to the brain via genetically modified bone marrow-derived mesenchymal stem cells (MSCs) offers a promising neuroprotective strategy for neurodegenerative diseases. However, MSCs delivered to the CNS typically show poor survival post-transplantation, which is accompanied by microglial activation and astrocyte recruitment at the graft site. Recent studies have shown the potential of biomaterials to provide a supportive matrix for transplanted cells which may assist in the grafting process. In this study, an in situ gelling type I collagen hydrogel was evaluated as an intracerebral transplantation matrix for delivery of glial cell line-derived neurotrophic factor (GDNF)-overexpressing MSCs to the rat brain (GDNF-MSCs). In vitro analyses demonstrated that this collagen hydrogel did not affect the viability of the GDNF-MSCs nor did it prevent GDNF secretion into the surrounding medium. In vivo analyses also confirmed that the collagen hydrogel did not negatively impact on the survival of the cells and permitted GDNF secretion into the striatal parenchyma. Importantly, this study also revealed that transplanting GDNF-MSCs in a collagen hydrogel significantly diminished the host brain's response to the cells by reducing the recruitment of both microglia and astrocytes at the site of delivery. In conclusion, this hydrogel, which is composed of the natural extracellular matrix, collagen, was shown to be a well-tolerated cell delivery platform technology which could be functionalised to further aid cell support and graft integration.

The neurotoxicity of gene vectors and its amelioration by packaging with collagen hollow spheres.

Over the last twenty years there have been several reports on the use of nonviral vectors to facilitate gene transfer in the mammalian brain. Whilst a large emphasis has been placed on vector transfection efficiency, the study of the adverse effects upon the brain, caused by the vectors themselves, remains completely overshadowed. To this end, a study was undertaken to study the tissue response to three commercially available transfection agents in the brain of adult Sprague Dawley rats. The response to these transfection agents was compared to adeno-associated viral vector (AAV), PBS and naked DNA. Furthermore, the use of a collagen hollow sphere (CHS) sustained delivery system was analysed for its ability to reduce striatal toxicity of the most predominantly studied polymer vector, polyethyleneimine (PEI). The size of the gross tissue loss at the injection site was analysed after immunohistochemical staining and was used as an indication of acute toxicity. Polymeric vectors showed similar levels of acute brain toxicity as seen with AAV, and CHS were able to significantly reduce the toxicity of the PEI vector. In addition; the host response to the vectors was measured in terms of reactive astrocytes and microglial cell recruitment. To understand whether this gross tissue loss was caused by the direct toxicity of the vectors themselves an in vitro study on primary astrocytes was conducted. All vectors reduced the viability of the cells which is brought about by direct necrosis and apoptosis. The CHS delivery system reduced cell necrosis in the early stages of post administration. In conclusion, whilst polymeric gene vectors cause acute necrosis, administration in the brain causes adverse effects no worse than that of an AAV vector. Furthermore, packaging the PEI vector with CHS reduces surface charge and direct toxicity without elevating the host response.