Local immunosuppression to improve the welfare of animals in neural transplantation experiments

Cell transplantation is a novel therapy for disorders of the nervous system such as Parkinson's disease, where the aim is to improve symptoms by replacing cells which have degenerated due to the disease. In order to determine that cells to be transplanted in patients are safe and have functional efficacy, they must first be rigorously tested in animal models, frequently rodents. As these experiments require the transplantation of human cells into rodent hosts, suppression of the immune system is required to prevent rejection of transplanted cells and allow integration and function to be assessed. This currently requires long term treatment with immunosuppressant drugs delivered via daily injections, which can lead to stress and side effects in the animals. Our proposed research aims to avoid altogether or reduce the need for these daily injections, by delivering the immunosuppressant treatment alongside transplanted cells in a novel microparticle drug delivery system. This will dramatically reduce the number of animal procedures required in the essential pre-clinical testing of cells to be used in cell therapies for a range of diseases. We have successfully developed microparticles which can be successfully injected into the rodent brain without causing inflammation. These have been loaded with the immunosuppressant tacrolimus, a drug frequently used in organ transplantation, and slowly release the drug for at least one month. We have also shown this dose of drug to be effective at preventing the immune response to peripheral nerve transplants in rats. Therefore, in this project we aim to test our novel microparticle immunosuppressant delivery system in a rat model of Parkinson's disease, in which rats will receive transplants of human cells to the brain. We will compare the immune response to transplanted cells at 3 weeks in treated and untreated animals, and graft survival and integration after 16 weeks.

Numerous clinical trials are underway or in development investigating transplantation of stem cell-derived neurons for neurodegenerative disorders such as Parkinson's disease (PD), Huntington's disease, and stroke. An essential part of this research is the preclinical evaluation of human cells in appropriate models of disease for validation of cell survival, safety, and functional efficacy. This work is frequently undertaken through xenotransplantation of human cells into rodents, which requires modulation of the immune system to allow survival of transplanted cells. We have developed a novel approach to immunosuppression; co-delivery of tacrolimus releasing microspheres alongside therapeutic cells, to promote graft survival and avoid welfare issues and side effects associated with conventional systemic immunosuppression. The aims of the project are to transfer this technology to Cardiff University for use in a rat model of PD, and demonstrate improvements in survival of transplanted human cells.
Pharmacological immunosuppression is commonly used in this model, however frequent administration is required, usually via daily intraperitoneal injection. As human cells require time to mature and integrate within the host prior to assessment of graft function, a typical experiment may be >20 weeks long, requiring host animals to undergo ~170 consecutive injections to prevent graft rejection. In addition to stress from injections, this results in significant side effects, ultimately leading to premature termination of experiments. Our alternative approach aims to directly improve 3Rs outcomes by:
i) Reducing the number of procedures each experimental animal will undergo during their lifetime (Refinement)
ii) Improving animal welfare by avoiding severe systemic side effects (Refinement)
iii) Producing more reliable graft survival thus increasing the power of in vivo experiments while reducing the number of experimental animals required (Reduction)