Stem cell transplantation as a novel cell-based approach to treat autoimmune-mediated demyelination

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) believed to be mediated by autoreactive T-cells, which initiate an immune-mediated attack on the myelin sheath and axons. Current treatments for MS predominantly target the immune component of the disease and have only been effective in a relatively small proportion of patients. Furthermore, patients with progressive neurological deterioration, due to the accumulation of axonal injury and neuronal loss, benefit little from existing MS therapies. The aim of this thesis was to investigate the effect of stem cell transplantation as a novel treatment strategy for MS, with the potential to modulate the autoimmune response as well as to exert neuroprotective effects. Two different types of adult stem cells, mesenchymal stem cells (MSCs) and neural stem cells (NSCs), were assessed for the ability to attenuate autoimmune-mediated demyelination in experimental autoimmune encephalomyelitis (EAE) induced with recombinant myelin oligodendrocyte glycoprotein. In the first part of this thesis, a comparative study of human MSCs isolated from three different tissue sources was carried out. In vitro, MSCs derived from the bone marrow (BM-MSCs) were identified as possessing more potent immunomodulatory properties compared to MSCs from adipose tissue (Ad-MSCs) or umbilical cord Wharton’s jelly. Despite these findings, only Ad-MSCs were found to have a significant impact on disease severity and CNS pathology when transplanted prior to the onset of clinical disease. This suppressive effect correlated with the broader expression of molecules involved in cellular migration. The efficacy of MSCs when transplanted prior to the onset of disease, as well as the enhanced therapeutic effect observed following intraperitoneal delivery, suggested a peripheral mechanism of action, rather than a direct effect on the CNS. The therapeutic efficacy of NSCs derived from different sources and expanded using various culture protocols was examined in the second part of this thesis. Neural differentiated mouse embryonic stem cells only exerted an inhibitory effect on peripheral immune responses and CNS pathology in EAE mice when multiple high dose intraperitoneal injections were delivered prior to the onset of clinical signs. This was consistent with their poor in vitro immunosuppressive ability compared to primary NSCs, and the lack of relevant homing molecules and in vivo migratory potential. The third part of this thesis investigated the use of gene modified stem cells as vehicles for delivery of anti-inflammatory cytokines. Given that interleukin (IL)-10 has been reported to suppress EAE, a lentiviral vector engineered to express human IL-10 was generated and used to transduce Ad-MSCs. By transplanting IL10-expressing Ad-MSCs during the priming phase of disease, the onset and severity of EAE was significantly ameliorated. In vitro studies demonstrating that gene modified Ad-MSCs could dramatically inhibit the function of myeloid dendritic cells (DCs), suggested that pathogenic T-cell responses may have been inhibited via the induction of tolerogenic DCs. Taken together, the data presented in this thesis demonstrates that stem cells are capable of dampening inflammatory immune responses in peripheral secondary lymphoid tissue, resulting in attenuation of EAE. Among the various MSCs studied, Ad-MSCs appear to be a promising cell type for the treatment of MS and thus offer an alternative system for the delivery of therapeutic proteins. The potential for stem cell therapies to impact the disease course in MS patients with progression disease, may rely on the ability of these cells to exert in situ neuroprotective effects. Thus, understanding the mechanisms controlling the trafficking of these cells in vivo will be critical for the development of stem cell transplantation as a novel treatment strategy for MS.