Antibody-mediated initiation and lymphocyte-targeting therapies in CNS demyelinating disease

Abstract

Multiple sclerosis is inflammatory central nervous system disease, characterised by areas of demyelination and axonal loss. The pathogenic mechanism behind the disease still remains unknown, however it is thought to be mainly T cell-mediated. Notwithstanding this, B cells have increasingly been recognized as key mediators of disease. This work focuses on three distinct characteristics of MS pathology in the animal model experimental autoimmune encephalomyelitis (EAE). The first project focused on establishing inhibition of Bruton´s tyrosine kinase (BTK) as a novel therapeutic approach. BTK is centrally placed in B cell receptor (BCR) signalling. In a B cell-mediated EAE model, induced by injection of MOG protein, we observed that evobrutinib, a novel BTK inhibitor, dose-dependently reduced clinical disease. Evobrutinib inhibited BCR-mediated phenotypic maturation of B cells from follicular (FO) II to FO I and reduced activation of B cells and T cells. It diminished calcium mobilization and cytokine production after BCR stimulation in murine and human B cells. Investigating MS patients, we did not observe a difference in B cell frequency, BTK expression or phosphorylation of BTK after BCR stimulation. Taken together, we demonstrated that BTK inhibition (BTKi) is a promising new strategy to control pathogenic B cell activity in a model of CNS autoimmunity. The second project investigated the effects of long-term high dose vitamin D supplementation on the peripheral immune system and EAE severity. We observed clinical and histological deterioration of EAE after long-term high dose supplementation of vitamin D. Further investigations traced this effect to a secondary hypercalcemia, which in contrast to vitamin D, increased the activation and differentiation of T cells both in vitro and in vivo. Since MS patients are often continuously supplemented with vitamin D over long periods of time, our work cautions patients and clinicians to be attentive of potential side effects by hypercalcemia. The third project focused on antibodies in the initiation of disease. We investigated the capacity of myelin-reactive antibodies to facilitate encephalitogenic responses via opsonisation of CNS antigen. We observed that antibody production in the absence of B cells was sufficient to induce EAE in a transgenic mouse model. Additionally, adoptive transfer of antibodies in mice containing MOG-specific T cells induced disease via otherwise unresponsive myeloid antigen-presenting cells (APCs). MOG-targeting antibodies enabled Fcreceptor (FcR) mediated recognition and phagocytosis in in vitro differentiated macrophages. Additionally, antibody preparations from neuromyelitis optica patients positive for MOG antibodies similarly facilitated recognition by myeloid APCs. These results establish opsonisation of CNS antigen by specific antibodies as a novel mechanism to trigger CNS demyelination.