Abstract
BACKGROUND AND OBJECTIVES: In multiple sclerosis (MS), a variety of immunosuppressive treatments are available. While effective, these approaches often lead to sustained impairment of essential components of the immune system, posing long-term safety concerns. Consequently, there is a growing interest in alternative therapeutic approaches that selectively limit pathogenic B-cell functions while preserving their physiologic roles. In this study, we investigated the therapeutic potential of inhibiting the enzyme Bruton tyrosine kinase (BTK), a key signaling molecule in both B-cell and myeloid cell activation. METHODS: The effects of the BTK inhibitor evobrutinib were evaluated in various experimental in vivo models of CNS demyelination, each representing different aspects of disease pathology as well as a naïve healthy condition. The impact on disease onset and severity was determined, and phenotypical alterations in different cell populations were assessed via flow cytometry. Furthermore, functional changes in both murine and human myeloid cells induced by BTK inhibition under specific Fc receptor-dependent stimulation were analyzed in in vitro settings using flow cytometry. RESULTS: In a naïve, healthy environment, evobrutinib promoted the development of regulatory B-cell properties. In various experimental models of CNS demyelination, BTK inhibition limited the differentiation of proinflammatory B cells while supporting their regulatory properties. Beyond modulating B-cell responses, BTK inhibition also attenuated the activation of myeloid cells after Fc receptor-mediated antigen uptake, a process assumed to be of importance in conditions, such as neuromyelitis optica spectrum disorder and myelin oligodendrocyte glycoprotein-antibody associated disease. In addition, BTK inhibition was shown to suppress the secretion of proinflammatory cytokines and reduce antigen presentation, further dampening pathogenic immune responses. DISCUSSION: These findings highlight the potential of BTK inhibition as a selective and sustainable immunomodulatory strategy for both B cells and myeloid cells in the context of chronic CNS inflammation. Despite their efficacy, broad-spectrum immunosuppressive therapies often fail to provide targeted immune modulation. By contrast, BTK inhibition promotes regulatory B-cell properties while leaving other B-cell functions intact, providing the basis for its broad use-potentially in combination with established anti-inflammatory agents.