By: Jennifer S. Sun, PhD - June 30, 2020
Harmful consequences arise when the immune system mistakes self-proteins as foreign antigens, with BTK promoting autoantibody secretion by autoreactive B cells.8,14,15 Autoimmune diseases such as Multiple Sclerosis (MS)16 result from this dysregulated production of autoantibodies, which leads to destruction of normal tissue.17 Malfunctioning BTK mutants have been linked to increased disease susceptibility, correlating with diminished numbers of mature B cells and immunoglobulin isotypes.18,19 BTK therefore serves as an important target for therapeutic agents that modulate innate immunity.
Interactions between T cells, B cells, and myeloid cells promote MS pathology,16 and BTK is a component of signaling events with a critical role in regulating hematopoietic cell circulation.20 MS is a chronic, inflammatory, demyelinating disease of the central nervous system21 and is the most common, nontraumatic, disabling neurological autoimmune disease, with approximately 2.3 million cases diagnosed worldwide.22 B cells contribute to MS pathogenesis as a result of being skewed toward a proinflammatory profile involving antibody production, antigen presentation, T-cell stimulation, production of proinflammatory cytokines, formation of ectopic meningeal germinal centers, and deposition of oligoclonal bands of immunoglobulin in areas of active demyelination.23-25 Briefly, the body’s immune system begins to attack myelin, a protective sheath covering nerve fibers. The nervous system is consequently “short-circuited,” potentially permanently.26
Treatments for MS aim to shorten the duration and severity of relapses, prolong the time between relapses, and delay progression of disability.27 The most well-studied type of therapy targeting B cells consists of monoclonal antibodies (mAbs) that deplete B cells through mechanisms of antibody-dependent cellular cytotoxicity and apoptosis.23 Rituximab, for example, a mAb targeting the B-cell antigen CD20, depletes B cells and reduces T cells in the cerebrospinal fluid. However, rituximab is incapable of penetrating the blood-brain barrier (BBB) or lymphoid organs and is unsuccessful in slowing disease progression.23,28 To overcome the limitations of mAbs,28 MS treatment efforts have turned to BTK inhibitors (FIGURE).29
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