Bruton's tyrosine kinase inhibitors rescue neuronal impairment caused by B cell-mediated lymphotoxin-a release

Although B cell depletion slows disability accrual in people with multiple sclerosis (pwMS), the role of B cells in MS-associated neuronal injury remains elusive. B cells release cytokines such as lymphotoxin-a (LTa), and this proinflammatory protein is also present in the cerebrospinal fluid (CSF) and meninges of pwMS. B cell-specific ablation of LTa alleviates disease severity in a preclinical model of MS. To further study the impact of B cell-derived cytokines on neuronal function, we performed patch-clamp recordings on human iPSC-derived neurons. Coculture with proinflammatory human B cells led to depolarization and aberrant firing. Pretreatment of proinflammatory B cells with a Bruton's tyrosine kinase inhibitor (BTKi), reported in patients to beneficially affect disability progression even in the absence of inflammatory relapse activity, prevented neuronal impairment and inhibited LTa release from B cells. Blocking LTa, tumor necrosis factor receptor 1 (TNFR1), or receptor-interacting protein kinase 1 or 3 also prevented neuronal impairment, but blocking TNFa or LTß had no such effect. Neuronal impairment was reversible by BTKi or blockage of LTa, and this reversibility was dependent on the activity of acid sphingomyelinase. In pwMS, LTa correlated with elevated neurofilament light chain (NfL) abundance in CSF, and anti-CD20 B cell-depletion therapy led to a reduction in circulating LTa, supporting the role of B cells as a regulator for LTa. These findings highlight the negative impact of B cell-derived LTa on neurons and suggest potential treatment avenues for MS-associated neuronal injury. Overall design: cultured human iPSC derived neuons were treated with BTKi (Evobrutinib, 1µM) or vehicle for 24h before cells were detached and RNA was isolated