Bruton's tyrosine kinase inhibitors rescue neuronal impairment caused by B cell-mediated lymphotoxin-α 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-α (LTα), and this proinflammatory protein is also present in the cerebrospinal fluid (CSF) and meninges of pwMS. B cell-specific ablation of LTα 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 LTα release from B cells. Blocking LTα, tumor necrosis factor receptor 1 (TNFR1), or receptor-interacting protein kinase 1 or 3 also prevented neuronal impairment, but blocking TNFα or LTβ had no such effect. Neuronal impairment was reversible by BTKi or blockage of LTα, and this reversibility was dependent on the activity of acid sphingomyelinase. In pwMS, LTα correlated with elevated neurofilament light chain (NfL) abundance in CSF, and anti-CD20 B cell-depletion therapy led to a reduction in circulating LTα, supporting the role of B cells as a regulator for LTα. These findings highlight the negative impact of B cell-derived LTα on neurons and suggest potential treatment avenues for MS-associated neuronal injury.