Expression of BTK in Leptomeningeal B-cell Rich Infiltrates in Two Models of Progressive MS and its Inhibition by Evobrutinib, Underscores BTK as a Target for Compartmentalized Neuroinflammation

Objective: We investigated BTK expression in central nervous system (CNS) tissue from two models of progressive multiple sclerosis (MS), spontaneous canine granulomatous meningoencephalomyelitis (GME) and progressive experimental autoimmune encephalomyelitis (pEAE), and tested the efficacy of evobrutinib in murine pEAE. Background: Anti-CD20 therapies illustrate the importance of B cells to MS disease process, notably in the CNS, as leptomeningeal aggregates rich in B cells associate with adjacent subpial cortical pathology and are predictive of aggressive disease and rapid disability. With CNS B cells being protected from direct anti-CD20 therapies, an alternative target is the inflammatory process in the CNS, through inhibiting Bruton’s tyrosine kinase (BTK), a critical enzyme in B cell activation and survival. BTK inhibitors may be able to enter the CNS and restrict B cell responses. Design/Methods: We studied leptomeningeal and parenchymal samples from GME (n=9) and pEAE (n=6) cases by immunofluorescent/confocal analysis, and treated pEAE mice prophylactically with evobrutinib. Results: Both models were characterized by prominent B cell infiltrates in the leptomeninges that associated with submeningeal injury in underlying parenchyma, reminiscent of subpial neuropathology in MS. In both models we found robust BTK expression within CD20+ B cell-rich leptomeningeal infiltrates. Meningeal B cell infiltration extended into parenchymal tissue via Virchow Robin spaces in penetrating vessels. BTK expression also existed in B cells within these spaces and in cells moving from perivascular space into parenchyma. In GME, BTK was also detected in microglia/macrophages in leptomeningeal infiltrates and neighboring parenchyma. Prophylactic treatment with evobrutinib significantly reduced disease disability in pEAE by robustly ameliorating inflammation and demyelination. Conclusions: The prominent expression of BTK in leptomeningeal and perivascular B-cell rich infiltrates, and its inhibition with evobrutinib, which reduced disease severity and the neuropathology of pEAE, underscores BTK as a candidate for targeting compartmentalized neuroinflammation to reduce MS disability progression. Disclosure: Ms. Kebir has received research support from Fonds de Recherche du Quebec-Sante. Ms. Kebir has received intellectual property interests from a discovery or technology relating to health care. Guadalupe Ceja has nothing to disclose. Miles Miller has nothing to disclose. Cen Li has received research support from Chinese Scholarship Council. The institution of Michael May has received research support from NIH. Charles Vite has nothing to disclose. Molly Church has nothing to disclose. Roland Grenningloh has received personal compensation for serving as an employee of EMD Serono. Jorge Alvarez has nothing to disclose.