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.

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.

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.

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.