Bruton's tyrosine kinase inhibition reduces disease severity in a model of secondary progressive autoimmune demyelination

Bruton's tyrosine kinase (BTK) is an emerging target in multiple sclerosis (MS). Alongside its role in B cell receptor signaling and B cell development, BTK regulates myeloid cell activation and inflammatory responses. Here we demonstrate efficacy of BTK inhibition in a model of secondary progressive autoimmune demyelination in Biozzi mice with experimental autoimmune encephalomyelitis (EAE). We show that late in the course of disease, EAE severity could not be reduced with a potent relapse inhibitor, FTY720 (fingolimod), indicating that disease was relapse-independent. During this same phase of disease, treatment with a BTK inhibitor reduced both EAE severity and demyelination compared to vehicle treatment. Compared to vehicle treatment, late therapeutic BTK inhibition resulted in fewer spinal cord-infiltrating myeloid cells, with lower expression of CD86, pro-IL-1β, CD206, and Iba1, and higher expression of Arg1, in both tissue-resident and infiltrating myeloid cells, suggesting a less inflammatory myeloid cell milieu. These changes were accompanied by decreased spinal cord axonal damage. We show similar efficacy with two small molecule inhibitors, including a novel, highly selective, central nervous system-penetrant BTK inhibitor, GB7208. These results suggest that through lymphoid and myeloid cell regulation, BTK inhibition reduced neurodegeneration and disease progression during secondary progressive EAE.

Immunization method influences EAE relapse rate in SJL mice (171.6)

We have discovered that administration of pertussis toxin as an adjuvant during induction of experimental autoimmune encephalomyelitis (EAE) in SJL mice results in a more severe first EAE wave, but fewer, milder and later relapses than if pertussis toxin is not used. This finding is inconsistent with the widely-accepted epitope spreading hypothesis, which predicts more severe relapses resulting from more severe tissue damage in the first wave. EAE in SJL mice immunized with PLP139-151/CFA is the mouse model which most closely resembles human remitting/relapsing multiple sclerosis. EAE develops in 90-100% of immunized mice 10-15 days after immunization. The first wave of EAE lasts several days and most mice recover from it. After a disease-free period from one day to several months, most mice relapse. 50-75% of mice develop a relapse during the first 6 weeks after immunization. It is not clear why relapses develop. It is widely accepted that relapses result from epitope spreading - new immune responses to epitopes of self antigens other than the PLP139-151. It is believed that tissue damage from the initial immune response allows “presentation” of new epitopes to auto-reactive T cells. Our findings appear to conflict with this hypothesis. Potential mechanisms of relapse suppression by pertussis toxin will be discussed.