Inhibition of effector B cells by ibrutinib in systemic sclerosis

Systemic sclerosis (SSc) is a connective tissue disease with a significant morbidity and reduced survival of patients. Effective treatment and clinical control of the disease remain challenging. In particular, the development of pulmonary and cardiac fibrosis and pulmonary hypertension are severe complications responsible for excessive mortality. Currently available treatment strategies only alleviate symptoms and slow disease progression. Here, we investigated the therapeutic potential of ibrutinib, a Bruton's tyrosine kinase (BTK) inhibitor used in B cell malignancies, to alter B cell pathology in SSc in an in vitro model of autoimmunity.

PBMCs and sorted B cells of 24 patients with SSc were used for functional testing after stimulation with hypomethylated DNA fragments (CpG) to induce an innate immune response. The effects of ibrutinib on cytokine production, autoantibody release, and activation of the transcription factor NFκB were evaluated.

Ibrutinib was able to reduce the production of the profibrotic hallmark cytokines IL-6 and TNF-α mainly from the effector B cell population in patients with SSc. Importantly, small doses of ibrutinib (0.1 μM) preserved the production of immunoregulatory IL-10 while effectively inhibiting hyperactivated, profibrotic effector B cells. In a flow cytometry analysis of phosphorylated NFκB, an important transcription factor in the induction of innate immune responses in B cells, significantly less activation was observed with ibrutinib treatment.

Our data could pave the avenue for a clinical application of ibrutinib for patients with SSc as a novel treatment option for the underlying pathogenetic immune imbalance contributing to disease onset and progression.