Introduction: Nintedanib is an anti-fibrotic tyrosine kinase inhibitor used to treat idiopathic pulmonary fibrosis (IPF). Although its primary target is the fibrotic process, it may also affect T cell receptor (TCR) and B cell receptor (BCR)-mediated signaling. However, whether and how nintedanib modulates adaptive immunity in IPF patients remains poorly understood.

Objectives: To identify effects of nintedanib treatment on T and B cell receptor signaling and effector function in HC blood samples in vitro, and in IPF patients in vivo. 

Materials and Methods: Peripheral blood mononuclear cells (PBMCs) from healthy controls (HCs) and IPF patients, collected before and after 7 weeks of nintedanib treatment, were pre-treated with nintedanib for 1 hour ex vivo. Subsequently, intracellular signaling and cytokine production were measured by (phospho)flowcytometry upon BCR (anti-Ig) or TCR (anti-CD3/CD28) stimulation.

Results: Naïve B cells, but not memory B cells from IPF patients showed increased BCR signaling (BTK phosphorylation) compared to HCs, suggesting a pre-activated phenotype in IPF. Furthermore, after 7 weeks of treatment, we observed opposite effects of nintedanib in vivo on BCR signaling, whereby low baseline BCR signaling correlated with higher post-treatment signaling, and vice versa. Upon pre-treatment with nintedanib in vitro, both BCR and TCR-mediated signaling were inhibited in HC PBMCs. Moreover, cytokine production, including IFNγ, by CD4 and CD8 T cells was significantly reduced upon treatment. 

Conclusions: Together, these data show that naïve B cells in IPF patients have a pre-activated state compared to HC, and signaling is rewired upon in vivo nintedanib treatment. In vitro treatment with nintedanib inhibits BCR and TCR-mediated signaling and cytokine production. These findings suggest that nintedanib exerts immunomodulatory effects extending beyond fibrosis, with implications for adaptive immunity as a therapeutic target in IPF.