Immune Checkpoints as Promising Targets for the Treatment of Idiopathic Pulmonary Fibrosis?

Abstract

Idiopathic pulmonary fibrosis is a rare, progressive and fatal lung disease which affects approximately 5 million persons worldwide. Although pirfenidone and/or nintedanib treatment improves patients' wellbeing, the prognosis of IPF remains poor with 5-year mortality rates still ranging from 70 to 80%. The promise of the anti-cancer agent nintedanib in IPF, in combination with the recent notion that IPF shares several pathogenic pathways with cancer, raised hope that immune checkpoint inhibitors, the novel revolutionary anticancer agents, could also be the eagerly awaited ground-breaking and unconventional novel treatment modality limiting IPF-related morbidity/mortality. In the current review, we analyse the available literature on immune checkpoint proteins in IPF to explore whether immune checkpoint inhibition may be as promising in IPF as it is in cancer. We conclude that despite several promising papers showing that inhibiting specific immune checkpoint proteins limits pulmonary fibrosis, overall the data seem to argue against a general role of immune checkpoint inhibition in IPF and suggest that only PD-1/PD-L1 inhibition may be beneficial.

Keywords: IPF; PD-L1; idiopathic pulmonary fibrosis; immune checkpoints.

Figure 1

Schematic representation of the proposed mechanism by which the PD-1/PD-L1 axis contributes to pulmonary fibrosis. During IPF, PD-1 is expressed on CD4⁺ T cells whereas PD-L1 is expressed on fibroblasts. The subsequent cross-talk leads to STAT3-mediated IL17A and TGF-β production by the CD4⁺ T cells and pro-fibrotic responses by fibroblasts.