Membrane PD-L1 expression and soluble PD-L1 plasma levels in idiopathic pulmonary fibrosis-a pilot study

Idiopathic pulmonary fibrosis (IPF) has common risk factors with cancer and significant similarities in the pathobiology process, both diseases having poor outcomes. Immune checkpoint PD-L1 has become the target of checkpoint inhibitory therapy that unleashes antitumor T cells and has revolutionized cancer treatment. This is a pilot study exploring membrane immune checkpoint PD-L1 expression in human IPF lung tissue samples and its soluble form, soluble PD-L1 (sPD-L1) plasma concentrations in IPF patients, in order to investigate potential role of PD-L1 as an IPF biomarker.

Twelve human IPF lung tissue samples (formalin-fixed, paraffin-embedded) obtained by surgical biopsy, have been tested for PD-L1 expression by PD-L1 IHC 22C3 pharmDx assay, while plasma samples for examination of sPD-L1 forms, PD-L1 (B7-H1/CD274) blood concentration, originated from 23 patients with IPF who did not undergo surgical biopsy.

Membrane PD-L1 expression in IPF lung tissue samples was positive to overexpression of PD-L1 in 9 samples out of 12. Only very few cells in the interstitium have shown a discrete PD-L1 expression, but not of a membrane type. As for sPD-L1 forms, we have found elevated concentrations of sPD-L1 in the serum of IPF patients 314.3 ng/L (117.7-483.1 ng/L), significantly higher compared with healthy control group 91.0 ng/L (52.4-119.7 ng/L), P<0.01.

For IPF with PD-L1 expression on alveolar macrophages, further studies are necessary to elucidate this phenomenon. Serum sPD-1/PD-L1 is easily detected in clinical practice and should be further evaluated as a potential prognostic or/and predictive biomarker in IPF.