In Europe, lung cancer is the second most diagnosed cancer in men and the third most diagnosed cancer in women. Tumor-infiltrating T cells are known to show the cell surface expression of programmed cell death protein 1 (PD-1) promoting immune suppression by programmed cell death 1 ligand 1 (PD-L1) interaction. Here we aimed to investigate the proportions of PD-1+ T cells in bronchoalveolar lavage (BAL) samples from lung cancer patients to evaluate its diagnostic potential.

In a prospective study, immune cells were isolated from BAL samples of patients with lung cancer (n=14), interstitial lung disease (ILD) (n=10) or asthma (n=10) at the Department of Pulmonology at the Medical University of Vienna in Austria. Flow cytometry was applied to identify proportions of PD-1 expressing CD4+ and CD8+ T cells.

BAL samples of patients with ILD showed the highest median proportion of PD-1+CD4+ and PD-1+CD8+ T cells (83.1% [IQR 72.1; 87.5] and 73.8% [IQR 60.3; 86.3]) followed by lung cancer (66.4% [IQR 59; 69] and 77.1% [IQR 35.8; 82.3]) and asthma (61.3% [IQR 57.4; 70.5] and 57.3% [IQR 46; 65]). Despite the difference in the proportion of PD-1+CD4+ BAL T cells between ILD patients and asthmatics (p=0.04), the PD-1+CD4+ and PD-1+CD8+ BAL T cell proportions between lung cancer patients, ILD patients and asthmatics were comparable (p>0.05).

BAL samples showed small differences in the proportions of PD1+ T cell subpopulations of lung cancer patients compared to ILD patients and asthmatics, which might be due to low sample size. However, the increased proportion of BAL PD1+CD4+ T cells of ILD patients warrants further investigation of their role in the PD-1/PD-L1 pathway in ILD pathobiology.