Evaluation of PD-1 T lymphocytes in bronchoalveolar lavage in lung cancer compared to benign lung diseases

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.