In contrast, Kwiecien et al. [27] looked at PD-1 expression on T cells in bronchoalveolar lavage fluids (BALF) and blood samples (PB) of NSCLC patients, and observed a significantly higher proportion of CD8+ and CD4+ cells with PD-1 expression in the BALF when compared with the PB. Here, CD4 is linked to non-small cell lung carcinoma.