Differential expression of PD­L1 and PD­L2 is associated with the tumor microenvironment of TILs and M2 TAMs and tumor differentiation in non­small cell lung cancer.

To improve the treatment strategy of immune­checkpoint inhibitors for non­small cell lung cancer (NSCLC), a comprehensive analysis of programmed death­ligand (PD­L)1 and PD­L2 expression is clinically important. The expression of PD­L1 and PD­L2 on both tumor cells (TCs) and tumor­infiltrating immune cells (ICs) was investigated, with respect to tumor­infiltrating lymphocytes (TILs) and M2 tumor­associated macrophages (TAMs), which are key components of the tumor microenvironment, in 175 patients with resected NSCLC. The TIL and M2 TAM densities were associated with the expression of PD­L1 on the two TCs (both P<0.0001) and ICs (both P<0.0001). The TIL and M2 TAM densities were also associated with the expression of PD­L2 on both TCs (P=0.0494 and P=0.0452, respectively) and ICs (P=0.0048 and P=0.0125, respectively). However, there was no correlation between the percentage of PD­L1­positive TCs and the percentage of PD­L2­positive TCs (r=0.019; P=0.8049). Meanwhile, tumor differentiation was significantly associated with the PD­L1 expression on TCs and ICs (P=0.0002 and P<0.0001, respectively). By contrast, tumor differentiation was inversely associated with the PD­L2 expression on both TCs and ICs (P=0.0260 and P=0.0326, respectively). In conclusion, the combined evaluation of PD­L1 and PD­L2 expression could be clinically important in the treatment strategy of immune­checkpoint inhibitors in patients with NSCLC. In particular, the evaluation of PD­L2 expression may be necessary for patients with PD­L1­negative NSCLC.