Variable density of CD8+ and CD25+ programmed cell death-1 (PD-1) ligand (PD-L1) CD4+ T cells within the tumor microenvironment causes differential responses to the PD-1/PD-L1 blockade

The programmed cell death-1 (PD-1)/programmed cell death-1 ligand (PD-L1) pathway has been shown to play a pivotal role in tumor evasion. Inhibition of PD-1 and its ligand PD-L1 using an immune checkpoint inhibitor has emerged as a promising immunotherapy for the treatment of various types of cancer. The expression of PD-L1 in tumor cells and tumor-infiltrating lymphocytes (TILs) has been shown to be correlated with improved efficacy of antibodies against PD-1 or PD-L1. Moreover, the density of CD8 TILs has been shown to be correlated with the response to immunotherapy. In this study, we examined the expression of PD-L1, CD25, PD-1, FoxP3, CD4, CD8, and EpCAM in 42 peripheral blood samples and fresh tumor specimens using multiparametric flow cytometry. Our results showed that the percentages of PDL1-expressing CD25 CD4 T cells were significantly higher in TILs than in peripheral blood lymphocytes (PBLs; TILs: mean, 48.6%; range, 23.6–81.5% versus PBLs: mean, 35.4%; range, 16.8–64.3%; P < 0.001). The density of CD25 PD-L1 CD4 TILs positively correlated with that of PD-1 CD8 TILs but negatively correlated with interferon (IFN)-g and tumor necrosis factor (TNF)-b CD8 TILs. However, the high ratio of CD8 TILs to that of CD25 PD-L1 CD4 TILs or to EpCAM tumor cells were associated with high percentages of IFN-g and TNF-b CD8 TILs. Moreover, inhibition of PD-L1 and PD-1 decreased the density of CD25 PD-L1 CD4 cells and PD-1 CD8 TILs but increased the percentage of IFN-g and TNF-b CD8 cells. High ratios of CD8 TILs to CD25 PD-L1 CD4 TILs or to EpCAM tumor cells enhanced the activity of tumor-specific CD8 T cells after PD-1/PD-L1 blockade therapy. Taken together, our results highlighted the importance of CD25 PD-L1 CD4 TILs in mediating the tumor microenvironment immune response. Our findings also indicated that high ratios of CD8 TILs to CD25 PDL1 CD4 TILs or to EpCAM tumor cells in patients may be more effective after PD-1/PD-L1 blockade therapy. Thus, the variable density of CD8 and CD25 PD-L1 CD4 T cells within the tumor microenvironment caused differential responses to PD-1/PD-L1 blockade.