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 PD-L1-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)-γ⁺ and tumor necrosis factor (TNF)-β⁺ 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-γ⁺ and TNF-β⁺ 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-γ⁺ and TNF-β⁺ 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⁺ PD-L1⁺ 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.

Figure 2

Correlation between the clinicopathologic characteristics and PD-1+CD8 TIL or PD-L1+CD4 TIL in 42 lung cancer patients.