Low CD8(+) T Cell Infiltration and High PD-L1 Expression Are Associated with Level of CD44(+)/CD133(+) Cancer Stem Cells and Predict an Unfavorable Prognosis in Pancreatic Cancer

Cancer immunotherapy targeting immune checkpoints has exhibited promising clinical outcomes in many cancers, but it offers only limited benefits for pancreatic cancer (PC). Cancer stem cells (CSCs), a minor subpopulation of cancer cells, play important roles in tumor initiation, progression, and drug resistance. Accumulating evidence suggests that CSCs employ immunosuppressive effects to evade immune system recognition. However, the clinical implications of the associations among CD8(+) T cells infiltration, programmed death receptor ligand-1 (PD-L1) expression, and CSCs existence are poorly understood in PC. Immunostaining and quantitative analysis were performed to assess CD8(+) T cells infiltration, PD-L1 expression, and their relationship with CD44(+)/CD133(+) CSCs and disease progression in PC. CD8(+) T cells infiltration was associated with better survival while PD-L1 expression was correlated with PC recurrence. Both the low CD8(+) T cells infiltration/high PD-L1 expression group and the high CD8(+) T cells infiltration/high PD-L1 expression group show high levels of CD44(+)/CD133(+) CSCs, but patients with low CD8(+) T cells infiltration/high PD-L1 expression had worse survival and higher recurrence risk than those with high CD8(+) T cells infiltration/high PD-L1 expression. Moreover, high infiltration of CD8(+) T cells could reduce unfavorable prognostic effect of high co-expression of PD-L1 and CD44/CD133. Our study highlights an interaction among CD8(+) T cells infiltration, PD-L1 expression, and CD44(+)/CD133(+) CSCs existence, which contributes to PC progression and immune evasion.