Abstract
Pancreatic ductal adenocarcinoma (PDA) is associated with an immunosuppressive tumor-microenvironment (TME) that supports the growth of tumors and mediates tumors enabling evasion of the immune system. Expression of programmed cell death ligand 1 (PD-L1) and loss of human leukocyte antigen (HLA) class I on tumor cells are methods by which tumors escape immunosurveillance. We examined immune cell infiltration, the expression of PD-L1 and HLA class I by PDA cells, and the correlation between these immunological factors and clinical prognosis. PDA samples from 36 patients were analyzed for HLA class I, HLA-DR, PD-L1, PD-1, CD4, CD8, CD56, CD68, and FoxP3 expression by immunohistochemistry. The correlations between the expression of HLA class I, HLA-DR, PD-L1 or PD-1 and the pattern of tumor infiltrating immune cells or the patients' prognosis were assessed. PD-L1 expression correlated with tumor infiltration by CD68+ and FoxP3+ cells. Low HLA class I expression was an only risk factor for poor survival. PD-L1 negative and HLA class I high-expressing PDA was significantly associated with higher numbers of infiltrating CD8+ T cells in the TME, and a better prognosis. Evaluation of both PD-L1 and HLA class I expression by PDA may be a good predictor of prognosis for patients. HLA class I expression by tumor cells should be evaluated when selecting PDA patients who may be eligible for treatment with PD-1/PD-L1 immune checkpoint blockade therapies.
The expression of PD-L1 did not alter the patients' prognosis if their tumors were HLA class I low, but it did for those with HLA class I high tumors. These findings suggest that the evaluation of PD-L1 and HLA class I expression is useful to predict the patients' prognosis and HLA class I should be a new biomarker to select patients who may benefit from anti-PD-1/PD-L1-based immunotherapy.
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