Apolipoprotein E is a prognostic factor for pancreatic cancer and associates with immune infiltration.

Background: The expression level of apolipoprotein E (APOE) in pancreatic ductal adenocarcinoma (PDAC) and its effect on the prognosis of PDAC patients are not clear. The effect of APOE on the immune status of patients with PDAC has not been elucidated.

Methods: We obtained pancreatic cancer data from the TCGA and GETx databases. Patients with PDAC who underwent pancreatic surgery at the Second Affiliated Hospital of Jiaxing University between 2012 and 2021 were included. Clinical pathological data were recorded, plasma APOE levels were measured, and tissue samples were collected. A tissue microarray was generated using the collected tissue samples. APOE and CD4 staining was performed to determine immunoreactive scores (IRSs). The expression of APOE in the plasma and tumour tissues of pancreatic cancer patients was analysed and compared. The correlations between plasma APOE levels, tissue APOE levels and clinicopathological characteristics were analysed. Survival prognosis was analysed using Kaplan-Meier survival analysis and Cox multivariate regression analysis. The correlations between APOE expression levels and immune biomarkers and immune cells were further analysed. Single-cell analysis of APOE distribution in various cells was performed on the TISCH website.

Results: APOE was highly expressed in the tumour tissue of pancreatic cancer patients, and high plasma APOE levels were associated with poor prognosis. Females, patients with high-grade disease and patients with pancreatic head carcinoma had high plasma APOE levels. High APOE expression in tumour tissues was associated with good prognosis. Mononuclear macrophages in the pancreatic cancer microenvironment primarily expressed APOE. APOE levels positively correlated with immune biomarkers, such as CD8A, PDCD1, GZMA, CXCL10, and CXCL9, in the tumour microenvironment. APOE promoted CD4 + T cell or dendritic cell infiltration in the tumour microenvironment.

Conclusions: APOE may affect the occurrence and development of pancreatic cancer by regulating the infiltration of immune cells in the tumour microenvironment.