Abstract:

Background and purpose: Tumor-associated macrophages (TAM) as the main stromal cells in the tumor microenvironment play an important role in tumor progression. This study aimed to explore the clinical significance of M1 type TAM infiltration in hepatocellular carcinoma (HCC). Methods: We collected tissue paraffin samples from 320 HCC patients who underwent surgery at the Affiliated Nantong Hospital Three of Nantong University from January 2012 to December 2020. Immunohistochemical methods were used to detect the distribution of CD86 labeled M1 type TAM in HCC tissues, and positive cell density was calculated. Groups were established according to cell density, high-density group had cells with greater than average density (29 cells/mm²), and low-density group had cells with less than or equal to average density. The correlation and prognostic significance of M1 TAM density with clinicopathologic features and tumor infiltrating CD8^＋ T lymphocytes of HCC were analyzed. Using immunohistochemistry to detect the expression of programmed death ligand-1 (PD-L1), the cases were divided into four groups based on the cell density of CD86 and PD-L1. In the CD86^＋ high-density group, PD-L1 high-density (CD86^highPD-L1^high) and PD-L1 low-density (CD86^highPD-L1^low) groups were included. In the CD86^＋ low-density group, the PD-L1 high-density (CD86^lowPD-L1^high) and PD-L1 low-density (CD86^lowPD-L1^low) groups were included. We analyzed the prognostic significance of CD86^＋ M1 type TAM density combined with PD-L1 expression. This study was approved by the Ethics Committee of Affiliated Nantong Hospital Three of Nantong University (ethics number: EK2022005). Results: CD86^＋ M1 type TAM was mainly distributed in the tumor stroma. Its high-density rate was 44.7% (143/320). The density of CD86^＋ M1 type TAM was positively correlated with tumor infiltrating CD8^＋ T lymphocyte density (P<0.001) and negatively correlated with hepatitis B virus surface antigen (HBsAg) positivity (P=0.003), and had no significant correlation with clinical and pathological features such as patient age, gender, cirrhosis, tumor size, histological grading and microvascular invasion. The CD86^＋ M1 type TAM high-density group had better overall survival (OS) and disease-free survival (DFS) than the low-density group, and the differences were statistically significant (all P<0.001). Multivariate Cox proportional hazards regression model analysis showed that low-density CD86^＋ M1 type TAM was an independent risk factor for evaluating OS and DFS (OS: HR=1.468, P=0.022; DFS: HR=2.233, P<0.001). The CD86^highPD-L1^high group had poor OS and DFS than the CD86^highPD-L1^low group, and the differences were statistically significant (both P<0.05). The CD86^lowPD-L1^high group had poor OS and DFS than the CD86^lowPD-L1^low group. The difference in OS between the two groups was statistically significant (P<0.05), while the difference in DFS was not statistically significant. Conclusion: The presence of high-density CD86^＋ M1 type TAM in HCC tissue suggests a good prognosis and is an independent prognostic factor. Expression of PD-L1 in HCC tissue suggests increased invasiveness and poorer prognosis.

Key words: Macrophage, Programmed death ligand 1, Hepatocellular carcinoma, Prognosis