Characterization of circulating immune cells and correlation with Tie2/Angiopoietins level in well differentiated neuroendocrine gastroenteropancreatic tumors: a cross-sectional analysis

Purpose: The immune environment represents a new, but little explored, tool for understanding neuroendocrine neoplasms (NENs) behavior. An immunosuppressed microenvironment is hypothesized to promote NENs progression. A missing profiling of circulating leukocyte and peripheral blood mononuclear cells (PBMCs) subpopulations would open new perspectives in the still limited diagnostic-therapeutic management of NENs. Methods: A cross-sectional case-control pilot study was performed recruiting 30 consecutive subjects: 15 patients naïve to treatment, with histologically proven gastroenteropancreatic (GEP) neuroendocrine tumors (NETs) and 15 healthy controls, matched for age and sex. PBMCs subpopulations were studied by flow cytometry. Soluble Tie2 (sTie2), Angiopoietin-1 (Ang-1), Angiopoietin-2 (Ang-2) were evaluated by ELISA. Results: Immune cell profiling revealed a significant lower CD3⁻CD56⁺natural killer (NK) cell count in NETs vs controls (p= 0.04). NK subset analysis showed a reduced relative count of CD56⁺CD16⁺NK cells (p=0.002) in NETs vs controls. Patients with NET showed a higher percentage of CD14⁺CD16⁺⁺non-classical monocytes (p= 0.01), and a lower percentage of CD14⁺CD16⁺intermediate monocytes (p= 0.04). A decrease in percentage (p= 0.004) of CD4⁺T-helper lymphocytes was found in NET patients. Evaluation of cellular and serum angiopoietin pathway mediators revealed in NET patients a higher relative count of Tie2-expressing monocytes (TEMs) (p< 0.001), and high levels of Ang-1 (p= 0.003) and Ang-2 (p= 0.002). Conclusions: Patients with GEP-NET presented an immunosuppressed environment characterized by a low count of cytotoxic NK cells, a high count of anti-inflammatory non-classical monocytes, and a low count of T-helper lymphocytes. Higher levels of TEMs and angiopoietins suggest a crosstalk between innate immunity and angiogenic pathways in NETs.