sHLA-G as a biomarker for colorectal cancer pathogenesis

Abstract

Objectives: Colorectal cancer (CRC) is a serious gastrointestinal disease. Cancer cells can survive in a microenvironment that includes distinct immune cells, various immune checkpoints including HLA-G, and different immune effectors such as interleukin-6 (IL-6), TNF-alpha (TNF-α), and interferon-gamma (IFN-γ). Thus, the objective of this study was to investigate HLA-G involvement in CRC as a prognostic factor in the Tunisian population, both in its soluble form (sHLA-G) and in its form linked to extracellular vesicles (HLA-GEV). Additionally, we examined its association to the secretion of cytokines. Methods: Fifty Tunisian patients, diagnosed with CRC, matched with ninety-eight healthy blood donors (HD) were enrolled in this study. Levels of sHLA-G, HLA-GEV, IL-6, TNF-α, and IFN-γ were dosed in plasma samples using specific ELISA. For the functional assay, we assessed sHLA-G effects on the production of cytokines by stimulated T lymphocytes. We measured the concentration of IL-6, TNF-α, and IFN-γ produced by activated T lymphocytes pre-stimulated by plasma sHLA-G and HLA-GEV. Results: Our case-control analysis showed high concentration of both sHLA-G (8.8 [0–63] ng/ml vs. 2.1 [0–63] ng/ml, p < 0.0001) and HLA-GEV (0.9 [0–17.8] ng/ml vs. 0.3 [0–31.0] ng/ml, p = 0.018) in CRC patients compared to HD. Concerning cytokines, IL-6 exclusively increased compared to HD (7.1[0.0–104.0] pg/ml vs. 3.6[0.0–58.22] pg/ml, p = 0.005). The evaluation of diagnostic performance using the receiver operating characteristic (ROC) curves and the area under the curve (AUC) showed sHLA-G (AUC = 0.828) as the more adequate biomarker in colorectal carcinoma prediction compared to HLA-GEV (AUC = 0.615) and IL-6 (AUC = 0.664). We found that sHLA-G is able to decrease IL-6, TNF-α, and IFN-γ production by stimulated T lymphocytes in a concentration-independent manner. Additionally, HLA-GEV appears to downregulate solely IL-6 release by stimulated T lymphocytes. Interestingly, HLA-GEV was related to lymph node infiltration, which represents the most common metastatic route for colorectal cancer via the lymphatic system. Conclusions: We outlined the importance of sHLA-G and HLA-GEV as substantial immune biomarkers in CRC. Our findings suggest that HLA-G could be an effective diagnostic tool for colorectal cancer.

Keywords

• Colorectal cancer
• sHLA-G
• Extracellular vesicles
• Cytokines
• T lymphocytes