Human Leukocyte Antigen-G Inhibits the Anti-Tumor Effect of Natural Killer Cells via Immunoglobulin-Like Transcript 2 in Gastric Cancer

Background/Aims: Human leukocyte antigen-G (HLA-G) plays an important role in inhibiting natural killer (NK) cell function and promoting immune escape. However, the specific mechanism of HLA-G on NK in gastric cancer (GC) remains not well understood. This study investigated the expression of HLA-G in GC and the role of HLA-G-effected NK cells in GC progression. Methods: HLA-G expression in GC tissues obtained from 49 patients with GC was analyzed by immunohistochemistry and western blot. The number of tumor-infiltrating NK cells and the expression of their surface receptors were analyzed by immunohistochemistry and flow cytometry, respectively. The effect of HLA-G on NK cell proliferation was examined by Cell Counting Kit-8 (CCK8) assay. LDH release assay was used to evaluate the effect of HLA-G on the cytotoxic activity of NK cells, and the levels of IFN-gamma and TNF-alpha in the co-cultured supernatant were detected by ELISA. Mice bearing a xenograft tumor model were used to examine the effect of HLA-G on the anti-tumor effect of NK cells. Results: HLA-G positive expression was detected in most of the GC tissues, and was correlated with the adverse prognosis of the disease. The expression of HLA-G was negatively associated with the number of tumor-infiltrating NK cells. Furthermore, GC cell lines with overexpressed HLA-G revealed their ability to inhibit the cell proliferation and cytotoxic activity of NK-92MI cells, and reduce the secretion of IFN-. and TNF-a through immunoglobulin-like transcript 2 (ILT2). Finally, this in vivo experiment was able to prove that HLA-G can inhibit the anti-tumor effect of NK cells through ILT2. Conclusion: The expression of HLA-G was strongly correlated with the adverse prognosis of GC. The reason may be that it inhibits the proliferation and cytotoxic activity of infiltrating NK cells through ILT2. (C) 2017 The Author(s) Published by S. Karger AG, Basel