Abstract B76: Tumor microenvironment immunosuppression: Role of neglected molecules iron and HLA-G
Authors: Elliott Robert L. , Jiang Xian P. 
Published: February 2019

Introduction: If we are to improve cancer immunotherapy in Stage IV patients, we must address numerous inhibitory molecules in the tumor microenvironment. Many inhibitory factors have been described and there are many reports on the possible role of HLA-G in cancer immunosuppression; but little has been done to attack the role of iron and HLA-G as a therapeutic target. This study was designed to determine if the neglected molecules, iron and HLA-G, contribute to tumor microenvironment immunosuppression, and might be therapeutic targets for cancer immunotherapy.

Methods: We manipulated intracellular iron levels of human MCF-7 and MDA-MB-231 breast cancer cell lines. The cytolysis of these cell lines was measured after exposure to the natural killer cell line NK-92 MI (NK). The production of nitric oxide (NO) and tumor necrosis factor alpha (TNFα) were determined, as was, the gene expression of ferritin heavy chain (FTH1). Reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC) were used to examine HLA-G expression in normal mammary and breast cancer cell lines and normal and human breast cancer tissues.

Results: NK-92 MI cells increased the synthesis and release of NO and TNF-α into the medium when co-cultured with MCF-7 and MDA-MB-231 cells. Addition of iron inhibited the cytolysis of the cancer cell lines. The iron chelator deferoxamine (DFOM) increased NK-92 MI cytolysis of MCF-7 and MDA-MB-231 cells. Iron reversed the cytotoxicity of breast cancer cells induced by NO released from S-nitroso-N-acetyl-penicillamine (NO donor). RT-PCR showed that iron upregulated the expression of FTH1, while the iron chelator reduced FTH1 expression.

The role of HLA-G expression in cancer immunosuppression was evaluated by RT-PCR. This confirmed that normal epithelial MCF-12A cells had no mRNA expression, while the cancer cell lines MCF-7, MDA-MB-231, and T-47D had various levels of HLA-G mRNA expression. IHC was performed on 12 normal and 38 breast cancer tissues. Fifty-eight percent (22/38) of cancers had medium to strong staining, while only 8% (1/12) of normal tissues had medium staining. The difference was significant (p &lt;0.05).

Summary and Conclusion: Increased iron in cancer cells and their microenvironment inhibits cancer cell cytolysis by NK cells by antagonizing NO and TNFα associated cytotoxicity and the up-regulation of ferritin expression. The HLA-G antigen immunotolerant molecule is expressed by trophoblastic placental cells to protect the fetus from maternal alloreactivity. Its expression in cancer cells also contributes to cancer immunosuppression. We hope by this presentation that researchers will be stimulated to investigate the role of iron and HLA-G as therapeutic targets of the cancer microenvironment. Inhibition of these targets will improve cancer immunotherapy in Stage IV patients.

Citation Format: Robert L. Elliott, Xian P. Jiang. Tumor microenvironment immunosuppression: Role of neglected molecules iron and HLA-G [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr B76.