Enhanced killing of triple-negative breast cancer cells by blocking LLT1-CD161 inhibitory signal to NK cells

Abstract

Abstract Triple-negative breast cancer (TNBC) is known to be the most invasive form of breast cancer due to the lack of expression of estrogen, progesterone, and human epidermal growth factor-2 receptors, which makes it difficult to eradicate tumor growth with conventional chemotherapeutic and hormonal treatments. TNBC accounts for approximately 20 percent of all breast cancer cases and is associated with poorer prognosis and higher incidences of relapse. Hence, natural killer cell-mediated immunotherapy is a promising option for treatment of TNBC. Natural killer cells (NK) are innate lymphoid cells that magnifies its role within the immune system to recognize and lyse infected and tumor cells. NK cells regulate its own function through its receptors interacting with activating and inhibitory ligands on target cells. Lectin-like Transcript-1 (LLT1, CLEC2D, OCIL) is a counter-receptor that interacts with CD161 (NKRP1A) and suppresses NK cell activation. We have identified the expression and function of LLT1 on TNBC cell lines MDA-MB-231 and MDA-MB-436 by flow cytometry, western blot, immunofluorescent microscopy, and chromium-release assay. Blocking LLT1 on TNBCs with antibodies disrupts interaction with CD161 and enhanced NK cell-mediated lysis of TNBCs. We have also shown that gene knockdown of LLT1 decreased cell surface expression of LLT1 and increased lysis of TNBCs. Our results demonstrate that expression of LLT1 on TNBCs function in evasion from immunosurveillance by NK cells. Blocking interaction of LLT1-CD161 on TNBCs activates NK-mediated lysis and will potentially open a new immunotherapeutic strategy for patients diagnosed with TNBC.