Immunoreceptor TIGIT inhibits the cytotoxicity of human cytokine-induced killer cells by interacting with CD155

T cell Ig and ITIM domain (TIGIT) is a newly identified inhibitory receptor expressed on T and natural killer (NK) cells. Cytokine-induced killer (CIK) cells express CD3 and CD56 molecules, and share functional properties with both NK and T cells. However, it remains unknown whether TIGIT is expressed in CIK cells. Here, we show that TIGIT is expressed by CIK cells and interacts with CD155. By blocking TIGIT using an anti-TIGIT functional antibody, we demonstrate that CIK cells display increased proliferation; higher cytotoxic targeting of tumor cells expressing CD155; and higher expression of interferon-γ (IFN-γ), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α). Furthermore, increases in IFN-γ and cytotoxicity by blockade of TIGIT were reduced by blocking DNAX accessory molecule-1 (DNAM-1) signaling, implying that TIGIT exerts immunosuppressive effects by competing with DNAM-1 for the same ligand, CD155. Our results provide evidence that blockade of TIGIT may be a novel strategy to improve the cytotoxic activity of CIK cells.