NKG2D engagement on human NK cells leads to DNAM-1 hypo-responsiveness through different converging mechanisms

Natural killer (NK) cell activation is regulated by activating and inhibitory receptors that facilitate diseased cell recognition. Among activating receptors, NKG2D and DNAM-1 play a pivotal role in anticancer immune responses since they bind ligands upregulated on transformed cells. During tumor progression, however, these receptors are frequently downmodulated and rendered functionally inactive. Of note, NKG2D internalization has been associated with the acquisition of a dysfunctional phenotype characterized by the cross-tolerization of unrelated activating receptors. However, our knowledge of the consequences of NKG2D engagement is still incomplete. Here, by cytotoxicity assays combined with confocal microscopy, we demonstrate that NKG2D engagement on human NK cells impairs DNAM-1-mediated killing through two different converging mechanisms: by the upregulation of the checkpoint inhibitory receptor TIGIT, that in turn suppresses DNAM-1-mediated cytotoxic function, and by direct inhibition of DNAM-1-promoted signaling. Our results highlight a novel interplay between NKG2D and DNAM-1/TIGIT receptors that may facilitate neoplastic cell evasion from NK cell-mediated clearance.

Automated summary

The activation of natural killer (NK) cells is influenced by activating and inhibitory receptors which aid in identifying diseased cells. Among these receptors, NKG2D and DNAM-1 are crucial for the immune response against cancer as they bind to ligands expressed on transformed cells. However, during tumor progression, these receptors are often downregulated and lose their functionality. NKG2D internalization has been associated with dysfunctional phenotype characterized by tolerance to other activating receptors. Nevertheless, the consequences of NKG2D engagement are still incompletely understood. In this study, we demonstrate that NKG2D engagement impairs DNAM-1-mediated killing on human NK cells through two converging mechanisms: upregulation of the inhibitory receptor TIGIT, which suppresses DNAM-1-mediated cytotoxic function, and direct inhibition of DNAM-1 signaling. These findings reveal a novel interplay between NKG2D and DNAM-1/TIGIT receptors that may enable neoplastic cells to evade clearance by NK cells.