CRTAM Receptor Engagement by Necl-2 on Tumor Cells Triggers Cell Death of Activated Vγ9Vδ2 T Cells

Human Vγ9Vδ2 T cells exert potent in vitro and in vivo antitumor activities, making them promising candidates for immunotherapy strategies. Recognition of tumor cells by Vγ9Vδ2 T cells requires engagement of the TCR and/or NK receptors. Recently, one of the novel NK receptors, the class I–restricted T cell–associated molecule (CRTAM), has been described to promote cytotoxic function of NK cells and to lead to IFN-γ secretion by CD8+ T cells through interaction with its ligand, Necl-2. A better understanding of the role of CRTAM in Vγ9Vδ2 T cell functions is highly relevant to optimize innate-like T cell–based cancer immunotherapy. In this article, we report that CRTAM is transiently expressed on activated Vγ9Vδ2 T lymphocytes following TCR engagement. However, CRTAM–Necl-2 interaction does not modify the cytotoxic function or IFN-γ secretion of Vγ9Vδ2 T cells. The expression of CRTAM in activated Vγ9Vδ2 T cells is quickly downregulated following interaction with Necl-2 on tumor cells. Of interest, CRTAM is concurrently acquired at the cell surface of Necl-2+ tumor cells through Vγ9Vδ2 T cell membrane capture. Finally, we highlight that coculture experiments with tumor cells expressing Necl-2 result in significant cell death of CRTAM+ Vγ9Vδ2 T cells. CRTAM-mediated cell death is dependent on an autophagic process, but not on apoptosis or necroptosis, as attested by the expression of characteristic markers and blocking experiments with specific inhibitors. On the basis of these findings, we propose that Necl-2 on tumor cells represents a new tumor counterattack mechanism and a potential target to improve efficiency of γδ T cell–based immunotherapy.