FcεRIγ reinforces double-negative T cell-mediated antibody-dependent cellular cytotoxicity against tumor cells.

Double-negative T (DNT) cells (TCRαβ+CD4-CD8-NK1.1-/CD56-) exhibit strong tumor-killing capabilities. Our single-cell transcriptome analysis has revealed high Fcer1g expression in DNT cells, but its role in tumor immunity remains unclear. In this study, we demonstrated that IgG1 stimulation significantly upregulated IgG Fc receptors and cytotoxic molecules in DNT cells, enhancing their cytotoxicity against MC38 tumor cells in vitro. FcεRIγ-deficient DNT cells failed to respond effectively to IgG1 stimulation. Inhibiting the downstream spleen tyrosine kinase (Syk) of FcεRIγ reduced cytotoxicity of DNT cells and phosphorylation levels of molecules such as AKT and NF-κB. In a subcutaneous tumor model, combined treatment with DNT cells and tumor-specific antibodies more effectively inhibited tumor growth compared to DNT cells alone, while FcεRIγ-deficient DNT cells combined with antibodies showed no significant difference in efficacy compared to DNT cells alone, suggesting that DNT cells enhance tumor cell killing via FcεRIγ-mediated antibody-dependent cellular cytotoxicity (ADCC). These results indicate that DNT cells mediate antitumor ADCC effects through high FcεRIγ expression. Binding of IgG1 to FcεRIγ activates the FcεRIγ/Syk/AKT/NF-κB pathway, consequently enhancing tumor cell killing. Thus, DNT cells may play a significant role in cancer immunity, providing a basis for novel immune cell and antibody combination therapies.