SUSD2 suppresses CD8⁺ T cell antitumor immunity by targeting IL-2 receptor signaling

Dysfunctional CD8⁺ T cells, which have defective production of antitumor effectors, represent a major mediator of immunosuppression in the tumor microenvironment. Here, we show that SUSD2 is a negative regulator of CD8⁺ T cell antitumor function. Susd2^−/− effector CD8⁺ T cells showed enhanced production of antitumor molecules, which consequently blunted tumor growth in multiple syngeneic mouse tumor models. Through a quantitative mass spectrometry assay, we found that SUSD2 interacted with interleukin (IL)-2 receptor α through sushi domain-dependent protein interactions and that this interaction suppressed the binding of IL-2, an essential cytokine for the effector functions of CD8⁺ T cells, to IL-2 receptor α. SUSD2 was not expressed on regulatory CD4⁺ T cells and did not affect the inhibitory function of these cells. Adoptive transfer of Susd2^−/− chimeric antigen receptor T cells induced a robust antitumor response in mice, highlighting the potential of SUSD2 as an immunotherapy target for cancer.