Because dysfunctional T cells exhibit reduced cytotoxicity[16b] and RNase1‐high expressing patients with head and neck squamous cell carcinoma (HNSC) and breast cancer associates with T‐cell exhaustion signatures (Figure 1D), we conducted T‐cell killing assays through RNase1 knockdown (sh‐R1#1 and sh‐R1#2) in FaDu HNSC cells or RNase1 knockout (KO‐R1) in KPL4 cells (Figure S2G,I, Supporting Information). Here, RNASE1 is linked to breast cancer.