NFKB1 and neoplasm: We found that tumor cell culture supernatants were superior to non‐tumor cell culture supernatants in inducting neutrophil PD‐L2 expression in both time‐ and dose‐dependent manners (Figure 5F; Figure S11A, Supporting Information) via activation of ERK‐NF‐κB signaling pathway (Figure S11B,C, Supporting Information).