STAT3 and neoplasm: Furthermore, blockade of G‐CSF in tumor cell culture supernatant/neutrophil co‐culture efficiently inhibited the induction of PD‐L2 on neutrophils; provision of exogenous G‐CSF into non‐tumor cell culture supernatant/neutrophil co‐culture significantly increased PD‐L2 expression on neutrophils (Figure 5G; Figure S11D, Supporting Information); STAT3 was predominantly phosphorylated in neutrophils after treatment with tumor cell culture supernatants, and this phosphorylation was abolished when blocking G‐CSF (Figure 5I).