STAT3 and glioblastoma: Furthermore, the enhancements of HM/GCM CM-induced or BMDM/ACM CM-induced PD-L1 expression in GBM were reduced by treatment with STAT3 inhibitor (S31-201) or MEK/ERK inhibitor (U0126) in human GBM (Figure 6E) and mouse GBM (Figure 6F).