IRF4 and melanoma: However, in a melanoma immunotherapy study, inhibiting SLC7A11 expression on tumor cells led to upregulation of intracellular transcription factors such as IRF4 (interferon regulatory factor 4) and EGR1 (early growth response protein 1), which in turn increased PD-L1 expression and significantly reduced the efficacy of PD-1/PD-L1 inhibitors [189].