Furthermore, PD-L1 reverse signaling is of importance in cancer stem cells (CSCs), where transcription factors like OCT4 or SOX2 were shown to upregulate PD-L1 expression, while PD-L1 signaling activated pathways regulating stemness, such as PI3K/AKT/mTOR, MAPK, or β-catenin [40]. Here, POU5F1 is linked to cancer.