PD-1/PD-L1 axis regulation in cancer therapy: The role of long non-coding RNAs and microRNAs.

Cancer immunotherapy is a growing field nowadays. Among different molecular pathways, PD-1/PD-L1 signaling pathway plays a significant role in the regulation of immune responses. It has been reported that stimulation of PD-1/PD-L1 axis is correlated with T cell exhaustion, T cell apoptosis, and their reduced capability in proliferation. PD-1/PD-L1 axis provides a condition for immune evasion of cancer cells and interferes with anti-tumor immunity. Much attention has been directed towards targeting PD-1/PD-L1 axis in cancer immunotherapy. It seems that identification of upstream modulators of this axis can broaden our understanding to develop novel anti-tumor drugs for cancer immunotherapy. MicroRNAs (miRs) and long non-coding RNAs (lncRNAs) are key subcategories of non-coding RNAs, since they can regulate various biological processes by targeting different molecular pathways. In this review, we demonstrate that onco-suppressor miRs and lncRNAs inhibit PD-1/PD-L1 axis to provide anti-tumor immunity and in this way, other molecular pathways such as STAT, ZEB, PI3K/Akt and so on may be targeted. In contrast, oncogene miRs and lncRNAs induce PD-1/PD-L1 axis. Identification of miR/PD-1 and lncRNA/PD-1 signaling pathways can help us in finding an effective drug for cancer immunotherapy, and can direct us towards genetic manipulation of the aforementioned pathways.