Recent studies have identified that low levels of some tumour suppressor microRNAs (miRNAs) in the blood contribute to tumour progression and poor outcomes in various cancers. However, no study has proved these miRNAs are associated with cancer immune mechanisms.

From a systematic review of the NCBI and miRNA databases, four tumour suppressor miRNA candidates were selected (miR-5193, miR-4443, miR-520h, miR-496) that putatively target programmed cell death ligand 1 (PD-L1).

Test-scale and large-scale analyses revealed that plasma levels of miR-5193 were significantly lower in gastric cancer (GC) patients than in healthy volunteers (HVs). Low plasma levels of miR-5193 were associated with advanced pathological stages and were an independent prognostic factor. Overexpression of miR-5193 in GC cells suppressed PD-L1 on the surface of GC cells, even with IFN-γ stimulation. In the coculture model of GC cells and T cells stimulated by anti-CD3/anti-CD28 beads, overexpression of miR-5193 increased anti-tumour activity of T cells by suppressing PD-L1 expression. Subcutaneous injection of miR-5193 also significantly enhanced the tumour-killing activity and trafficking of T cells in mice.

Low blood levels of miR-5193 are associated with GC progression and poor outcomes and could be a target of nucleic acid immunotherapy in GC patients.