Immune modulatory microRNAs as a novel mechanism to revert immune escape of tumors.

Tumors have developed different strategies to escape immune recognition. This could be due to altered expression of classical and non-classical human leukocyte antigens (HLA), co-inhibitory or co-stimulatory molecules as well as components of the interferon signaling pathway. Furthermore, changes in the tumor microenvironment negatively interfere with anti-tumor immune responses and the frequency and activity of immune effector cells and professional antigen presenting cells (APC), while the number of immune suppressive cells is increased. Recently, microRNAs (miRNA) identified known as important players in the posttranscriptional regulation of gene expression have been demonstrated to be differentially expressed in tumors of distinct origin and present in nanovesicles secreted by tumors. They not only exhibit tumor suppressive and oncogenic potential, but also immune modulatory functions. This review focusses on the role of miRNA in posttranscriptional control of immune modulatory molecules in tumors and in exosomes, which might represent prognostic biomarkers and novel therapeutic targets.