Human CD8+CD25 +CD127 low regulatory T cells: microRNA signature and impact on TGF-β and IL-10 expression

Regulatory T cells (Tregs) are central for maintaining immune balance and their dysfunction drives the expansion of critical immunologic disorders. During the past decade, microRNAs (miRNAs) have emerged as potent regulators of gene expression among which immune-related genes and their immunomodulatory properties have been associated with different immune-based diseases. The miRNA signature of human peripheral blood (PB) CD8(+)CD25 (+)CD127 (low) Tregs has not been described yet. We thus identified, using TaqMan low-density array (TLDA) technique followed by individual quantitative real-time polymerase chain reaction (qRT-PCR) confirmation, 14 miRNAs, among which 12 were downregulated whereas two were upregulated in CD8 (+)CD25 (+)CD127 (low) Tregs in comparison to CD8 (+)CD25 (-) T cells. In the next step, microRNA Data Integration Portal (mirDIP) was used to identify potential miRNA target sites in the 3 '-untranslated region (3 '-UTR) of key Treg cell-immunomodulatory genes with a special focus on interleukin 10 (IL-10) and transforming growth factor beta (TGF-beta). Having identified potential miR target sites in the 3 '-UTR of IL-10 (miR-27b-3p and miR-340-5p) and TGF-beta (miR-330-3p), we showed through transfection and transduction assays that the overexpression of two underexpressed miRNAs, miR-27b-3p and miR-340-5p, downregulated IL-10 expression upon targeting its 3 '-UTR. Similarly, overexpression of miR-330-3p negatively regulated TGF-beta expression. These results highlighted an important impact of the CD8 (+) Treg mirnome on the expression of genes with significant implication on immunosuppression. These observations could help in better understanding the mechanism(s) orchestrating Treg immunosuppressive function toward unraveling new targets for treating autoimmune pathologies and cancer.