MicroRNAs are small noncoding RNAs that regulate gene expression post-transcriptionally. Here we applied microRNA profiling to 17 human lymphocyte subsets to identify microRNA signatures that were distinct among various subsets and different from those of mouse lymphocytes. One of the signature microRNAs of naive CD4+ T cells, miR-125b, regulated the expression of genes encoding molecules involved in T cell differentiation, including IFNG, IL2RB, IL10RA and PRDM1. The expression of synthetic miR-125b and lentiviral vectors encoding the precursor to miR-125b in naive lymphocytes inhibited differentiation to effector cells. Our data provide an 'atlas' of microRNA expression in human lymphocytes, define subset-specific signatures and their target genes and indicate that the naive state of T cells is enforced by microRNA.

No abstract

Follicular helper T cells (Ts) are a key component of adaptive immune responses as they help antibody production by B cells. Differentiation and function of T cells are controlled by the master gene , but it is largely unclear how this transcription repressor specifies the T program. Here we asked whether BCL6 controlled helper function through down-regulation of specific microRNAs (miRNAs). We first assessed miRNA expression in T cells and defined a T-specific miRNA signature. We report that hsa-miR-31-5p (miR-31) is down-regulated in T; we showed that BCL6 suppresses miR-31 expression by binding to its promoter; and we demonstrated that miR-31 inhibits the expression of molecules that control T-helper function, such as CD40L and SAP. These findings identify a BCL6-initiated inhibitory circuit that stabilizes the follicular helper T cell program at least in part through the control of miRNA transcription. Although BCL6 controls T activity in human and mouse, the role of miR-31 is restricted to human T cell differentiation, reflecting a species specificity of the miR-31 action. Our findings highlight miR-31 as a possible target to modulate human T cell dependent antibody responses in the settings of infection, vaccination, or immune dysregulation.

Adenosine deaminase (ADA)-SCID is characterized by increased purine metabolites and severe combined immunodeficiency. Autoimmune manifestations have been observed in milder forms or after enzyme replacement therapy (ERT), and recently in patients following gene therapy (GT). nTregs have a full enzymatic machinery to generate and sustain high concentrations of extracellular adenosine and may be involved in the pathogenesis of autoimmunity. We analyzed the frequency of CD4+CD25+FOXP3+CD127- in the peripheral blood, the methylation profile of the FoxP3 gene and the suppressive function of nTreg in ADA-SCID patients following ERT, GT or bone marrow transplant (BMT) as compared to controls. We found that the proportion and function of nTregs after GT mirrored that of controls, while nTreg from the ERT group showed a reduced frequency and impaired function. We also investigated the maturation state of B cells in the peripheral blood of ADA-SCID patients. After ERT and early after GT, patients displayed an increased proportion of transitional B cells (CD24highCD38high) and of cells with an incomplete BCR (CD21-CD35-) as compared to BMT and healthy controls. At later follow up patients treated with GT showed a tendency to normalize the phenotype in parallel to an increased frequency of gene corrected cells. Collectively, these data provide a first indication of predisposition to autoimmunity in ADA-SCID and the role of different treatments in the maintenance of peripheral tolerance.

In Supplementary Table 7, the sequence of the primer hTelo forward was incorrectly listed as 5'-GGA CAC GTT ATT TAC CCT GTT TCG-3'. The correct sequence is 5'-GGC ACA CGT GGC TTT TCG-3' .