Targeting microRNAs for immunomodulation

microRNAs (miRNA) are small regulatory RNAs exerting pleiotropic functions in virtually any immune cell-type. Dozens of miRNAs with a known function in the immune system constitute interesting drug targets for immunomodulation. Chemical modifications of nucleic acid-based miRNA mimics and inhibitors largely solved instability issues but delivery to immune cells remains a major challenge. However, recent success targeting the acidic tumor microenvironment is very promising for inflammatory diseases. Moreover, small molecules are being explored as an interesting alternative. Although RNA is often considered 'undruggable' by small molecules recent progress modulating miRNA function through small molecules is encouraging. Computational approaches even allow predictions about specific small molecule/RNA interactions. Finally, recent clinical success demonstrates that drugs targeting RNAs work in humans

microRNA-17-92 regulates IL-10 production by regulatory T cells and control of experimental autoimmune encephalomyelitis

microRNAs (miRNA) are essential for regulatory T cell (Treg) function but little is known about the functional relevance of individual miRNA loci. We identified the miR-17-92 cluster as CD28 costimulation dependent, suggesting that it may be key for Treg development and function. Although overall immune homeostasis was maintained in mice with miR-17-92-deficient Tregs, expression of the miR-17-92 miRNA cluster was critical for Treg accumulation and function during an acute organ-specific autoimmune disease in vivo. Treg-specific loss of miR-17-92 expression resulted in exacerbated experimental autoimmune encephalitis and failure to establish clinical remission. Using peptide-MHC tetramers, we demonstrate that the miR-17-92 cluster was specifically required for the accumulation of activated Ag-specific Treg and for differentiation into IL-10-producing effector Treg

microRNA-17–92 Regulates IL-10 Production by Regulatory T Cells and Control of Experimental Autoimmune Encephalomyelitis

microRNAs (miRNA) are essential for regulatory T cell (Treg) function but little is known about the functional relevance of individual miRNA loci. We identified the miR-17–92 cluster as CD28 costimulation dependent, suggesting that it may be key for Treg development and function. Although overall immune homeostasis was maintained in mice with miR-17–92–deficient Tregs, expression of the miR-17–92 miRNA cluster was critical for Treg accumulation and function during an acute organ-specific autoimmune disease in vivo. Treg-specific loss of miR-17–92 expression resulted in exacerbated experimental autoimmune encephalitis and failure to establish clinical remission. Using peptide-MHC tetramers, we demonstrate that the miR-17–92 cluster was specifically required for the accumulation of activated Ag-specific Treg and for differentiation into IL-10–producing effector Treg

MicroRNAs 24 and 27 Suppress Allergic Inflammation and Target a Network of Regulators of T Helper 2 Cell-Associated Cytokine Production

MicroRNAs (miRNAs) are important regulators of cell fate decisions in immune responses. They act by coordinate repression of multiple target genes, a property that we exploited to uncover regulatory networks that govern T helper-2 (Th2) cells. A functional screen of individual miRNAs in primary T cells uncovered multiple miRNAs that inhibited Th2 cell differentiation. Among these were miR-24 and miR-27, miRNAs coexpressed from two genomic clusters, which each functioned independently to limit interleukin-4 (IL-4) production. Mice lacking both clusters in T cells displayed increased Th2 cell responses and tissue pathology in a mouse model of asthma. Gene expression and pathway analyses placed miR-27 upstream of genes known to regulate Th2 cells. They also identified targets not previously associated with Th2 cell biology which regulated IL-4 production in unbiased functional testing. Thus, elucidating the biological function and target repertoire of miR-24 and miR-27 reveals regulators of Th2 cell biology

Identification of MiR-205 As a MicroRNA That Is Highly Expressed in Medullary Thymic Epithelial Cells

<div><p>Thymic epithelial cells (TECs) support T cell development in the thymus. Cortical thymic epithelial cells (cTECs) facilitate positive selection of developing thymocytes whereas medullary thymic epithelial cells (mTECs) facilitate the deletion of self-reactive thymocytes in order to prevent autoimmunity. The mTEC compartment is highly dynamic with continuous maturation and turnover, but the genetic regulation of these processes remains poorly understood. MicroRNAs (miRNAs) are important regulators of TEC genetic programs since miRNA-deficient TECs are severely defective. However, the individual miRNAs important for TEC maintenance and function and their mechanisms of action remain unknown. Here, we demonstrate that miR-205 is highly and preferentially expressed in mTECs during both thymic ontogeny and in the postnatal thymus. This distinct expression is suggestive of functional importance for TEC biology. Genetic ablation of miR-205 in TECs, however, neither revealed a role for miR-205 in TEC function during homeostatic conditions nor during recovery from thymic stress conditions. Thus, despite its distinct expression, miR-205 on its own is largely dispensable for mTEC biology.</p></div

Validation of miR-205 ablation in TECs.

<p><b>(A)</b> mTECs from 4–6 week old <i>miR-205</i>^CTRL and <i>miR-205</i>^ΔTEC mice were sorted to analyze miR-205 expression by qPCR. Reactions were normalized to sno202 and normalized to CD45⁺ cells. Values depict mean ±SD. Data is representative of two independent experiments. <b>(B)</b><i>in situ</i> hybridizations were performed using a miR-205 probe on frozen thymic sections from 4–6 week old <i>miR-205</i>^CTRL and <i>miR-205</i>^ΔTEC mice to confirm the uniform deletion of miR-205 in mTECs. Scale bars = 200 μm (top), and 100 μm (bottom).</p

Extralymphatic virus sanctuaries as a consequence of potent T-cell activation

T helper cells can support the functions of CD8(+) T cells against persistently infecting viruses such as murine lymphocytic choriomeningitis virus (LCMV), cytomegalovirus, hepatitis C virus and HIV. These viruses often resist complete elimination and remain detectable at sanctuary sites, such as the kidneys and other extralymphatic organs. The mechanisms underlying this persistence are not well understood. Here we show that mice with potent virus-specific T-cell responses have reduced levels and delayed formation of neutralizing antibodies, and these mice fail to clear LCMV from extralymphatic epithelia. Transfer of virus-specific B cells but not virus-specific T cells augmented virus clearance from persistent sites. Virus elimination from the kidneys was associated with the formation of IgG deposits in the interstitial space, presumably from kidney-infiltrating B cells. CD8(+) T cells in the kidneys of mice that did not clear virus from this site were activated but showed evidence of exhaustion. Thus, we conclude that in this model of infection, site-specific virus persistence develops as a consequence of potent immune activation coupled with reductions in virus-specific neutralizing antibodies. Our results suggest that sanctuary-site formation depends both on organ anatomy and on the induction of different adaptive immune effector mechanisms. Boosting T-cell responses alone may not reduce virus persistence

TEC miRNA profiling identifies miR-205 as highly expressed in mTECs.

<p><b>(A)</b> Thymic subsets were purified from 4–5 week old <i>NOD</i> wildtype mice for miRNA profiling by microarray analysis. The heatmap depicts the union of differentially expressed miRNAs from any comparison (FDR <0.05) with an absolute log2 fold change >1 relative to the signal intensity of CD45⁺ cells. <b>(B)</b> Plot depicts average log2 fold change (FC) between mTEC vs CD45⁺ cells on the <i>y</i>-axis and average log2 signal intensity across all samples on the <i>x</i>-axis. Red dots indicate genes that are differentially expressed in mTECs vs CD45⁺ cells with an FDR <0.05. <b>(C)</b> Thymic stromal subsets were FACS-purified from 4–6 week old <i>B6</i> wildtype mice to confirm the expression of miR-205 in mTECs by qPCR analysis. All reactions were standardized to sno202 and then normalized to CD45⁺ cells with error bars depicting mean ±SD.</p