An essential role for miR-15/16 in Treg suppression and restriction of proliferation.

The miR-15/16 family is a highly expressed group of tumor suppressor miRNAs that target a large network of genes in T cells to restrict their cell cycle, memory formation and survival. Upon T cell activation, miR-15/16 are downregulated, allowing rapid expansion of differentiated effector T cells to mediate a sustained immune response. Here, using conditional deletion of miR-15/16 in immunosuppressive regulatory T cells (Tregs) that express FOXP3, we identify new functions of the miR-15/16 family in T cell immunity. miR-15/16 are indispensable to maintain peripheral tolerance by securing efficient suppression by a limited number of Tregs. miR-15/16-deficiency alters Treg expression of critical functional proteins including FOXP3, IL2Rα/CD25, CTLA4, PD-1 and IL7Rα/CD127, and results in accumulation of functionally impaired FOXP3loCD25loCD127hi Tregs. Excessive proliferation in the absence of miR-15/16 inhibition of cell cycle programs shifts Treg diversity and produces an effector Treg phenotype characterized by low expression of TCF1, CD25 and CD62L, and high expression of CD44. These Tregs fail to control immune activation of CD4+ effector T cells, leading to spontaneous multi-organ inflammation and increased allergic airway inflammation in a mouse model of asthma. Together, our results demonstrate that miR-15/16 expression in Tregs is essential to maintain immune tolerance.

miR-15/16 Restrain Memory T Cell Differentiation, Cell Cycle, and Survival.

Coordinate control of T cell proliferation, survival, and differentiation are essential for host protection from pathogens and cancer. Long-lived memory cells, whose precursors are formed during the initial immunological insult, provide protection from future encounters, and their generation is the goal of many vaccination strategies. microRNAs (miRNAs) are key nodes in regulatory networks that shape effective T cell responses through the fine-tuning of thousands of genes. Here, using compound conditional mutant mice to eliminate miR-15/16 family miRNAs in T cells, we show that miR-15/16 restrict T cell cycle, survival, and memory T cell differentiation. High throughput sequencing of RNA isolated by cross-linking immunoprecipitation of AGO2 combined with gene expression analysis in miR-15/16-deficient T cells indicates that these effects are mediated through the direct inhibition of an extensive network of target genes within pathways critical to cell cycle, survival, and memory.

Transcriptional Programming of Normal and Inflamed Human Epidermis at Single-Cell Resolution.

Perturbations in the transcriptional programs specifying epidermal differentiation cause diverse skin pathologies ranging from impaired barrier function to inflammatory skin disease. However, the global scope and organization of this complex cellular program remain undefined. Here we report single-cell RNA sequencing profiles of 92,889 human epidermal cells from 9 normal and 3 inflamed skin samples. Transcriptomics-derived keratinocyte subpopulations reflect classic epidermal strata but also sharply compartmentalize epithelial functions such as cell-cell communication, inflammation, and WNT pathway modulation. In keratinocytes, ∼12% of assessed transcript expression varies in coordinate patterns, revealing undescribed gene expression programs governing epidermal homeostasis. We also identify molecular fingerprints of inflammatory skin states, including S100 activation in the interfollicular epidermis of normal scalp, enrichment of a CD1C+CD301A+ myeloid dendritic cell population in psoriatic epidermis, and IL1ßhiCCL3hiCD14+ monocyte-derived macrophages enriched in foreskin. This compendium of RNA profiles provides a critical step toward elucidating epidermal diseases of development, differentiation, and inflammation.

Nuclear receptor Nr4a1 modulates both regulatory T-cell (Treg) differentiation and clonal deletion.

Immature thymocytes expressing autoreactive T-cell receptors (TCR) can adopt differing cell fates: clonal deletion by apoptosis or deviation into alternative lineages such as FoxP3(+) regulatory T cells (Treg). We revisited the role of the transcription factor Nr4a1 (Nur77), an immediate-early response gene induced by TCR engagement. Nr4a1KO mice show clear quantitative defects in antigen-induced clonal deletion. The impact of the Nr4a1 deletion is not enhanced by deletion of the proapoptotic factor Bim. In addition, Nr4a1 curtails initial differentiation into the Treg lineage in TCR transgenic mice and in nontransgenic mice. Transcriptional profiling of Nr4a1KO thymocytes under selection conditions reveals that Nr4a1 activates the transcription of several targets, consistent with these diverse actions: (i) Nr4a1 partakes in the induction of Bim after TCR triggering; (ii) perhaps paradoxically, Nr4a1 positively controls several transcripts of the Treg signature, in particular Ikzf2 and Tnfrsf9; (iii) consistent with its prosurvival and metabolic role in the liver, Nr4a1 is also required for the induction by TCR of a coordinated set of enzymes of the glycolytic and Krebs cycle pathways, which we propose may antagonize Treg selection as does activation of mTOR/Akt. Thus, Nr4a1 appears to act as a balancing molecule in fate determination at a critical juncture of T-cell differentiation.

Viral evasion of natural killer cells.

Viruses have evolved mechanisms to avoid the host immune system, including means of escaping detection by both the innate and adaptive immune responses. Natural killer (NK) cells are a central component of the innate immune system and are crucial in defense against certain viruses. To attain a state of chronic infection, some successful viruses have developed specific mechanisms to evade detection by and activation of NK cells. These NK cell-specific evasion mechanisms fall into distinct mechanistic categories used in numerous virus families.