MicroRNAs (miRNAs) can be transferred between cells, representing an exciting new dimension to intercellular communication, referred to as non-cell-autonomous gene regulation. We recently identified that distinct miRNAs are packaged and exported from TREG cells and delivered directly to TH1 cells, suppressing T cell-mediated disease. Different T cell populations express different miRNAs and release a distinctive set of extracellular miRNAs. In this proposal we will identify whether the transfer of miRNAs between cells contributes to T cell development, T cell differentiation and TH2-mediated allergy and anti-helminth immunity. miRNA-mediated gene silencing requires one of four catalytically active Argonaut (Ago) proteins to regulate gene expression. To investigate miRNA transport between cells, we have generated novel mice with miRNA-deficient T cells that can (Dicer–/–) or cannot (Dicer–/–Ago-1,-3,-4–/– Ago-2fl/fl) respond to exogenous miRNAs. Using these novel mice we will identify which Ago protein(s) specific miRNAs associate with and which Ago proteins are required for miRNA-mediated gene regulation in T cells. TH2 cells express unique miRNAs, which can be found within TH2 cells and in extracellular vesicles released from TH2 cells. We have generated several new TH2-associated miRNA-deficient mice to investigate the cell intrinsic (cell-autonomous) and extrinsic (non-cell-autonomous) role of these miRNAs in TH2-mediated allergy and anti-helminth immunity. Studies in plants and worms have identified various mechanisms of RNA transfer between cells, involving cell-contact dependent and independent mechanisms. We will translate these observations into mammalian systems and identify the mechanisms of miRNA transfer. Results from this work will identify novel miRNA-mediated pathways and incentivise state-of-the-art approaches for novel therapeutic intervention to treat inflammatory diseases.