SummaryFoxp3+ T regulatory (Treg) cells prevent inflammatory disease but the mechanistic basis of suppression is not understood completely. Gene silencing by RNA interference can act in a cell-autonomous and non-cell-autonomous manner, providing mechanisms of intercellular regulation. Here, we demonstrate that non-cell-autonomous gene silencing, mediated by miRNA-containing exosomes, is a mechanism employed by Treg cells to suppress T-cell-mediated disease. Treg cells transferred microRNAs (miRNA) to various immune cells, including T helper 1 (Th1) cells, suppressing Th1 cell proliferation and cytokine secretion. Use of Dicer-deficient or Rab27a and Rab27b double-deficient Treg cells to disrupt miRNA biogenesis or the exosomal pathway, respectively, established a requirement for miRNAs and exosomes for Treg-cell-mediated suppression. Transcriptional analysis and miRNA inhibitor studies showed that exosome-mediated transfer of Let-7d from Treg cell to Th1 cells contributed to suppression and prevention of systemic disease. These studies reveal a mechanism of Treg-cell-mediated suppression mediated by miRNA-containing exosomes.

Immunity to many human and murine gastrointestinal helminth parasites requires interleukin-4 (IL-4)-directed type 2 helper (TH2) differentiation of CD4+ T cells to elicit type-2 immunity. Despite a good understanding of the inflammatory cascade elicited following helminth infection, the initial source of IL-4 is unclear. Previous studies using the rat helminth parasite Nippostronglyus brasiliensis, identified an important role for basophil-derived IL-4 for TH2 differentiation. However, basophils are redundant for TH2 differentiation following infection with the natural helminth parasite of mice Heligmosomoides polygyrus, indicating that other sources of IL-4 are required. In this study using H. polygyrus, which is controlled by IL-4-dependent immunity, we identified that group-2 innate lymphoid cells (ILC2s) produced significant amounts of IL-4 and IL-2 following H. polygyrus infection. Leukotriene D4 was sufficient to stimulate IL-4 secretion by ILC2s, and the supernatant from activated ILC2s could potently drive TH2 differentiation in vitro in an IL-4-dependent manner. Furthermore, specific deletion of IL-4 from ILC2s compromised TH2 differentiation in vivo. Overall, this study highlights a previously unrecognized and important role for ILC2-derived IL-4 for TH2 differentiation in a natural TH2-dependent model of human helminthiasis.

Highlights d NK cells drive broad inflammatory remodeling characteristic of T-cell-inflamed tumors d PGE2 acting on EP2 and EP4 on NK cells prevents the TME switch enabling immune escape d Opposing inflammatory profiles found in many human cancer types have prognostic value d A signature capturing pro-and anti-tumor factors predicts response to immunotherapy

Significance The rising prevalence of allergic diseases throughout the world demands new approaches to treat this inflammatory disorder. CD4 + Th2 cells orchestrate the allergic cascade, stimulating IgE production, activating innate cells, and stimulating local tissue. This study took a comprehensive approach to identify the unique transcriptional features of pathogenic Th2 cells with the aim of identifying novel molecular regulators. Highly purified Th1, Th2, Th9, Th17, and Treg cells isolated from mice with allergy, infection, and autoimmunity identified unique mRNA and microRNAs (miRNAs) expressed in Th2 cells. Functional and mechanistic studies using miRNA-deficient mice, luciferase assays, miRNA inhibitors, and siRNA in combination with state-of-the-art adoptive transfer systems, identified a critical role for miR-155–regulated S1pr1 in the pathogenesis of Th2-mediated allergy.

Interleukin-10 (IL-10) is an important regulatory cytokine required to control allergy and asthma. IL-10-mediated regulation of T cell-mediated responses was previously thought to occur indirectly via antigen-presenting cells. However, IL-10 can act directly on regulatory T cells and T helper type 17 (Th17) cells. In the context of allergy, it is therefore unclear whether IL-10 can directly regulate T helper type 2 (Th2) cells and whether this is an important regulatory axis during allergic responses. We sought to determine whether IL-10 signaling in CD4 Th2 cells was an important mechanism of immune regulation during airway allergy. We demonstrate that IL-10 directly limits Th2 cell differentiation and survival in vitro and in vivo. Ablation of IL-10 signaling in Th2 cells led to enhanced Th2 cell survival and exacerbated pulmonary inflammation in a murine model of house dust mite allergy. Mechanistically, IL-10R signaling regulated the expression of several genes in Th2 cells, including granzyme B. Indeed, IL-10 increased granzyme B expression in Th2 cells and led to increased Th2 cell death, identifying an IL-10-regulated granzyme B axis in Th2 cells controlling Th2 cell survival. This study provides clear evidence that IL-10 exerts direct effects on Th2 cells, regulating the survival of Th2 cells and severity of Th2-mediated allergic airway inflammation.

Identifying strategies to improve the efficacy of immune checkpoint blockade (ICB) remains a major clinical need. Here, we show that therapeutically targeting the COX-2/PGE 2 /EP2-4 pathway with widely used non-steroidal and steroidal antiinflammatory drugs synergized with ICB in mouse cancer models. We exploited a bilateral surgery model to distinguish responders from non-responders shortly following treatment and identified acute IFN-γ-driven transcriptional remodeling in responder mice, which was also associated with patient benefit to ICB. Monotherapy with COX-2 inhibitors or EP2-4 PGE 2 receptor antagonists rapidly induced this response program and, in combination with ICB, increased the intratumoral accumulation of effector T cells. Treatment of patient-derived tumor fragments from multiple cancer types revealed a similar shift in the tumor inflammatory environment to favor T cell activation. Our findings establish the COX-2/PGE 2 /EP2-4 axis as an independent immune checkpoint and a readily translatable strategy to rapidly switch the tumor inflammatory profile from cold to hot.

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Pelly et al. use novel mouse reporter systems to show that a proportion of Th2 cells develop from Foxp3-expressing cells in an IL-4–dependent manner, highlighting the potential to subvert T reg cell–mediated suppression in favor of type 2 immunity.