Activation of the RIG-I or STING pathways results in a type I interferon response that protects gut integrity after irradiation- or immune-induced tissue injury.

Achieving durable clinical responses to immune checkpoint inhibitors remains a challenge. Here, we demonstrate that immunotherapy with anti–CTLA-4 and its combination with anti–PD-1 rely on tumor cell–intrinsic activation of the cytosolic RNA receptor RIG-I. Mechanistically, tumor cell–intrinsic RIG-I signaling induced caspase-3–mediated tumor cell death, cross-presentation of tumor-associated antigen by CD103⁺ dendritic cells, subsequent expansion of tumor antigen–specific CD8⁺ T cells, and their accumulation within the tumor tissue. Consistently, therapeutic targeting of RIG-I with 5′– triphosphorylated RNA in both tumor and nonmalignant host cells potently augmented the efficacy of CTLA-4 checkpoint blockade in several preclinical cancer models. In humans, transcriptome analysis of primary melanoma samples revealed a strong association between high expression of DDX58 (the gene encoding RIG-I), T cell receptor and antigen presentation pathway activity, and prolonged overall survival. Moreover, in patients with melanoma treated with anti–CTLA-4 checkpoint blockade, high DDX58 RIG-I transcriptional activity significantly associated with durable clinical responses. Our data thus identify activation of RIG-I signaling in tumors and their microenvironment as a crucial component for checkpoint inhibitor–mediated immunotherapy of cancer.

Maintaining immune tolerance requires the production of Foxp3-expressing regulatory T (Treg) cells in the thymus. Activation of NF-κB transcription factors is critically required for Treg cell development, partly via initiating Foxp3 expression. NF-κB activation is controlled by a negative feedback regulation through the ubiquitin editing enzyme A20, which reduces proinflammatory signaling in myeloid cells and B cells. In naive CD4+ T cells, A20 prevents kinase RIPK3-dependent necroptosis. Using mice deficient for A20 in T lineage cells, we show that thymic and peripheral Treg cell compartments are quantitatively enlarged because of a cell-intrinsic developmental advantage of A20-deficient thymic Treg differentiation. A20-deficient thymic Treg cells exhibit reduced dependence on IL-2 but unchanged rates of proliferation and apoptosis. Activation of the NF-κB transcription factor RelA was enhanced, whereas nuclear translocation of c-Rel was decreased in A20-deficient thymic Treg cells. Furthermore, we found that the increase in Treg cells in T cell–specific A20-deficient mice was already observed in CD4+ single-positive CD25+ GITR+ Foxp3− thymic Treg cell progenitors. Treg cell precursors expressed high levels of the tumor necrosis factor receptor superfamily molecule GITR, whose stimulation is closely linked to thymic Treg cell development. A20-deficient Treg cells efficiently suppressed effector T cell–mediated graft-versus-host disease after allogeneic hematopoietic stem cell transplantation, suggesting normal suppressive function. Holding thymic production of natural Treg cells in check, A20 thus integrates Treg cell activity and increased effector T cell survival into an efficient CD4+ T cell response.

NKT cells represent a small subset of glycolipid-recognizing T cells that are heavily implicated in human allergic, autoimmune, and malignant diseases. In the thymus, precursor cells recognize self-glycolipids by virtue of their semi-invariant TCR, which triggers NKT cell lineage commitment and maturation. During their development, NKT cells are polarized into the NKT1, NKT2, and NKT17 subsets, defined through their cytokine-secretion patterns and the expression of key transcription factors. However, we have largely ignored how the differentiation into the NKT cell subsets is regulated. In this article, we describe the mRNA-binding Roquin-1 and -2 proteins as central regulators of murine NKT cell fate decisions. In the thymus, T cell–specific ablation of the Roquin paralogs leads to a dramatic expansion of NKT17 cells, whereas peripheral mature NKT cells are essentially absent. Roquin-1/2–deficient NKT17 cells show exaggerated lineage-specific expression of nearly all NKT17-defining proteins tested. We show through mixed bone marrow chimera experiments that NKT17 polarization is mediated through cell-intrinsic mechanisms early during NKT cell development. In contrast, the loss of peripheral NKT cells is due to cell-extrinsic factors. Surprisingly, Roquin paralog–deficient NKT cells are, in striking contrast to conventional T cells, compromised in their ability to secrete cytokines. Altogether, we show that Roquin paralogs regulate the development and function of NKT cell subsets in the thymus and periphery.