Summary Infection is restrained by the concerted activation of tissue-resident and circulating immune cells. Whether tissue-resident lymphocytes confer early antiviral immunity at local sites of primary infection prior to the initiation of circulating responses is not well understood. Furthermore, the kinetics of initial antiviral responses at sites of infection remain unclear. Here, we show that tissue-resident type 1 innate lymphoid cells (ILC1) serve an essential early role in host immunity through rapid production of interferon (IFN)-γ following viral infection. Ablation of Zfp683-dependent liver ILC1 lead to increased viral load in the presence of intact adaptive and innate immune cells critical for mouse cytomegalovirus (MCMV) clearance. Swift production of IL-12 by tissue-resident XCR1+ conventional dendritic cells (cDC1) promoted ILC1 production of IFN-γ in a STAT4-dependent manner to limit early viral burden. Thus, ILC1 contribute an essential role in viral immunosurveillance at sites of initial infection in response to local cDC1-derived proinflammatory cytokines.

Summary Hematopoietic stem cells (HSCs) sustain long-term reconstitution of hematopoiesis in transplantation recipients, yet their role in the endogenous steady-state hematopoiesis remains unclear. In particular, recent studies suggested that HSCs provide a relatively minor contribution to immune cell development in the adults. We directed transgene expression in a fraction of HSCs that maintained reconstituting activity during serial transplantations. Inducible genetic labeling showed that transgene-expressing HSCs gave rise to other phenotypic HSCs, confirming their top position in the differentiation hierarchy. The labeled HSCs rapidly contributed to committed progenitors of all lineages and to mature myeloid cells and lymphocytes, but not to B-1a cells or tissue macrophages. Importantly, labeled HSCs gave rise to more than two-thirds of all myeloid cells and platelets in adult mice, and this contribution could be accelerated by an induced interferon response. Thus, classically defined HSCs maintain immune cell development in the steady state and during systemic cytokine responses.

Clonal expansion and immunological memory are hallmark features of the mammalian adaptive immune response and essential for prolonged host control of pathogens. Recent work demonstrates that natural killer (NK) cells of the innate immune system also exhibit these adaptive traits during infection. Here we demonstrate that differentiating and ‘memory’ NK cells possess distinct chromatin accessibility states and that their epigenetic profiles reveal a ‘poised’ regulatory program at the memory stage. Furthermore, we elucidate how individual STAT transcription factors differentially control epigenetic and transcriptional states early during infection. Finally, concurrent chromatin profiling of the canonical CD8+ T cell response against the same infection demonstrated parallel and distinct epigenetic signatures defining NK cells and CD8+ T cells. Overall, our study reveals the dynamic nature of epigenetic modifications during the generation of innate and adaptive lymphocyte memory.

SummaryThe IRF8-dependent subset of classical dendritic cells (cDCs), termed cDC1, is important for cross-priming cytotoxic T cell responses against pathogens and tumors. Culture of hematopoietic progenitors with DC growth factor FLT3 ligand (FLT3L) yields very few cDC1s (in humans) or only immature “cDC1-like” cells (in the mouse). We report that OP9 stromal cells expressing the Notch ligand Delta-like 1 (OP9-DL1) optimize FLT3L-driven development of cDC1s from murine immortalized progenitors and primary bone marrow cells. Co-culture with OP9-DL1 induced IRF8-dependent cDC1s with a phenotype (CD103+ Dec205+ CD8α+) and expression profile resembling primary splenic cDC1s. OP9-DL1-induced cDC1s showed preferential migration toward CCR7 ligands in vitro and superior T cell cross-priming and antitumor vaccination in vivo. Co-culture with OP9-DL1 also greatly increased the yield of IRF8-dependent CD141+ cDC1s from human bone marrow progenitors cultured with FLT3L. Thus, Notch signaling optimizes cDC generation in vitro and yields authentic cDC1s for functional studies and translational applications.

Natural killer (NK) cells are innate lymphocytes that display features of adaptive immunity during viral infection. Biallelic mutations in IRF8 have been reported to cause familial NK cell deficiency and susceptibility to severe viral infection in humans; however, the precise role of this transcription factor in regulating NK cell function remains unknown. Here, we show that cell-intrinsic IRF8 was required for NK-cell-mediated protection against mouse cytomegalovirus infection. During viral exposure, NK cells upregulated IRF8 through interleukin-12 (IL-12) signaling and the transcription factor STAT4, which promoted epigenetic remodeling of the Irf8 locus. Moreover, IRF8 facilitated the proliferative burst of virus-specific NK cells by promoting expression of cell-cycle genes and directly controlling Zbtb32, a master regulator of virus-driven NK cell proliferation. These findings identify the function and cell-type-specific regulation of IRF8 in NK-cell-mediated antiviral immunity and provide a mechanistic understanding of viral susceptibility in patients with IRF8 mutations.