Colleen M. Lau

The cohesin complex extrudes chromatin loops, stopping at sites bound by CCCTC-binding factor (CTCF) and organizing chromosomes into topologically associated domains, yet biological implications of this process remain obscure. We show that cohesin controls the in vivo differentiation and function of murine antigen-presenting dendritic cells (DCs), particularly antigen cross-presentation and interleukin-12 (IL-12) secretion by type 1 conventional DCs (cDC1s). The chromatin organization of DCs was shaped by cohesin and the transcription factor IRF8, which facilitated chromatin looping and chromosome compartmentalization, respectively. Optimal expression of IRF8 itself required CTCF/cohesin binding sites demarcating the Irf8 gene. During DC activation, cohesin enabled the induction of a subset of genes that were preferentially located in Polycomb-repressed regions and enriched in more distal enhancers. Accordingly, deletion of CTCF sites flanking the Il12b gene in mice reduced IL-12 production by cDC1s. Our data reveal an essential role of cohesin-mediated chromatin folding in cell differentiation and function in vivo and its bidirectional cross-talk with lineage-specifying transcription factors.

Interferonopathies drive autoimmunity but can also impair host responses to pathogens, including viral infections. To better understand viral susceptibility of patients with STAT1 gain-of-function (GOF) mutations, we generated conditional knockin mouse models to elucidate disease mechanisms and relevance of different immune subsets. Virally infected Stat1 GOF mice exhibited impaired early IFN-γ production from innate lymphocytes and lethality because of excess prolonged multicytokine production. The presence of the Stat1 GOF allele resulted in premature usage of interferon-stimulated gene factor 3 (ISGF3) over the normal STAT4–AP-1–dependent transcriptomic program in activated innate lymphocytes. Administration of anti–IFN-γ antibodies in wild-type (WT) mice after infection phenocopied Stat1 GOF mice presenting exaggerated inflammation despite viral control. Conversely, early administration of exogenous IFN-γ to infected Stat1 GOF mice prevented lethality and exaggerated cytokine response. Although Stat1 GOF mutations facilitate IFN-γ–mediated autoimmunity, early IFN-γ responses to viral infection via a normal STAT4 program were impaired, leading to overcompensated inflammatory responses in Stat1 GOF mice.

Latent viral infections rely on a precise coordination of the immune response to control sporadic viral reactivation. CD8+ T cells play a crucial role in controlling viral latency by generating diverse memory responses in an epitope-specific manner. Among these distinct responses, conventional and inflationary memory responses have been described during herpesvirus infections. Using a newly generated TCR transgenic mouse strain, we investigated the transcriptomic and epigenetic remodeling of distinct epitope-specific CD8+ T cells during CMV infection across tissues at both population and single-cell levels. Our findings reveal that whereas the transcriptomic and epigenetic landscapes of conventional and inflationary memory responses diverge in the spleen and liver, these molecular programs converge in the salivary gland, a site of CMV persistence. Thus, we provide evidence that the dynamics of memory CD8+ T cell responses are distinct between tissues.

This year at JEM, we are highlighting women in science by sharing their stories and amplifying their voices. In this Viewpoint, we hear from a cross section of women, across multiple research fields, discussing their science and the process of setting up a lab as an independent researcher.

The development of dendritic cells (DCs), including antigen-presenting conventional DCs (cDCs) and cytokine-producing plasmacytoid DCs (pDCs), is controlled by the growth factor Flt3 ligand (Flt3L) and its receptor Flt3. We genetically dissected Flt3L-driven DC differentiation using CRISPR-Cas9–based screening. Genome-wide screening identified multiple regulators of DC differentiation including subunits of TSC and GATOR1 complexes, which restricted progenitor growth but enabled DC differentiation by inhibiting mTOR signaling. An orthogonal screen identified the transcriptional repressor Trim33 (TIF-1γ) as a regulator of DC differentiation. Conditional targeting in vivo revealed an essential role of Trim33 in the development of all DCs, but not of monocytes or granulocytes. In particular, deletion of Trim33 caused rapid loss of DC progenitors, pDCs, and the cross-presenting cDC1 subset. Trim33-deficient Flt3 ⁺ progenitors up-regulated pro-inflammatory and macrophage-specific genes but failed to induce the DC differentiation program. Collectively, these data elucidate mechanisms that control Flt3L-driven differentiation of the entire DC lineage and identify Trim33 as its essential regulator.

Natural killer (NK) cells are critical to immune surveillance against infections and cancer. Their role in immune surveillance requires that NK cells are present within tissues in a quiescent state. Mechanisms by which NK cells remain quiescent in tissues are incompletely elucidated. The transcriptional repressor BACH2 plays a critical role within the adaptive immune system, but its function within innate lymphocytes has been unclear. Here, we show that BACH2 acts as an intrinsic negative regulator of NK cell maturation and function. BACH2 is expressed within developing and mature NK cells and promotes the maintenance of immature NK cells by restricting their maturation in the presence of weak stimulatory signals. Loss of BACH2 within NK cells results in accumulation of activated NK cells with unrestrained cytotoxic function within tissues, which mediate augmented immune surveillance to pulmonary cancer metastasis. These findings establish a critical function of BACH2 as a global negative regulator of innate cytotoxic function and tumor immune surveillance by NK cells.

Immunological memory is the underlying mechanism by which the immune system remembers previous encounters with pathogens to produce an enhanced secondary response upon re‐encounter. It stands as the hallmark feature of the adaptive immune system and the cornerstone of vaccine development. Classic recall responses are executed by conventional T and B cells, which undergo somatic recombination and modify their receptor repertoire to ensure recognition of a vast number of antigens. However, recent evidence has challenged the dogma that memory responses are restricted to the adaptive immune system, which has prompted a reevaluation of what delineates “immune memory.” Natural killer (NK) cells of the innate immune system have been at the forefront of these pushed boundaries, and have proved to be more “adaptable” than previously thought. Like T cells, we now appreciate that their “natural” abilities actually require a myriad of signals for optimal responses. In this review, we discuss the many signals required for effector and memory NK cell responses and the epigenetic mechanisms that ultimately endow their enhanced features.

Human CMV (HCMV) is a ubiquitous pathogen that indelibly shapes the NK cell repertoire. Using transcriptomic, epigenomic, and proteomic approaches to evaluate peripheral blood NK cells from healthy human volunteers, we find that prior HCMV infection promotes NK cells with a T cell–like gene profile, including the canonical markers CD3ε, CD5, and CD8β, as well as the T cell lineage–commitment transcription factor Bcl11b. Although Bcl11b expression is upregulated during NK maturation from CD56^bright to CD56^dim, we find a Bcl11b-mediated signature at the protein level for FcεRIγ, PLZF, IL-2Rβ, CD3γ, CD3δ, and CD3ε in later-stage, HCMV-induced NK cells. BCL11B is targeted by Notch signaling in T cell development, and culture of NK cells with Notch ligand increases cytoplasmic CD3ε expression. The Bcl11b-mediated gain of CD3ε, physically associated with CD16 signaling molecules Lck and CD247 in NK cells is correlated with increased Ab-dependent effector function, including against HCMV-infected cells, identifying a potential mechanism for their prevalence in HCMV-infected individuals and their prospective clinical use in Ab-based therapies. Key Points HCMV infection promotes expression of canonical T cell molecules in NK cells. CD3-positive NK cells are functionally superior in ADCC response.

The responsiveness of mouse and human natural killer cells is inversely correlated with the abundance of the phosphatase SHP-1.

NKG2C ⁺ CD8 ⁺ T cells, found in 40% of HCMV-seropositive individuals, have lost BCL11B expression and adopt an innate-like identity.