Role of interferon regulatory factor 5 (IRF5) in tumor progression: Prognostic and therapeutic potential

Canonically, the transcription factor interferon regulatory factor 5 (IRF5) is a key mediator of innate and adaptive immunity downstream of pathogen recognition receptors such as Toll-like receptors (TLRs). Hence, dysregulation of IRF5 function has been widely implicated in inflammatory and autoimmune diseases. Over the last few decades, dysregulation of IRF5 expression has been also reported in hematologic malignancies and solid cancers that support a role for IRF5 in malignant transformation, tumor immune regulation, clinical prognosis, and treatment response. This review will provide an in-depth overview of the current literature regarding the mechanisms by which IRF5 functions as either a tumor suppressor or oncogene, its role in metastasis, regulation of the tumor-immune microenvironment, utility as a prognostic indicator of disease, and new developments in IRF5 therapeutics that may be used to remodel tumor immunity.

Identification of pan-cancer/testis genes and validation of therapeutic targeting in triple-negative breast cancer: Lin28a-based and Siglece-based vaccination induces antitumor immunity and inhibits metastasis

BACKGROUND

Cancer-testis (CT) genes are targets for tumor antigen-specific immunotherapy given that their expression is normally restricted to the immune-privileged testis in healthy individuals with aberrant expression in tumor tissues. While they represent targetable germ tissue antigens and play important functional roles in tumorigenesis, there is currently no standardized approach for identifying clinically relevant CT genes. Optimized algorithms and validated methods for accurate prediction of reliable CT antigens (CTAs) with high immunogenicity are also lacking.

METHODS

Sequencing data from the Genotype-Tissue Expression (GTEx) and The Genomic Data Commons (GDC) databases was used for the development of a bioinformatic pipeline to identify CT exclusive genes. A CT germness score was calculated based on the number of CT genes expressed within a tumor type and their degree of expression. The impact of tumor germness on clinical outcome was evaluated using healthy GTEx and GDC tumor samples. We then used a triple-negative breast cancer mouse model to develop and test an algorithm that predicts epitope immunogenicity based on the identification of germline sequences with strong major histocompatibility complex class I (MHCI) and MHCII binding affinities. Germline sequences for CT genes were synthesized as long synthetic peptide vaccines and tested in the 4T1 triple-negative model of invasive breast cancer with Poly(I:C) adjuvant. Vaccine immunogenicity was determined by flow cytometric analysis of in vitro and in vivo T-cell responses. Primary tumor growth and lung metastasis was evaluated by histopathology, flow cytometry and colony formation assay.

RESULTS

We developed a new bioinformatic pipeline to reliably identify CT exclusive genes as immunogenic targets for immunotherapy. We identified CT genes that are exclusively expressed within the testis, lack detectable thymic expression, and are significantly expressed in multiple tumor types. High tumor germness correlated with tumor progression but not with tumor mutation burden, supporting CTAs as appealing targets in low mutation burden tumors. Importantly, tumor germness also correlated with markers of antitumor immunity. Vaccination of 4T1 tumor-bearing mice with Siglece and Lin28a antigens resulted in increased T-cell antitumor immunity and reduced primary tumor growth and lung metastases.

CONCLUSION

Our results present a novel strategy for the identification of highly immunogenic CTAs for the development of targeted vaccines that induce antitumor immunity and inhibit metastasis.

Human TLR8 induces inflammatory bone marrow erythromyeloblastic islands and anemia in SLE-prone mice

Anemia commonly occurs in systemic lupus erythematosus, a disease characterized by innate immune activation by nucleic acids. Overactivation of cytoplasmic sensors by self-DNA or RNA can cause erythroid cell death, while sparing other hematopoietic cell lineages. Whereas chronic inflammation is involved in this mechanism, less is known about the impact of systemic lupus erythematosus on the BM erythropoietic niche. We discovered that expression of the endosomal ssRNA sensor human TLR8 induces fatal anemia in Sle1.Yaa lupus mice. We observed that anemia was associated with a decrease in erythromyeloblastic islands and a block in differentiation at the CFU-E to proerythroblast transition in the BM. Single-cell RNAseq analyses of isolated BM erythromyeloblastic islands from human TLR8-expressing mice revealed that genes associated with essential central macrophage functions including adhesion and provision of nutrients were down-regulated. Although compensatory stress erythropoiesis occurred in the spleen, red blood cell half-life decreased because of hemophagocytosis. These data implicate the endosomal RNA sensor TLR8 as an additional innate receptor whose overactivation causes acquired failure of erythropoiesis via myeloid cell dysregulation.

A New Methodology for the Quantification of Neutrophil Extracellular Traps in Patient Plasma

Neutrophil extracellular traps (NETs) are web-like structures made up of decondensed chromatin fibers along with neutrophil granular proteins that are extruded by neutrophils after activation or in response to foreign microorganisms. NETs have been associated with autoimmune and inflammatory diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis, coronavirus disease 2019 (COVID-19), and others. There are reliable methods available to quantitate NETs from neutrophils, but their accurate quantification in patient plasma or serum remains a challenge. We developed a highly sensitive ELISA to detect NETs in serum/plasma and designed a novel smear immunofluorescence assay to detect NETs in as little as 1 μL of serum/plasma. We further validated our technology on plasma samples from SLE patients and healthy donors that carry interferon regulatory factor 5 genetic risk. The multiplex ELISA combines the use of three antibodies against myeloperoxidase (MPO), citrullinated histone H3 (CitH3), and DNA to detect the NET complexes with higher specificities. The immunofluorescence smear assay can visually detect intact structures of NETs in 1 μL of serum/plasma and provide similar results that correlate with findings from the multiplex ELISA. Furthermore, the smear assay is a relatively simple, inexpensive, and quantifiable method of NET detection for small volumes.

The TLR7-IRF-5 axis sensitizes memory CD4+ T cells to Fas-mediated apoptosis during HIV-1 infection

HIV-1 infection is characterized by a strong inflammatory environment, tissue disruption, and a progressive decline in CD4+ T cell count. Despite treatment with antiretroviral therapy (ART), the majority of persons living with HIV (PLWH) maintain residual levels of inflammation, low degree of immune activation, and higher sensitivity to cell death in their memory CD4+ T-cell compartment. To date, the mechanisms responsible for this high sensitivity remain elusive. We have identified the transcription factor IRF-5 to be involved in impairing the maintenance of murine CD4+ T cells in a chronic inflammatory environment. Here, we investigate whether IRF-5 also contributes to memory CD4+ T cell loss during HIV-1 infection. We show that TLR7 and IRF-5 were upregulated in memory CD4+ T cells from PLWH, when compared with naturally protected elite controllers and HIVfree participants. TLR7 was upstream of IRF-5, promoting Caspase 8 expression in CD4+ T cells from ART HIV-1+ but not from HIVfree participants. Moreover, IRF-5 and TLR7 expression inversely correlated with CD4+ T cell counts in primary HIV infection. Interestingly, the TLR7-IRF-5 axis acted synergistically with the Fas/FasL pathway, suggesting that TLR7 and IRF-5 expression in ART HIV-1+ memory CD4+ T cells represents an imprint that predisposes cells to Fas-mediated apoptosis. This predisposition could be blocked using IRF-5 inhibitory peptides. Thus, we propose IRF-5 blockade as a possible therapy to prevent memory CD4+ T cell loss in PLWH.

Identification of pan-cancer/testis genes and validation of therapeutic targeting in triple-negative breast cancer: Lin28a- and Siglece-based vaccination induces anti-tumor immunity and inhibits metastasis

Background

Cancer-testis (CT) genes are targets for tumor antigen-specific immunotherapy given that their expression is normally restricted to the immune-privileged testis in healthy individuals with aberrant expression in tumor tissues. While they represent targetable germ-tissue antigens and play important functional roles in tumorigenesis, there is currently no standardized approach for identifying clinically relevant CT genes. Optimized algorithms and validated methods for accurate prediction of reliable CT antigens with high immunogenicity are also lacking.

Methods

Sequencing data from the Genotype-Tissue Expression (GTEx) and The Genomic Data Commons (GDC) databases was utilized for the development of a bioinformatic pipeline to identify CT exclusive genes. A CT germness score was calculated based on the number of CT genes expressed within a tumor type and their degree of expression. The impact of tumor germness with clinical outcome was evaluated using healthy GTEx and GDC tumor samples. We then used a triple-negative breast cancer mouse model to develop and test an algorithm that predicts epitope immunogenicity based on the identification of germline sequences with strong MHCI and MHCII binding affinities. Germline sequences for CT genes were synthesized as long synthetic peptide vaccines and tested in the 4T1 triple-negative model of invasive breast cancer with Poly(I:C) adjuvant. Vaccine immunogenicity was determined by flow cytometric analysis of in vitro and in vivo T cell responses. Primary tumor growth and lung metastasis was evaluated by histopathology, flow cytometry and colony formation assay.

Results

We developed a new bioinformatic pipeline to reliably identify CT exclusive genes as immunogenic targets for immunotherapy. We identified CT genes that are exclusively expressed within the testis, lack detectable thymic expression, and are significantly expressed in multiple tumor types. High tumor germness correlated with tumor progression but not with tumor mutation burden, supporting CT antigens as appealing targets in low mutation burden tumors. Importantly, tumor germness also correlated with markers of anti-tumor immunity. Vaccination of 4T1 tumor bearing mice with Siglece and Lin28a antigens resulted in increased T cell anti-tumor immunity and reduced primary tumor growth and lung metastases.

Conclusion

Our results present a novel strategy for the identification of highly immunogenic CT antigens for the development of targeted vaccines that induce anti-tumor immunity and inhibit metastasis.

Navigating the marrow sea towards erythromyeloblastic islands under normal and inflammatory conditions

PURPOSE OF REVIEW

Terminal erythroid differentiation occurs in specialized niches called erythroblastic islands. Since their discovery in 1958, these niches have been described as a central macrophage surrounded by differentiating erythroblasts. Here, we review the recent advances made in the characterization of these islands and the role they could play in anaemia of inflammation.

RECENT FINDINGS

The utilization of multispectral imaging flow cytometry (flow cytometry with microscopy) has enabled for a more precise characterization of the niche that revealed the presence of maturing granulocytes in close contact with the central macrophage. These erythromyeloblastic islands (EMBIs) can adapt depending on the peripheral needs. Indeed, during inflammation wherein inflammatory cytokines limit erythropoiesis and promote granulopoiesis, EMBIs present altered structures with increased maturing granulocytes and decreased erythroid precursors.

SUMMARY

Regulation of the structure and function of the EMBI in the bone marrow emerges as a potential player in the pathophysiology of acute and chronic inflammation and its associated anaemia.

Loss of IRF5 increases ribosome biogenesis leading to alterations in mammary gland architecture and metastasis

Despite the progress made in identifying cellular factors and mechanisms that predict progression and metastasis, breast cancer remains the second leading cause of death for women in the US. Using The Cancer Genome Atlas and mouse models of spontaneous and invasive mammary tumorigenesis, we identified that loss of function of interferon regulatory factor 5 (IRF5) is a predictor of metastasis and survival. Histologic analysis of Irf5 ^-/- mammary glands revealed expansion of luminal and myoepithelial cells, loss of organized glandular structure, and altered terminal end budding and migration. RNA-seq and ChIP-seq analyses of primary mammary epithelial cells from Irf5 ^+/+ and Irf5 ^-/- littermate mice revealed IRF5-mediated transcriptional regulation of proteins involved in ribosomal biogenesis. Using an invasive model of breast cancer lacking Irf5 , we demonstrate that IRF5 re-expression inhibits tumor growth and metastasis via increased trafficking of tumor infiltrating lymphocytes and altered tumor cell protein synthesis. These findings uncover a new function for IRF5 in the regulation of mammary tumorigenesis and metastasis.

Highlights

Loss of IRF5 is a predictor of metastasis and survival in breast cancer.IRF5 contributes to the regulation of ribosome biogenesis in mammary epithelial cells.Loss of IRF5 function in mammary epithelial cells leads to increased protein translation.

Erythroblastic islands foster granulopoiesis in parallel to terminal erythropoiesis

The erythroblastic island (EBI), composed of a central macrophage surrounded by maturing erythroblasts, is the erythroid precursor niche. Despite numerous studies, its precise composition is still unclear. Using multispectral imaging flow cytometry, in vitro island reconstitution, and single-cell RNA sequencing of adult mouse bone marrow (BM) EBI-component cells enriched by gradient sedimentation, we present evidence that the CD11b+ cells present in the EBIs are neutrophil precursors specifically associated with BM EBI macrophages, indicating that erythro-(myelo)-blastic islands are a site for terminal granulopoiesis and erythropoiesis. We further demonstrate that the balance between these dominant and terminal differentiation programs is dynamically regulated within this BM niche by pathophysiological states that favor granulopoiesis during anemia of inflammation and favor erythropoiesis after erythropoietin stimulation. Finally, by molecular profiling, we reveal the heterogeneity of EBI macrophages by cellular indexing of transcriptome and epitope sequencing of mouse BM EBIs at baseline and after erythropoietin stimulation in vivo and provide a searchable online viewer of these data characterizing the macrophage subsets serving as hematopoietic niches. Taken together, our findings demonstrate that EBIs serve a dual role as niches for terminal erythropoiesis and granulopoiesis and the central macrophages adapt to optimize production of red blood cells or neutrophils.

Detection of neutrophil extracellular traps in patient plasma: method development and validation in systemic lupus erythematosus and healthy donors that carry IRF5 genetic risk

Neutrophil extracellular traps (NETs) are web-like structures extruded by neutrophils after activation or in response to microorganisms. These extracellular structures are decondensed chromatin fibers loaded with antimicrobial granular proteins, peptides, and enzymes. NETs clear microorganisms, thus keeping a check on infections at an early stage, but if dysregulated, may be self-destructive to the body. Indeed, NETs have been associated with autoimmune diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), antiphospholipid syndrome (APS), psoriasis, and gout. More recently, increased NETs associate with COVID-19 disease severity. While there are rigorous and reliable methods to quantify NETs from neutrophils via flow cytometry and immunofluorescence, the accurate quantification of NETs in patient plasma or serum remains a challenge. Here, we developed new methodologies for the quantification of NETs in patient plasma using multiplex ELISA and immunofluorescence methodology. Plasma from patients with SLE, non-genotyped healthy controls, and genotyped healthy controls that carry either the homozygous risk or non-risk IRF5-SLE haplotype were used in this study. The multiplex ELISA using antibodies detecting myeloperoxidase (MPO), citrullinated histone H3 (CitH3) and DNA provided reliable detection of NETs in plasma samples from SLE patients and healthy donors that carry IRF5 genetic risk. An immunofluorescence smear assay that utilizes only 1 µl of patient plasma provided similar results and data correlate to multiplex ELISA findings. The immunofluorescence smear assay is a relatively simple, inexpensive, and quantifiable method of NET detection for small volumes of patient plasma.

Neutrophil phenotypes and functions in cancer: A consensus statement

Neutrophils are the first responders to infection and inflammation and are thus a critical component of innate immune defense. Understanding the behavior of neutrophils as they act within various inflammatory contexts has provided insights into their role in sterile and infectious diseases; however, the field of neutrophils in cancer is comparatively young. Here, we summarize key concepts and current knowledge gaps related to the diverse roles of neutrophils throughout cancer progression. We discuss sources of neutrophil heterogeneity in cancer and provide recommendations on nomenclature for neutrophil states that are distinct in maturation and activation. We address discrepancies in the literature that highlight a need for technical standards that ought to be considered between laboratories. Finally, we review emerging questions in neutrophil biology and innate immunity in cancer. Overall, we emphasize that neutrophils are a more diverse population than previously appreciated and that their role in cancer may present novel unexplored opportunities to treat cancer.

HMGB1-mediated restriction of EPO signaling contributes to anemia of inflammation

Anemia of inflammation, also known as anemia of chronic disease, is refractory to erythropoietin (EPO) treatment, but the mechanisms underlying the EPO refractory state are unclear. Here, we demonstrate that high mobility group box-1 protein (HMGB1), a damage-associated molecular pattern molecule recently implicated in anemia development during sepsis, leads to reduced expansion and increased death of EPO-sensitive erythroid precursors in human models of erythropoiesis. HMGB1 significantly attenuates EPO-mediated phosphorylation of the Janus kinase 2/STAT5 and mTOR signaling pathways. Genetic ablation of receptor for advanced glycation end products, the only known HMGB1 receptor expressed by erythroid precursors, does not rescue the deleterious effects of HMGB1 on EPO signaling, either in human or murine precursors. Furthermore, surface plasmon resonance studies highlight the ability of HMGB1 to interfere with the binding between EPO and the EPOR. Administration of a monoclonal anti-HMGB1 antibody after sepsis onset in mice partially restores EPO signaling in vivo. Thus, HMGB1-mediated restriction of EPO signaling contributes to the chronic phase of anemia of inflammation.

STK25 acts as a regulator of leukocyte migration

The recruitment of leukocytes to sites of infection is an essential component of the innate immune response to pathogens. Defects in leukocyte migration can render the host susceptible to recurrent infections. In our efforts to identify new mediators of innate immunity, we found that serine/threonine protein kinase 25 (STK25) promotes TLR-induced proinflammatory cytokine production. While STK25 has previously been implicated in the regulation of cell migration, its role in leukocyte trafficking has not been defined. To investigate the involvement of STK25 in leukocyte migration, we evaluated baseline hematological parameters from Stk25-deficient (Stk25−/−) mice via a Hemavet. We found that Stk25−/− mice exhibit reduced circulating lymphocytes, neutrophils, and monocytes at steady-state compared to age- and gender-matched wild-type littermate (WT) mice. Immunophenotyping by flow cytometry confirmed these findings and revealed a significant reduction in the frequency of Ly6Chi inflammatory monocytes in Stk25−/− peripheral blood (PB) relative to WT. In contrast, we observed no apparent change in the frequencies of neutrophils and Ly6Chi inflammatory monocytes in Stk25−/− bone marrow, suggesting a defect in leukocyte migration. Finally, we examined the role of STK25 in neutrophil trafficking via an in vitro chemotaxis assay. We found that PB neutrophils from Stk25−/− mice displayed a defect in migration toward WT serum, suggesting a cell-intrinsic role for STK25 in the control of cell trafficking. Additionally, PB neutrophils from WT mice exhibited reduced migration toward Stk25−/− serum, supporting a cell-extrinsic function for STK25. Thus, our data support a new role for STK25 as a mediator of leukocyte trafficking.

IRF5 risk variants contribute to pre-symptomatic SLE by enhancing the levels of circulating NET antigens

SLE is a complex multifactorial autoimmune disease characterized by high levels of autoantibodies that impact many organs. Neutrophil extracellular traps (NETs) are a potential source of antigen leading to the production of autoantibodies, as antibodies against NET components are detected in SLE patients. Higher level of NETs and decreased clearance of NETs are associated with SLE and other autoimmune diseases. Neutrophils play an key role in pediatric lupus and NETs from pediatric lupus patients activate plasmacytoid dendritic cells (pDCs) to produce high levels of IFN-α. Polymorphisms within and around the IRF5 gene associate with risk of developing SLE. We previously reported that healthy donor neutrophils from IRF5 homozygous risk carriers underwent increased spontaneous NETosis, as compared to non-risk donors, that resulted in increased IFN-α production, plasma cell differentiation and autoantibody production. Whether the observed increase in neutrophil-mediated ETosis is a systemic signature of IRF5-driven pre-symptomatic SLE is not known, nor is it known whether these IRF5 risk carriers have defects in NET clearance. We thus developed and optimized new assays to detect small quantities of NET remnants in plasma samples using a combined MPO-CitH3 antibody cocktail followed by detection of DNA by ELISA. Further, we designed a novel immunofluorescence technique to visualize and quantify plasma NETs in healthy donor risk and non-risk carriers, as compared to pediatric and adult SLE patients. In addition, plasma DNase 1 and DNase 1L3 levels were measured. This study will report on the mechanisms by which circulating NETs are increased in pediatric and adult SLE, as well as the contribution of IRF5 genetic risk to NET clearance.

Supported by Lupus Research Alliance Department of Defense CDMRP LRP W81XWH-18-1-0674

STK25 functions as an IRF5 kinase to promote TLR7/8-mediated inflammation

Toll-like receptors (TLRs) represent a subset of pathogen-recognition receptors (PRRs) employed by the innate immune system to detect pathogen-associated molecular patterns (PAMPs) and initiate the response to invading microbes. The transcription factor interferon regulatory factor 5 (IRF5) functions as an important mediator of the inflammatory response downstream of myeloid differentiation factor 88 (MyD88)-dependent TLR activation. While the dysregulation of IRF5 activity has been implicated in the development of several autoimmune diseases including systemic lupus erythematosus and rheumatoid arthritis, the factors that modulate TLR-induced IRF5 post-translational modifications (PTMs) are poorly understood. Therefore, the focus of this study is to identify protein kinases involved in the regulation of TLR7/8 signaling. We performed a kinome-based siRNA screen in human THP-1 monocytic cells and human primary myeloid cells to identify important mediators of TLR7/8-induced TNF-α and IL-6 production. We identified serine/threonine protein kinase 25 (STK25) as a positive regulator of proinflammatory cytokine production in response to TLR7/8 activation in human myeloid cells. We determined that STK25 phosphorylates IRF5 in vitro via multiple biochemical assays. Phosphopeptide mapping by mass spectrometry revealed that STK25 phosphorylates IRF5 at a highly conserved threonine residue. Thus, our data implicate STK25 as a regulator of TLR7/8 signaling through the modulation of IRF5 activity.

The Interleukin-1 Receptor-Associated Kinase 4 Inhibitor PF-06650833 Blocks Inflammation in Preclinical Models of Rheumatic Disease and in Humans Enrolled in a Randomized Clinical Trial

OBJECTIVE

To investigate the role of PF-06650833, a highly potent and selective small-molecule inhibitor of interleukin-1-associated kinase 4 (IRAK4), in autoimmune pathophysiology in vitro, in vivo, and in the clinical setting.

METHODS

Rheumatoid arthritis (RA) inflammatory pathophysiology was modeled in vitro through 1) stimulation of primary human macrophages with anti-citrullinated protein antibody immune complexes (ICs), 2) RA fibroblast-like synoviocyte (FLS) cultures stimulated with Toll-like receptor (TLR) ligands, as well as 3) additional human primary cell cocultures exposed to inflammatory stimuli. Systemic lupus erythematosus (SLE) pathophysiology was simulated in human neutrophils, dendritic cells, B cells, and peripheral blood mononuclear cells stimulated with TLR ligands and SLE patient ICs. PF-06650833 was evaluated in vivo in the rat collagen-induced arthritis (CIA) model and the mouse pristane-induced and MRL/lpr models of lupus. Finally, RNA sequencing data generated with whole blood samples from a phase I multiple-ascending-dose clinical trial of PF-06650833 were used to test in vivo human pharmacology.

RESULTS

In vitro, PF-06650833 inhibited human primary cell inflammatory responses to physiologically relevant stimuli generated with RA and SLE patient plasma. In vivo, PF-06650833 reduced circulating autoantibody levels in the pristane-induced and MRL/lpr murine models of lupus and protected against CIA in rats. In a phase I clinical trial (NCT02485769), PF-06650833 demonstrated in vivo pharmacologic action pertinent to SLE by reducing whole blood interferon gene signature expression in healthy volunteers.

CONCLUSION

These data demonstrate that inhibition of IRAK4 kinase activity can reduce levels of inflammation markers in humans and provide confidence in the rationale for clinical development of IRAK4 inhibitors for rheumatologic indications.

Aim2 Couples With Ube2i for Sumoylation-Mediated Repression of Interferon Signatures in Systemic Lupus Erythematosus

OBJECTIVE

Systemic lupus erythematosus (SLE) involves kidney damage, and the inflammasome-caspase-1 axis has been demonstrated to promote renal pathogenesis. The present study was designed to explore the function of the Absent in Melanoma 2 (Aim2) protein in SLE.

METHODS

Female wild-type Aim2^-/- , Aim2^-/- Ifnar1^-/- , Aim2^-/- Rag1^-/- , and Asc^-/- mice ages 8-10 weeks received 1 intraperitoneal injection of 500 μl pristane or saline, and survival of mice was monitored twice a week for 6 months.

RESULTS

The absence of Aim2, but not Asc, led to enhanced SLE in mice that received pristane treatment. Increased immune cell infiltration and type I interferon (IFN) signatures in the kidneys of Aim2^-/- mice coincided with severity of lupus, which was alleviated by blockade of Ifnar1-mediated signal. Adaptive immune cells were also involved in the glomerular lesions of Aim2^-/- mice after pristane challenge. Importantly, even in the absence of pristane, plasmacytoid dendritic cells in the kidneys of Aim2^-/- mice were significantly increased compared to control animals. Accordingly, transcriptome analysis revealed that Aim2 deficiency led to enhanced expression of type I IFN-induced genes in the kidneys even at an early developmental stage. Mechanistically, Aim2 bound ubiquitin-conjugating enzyme 2i (Ube2i), which mediates sumoylation-based suppression of type I IFN expression deficiency of Aim2 decreased cellular sumoylation, resulting in an augmented type I IFN signature and kidney pathogenesis.

CONCLUSION

The present study demonstrates a critical role for Aim2 in an optimal Ube2i-mediated sumoylation-based suppression of type I IFN generation and development of SLE. As such, the Aim2-Ube2i axis can thus be a novel target for intervention in SLE.

Intracellular IRF5 Dimerization Assay

The intracellular interferon regulatory factor 5 (IRF5) dimerization assay is a technique designed to measure molecular interaction(s) with endogenous IRF5. Here, we present two methods that detect endogenous IRF5 homodimerization and interaction of endogenous IR5 with cell penetrating peptide (CPP) inhibitors. Briefly, to detect endogenous IRF5 dimers, THP-1 cells are incubated in the presence or absence of the IRF5-targeted CPP (IRF5-CPP) inhibitor for 30 min then the cells are stimulated with R848 for 1 h. Cell lysates are separated by native-polyacrylamide gel electrophoresis (PAGE) and IRF5 dimers are detected by immunoblotting with IRF5 antibodies. To detect endogenous interactions between IRF5 and FITC-labeled IRF5-CPP, an in-cell fluorescence resonance energy transfer (FRET) assay is used. In this assay, THP-1 cells are left untreated or treated with FITC-IRF5-CPP conjugated inhibitors for 1 h. Next, cells are fixed, permeabilized, and stained with anti-IRF5 and TRITC-conjugated secondary antibodies. Transfer of fluorescence can be measured and calculated as FRET units. These methods provide rapid and accurate assays to detect IRF5 molecular interactions.

Tumor-intrinsic IRF5 reprograms the tumor immune microenvironment to inhibit breast cancer metastasis

Metastasis of breast cancer and recurrence to incurable disease are leading causes of mortality. Metastasis is driven by extensive cooperation between a tumor and its microenvironment, resulting in the adaptation of molecular mechanisms that evade the immune system and enable pre-metastatic niche (PMN) formation. Little is known of the tumor-intrinsic factors that regulate these mechanisms. Here we show that expression of the transcription factor interferon regulatory factor 5 (IRF5) in breast cancer clinically correlates with tumor immunogenicity, increased T cell and M1 macrophage recruitment and prolonged survival. Conversely, loss of tumor-intrinsic Irf5 establishes a tumor microenvironment and PMN that supports metastasis. Mechanistically, Irf5 alters the composition and secretion of tumor-derived extracellular vesicles (t-dEVs). Upon whole-body pre-conditioning with t-dEVs from Irf5-positive or −negative breast cancer cells, we found increased lung metastatic colonization that replicated findings from orthotopically implanted breast cancer cells. Collectively, our findings uncover an essential role for IRF5 in breast cancer metastasis through its regulation of t-dEV and immune reprogramming.

T Cell-Intrinsic IRF5 Regulates T Cell Signaling, Migration, and Differentiation and Promotes Intestinal Inflammation

IRF5 polymorphisms are associated with multiple immune-mediated diseases, including ulcerative colitis. IRF5 contributions are attributed to its role in myeloid lineages. How T cell-intrinsic IRF5 contributes to inflammatory outcomes is not well understood. We identify a previously undefined key role for T cell-intrinsic IRF5. In mice, IRF5 in CD4⁺ T cells promotes Th1- and Th17-associated cytokines and decreases Th2-associated cytokines. IRF5 is required for the optimal assembly of the TCR-initiated signaling complex and downstream signaling at early times, and at later times binds to promoters of Th1- and Th17-associated transcription factors and cytokines. IRF5 also regulates chemokine receptor-initiated signaling and, in turn, T cell migration. In vivo, IRF5 in CD4⁺ T cells enhances the severity of experimental colitis. Importantly, human CD4⁺ T cells from high IRF5-expressing disease-risk genetic carriers demonstrate increased chemokine-induced migration and Th1/Th17 cytokines and reduced Th2-associated and anti-inflammatory cytokines. These data demonstrate key roles for T cell-intrinsic IRF5 in inflammatory outcomes.

Inhibition of IRF5 hyperactivation protects from lupus onset and severity

The transcription factor IFN regulatory factor 5 (IRF5) is a central mediator of innate and adaptive immunity. Genetic variations within IRF5 are associated with a risk of systemic lupus erythematosus (SLE), and mice lacking Irf5 are protected from lupus onset and severity, but how IRF5 functions in the context of SLE disease progression remains unclear. Using the NZB/W F1 model of murine lupus, we show that murine IRF5 becomes hyperactivated before clinical onset. In patients with SLE, IRF5 hyperactivation correlated with dsDNA titers. To test whether IRF5 hyperactivation is a targetable function, we developed inhibitors that are cell permeable, nontoxic, and selectively bind to the inactive IRF5 monomer. Preclinical treatment of NZB/W F1 mice with an inhibitor attenuated lupus pathology by reducing serum antinuclear autoantibodies, dsDNA titers, and the number of circulating plasma cells, which alleviated kidney pathology and improved survival. Clinical treatment of MRL/lpr and pristane-induced lupus mice with an inhibitor led to significant reductions in dsDNA levels and improved survival. In ex vivo human studies, the inhibitor blocked SLE serum-induced IRF5 activation and reversed basal IRF5 hyperactivation in SLE immune cells. We believe this study provides the first in vivo clinical support for treating patients with SLE with an IRF5 inhibitor.

The Versatility of Sirtuin-1 in Endocrinology and Immunology

Sirtuins belong to the class III family of NAD-dependent histone deacetylases (HDAC) and are involved in diverse physiological processes that range from regulation of metabolism and endocrine function to coordination of immunity and cellular responses to stress. Sirtuin-1 (SIRT1) is the most well-studied family member and has been shown to be critically involved in epigenetics, immunology, and endocrinology. The versatile roles of SIRT1 include regulation of energy sensing metabolic homeostasis, deacetylation of histone and non-histone proteins in numerous tissues, neuro-endocrine regulation via stimulation of hypothalamus-pituitary axes, synthesis and maintenance of reproductive hormones via steroidogenesis, maintenance of innate and adaptive immune system via regulation of T- and B-cell maturation, chronic inflammation and autoimmune diseases. Moreover, SIRT1 is an appealing target in various disease contexts due to the promise of pharmacological and/or natural modulators of SIRT1 activity within the context of endocrine and immune-related disease models. In this review we aim to provide a broad overview on the role of SIRT1 particularly within the context of endocrinology and immunology.

CD4 T Follicular Helper Cells Prevent Depletion of Follicular B Cells in Response to Cecal Ligation and Puncture

Recent studies have demonstrated that induction of a diverse repertoire of memory T cells (“immune education”) affects responses to murine cecal ligation and puncture (CLP), the most widely – used animal model of sepsis. Among the documented effects of immune education on CLP are changes in T cell, macrophage and neutrophil activity, more pronounced organ dysfunction and reduced survival. Little is known, however, about the effects of CLP on B cell responses, and how these responses might be altered by immune education. Importantly, effective B cell responses are modulated by IL21 produced by CD4⁺/CXCR5⁺/PD1⁺ T follicular helper (Tfh) cells. We examined the B cell population in control and immune educated mice 24 h and 60 days after CLP. Education alone increased Tfh cells. Twenty-four hours after CLP, Tfh cells were depleted. However, this reduction was less pronounced in immune educated mice than in controls and the percentage of CD4 T cells expressing a Tfh phenotype increased in the animals. CLP did not alter splenic architecture and decreased numbers of follicular, marginal, and germinal center B cells. CLP induced changes were not, however, noted following CLP in immune educated mice. At 60 days post – CLP, numbers of follicular, germinal center and marginal zone B cells were increased; this increase was more pronounced in immune educated mice. Finally, while CLP reduced the induction of antigen specific B cells in controls, this response was maintained following CLP in immune educated mice. Our data suggest that preexisting Tfh assists in rescuing the B cell response to CLP.

Frontline Science: AMPK regulates metabolic reprogramming necessary for interferon production in human plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) play a crucial role in innate viral immunity as the most potent producers of type I interferons (IFN) in the human body. However, the metabolic regulation of IFN production in such vast quantity remains poorly understood. In this study, AMP-activated protein kinase (AMPK) is strongly implicated as a driver of metabolic reprogramming that the authors and others have observed in pDCs after activation via TLR7/9. Oxygen consumption and mitochondrial membrane potential (MMP) were elevated following stimulation of pDCs with influenza or herpes simplex virus. Blocking these changes using mitochondrial inhibitors abrogated IFN-α production. While it appears that multiple carbon sources can be used by pDCs, blocking pyruvate metabolism had the strongest effect on IFN-α production. Furthermore, we saw no evidence of aerobic glycolysis (AG) during pDC activation and blocking lactate dehydrogenase activity did not inhibit IFN-α. TLR7/9 ligation induces a posttranslational modification in Raptor that is catalyzed by AMPK, and blocking TLR7/9 before virus introduction prevents this change. Finally, it is demonstrated that Dorsomorphin, an AMPK inhibitor, inhibited both IFN-α production and MMP in a dose-dependent manner. Taken together, these data reveal a potential cellular mechanism for the metabolic reprogramming in TLR 7/9-activated pDCs that supports activation and IFN-α production.

Neutrophil extracellular traps in COVID-19

In severe cases of coronavirus disease 2019 (COVID-19), viral pneumonia progresses to respiratory failure. Neutrophil extracellular traps (NETs) are extracellular webs of chromatin, microbicidal proteins, and oxidant enzymes that are released by neutrophils to contain infections. However, when not properly regulated, NETs have the potential to propagate inflammation and microvascular thrombosis - including in the lungs of patients with acute respiratory distress syndrome. We now report that sera from patients with COVID-19 have elevated levels of cell-free DNA, myeloperoxidase-DNA (MPO-DNA), and citrullinated histone H3 (Cit-H3); the latter 2 are specific markers of NETs. Highlighting the potential clinical relevance of these findings, cell-free DNA strongly correlated with acute-phase reactants, including C-reactive protein, D-dimer, and lactate dehydrogenase, as well as absolute neutrophil count. MPO-DNA associated with both cell-free DNA and absolute neutrophil count, while Cit-H3 correlated with platelet levels. Importantly, both cell-free DNA and MPO-DNA were higher in hospitalized patients receiving mechanical ventilation as compared with hospitalized patients breathing room air. Finally, sera from individuals with COVID-19 triggered NET release from control neutrophils in vitro. Future studies should investigate the predictive power of circulating NETs in longitudinal cohorts and determine the extent to which NETs may be novel therapeutic targets in severe COVID-19.

Potential T Cell-Intrinsic Regulatory Roles for IRF5 via Cytokine Modulation in T Helper Subset Differentiation and Function

Interferon Regulatory Factor 5 (IRF5) is one of nine members of the IRF family of transcription factors. Although initially discovered as a key regulator of the type I interferon and pro-inflammatory cytokine arm of the innate immune response, IRF5 has now been found to also mediate pathways involved in cell growth and differentiation, apoptosis, metabolic homeostasis and tumor suppression. Hyperactivation of IRF5 has been implicated in numerous autoimmune diseases, chief among them systemic lupus erythematosus (SLE). SLE is a heterogeneous autoimmune disease in which patients often share similar characteristics in terms of autoantibody production and strong genetic risk factors, yet also possess unique disease signatures. IRF5 pathogenic alleles contribute one of the strongest risk factors for SLE disease development. Multiple models of murine lupus have shown that loss of Irf5 is protective against disease development. In an attempt to elucidate the regulatory role(s) of IRF5 in driving SLE pathogenesis, labs have begun to examine the function of IRF5 in several immune cell types, including B cells, macrophages, and dendritic cells. A somewhat untouched area of research on IRF5 is in T cells, even though Irf5 knockout mice were reported to have skewing of T cell subsets from T helper 1 (Th1) and T helper 17 (Th17) toward T helper 2 (Th2), indicating a potential role for IRF5 in T cell regulation. However, most studies attributed this T cell phenotype in Irf5 knockout mice to dysregulation of antigen presenting cell function rather than an intrinsic role for IRF5 in T cells. In this review, we offer a different interpretation of the literature. The role of IRF5 in T cells, specifically its control of T cell effector polarization and the resultant T cell-mediated cytokine production, has yet to be elucidated. A strong understanding of the regulatory role(s) of this key transcription factor in T cells is necessary for us to grasp the full picture of the complex pathogenesis of autoimmune diseases like SLE.

Targeting potential drivers of COVID-19: Neutrophil extracellular traps

Coronavirus disease 2019 (COVID-19) is a novel, viral-induced respiratory disease that in ∼10-15% of patients progresses to acute respiratory distress syndrome (ARDS) triggered by a cytokine storm. In this Perspective, autopsy results and literature are presented supporting the hypothesis that a little known yet powerful function of neutrophils-the ability to form neutrophil extracellular traps (NETs)-may contribute to organ damage and mortality in COVID-19. We show lung infiltration of neutrophils in an autopsy specimen from a patient who succumbed to COVID-19. We discuss prior reports linking aberrant NET formation to pulmonary diseases, thrombosis, mucous secretions in the airways, and cytokine production. If our hypothesis is correct, targeting NETs directly and/or indirectly with existing drugs may reduce the clinical severity of COVID-19.

Modulating Cytokine Production via Select Packaging and Secretion From Extracellular Vesicles

Cytokines are soluble factors that play vital roles in systemic function due to their ability to initiate and mediate cell-to-cell communication. Another important mechanism of intercellular communication that has gained significant attention in the past 10 years is the release of extracellular vesicles (EVs). EVs are released by all cells during normal physiology, in states of resting and activation, as well as during disease. Accumulating evidence indicates that cytokines may be packaged into EVs, and the packaging of cytokines into EVs, along with their ultimate secretion, may also be regulated by cytokines. Importantly, the repertoire of biomolecules packaged into EVs is shaped by the biological state of the cell (resting vs. activated and healthy vs. disease) and the EV biogenesis pathway involved, thus providing mechanisms by which EV packaging and secretion may be modulated. Given the critical role of cytokines in driving acute and chronic inflammatory and autoimmune diseases, as well as their role in establishing the tumor immune microenvironment, in this review, we will focus on these disease settings and summarize recent progress and mechanisms by which cytokines may be packaged within and modulated by EVs, as a therapeutic option for regulating innate and adaptive immunity.

Nebulized in-line endotracheal dornase alfa and albuterol administered to mechanically ventilated COVID-19 patients: A case series

Background

Mechanically ventilated patients with coronavirus disease 2019 (COVID-19) have a mortality of 24–53%, in part due to distal mucopurulent secretions interfering with ventilation. Dornase alfa is recombinant human DNase 1 and digests DNA in mucoid sputum. Nebulized dornase alfa is FDA-approved for cystic fibrosis treatment. DNA from neutrophil extracellular traps (NETs) contributes to the viscosity of mucopurulent secretions. NETs are found in the serum of patients with severe COVID-19, and targeting NETs reduces mortality in animal models of acute respiratory distress syndrome (ARDS). Thus, dornase alfa may be beneficial to patients with severe COVID-19—acting as a mucolytic and targeting NETs. However, delivery of nebulized drugs can aerosolize SARS-CoV-2, which causes COVID-19, increasing the infection risk for staff. Here, we report a single center case series where dornase alfa was administered through an in-line nebulizer system to minimize risk of virus aerosolization.

Methods

Demographic, clinical data, and outcomes were collected from the electronic medical records of five mechanically ventilated patients with COVID-19—including three requiring veno-venous extracorporeal membrane oxygenation (VV-ECMO)—treated with nebulized in-line endotracheal dornase alfa co-administered with albuterol (used to increase delivery to the alveoli), between March 31 and April 24, 2020. Data on tolerability and responses, including longitudinal values capturing respiratory function and inflammatory status, were analyzed.

Results

Following nebulized in-line administration of dornase alfa with albuterol, the fraction of inspired oxygen requirements was reduced for all five patients. All patients remain alive and two patients have been discharged from the intensive care unit. No drug associated toxicities were identified.

Conclusions

The results presented in this case series suggest that dornase alfa will be well-tolerated by critically ill patients with COVID-19. Clinical trials are required to formally test the dosing, safety, and efficacy of dornase alfa in COVID-19, and two have recently been registered (NCT04359654 and NCT04355364). With this case series, we hope to contribute to the development of management approaches for critically ill patients with COVID-19.

Targeting interferon regulatory factor 5 (IRF5) activation with a peptide inhibitor ameliorates clinical lupus in MRL/lpr mice

Systemic lupus erythematosus (SLE) is associated with high levels of inflammatory cytokines as well as increased autoantibodies. Accumulating evidence show that loss and/or inhibition of the transcription factor interferon regulatory factor 5 (Irf5) ameliorates disease severity. Previously, we characterized a peptide inhibitor targeting Irf5 activation in the NZB/W F1 murine model of lupus and showed therapeutic protection when treated before disease onset. Here, we expanded our study to include a clinical treatment arm in the MRL/lpr lupus model after disease onset. 8 week-old MRL/lpr female mice were IP-injected with PBS or inhibitor at a dose of 100ug/mouse/injection on D0, D1, D4, D7 and D14. Proteinuria was monitored weekly; serum auto-antibodies were measured by ANA-HEp-2; anti-dsDNA IgG by ELISA, and kidney pathology was assessed. Blood was collected weekly to examine Irf5 expression and activation in immune cell subsets by imaging flow cytometry. At 8 weeks-old and before treatment, MRL/lpr mice were positive for anti-nuclear antibodies (ANA). At week 17, IgG and IgM staining on HEp-2 cells showed stronger fluorescence intensity in the control group (p=0.0053 for IgG; p<0.0001 for IgM). Serum anti-dsDNA IgG levels were also higher in the control group (782179 ± 337490 U/mL, n=7) as compared to treated (385947 ± 156487 U/mL, n=9). By week 17, 2 out of 9 mice in the control group had died, while all mice in the treated group survived. Proteinuria and body weights remained similar between groups. Data indicate that direct inhibition of murine Irf5 in multiple lupus models (NZB/W F1 and MRL/lpr) ameliorates disease severity. The inhibitor was also well-tolerated supporting the therapeutic utility of IRF5 inhibitors in the clinic.

Inhibition of IRF5 cellular activity with cell-penetrating peptides that target homodimerization

The transcription factor interferon regulatory factor 5 (IRF5) plays essential roles in pathogen-induced immunity downstream of Toll-, nucleotide-binding oligomerization domain-, and retinoic acid-inducible gene I-like receptors and is an autoimmune susceptibility gene. Normally, inactive in the cytoplasm, upon stimulation, IRF5 undergoes posttranslational modification(s), homodimerization, and nuclear translocation, where dimers mediate proinflammatory gene transcription. Here, we report the rational design of cell-penetrating peptides (CPPs) that disrupt IRF5 homodimerization. Biochemical and imaging analysis shows that IRF5-CPPs are cell permeable, noncytotoxic, and directly bind to endogenous IRF5. IRF5-CPPs were selective and afforded cell type- and species-specific inhibition. In plasmacytoid dendritic cells, inhibition of IRF5-mediated interferon-α production corresponded to a dose-dependent reduction in nuclear phosphorylated IRF5 [p(Ser⁴⁶²)IRF5], with no effect on pIRF5 levels. These data support that IRF5-CPPs function downstream of phosphorylation. Together, data support the utility of IRF5-CPPs as novel tools to probe IRF5 activation and function in disease.

Immune-phenotyping IRF5 genetic risk and in vivo targeting of Irf5 hyper-activation in mouse models of lupus

Genetic variations within interferon regulatory factor 5 (IRF5) associate with risk of systemic lupus erythematosus (SLE) and mice lacking Irf5 are protected from lupus onset and severity. Exactly how IRF5 functions in the context of SLE disease progression remains unclear. We sought to determine how IRF5 genetic risk contributes to SLE disease onset and severity, and whether targeting IRF5 with select inhibitors would alleviate disease severity and mortality. Studies were performed in blood from genotyped healthy donors, SLE patients and mouse models of murine lupus. In NZB/W F1 lupus mice, we found that Irf5 is already hyper-activated before clinical onset in a cell type-specific manner. In healthy donors carrying IRF5 genetic risk, we detected IRF5 hyper-activation in the myeloid compartment that drives a pre-symptomatic SLE immune-phenotype. In SLE patients, IRF5 hyper-activation correlates with SLEDAI and dsDNA titers. To test whether IRF5 hyper-activation is a targetable function, we developed novel inhibitors that are cell permeable, non-toxic and selectively bind to the inactive IRF5 monomer. Treatment of NZB/W F1 and MRL/lpr mice with inhibitor attenuated lupus pathology by reducing serum ANA and dsDNA titers. In NZB/W F1 mice, we detected significant reductions in the number of circulating plasma cells and age- or autoimmune-associated B cells (ABCs), which alleviated kidney pathology and improved overall survival. In ex vivo human studies, the inhibitor blocked SLE serum-induced IRF5 activation in healthy immune cells and reversed basal IRF5 hyper-activation in SLE immune cells. This study provides the first in vivo pre-clinical support for treating SLE patients with an IRF5 inhibitor.

Novel role(s) for Irf5 in controlling myelopoiesis and erythropoiesis

Causes of erythropoiesis dysregulation during anemia of inflammation remain largely unknown. Mammalian erythropoiesis can be divided into differentiation of early progenitors and maturation of precursors within anatomic niches called erythroblastic islands (EBI). EBIs consist of a central macrophage surrounded by differentiating erythroblasts and myeloid cells. While recent studies have focused on interactions of the macrophage and surrounding cells, much less is known about the transcription factors that regulate EBI formation and function. Data from scRNAseq revealed that interferon regulatory factor 5 (Irf5) is expressed by the central macrophage within EBIs. At steady state, Irf5−/− mice have decreased numbers of EBIs in the bone marrow (BM) with altered composition - increased CD71 (erythroid marker) and CD11b and Ly6G (myeloid markers). We also found increased numbers of reticulocytes in Irf5−/− BM. We hypothesize that Irf5 has a conserved function in mammalian blood formation by regulating the cellular output of erythroid and myeloid cells. To test this, we induced stress erythropoiesis in wild-type (wt) and Irf5−/− age- and littermate-matched mice by submandibular bleeding. Mice were bled twice (Day 0 and 2) and complete blood counts, erythropoiesis, and EBI formation monitored over recovery (12 days). Using CD44/Ter119 and Forward Scatter as markers of terminal erythropoiesis, we found that erythroid differentiation was significantly delayed in Irf5−/− mice resulting in increased mortality and corresponding to a significant decrease in EBI formation. These data identify Irf5 as a new regulator of the erythroid-myeloid balance within the EBI that results in altered function(s) during anemia of inflammation.

Molecular mechanisms by which interferon regulatory factor 5 (IRF5) transduces signaling downstream of BCR and BCR/TLR9 pathways

The transcription factor IRF5 modulates human B cell activation, proliferation, and plasmablast differentiation via an intrinsic mechanism. Targeted knockdown of IRF5 in human primary naïve B cells revealed a significant reduction in CD19+CD86+ B cells, which demarcate early activated B cells, after BCR/TLR9 stimulation, resulting in reduced clonal expansion and plasmablast differentiation. The mechanism(s) by which IRF5 modulates early B cell activation is not known. We previously found that BCR stimulation alone was insufficient to induce IRF5 nuclear translocation (activation), while BCR/TLR9 stimulation induced robust IRF5 activation. Thus, the focus of this study is to determine the mechanism(s) by which IRF5 functions downstream of BCR and dual BCR/TLR9 signaling at the early time points of activation (5 and 15 min). Experiments were performed in human B cells and B cells from wild-type and Irf5−/− mice. Signaling and protein interactions were examined by Western blot, immunoprecipitation, flow cytometry, and biochemical assay. We identified Bruton’s tyrosine kinase (Btk) as a novel interacting partner of IRF5 in both unstimulated and stimulated human and murine B cells. Of note, active phosphorylated Btk was bound to IRF5 only in stimulated cells. Preliminary data also suggest a defect downstream of Btk activation in Irf5−/− B cells. Together, these data indicate a conserved role for IRF5 in the early stages of B cell activation via BCR/TLR9 signaling.

In vivo mechanisms by which Irf5 regulates BCR-, TCR- and TLR-induced plasma cell generation and antibody secretion

Generation of antibody secreting cells (ASCs) requires multiple B cell activation pathways, including B cell receptor (BCR), T cell receptor (TCR), and Toll-like receptors (TLRs). In human naïve B cells, we reported that knockdown of interferon regulatory factor 5 (IRF5) resulted in IgD retention, reduced proliferation and plasma cell differentiation, and reduced IgG secretion. Defects were due to early impairments in B cell activation and clonal expansion. Conversely, murine Irf5 was reported to regulate antibody production through direct control of class switch recombination (CSR) at the γ2a locus. To further elucidate distinct and overlapping roles between human and murine IRF5 in the regulation of plasma cell differentiation and antibody production, we performed in vivo analysis of B and T cell differentiation and function in wild-type (wt) and Irf5 knockout (ko) littermate mice after immunization. B and T cell subsets were analyzed by multi-color flow cytometry. Naïve B cells were in vitro differentiated to ASCs with CpG-B, anti-IgM, anti-CD40 and IL-21. Kinetics of B cell activation, AID expression and IgG production were determined. BCR and TCR signaling were examined by phospho-flow. A combination of T-dependent/independent and TLR-dependent/independent immunizations were used to study ASC differentiation. RAG−/− mice were used to determine cell type-specific effects. Results indicate distinct roles for human and murine IRF5 at the early stages of BCR signaling and redundant roles at the later stages of CSR, plasma cell differentiation and antibody secretion via regulation of AID.

Neutrophil extracellular traps (NETs) as markers of disease severity in COVID-19

In severe cases of coronavirus disease 2019 (COVID-19), viral pneumonia progresses to respiratory failure. Neutrophil extracellular traps (NETs) are extracellular webs of chromatin, microbicidal proteins, and oxidant enzymes that are released by neutrophils to contain infections. However, when not properly regulated, NETs have potential to propagate inflammation and microvascular thrombosis, including in the lungs of patients with acute respiratory distress syndrome. While elevated levels of blood neutrophils predict worse outcomes in COVID-19, the role of NETs has not been investigated. We now report that sera from patients with COVID-19 (n=50 patients, n=84 samples) have elevated levels of cell-free DNA, myeloperoxidase(MPO)-DNA, and citrullinated histone H3 (Cit-H3); the latter two are highly specific markers of NETs. Highlighting the potential clinical relevance of these findings, cell-free DNA strongly correlated with acute phase reactants including C-reactive protein, D-dimer, and lactate dehydrogenase, as well as absolute neutrophil count. MPO-DNA associated with both cell-free DNA and absolute neutrophil count, while Cit-H3 correlated with platelet levels. Importantly, both cell-free DNA and MPO-DNA were higher in hospitalized patients receiving mechanical ventilation as compared with hospitalized patients breathing room air. Finally, sera from individuals with COVID-19 triggered NET release from control neutrophils in vitro. In summary, these data reveal high levels of NETs in many patients with COVID-19, where they may contribute to cytokine release and respiratory failure. Future studies should investigate the predictive power of circulating NETs in longitudinal cohorts, and determine the extent to which NETs may be novel therapeutic targets in severe COVID-19.

IRF5 genetic risk variants drive myeloid-specific IRF5 hyperactivation and presymptomatic SLE

Genetic variants within or near the interferon regulatory factor 5 (IRF5) locus associate with systemic lupus erythematosus (SLE) across ancestral groups. The major IRF5-SLE risk haplotype is common across populations, yet immune functions for the risk haplotype are undefined. We characterized the global immune phenotype of healthy donors homozygous for the major risk and nonrisk haplotypes and identified cell lineage-specific alterations that mimic presymptomatic SLE. Contrary to previous studies in B lymphoblastoid cell lines and SLE immune cells, IRF5 genetic variants had little effect on IRF5 protein levels in healthy donors. Instead, we detected basal IRF5 hyperactivation in the myeloid compartment of risk donors that drives the SLE immune phenotype. Risk donors were anti-nuclear antibody positive with anti-Ro and -MPO specificity, had increased circulating plasma cells and plasmacytoid dendritic cells, and had enhanced spontaneous NETosis. The IRF5-SLE immune phenotype was conserved over time and probed mechanistically by ex vivo coculture, indicating that risk neutrophils are drivers of the global immune phenotype. RNA-Seq of risk neutrophils revealed increased IRF5 transcript expression, IFN pathway enrichment, and decreased expression of ROS pathway genes. Altogether, the data support that individuals carrying the IRF5-SLE risk haplotype are more susceptible to environmental/stochastic influences that trigger chronic immune activation, predisposing to the development of clinical SLE.

RNAi Transfection Optimized in Primary Naïve B Cells for the Targeted Analysis of Human Plasma Cell Differentiation

Upon antigen recognition, naïve B cells undergo rapid proliferation followed by differentiation to specialized antibody secreting cells (ASCs), called plasma cells. Increased circulating plasma cells are reported in patients with B cell-associated malignancies, chronic graft-vs.-host disease, and autoimmune disorders. Our aim was to optimize an RNAi-based method that efficiently and reproducibly knocks-down genes of interest in human primary peripheral B cells for the targeted analysis of ASC differentiation. The unique contributions of transcriptional diversity in species-specific regulatory networks and the mechanisms of gene function need to be approached directly in human B cells with tools to hone our basic inferences from animal models to human biology. To date, methods for gene knockdown in human primary B cells, which tend to be more refractory to transfection than immortalized B cell lines, have been limited by losses in cell viability and ineffective penetrance. Our single-step siRNA nucleofector-based approach for human primary naïve B cells demonstrates reproducible knockdown efficiency (~40–60%). We focused on genes already known to play key roles in murine ASC differentiation, such as interferon regulatory factor 4 (IRF4) and AID. This study reports a validated non-viral method of siRNA delivery into human primary B cells that can be applied to study gene regulatory networks that control human ASC differentiation.

Chronic TLR7 and TLR9 signaling drives anemia via differentiation of specialized hemophagocytes

Cytopenias are an important clinical problem associated with inflammatory disease and infection. We show that specialized phagocytes that internalize red blood cells develop in Toll-like receptor 7 (TLR7)-driven inflammation. TLR7 signaling caused the development of inflammatory hemophagocytes (iHPCs), which resemble splenic red pulp macrophages but are a distinct population derived from Ly6C^hi monocytes. iHPCs were responsible for anemia and thrombocytopenia in TLR7-overexpressing mice, which have a macrophage activation syndrome (MAS)-like disease. Interferon regulatory factor 5 (IRF5), associated with MAS, participated in TLR7-driven iHPC differentiation. We also found iHPCs during experimental malarial anemia, in which they required endosomal TLR and MyD88 signaling for differentiation. Our findings uncover a mechanism by which TLR7 and TLR9 specify monocyte fate and identify a specialized population of phagocytes responsible for anemia and thrombocytopenia associated with inflammation and infection.

Coordination between innate immune cells, type I IFNs and IRF5 drives SLE pathogenesis

Systemic lupus erythematosus (SLE) is a complex autoimmune disease which affects multiple organs. The type I interferon (IFN) gene signature and circulating autoantibodies are hallmarks of SLE. Plasmacytoid dendritic cells (pDCs) are considered the main producers of type I IFN and production is modulated by multiple other immune cell types. In SLE, essentially every immune cell type is dysregulated and aberrant deregulation is thought to be due, in part, to direct or indirect exposure to IFN. Genetic variants within or around the transcription factor interferon regulatory factor 5 (IRF5) associate with SLE risk. Elevated IFNα activity was detected in the sera of SLE patients carrying IRF5 risk polymorphisms who were positive for either anti-RNA binding protein (anti-RBP) or anti-double-stranded DNA (anti-dsDNA) autoantibodies. Neutrophils are also an important source of type I IFNs and are found in abundance in human blood. Neutrophil extracellular traps (NETs) are considered a potential source of antigenic trigger in SLE that can lead to type I IFN gene induction, as well as increased autoantibody production. In this review, we will focus on immune cell types that produce type I IFNs and/or are affected by type I IFN in SLE. In addition, we will discuss potential inducers of endogenous type I IFN production in SLE. Last, we will postulate how the different immune cell populations may be affected by an IRF5-SLE risk haplotype.

Insulin-like growth factor receptor signaling in breast tumor epithelium protects cells from endoplasmic reticulum stress and regulates the tumor microenvironment

BACKGROUND

Early analyses of human breast cancer identified high expression of the insulin-like growth factor type 1 receptor (IGF-1R) correlated with hormone receptor positive breast cancer and associated with a favorable prognosis, whereas low expression of IGF-1R correlated with triple negative breast cancer (TNBC). We previously demonstrated that the IGF-1R acts as a tumor and metastasis suppressor in the Wnt1 mouse model of TNBC. The mechanisms for how reduced IGF-1R contributes to TNBC phenotypes is unknown.

METHODS

We analyzed the METABRIC dataset to further stratify IGF-1R expression with patient survival and specific parameters of TNBC. To investigate molecular events associated with the loss of IGF-1R function in breast tumor cells, we inhibited IGF-1R in human cell lines using an IGF-1R blocking antibody and analyzed MMTV-Wnt1-mediated mouse tumors with reduced IGF-1R function through expression of a dominant-negative transgene.

RESULTS

Our analysis of the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) dataset revealed association between low IGF-1R and reduced overall patient survival. IGF-1R expression was inversely correlated with patient survival even within hormone receptor-positive breast cancers, indicating reduced overall patient survival with low IGF-1R was not due simply to low IGF-1R expression within TNBCs. Inhibiting IGF-1R in either mouse or human tumor epithelial cells increased reactive oxygen species (ROS) production and activation of the endoplasmic reticulum stress response. IGF-1R inhibition in tumor epithelial cells elevated interleukin (IL)-6 and C-C motif chemokine ligand 2 (CCL2) expression, which was reversed by ROS scavenging. Moreover, the Wnt1/dnIGF-1R primary tumors displayed a tumor-promoting immune phenotype. The increased CCL2 promoted an influx of CD11b⁺ monocytes into the primary tumor that also had increased matrix metalloproteinase (MMP)-2, MMP-3, and MMP-9 expression. Increased MMP activity in the tumor stroma was associated with enhanced matrix remodeling and collagen deposition. Further analysis of the METABRIC dataset revealed an increase in IL-6, CCL2, and MMP-9 expression in patients with low IGF-1R, consistent with our mouse tumor model and data in human breast cancer cell lines.

CONCLUSIONS

Our data support the hypothesis that reduction of IGF-1R function increases cellular stress and cytokine production to promote an aggressive tumor microenvironment through infiltration of immune cells and matrix remodeling.

Therapeutic Targeting of IRFs: Pathway-Dependence or Structure-Based?

The interferon regulatory factors (IRFs) are a family of master transcription factors that regulate pathogen-induced innate and acquired immune responses. Aberration(s) in IRF signaling pathways due to infection, genetic predisposition and/or mutation, which can lead to increased expression of type I interferon (IFN) genes, IFN-stimulated genes (ISGs), and other pro-inflammatory cytokines/chemokines, has been linked to the development of numerous diseases, including (but not limited to) autoimmune and cancer. What is currently lacking in the field is an understanding of how best to therapeutically target these transcription factors. Many IRFs are regulated by post-translational modifications downstream of pattern recognition receptors (PRRs) and some of these modifications lead to activation or inhibition. We and others have been able to utilize structural features of the IRFs in order to generate dominant negative mutants that inhibit function. Here, we will review potential therapeutic strategies for targeting all IRFs by using IRF5 as a candidate targeting molecule.

IRF5 hyper-activation is a driver of systemic lupus erythematosus (SLE) onset and severity

The transcription factor interferon regulatory factor 5 (IRF5) is a central mediator of innate and adaptive immunity. Genetic variations within IRF5 associate with risk for systemic lupus erythematosus (SLE) and mice lacking Irf5 are protected from lupus onset and severity. Here we show that IRF5 genetic variants confer risk by increasing basal IRF5 activation in plasmacytoid dendritic cells resulting in elevated IFNα production. IRF5 hyperactivation in SLE immune cells correlates with SLEDAI and dsDNA titers. Upon characterization of immune cells from NZB/W F1 lupus-prone mice, we found that Irf5 was hyperactivated at 19 weeks-old, which precedes clinical onset. To test whether IRF5 hyperactivation is a driver of SLE, we developed novel therapeutics targeting IRF5 activation. Inhibitors are cell permeable, non-toxic and selectively bind to full-length inactive IRF5 monomer. In vivo analysis revealed functional mimicry with Irf5 knockout mice and treatment of NZB/W F1 mice for a two-week period prior to clinical onset gave significantly reduced dsDNA titers, anti-nuclear antibody (ANA) staining, and improved survival. The IRF5 inhibitor also blocked ex vivo SLE serum-induced IRF5 activation and reversed IRF5 hyperactivation detected in SLE immune cells. Results implicate IRF5 hyperactivation as a risk factor that drives SLE and provide the first pre-clinical support for treating SLE patients or those at risk of SLE with IRF5 inhibitors.

IRF4 and IRF5 transcription factors exhibit shared and distinct roles in regulating human B cell differentiation and function

Upon recognition of antigen, B cells undergo rapid proliferation followed by differentiation to specialized antibody secreting cells (ASCs). Increased levels of ASCs are seen in autoimmune diseases, such as systemic lupus erythematosus (SLE), and some B cell-associated malignancies. Studies suggest that altered transcription factor (TF) expression and/or activation play a role in the imbalance of B cell subsets in these diseases. Interferon regulatory factor 5 (IRF5) is one such TF, as polymorphisms in IRF5 associate with risk of numerous autoimmune diseases and correlate with elevated IRF5 expression in SLE patients. Recent findings from IRF5 knockdown (KD) in purified naïve B cells identified IRF5 as an early intrinsic regulator of B cell activation, proliferation and plasma cell differentiation in response to TLR9 activation. In this study, IRF4 was identified as a new IRF5 target gene by ChIP-Seq and RNA-Seq analysis. IRF4 expression is high in ASCs and murine studies show that it plays an essential, cell-intrinsic role in the generation of germinal center B cells. To date, little is known of IRF4 function in human ASC differentiation or whether these two factors (IRF4 and 5) cooperate. Activation of TLR9 and B cell receptor (BCR) revealed distinct kinetic changes in IRF4 and IRF5 during the early transition of naïve B cells to ASCs. Moreover, IRF4 KD of human primary naïve B cells resulted in significant IgD retention and reduced plasmablast (PB) differentiation without loss of early B cell activation (CD86) or key regulatory factors of class switch recombination in response to TLR9/BCR stimulation. Together, these results show that IRF4 and IRF5 are kinetically distinct TFs that have non-redundant roles in human ASC differentiation.

B Cell-Intrinsic Role for IRF5 in TLR9/BCR-Induced Human B Cell Activation, Proliferation, and Plasmablast Differentiation

Upon recognition of antigen, B cells undergo rapid proliferation followed by differentiation to specialized antibody secreting cells (ASCs). During this transition, B cells are reliant upon a multilayer transcription factor network to achieve a dramatic remodeling of the B cell transcriptional landscape. Increased levels of ASCs are often seen in autoimmune diseases and it is believed that altered expression of regulatory transcription factors play a role in this imbalance. The transcription factor interferon regulatory factor 5 (IRF5) is one such candidate as polymorphisms in IRF5 associate with risk of numerous autoimmune diseases and correlate with elevated IRF5 expression. IRF5 genetic risk has been widely replicated in systemic lupus erythematosus (SLE), and loss of Irf5 ameliorates disease in murine lupus models, in part, through the lack of pathogenic autoantibody secretion. It remains unclear, however, whether IRF5 is contributing to autoantibody production through a B cell-intrinsic function. To date, IRF5 function in healthy human B cells has not been characterized. Using human primary naive B cells, we define a critical intrinsic role for IRF5 in B cell activation, proliferation, and plasmablast differentiation. Targeted IRF5 knockdown resulted in significant immunoglobulin (Ig) D retention, reduced proliferation, plasmablast differentiation, and IgG secretion. The observed decreases were due to impaired B cell activation and clonal expansion. Distinct from murine studies, we identify and confirm new IRF5 target genes, IRF4, ERK1, and MYC, and pathways that mediate IRF5 B cell-intrinsic function. Together, these results identify IRF5 as an early regulator of human B cell activation and provide the first dataset in human primary B cells to map IRF5 dysfunction in SLE.

Interferon regulatory factor 5 (IRF5) suppresses hepatitis C virus (HCV) replication and HCV-associated hepatocellular carcinoma

Hepatitis C virus (HCV) infection is a major risk factor for the development of chronic liver disease. The disease typically progresses from chronic HCV to fibrosis, cirrhosis, hepatocellular carcinoma (HCC), and death. Chronic inflammation associated with HCV infection is implicated in cirrhosis and HCC, but the molecular players and signaling pathways contributing to these processes remain largely unknown. Interferon regulatory factor 5 (IRF5) is a molecule of interest in HCV-associated HCC because it has critical roles in virus-, Toll-like receptor (TLR)-, and IFN-induced signaling pathways. IRF5 is also a tumor suppressor, and its expression is dysregulated in several human cancers. Here, we present first evidence that IRF5 expression and signaling are modulated during HCV infection. Using HCV infection of human hepatocytes and cells with autonomously replicating HCV RNA, we found that levels of IRF5 mRNA and protein expression were down-regulated. Of note, reporter assays indicated that IRF5 re-expression inhibited HCV protein translation and RNA replication. Gene expression analysis revealed significant differences in the expression of cancer pathway mediators and autophagy proteins rather than in cytokines between IRF5- and empty vector-transfected HCV replicon cells. IRF5 re-expression induced apoptosis via loss in mitochondrial membrane potential, down-regulated autophagy, and inhibited hepatocyte cell migration/invasion. Analysis of clinical HCC specimens supports a pathologic role for IRF5 in HCV-induced HCC, as IRF5 expression was down-regulated in livers from HCV-positive versus HCV-negative HCC patients or healthy donor livers. These results identify IRF5 as an important suppressor of HCV replication and HCC pathogenesis.

Interferon regulatory factor signaling in autoimmune disease

Interferon regulatory factors (IRFs) play critical roles in pathogen-induced innate immune responses and the subsequent induction of adaptive immune response. Dysregulation of IRF signaling is therefore thought to contribute to autoimmune disease pathogenesis. Indeed, numerous murine in vivo studies have documented protection from or enhanced susceptibility to particular autoimmune diseases in Irf-deficient mice. What has been lacking, however, is replication of these in vivo observations in primary immune cells from patients with autoimmune disease. These types of studies are essential as the majority of in vivo data support a protective role for IRFs in Irf-deficient mice, yet IRFs are often found to be overexpressed in patient immune cells. A significant body of work is beginning to emerge from both of these areas of study - mouse and human.

A conserved region within interferon regulatory factor 5 controls breast cancer cell migration through a cytoplasmic and transcription-independent mechanism

Background

Migration of breast cancer cells out of a duct or lobule is a prerequisite for invasion and metastasis. However, the factors controlling breast cancer cell migration are not fully elucidated. We previously found that expression of the transcription factor interferon regulatory factor 5 (IRF5) is significantly decreased as a breast lesion progresses from a non-malignant stage to ductal carcinoma in situ and is eventually lost in ~80% of invasive ductal carcinomas examined. Human in vitro and murine in vivo models of invasive breast cancer confirmed an important role for IRF5 in regulating cell motility, invasion and/or metastasis; yet, the mechanism(s) by which this occurs is not known. Since IRF5 is primarily expressed in the cytoplasm of human mammary epithelial cells, we hypothesized that IRF5 may function in a transcription-independent manner to control intrinsic cell migration.

Results

A series of IRF5 deletion mutants were tested in cell motility, invasion and migration assays. A novel, conserved 10 amino acid domain was identified that regulates mammary epithelial cell migration. This region (∆115-125) is downstream of IRF5′s DNA binding domain and therefore when absent, retains IRF5 transcription activity but loses cell migration control. An IRF5 construct with a mutated nuclear localization signal further confirmed that IRF5 controls migration in a cytoplasmic and transcription-independent manner. Candidate cytoskeletal molecules were identified in MDA-MB-231 cells to interact with IRF5 by immunoprecipitation and mass spectrometry analysis. α6-tubulin was independently confirmed to interact with endogenous IRF5 in MCF-10A cells. Alterations in F-actin bundling after staining EV- and IRF5-231 cells with phalloidin suggests that IRF5 may control cell migration/motility through its interaction with cytoskeletal molecules that contribute to the formation of F-actin networks. Last and most notably, we found that IRF5′s control of cell migration is not restricted to mammary epithelial cells but functions in other epithelial cell types suggesting a more global role for this newly identified cell migratory function of IRF5.

Conclusions

These findings are significant as they identify a new regulator of epithelial cell migration and provide specific insight into the mechanism(s) by which loss of IRF5 expression in mammary epithelial cells contributes to breast cancer metastasis.

Role of Tertiary Lymphoid Structures (TLS) in Anti-Tumor Immunity: Potential Tumor-Induced Cytokines/Chemokines that Regulate TLS Formation in Epithelial-Derived Cancers

Following the successes of monoclonal antibody immunotherapies (trastuzumab (Herceptin^®) and rituximab (Rituxan^®)) and the first approved cancer vaccine, Provenge^® (sipuleucel-T), investigations into the immune system and how it can be modified by a tumor has become an exciting and promising new field of cancer research. Dozens of clinical trials for new antibodies, cancer and adjuvant vaccines, and autologous T and dendritic cell transfers are ongoing in hopes of identifying ways to re-awaken the immune system and force an anti-tumor response. To date, however, few consistent, reproducible, or clinically-relevant effects have been shown using vaccine or autologous cell transfers due in part to the fact that the immunosuppressive mechanisms of the tumor have not been overcome. Much of the research focus has been on re-activating or priming cytotoxic T cells to recognize tumor, in some cases completely disregarding the potential roles that B cells play in immune surveillance or how a solid tumor should be treated to maximize immunogenicity. Here, we will summarize what is currently known about the induction or evasion of humoral immunity via tumor-induced cytokine/chemokine expression and how formation of tertiary lymphoid structures (TLS) within the tumor microenvironment may be used to enhance immunotherapy response.