IRF8 mutations and human dendritic-cell immunodeficiency

FLT3L governs the development of partially overlapping hematopoietic lineages in humans and mice

FMS-related tyrosine kinase 3 ligand (FLT3L), encoded by FLT3LG, is a hematopoietic factor essential for the development of natural killer (NK) cells, B cells, and dendritic cells (DCs) in mice. We describe three humans homozygous for a loss-of-function FLT3LG variant with a history of various recurrent infections, including severe cutaneous warts. The patients' bone marrow (BM) was hypoplastic, with low levels of hematopoietic progenitors, particularly myeloid and B cell precursors. Counts of B cells, monocytes, and DCs were low in the patients' blood, whereas the other blood subsets, including NK cells, were affected only moderately, if at all. The patients had normal counts of Langerhans cells (LCs) and dermal macrophages in the skin but lacked dermal DCs. Thus, FLT3L is required for B cell and DC development in mice and humans. However, unlike its murine counterpart, human FLT3L is required for the development of monocytes but not NK cells.

STATs signaling pathways in dendritic cells: As potential therapeutic targets?

Dendritic cells (DCs) are professional antigen-presenting cells (APCs), including heterogenous populations with phenotypic and functional diversity that coordinate bridging innate and adaptive immunity. Signal transducer and activator of transcriptions (STAT) factors as key proteins in cytokine signaling were shown to play distinct roles in the maturation and antigen presentation of DCs and play a pivotal role in modulating immune responses mediated by DCs such as differentiation of T cells to T helper (Th) 1, Th2 or regulatory T (Treg) cells. This review sheds light on the importance of STAT transcription factors' signaling pathways in different subtypes of DCs and highlights their targeting potential usages for improving DC-based immunotherapies for patients who suffer from cancer or diverse autoimmune conditions according to the type of the STAT transcription factor and its specific activating or inhibitory agent.

Genetic, immunologic, and clinical features of 830 patients with Mendelian susceptibility to mycobacterial diseases (MSMD): A systematic review

BACKGROUND

Mendelian susceptibility to mycobacterial diseases (MSMD) is a rare clinical syndrome characterized by vulnerability to weakly virulent mycobacterial species, including Bacillus Calmette-Guérin (BCG) vaccines and environmental mycobacteria.

OBJECTIVE

We sought to perform a systematic review of the genetic, immunologic, and clinical findings for reported patients with MSMD.

METHODS

We searched PubMed, Web of Science, and Scopus databases for publications in English relating to MSMD. All full texts were evaluated for eligibility for inclusion. Two reviewers independently selected the publications, with a third reviewer consulted in cases of disagreement.

RESULTS

A primary systematic search and searches of other resources identified 16,155 articles. In total, 158 articles from 63 countries were included in qualitative and quantitative analyses. In total, 830 patients-436 males (52.5%), 369 females (44.5%), and 25 patients of unknown sex (3.0%)-from 581 families were evaluated. A positive family history was reported in 347 patients (45.5%). The patients had a mean age of 10.41 ± 0.42 (SEM) years. The frequency of MSMD was highest in Iran, Turkey, and Saudi Arabia. Lymphadenopathy was the most common clinical manifestation of MSMD, reported in 378 (45.5%) cases and multifocal in 35.1%. Fever, organomegaly, and sepsis were the next most frequent findings, reported in 251 (30.2%), 206 (24.8%), and 171 (20.8%) cases, respectively. In total, 299 unique mutations in 21 genes known to be involved in MSMD were reported: 100 missense (34%), 80 indel-frameshift (insertion or deletion, 27%), 53 nonsense (18%), 35 splice site (12%), 10 indel-in frame (2.7%), 6 indel (2%), and 15 large deletion/duplication mutations. Finally, 61% of the reported patients with MSMD had mutations of IL12RB1 (41%) or IFNGR1 (20%). At the time of the report, 177 of the patients (21.3%) were dead and 597 (71.9%) were still alive.

CONCLUSIONS

MSMD is associated with a high mortality rate, mostly due to impaired control of infection. Preexposure strategies, such as changes in vaccination policy in endemic areas, the establishment of a worldwide registry of patients with MSMD, and precise follow-up over generations in affected families, appear to be vital to decrease MSMD-related mortality.

Physical and functional interaction among Irf8 enhancers during dendritic cell differentiation

The production of type 1 conventional dendritic cells (cDC1s) requires high expression of the transcription factor IRF8. Three enhancers at the Irf8 3' region function in a differentiation stage-specific manner. However, whether and how these enhancers interact physically and functionally remains unclear. Here, we show that the Irf8 3' enhancers directly interact with each other and contact the Irf8 gene body during cDC1 differentiation. The +56 kb enhancer, which functions from multipotent progenitor stages, activates the other 3' enhancers through an IRF8-dependent transcription factor program, that is, in trans. Then, the +32 kb enhancer, which operates in cDC1-committed cells, reversely acts in cis on the other 3' enhancers to maintain the high expression of Irf8. Indeed, mice with compound heterozygous deletion of the +56 and +32 kb enhancers are unable to generate cDC1s. These results illustrate how multiple enhancers cooperate to induce a lineage-determining transcription factor gene during cell differentiation.

Inhibitory receptors of plasmacytoid dendritic cells as possible targets for checkpoint blockade in cancer

Plasmacytoid dendritic cells (pDCs) are the major producers of type I interferons (IFNs), which are essential to mount antiviral and antitumoral immune responses. To avoid exaggerated levels of type I IFNs, which pave the way to immune dysregulation and autoimmunity, pDC activation is strictly regulated by a variety of inhibitory receptors (IRs). In tumors, pDCs display an exhausted phenotype and correlate with an unfavorable prognosis, which largely depends on the accumulation of immunosuppressive cytokines and oncometabolites. This review explores the hypothesis that tumor microenvironment may reduce the release of type I IFNs also by a more pDC-specific mechanism, namely the engagement of IRs. Literature shows that many cancer types express de novo, or overexpress, IR ligands (such as BST2, PCNA, CAECAM-1 and modified surface carbohydrates) which often represent a strong predictor of poor outcome and metastasis. In line with this, tumor cells expressing ligands engaging IRs such as BDCA-2, ILT7, TIM3 and CD44 block pDC activation, while this blocking is prevented when IR engagement or signaling is inhibited. Based on this evidence, we propose that the regulation of IFN secretion by IRs may be regarded as an "innate checkpoint", reminiscent of the function of "classical" adaptive immune checkpoints, like PD1 expressed in CD8+ T cells, which restrain autoimmunity and immunopathology but favor chronic infections and tumors. However, we also point out that further work is needed to fully unravel the biology of tumor-associated pDCs, the neat contribution of pDC exhaustion in tumor growth following the engagement of IRs, especially those expressed also by other leukocytes, and their therapeutic potential as targets of combined immune checkpoint blockade in cancer immunotherapy.

Multiple genetic loci influence vaccine-induced protection against Mycobacterium tuberculosis in genetically diverse mice

Mycobacterium tuberculosis (M.tb.) infection leads to over 1.5 million deaths annually, despite widespread vaccination with BCG at birth. Causes for the ongoing tuberculosis endemic are complex and include the failure of BCG to protect many against progressive pulmonary disease. Host genetics is one of the known factors implicated in susceptibility to primary tuberculosis, but less is known about the role that host genetics plays in controlling host responses to vaccination against M.tb. Here, we addressed this gap by utilizing Diversity Outbred (DO) mice as a small animal model to query genetic drivers of vaccine-induced protection against M.tb. DO mice are a highly genetically and phenotypically diverse outbred population that is well suited for fine genetic mapping. Similar to outcomes in people, our previous studies demonstrated that DO mice have a wide range of disease outcomes following BCG vaccination and M.tb. challenge. In the current study, we used a large population of BCG-vaccinated/M.tb.-challenged mice to perform quantitative trait loci mapping of complex infection traits; these included lung and spleen M.tb. burdens, as well as lung cytokines measured at necropsy. We found sixteen chromosomal loci associated with complex infection traits and cytokine production. QTL associated with bacterial burdens included a region encoding major histocompatibility antigens that are known to affect susceptibility to tuberculosis, supporting validity of the approach. Most of the other QTL represent novel associations with immune responses to M.tb. and novel pathways of cytokine regulation. Most importantly, we discovered that protection induced by BCG is a multigenic trait, in which genetic loci harboring functionally-distinct candidate genes influence different aspects of immune responses that are crucial collectively for successful protection. These data provide exciting new avenues to explore and exploit in developing new vaccines against M.tb.

Murine IRF8 Mutation Offers New Insight into Osteoclast and Root Resorption

Interferon regulatory factor 8 (IRF8), a transcription factor expressed in immune cells, functions as a negative regulator of osteoclasts and helps maintain dental and skeletal homeostasis. Previously, we reported that a novel mutation in the IRF8 gene increases susceptibility to multiple idiopathic cervical root resorption (MICRR), a form of tooth root resorption mediated by increased osteoclast activity. The IRF8 G388S variant in the highly conserved C-terminal motif is predicted to alter the protein structure, likely impairing IRF8 function. To investigate the molecular basis of MICRR and IRF8 function in osteoclastogenesis, we generated Irf8 knock-in (KI) mice using CRISPR/Cas9 technique modeling the human IRF8G388S mutation. The heterozygous (Het) and homozygous (Homo) Irf8 KI mice showed no gross morphological defects, and the development of hematopoietic cells was unaffected and similar to wild-type (WT) mice. The Irf8 KI Het and Homo mice showed no difference in macrophage gene signatures important for antimicrobial defenses and inflammatory cytokine production. Consistent with the phenotype observed in MICRR patients, Irf8 KI Het and Homo mice demonstrated significantly increased osteoclast formation and resorption activity in vivo and in vitro when compared to WT mice. The oral ligature-inserted Het and Homo mice displayed significantly increased root resorption and osteoclast-mediated alveolar bone loss compared to WT mice. The increased osteoclastogenesis noted in KI mice is due to the inability of IRF8G388S mutation to inhibit NFATc1-dependent transcriptional activation and downstream osteoclast specific transcripts, as well as its impact on autophagy-related pathways of osteoclast differentiation. This translational study delineates the IRF8 domain important for osteoclast function and provides novel insights into the IRF8 mutation associated with MICRR. IRF8G388S mutation mainly affects osteoclastogenesis while sparing immune cell development and function. These insights extend beyond oral health and significantly advance our understanding of skeletal disorders mediated by increased osteoclast activity and IRF8's role in osteoclastogenesis.

Recombinant IFN-γ1b Treatment in a Patient with Inherited IFN-γ Deficiency

PURPOSE

Inborn errors of IFN-γ immunity underlie Mendelian susceptibility to mycobacterial disease (MSMD). Twenty-two genes with products involved in the production of, or response to, IFN-γ and variants of which underlie MSMD have been identified. However, pathogenic variants of IFNG encoding a defective IFN-γ have been described in only two siblings, who both underwent hematopoietic stem cell transplantation (HCST).

METHODS

We characterized a new patient with MSMD by genetic, immunological, and clinical means. Therapeutic decisions were taken on the basis of these findings.

RESULTS

The patient was born to consanguineous Turkish parents and developed bacillus Calmette-Guérin (BCG) disease following vaccination at birth. Whole-exome sequencing revealed a homozygous private IFNG variant (c.224 T > C, p.F75S). Upon overexpression in recipient cells or constitutive expression in the patient's cells, the mutant IFN-γ was produced within the cells but was not correctly folded or secreted. The patient was treated for 6 months with two or three antimycobacterial drugs only and then for 30 months with subcutaneous recombinant IFN-γ1b plus two antimycobacterial drugs. Treatment with IFN-γ1b finally normalized all biological parameters. The patient presented no recurrence of mycobacterial disease or other related infectious diseases. The treatment was well tolerated, without the production of detectable autoantibodies against IFN-γ.

CONCLUSION

We describe a patient with a new form of autosomal recessive IFN-γ deficiency, with intracellular, but not extracellular IFN-γ. IFN-γ1b treatment appears to have been beneficial in this patient, with no recurrence of mycobacterial infection over a period of more than 30 months. This targeted treatment provides an alternative to HCST in patients with complete IFN-γ deficiency or at least an option to better control mycobacterial infection prior to HCST.

Antigen cross-presentation by dendritic cells: A critical axis in cancer immunotherapy

Dendritic cells (DCs) are professional antigen-presenting cells that play a key role in shaping adaptive immunity. DCs have a unique ability to sample their environment, capture and process exogenous antigens into peptides that are then loaded onto major histocompatibility complex class I molecules for presentation to CD8+ T cells. This process, called cross-presentation, is essential for initiating and regulating CD8+ T cell responses against tumors and intracellular pathogens. In this review, we will discuss the role of DCs in cancer immunity, the molecular mechanisms underlying antigen cross-presentation by DCs, the immunosuppressive factors that limit the efficiency of this process in cancer, and approaches to overcome DC dysfunction and therapeutically promote antitumoral immunity.

GWAS for systemic sclerosis identifies six novel susceptibility loci including one in the Fcγ receptor region

Here we report the largest Asian genome-wide association study (GWAS) for systemic sclerosis performed to date, based on data from Japanese subjects and comprising of 1428 cases and 112,599 controls. The lead SNP is in the FCGR/FCRL region, which shows a penetrating association in the Asian population, while a complete linkage disequilibrium SNP, rs10917688, is found in a cis-regulatory element for IRF8. IRF8 is also a significant locus in European GWAS for systemic sclerosis, but rs10917688 only shows an association in the presence of the risk allele of IRF8 in the Japanese population. Further analysis shows that rs10917688 is marked with H3K4me1 in primary B cells. A meta-analysis with a European GWAS detects 30 additional significant loci. Polygenic risk scores constructed with the effect sizes of the meta-analysis suggest the potential portability of genetic associations beyond populations. Prioritizing the top 5% of SNPs of IRF8 binding sites in B cells improves the fitting of the polygenic risk scores, underscoring the roles of B cells and IRF8 in the development of systemic sclerosis. The results also suggest that systemic sclerosis shares a common genetic architecture across populations.

IRF8 in Conjunction With CD123 and CD20 to Distinguish Lupus Erythematosus Panniculitis From Subcutaneous Panniculitis-like T-Cell Lymphoma

Distinguishing lupus erythematosus panniculitis (LEP) from subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a diagnostic challenge with important clinical implications. Immunohistochemical expression of interferon regulatory factor 8 (IRF8) has been shown to highlight cells with plasmacytoid dendritic cell differentiation. Considering that the presence of plasmacytoid dendritic cells highlighted by CD123 immunolabeling is a well-described feature that supports LEP over SPTCL, we hypothesized that IRF8 immunohistochemistry can be used as a diagnostic test to improve accuracy in differentiating LEP from SPTCL. In this study, we assessed the expression of IRF8, CD123, and CD20 in 35 cutaneous biopsies from 31 distinct patients, which included 22 cases of LEP and 13 cases of SPTCL. We found that clusters of IRF8-positive cells within the dermis, and away from subcutaneous fat, could discriminate LEP from SPTCL ( P =0.005). Similarly, CD123-positive clusters in any location were observed in LEP but absent in all cases of SPTCL. In addition, we found that dermal CD20-predominant lymphoid aggregates could help discriminate LEP from SPTCL ( P =0.022). As individual assays, IRF8, CD123, and CD20 were highly specific (100%, 100%, and 92%, respectively) though poorly sensitive (45%, 29%, and 50%, respectively). However, a panel combining IRF8, CD123, and CD20, with at least 1 positive marker was more accurate than any individual marker by receiver operating characteristic curve analysis. Our study provides a rationale for potentially including IRF8 as part of an immunohistochemical panel composed of other currently available markers used to differentiate LEP from SPTCL.

Host Susceptibility to Nontuberculous Mycobacterial Pulmonary Disease

Nontuberculous mycobacteria (NTM) pulmonary disease is a chronic progressive pulmonary infectious disease caused by low virulence pathogens. The existence of host susceptibility to NTM infection has been recognized from a high incidence among Asians compared to other populations in the United States, a high incidence among slender, middle-aged women, and the presence of familial clusters. Recent whole exome sequencing and genome-wide association studies have identified immune, CFTR, cilia, connective tissue and ion homeostasis genes as host susceptibility genes. Large-scale international collaborative studies and functional analyses are expected to elucidate host susceptibility in the future.

The role of GATA2 in adult hematopoiesis and cell fate determination

The correct maintenance and differentiation of hematopoietic stem cells (HSC) in bone marrow is vital for the maintenance and operation of the human blood system. GATA2 plays a critical role in the maintenance of HSCs and the specification of HSCs into the different hematopoietic lineages, highlighted by the various defects observed in patients with heterozygous mutations in GATA2, resulting in cytopenias, bone marrow failure and increased chance of myeloid malignancy, termed GATA2 deficiency syndrome. Despite this, the mechanisms underlying GATA2 deficiency syndrome remain to be elucidated. The detailed description of how GATA2 regulates HSC maintenance and blood lineage determination is crucial to unravel the pathogenesis of GATA2 deficiency syndrome. In this review, we summarize current advances in elucidating the role of GATA2 in hematopoietic cell fate determination and discuss the challenges of modeling GATA2 deficiency syndrome.

Human MCTS1-dependent translation of JAK2 is essential for IFN-γ immunity to mycobacteria

Human inherited disorders of interferon-gamma (IFN-γ) immunity underlie severe mycobacterial diseases. We report X-linked recessive MCTS1 deficiency in men with mycobacterial disease from kindreds of different ancestries (from China, Finland, Iran, and Saudi Arabia). Complete deficiency of this translation re-initiation factor impairs the translation of a subset of proteins, including the kinase JAK2 in all cell types tested, including T lymphocytes and phagocytes. JAK2 expression is sufficiently low to impair cellular responses to interleukin-23 (IL-23) and partially IL-12, but not other JAK2-dependent cytokines. Defective responses to IL-23 preferentially impair the production of IFN-γ by innate-like adaptive mucosal-associated invariant T cells (MAIT) and γδ T lymphocytes upon mycobacterial challenge. Surprisingly, the lack of MCTS1-dependent translation re-initiation and ribosome recycling seems to be otherwise physiologically redundant in these patients. These findings suggest that X-linked recessive human MCTS1 deficiency underlies isolated mycobacterial disease by impairing JAK2 translation in innate-like adaptive T lymphocytes, thereby impairing the IL-23-dependent induction of IFN-γ.

IRF8-mutant B cell lymphoma evades immunity through a CD74-dependent deregulation of antigen processing and presentation in MHC CII complexes

In diffuse large B-cell lymphoma (DLBCL), the transcription factor IRF8 is the target of a series of potentially oncogenic events, including, chromosomal translocation, focal amplification, and super-enhancer perturbations. IRF8 is also frequently mutant in DLBCL, but how these variants contribute to lymphomagenesis is unknown. We modeled IRF8 mutations in DLBCL and found that they did not meaningfully impact cell fitness. Instead, IRF8 mutants, mapping either to the DNA-binding domain (DBD) or c-terminal tail, displayed diminished transcription activity towards CIITA, a direct IRF8 target. In primary DLBCL, IRF8 mutations were mutually exclusive with mutations in genes involved in antigen presentation. Concordantly, expression of IRF8 mutants in murine B cell lymphomas uniformly suppressed CD4, but not CD8, activation elicited by antigen presentation. Unexpectedly, IRF8 mutation did not modify MHC CII expression on the cell surface, rather it downmodulated CD74 and HLA- DM, intracellular regulators of antigen peptide processing/loading in the MHC CII complex. These changes were functionally relevant as, in comparison to IRF8 WT, mice harboring IRF8 mutant lymphomas displayed a significantly higher tumor burden, in association with a substantial remodeling of the tumor microenvironment (TME), typified by depletion of CD4, CD8, Th1 and NK cells, and increase in T-regs and Tfh cells. Importantly, the clinical and immune phenotypes of IRF8-mutant lymphomas were rescued in vivo by ectopic expression of CD74. Deconvolution of bulk RNAseq data from primary human DLBCL recapitulated part of the immune remodeling detected in mice and pointed to depletion of dendritic cells as another feature of IRF8 mutant TME. We concluded that IRF8 mutations contribute to DLBCL biology by facilitating immune escape.

Human inborn errors of immunity associated with IRF4

The transcription factor interferon regulatory factor 4 (IRF4) belongs to the IRF family and has several important functions for the adaptive immune response. Mutations affecting IRF family members IRF1, IRF3, IRF7, IRF8, or IRF9 have been described in patients presenting with inborn errors of immunity (IEI) highlighting the importance of these factors for the cellular host defense against mycobacterial and/or viral infections. IRF4 deficiency and haploinsufficiency have been associated with IEI. More recently, two novel IRF4 disease-causing mechanisms have been described due to the characterization of IEI patients presenting with cellular immunodeficiency associated with agammaglobulinemia. Here, we review the phenotypes and physiopathological mechanisms underlying IEI of IRF family members and, in particular, IRF4.

Circulating IRF8-expressing CD123+CD127+ lymphoid progenitors: key players in human hematopoiesis

Lymphopoiesis is the process in which B and T cells, and innate lymphoid cells (ILCs) develop from hematopoietic progenitors that exhibit early lymphoid priming. The branching points where lymphoid-primed human progenitors are further specified to B/T/ILC differentiation trajectories remain unclear. Here, we discuss the emerging role of interferon regulatory factor (IRF)8 as a key factor to bridge human lymphoid and dendritic cell (DC) differentiation, and the current evidence for the existence of circulating and tissue-resident CD123+CD127+ lymphoid progenitors. We propose a model whereby DC/B/T/ILC lineage programs in circulating CD123+CD127+ lymphoid progenitors are expressed in balance. Upon tissue seeding, the tissue microenvironment tilts this molecular balance towards a specific lineage, thereby determining in vivo lineage fates. Finally, we discuss the translational implication of these lymphoid precursors.

Modulation of Human Dendritic Cell Functions by Phosphodiesterase-4 Inhibitors: Potential Relevance for the Treatment of Respiratory Diseases

Inhibitors of phosphodiesterase-4 (PDE4) are small-molecule drugs that, by increasing the intracellular levels of cAMP in immune cells, elicit a broad spectrum of anti-inflammatory effects. As such, PDE4 inhibitors are actively studied as therapeutic options in a variety of human diseases characterized by an underlying inflammatory pathogenesis. Dendritic cells (DCs) are checkpoints of the inflammatory and immune responses, being responsible for both activation and dampening depending on their activation status. This review shows evidence that PDE4 inhibitors modulate inflammatory DC activation by decreasing the secretion of inflammatory and Th1/Th17-polarizing cytokines, although preserving the expression of costimulatory molecules and the CD4+ T cell-activating potential. In addition, DCs activated in the presence of PDE4 inhibitors induce a preferential Th2 skewing of effector T cells, retain the secretion of Th2-attracting chemokines and increase the production of T cell regulatory mediators, such as IDO1, TSP-1, VEGF-A and Amphiregulin. Finally, PDE4 inhibitors selectively induce the expression of the surface molecule CD141/Thrombomodulin/BDCA-3. The result of such fine-tuning is immunomodulatory DCs that are distinct from those induced by classical anti-inflammatory drugs, such as corticosteroids. The possible implications for the treatment of respiratory disorders (such as COPD, asthma and COVID-19) by PDE4 inhibitors will be discussed.

Interferon regulatory factor-8-dependent innate immune alarm senses GATA2 deficiency to alter hematopoietic differentiation and function

PURPOSE OF REVIEW

Recent discoveries have provided evidence for mechanistic links between the master regulator of hematopoiesis GATA2 and the key component of interferon and innate immunity signaling pathways, interferon-regulatory factor-8 (IRF8). These links have important implications for the control of myeloid differentiation in physiological and pathological states.

RECENT FINDINGS

GATA2 deficiency resulting from loss of the Gata2 -77 enhancer in progenitors triggers an alarm that instigates the transcriptional induction of innate immune signaling and distorts a myeloid differentiation program. This pathological alteration renders progenitors hyperresponsive to interferon γ, toll-like receptor and interleukin-6 signaling and impaired in granulocyte-macrophage colony-stimulating factor signaling. IRF8 upregulation in -77-/- progenitors promotes monocyte and dendritic cell differentiation while suppressing granulocytic differentiation. As PU.1 promotes transcription of Irf8 and other myeloid and B-lineage genes, GATA2-mediated repression of these genes opposes the PU.1-dependent activating mechanism.

SUMMARY

As GATA2 deficiency syndrome is an immunodeficiency disorder often involving myelodysplastic syndromes and acute myeloid leukemia, elucidating how GATA2 commissions and decommissions genome activity and developmental regulatory programs will unveil mechanisms that go awry when GATA2 levels and/or activities are disrupted.

Signaling pathways involved in the biological functions of dendritic cells and their implications for disease treatment

The ability of dendritic cells (DCs) to initiate and regulate adaptive immune responses is fundamental for maintaining immune homeostasis upon exposure to self or foreign antigens. The immune regulatory function of DCs is strictly controlled by their distribution as well as by cytokines, chemokines, and transcriptional programming. These factors work in conjunction to determine whether DCs exert an immunosuppressive or immune-activating function. Therefore, understanding the molecular signals involved in DC-dependent immunoregulation is crucial in providing insight into the generation of organismal immunity and revealing potential clinical applications of DCs. Considering the many breakthroughs in DC research in recent years, in this review we focused on three basic lines of research directly related to the biological functions of DCs and summarized new immunotherapeutic strategies involving DCs. First, we reviewed recent findings on DC subsets and identified lineage-restricted transcription factors that guide the development of different DC subsets. Second, we discussed the recognition and processing of antigens by DCs through pattern recognition receptors, endogenous/exogenous pathways, and the presentation of antigens through peptide/major histocompatibility complexes. Third, we reviewed how interactions between DCs and T cells coordinate immune homeostasis in vivo via multiple pathways. Finally, we summarized the application of DC-based immunotherapy for autoimmune diseases and tumors and highlighted potential research prospects for immunotherapy that targets DCs. This review provides a useful resource to better understand the immunomodulatory signals involved in different subsets of DCs and the manipulation of these immune signals can facilitate DC-based immunotherapy.

Reconciling Mouse and Human Immunology at the Altar of Genetics

Immunity to infection has been extensively studied in humans and mice bearing naturally occurring or experimentally introduced germline mutations. Mouse studies are sometimes neglected by human immunologists, on the basis that mice are not humans and the infections studied are experimental and not natural. Conversely, human studies are sometimes neglected by mouse immunologists, on the basis of the uncontrolled conditions of study and small numbers of patients. However, both sides would agree that the infectious phenotypes of patients with inborn errors of immunity often differ from those of the corresponding mutant mice. Why is that? We argue that this important question is best addressed by revisiting and reinterpreting the findings of both mouse and human studies from a genetic perspective. Greater caution is required for reverse-genetics studies than for forward-genetics studies, but genetic analysis is sufficiently strong to define the studies likely to stand the test of time. Genetically robust mouse and human studies can provide invaluable complementary insights into the mechanisms of immunity to infection common and specific to these two species.

Origin and Heterogeneity of Tissue Myeloid Cells: A Focus on GMP-Derived Monocytes and Neutrophils

Myeloid cells are a significant proportion of leukocytes within tissues, comprising granulocytes, monocytes, dendritic cells, and macrophages. With the identification of various myeloid cells that perform separate but complementary functions during homeostasis and disease, our understanding of tissue myeloid cells has evolved significantly. Exciting findings from transcriptomics profiling and fate-mapping mouse models have facilitated the identification of their developmental origins, maturation, and tissue-specific specializations. This review highlights the current understanding of tissue myeloid cells and the contributing factors of functional heterogeneity to better comprehend the complex and dynamic immune interactions within the healthy or inflamed tissue. Specifically, we discuss the new understanding of the contributions of granulocyte-monocyte progenitor-derived phagocytes to tissue myeloid cell heterogeneity as well as the impact of niche-specific factors on monocyte and neutrophil phenotype and function. Lastly, we explore the developing paradigm of myeloid cell heterogeneity during inflammation and disease.

[Principles of the diagnostics of inborn errors of immunity]

Inborn errors of immunity (IEI) are a heterogeneous group of nearly 500 diseases characterized by a congenital dysfunction of the immune system. The vast majority of IEIs are rare diseases but all IEIs share a cumulative prevalence of 1:1200-1:2000. In addition to a pathological susceptibility to infections, IEIs can also present with lymphoproliferative, autoimmune or autoinflammatory manifestations. There is often an overlap with classical rheumatic and inflammatory disease patterns. Therefore, a basic knowledge of the clinical presentation and the diagnostics of IEIs is also relevant for the practicing rheumatologist.

Inborn errors of human transcription factors governing IFN-γ antimycobacterial immunity

Inborn errors of immunity (IEI) delineate redundant and essential defense mechanisms in humans. We review 15 autosomal-dominant (AD) or -recessive (AR) IEI involving 11 transcription factors (TFs) and impairing interferon-gamma (IFN-γ) immunity, conferring a predisposition to mycobacterial diseases. We consider three mechanism-based categories: 1) IEI mainly affecting myeloid compartment development (AD GATA2 and AR and AD IRF8 deficiencies), 2) IEI mainly affecting lymphoid compartment development (AR FOXN1, AR PAX1, AR RORγ/RORγT, AR T-bet, AR c-Rel, AD STAT3 gain-of-function (GOF), and loss-of-function (LOF) deficiencies), and 3) IEI mainly affecting myeloid and/or lymphoid function (AR and AD STAT1 LOF, AD STAT1 GOF, AR IRF1, and AD NFKB1 deficiencies). We discuss the contribution of the discovery and study of inborn errors of TFs essential for host defense against mycobacteria to molecular and cellular analyses of human IFN-γ immunity.

Human IRF1 governs macrophagic IFN-γ immunity to mycobacteria

Inborn errors of human IFN-γ-dependent macrophagic immunity underlie mycobacterial diseases, whereas inborn errors of IFN-α/β-dependent intrinsic immunity underlie viral diseases. Both types of IFNs induce the transcription factor IRF1. We describe unrelated children with inherited complete IRF1 deficiency and early-onset, multiple, life-threatening diseases caused by weakly virulent mycobacteria and related intramacrophagic pathogens. These children have no history of severe viral disease, despite exposure to many viruses, including SARS-CoV-2, which is life-threatening in individuals with impaired IFN-α/β immunity. In leukocytes or fibroblasts stimulated in vitro, IRF1-dependent responses to IFN-γ are, both quantitatively and qualitatively, much stronger than those to IFN-α/β. Moreover, IRF1-deficient mononuclear phagocytes do not control mycobacteria and related pathogens normally when stimulated with IFN-γ. By contrast, IFN-α/β-dependent intrinsic immunity to nine viruses, including SARS-CoV-2, is almost normal in IRF1-deficient fibroblasts. Human IRF1 is essential for IFN-γ-dependent macrophagic immunity to mycobacteria, but largely redundant for IFN-α/β-dependent antiviral immunity.

Dendritic cells in inborn errors of immunity

Dendritic cells (DCs) are crucial cells for initiating and maintaining immune response. They play critical role in homeostasis, inflammation, and autoimmunity. A number of molecules regulate their functions including synapse formation, migration, immunity, and induction of tolerance. A number of IEI are characterized by mutations in genes encoding several of these molecules resulting in immunodeficiency, inflammation, and autoimmunity in IEI. Currently, there are 465 Inborn errors of immunity (IEI) that have been grouped in 10 different categories. However, comprehensive studies of DCs have been reported in only few IEI. Here we have reviewed biology of DCs in IEI classified according to recently published IUIS classification. We have reviewed DCs in selected IEI in each group category and discussed in depth changes in DCs where significant data are available regarding role of DCs in clinical and immunological manifestations. These include severe immunodeficiency diseases, antibody deficiencies, combined immunodeficiency with associated and syndromic features, especially disorders of synapse formation, and disorders of immune regulation.

Single-cell analysis of myeloid cells in HPV+ tonsillar cancer

The incidence of human papillomavirus-positive (HPV⁺) tonsillar cancer has been sharply rising during the last decades. Myeloid cells represent an appropriate therapeutic target due to their proximity to virus-infected tumor cells, and their ability to orchestrate antigen-specific immunity, within the tonsil. However, the interrelationship of steady-state and inflammatory myeloid cell subsets, and their impact on patient survival remains unexplored. Here, we used single-cell RNA-sequencing to map the myeloid compartment in HPV⁺ tonsillar cancer. We observed an expansion of the myeloid compartment in HPV⁺ tonsillar cancer, accompanied by interferon-induced cellular responses both in dendritic cells (DCs) and monocyte-macrophages. Our analysis unveiled the existence of four DC lineages, two macrophage polarization processes, and their sequential maturation profiles. Within the DC lineages, we described a balance shift in the frequency of progenitor and mature cDC favoring the cDC1 lineage in detriment of cDC2s. Furthermore, we observed that all DC lineages apart from DC5s matured into a common activated DC transcriptional program involving upregulation of interferon-inducible genes. In turn, the monocyte-macrophage lineage was subjected to early monocyte polarization events, which give rise to either interferon-activated or CXCL-producing macrophages, the latter enriched in advanced tumor stages. We validated the existence of most of the single-cell RNA-seq clusters using 26-plex flow cytometry, and described a positive impact of cDC1 and interferon-activated DCs and macrophages on patient survival using gene signature scoring. The current study contributes to the understanding of myeloid ontogeny and dynamics in HPV-driven tonsillar cancer, and highlights myeloid biomarkers that can be used to assess patient prognosis.

Mendelian susceptibility to mycobacterial disease: an overview

Background

Mycobacteria include ubiquitous species of varying virulence. However, environmental and individual-specific factors, particularly host genetics, play a crucial role in the outcome of exposure to mycobacteria. The first molecular evidence of a monogenic predisposition to mycobacteria came from the study of Mendelian susceptibility to mycobacterial disease (MSMD), a rare inborn error of IFN-γ immunity conferring a selective susceptibility to infections even with low virulent mycobacteria, in patients, mostly children, without recognizable immune defects in routine tests. This article provides a global and updated description of the most important molecular, cellular, and clinical features of all known monogenic defects of MSMD.

Results

Over the last 20 years, 19 genes were found to be mutated in MSMD patients (IFNGR1, IFNGR2, IFNG, IL12RB1, IL12RB2, IL23R, IL12B, ISG15, USP18, ZNFX1, TBX21, STAT1, TYK2, IRF8, CYBB, JAK1, RORC, NEMO, and SPPL2A), and the allelic heterogeneity at these loci has led to the definition of 35 different genetic defects. Despite the clinical and genetic heterogeneity, almost all genetic etiologies of MSMD alter the interferon gamma (IFN-γ)-mediated immunity, by impairing or abolishing IFN-γ production or the response to this cytokine or both. It was proven that the human IFN-γ level is a quantitative trait that defines the outcome of mycobacterial infection.

Conclusion

The study of these monogenic defects contributes to understanding the molecular mechanism of mycobacterial infections in humans and to the development of new diagnostic and therapeutic approaches to improve care and prognosis. These discoveries also bridge the gap between the simple Mendelian inheritance and complex human genetics.

Distinct Lymphocyte Immunophenotyping and Quantitative Anti-Interferon Gamma Autoantibodies in Taiwanese HIV-Negative Patients with Non-Tuberculous Mycobacterial Infections

PURPOSE

The presence of anti-interferon-γ autoantibodies (AutoAbs-IFN-γ) is not rare in patients suffering from persistent non-tuberculous mycobacterial (NTM) infections that are characteristic of adult-onset immunodeficiency syndrome. The immune disturbances in this distinct disorder remain to be elucidated.

METHODS

Patients with NTM infections but without effective response over 3 months' treatment were referred to our institute to quantify their level of AutoAbs-IFN-γ after excluding defective IL12/23-IFN-γ circuit and reactive oxygen species production. The AutoAbs-IFN-γ and percentage of lymphocyte subpopulations most relevant to T and B cell pools were assessed and compared with age-matched healthy controls.

RESULTS

A total of 31 patients were enrolled during the 15-year study period (2008-2022), 20 patients with > 50% suppression of IFN-γ detection at 1:100 serum dilution were classified into the Auto-NTM group. The remaining 11 with negligible suppression were assigned to the No Auto-NTM group. Mycobacterium chimaera-intracellulare group (MAC), M. kansasii, and M. abscessus were the most common pathogens. Pneumonia (19 vs 7), lymphadenitis (11 vs 5), Salmonella sepsis (6 vs 2), osteomyelitis (5 vs 1), and cutaneous herpes zoster (4 vs 4) were the main manifestations in both the Auto-NTM and No Auto-NTM groups who had similar onset-age (55.3 vs 53.6 years; p = 0.73) and follow-up duration (71.9 vs 54.6 months; p = 0.45). The Auto-NTM group had significantly higher transitional (IgM +  + CD38 + +), CD19 + CD21-low, and plasmablast (IgM-CD38 + +) in the B cell pool, with higher effector memory (CD4 + /CD8 + CD45RO + CCR7 -), senescent CD8 + CD57 + , and Th17 cells, but lower naïve (CD4 + /CD8 + CD45RO - CCR7 +) and Treg cells in the T cell pool when compared to the No Auto-NTM and healthy groups. NTM patients with/without AutoAbs-IFN-γ had lower Th1-like Tfh (CD4 + CXCR5 + CXCR3 + CCR6 -) cells. All Auto-NTM patients still had non-remitted mycobacterial infections and higher AutoAbs-IFN-γ despite anti-CD20 therapy in 3 patients.

CONCLUSION

In patients with suspected adult-onset immunodeficiency syndrome, two thirds (20/31) were recognized as having significantly inhibitory AutoAbs-IFN-γ with higher antibody-enhancing transitional, CD19 + CD21-low and plasmablast B cells; as well as higher effector memory, senescent CD8 + CD57 + and Th17 cells, but lower naïve T and Treg cells in contrast to those with negligible AutoAbs-IFN-γ. Such immunophenotyping disturbances might correlate with the presence of AutoAbs-IFN-γ. However, the mutual mechanisms need to be further clarified.

The Conventional Dendritic Cell 1 Subset Primes CD8+ T Cells and Traffics Tumor Antigen to Drive Antitumor Immunity in the Brain

The central nervous system (CNS) antigen-presenting cell (APC) that primes antitumor CD8+ T-cell responses remains undefined. Elsewhere in the body, the conventional dendritic cell 1 (cDC1) performs this role. However, steady-state brain parenchyma cDC1 are extremely rare; cDCs localize to the choroid plexus and dura. Thus, whether the cDC1 play a function in presenting antigen derived from parenchymal sources in the tumor setting remains unknown. Using preclinical glioblastoma (GBM) models and cDC1-deficient mice, we explored the presently unknown role of cDC1 in CNS antitumor immunity. We determined that, in addition to infiltrating the brain tumor parenchyma itself, cDC1 prime neoantigen-specific CD8+ T cells against brain tumors and mediate checkpoint blockade-induced survival benefit. We observed that cDC, including cDC1, isolated from the tumor, the dura, and the CNS-draining cervical lymph nodes harbored a traceable fluorescent tumor antigen. In patient samples, we observed several APC subsets (including the CD141+ cDC1 equivalent) infiltrating glioblastomas, meningiomas, and dura. In these same APC subsets, we identified a tumor-specific fluorescent metabolite of 5-aminolevulinic acid, which fluorescently labeled tumor cells during fluorescence-guided GBM resection. Together, these data elucidate the specialized behavior of cDC1 and suggest that cDC1 play a significant role in CNS antitumor immunity.

Transplanting rejuvenated blood stem cells extends lifespan of aged immunocompromised mice

One goal of regenerative medicine is to rejuvenate tissues and extend lifespan by restoring the function of endogenous aged stem cells. However, evidence that somatic stem cells can be targeted in vivo to extend lifespan is still lacking. Here, we demonstrate that after a short systemic treatment with a specific inhibitor of the small RhoGTPase Cdc42 (CASIN), transplanting aged hematopoietic stem cells (HSCs) from treated mice is sufficient to extend the healthspan and lifespan of aged immunocompromised mice without additional treatment. In detail, we show that systemic CASIN treatment improves strength and endurance of aged mice by increasing the myogenic regenerative potential of aged skeletal muscle stem cells. Further, we show that CASIN modifies niche localization and H4K16ac polarity of HSCs in vivo. Single-cell profiling reveals changes in HSC transcriptome, which underlie enhanced lymphoid and regenerative capacity in serial transplantation assays. Overall, we provide proof-of-concept evidence that a short systemic treatment to decrease Cdc42 activity improves the regenerative capacity of different endogenous aged stem cells in vivo, and that rejuvenated HSCs exert a broad systemic effect sufficient to extend murine health- and lifespan.

An ELF4 hypomorphic variant results in NK cell deficiency

NK cell deficiencies (NKD) are a type of primary immune deficiency in which the major immunologic abnormality affects NK cell number, maturity, or function. Since NK cells contribute to immune defense against virally infected cells, patients with NKD experience higher susceptibility to chronic, recurrent, and fatal viral infections. An individual with recurrent viral infections and mild hypogammaglobulinemia was identified to have an X-linked damaging variant in the transcription factor gene ELF4. The variant does not decrease expression but disrupts ELF4 protein interactions and DNA binding, reducing transcriptional activation of target genes and selectively impairing ELF4 function. Corroborating previous murine models of ELF4 deficiency (Elf4-/-) and using a knockdown human NK cell line, we determined that ELF4 is necessary for normal NK cell development, terminal maturation, and function. Through characterization of the NK cells of the proband, expression of the proband's variant in Elf4-/- mouse hematopoietic precursor cells, and a human in vitro NK cell maturation model, we established this ELF4 variant as a potentially novel cause of NKD.

Hepatic interferon regulatory factor 8 expression suppresses hepatocellular carcinoma progression and enhances the response to anti-programmed cell death protein-1 therapy

BACKGROUND AND AIMS

Therapeutic blockade of the programmed cell death protein-1 (PD-1) immune checkpoint pathways has resulted in significant reactivation of T cell-mediated antitumor immunity and is a promising clinical anticancer treatment modality in several tumor types, but the durable response rate remains relatively low (15%-20%) in most patients with HCC for unknown reasons. Evidence reveals that the interferon signaling pathway plays a critical role in modulating the efficacy and sensitivity of anti-PD-1 therapy against multiple tumor types, but the mechanisms are unclear.

APPROACH AND RESULTS

Using Kaplan-Meier survival analysis based on HCC databases, we found that deceased expression of interferon regulatory factor (IRF) 8 in HCC, among all the nine IRF members that regulate interferon signals, was associated with poor prognosis of patients with HCC. Moreover, gene set enrichment analysis identified the interferon-gamma and PD-1 signaling signatures as the top suppressed pathways in patients with IRF8-low HCC. Contrarily, overexpression of IRF8 in HCC cells significantly enhanced antitumor effects in immune-competent mice, modulating infiltration of tumor-associated macrophages (TAMs) and T cell exhaustion in tumor microenvironment. We further demonstrated that IRF8 regulated recruitment of TAMs by inhibiting the expression of chemokine (C-C motif) ligand 20 (CCL20). Mechanically, IRF8-mediated repression of c-fos transcription resulted in decreased expression of CCL20, rather than directly bound to CCL20 promoter region. Importantly, adeno-associated virus 8-mediated hepatic IRF8 rescue significantly suppressed HCC progression and enhanced the response to anti-PD-1 therapy.

CONCLUSIONS

This work identified IRF8 as an important prognostic biomarker in patients with HCC that predicted the response and sensitivity to anti-PD-1 therapy and uncovered it as a therapeutic target for enhancing the efficacy of immune therapy.

COVID-19 and systemic lupus erythematosus genetics: A balance between autoimmune disease risk and protection against infection

Genome wide association studies show there is a genetic component to severe COVID-19. We find evidence that the genome-wide genetic association signal with severe COVID-19 is correlated with that of systemic lupus erythematosus (SLE), having formally tested this using genetic correlation analysis by LD score regression. To identify the shared associated loci and gain insight into the shared genetic effects, using summary level data we performed meta-analyses, a local genetic correlation analysis and fine-mapping using stepwise regression and functional annotation. This identified multiple loci shared between the two traits, some of which exert opposing effects. The locus with most evidence of shared association is TYK2, a gene critical to the type I interferon pathway, where the local genetic correlation is negative. Another shared locus is CLEC1A, where the direction of effects is aligned, that encodes a lectin involved in cell signaling, and the anti-fungal immune response. Our analyses suggest that several loci with reciprocal effects between the two traits have a role in the defense response pathway, adding to the evidence that SLE risk alleles are protective against infection.

We observed a correlation between the genetic associations with severe COVID-19 and those with systemic lupus erythematosus (SLE, Lupus), and aimed to discover which genetic loci were shared by these diseases and what biological processes were involved. This resulted in the discovery of several genetic loci, some of which had alleles that were risk for both diseases and some of which were risk for severe COVID-19 yet protective for SLE. The locus with most evidence of shared association (TYK2) is involved in interferon production, a process that is important in response to viral infection and known to be dysregulated in SLE patients. Other shared associated loci contained genes also involved in the defense response and the immune system signaling. These results add to the growing evidence that there are alleles in the human genome that provide protection against viral infection yet are risk for autoimmune disease.

Human dendritic cell subsets: An updated view of their ontogeny and functional specialization

Human DCs have been divided into several subsets based on their phenotype and ontogeny. Recent high throughput single-cell methods have revealed additional heterogeneity within human DC subsets, and new subpopulations have been proposed. In this review, we provide an updated view of the human DC subsets and of their ontogeny supported by recent clinical studies . We also summarize their main characteristics including their functional specialization.

Traumatic brain injury alters dendritic cell differentiation and distribution in lymphoid and non-lymphoid organs

Background

Pathophysiological consequences of traumatic brain injury (TBI) mediated secondary injury remain incompletely understood. In particular, the impact of TBI on the differentiation and maintenance of dendritic cells (DCs), which are regarded as the most professional antigen presenting cells of the immune system, remains completely unknown. Here, we report that DC-differentiation, maintenance and functions are altered on day 3 and day 7 after TBI.

Methods

Long bones, spleen, peripheral lymph nodes (pLNs), mesenteric lymph nodes (mLNs), liver, lungs, skin and blood were collected from mice with either moderate-level cortical impact (CCI) or sham on day 1, day 3 or day 7 after TBI. Bone marrow cells were isolated from the tibias and femurs of hind limb through flushing. Tissues were digested with Collagenase-D and DNase I. Skin biopsies were digested in the presence of liberase + DNase I. Single cell suspensions were made, red blood cells were lysed with Ammonium chloride (Stem Cell Technology) and subsequently filtered using a 70 μM nylon mesh. DC subsets of the tissues and DC progenitors of the BM were identified through 10-color flow cytometry-based immunophenotyping studies. Intracellular reactive oxygen species (ROS) were identified through H2DCFDA staining.

Results

Our studies identify that; (1) frequencies and absolute numbers of DCs in the spleen and BM are altered on day 3 and day 7 after TBI; (2) surface expression of key molecules involved in antigen presentation of DCs were affected on day 3 and day 7 after TBI; (3) distribution and functions of tissue-specific DC subsets of both circulatory and lymphatic systems were imbalanced following TBI; (4) early differentiation program of DCs, especially the commitment of hematopoietic stem cells to common DC progenitors (CDPs), were deregulated after TBI; and (5) intracellular ROS levels were reduced in DC progenitors and differentiated DCs on day 3 and day 7 after TBI.

Conclusions

Our data demonstrate, for the first time, that TBI affects the distribution pattern of DCs and induces an imbalance among DC subsets in both lymphoid and non-lymphoid organs. In addition, the current study demonstrates that TBI results in reduced levels of ROS in DCs on day 3 and day 7 after TBI, which may explain altered DC differentiation paradigm following TBI. A deeper understanding on the molecular mechanisms that contribute to DC defects following TBI would be essential and beneficial in treating infections in patients with acute central nervous system (CNS) injuries, such as TBI, stroke and spinal cord injury.

Genetic architecture of tuberculosis susceptibility: A comprehensive research synopsis, meta-analyses, and epidemiological evidence

To date, many studies have been conducted to investigate associations between variants and tuberculosis risk; however, the results have been inconclusive. Here, we systematically provide a summary of the understanding of the genetic architecture of tuberculosis susceptibility. We searched PubMed, Embase and Web of Science to identify genetic association studies of tuberculosis published through October 31, 2021. We conducted meta-analyses for the genetic association with tuberculosis risk. We graded levels of cumulative epidemiological evidence of significant associations with risk of tuberculosis and false-positive report probability tests. We performed functional annotations for these variants using data from the Encyclopedia of DNA Elements (ENCODE) Project and other databases. We identified 703 eligible articles comprising 298,074 cases and 879,593 controls through screening a total of 24,398 citations. Meta-analyses were conducted for 614 genetic variants in 469 genes or loci. We found 39 variants that were nominally significantly associated with tuberculosis risk. Cumulative epidemiological evidence for a significant association was graded strong for 9 variants in or near 9 genes. Among them, 5 variants were associated with tuberculosis risk in at least three main ethnicity (African, Asian and White) which together explained approximately 9.59% of the familial relative risk of tuberculosis. Data from ENCODE and other databases suggested that 8 of these 9 genetic variants with strong evidence might fall within putative functional regions. Our study summarizes the current literature on the genetic architecture of tuberculosis susceptibility and provides useful data for designing future studies to investigate the genetic association with tuberculosis risk.

IRF8: Mechanism of Action and Health Implications

Interferon regulatory factor 8 (IRF8) is a transcription factor of the IRF protein family. IRF8 was originally identified as an essentialfactor for myeloid cell lineage commitment and differentiation. Deletion of Irf8 leads to massive accumulation of CD11b⁺Gr1⁺ immature myeloid cells (IMCs), particularly the CD11b⁺Ly6C^hi/+Ly6G⁻ polymorphonuclear myeloid-derived suppressor cell-like cells (PMN-MDSCs). Under pathological conditions such as cancer, Irf8 is silenced by its promoter DNA hypermethylation, resulting in accumulation of PMN-MDSCs and CD11b⁺ Ly6G⁺Ly6C^lo monocytic MDSCs (M-MDSCs) in mice. IRF8 is often silenced in MDSCs in human cancer patients. MDSCs are heterogeneous populations of immune suppressive cells that suppress T and NK cell activity to promote tumor immune evasion and produce growth factors to exert direct tumor-promoting activity. Emerging experimental data reveals that IRF8 is also expressed in non-hematopoietic cells. Epithelial cell-expressed IRF8 regulates apoptosis and represses Osteopontin (OPN). Human tumor cells may use the IRF8 promoter DNA methylation as a mechanism to repress IRF8 expression to advance cancer through acquiring apoptosis resistance and OPN up-regulation. Elevated OPN engages CD44 to suppress T cell activation and promote tumor cell stemness to advance cancer. IRF8 thus is a transcription factor that regulates both the immune and non-immune components in human health and diseases.

Transcription-independent regulation of STING activation and innate immune responses by IRF8 in monocytes

Sensing of cytosolic DNA of microbial or cellular/mitochondrial origin by cGAS initiates innate immune responses via the adaptor protein STING. It remains unresolved how the activity of STING is balanced between a productive innate immune response and induction of autoimmunity. Here we show that interferon regulatory factor 8 (IRF8) is essential for efficient activation of STING-mediated innate immune responses in monocytes. This function of IRF8 is independent of its transcriptional role in monocyte differentiation. In uninfected cells, IRF8 remains inactive via sequestration of its IRF-associated domain by its N- and C-terminal tails, which reduces its association with STING. Upon triggering the DNA sensing pathway, IRF8 is phosphorylated at Serine 151 to allow its association with STING via the IRF-associated domain. This is essential for STING polymerization and TBK1-mediated STING and IRF3 phosphorylation. Consistently, IRF8-deficiency impairs host defense against the DNA virus HSV-1, and blocks DNA damage-induced cellular senescence. Bone marrow-derived mononuclear cells which have an autoimmune phenotype due to deficiency of Trex1, respond to IRF-8 deletion with reduced pro-inflammatory cytokine production. Peripheral blood mononuclear cells from systemic lupus erythematosus patients are characterized by elevated phosphorylation of IRF8 at the same Serine residue we find to be important in STING activation, and in these cells STING is hyper-active. Taken together, the transcription-independent function of IRF8 we describe here appears to mediate STING activation and represents an important regulatory step in the cGAS/STING innate immune pathway in monocytes.

The transcription factor IRF8 has been shown to regulate monocyte differentiation via its DNA-binding activity. Here authors show that IRF8 is also involved in cytosolic DNA sensing via its phosphorylation-dependent association to the adaptor protein STING, thus representing an important checkpoint between immune response and autoimmunity in monocytes.

Mycobacterium abscessus: It’s Complex

Mycobacterium abscessus (M. abscessus) is an opportunistic pathogen usually colonizing abnormal lung airways and is often seen in patients with cystic fibrosis. Currently, there is no vaccine available for M. abscessus in clinical development. The treatment of M. abscessus-related pulmonary diseases is peculiar due to intrinsic resistance to several commonly used antibiotics. The development of either prophylactic or therapeutic interventions for M. abscessus pulmonary infections is hindered by the absence of an adequate experimental animal model. In this review, we outline the critical elements related to M. abscessus virulence mechanisms, host–pathogen interactions, and treatment challenges associated with M. abscessus pulmonary infections. The challenges of effectively combating this pathogen include developing appropriate preclinical animal models of infection, developing proper diagnostics, and designing novel strategies for treating drug-resistant M. abscessus.

Class I PI3K regulatory subunits control differentiation of dendritic cell subsets and regulate Flt3L mediated signal transduction

Dendritic cells (DCs) play pivotal roles in initiating and shaping both innate and adaptive immune responses. The spatiotemporal expression of transcription factor networks and activation of specific signal transduction pathways determine the specification, distribution and differentiation of DC subsets. Even though pioneering studies have established indispensable roles for specific catalytic subunits (p110δ and p110γ) in immune cells, functions of the regulatory subunits, particularly of Class I PI3K, within the hematopoietic system remain incompletely understood. In the study presented here, we deleted the key regulatory subunits—p85α and p85β of the Class I_A PI3K in hematopoietic cells and studied its impact on DC differentiation. Our studies identify that a deficiency of p85 causes increased differentiation of conventional DC (cDC) 2 and plasmacytoid DC (pDC) subsets in the spleen. On the other hand, DC numbers in the bone marrow (BM), thymus and lymph nodes were decreased in p85 mutant mice. Analysis of DC-specific progenitors and precursors indicated increased numbers in the BM and spleen of p85 deficient mice. In-vitro differentiation studies demonstrated augmented DC-differentiation capacities of p85 deficient BM cells in the presence of GM-CSF and Flt3L. BM chimera studies established that p85 deficiency affects DC development through cell intrinsic mechanisms. Molecular studies revealed increased proliferation of DCs and common DC progenitors (CDPs) in the absence of p85 and altered signal transduction pathways in p85 mutant DC subsets in response to Flt3L. In essence, data presented here, for the first time, unequivocally establish that the P85α subunit of class I_A PI3Ks has an indispensable role in the development and maintenance of DCs.

An Updated Review on MSMD Research Globally and A Literature Review on the Molecular Findings, Clinical Manifestations, and Treatment Approaches in China

Mendelian susceptibility to mycobacterial disease (MSMD) arises from a group of rare inherited errors of immunity that result in selective susceptibility of otherwise healthy people to clinical disease caused by low virulence strains of mycobacteria, such as Mycobacterium bovis Bacille Calmette-Guérin (BCG) and environmental mycobacteria. Patients have normal resistance to other pathogens and no overt abnormalities in routine immunological and hematological evaluations for primary immunodeficiencies. At least 19 genes and 34 clinical phenotypes have been identified in MSMD. However, there have been no systematic reports on the clinical characteristics and genetic backgrounds of MSMD in China. In this review, on the one hand, we summarize an update findings on molecular defects and immunological mechanisms in the field of MSMD research globally. On the other hand, we undertook a systematic review of PubMed (MEDLINE), the Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science, EMBASE, CNKI, and Wanfang to identify articles published before Jan 23, 2022, to summarize the clinical characteristics, diagnosis, treatment, and prognosis of MSMD in China. All the English and Chinese publications were searched without any restriction on article types.

Plasticity of monocytes and macrophages in cirrhosis of the liver

Cirrhosis of the liver is a systemic condition with raising prevalence worldwide. Patients with cirrhosis are highly susceptible to develop bacterial infections leading to acute decompensation and acute-on-chronic liver failure both associated with a high morbidity and mortality and sparse therapeutic options other than transplantation. Mononuclear phagocytes play a central role in innate immune responses and represent a first line of defence against pathogens. Their function includes phagocytosis, killing of bacteria, antigen presentation, cytokine production as well as recruitment and activation of immune effector cells. Liver injury and development of cirrhosis induces activation of liver resident Kupffer cells and recruitment of monocytes to the liver. Damage- and pathogen-associated molecular patterns promote systemic inflammation which involves multiple compartments besides the liver, such as the circulation, gut, peritoneal cavity and others. The function of circulating monocytes and tissue macrophages is severely impaired and worsens along with cirrhosis progression. The underlying mechanisms are complex and incompletely understood. Recent 'omics' technologies help to transform our understanding of cellular diversity and function in health and disease. In this review we point out the current state of knowledge on phenotypical and functional changes of monocytes and macrophages during cirrhosis evolution in different compartments and their role in disease progression. We also discuss the value of potential prognostic markers for cirrhosis-associated immuneparesis, and future immunotherapeutic strategies that may reduce the need for transplantation and death.

Anti-cytokine autoantibodies and inborn errors of immunity

The past quarter of a century has witnessed an inordinate increase in our understanding of primary immunodeficiencies / inborn errors of immunity. These include a significant increase in the number of identified conditions, broadening the phenotypes of existing entities, delineation of classical inborn errors of immunity from those with a narrow phenotype, and a gradual shift from supportive to definitive care in patients afflicted with these diseases. It has also seen the discovery of conditions broadly defined as phenocopies of primary immunodeficiencies, where somatic mutations or autoantibodies mimic a recognised primary immunodeficiency's presentation in the absence of the underlying genetic basis for that disease. This article will provide a review of the anti-cytokine autoantibody-mediated phenocopies of inborn errors of immunity and discuss the therapeutic and laboratory aspects of this group of diseases.

Pulmonary Alveolar Proteinosis and Multiple Infectious Diseases in a Child with Autosomal Recessive Complete IRF8 Deficiency

BACKGROUND

Autosomal recessive (AR) complete IRF8 deficiency is a rare severe inborn error of immunity underlying an absence of blood myeloid mononuclear cells, intracerebral calcifications, and multiple infections. Only three unrelated patients have been reported.

MATERIALS AND METHODS

We studied an Argentinian child with multiple infectious diseases and severe pulmonary alveolar proteinosis (PAP). We performed whole-exome sequencing (WES) and characterized his condition by genetic, immunological, and clinical means.

RESULTS

The patient was born and lived in Argentina. He had a history of viral pulmonary diseases, disseminated disease due to bacillus Calmette-Guérin (BCG), PAP, and cerebral calcifications. He died at the age of 10 months from refractory PAP. WES identified two compound heterozygous variants in IRF8: c.55del and p.R111*. In an overexpression system, the p.R111* cDNA was loss-of-expression, whereas the c.55del cDNA yielded a protein with a slightly lower molecular weight than the wild-type protein. The mutagenesis of methionine residues downstream from c.55del revealed a re-initiation of translation. However, both variants were loss-of-function in a luciferase assay, suggesting that the patient had AR complete IRF8 deficiency. The patient had no blood monocytes or dendritic cells, associated with neutrophilia, and normal counts of NK and other lymphoid cell subsets.

CONCLUSION

We describe the fourth patient with AR complete IRF8 deficiency. This diagnosis should be considered in children with PAP, which is probably due to the defective development or function of alveolar macrophages.

A partial form of inherited human USP18 deficiency underlies infection and inflammation

Human USP18 is an interferon (IFN)-stimulated gene product and a negative regulator of type I IFN (IFN-I) signaling. It also removes covalently linked ISG15 from proteins, in a process called deISGylation. In turn, ISG15 prevents USP18 from being degraded by the proteasome. Autosomal recessive complete USP18 deficiency is life-threatening in infancy owing to uncontrolled IFN-I–mediated autoinflammation. We report three Moroccan siblings with autoinflammation and mycobacterial disease who are homozygous for a new USP18 variant. We demonstrate that the mutant USP18 (p.I60N) is normally stabilized by ISG15 and efficient for deISGylation but interacts poorly with the receptor-anchoring STAT2 and is impaired in negative regulation of IFN-I signaling. We also show that IFN-γ–dependent induction of IL-12 and IL-23 is reduced owing to IFN-I–mediated impairment of myeloid cells to produce both cytokines. Thus, insufficient negative regulation of IFN-I signaling by USP18-I60N underlies a specific type I interferonopathy, which impairs IL-12 and IL-23 production by myeloid cells, thereby explaining predisposition to mycobacterial disease.

Global assessment of IRF8 as a novel cancer biomarker

Interferon regulatory factor 8 (IRF8) is a member of the IRF family that is specific to the hematopoietic cell and is involved in regulating the development of human monocytic and dendritic-lineage cells, as well as B-cells. Because its utility as a sensitive and specific monoblast marker in the context of acute monocytic leukemias has been recently demonstrated, we hypothesized that it may also be useful as a novel immunohistochemical marker in myeloid sarcomas and blastic plasmacytoid dendritic cell neoplasms (BPDCNs) with respect to their differential diagnoses. In this retrospective study, we analyzed the IHC expression pattern of IRF8 in 385 patient samples across 30 types of cancers, referenced to their mRNA expression data available through The Cancer Genome Atlas. In addition, we assessed IRF8 in 35 myeloid sarcomas and 15 BPDCNs. Twenty-four of 35 cases of myeloid sarcomas (68.5%) showed positivity for IRF8, with six cases (17.1%) demonstrating IRF8 expression in the absence of CD34 and MPO. All 15 of 15 BPDCNs (100%) showed strong uniform expression of IRF8 and were occasionally more definitive than CD123. IRF8 was negative in all desmoplastic small round cell tumors, Ewing sarcomas, synovial sarcomas, and undifferentiated pleomorphic sarcomas, as well as all epithelial malignancies tested except for 2 triple negative breast cancers that showed subset weak staining. In conclusion, IRF8 is a novel marker helpful in identifying extranodal hematopoietic tumors that can otherwise be difficult to diagnose given the broad differential diagnoses and frequent loss of more common lineage-defining markers.

An Experimental Model of Neuro-Immune Interactions in the Eye: Corneal Sensory Nerves and Resident Dendritic Cells

The cornea is an avascular connective tissue that is crucial, not only as the primary barrier of the eye but also as a proper transparent refractive structure. Corneal transparency is necessary for vision and is the result of several factors, including its highly organized structure, the physiology of its few cellular components, the lack of myelinated nerves (although it is extremely innervated), the tightly controlled hydration state, and the absence of blood and lymphatic vessels in healthy conditions, among others. The avascular, immune-privileged tissue of the cornea is an ideal model to study the interactions between its well-characterized and dense sensory nerves (easily accessible for both focal electrophysiological recording and morphological studies) and the low number of resident immune cell types, distinguished from those cells migrating from blood vessels. This paper presents an overview of the corneal structure and innervation, the resident dendritic cell (DC) subpopulations present in the cornea, their distribution in relation to corneal nerves, and their role in ocular inflammatory diseases. A mouse model in which sensory axons are constitutively labeled with tdTomato and DCs with green fluorescent protein (GFP) allows further analysis of the neuro-immune crosstalk under inflammatory and steady-state conditions of the eye.

Bioinformatics Approach to Identify Significant Biomarkers, Drug Targets Shared Between Parkinson's Disease and Bipolar Disorder: A Pilot Study

Parkinson’s disease (PD) is a neurodegenerative disorder responsible for shaking, rigidity, and trouble in walking and patients’ coordination ability and physical stability deteriorate day by day. Bipolar disorder (BD) is a psychiatric disorder which is the reason behind extreme shiftiness in mood, and frequent mood inversion may reach too high called mania. People with BD have a greater chance of developing PD during the follow-up period. A lot of work has been done to understand the key factors for developing these 2 diseases. But the molecular functionalities that trigger the development of PD in people with BD are not clear yet. In our study, we are intended to identify the molecular biomarkers and pathways shared between BD and PD. We have investigated the RNA-Seq gene expression data sets of PD and BD. A total of 45 common unique genes (32 up-regulated and 13 down-regulated) abnormally expressed in both PD and BD were identified by applying statistical methods on the GEO data sets. Gene ontology (GO) and BioCarta, KEGG, and Reactome pathways analysis of these 45 common dysregulated genes identified numerous altered molecular pathways such as mineral absorption, Epstein-Barr virus infection, HTLV-I infection, antigen processing, and presentation. Analysis of protein-protein interactions revealed 9 significant hub-proteins, namely RPL21, RPL34, CKS2, B2M, TNFRSF10A, DTX2, HLA-B, ATP2A3, and TAPBP. Significant transcription factors (IRF8, SPI1, RUNX1, and FOXA1) and posttranscriptional regulator microRNAs (hsa-miR-491-3p and hsa-miR-1246) are also found by analyzing gene-transcription factors and gene-miRNAs interactions, respectively. Protein-drug interaction analysis revealed hub-protein B2M’s interaction with molecular drug candidates like N-formylmethionine, 3-indolebutyric acid, and doxycycline. Finally, a link between pathological processes of PD and BD is identified at transcriptional level. This study may help us to predict the development of PD among the people suffering from BD and gives some clue to understand significant pathological mechanisms.