An animal model of hemophagocytic lymphohistiocytosis (HLH): CD8+ T cells and interferon gamma are essential for the disorder

An Update on the Use of Immunomodulators in Primary Immunodeficiencies

The genomic revolution in the past decade fuelled by breathtaking advances in sequencing technologies has defined several new genetic diseases of the immune system. Many of these newly characterized diseases are a result of defects in genes involved in immune regulation. The discovery of these diseases has opened a vista of new therapeutic possibilities. Immunomodulatory agents, a hitherto unexplored therapeutic option in primary immunodeficiency diseases have been tried in a host of these newly described maladies. These agents have been shown conclusively to favorably modulate immune responses, resulting in abatement of clinical manifestations both in experimental models and patients. While some of the treatment options have been approved for therapeutic use or have been shown to be of merit in open-label trials, others have been shown to be efficacious in a handful of clinical cases, animal models, and cell lines. Interferon γ is approved for use in chronic granulomatous disease (CGD) to reduce the burden of infection and and has a good long-term efficacy. Recombinant human IL7 therapy has been shown increase the peripheral CD4 and CD8 T cell counts in patients with idiopathic CD4. Anti-IL1 agents are approved for the management of cryopyrin-related autoinflammatory syndrome, and their therapeutic efficacy is being increasingly recognized in other autoinflammatory syndromes and CGD. Mammalian target of rapamycin (mTOR) inhibitors have been proven useful in autoimmune lymphoproliferative syndrome (ALPS) and in IPEX syndrome. Therapies reported to be potential use in case reports include abatacept in CTLA4 haploinsufficiency and LRBA deficiency, ruxolitinib in gain-of-function STAT1, tocilizumab in gain-of-function STAT3 defect, mTOR inhibitors in PIK3CD activation, magnesium in XMEN syndrome, and pioglitazone in CGD. Treatment options of merit in human cell lines include interferon α and interferon β in TLR3 and UNC-93B deficiencies, anti-interferon therapy in SAVI, and Rho-kinase inhibitors in TTC7A deficiency. Anti-IL17 agents have show efficacy in animal models of leukocyte adhesion defect (LAD) and ALPS. This topical review explores the use of various immunomodulators and other biological agents in the context of primary immunodeficiency and autoinflammatory diseases.

Pharmacological targeting of plasmin prevents lethality in a murine model of macrophage activation syndrome

Macrophage activation syndrome (MAS) is a life-threatening disorder characterized by a cytokine storm and multiorgan dysfunction due to excessive immune activation. Although abnormalities of coagulation and fibrinolysis are major components of MAS, the role of the fibrinolytic system and its key player, plasmin, in the development of MAS remains to be solved. We established a murine model of fulminant MAS by repeated injections of Toll-like receptor-9 (TLR-9) agonist and d-galactosamine (DG) in immunocompetent mice. We found plasmin was excessively activated during the progression of fulminant MAS in mice. Genetic and pharmacological inhibition of plasmin counteracted MAS-associated lethality and other related symptoms. We show that plasmin regulates the influx of inflammatory cells and the production of inflammatory cytokines/chemokines. Collectively, our findings identify plasmin as a decisive checkpoint in the inflammatory response during MAS and a potential novel therapeutic target for MAS.

Pathophysiology of Pediatric Multiple Organ Dysfunction Syndrome

OBJECTIVE

To describe the pathophysiology associated with multiple organ dysfunction syndrome in children.

DATA SOURCES

Literature review, research data, and expert opinion.

STUDY SELECTION

Not applicable.

DATA EXTRACTION

Moderated by an experienced expert from the field, pathophysiologic processes associated with multiple organ dysfunction syndrome in children were described, discussed, and debated with a focus on identifying knowledge gaps and research priorities.

DATA SYNTHESIS

Summary of presentations and discussion supported and supplemented by relevant literature.

CONCLUSIONS

Experiment modeling suggests that persistent macrophage activation may be a pathophysiologic basis for multiple organ dysfunction syndrome. Children with multiple organ dysfunction syndrome have 1) reduced cytochrome P450 metabolism inversely proportional to inflammation; 2) increased circulating damage-associated molecular pattern molecules from injured tissues; 3) increased circulating pathogen-associated molecular pattern molecules from infection or endogenous microbiome; and 4) cytokine-driven epithelial, endothelial, mitochondrial, and immune cell dysfunction. Cytochrome P450s metabolize endogenous compounds and xenobiotics, many of which ameliorate inflammation, whereas damage-associated molecular pattern molecules and pathogen-associated molecular pattern molecules alone and together amplify the cytokine production leading to the inflammatory multiple organ dysfunction syndrome response. Genetic and environmental factors can impede inflammation resolution in children with a spectrum of multiple organ dysfunction syndrome pathobiology phenotypes. Thrombocytopenia-associated multiple organ dysfunction syndrome patients have extensive endothelial activation and thrombotic microangiopathy with associated oligogenic deficiencies in inhibitory complement and a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13. Sequential multiple organ dysfunction syndrome patients have soluble Fas ligand-Fas-mediated hepatic failure with associated oligogenic deficiencies in perforin and granzyme signaling. Immunoparalysis-associated multiple organ dysfunction syndrome patients have impaired ability to resolve infection and have associated environmental causes of lymphocyte apoptosis. These inflammation phenotypes can lead to macrophage activation syndrome. Resolution of multiple organ dysfunction syndrome requires elimination of the source of inflammation. Full recovery of organ functions is noted 6-18 weeks later when epithelial, endothelial, mitochondrial, and immune cell regeneration and reprogramming is completed.

Application of an improved flow cytometry-based NK cell activity assay in adult hemophagocytic lymphohistiocytosis

Low or absent natural killer (NK) cell activity is included as one of the HLH-2004 diagnostic criteria. To improve the diagnosis of HLH, we aimed to establish a rapid and reliable NK cell activity assay that avoids the use of radioactivity. The K562 cell line, as standard NK target cells, was engineered to stably express enhanced green fluorescent protein (EGFP), which can be quantified by flow cytometry. The EGFP-flow cytometry method for measuring NK cell activity was improved by double staining of early and late apoptotic target cells. Whole-blood samples from healthy volunteers were assessed with this method, which demonstrated that optimal conditions were effector-target ratio of 10:1 and incubation time of 4 h. This method was further evaluated for samples from 113 HLH patients and 64 healthy volunteers. Mean NK cell activity in either primary or secondary HLH patients was significantly lower (P < 0.001) than in healthy individuals (20.23 ± 4.12%). Furthermore, primary HLH patients (10.76 ± 2.54%) exhibited even lower (P < 0.001) NK cell activity compared with secondary HLH patients (15.01 ± 3.62%). We have optimized and implemented this method in clinically relevant samples.

Weathering the storm: Improving therapeutic interventions for cytokine storm syndromes by targeting disease pathogenesis

Cytokine storm syndromes require rapid diagnosis and treatment to limit the morbidity and mortality caused by the hyperinflammatory state that characterizes these devastating conditions. Herein, we discuss the current knowledge that guides our therapeutic decision-making and personalization of treatment for patients with cytokine storm syndromes. Firstly, ICU-level supportive care is often required to stabilize patients with fulminant disease while additional diagnostic evaluations proceed to determine the underlying cause of cytokine storm. Pharmacologic interventions should be focused on removing the inciting trigger of inflammation and initiation of an individualized immunosuppressive regimen when immune activation is central to the underlying disease pathophysiology. Monitoring for a clinical response is required to ensure that changes in the therapeutic regimen can be made as clinically warranted. Escalation of immunosuppression may be required if patients respond poorly to the initial therapeutic interventions, while a slow wean of immunosuppression in patients who improve can limit medication-related toxicities. In certain scenarios, a decision must be made whether an individual patient requires hematopoietic cell transplantation to prevent recurrence of disease. Despite these interventions, significant morbidity and mortality remains for cytokine storm patients. Therefore, we use this review to propose a clinical schema to guide current and future attempts to design rational therapeutic interventions for patients suffering from these devastating conditions, which we believe speeds the diagnosis of disease, limits medication-related toxicities, and improves clinical outcomes by targeting the heterogeneous and dynamic mechanisms driving disease in each individual patient.

From the Cradle to the Grave: The Role of Macrophages in Erythropoiesis and Erythrophagocytosis

Erythropoiesis is a highly regulated process where sequential events ensure the proper differentiation of hematopoietic stem cells into, ultimately, red blood cells (RBCs). Macrophages in the bone marrow play an important role in hematopoiesis by providing signals that induce differentiation and proliferation of the earliest committed erythroid progenitors. Subsequent differentiation toward the erythroblast stage is accompanied by the formation of so-called erythroblastic islands where a central macrophage provides further cues to induce erythroblast differentiation, expansion, and hemoglobinization. Finally, erythroblasts extrude their nuclei that are phagocytosed by macrophages whereas the reticulocytes are released into the circulation. While in circulation, RBCs slowly accumulate damage that is repaired by macrophages of the spleen. Finally, after 120 days of circulation, senescent RBCs are removed from the circulation by splenic and liver macrophages. Macrophages are thus important for RBCs throughout their lifespan. Finally, in a range of diseases, the delicate interplay between macrophages and both developing and mature RBCs is disturbed. Here, we review the current knowledge on the contribution of macrophages to erythropoiesis and erythrophagocytosis in health and disease.

Use of a mouse model to identify a blood biomarker for IFNγ activity in pediatric secondary hemophagocytic lymphohistiocytosis

Life-threatening cytokine release syndromes include primary (p) and secondary (s) forms of hemophagocytic lymphohistiocytosis (HLH). Below detection in healthy individuals, interferon γ (IFNγ) levels are elevated to measurable concentrations in these afflictions suggesting a central role for this cytokine in the development and maintenance of HLH. Mimicking an infection-driven model of sHLH in mice, we observed that the tissue-derived levels of IFNγ are actually 500- to 2000-fold higher than those measured in the blood. To identify a blood biomarker, we postulated that the IFNγ gene products, CXCL9 and CXCL10 would correlate with disease parameters in the mouse model. To translate this into a disease relevant biomarker, we investigated whether CXCL9 and CXCL10 levels correlated with disease activity in pediatric sHLH patients. Our data demonstrate that disease control in mice correlates with neutralization of IFNγ activity in tissues and that the 2 chemokines serve as serum biomarkers to reflect disease status. Importantly, CXCL9 and CXCL10 levels in pediatric sHLH were shown to correlate with key disease parameters and severity in these patients. Thus, the translatability of the IFNγ-biomarker correlates from mouse to human, advocating the use of serum CXCL9 or CXCL10 as a means to monitor total IFNγ activity in patients with sHLH.

Macrophage Activation Syndrome: different mechanisms leading to a one clinical syndrome

BACKGROUND

Macrophage activation syndrome (MAS) is a severe complication of rheumatic disease in childhood, particularly in systemic Juvenile Idiopathic Arthritis (sJIA). It is characterize by an uncontrolled activation and proliferation of T lymphocytes and macrophages.

MAIN CONTENT

MAS is currently classified among the secondary or acquired forms of haemophagocytic lymphohistiocytosis (sHLH). The reason is that MAS shares clinical and laboratory features with primary genetic HLH (pHLH). In this context is conceivable that some of the pathogenic mechanisms of pHLH may be involved in other forms of HLH. Heterozygosity for mutations of genes involved in pHLH may lead to a cytotoxic defect and to a development of clinical overt disease. But other different contributors might be involved to the development of MAS such as infections or underlying inflammation. In MAS, the inflammatory status of the patient is a major contributor of the disease. Indeed, the majority of the MAS episodes occurs during active disease phases or at disease onset. In addition, recent evidence in animals and humans suggest that genetics may also play a major role in contributing to hyperinflammation and particularly to macrophages hyper-responses.

CONCLUSIONS

We hypothesize that HLH may be one unique clinical syndrome, to whose generation different mechanisms may contribute, and maintained by one final effector mechanism.

Primary and secondary hemophagocytic lymphohistiocytosis have different patterns of T-cell activation, differentiation and repertoire

Hemophagocytic lymphohistiocytosis (HLH) is a life‐threatening inflammatory syndrome characterized by hyperactivation of lymphocytes and histiocytes. T cells play a key role in HLH pathogenesis, but their differentiation pattern is not well characterized in patients with active HLH. We compared T‐cell activation patterns between patients with familial HLH (1°HLH), 2°HLH without apparent infectious trigger (2°HLH) and 2°HLH induced by a viral infection (2°V‐HLH). Polyclonal CD8⁺ T cells are highly activated in 1°HLH and 2°V‐HLH, but less in 2°HLH as assessed by HLA‐DR expression and marker combination with CD45RA, CCR7, CD127, PD‐1 and CD57. Absence of increased HLA‐DR expression on T cells excluded active 1° HLH with high sensitivity and specificity. A high proportion of polyclonal CD127⁻CD4⁺ T cells expressing HLA‐DR, CD57, and perforin is a signature of infants with 1°HLH, much less prominent in virus‐associated 2°HLH. The similar pattern and extent of CD8⁺ T‐cell activation compared to 2° V‐HLH is compatible with a viral trigger of 1°HLH. However, in most 1°HLH patients no triggering infection was documented and the unique activation of cytotoxic CD4⁺ T cells indicates that the overall T‐cell response in 1°HLH is different. This may reflect different pathways of pathogenesis of these two HLH variants.

Elevated circulating levels of interferon-γ and interferon-γ-induced chemokines characterise patients with macrophage activation syndrome complicating systemic juvenile idiopathic arthritis

OBJECTIVES

Interferon-γ (IFNγ) is the pivotal mediator in murine models of primary haemophagocytic lymphohistiocytosis (pHLH). Given the similarities between primary and secondary HLH (sec-HLH), including macrophage activation syndrome (MAS), we investigate the involvement of the IFNγ pathway in MAS by evaluating levels of IFNγ and of the induced chemokines, and their relation with laboratory parameters of MAS in systemic juvenile idiopathic arthritis (sJIA) patients with MAS and in a murine MAS model.

METHODS

The Luminex multiplexing assay was used to assess serum levels of interleukin (IL)-1β, IL-6, IFNγ and of the IFNγ-induced chemokines CXCL9, CXCL10 and CXCL11 in patients with sec-HLH (n=11) and in patients with sJIA (n=54), of whom 20 had active MAS at sampling. Expression of IFNγ-induced chemokines was assessed in IL-6 transgenic mice in which MAS is induced by TLR4 stimulation with lipopolysaccharide.

RESULTS

Levels of IFNγ and of IFNγ-induced chemokines were markedly elevated during active MAS and sec-HLH and were significantly higher in patients with MAS compared with active sJIA without MAS. Levels in patients with active sJIA without MAS were comparable to those of patients with clinically inactive sJIA. During MAS, ferritin and alanine transferase levels and neutrophil and platelet counts were significantly correlated with serum levels of IFNγ and CXCL9. In murine MAS, serum levels of ferritin were significantly correlated with mRNA levels of Cxcl9 in liver and spleen.

CONCLUSIONS

The high levels of IFNγ and of IFNγ-induced chemokines and their correlation with the severity of laboratory abnormalities of MAS suggest a pivotal role of IFNγ in MAS.

Hemophagocytic Lymphohistiocytosis in a Patient With Hodgkin lymphoma and Concurrent EBV, CMV, and Candida Infections

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome characterized by immune activation and subsequent widespread organ damage. Patients affected by HLH commonly develop fever, cytopenias, liver damage, neurologic manifestations, and hypercytokinemia. In this case, we describe a 60-year-old male who presented with HLH and concurrent Epstein-Barr virus, cytomegalovirus, and Candida infections and was subsequently diagnosed with a Hodgkin lymphoma. This case highlights the importance of considering a cancer diagnosis in the differential diagnosis of patients presenting with HLH.

IL-10 distinguishes a unique population of activated, effector-like CD8+ T cells in murine acute liver inflammation

Immune-mediated liver injury is a central feature of hyperinflammatory diseases, such as hemophagocytic syndromes, yet the immunologic mechanisms underlying those processes are incompletely understood. In this study, we used the toll-like receptor 9 (TLR9)-mediated model of a hemophagocytic syndrome known as macrophage activation syndrome (MAS) to dissect the predominant immune cell populations infiltrating the liver during inflammation. We identified CD8⁺ T cells that unexpectedly produce interleukin-10 (IL-10) in addition to interferon-γ (IFN-γ) as a major hepatic population induced by TLR9 stimulation. Despite their ability to produce this anti-inflammatory cytokine, IL-10⁺ hepatic CD8⁺ T cells in TLR9-MAS mice did not resemble CD8⁺ T suppressor cells. Instead, the induction of these cells occurred independently of antigen stimulation and was partially dependent on IFN-γ. IL-10⁺ hepatic CD8⁺ T cells demonstrated an activated phenotype and high turnover rate, consistent with an effector-like identity. Transcriptional analysis of this population confirmed a gene signature of effector CD8⁺ T cells yet suggested responsiveness to liver injury-associated growth factors. Together, these findings suggest that IL-10⁺ CD8⁺ T cells induced by systemic inflammation to infiltrate the liver have initiated an inflammatory, rather than regulatory, program and may thus have a pathogenic role in severe, acute hepatitis.

Impairment of Immune Function in Children with Familial Hemophagocytic Lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a severe systemic syndrome associated with hyperactivation of macrophages and impaired regulation of the immune system. Two forms of HLH are currently recognized: genetically determined or familial (FHLH), and secondarily developed in the course of primary diseases, like autoimmune disorders, rheumatoid disorders, cancers, or infections. In the Polish population, FHLH is rather rare. The aim of the present study was to assess the immune function in a group of children with clinical symptoms suggesting FHLH. Forty five children with suspected HLH of the median age of 4 years and 15 healthy children, taken as a control group, were enrolled into the study. All presented results were obtained with the use of flow cytometry. In the HLH group, there were only three cases identified with the UNC13D gene mutation responsible for the FHLH3 phenotype. Another four children, without known mutation, were classified as FHLH because of frequent recurrence of the disease. In all cases of FHLH, cell cytotoxicity was impaired compared with healthy children (p = 0.003). Perforin expression in FHLH was normal or higher than that observed in controls (p = 0.09). In case of patients with mutation in the Munc13 protein, degranulation was lower than that in healthy children (<5 %). The findings of this study demonstrate that children with known mutations responsible for the FHLH development are immunocompromised. However, it requires further elucidation whether the presence of currently unknown mutations could lead to a similar phenotype.

Rituximab, etoposide, methylprednisolone, high-dose cytarabine, and cisplatin in the treatment of secondary hemophagocytic lymphohistiocytosis with classical Hodgkin lymphoma: a case report and review of the literature

Background

Hemophagocytic lymphohistiocytosis is becoming an increasingly recognized disorder in adults. Classical Hodgkin lymphoma is a relatively uncommon etiology of hemophagocytic lymphohistiocytosis and may complicate treatment options. Rituximab, etoposide, methylprednisolone, high-dose cytarabine, and cisplatin are discussed here as a treatment regimen.

Case presentation

A 66-year-old Hispanic man previously in good health presented with a 1-month history of recurrent fevers, chills, and night sweats and a 3-week history of new onset jaundice. A bone marrow biopsy revealed a normocellular bone marrow with increased histiocytes with areas of hemophagocytic activity. He met five out of eight criteria for hemophagocytic lymphohistiocytosis diagnosis including fevers, pancytopenia, hemophagocytosis, ferritin of 23,292 ng/mL (>500 ng/mL), and soluble-CD25 of 15,330 pg/mL (>1033 pg/mL). A right cervical lymph node biopsy revealed CD15, CD30, MUM-1, and Epstein–Barr virus-encoded small ribonucleic acid-positive cells with morphologic findings of classical Hodgkin lymphoma, lymphocyte-rich subtype. He completed 2 weeks of hemophagocytic lymphohistiocytosis-directed therapy with etoposide and dexamethasone, but then was switched to rituximab, etoposide, methylprednisolone, high-dose cytarabine, and cisplatin due to minimal improvement in his pancytopenia and hepatic impairment. He completed one full cycle of rituximab, etoposide, methylprednisolone, high-dose cytarabine, and cisplatin with notable improvement in serial hepatic function panels and had an undetectable Epstein–Barr virus viral load. However, he eventually died due to complications of Enterococcus faecalis bacteremia and colonic microperforation in the setting of persistent pancytopenia.

Conclusions

This case discusses the challenges facing treatment of adult malignancy-associated hemophagocytic lymphohistiocytosis. Rituximab, etoposide, methylprednisolone, high-dose cytarabine, and cisplatin may be a viable option for patients with secondary hemophagocytic lymphohistiocytosis and Hodgkin lymphoma who cannot tolerate standard therapies due to hepatic impairment. Targeted therapy and immunotherapy are promising new areas of developing treatments.

Familial haemophagocytosis lymphohisticytosis type 3: A case report

Familial hemophagocytic lymphohistiocytosis (FHL) is a rare autosomal recessive disorder of immune regulation. Here, we report on a fatal case of type 3 FHL (FHL3) in a 45-day-old boy. Clinically, the infant presented with fever and hepatosplenomegaly. Biology showed pancytopenia, elevated ferritin, and decreased fibrinogen. Images of hemophagocytosis were found at the bone morrow examination. The diagnosis of FHL type 3 was made by the identification of homozygous mutation in the Munc13-4 gene (UNC13D) located in exon 20: 1822 del 12bp (V608fs). This mutation was previously observed in a Tunisian and in Moroccan families.

Severe Epstein-Barr virus infection in primary immunodeficiency and the normal host

Epstein-Barr virus (EBV) infection is ubiquitous in humans, but the majority of infections have an asymptomatic or self-limiting clinical course. Rarely, individuals may develop a pathological EBV infection with a variety of life threatening complications (including haemophagocytosis and malignancy) and others develop asymptomatic chronic EBV viraemia. Although an impaired ability to control EBV infection has long been recognised as a hallmark of severe T-cell immunodeficiency, the advent of next generation sequencing has identified a series of Primary Immunodeficiencies in which EBV-related pathology is the dominant feature. Chronic active EBV infection is defined as chronic EBV viraemia associated with systemic lymphoproliferative disease, in the absence of immunodeficiency. Descriptions of larger cohorts of patients with chronic active EBV in recent years have significantly advanced our understanding of this clinical syndrome. In this review we summarise the current understanding of the pathophysiology and natural history of these diseases and clinical syndromes, and discuss approaches to the investigation and treatment of severe or atypical EBV infection.

A retrospective analysis of 56 children with hemophagocytic lymphohistiocytosis

Aim

The aim of this study was to investigate the etiological factors, clinical features, and prognostic factors in children with hemophagocytic lymphohistiocytosis (HLH).

Methods

Fifty-six children with HLH in Wuhan Union Hospital, People’s Republic of China, were retrospectively analyzed in recent years. We reviewed the medical records of 56 HLH children hospitalized from 2000 to 2013 to identify the possible prognostic factors.

Results

In more than half of the cases (64.29%), the etiological factor was found to be infection. Clinical characteristics such as prolonged fever (100.00%), hepatosplenomegaly (95.24%), and pancytopenia (100.00%) were observed. Characteristic laboratory values presented with increased ferritin (64.29%), triglycerides (78.57%), transaminases (80.95%), bilirubin (67.54%), lactate dehydrogenase (95.23%), and decreased fibrinogen (61.90%), natrium (40.48%), and potassium (30.94%). Bone marrow aspiration showed hemophagocytosis in 48 cases (85.71%). Forty-two patients were treated according to HLH-2004 protocol. Out of the 42 patients, 19 cases acquired remission and 13 cases died. Ten cases lost follow-up. High lactate dehydrogenase (>2,000 U/L), high bilirubin (>2 mg/mL), and younger age (<2 years) at the time of diagnosis were adverse prognostic factors.

Conclusion

HLH is a life-threatening syndrome caused by complicated etiology. The level of lactate dehydrogenase and bilirubin accompanied with younger age were adverse factors.

High Level of Perforin Expression Is Required for Effective Correction of Hemophagocytic Lymphohistiocytosis

Perforin-1 mutations result in a potentially fatal hemophagocytic lymphohistiocytosis (HLH) with heightened immune activation, hypercytokinemia, pancytopenia, and end-organ damage. At present, hematopoietic stem cell (HSC) transplantation is curative, but limited by donor availability and associated mortality, making gene therapy an attractive alternative approach for HLH. We reported that perforin expression driven by cellular promoters in lentiviral (LV) vectors resulted in significant, albeit partial, correction of the inflammatory features in a murine model of HLH. We hypothesized that the level of perforin expression achieved per cell from ectopic moderate-strength cellular promoters (phosphoglycerate kinase gene/perforin-1 gene) is inadequate and thus engineered an LV vector using a viral promoter (MND; a modified Moloney murine leukemia virus long terminal repeat with myeloproliferative sarcoma virus enhancer) containing microRNA126 target sequences to restrict perforin expression in HSCs. We show here that the MND-LV vector restored perforin expression to normal levels in a perforin-deficient human natural killer cell line and perforin gene-corrected Perforin1-/- transplant recipients, whereas cellular promoters drove only partial correction. On lymphocytic choriomeningitis virus challenge, the clinical scores and survival improved only with the MND-LV vector, but inflammatory markers and cytotoxicity were improved with all LV vectors. Our studies suggest that although moderate levels of expression can result in partial amelioration of the HLH phenotype, high levels of perforin expression per cell are required for complete correction of HLH.

A xenograft model of macrophage activation syndrome amenable to anti-CD33 and anti-IL-6R treatment

Transgenic expression of key myelosupportive human cytokines in immune-deficient mice corrects for the lack of cross-species activities of stem cell factor (SCF), IL-3, and GM-CSF. When engrafted with human umbilical cord blood (UCB), these triple-transgenic mice produce BM and spleen grafts with much higher myeloid composition, relative to nontransgenic controls. Shortly after engraftment with UCB, these mice develop a severe, fatal macrophage activation syndrome (MAS) characterized by a progressive drop in rbc numbers, increased reticulocyte counts, decreased rbc half-life, progressive cytopenias, and evidence of chronic inflammation, including elevated human IL-6. The BM becomes strikingly hypocellular, and spleens are significantly enlarged with evidence of extramedullary hematopoiesis and activated macrophages engaged in hemophagocytosis. This manifestation of MAS does not respond to lymphocyte-suppressive therapies such as steroids, i.v. immunoglobulin, or antibody-mediated ablation of human B and T cells, demonstrating a lymphocyte-independent mechanism of action. In contrast, elimination of human myeloid cells using gemtuzumab ozogamicin (anti-CD33) completely reversed the disease. Additionally, the IL-6R antibody tocilizumab delayed progression and prolonged lifespan. This new model of MAS provides an opportunity for investigation of the mechanisms driving this disease and for the testing of directed therapies in a humanized mouse.

Hemophagocytic lymphohistiocytosis: Pathogenesis, diagnosis, and management

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome that is classified into primary and secondary HLH. Primary HLH consists of monogenic disorders that mainly affect the perforin-mediated cytotoxicity of cytotoxic T lymphocytes and natural killer cells. Secondary HLH occurs as a complication in various settings such as infection, malignancy, autoimmune disease, and post-allogeneic hematopoietic stem cell transplantation. Both primary and secondary HLH are characterized by uncontrolled hypercytokinemia that results in myelosuppression and vascular endothelium damage. More than 10% of patients with HLH die within 2 months of diagnosis due to bleeding in the visceral organs, opportunistic infection due to neutropenia, or multiple organ failure. The most obvious presentations of HLH are persistent fever refractory to antimicrobial agents and hyperferritinemia due to hypersecretion of various cytokines. The first rule is not to overlook signs of hypercytokinemia and to settle the hyperactivated immunological state as soon as possible. In addition, to improve outcome, it is essential to identify the disorders underlying HLH and provide disorder-appropriate treatment.

Plasmacytoid Dendritic Cells Die by the CD8 T Cell-Dependent Perforin Pathway during Acute Nonviral Inflammation

Regulation of the inflammatory response involves the control of dendritic cell survival. To our knowledge, nothing is known about the survival of plasmacytoid dendritic cells (pDC) in such situation. pDC are specialized in type I IFN (IFN-I) secretion to control viral infections, and IFN-I also negatively regulate pDC survival during the course of viral infections. In this study, we asked about pDC behavior in the setting of virus-free inflammation. We report that pDC survival was profoundly reduced during different nonviral inflammatory situations in the mouse, through a mechanism independent of IFN-I and TLR signaling. Indeed, we demonstrated that during inflammation, CD8(+) T cells induced pDC apoptosis through the perforin pathway. The data suggest, therefore, that pDC have to be turned down during ongoing acute inflammation to not initiate autoimmunity. Manipulating CD8(+) T cell response may therefore represent a new therapeutic opportunity for the treatment of pDC-associated autoimmune diseases, such as lupus or psoriasis.

Therapeutic effect of JAK1/2 blockade on the manifestations of hemophagocytic lymphohistiocytosis in mice

Treatment with clinical dose of JAK1/2 inhibitor (ruxolitinib) countered manifestations of HLH in 2 cytotoxicity-impaired murine models. JAK1/2 inhibitor therapy in mice is effective on survival, cytopenia, inflammatory syndrome, central nervous system involvement, and liver tissue repair.

Profiling of EBV-Encoded microRNAs in EBV-Associated Hemophagocytic Lymphohistiocytosis

Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis (EBV-HLH) is a life-threatening complication of EBV infection. MicroRNAs (miRNAs) were small non-coding RNA, and EBV could encode miRNAs that are involved in the progression of infection. However, the profiles of EBV-miRNAs in EBV-HLH were unknown. Here, we aimed to profile the expression of EBV-miRNAs in children with EBV-HLH by analyzing 44 known EBV-miRNAs, encoded within the BamHI fragment H rightward open reading frame 1 (BHRF1) and the BamHI-A region rightward transcript (BART), in plasma and cellular targets by real-time quantitative PCR. The study included 15 children with EBV-HLH, 15 children with infectious mononucleosis (IM), and 15 healthy controls. CD8(+) T cells were found to be the cellular target of EBV infection in EBV-HLH, while CD19(+) B cells were infected with EBV in IM. We also found the greater levels of several miRNAs encoded by BART in EBV-HLH, compared to those in IM and healthy controls, whereas the levels of BHRF1 miRNAs were lower than those in IM. The profile and pattern of EBV-miRNAs in EBV-HLH indicated that EBV could display type II latency in EBV-HLH. Importantly, the level of plasma miR-BART16-1 continued decreasing during the whole chemotherapy, suggesting that plasma miR-BART16-1 could be a potential biomarker for monitoring EBV-HLH progression. The pathogenesis of EBV-HLH might be attributed to the abundance of EBV-miRNAs in EBV-HLH. These findings help elucidate the roles of EBV miRNAs in EBV-HLH, enabling the understanding of the basis of this disease and providing clues for its treatment.

Investigating the Role of TNF-α and IFN-γ Activation on the Dynamics of iNOS Gene Expression in LPS Stimulated Macrophages

Macrophage produced inducible nitric oxide synthase (iNOS) is known to play a critical role in the proinflammatory response against intracellular pathogens by promoting the generation of bactericidal reactive nitrogen species. Robust and timely production of nitric oxide (NO) by iNOS and analogous production of reactive oxygen species are critical components of an effective immune response. In addition to pathogen associated lipopolysaccharides (LPS), iNOS gene expression is dependent on numerous proinflammatory cytokines in the cellular microenvironment of the macrophage, two of which include interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α). To understand the synergistic effect of IFN-γ and TNF-α activation, and LPS stimulation on iNOS expression dynamics and NO production, we developed a systems biology based mathematical model. Using our model, we investigated the impact of pre-infection cytokine exposure, or priming, on the system. We explored the essentiality of IFN-γ priming to the robustness of initial proinflammatory response with respect to the ability of macrophages to produce reactive species needed for pathogen clearance. Results from our theoretical studies indicated that IFN-γ and subsequent activation of IRF1 are essential in consequential production of iNOS upon LPS stimulation. We showed that IFN-γ priming at low concentrations greatly increases the effector response of macrophages against intracellular pathogens. Ultimately the model demonstrated that although TNF-α contributed towards a more rapid response time, measured as time to reach maximum iNOS production, IFN-γ stimulation was significantly more significant in terms of the maximum expression of iNOS and the concentration of NO produced.

Advances in the pathogenesis of primary and secondary haemophagocytic lymphohistiocytosis: differences and similarities

Haemophagocytic lymphohistiocytosis (HLH) comprises a heterogeneous spectrum of hyperinflammatory conditions that are inherited (primary HLH) or acquired in a context of infections, malignancies or autoimmune/autoinflammatory disorders (secondary HLH). Genetic defects in the cytotoxic machinery of natural killer and CD8(+) T cells underlie primary HLH, with residual cytotoxicity determining disease severity. Improved sequencing techniques have expanded the range of causal mutations and have redefined many cases of secondary HLH as primary HLH and vice versa, blurring the distinction between both subtypes. These insights allow HLH to be conceptualized as a threshold disease, in which interplay between various genetic and environmental factors causes progressive inflammation into a critical point, beyond which uncontrolled activation of immune cells and excessive cytokine production give rise to the cardinal symptoms of HLH. Various pathogenic pathways may thus converge to a common end stage of fulminant HLH.

Haemophagocytic lymphohistiocytosis presenting as neonatal liver failure: A case series

BACKGROUND AND STUDY AIM

Haemophagocytic lymphohistiocytosis (HLH) is a life-threatening clinical syndrome with liver involvement varying from mild dysfunction to severe fulminant failure. The aim of this study was to present a case series of four HLH patients presenting with acute liver failure (ALF) in the neonatal period.

PATIENTS AND METHODS

All four patients were neonates at the onset of symptoms. They presented to Cairo University Pediatric Hospital with ALF; they underwent prompt investigations including determination of ferritin, fibrinogen, and triglyceride levels as part of our ALF workup. Further investigations were tailored according to the associated clinical features and the results of preliminary investigations.

RESULTS

HLH was diagnosed according to HLH-2004 criteria. Three patients fulfilled at least five out of eight criteria. Fever, splenomegaly, elevated ferritin levels, and low fibrinogen levels were present in all patients. The fourth patient had a serum ferritin level >10,000ng/ml, favouring the diagnosis of HLH, despite fulfilling only four out of eight criteria. For three patients, positive consanguinity and previous sibling death were reported, suggesting a genetic aetiology of HLH.

CONCLUSION

ALF can be the presenting feature of HLH; thus, a high index of suspicion is necessary. Fever is a hallmark, especially in neonates. Diagnosis is important for this potentially treatable condition.

Asparagine endopeptidase is an innovative therapeutic target for neurodegenerative diseases

INTRODUCTION

Asparagine endopeptidase (AEP) is a pH-dependent endolysosomal cysteine protease that cleaves its substrates after asparagine residues. Our most recent study identifies that it possesses the delta-secretase activity, and that it is implicated in numerous neurological diseases such as Alzheimer's disease (AD) and stroke. Accumulating evidence supports that the inhibition of AEP exhibits beneficial effects for treating these devastating diseases.

AREAS COVERED

Based on recent evidence, it is clear that AEP cleaves its substrate, such as amyloid precursor protein (APP), tau and SET, and plays a critical role in neuronal cell death in various neurodegenerative diseases and stroke. In this article, the basic biology of AEP, its knockout phenotypes in mouse models, its substrates in neurodegenerative diseases, and its small peptidyl inhibitors and prodrugs are discussed. In addition, we discuss the potential of AEP as a novel therapeutic target for neurodegenerative diseases.

EXPERT OPINION

AEP plays a unique role in numerous biological processes, depending on both pH and context. Most striking is our most recent finding; that AEP is activated in an age-dependent manner and simultaneously cleaves both APP and tau, thereby unifying both major pathological events in AD. Thus, AEP acts as an innovative trigger for neurodegenerative diseases. Inhibition of AEP will provide a disease-modifying treatment for neurodegenerative diseases including AD.

Rate and Clinical Presentation of Macrophage Activation Syndrome in Patients With Systemic Juvenile Idiopathic Arthritis Treated With Canakinumab

OBJECTIVE

In pivotal trials, canakinumab has been shown to be effective in the treatment of systemic juvenile idiopathic arthritis (JIA), but reported adverse events have included macrophage activation syndrome (MAS). This study was undertaken to assess the impact of canakinumab on MAS incidence.

METHODS

An independent MAS Adjudication Committee (MASAC), consisting of 3 of the authors, was convened, and a search of databases from clinical studies of canakinumab treatment in systemic JIA was performed using MASAC-specified adverse event terms to identify potential MAS events. These were then adjudicated as "probable MAS," "possible MAS," or "MAS unlikely," using criteria developed by the MASAC. MAS rates were expressed as numbers of cases per 100 patient-years.

RESULTS

Of 72 potential MAS cases identified, 21 events (19 with canakinumab treatment; 2 with placebo treatment) in 19 patients were adjudicated as being probable MAS and 10 events in 9 patients as being possible MAS. Systemic JIA was well controlled in the majority of canakinumab-treated patients at the time of MAS. The time period between initiation of canakinumab treatment and onset of MAS ranged from 3 to 1,358 days (median 292 days). When the rates of probable MAS events were compared between canakinumab-treated patients (2.8 per 100 patient-years) and placebo-treated patients (7.7 per 100 patient-years), the difference was not significant (-4.9 [95% confidence interval -15.6, 5.9]). There were 3 deaths due to MAS-related complications (2 in patients receiving canakinumab; 1 in a patient receiving placebo); full recovery was reported in all other patients. Infections were the most common trigger of MAS, and the clinical features of MAS were not modified by canakinumab.

CONCLUSION

Canakinumab does not have a significant effect on MAS risk or its clinical features in patients with systemic JIA. Infections are the most common trigger, and MAS occurs even in patients whose systemic JIA is well controlled with this treatment.

Large granules in the peripheral blood smear and bone marrow aspirate of a 3-year-old male with lymphadenopathy and fever

A 3-year-old male with oculocutaneous albinism presented with lymphadenopathy and fever. Serological testing revealed Epstein-Barr virus (EBV)-specific immunoglobulin M (IgM) and a diagnosis of infectious mononucleosis was made. A complete blood count and peripheral blood smear demonstrated mild anemia, thrombocytopenia, and neutropenia with leukocytes that contained large azurophilic and eosinophilic granules. Bone marrow examination demonstrated increased hemophagocytic histiocytes along with granulocytes that contained large eosinophilic granules. In addition to hemophagocytic lymphohistiocytosis, presumably due to acute EBV infection, the patient was diagnosed with Chediak-Higashi syndrome based on the pathognomonic granules within peripheral leukocytes and precursors. The differential diagnosis of a young patient with oculocutaneous albinism presenting with an acute viral infection includes a relatively narrow range of genetic syndromes based solely on the history of albinism. This case demonstrates the application of clinical laboratory data to presumptively diagnose Chediak-Higashi syndrome in the midst of a presentation of hemophagocytic lymphohistiocytosis secondary to acute EBV infection.

Macrophage activation syndrome in the era of biologic therapy

Macrophage activation syndrome (MAS) refers to acute overwhelming inflammation caused by a 'cytokine storm'. Although increasingly recognized as a life-threatening complication of various rheumatic diseases, clinically, MAS is strikingly similar to primary and secondary forms of haemophagocytic lymphohistiocytosis (HLH). Not surprisingly, many rheumatologists prefer the term secondary HLH rather than MAS to describe this condition, and efforts to change the nomenclature are in progress. The pathophysiology of MAS remains elusive, but observations in animal models, as well as data on the effects of new anticytokine therapies on rates and clinical presentations of MAS in patients with systemic juvenile idiopathic arthritis (sJIA), provide clues to the understanding of this perplexing clinical phenomenon. In this Review, we explore the latest available evidence and discuss potential diagnostic challenges in the era of increasing use of biologic therapies.

Normalizing the environment recapitulates adult human immune traits in laboratory mice

Our current understanding of immunology was largely defined in laboratory mice, partly because they are inbred and genetically homogeneous, can be genetically manipulated, allow kinetic tissue analyses to be carried out from the onset of disease, and permit the use of tractable disease models. Comparably reductionist experiments are neither technically nor ethically possible in humans. However, there is growing concern that laboratory mice do not reflect relevant aspects of the human immune system, which may account for failures to translate disease treatments from bench to bedside. Laboratory mice live in abnormally hygienic specific pathogen free (SPF) barrier facilities. Here we show that standard laboratory mouse husbandry has profound effects on the immune system and that environmental changes produce mice with immune systems closer to those of adult humans. Laboratory mice--like newborn, but not adult, humans--lack effector-differentiated and mucosally distributed memory T cells. These cell populations were present in free-living barn populations of feral mice and pet store mice with diverse microbial experience, and were induced in laboratory mice after co-housing with pet store mice, suggesting that the environment is involved in the induction of these cells. Altering the living conditions of mice profoundly affected the cellular composition of the innate and adaptive immune systems, resulted in global changes in blood cell gene expression to patterns that more closely reflected the immune signatures of adult humans rather than neonates, altered resistance to infection, and influenced T-cell differentiation in response to a de novo viral infection. These data highlight the effects of environment on the basal immune state and response to infection and suggest that restoring physiological microbial exposure in laboratory mice could provide a relevant tool for modelling immunological events in free-living organisms, including humans.

Hemophagocytosis in Experimental Visceral Leishmaniasis by Leishmania donovani

Hemophagocytosis is a phenomenon in which macrophages phagocytose blood cells. There are reports on up-regulated hemophagocytosis in patients with infectious diseases including typhoid fever, tuberculosis, influenza and visceral leishmaniasis (VL). However, mechanisms of infection-associated hemophagocytosis remained elusive due to a lack of appropriate animal models. Here, we have established a mouse model of VL with hemophagocytosis. At 24 weeks after infection with 1 x 10⁷Leishmania donovani promastigotes, BALB/cA mice exhibited splenomegaly with an average tissue weight per body weight of 2.96%. In the tissues, 28.6% of macrophages contained phagocytosed erythrocytes. All of the hemophagocytosing macrophages were parasitized by L. donovani, and higher levels of hemophagocytosis was observed in heavily infected cells. Furthermore, more than half of these hemophagocytes had two or more macrophage-derived nuclei, whereas only 15.0% of splenic macrophages were bi- or multi-nuclear. These results suggest that direct infection by L. donovani causes hyper-activation of host macrophages to engulf blood cells. To our knowledge, this is the first report on hemophagocytosis in experimental Leishmania infections and may be useful for further understanding of the pathogenesis.

Anemia is one of the major clinical manifestations during visceral leishmaniasis (VL), whereas mechanisms behind this symptom remain elusive. To get a better understanding of the responsible mechanism(s), we have developed for the first time a mouse model of VL exhibiting anemia. Mice chronically infected with L. donovani had low hematocrit, hemoglobin and erythrocyte counts while having up-regulated erythropoiesis, suggesting hemolytic events due to infection. We propose here that hemophagocytosis is one of the hemolytic events associated with anemia in the infected mice. The spleen is the major place for hemophagocytosis; there, multinucleated giant cells heavily infected with amastigotes are markedly observed and are the major cell type phagocytosing erythrocytes. These results suggest that heavy infection of macrophages with Leishmania parasites triggers phagocytosis of erythrocytes resulting in anemia during murine VL. Because hemophagocytosis has been reported in human VL cases, reproduction of the pathology in mice may facilitate an understanding of the mechanisms leading to anemia during VL.

IL-2 consumption by highly activated CD8 T cells induces regulatory T-cell dysfunction in patients with hemophagocytic lymphohistiocytosis

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is a severe inflammatory condition driven by excessive CD8(+) T-cell activation. HLH occurs as both acquired and familial hemophagocytic lymphohistiocytosis (FHL) forms. In both conditions, a sterile or infectious trigger is required for disease initiation, which then becomes self-sustaining and life-threatening. Recent studies have attributed the key distal event to excessive IFN-γ production; however, the proximal events driving immune dysregulation have remained undefined.

OBJECTIVE

We sought to investigate the role of regulatory T (Treg) cells in the pathophysiology of experimental FHL.

METHODS

Because mutation in perforin is a common cause of FHL, we used an experimental FHL mouse model in which disease in perforin-deficient mice is triggered by lymphocytic choriomeningitis virus (LCMV). We assessed Treg and CD8(+) T-cell homeostasis and activation during the changing systemic conditions in the mice. In addition, human blood samples were collected and analyzed during the HLH episode.

RESULTS

We found no primary Treg cell defects in perforin-deficient mice. However, Treg cell numbers collapsed after LCMV inoculation. The collapse of Treg cell numbers in LCMV-triggered perforin-deficient, but not wild-type, mice was accompanied by the combination of lower IL-2 secretion by conventional CD4(+) T cells, increased IL-2 consumption by activated CD8(+) T cells, and secretion of competitive soluble CD25. Moreover low Treg cell numbers were observed in untreated patients experiencing HLH flares.

CONCLUSION

These results demonstrate that excessive CD8(+) T-cell activation rewires the IL-2 homeostatic network away from Treg cell maintenance and toward feed-forward inflammation. These results also provide a potential mechanistic pathway for the progression of infectious inflammation to persistent inflammation in patients with HLH.

IDO1 Deficiency Does Not Affect Disease in Mouse Models of Systemic Juvenile Idiopathic Arthritis and Secondary Hemophagocytic Lymphohistiocytosis

OBJECTIVES

Indoleamine 2,3-dioxygenase-1 (IDO1) is an immune-modulatory enzyme that catalyzes the degradation of tryptophan (Trp) to kynurenine (Kyn) and is strongly induced by interferon (IFN)-γ. We previously reported highly increased levels of IFN-γ and corresponding IDO activity in patients with hemophagocytic lymphohistiocytosis (HLH), a hyper-inflammatory syndrome. On the other hand, IFN-γ and IDO were low in patients with systemic juvenile idiopathic arthritis (sJIA), an autoinflammatory syndrome. As HLH can occur as a complication of sJIA, the opposing levels of both IFN-γ and IDO are remarkable. In animal models for sJIA and HLH, the role of IFN-γ differs from being protective to pathogenic. In this study, we aimed to unravel the role of IDO1 in the pathogenesis of sJIA and HLH.

METHODS

Wild-type and IDO1-knockout (IDO1-KO) mice were used in 3 models of sJIA or HLH: complete Freund's adjuvant (CFA)-injected mice developed an sJIA-like syndrome and secondary HLH (sHLH) was evoked by either repeated injection of unmethylated CpG oligonucleotide or by primary infection with mouse cytomegalovirus (MCMV). An anti-CD3-induced cytokine release syndrome was used as a non-sJIA/HLH control model.

RESULTS

No differences were found in clinical, laboratory and hematological features of sJIA/HLH between wild-type and IDO1-KO mice. As IDO modulates the immune response via induction of regulatory T cells and inhibition of T cell proliferation, we investigated both features in a T cell-triggered cytokine release syndrome. Again, no differences were observed in serum cytokine levels, percentages of regulatory T cells, nor of proliferating or apoptotic thymocytes and lymph node cells.

CONCLUSIONS

Our data demonstrate that IDO1 deficiency does not affect inflammation in sJIA, sHLH and a T cell-triggered cytokine release model. We hypothesize that other tryptophan-catabolizing enzymes like IDO2 and tryptophan 2,3-dioxygenase (TDO) might compensate for the lack of IDO1.

Mouse Cytomegalovirus Infection in BALB/c Mice Resembles Virus-Associated Secondary Hemophagocytic Lymphohistiocytosis and Shows a Pathogenesis Distinct from Primary Hemophagocytic Lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening immunological disorder that is characterized by systemic inflammation, widespread organ damage, and hypercytokinemia. Primary HLH is caused by mutations in granule-mediated cytotoxicity, whereas secondary HLH occurs, without a known genetic background, in a context of infections, malignancies, or autoimmune and autoinflammatory disorders. Clinical manifestations of both HLH subtypes are often precipitated by a viral infection, predominantly with Herpesviridae. Exploiting this knowledge, we established an animal model of virus-associated secondary HLH by infecting immunocompetent wild-type mice with the β-herpesvirus murine CMV. C57BL/6 mice developed a mild inflammatory phenotype, whereas BALB/c mice displayed the clinicopathologic features of HLH, as set forth in the Histiocyte Society diagnostic guidelines: fever, cytopenia, hemophagocytosis, hyperferritinemia, and elevated serum levels of soluble CD25. BALB/c mice also developed lymphadenopathy, liver dysfunction, and decreased NK cell numbers. Lymphoid and myeloid cells were in a hyperactivated state. Nonetheless, depletion of CD8(+) T cells could not inhibit or cure the HLH-like syndrome, highlighting a first dissimilarity from mouse models of primary HLH. Immune cell hyperactivation in BALB/c mice was accompanied by a cytokine storm. Notably, plasma levels of IFN-γ, a key pathogenic cytokine in models of primary HLH, were the highest. Nevertheless, murine CMV-infected IFN-γ-deficient mice still developed the aforementioned HLH-like symptoms. In fact, IFN-γ-deficient mice displayed a more complete spectrum of HLH, including splenomegaly, coagulopathy, and decreased NK cell cytotoxicity, indicating a regulatory role for IFN-γ in the pathogenesis of virus-associated secondary HLH as opposed to its central pathogenic role in primary HLH.

Polygenic mutations in the cytotoxicity pathway increase susceptibility to develop HLH immunopathology in mice

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory disease. Inherited forms of HLH are caused by biallelic mutations in several effectors of granule-dependent lymphocyte-mediated cytotoxicity. A small proportion of patients with a so-called "secondary" form of HLH, which develops in the aftermath of infection, autoimmunity, or cancer, carry a monoallelic mutation in one or more HLH-associated genes. Although this observation suggests that HLH may have a polygenic mode of inheritance, the latter is very difficult to prove in humans. In order to determine whether the accumulation of partial genetic defects in lymphocyte-mediated cytotoxicity can contribute to the development of HLH, we generated mice that were doubly or triply heterozygous for mutations in HLH-associated genes, those coding for perforin, Rab27a, and syntaxin-11. We found that the accumulation of monoallelic mutations did indeed increase the risk of developing HLH immunopathology after lymphocytic choriomeningitis virus infection. In mechanistic terms, the accumulation of heterozygous mutations in the two degranulation genes Rab27a and syntaxin-11, impaired the dynamics and secretion of cytotoxic granules at the immune synapse of T lymphocytes. In addition, the accumulation of heterozygous mutations within the three genes impaired natural killer lymphocyte cytotoxicity in vivo. The genetic defects can be ranked in terms of the severity of the resulting HLH manifestations. Our results form the basis of a polygenic model of the occurrence of secondary HLH.

Janus kinase inhibition lessens inflammation and ameliorates disease in murine models of hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) comprises an emerging spectrum of inherited and noninherited disorders of the immune system characterized by the excessive production of cytokines, including interferon-γ and interleukins 2, 6, and 10 (IL-2, IL-6, and IL-10). The Janus kinases (JAKs) transduce signals initiated following engagement of specific receptors that bind a broad array of cytokines, including those overproduced in HLH. Based on the central role for cytokines in the pathogenesis of HLH, we sought to examine whether the inhibition of JAK function might lessen inflammation in murine models of the disease. Toward this end, we examined the effects of JAK inhibition using a model of primary (inherited) HLH in which perforin-deficient (Prf1(-∕-)) mice are infected with lymphocytic choriomeningitis virus (LCMV) and secondary (noninherited) HLH in which C57BL/6 mice receive repeated injections of CpG DNA. In both models, treatment with the JAK1/2 inhibitor ruxolitinib significantly lessened the clinical and laboratory manifestations of HLH, including weight loss, organomegaly, anemia, thrombocytopenia, hypercytokinemia, and tissue inflammation. Importantly, ruxolitinib treatment also significantly improved the survival of LCMV-infectedPrf1(-∕-)mice. Mechanistic studies revealed that in vivo exposure to ruxolitinib inhibited signal transducer and activation of transcription 1-dependent gene expression, limited CD8(+)T-cell expansion, and greatly reduced proinflammatory cytokine production, without effecting degranulation and cytotoxic function. Collectively, these findings highlight the JAKs as novel, druggable targets for mitigating the cytokine-driven hyperinflammation that occurs in HLH. These observations also support the incorporation of JAK inhibitors such as ruxolitinib into future clinical trials for patients with these life-threatening disorders.

Cord Blood Transplantation Following Reduced-intensity Conditioning for Adult-onset Inherited Hemophagocytic Lymphohistiocytosis

Inherited hemophagocytic lymphohistiocytosis (HLH) is a genetic anomaly disorder in which abnormally activated cytotoxic T lymphocytes cannot induce the apoptosis of target cells and antigen-presenting cells, leading to hemophagocytosis, pancytopenia, and a variety of symptoms such as a high fever. The present patient with adult-onset HLH developed refractory disease despite receiving immunosuppressive treatments. He underwent a reduced-intensity conditioning (RIC) regimen that comprised antithymocyte globulin (ATG) followed by cord blood transplantation (RIC-CBT). He achieved and maintained a complete donor type. The incorporation of ATG into RIC-CBT may prevent graft failure and control hemophagocytosis, however, further efforts are necessary to reduce infectious complications.

Cytosine-Phosphorothionate-Guanine Oligodeoxynucleotides Exacerbates Hemophagocytosis by Inducing Tumor Necrosis Factor-Alpha Production in Mice after Bone Marrow Transplantation

Hemophagocytic syndrome (HPS) is frequently associated with hematopoietic stem cell transplantation and is treated with some benefit derived from TNF-α inhibitors. However, the mechanisms of how HPS occurs and how a TNF-α inhibitor exerts some benefit to HPS management have remained unclear. We evaluated the effect of toll-like receptor (TLR) ligands, especially focusing on cytosine-phosphorothionate-guanine oligodeoxynucleotide (CpG), a TLR9 ligand, on HPS in mice that underwent transplantation with syngeneic or allogeneic bone marrow (BM) cells (Syn-BMT, Allo-BMT), or with allogeneic BM cells plus splenocytes to promote graft-versus-host disease (GVHD mice). Hemophagocytosis was a common feature early after all BMT, but it subsided in Syn-BMT and Allo-BMT mice. In GVHD mice, however, hemophagocytosis persisted and was accompanied by upregulated production of IFN-γ but not TNF-α, and it was suppressed by blockade of IFN-γ but not TNF-α. A single injection of the TLR9 ligand CpG promoted HPS in all BMT mice and was lethal in GVHD mice, accompanied by greatly upregulated production of TNF-α, IL-6, and IFN-γ. Blocking of TNF-α, but not IL-6 or IFN-γ, suppressed CpG-induced HPS in all BMT mice and rescued GVHD mice from CpG-induced mortality. Thus, TLR9 signaling mediates TNF-α-driven HPS in BMT mice and is effectively treated through TNF-α inhibition.

Targeted high-throughput sequencing for genetic diagnostics of hemophagocytic lymphohistiocytosis

Background

Hemophagocytic lymphohistiocytosis (HLH) is a rapid-onset, potentially fatal hyperinflammatory syndrome. A prompt molecular diagnosis is crucial for appropriate clinical management. Here, we validated and prospectively evaluated a targeted high-throughput sequencing approach for HLH diagnostics.

Methods

A high-throughput sequencing strategy of 12 genes linked to HLH was validated in 13 patients with previously identified HLH-associated mutations and prospectively evaluated in 58 HLH patients. Moreover, 2504 healthy individuals from the 1000 Genomes project were analyzed in silico for variants in the same genes.

Results

Analyses revealed a mutation detection sensitivity of 97.3 %, an average coverage per gene of 98.0 %, and adequate coverage over 98.6 % of sites previously reported as mutated in these genes. In the prospective cohort, we achieved a diagnosis in 22 out of 58 patients (38 %). Genetically undiagnosed HLH patients had a later age at onset and manifested higher frequencies of known secondary HLH triggers. Rare, putatively pathogenic monoallelic variants were identified in nine patients. However, such monoallelic variants were not enriched compared with healthy individuals.

Conclusions

We have established a comprehensive high-throughput platform for genetic screening of patients with HLH. Almost all cases with reduced natural killer cell function received a diagnosis, but the majority of the prospective cases remain genetically unexplained, highlighting genetic heterogeneity and environmental impact within HLH. Moreover, in silico analyses of the genetic variation affecting HLH-related genes in the general population suggest caution with respect to interpreting causality between monoallelic mutations and HLH. A complete understanding of the genetic susceptibility to HLH thus requires further in-depth investigations, including genome sequencing and detailed immunological characterization.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-015-0244-1) contains supplementary material, which is available to authorized users.

Natural killer cell biology illuminated by primary immunodeficiency syndromes in humans

Natural killer (NK) cells are innate immune cytotoxic effector cells well known for their role in antiviral immunity and tumor immunosurveillance. In parts, this knowledge stems from rare inherited immunodeficiency disorders in humans that abrogate NK cell function leading to immune impairments, most notably associated with a high susceptibility to viral infections. Phenotypically, these disorders range from deficiencies selectively affecting NK cells to complex general immune defects that affect NK cells but also other immune cell subsets. Moreover, deficiencies may be associated with reduced NK cell numbers or rather impair specific NK cell effector functions. In recent years, genetic defects underlying the various NK cell deficiencies have been uncovered and have triggered investigative efforts to decipher the molecular mechanisms underlying these disorders. Here we review the associations between inherited human diseases and NK cell development as well as function, with a particular focus on defects in NK cell exocytosis and cytotoxicity. Furthermore we outline how reports of diverse genetic defects have shaped our understanding of NK cell biology.

Hemophagocytic lymphohistiocytosis in a patient with CD3δ deficiency

Introduction: Primary hemophagocytic lymphohistiocytosis (HLH) is a life-threatening inflammatory process that has been linked to abnormal cytotoxic T-cell and natural killer (NK) cell function. We report on the first case of severe combined immunodeficiency (SCID) caused by a CD3δ mutation presenting with HLH in a female of Mennonite descent.

Case Description: A Low-German-speaking Mennonite female with past medical history of eczema, mouth sores, and refractory oral and diaper candidiasis presented at the age of 6 months with vomiting, diarrhea, and lethargy. The patient developed HLH that was refractory to treatment and led to multi-organ failure. Immunological evaluation was diagnostic for SCID and post-mortem genetic testing confirmed a homozygous mutation in CD3δ that was previously described in Mennonites.

Method: Targeted molecular testing for CD3δ deficiency confirmed a homozygous C-to-T transition at nucleotide position 202, predicting a premature stop codon, with a truncation at residue 68 (R68X) in the extracellular domain of the protein.

Discussion: Many primary immunodeficiency diseases (PID) that affect cytotoxic T cells and NK cells have presented with HLH. However, a growing number of PID with no obvious NK-cell defect have also been found to predispose patients to HLH, suggesting that failure of NK activity is not the only mechanism leading to this unusual form of inflammation.

Conclusion: CD3δ is known to be critical for T-cell but not NK-cell development, which may suggest an alternate mechanism for overwhelming inflammation leading to HLH.

Statement of novelty: This is the first case report of CD3δ deficiency presenting with HLH.

Therapeutic Potential of Interferon-γ and Its Antagonists in Autoinflammation: Lessons from Murine Models of Systemic Juvenile Idiopathic Arthritis and Macrophage Activation Syndrome

Interferon-γ (IFN-γ) affects immune responses in a complex fashion. Its immunostimulatory actions, such as macrophage activation and induction of T helper 1-type responsiveness, are widely acknowledged, however, as documented by a large body of literature, IFN-γ has also the potential to temper inflammatory processes via other pathways. In autoimmune and autoinflammatory disorders, IFN-γ can either play a disease-enforcing role or act as protective agent, depending on the nature of the disease. In animal models of any particular autoimmune disease, certain changes in the induction procedure can reverse the net outcome of introduction or ablation of IFN-γ. Here, we review the role of endogenous IFN-γ in inflammatory disorders and related murine models, with a focus on systemic juvenile idiopathic arthritis (sJIA) and macrophage activation syndrome (MAS). In particular, we discuss our recent findings in a mouse model of sJIA, in which endogenous IFN-γ acts as a regulatory agent, and compare with results from mouse models of MAS. Also, we elaborate on the complexity in the activity of IFN-γ and the resulting difficulty of predicting its value or that of its antagonists as treatment option.