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Primary hemophagocytic lymphohistiocytosis, a rare genetic immune disorder characterized by hyperinflammation, manifests in infancy and is associated with high mortality. In a study involving 34 children, an antibody to interferon-γ (emapalumab) produced responses in 65%; it served as a bridge to marrow transplantation in 70% of those who had received previous treatment.

Interferon-γ (IFNγ) is a pleiotropic cytokine with multiple effects on the inflammatory response and on innate and adaptive immunity. Overproduction of IFNγ underlies several, potentially fatal, hyperinflammatory or immune-mediated diseases. Several data from animal models and/or from translational research in patients point to a role of IFNγ in hyperinflammatory diseases, such as primary haemophagocytic lymphohistiocytosis, various forms of secondary haemophagocytic lymphohistiocytosis, including macrophage activation syndrome, and cytokine release syndrome, all of which are often managed by rheumatologists or in consultation with rheumatologists. Given the effects of IFNγ on B cells and T follicular helper cells, a role for IFNγ in systemic lupus erythematosus pathogenesis is emerging. To improve our understanding of the role of IFNγ in human disease, IFNγ-related biomarkers that are relevant for the management of hyperinflammatory diseases are progressively being identified and studied, especially because circulating levels of IFNγ do not always reflect its overproduction in tissue. These biomarkers include STAT1 (specifically the phosphorylated form), neopterin and the chemokine CXCL9. IFNγ-neutralizing agents have shown efficacy in the treatment of primary haemophagocytic lymphohistiocytosis in clinical trials and initial promising results have been obtained in various forms of secondary haemophagocytic lymphohistiocytosis, including macrophage activation syndrome. In clinical practice, there is a growing body of evidence supporting the usefulness of circulating CXCL9 levels as a biomarker reflecting IFNγ production.Interferon-γ (IFNγ) is important in innate and adaptive immunity and its overproduction is also implicated in hyperinflammation. Here, De Benedetti and colleagues discuss the evidence for a pathogenetic role of IFNγ in hyperinflammatory diseases, the search for IFNγ biomarkers, and the results of clinical trials of IFNγ-neutralizing therapeutics.

To describe the prognostic factors and outcomes of adults with hemophagocytic lymphohistiocytosis (HLH), a rare disorder caused by pathologic activation of the immune system. The study population consisted of a consecutive cohort of adult (age ≥18 years) patients treated at Mayo Clinic in Rochester, Minnesota, from January 1, 1996, through December 31, 2011, in whom a diagnosis of HLH was suspected and subsequently confirmed by retrospective review using the HLH-04 diagnostic criteria. Of 250 adult patients suspected of having HLH, 62 met the HLH-04 diagnostic criteria and were included in the final analysis. The median age was 49 years (range, 18-87 years), and 42 (68%) were male. The underlying cause of HLH was malignant tumor in 32 patients (52%), infection in 21 patients (34%), autoimmune disorder in 5 patients (8%), and idiopathic disease in 4 patients (6%). After a median follow-up of 42 months, 41 patients (66%) had died. The median overall survival of the entire cohort was 2.1 months. The median overall survival of patients with tumor–associated HLH was 1.4 months compared with 22.8 months for patients with non-tumor–associated HLH (P=.01). The presence of a malignant tumor and hypoalbuminemia were significant predictors of inferior survival on multivariate analysis. In this large series of adults with secondary HLH treated at a single tertiary care center, patients with low serum albumin levels and tumor–associated HLH had a markedly worse survival. Hemophagocytic lymphohistiocytosis remains elusive and challenging to clinicians who must maintain a high index of suspicion. The recent discovery of several novel diagnostic and therapeutic modalities may improve outcomes of adult patients with HLH.

BackgroundHemophagocytic Lymphohistiocytosis (HLH) is a rare and life-threatening condition characterized by a severe impairment of the immune homeostasis. While Familial-HLH (FHL) is a known cause, the involvement of other Inborn Errors of Immunity (IEI) in pediatric-HLH remains understudied.ObjectiveThis systematic review aimed to assess the clinical features, triggers, laboratory data, treatment, and outcomes of pediatric HLH patients with IEI other than FHL (IEInotFHL), emphasizing the importance of accurate identification and management.MethodsA systematic search for studies meeting inclusion criteria was conducted in PubMed, EMBASE, MEDLINE, and Cochrane Central. Quality assessment was performed through JBI criteria.ResultsA comprehensive search yielded 108 records meeting inclusion criteria, involving 178 patients. We identified 46 different IEI according to IUIS 2022 Classification. Combined immunodeficiencies, immune dysregulation disorders, and phagocyte defects were the IEI most frequently associated with HLH. In 75% of cases, HLH preceded the IEI diagnosis, often with an unrecognized history of severe infections. Triggers reflected the specific infection susceptibilities within IEI groups. Liver and central nervous system involvement were less common than in FHL cases. Treatment approaches and outcomes varied, with limited long-term follow-up data, limiting the assessment of therapeutic efficacy across IEI groups.ConclusionA comprehensive evaluation encompassing immunological, infectious, and genetic aspects is essential in pediatric-HLH. Relying solely on FHL or EBV susceptibility disorders tests is insufficient, as diverse other IEI can contribute to HLH. Early recognition of HLH as a potential warning sign can guide timely diagnostic investigations and facilitate tailored therapeutic interventions for improved outcomes.Systematic review registrationhttps://www.crd.york.ac.uk/prospero/display_record.php?RecordID=371425, PROSPERO, CRD42022371425.

Hemophagocytic lymphohistiocytosis (HLH) is a rapidly progressing, life-threatening syndrome characterized by excessive immune activation, often presenting as a complex cytokine storm. This hyperactive immune response can lead to multi-organ failure and systemic damage, resulting in an extremely short survival period if left untreated. Over the past decades, although HLH has garnered increasing attention from researchers, there have been few advancements in its treatment. The cytokine storm plays a crucial role in the treatment of HLH. Investigating the detailed mechanisms behind cytokine storms offers insights into targeted therapeutic approaches, potentially aiding in early intervention and improving the clinical outcome of HLH patients. To date, there is only one targeted therapy, emapalumab targeting interferon-γ, that has gained approval for primary HLH. This review aims to summarize the current treatment advances, emerging targeted therapeutics and underlying mechanisms of HLH, highlighting its newly discovered targets potentially involved in cytokine storms, which are expected to drive the development of novel treatments and offer fresh perspectives for future studies. Besides, multi-targeted combination therapy may be essential for disease control, but further trials are required to determine the optimal treatment mode for HLH.

Key Points A 'cytokine storm' is the final pathophysiological pathway in macrophage activation syndrome (MAS), and blocking various cytokines could be an attractive therapeutic strategy Standard doses of anti-IL-1 and anti-IL-6 biologic therapies do not have a major effect on MAS rates even if the underlying disease responds well to the treatment Several case reports suggest that anakinra might be effective at least in some patients with systemic juvenile idiophatic arthritis (sJIA)-associated MAS, particularly when used in high doses Findings from several studies support IFN-γ blockade as a novel therapy for haemophagocytic lymphohistiocytosis (HLH); increasing evidence suggests the same approach could be beneficial in MAS presenting as a complication of rheumatic diseases The exact mechanism of predisposition to MAS in sIJA is yet to be defined, but might be independent of underlying sJIA activity and similar to infection-associated secondary HLH Whole-exome/genome sequencing approaches exploring hypomorphic mutations that affect the cytolytic pathway to support this theory might reveal promising therapeutic alternatives Macrophage activation syndrome (MAS) is a potentially fatal complication of rheumatic disease, most notably systemic juvenile idiopathic arthritis. Findings from studies in animal models and from clinical observations, particularly in relation to the effects of anticytokine biologic therapies, have led to new concepts of the pathophysiology of this phenomenon. 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.

A recurrent ECSIT mutation in individuals with extranodal natural killer/T cell lymphoma induces NFκB in cancer cells, leading to macrophage activation, and associates with progression to fatal hemophagocytic syndrome. NFκB-targeting therapy produced stable remission in two patients. Hemophagocytic syndrome (HPS) is a fatal hyperinflammatory disease with a poorly understood mechanism that occurs most frequently in extranodal natural killer/T cell lymphoma (ENKTL). Through exome sequencing of ENKTL tumor–normal samples, we have identified a hotspot mutation (c.419T>C) in the evolutionarily conserved signaling intermediate in Toll pathway ( ECSIT ) gene, encoding a V140A variant of ECSIT. ECSIT-V140A activated NF-κB more potently than the wild-type protein owing to its increased affinity for the S100A8 and S100A9 heterodimer, which promotes NADPH oxidase activity. ECSIT -T419C knock-in mice showed higher peritoneal NADPH oxidase activity than mice with wild-type ECSIT in response to LPS. ECSIT -T419C-transfected ENKTL cell lines produced tumor necrosis factor (TNF)-α and interferon (IFN)-γ, which induced macrophage activation and massive cytokine secretion in cell culture and mouse xenografts. In individuals with ENKTL, ECSIT-V140A was associated with activation of NF-κB, higher HPS incidence, and poor prognosis. The immunosuppressive drug thalidomide prevented NF-κB from binding to the promoters of its target genes (including TNF and IFNG ), and combination treatment with thalidomide and dexamethasone extended survival of mice engrafted with ECSIT -T419C-transfected ENKTL cells. We added thalidomide to the conventional dexamethasone-containing therapy regimen for two patients with HPS who expressed ECSIT-V140A, and we observed reversal of their HPS and disease-free survival for longer than 3 years. These findings provide mechanistic insights and a potential therapeutic strategy for ENKTL-associated HPS.

Hemophagocytic lymphohistiocytosis (HLH), as a life-threatening hyperinflammatory syndrome, rarely presents as a harbinger of aggressive large B cell lymphoma (LBCL), with a rapidly progressive clinical course and poor prognosis. A total of 30 patients diagnosed with aggressive LBCL concurrent with HLH were retrospectively reviewed in this study. Median age was 60 years (range, 24 to 85 years). Thirteen (43.3%) patients treated with ruxolitinib combined with corticosteroid (Ru-D) regimen achieved the highest overall response rate (ORR) of 84.6%, which was significantly higher than that of 40.0% in the etoposide and corticosteroid group and 33.3% in the corticosteroid group ( P  = 0.019). The median overall survival (OS) was 16.2 months, with corresponding 1-year and 2-year OS rates of 63.3% and 38.4%, respectively. The 8-week mortality rate was 26.7%. Patients responded to anti-HLH therapy within 2 weeks had significantly better OS than non-responsive group ( P  = 0.009). Low-intensity chemotherapy without anthracycline as the first-line of anti-lymphoma therapy followed by RCHOP did not compromise survival, and the median OS was 13 months and 19.1 months, respectively ( P  = 0.457). Ferritin levels ≥ 3606 ng/mL and uncontrolled HLH within 2 weeks were the independent risk factors associated with inferior OS. Our findings highlight the high early mortality and short survival of these patients and underscore the urgent need for developing more effective treatment strategies to improve prognosis.

Improved awareness of hemophagocytic lymphohistiocytosis (HLH) among clinicians has led to an increase in its diagnosis. Often diagnosis is made based on the HLH- 2004 criteria. While these criteria have considerable strengths, they lack specificity and may be fulfilled in the setting of many pro-inflammatory disorders. Genetic defects affecting cellular cytotoxicity cause familial (primary) HLH. On the other hand, secondary HLH is more a pathophysiologic process common to many conditions, rather than a singular disease entity. Improved genetic, immunologic, and functional testing have changed not only the way we diagnose HLH, but also how we treat it. In 2004, there were few active agents and regimens. In 2024, there are multiple safe and effective targeted therapies. We have begun to understand that routine and immediate use of etoposide-based therapy in secondary HLH is likely not appropriate, and emerging cytokine-directed therapies may be more rational interventions. Moreover, it is recognized that identifying and treating the driver of secondary HLH is at least as important as treating the cytokine storm and immune dysregulation. Unfortunately, over-reliance on, and narrow interpretation of, the HLH- 2004 criteria can lead to overdiagnosis, misdiagnosis, and unneeded exposure to drugs that can be harmful. It is important that clinicians understand the limitations of the current diagnostic paradigms for secondary HLH, and the shortcomings of reflexive use of etoposide-based therapy. Herein we will discuss the pros and cons of the current paradigm for the recognition, diagnosis, and treatment of secondary HLH.

This article presents a case of an acute onset in a middle-aged male who exhibited persistent high fever (temperature > 40 °C), delirium, and respiratory distress. Initial chest CT only suggested \"bilateral pneumonia,\" and empirical anti-infection treatment proved ineffective. The patient subsequently developed pancytopenia, splenomegaly, and markedly elevated ferritin levels (848.90 μg/L). Bone marrow aspiration demonstrated hemophagocytic activity and granulomatous lesions. A positive TB-PCR, confirmed the diagnosis of early hematogenous disseminated tuberculosis complicated by the hemophagocytic syndrome (HLH). The patient's condition gradually improved Following, individualized anti-tuberculosis therapy and immunosuppressive treatment. The uniqueness of this case lies in two main aspects: (1) early imaging did not show typical miliary nodules, which could have led to misdiagnosis as common pneumonia; (2) the dissemination of tuberculosis and onset of HLH occurred almost simultaneously, creating a therapeutic dilemma. Although tuberculosis complicated by HLH is rare, it poses significant danger. The cornerstone of treatment is effective control of the tuberculosis infection while simultaneously suppressing the excessive immune response. This case highlights the importance of considering tuberculosis complicated by HLH in patients with recurrent fever and pulmonary infiltrates. Early diagnosis and prompt treatment are crucial for improving prognosis. The article also discusses the underlying pathogenesis, offering valuable insights for clinical practice.