Myeloid cells from Langerhans cell histiocytosis patients exhibit increased vesicle trafficking and an altered secretome capable of activating NK cells.

Langerhans cell histiocytosis (LCH) is a potentially life-threatening inflammatory myeloid neoplasia linked to pediatric neurodegeneration, whereby transformed LCH cells form agglomerated lesions in various organs. Although MAP-kinase pathway mutations have been identified in LCH cells, the functional consequences of these mutations and the mechanisms that cause the pathogenic behavior of LCH cells are not well understood. In our study, we used an in vitro differentiation system and RNA-sequencing to compare monocyte-derived dendritic cells from LCH patients to those derived from healthy controls or patients with Crohn's disease, a non-histiocytic inflammatory disease. We observed that interferon-γ treatment exacerbated intrinsic differences between LCH patient and control cells, including strikingly increased endo- and exocytosis gene activity in LCH patients. We validated these transcriptional patterns in lesions and functionally confirmed that LCH cells exhibited increased endo- and exocytosis. Furthermore, RNA-sequencing of extracellular vesicles revealed the enrichment of pathological transcripts involved in cell adhesion, MAP-kinase pathway, vesicle trafficking and T-cell activation in LCH patients. Thus, we tested the effect of the LCH secretome on lymphocyte activity and found significant activation of NK cells. These findings implicate extracellular vesicles in the pathology of LCH for the first time, in line with their established roles in the formation of various other tumor niches. Thus, we describe novel traits of LCH patient cells and suggest a pathogenic mechanism of potential therapeutic and diagnostic importance.

Clinicogenomic associations in childhood Langerhans cell histiocytosis: an international cohort study.

Langerhans cell histiocytosis (LCH) is a rare neoplastic disorder caused by somatic genetic alterations in hematopoietic precursor cells differentiating into CD1a+/CD207+ histiocytes. LCH clinical manifestation is highly heterogeneous. BRAF and MAP2K1 mutations account for ∼80% of genetic driver alterations in neoplastic LCH cells. However, their clinical associations remain incompletely understood. Here, we present an international clinicogenomic study of childhood LCH, investigating 377 patients genotyped for at least BRAFV600E. MAPK pathway gene alterations were detected in 300 (79.6%) patients, including 191 (50.7%) with BRAFV600E, 54 with MAP2K1 mutations, 39 with BRAF exon 12 mutations, 13 with rare BRAF alterations, and 3 with ARAF or KRAS mutations. Our results confirm that BRAFV600E associates with lower age at diagnosis and higher prevalence of multisystem LCH, high-risk disease, and skin involvement. Furthermore, BRAFV600E appeared to correlate with a higher prevalence of central nervous system (CNS)-risk bone lesions. In contrast, MAP2K1 mutations associated with a higher prevalence of single-system (SS)-bone LCH, and BRAF exon 12 deletions seemed to correlate with more lung involvement. Although BRAFV600E correlated with reduced event-free survival in the overall cohort, neither BRAF nor MAP2K1 mutations associated with event-free survival when patients were stratified by disease extent. Thus, the correlation of BRAFV600E with inferior clinical outcome is (primarily) driven by its association with disease extents known for high rates of progression or relapse, including multisystem LCH. These findings advance our understanding of factors underlying the remarkable clinical heterogeneity of LCH but also question the independent prognostic value of lesional BRAFV600E status.

Notch-dependent cooperativity between myeloid lineages promotes Langerhans cell histiocytosis pathology.

Langerhans cell histiocytosis (LCH) is a potentially fatal neoplasm characterized by the aberrant differentiation of mononuclear phagocytes, driven by mitogen-activated protein kinase (MAPK) pathway activation. LCH cells may trigger destructive pathology yet remain in a precarious state finely balanced between apoptosis and survival, supported by a unique inflammatory milieu. The interactions that maintain this state are not well known and may offer targets for intervention. Here, we used single-cell RNA-seq and protein analysis to dissect LCH lesions, assessing LCH cell heterogeneity and comparing LCH cells with normal mononuclear phagocytes within lesions. We found LCH discriminatory signatures pointing to senescence and escape from tumor immune surveillance. We also uncovered two major lineages of LCH with DC2- and DC3/monocyte-like phenotypes and validated them in multiple pathological tissue sites by high-content imaging. Receptor-ligand analyses and lineage tracing in vitro revealed Notch-dependent cooperativity between DC2 and DC3/monocyte lineages during expression of the pathognomonic LCH program. Our results present a convergent dual origin model of LCH with MAPK pathway activation occurring before fate commitment to DC2 and DC3/monocyte lineages and Notch-dependent cooperativity between lineages driving the development of LCH cells.

Plasma Signaling Factors in Patients With Langerhans Cell Histiocytosis (LCH) Correlate With Relative Frequencies of LCH Cells and T Cells Within Lesions.

Langerhans cell histiocytosis (LCH) lesions contain an inflammatory infiltrate of immune cells including myeloid-derived LCH cells. Cell-signaling proteins within the lesion environment suggest that LCH cells and T cells contribute majorly to the inflammation. Foxp3+ regulatory T cells (Tregs) are enriched in lesions and blood from patients with LCH and are likely involved in LCH pathogenesis. In contrast, mucosal associated invariant T (MAIT) cells are reduced in blood from these patients and the consequence of this is unknown. Serum/plasma levels of cytokines have been associated with LCH disease extent and may play a role in the recruitment of cells to lesions. We investigated whether plasma signaling factors differed between patients with active and non-active LCH. Cell-signaling factors (38 analytes total) were measured in patient plasma and cell populations from matched lesions and/or peripheral blood were enumerated. This study aimed at understanding whether plasma factors corresponded with LCH cells and/or LCH-associated T cell subsets in patients with LCH. We identified several associations between plasma factors and lesional/circulating immune cell populations, thus highlighting new factors as potentially important in LCH pathogenesis. This study highlights plasma cell-signaling factors that are associated with LCH cells, MAIT cells or Tregs in patients, thus they are potentially important in LCH pathogenesis. Further study into these associations is needed to determine whether these factors may become suitable prognostic indicators or therapeutic targets to benefit patients.

Screening for neurodegeneration in Langerhans cell histiocytosis with neurofilament light in plasma.

Patients with Langerhans cell histiocytosis (LCH) may develop progressive neurodegeneration in the central nervous system (ND-CNS-LCH). Neurofilament light protein (NFL) in cerebrospinal fluid (CSF) is a promising biomarker to detect and monitor ND-CNS-LCH. We compared paired samples of NFL in plasma (p-NFL) and CSF in 10 patients (19 samples). Nine samples had abnormal CSF-NFL (defined as ≥380 ng/l) with corresponding p-NFL ≥ 2 ng/l. Ten samples had CSF-NFL < 380 ng/l; eight (80%) with p-NFL < 2 ng/l (p < 0.001; Fisher's exact test). Thus, our results suggest that p-NFL may be used to screen for ND-CNS-LCH. Further studies are encouraged, including the role of p-NFL for monitoring of ND-CNS-LCH.

Consensus-Based Guidelines for the Recognition, Diagnosis, and Management of Hemophagocytic Lymphohistiocytosis in Critically Ill Children and Adults.

OBJECTIVE: Hemophagocytic lymphohistiocytosis is a hyperinflammatory syndrome that often requires critical care support and remains difficult to diagnose. These guidelines are meant to aid in the early recognition, diagnosis, supportive care, and treatment of patients with hemophagocytic lymphohistiocytosis in ICUs. DATA SOURCES: The literature searches were performed with PubMed (MEDLINE). STUDY SELECTION: Keywords and medical subject headings terms for literature search included "macrophage activation syndrome," hemophagocytic lymphohistiocytosis," and "hemophagocytic syndrome." DATA EXTRACTION: The Histiocyte Society developed these consensus recommendations on the basis of published reports and expert opinions with level of evidence provided for each recommendation. They were endorsed by the Society of Critical Care Medicine. DATA SYNTHESIS: Testing for hemophagocytic lymphohistiocytosis should be initiated promptly in all patients admitted to ICUs with an unexplained or disproportionate inflammatory response, especially those with rapid clinical deterioration. Meeting five or more of eight hemophagocytic lymphohistiocytosis 2004 diagnostic criteria serves as a valuable diagnostic tool for hemophagocytic lymphohistiocytosis. Early aggressive critical care interventions are often required to manage the multisystem organ failure associated with hemophagocytic lymphohistiocytosis. Thorough investigation of the underlying triggers of hemophagocytic lymphohistiocytosis, including infections, malignancies, and autoimmune/autoinflammatory diseases, is essential. Early steroid treatment is indicated for patients with familial hemophagocytic lymphohistiocytosis and is often valuable in patients with acquired hemophagocytic lymphohistiocytosis (i.e., secondary hemophagocytic lymphohistiocytosis) without previous therapy, including macrophage activation syndrome (hemophagocytic lymphohistiocytosis secondary to autoimmune/autoinflammatory disease) without persistent or relapsing disease. Steroid treatment should not be delayed, particularly if organ dysfunction is present. In patients with macrophage activation syndrome, whose disease does not sufficiently respond, interleukin-1 inhibition and/or cyclosporine A is recommended. In familial hemophagocytic lymphohistiocytosis and severe, persistent, or relapsing secondary macrophage activation syndrome, the addition of prompt individualized, age-adjusted etoposide treatment is recommended. CONCLUSIONS: Further studies are needed to determine optimal treatment for patients with hemophagocytic lymphohistiocytosis in ICUs, including the use of novel and adjunct therapies.

Efficacy of Moderately Dosed Etoposide in Macrophage Activation Syndrome-Hemophagocytic Lymphohistiocytosis.

OBJECTIVE: Macrophage activation syndrome (MAS) constitutes 1 subtype of the hyperinflammatory syndrome hemophagocytic lymphohistiocytosis (HLH), and the term MAS-HLH was recently proposed for HLH with underlying autoimmune/autoinflammatory conditions. The mortality of MAS-HLH has been estimated at 5-10%. Here we report our experiences with moderately dosed etoposide in severe MAS-HLH; the objective was to effectively reduce severe hyperinflammatory activity with limited side effects. METHODS: In addition to conventional antiinflammatory treatment, moderately dosed etoposide was administered to 7 children affected by rapidly progressing MAS-HLH with central nervous system (n = 5) and/or pulmonary (n = 5) involvement. Three had underlying systemic juvenile idiopathic arthritis (sJIA), 2 had atypical sJIA (no arthritis at diagnosis), and 2 had systemic lupus erythematosus. We performed lymphocyte cytotoxicity analyses in all 7 and genetic analyses in 6. RESULTS: All children promptly responded to moderately dosed etoposide (50-100 mg/m2 once weekly), added to conventional MAS-HLH treatment that was considered insufficient. The mean accumulated etoposide dose was 671 mg/m2 (range 300-1050 mg/m2) as compared to 1500 mg/m2 recommended in the first 8 weeks of the HLH-94/HLH-2004 protocols. One child developed neutropenic fever and another neutropenic sepsis (neutrophils 0.3 × 109/L at therapy onset). Five of 7 children had low percentages (< 5%) of circulating natural killer (NK) cells prior to or in association with diagnosis; NK cell activity was pathologically low in 2 of 5 children studied. Disease-causing variants in HLH-associated genes were not found. All children were alive at latest follow-up (2-9 yrs after onset); neurological symptoms had normalized in 4 of 5 affected children. CONCLUSION: Moderately dosed etoposide may be beneficial in severe and/or refractory MAS-HLH.

Patients with both Langerhans cell histiocytosis and Crohn's disease highlight a common role of interleukin-23.

AIM: To present the first case series of patients with Langerhans cell histiocytosis (LCH) also affected by Crohn's disease (CD), both of which are granulomatous diseases, and in LCH investigate the role of interleukin (IL)-23, which is a well-described disease mediator in CD. METHODS: A case series of three patients with LCH and CD were described; a cohort of LCH patients (n = 55) as well as controls (n = 55) were analysed for circulating IL-23 levels; and the relation between the percentage of LCH cells in lesions and circulating IL-23 levels was analysed in seven LCH patients. RESULTS: Differential diagnostic challenges for these two granulomatous diseases were highlighted in the case series, and it took up to 3 years to diagnose CD. Elevated IL-23 levels were found in LCH patients. The amount of lesional LCH cells correlated with the levels of circulating IL-23. CONCLUSION: Both CD and LCH should be considered in patients with inflammatory gastrointestinal involvement. The IL-23 pathway is a common immunological trait between these two granulomatous diseases.

Clinical and laboratory signs of haemophagocytic lymphohistiocytosis associated with pandemic influenza A (H1N1) infection in patients needing extracorporeal membrane oxygenation: A retrospective observational study.

BACKGROUND: Severe pandemic influenza has been associated with the hyperinflammatory condition secondary haemophagocytic lymphohistiocytosis (HLH). OBJECTIVES: To determine the frequency, degree, character and possible cause of influenza-associated HLH in critically ill patients with severe acute respiratory distress syndrome due to influenza A (H1N1) infection requiring extracorporeal membrane oxygenation (ECMO) support at our hospital. DESIGN: A retrospective observational study. PATIENTS AND SETTING: Medical data were retrieved retrospectively from 11 consenting patients of thirteen adults infected with pandemic influenza A (H1N1) 2009 requiring ECMO between July 2009 and January 2010 at the ECMO Centre of Karolinska University Hospital, Stockholm, Sweden. All patients were evaluated for HLH using HLH-2004 criteria and HScore. RESULTS: Eleven patients (median age 31 years) were included in the study and all survived. All patients showed signs of multiple organ dysfunction and pronounced inflammation, more severe in the four patients with HLH who had significantly higher peak serum concentrations of ferritin (P = 0.024), alkaline phosphatase (P = 0.012) and gamma-glutamyl transferase (P = 0.024), lower concentration of albumin (P = 0.0086) and more frequently hepatomegaly (P = 0.048). Abnormal lymphocyte cytotoxicity (lytic units <10) and a low proportion of natural killer (NK) cells were observed in three of four patients with HLH. Notably, we found a significant inverse correlation between serum ferritin concentration and NK cell and cytotoxic T lymphocyte percentages (rs = -0.74, P = 0.0013 and rs = -0.79, P = 0.0025, respectively). One HLH patient received HLH-directed cytotoxic therapy, another intravenous immunoglobulin and the other two no specific HLH-directed therapy. CONCLUSION: Critically ill patients, including healthy young adults, with pandemic influenza may develop HLH and should be monitored for signs of hyperinflammation and increasing organ dysfunction, and evaluated promptly for HLH because HLH-directed therapy may then be beneficial. The association of low NK percentages with hyperferritinaemia may suggest a role for reduced NK cell numbers, possibly also cytotoxic T lymphocytes, and subsequently reduced lymphocyte cytotoxicity, in the pathogenesis of hyperinflammation and secondary HLH.

Foxp3+ Tregs from Langerhans cell histiocytosis lesions co-express CD56 and have a definitively regulatory capacity.

Langerhans cell histiocytosis (LCH) lesions contain myeloid lineage 'LCH' cells. Regulatory T cells (Tregs) are also enriched within lesions, although their role in LCH pathogenesis is unknown. LCH cells are thought to produce the transforming growth factor beta (TGF-ß) within lesions, however whether Tregs contribute is unestablished. Using flow cytometry, we analyzed relative frequencies of live Tregs from LCH patients and identified CD56 expression and TGF-ß production by lesion Tregs. While CD56+ Tregs were enriched in lesions, overall CD56+ T cells were reduced in the blood from active LCH patients compared to non-active disease patients, and there was a negative correlation between CD8+CD56+ T cells and Tregs. We propose that inducing a Treg phenotype in T cells such as CD56+ T cells may be a mechanism by which LCH cells divert inflammatory T cell responses. Thus, Tregs within LCH lesions are likely an important component in LCH pathogenesis.

Dengue Infection Complicated by Hemophagocytic Lymphohistiocytosis: Experiences From 180 Patients With Severe Dengue.

BACKGROUND: Globally, ~500 000 people with severe dengue (SD) require hospitalization yearly; ~12 500 (2.5%) die. Secondary hemophagocytic lymphohistiocytosis (sHLH) is a potentially fatal hyperinflammatory condition for which HLH-directed therapy (as etoposide and dexamethasone) can be life-saving. Prompted by the high mortality in SD and the increasing awareness that patients with SD may develop sHLH, our objectives were to (1) determine the frequency of dengue-HLH in SD, (2) describe clinical features of dengue-HLH, (3) assess mortality rate in SD and dengue-HLH, and (4) identify mortality-associated risk factors in SD. METHODS: A 5-year retrospective single-center study in all adult patients with SD admitted to a tertiary intensive care unit in Malaysia. RESULTS: Thirty-nine of 180 (22%) patients with SD died. Twenty-one of 180 (12%) had HLH defined as an HLH probability ≥70% according to histo score (HScore); 9 (43%) died. Similarly, 12 of 31 (39%) fulfilling ≥4 and 7 of 9 (78%) fulfilling ≥5 HLH-2004 diagnostic criteria died. Peak values of aspartate aminotransferase (AST), alanine aminotransferase, lactate dehydrogenase, and creatinine correlated to fatality (odds ratios [ORs], 2.9, 3.4, 5.8, and 31.9; all P < .0001), as did peak ferritin (OR, 2.5; P = .0028), nadir platelets (OR, 1.9; P = .00068), hepatomegaly (OR, 2.9; P = .012), and increasing age (OR, 1.2; P = .0043). Multivariable logistic regression revealed peak AST (OR, 2.8; P = .0019), peak creatinine (OR, 7.3; P = .0065), and SOFA (Sequential Organ Failure Assessment) score (OR, 1.4; P = .0051) as independent risk factors of death. CONCLUSIONS: Be observant of dengue-HLH due to its high mortality. A prospective study is suggested on prompt HLH-directed therapy in SD patients with hyperinflammation and evolving multiorgan failure at risk of developing dengue-HLH.

Elevated ferritin and soluble CD25 in critically ill patients are associated with parameters of (hyper) inflammation and lymphocyte cytotoxicity.

BACKGROUND: Critically ill patients may develop a potentially fatal hyperinflammatory condition known as secondary (acquired) hemophagocytic lymphohistiocytosis (sHLH), the cause of which is unclear. We evaluated serum ferritin and soluble CD25 (sCD25) in critically ill patients, and their association with other parameters of inflammation and critical illness. Moreover, aiming to better understand the pathogenesis of sHLH, we also evaluated lymphocyte cytotoxicity parameters and correlations with the inflammatory markers ferritin and sCD25. METHODS: In a prospective observational study, 32 patients with ferritin ≥500 µg/L (24 with sepsis) were studied on admission to an intensive care unit (ICU) with regard to ferritin and corresponding clinical and laboratory features including sCD25, and detailed lymphocyte cytotoxicity and genetic analyses whenever possible. RESULTS: Critically ill patients had elevated, positively correlated levels of serum ferritin and sCD25 (rs=0.465, P=0.008); both associated with other risk factors of poor outcome in critically ill, such as thrombocytopenia (rs=-0.534, P=0.002 and rs=-0.421, P=0.018, respectively), and sCD25 with hypoalbuminemia (rs=-0.678, P<0.001) and life support treatments (rs=0.479, P=0.006). Interestingly, ferritin levels were inversely associated with natural killer (NK)-cell cytotoxicity (rs=-0.462, P=0.047) and degranulation (rs=-0.504, P=0.030). Moreover, of four patients with abnormally low cytotoxicity, three (75%) had <5% circulating NK-cells. CONCLUSIONS: Our study suggests that hyperferritinemia and sCD25 correlate with other laboratory parameters indicative of severe hyperinflammation and organ dysfunction in critically ill ICU-patients, indicating their value in identifying hyperinflammatory critically ill patients for early intervention. Furthermore, it suggests that hyperferritinemia and hyperinflammation may partly be associated with a low percentage circulating NK-cells, and hence, the associated low lymphocyte cytotoxicity.

Recommendations for the management of hemophagocytic lymphohistiocytosis in adults.

Hemophagocytic lymphohistiocytosis (HLH) is a severe hyperinflammatory syndrome induced by aberrantly activated macrophages and cytotoxic T cells. The primary (genetic) form, caused by mutations affecting lymphocyte cytotoxicity and immune regulation, is most common in children, whereas the secondary (acquired) form is most frequent in adults. Secondary HLH is commonly triggered by infections or malignancies but may also be induced by autoinflammatory/autoimmune disorders, in which case it is called macrophage activation syndrome (MAS; or MAS-HLH). Most information on the diagnosis and treatment of HLH comes from the pediatric literature. Although helpful in some adult cases, this raises several challenges. For example, the HLH-2004 diagnostic criteria developed for children are commonly applied but are not validated for adults. Another challenge in HLH diagnosis is that patients may present with a phenotype indistinguishable from sepsis or multiple organ dysfunction syndrome. Treatment algorithms targeting hyperinflammation are frequently based on pediatric protocols, such as HLH-94 and HLH-2004, which may result in overtreatment and unnecessary toxicity in adults. Therefore, dose reductions, individualized tailoring of treatment duration, and an age-dependent modified diagnostic approach are to be considered. Here, we present expert opinions derived from an interdisciplinary working group on adult HLH, sponsored by the Histiocyte Society, to facilitate knowledge transfer between physicians caring for pediatric and adult patients with HLH, with the aim to improve the outcome for adult patients affected by HLH.

Altered Populations of Unconventional T Cell Lineages in Patients with Langerhans Cell Histiocytosis.

Langerhans cell histiocytosis (LCH) lesions are defined by the presence of CD1a+/CD207+ myeloid cells, but many other immune cells are present including unconventional T cells, which have powerful immunoregulatory functions. Unconventional T cell lineages include mucosal-associated invariant T (MAIT) cells, type I natural killer T (NKT) cells and gamma-delta (γδ) T cells, which are associated with many inflammatory conditions, although their importance has not been studied in LCH. We characterized their phenotype and function in blood and lesions from patients with LCH, and identified a deficiency in MAIT cell frequency and abnormalities in the subset distributions of γδ T cells and NKT cells. Such abnormalities are associated with immune dysregulation in other disease settings and are therefore potentially important in LCH. Our study is the first to recognize alterations to MAIT cell proportions in patients with LCH. This finding along with other abnormalities identified amongst unconventional T cells could potentially influence the onset and progression of LCH, thereby highlighting potential targets for new immune based therapies.

Recommendations for the Use of Etoposide-Based Therapy and Bone Marrow Transplantation for the Treatment of HLH: Consensus Statements by the HLH Steering Committee of the Histiocyte Society.

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome requiring aggressive immunosuppressive therapy. Following 2 large international studies mainly targeting pediatric patients with familial disease and patients without underlying chronic or malignant disease, the HLH-94 protocol is recommended as the standard of care when using etoposide-based therapy by the Histiocyte Society. However, in clinical practice, etoposide-based therapy has been widely used beyond the study inclusion criteria, including older patients and patients with underlying diseases (secondary HLH). Many questions remain around these extended indications and published reports do not address several practical issues. To tackle these concerns, the HLH Steering Committee of the Histiocyte Society decided to issue guidance for use of the HLH-94 protocol. The group convened in a structured consensus finding process to define recommendations that are based largely on expert opinion backed up by available data from the literature. The recommendations address all main elements of HLH-94 including corticosteroids, cyclosporin, etoposide, intrathecal therapy, and hematopoietic stem cell transplantation (HSCT) and consider various forms of HLH and all age groups. Aspects covered include indications, applications, dosing, side effects, duration of therapy, salvage therapy, and HSCT. These recommendations aim to provide a framework to guide treatment decisions in this severe disease.