Childhood Langerhans cell histiocytosis hematological involvement: severity associated with BRAFV600E loads.

Hematological involvement (HI) is one of the life-threatening risk organs (ROs) in Langerhans cell histiocytosis (LCH). Lahey criteria have defined HI since 1975 as hemoglobin <10 g/dL and/or platelets <100 G/L and/or leukopenia (white blood cell count <4 G/L) and/or neutrophils <1.5 G/. Among the 2313 patients <18 years old enrolled in the French National Histiocytosis Registry (1983-2023), 331 developed HI (median age at diagnosis: 1 year); median follow-up lasted 8.1 years. Bone-marrow aspirate smears and biopsies may show reactive histiocytes, hemophagocytosis or myelofibrosis but never confirm the diagnosis. Fifty-eight (17%) patients developed macrophage-activation syndrome, sometimes related to acute Epstein-Barr virus or cytomegalovirus infection, sometimes months before typical LCH manifestations appeared. Hemoglobin and platelet thresholds for initiating transfusion(s) appear to accurately distinguish 2 groups: mild HI (MHI; >7 g/dL and >20 G/L, respectively) and severe HI (SHI; ≤7 g/dL and ≤20 G/L). Each entity has different organ involvements, laboratory parameters, mutational status, blood BRAFV600E loads, drug sensitivities and outcomes (respective MHI and SHI 10-year survival rates: 98% and 73%). Since 1998, mortality first declined with combination Cladribine-cytarabine therapy, and then with mitogen-activated protein-kinase inhibitors since 2014. Forty-one (12%) patients developed neurodegenerative complications that have emerged as a risk for long-term survivors. These results suggest limiting the HI-RO definition to SHI, as it encompasses almost all medical complications of LCH. Future clinical trials might demonstrate that targeted-therapy approaches would be better adapted for these patients, while MHI can be managed with classic therapies.

Hemophagocytic lymphohistiocytosis in Egyptian children: diagnosis, treatment challenges, and outcome.

BACKGROUND: Hemophagocyticlymphohistiocytosis (HLH) is a spectrum of immune activation which could be genetically determined, or secondary to an underlying illness. Our aim was to present the clinico-genetic aspects of HLH among Egyptian children and to evaluate the patterns of reactivation and outcome with illustrations of overlap manifestations. RESEARCH DESIGNAND METHODS: We retrospectively collected the data of 55 patients with HLH, registered at Ain Shams University Children's Hospital,Cairo, Egypt. RESULTS: Median age at diagnosis was 19 months (range 2-180), 33 patients (60%) fulfilled the diagnostic HLH criteria at presentation. Fourteen (25.45%) patients had secondary HLH, 15 (27.27%) patients had genetically documented familial HLH (11 had variants in UNC13D gene and one in PRF1 gene), 3 had Griscelli and Chediak-Higashi syndromes. Sixteen patients (29.1%) had reactivations, 8 (50%) of them had molecularly confirmed HLH. We report the death of 40 patients, the median duration from the diagnosis to death of 5 months mostly due to disease activity. CONCLUSIONS: This study confirms that the nonspecific signs and symptoms of HLH are challenging. Genetic testing, though expensive and sophisticated, is integral for the diagnosis. The difficulty in finding non-related donors for stem cell transplantation and the early reactivations are the causes of the inferior outcome.

Severe adult hemophagocytic lymphohistiocytosis (HLHa) correlates with HLH-related gene variants.

BACKGROUND: The contribution of genetic factors to the severity of adult hemophagocytic lymphohistiocytosis (HLHa) remains unclear. OBJECTIVE: We sought to assess a potential link between HLHa outcomes and HLH-related gene variants. METHODS: Clinical characteristics of 130 HLHa patients (age ≥ 18 years and HScore ≥ 169) and genotype of 8 HLH-related genes (LYST, PRF1, UNC13-D, STX11, STXBP2, RAB27A, XIAP, and SAP) were collected. A total of 34 variants found in only 6 genes were selected on the basis of their frequency and criteria predicted to impair protein function. Severity was defined by refractory disease to HLH treatment, death, or transfer to an intensive care unit. RESULTS: HLHa-associated diseases (ADs) were neoplasia (n = 49 [37.7%]), autoimmune/inflammatory disease (n = 33 [25.4%]), or idiopathic when no AD was identified (n = 48 [36.9%]). Infectious events occurred in 76 (58.5%) patients and were equally distributed in all ADs. Severe and refractory HLHa were observed in 80 (61.5%) and 64 (49.2%) patients, respectively. HScore, age, sex ratio, AD, and infectious events showed no significant association with HLHa severity. Variants were identified in 71 alleles and were present in 56 (43.1%) patients. They were distributed as follows: 44 (34.4%), 9 (6.9%), and 3 (2.3%) patients carrying 1, 2, and 3 variant alleles, respectively. In a logistic regression model, only the number of variants was significantly associated with HLHa severity (1 vs 0: 3.86 [1.73-9.14], P = .0008; 2-3 vs 0: 29.4 [3.62-3810], P = .0002) and refractoriness (1 vs 0: 2.47 [1.17-5.34], P = .018; 2-3 vs 0: 13.2 [2.91-126.8], P = .0003). CONCLUSIONS: HLH-related gene variants may be key components to the severity and refractoriness of HLHa.

Actin dynamics regulation by TTC7A/PI4KIIIα limits DNA damage and cell death under confinement.

BACKGROUND: The actin cytoskeleton has a crucial role in the maintenance of the immune homeostasis by controlling various cellular processes, including cell migration. Mutations in TTC7A have been described as the cause of a primary immunodeficiency associated to different degrees of gut involvement and alterations in the actin cytoskeleton dynamics. OBJECTIVES: This study investigates the impact of TTC7A deficiency in immune homeostasis. In particular, the role of the TTC7A/phosphatidylinositol 4 kinase type III α pathway in the control of leukocyte migration and actin dynamics. METHODS: Microfabricated devices were leveraged to study cell migration and actin dynamics of murine and patient-derived leukocytes under confinement at the single-cell level. RESULTS: We show that TTC7A-deficient lymphocytes exhibit an altered cell migration and reduced capacity to deform through narrow gaps. Mechanistically, TTC7A-deficient phenotype resulted from impaired phosphoinositide signaling, leading to the downregulation of the phosphoinositide 3-kinase/AKT/RHOA regulatory axis and imbalanced actin cytoskeleton dynamics. TTC7A-associated phenotype resulted in impaired cell motility, accumulation of DNA damage, and increased cell death in dense 3-dimensional gels in the presence of chemokines. CONCLUSIONS: These results highlight a novel role of TTC7A as a critical regulator of lymphocyte migration. Impairment of this cellular function is likely to contribute to the pathophysiology underlying progressive immunodeficiency in patients.

Small Molecule Inhibitors of Interferon-Induced JAK-STAT Signalling.

Interferons (IFN) are cytokines which, upon binding to cell surface receptors, trigger a series of downstream biochemical events including Janus Kinase (JAK) activation, phosphorylation of Signal Transducer and Activator of Transcription protein (STAT), translocation of pSTAT to the nucleus and transcriptional activation. Dysregulated IFN signalling has been linked to cancer progression and auto-immune diseases. Here, we report the serendipitous discovery of a small molecule that blocks IFNγ activation of JAK-STAT signalling. Further lead optimisation gave rise to a potent and more selective analogue that exerts its activity by a mechanism consistent with direct IFNγ targeting in vitro, which reduces bleeding in model of haemorrhagic colitis in vivo. This first-in-class small molecule also inhibits type I and III IFN-induced STAT phosphorylation in vitro. Our work provides the basis for the development of pan-IFN inhibitory drugs.

Rab44 regulates murine mast cell-driven anaphylaxis through kinesin-1-dependent secretory granule translocation.

BACKGROUND: Mast cells (MCs) are key effectors of the allergic response. Following the cross-linking of IgE receptors (FcεRIs), they release crucial inflammatory mediators through degranulation. Although degranulation depends critically on secretory granule (SG) trafficking toward the plasma membrane, the molecular machinery underlying this transport has not been fully characterized. OBJECTIVES: This study analyzed the function of Rab44, a large, atypical Rab guanosine triphosphatase highly expressed in MC, in the MC degranulation process. METHODS: Murine knockout (KO) mouse models (KORab44 and DKOKif5b/Rab44) were used to perform passive cutaneous anaphylaxis experiments and analyze granule translocation in bone marrow-derived MCs during degranulation. RESULTS: This study demonstrate that mice lacking Rab44 (KORab44) in their bone marrow-derived MCs are impaired in their ability to translocate and degranulate SGs at the plasma membrane on FcεRI stimulation. Accordingly, KORab44 mice were less sensitive to IgE-mediated passive cutaneous anaphylaxis in vivo. A lack of Rab44 did not impair early FcεRI-stimulated signaling pathways, microtubule reorganization, lipid mediator release, or cytokine secretion. Mechanistically, Rab44 appears to interact with and function as part of the previously described kinesin-1-dependent transport pathway. CONCLUSIONS: These results highlight a novel role of Rab44 as a regulator of SG transport during degranulation and anaphylaxis acting through the kinesin-1-dependent microtubule transport machinery. Rab44 can thus be considered a potential target for modulating MC degranulation and inhibiting IgE-mediated allergic reactions.

Hemophagocytic Lymphohistiocytosis Gene Mutations in Adult Patients Presenting With CLIPPERS-Like Syndrome.

OBJECTIVE: To determine whether adult cases of Chronic Lymphocytic Inflammation with Pontine Perivascular Enhancement Responsive to Steroids (CLIPPERS) may be related to familial hemophagocytic lymphohistiocytosis (HLH) causes, we have screened patients with adult-onset CLIPPERS for mutations in primary HLH-associated genes. METHODS: In our cohort of 36 patients fulfilling the criteria for probable or definite CLIPPERS according to the CLIPPERS-2017 criteria, we conducted a first study on 12 patients who consented to genetic testing. In these 12 patients, systemic HLH criteria were searched, and genetic analysis of 8 genes involved in primary HLH was performed. RESULTS: Four definite and 8 probable CLIPPERS were enrolled (n = 12). Mutations involved in HLH were identified in 2 definite and 2 probable CLIPPERS (4/12). Three of them had biallelic PRF1 mutations with reduced perforin expression in natural killer cells. The remaining patient had biallelic UNC13D mutations with cytotoxic lymphocyte impaired degranulation. None of the mutated patients reached the criteria for systemic HLH. During follow-up, 3 of them displayed atypical findings for CLIPPERS, including emergence of systemic non-Hodgkin lymphoma (1/3) and confluent gadolinium-enhancing lesions on brain MRI (3/3). CONCLUSIONS: In our patients presenting with adult-onset CLIPPERS, one-third have HLH gene mutations. This genetic treatable condition should be searched in patients with CLIPPERS, especially in those presenting with atypical findings.

Functional and genetic testing in adults with HLH reveals an inflammatory profile rather than a cytotoxicity defect.

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory condition. Primary HLH occurs early in life as a result of monogenic biallelic mutations affecting lymphocyte cytotoxicity. Secondary HLH occurs mostly in adults secondary to infection, lymphoma, or rheumatic disease. In this latter setting, lymphocyte cytotoxicity status is not known. We conducted a systematic evaluation of natural killer (NK) cell cytotoxicity in adult patients with secondary HLH. Adult patients with secondary HLH were prospectively studied ex vivo for total lymphocyte count and subtype, NK cell phenotype, perforin expression and degranulation, and natural or antibody-dependent cell cytotoxicity, in comparison with patients affected by the same underlying disease without HLH (disease controls [DCs]) and with healthy controls (HCs). Screening for variants of cytotoxity genes was systematically performed. 68 patients were included in the HLH group and 34 each in the DC and HC groups. In HLH patients, severe and transient lymphopenia, activated NK cell phenotype (eg, increased CD69, ICAM-1, HLADR, and CCR5 expression), and decreased capacity of interferon γ production were observed; mean perforin expression was normal; and degranulation tests and NK cell cytotoxicity were not different from those in DCs. A monoallelic variant of uncertain significance affecting a lymphocyte cytotoxicity gene or the perforin variant A91V was observed in almost 50% of the patients. We detected no major intrinsic cytotoxicity dysfunction in secondary HLH patients compared with DCs and no predicted pathogenic gene variant. The activated NK phenotype profile associated with decreased interferon γ production seems similar to those of other hyperinflammatory diseases such as sepsis or systemic juvenile idiopathic arthritis.

Kinesin-1 regulates antigen cross-presentation through the scission of tubulations from early endosomes in dendritic cells.

Dendritic cells (DCs) constitute a specialized population of immune cells that present exogenous antigen (Ag) on major histocompatibility complex (MHC) class I molecules to initiate CD8 + T cell responses against pathogens and tumours. Although cross-presentation depends critically on the trafficking of Ag-containing intracellular vesicular compartments, the molecular machinery that regulates vesicular transport is incompletely understood. Here, we demonstrate that mice lacking Kif5b (the heavy chain of kinesin-1) in their DCs exhibit a major impairment in cross-presentation and thus a poor in vivo anti-tumour response. We find that kinesin-1 critically regulates antigen cross-presentation in DCs, by controlling Ag degradation, the endosomal pH, and MHC-I recycling. Mechanistically, kinesin-1 appears to regulate early endosome maturation by allowing the scission of endosomal tubulations. Our results highlight kinesin-1's role as a molecular checkpoint that modulates the balance between antigen degradation and cross-presentation.

Ttc7a regulates hematopoietic stem cell functions while controlling the stress-induced response.

The molecular machinery that regulates the balance between self-renewal and differentiation properties of hematopoietic stem cells (HSC) has yet to be characterized in detail. Here we found that the tetratricopeptide repeat domain 7 A (Ttc7a) protein, a putative scaffold protein expressed by HSC, acts as an intrinsic regulator of the proliferative response and the self-renewal potential of murine HSC in vivo Loss of Ttc7a consistently enhanced the competitive repopulating ability of HSC and their intrinsic capacity to replenish the hematopoietic system after serial cell transplantations, relative to wildtype cells. Ttc7a-deficient HSC exhibit a different transcriptomic profile for a set of genes controlling the cellular response to stress, which was associated with increased proliferation in response to chemically induced stress in vitro and myeloablative stress in vivo Our results therefore revealed a previously unrecognized role of Ttc7a as a critical regulator of HSC stemness. This role is related, at least in part, to regulation of the endoplasmic reticulum stress response.

Chronic Intestinal Pseudo-Obstruction and Lymphoproliferative Syndrome as a Novel Phenotype Associated With Tetratricopeptide Repeat Domain 7A Deficiency.

Mutations in the tetratricopeptide repeat domain 7A (TTC7A) gene cause very early onset inflammatory bowel diseases (VOIBD) or multiple intestinal atresia associated with immune deficiency of various severities, ranging from combined immune deficiency to mild lymphopenia. In this manuscript, we report the clinical, biological and molecular features of a patient born from consanguineous parents, presenting with recurrent lymphoproliferative syndrome and pan-hypergammaglobulinemia associated with chronic intestinal pseudo obstruction (CIPO). Genetic screening revealed the novel c.974G>A (p.R325Q) mutation in homozygosity in the TTC7A gene. The patient's phenotype differs significantly from that previously associated with TTC7A deficiency in humans. It becomes closer to the one reported in the ttc7a-deficient mice that invariably develop a proliferative lymphoid and myeloid disorder. Functional studies showed that the extreme variability in the clinical phenotype couldn't be explained by the cellular phenotype. Indeed, the patient's TTC7A mutation, as well as the murine-ttc7 mutant, have the same functional impact on protein expression, DNA instability and chromatin compaction, as the other mutations that lead to classical TTC7A-associated phenotypes. Co-inheritance of genetic variants may also contribute to the unique nature of the patient's phenotype. The present case report shows that the clinical spectrum of TTC7A deficiency is much broader than previously suspected. Our findings should alert the physicians to consider screening of TTC7A mutations in patients with lymphoproliferative syndrome and hypergammaglobulinemia and/or chronic intestinal pseudo-obstruction.

A 1-Year Prospective French Nationwide Study of Emergency Hospital Admissions in Children and Adults with Primary Immunodeficiency.

PURPOSE: Patients with primary immunodeficiency (PID) are at risk of serious complications. However, data on the incidence and causes of emergency hospital admissions are scarce. The primary objective of the present study was to describe emergency hospital admissions among patients with PID, with a view to identifying "at-risk" patient profiles. METHODS: We performed a prospective observational 12-month multicenter study in France via the CEREDIH network of regional PID reference centers from November 2010 to October 2011. All patients with PIDs requiring emergency hospital admission were included. RESULTS: A total of 200 admissions concerned 137 patients (73 adults and 64 children, 53% of whom had antibody deficiencies). Thirty admissions were reported for 16 hematopoietic stem cell transplantation recipients. When considering the 170 admissions of non-transplant patients, 149 (85%) were related to acute infections (respiratory tract infections and gastrointestinal tract infections in 72 (36%) and 34 (17%) of cases, respectively). Seventy-seven percent of the admissions occurred during winter or spring (December to May). The in-hospital mortality rate was 8.8% (12 patients); death was related to a severe infection in 11 cases (8%) and Epstein-Barr virus-induced lymphoma in 1 case. Patients with a central venous catheter (n = 19, 13.9%) were significantly more hospitalized for an infection (94.7%) than for a non-infectious reason (5.3%) (p = 0.04). CONCLUSION: Our data showed that the annual incidence of emergency hospital admission among patients with PID is 3.4%. The leading cause of emergency hospital admission was an acute infection, and having a central venous catheter was associated with a significantly greater risk of admission for an infectious episode.

Human RIPK1 deficiency causes combined immunodeficiency and inflammatory bowel diseases.

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is a critical regulator of cell death and inflammation, but its relevance for human disease pathogenesis remains elusive. Studies of monogenic disorders might provide critical insights into disease mechanisms and therapeutic targeting of RIPK1 for common diseases. Here, we report on eight patients from six unrelated pedigrees with biallelic loss-of-function mutations in RIPK1 presenting with primary immunodeficiency and/or intestinal inflammation. Mutations in RIPK1 were associated with reduced NF-κB activity, defective differentiation of T and B cells, increased inflammasome activity, and impaired response to TNFR1-mediated cell death in intestinal epithelial cells. The characterization of RIPK1-deficient patients highlights the essential role of RIPK1 in controlling human immune and intestinal homeostasis, and might have critical implications for therapies targeting RIPK1.

Author Correction: Germline HAVCR2 mutations altering TIM-3 characterize subcutaneous panniculitis-like T cell lymphomas with hemophagocytic lymphohistiocytic syndrome.

In the version of this article originally published, the main-text sentence "In three patients of European ancestry, we identified the germline variant encoding p.Ile97Met in TIM-3, which was homozygous in two (P12 and P13) and heterozygous in one (P15) in the germline but with no TIM-3 plasma membrane expression in the tumor" misstated the identifiers of the two homozygous individuals, which should have been P13 and P14. The error has been corrected in the HTML, PDF and print versions of the paper.

Tetratricopeptide repeat domain 7A is a nuclear factor that modulates transcription and chromatin structure.

A loss-of-function mutation in tetratricopeptide repeat domain 7A (TTC7A) is a recently identified cause of human intestinal and immune disorders. However, clues to related underlying molecular dysfunctions remain elusive. It is now shown based on the study of TTC7A-deficient and wild-type cells that TTC7A is an essential nuclear protein. It binds to chromatin, preferentially at actively transcribed regions. Its depletion results in broad range of epigenomic changes at proximal and distal transcriptional regulatory elements and in altered control of the transcriptional program. Loss of WT_TTC7A induces general decrease in chromatin compaction, unbalanced cellular distribution of histones, higher nucleosome accessibility to nuclease digestion along with genome instability, and reduced cell viability. Our observations characterize for the first time unreported functions for TTC7A in the nucleus that exert a critical role in chromatin organization and gene regulation to safeguard healthy immune and intestinal status.

Dynamic Formation of Microvillus Inclusions During Enterocyte Differentiation in Munc18-2-Deficient Intestinal Organoids.

Background & Aims: Microvillus inclusion disease (MVID) is a congenital intestinal malabsorption disorder caused by defective apical vesicular transport. Existing cellular models do not fully recapitulate this heterogeneous pathology. The aim of this study was to characterize 3-dimensional intestinal organoids that continuously generate polarized absorptive cells as an accessible and relevant model to investigate MVID. Methods: Intestinal organoids from Munc18-2/Stxbp2-null mice that are deficient for apical vesicular transport were subjected to enterocyte-specific differentiation protocols. Lentiviral rescue experiments were performed using human MUNC18-2 variants. Apical trafficking and microvillus formation were characterized by confocal and transmission electron microscopy. Spinning disc time-lapse microscopy was used to document the lifecycle of microvillus inclusions. Results: Loss of Munc18-2/Stxbp2 recapitulated the pathologic features observed in patients with MUNC18-2 deficiency. The defects were fully restored by transgenic wild-type human MUNC18-2 protein, but not the patient variant (P477L). Importantly, we discovered that the MVID phenotype was correlated with the degree of enterocyte differentiation: secretory vesicles accumulated already in crypt progenitors, while differentiated enterocytes showed an apical tubulovesicular network and enlarged lysosomes. Upon prolonged enterocyte differentiation, cytoplasmic F-actin-positive foci were observed that further progressed into classic microvillus inclusions. Time-lapse microscopy showed their dynamic formation by intracellular maturation or invagination of the apical or basolateral plasma membrane. Conclusions: We show that prolonged enterocyte-specific differentiation is required to recapitulate the entire spectrum of MVID. Primary organoids can provide a powerful model for this heterogeneous pathology. Formation of microvillus inclusions from multiple membrane sources showed an unexpected dynamic of the enterocyte brush border.