Perforin gene defects in familial hemophagocytic lymphohistiocytosis

The Immunology of Macrophage Activation Syndrome

Synonymous with secondary hemophagocytic lymphohistiocytosis, macrophage activation syndrome (MAS) is a term used by rheumatologists to describe a potentially life-threatening complication of systemic inflammatory disorders, most commonly systemic juvenile idiopathic arthritis (sJIA) and systemic lupus erythematosus (SLE). Clinical and laboratory features of MAS include sustained fever, hyperferritinemia, pancytopenia, fibrinolytic coagulopathy, and liver dysfunction. Soluble interleukin-2 receptor alpha chain (sCD25) and sCD163 may be elevated, and histopathology often reveals characteristic increased hemophagocytic activity in the bone marrow (and other tissues), with positive CD163 (histiocyte) staining. A common hypothesis as to the pathophysiology of many cases of MAS proposes a defect in lymphocyte cytolytic activity. Specific heterozygous gene mutations in familial HLH-associated cytolytic pathway genes (e.g., PRF1, UNC13D) have been linked to a substantial subset of MAS patients. In addition, the pro-inflammatory cytokine environment, particularly IL-6, has been shown to decrease NK cell cytolytic function. The inability of NK cells and cytolytic CD8 T cells to lyse infected and otherwise activated antigen presenting cells results in prolonged cell-to-cell (innate and adaptive immune cells) interactions and amplification of a pro-inflammatory cytokine cascade. The cytokine storm results in activation of macrophages, causing hemophagocytosis, as well as contributing to multi-organ dysfunction. In addition to macrophages, dendritic cells likely play a critical role in antigen presentation to cytolytic lymphocytes, as well as contributing to cytokine expression. Several cytokines, including tumor necrosis factor, interferon-gamma, and numerous interleukins (i.e., IL-1, IL-6, IL-18, IL-33), have been implicated in the cytokine cascade. In addition to broadly immunosuppressive therapies, novel cytokine targeted treatments are being explored to dampen the overly active immune response that is responsible for much of the pathology seen in MAS.

Hemophagocytic lymphohistiocytosis followed by an episode of peritoneal dialysis associated peritonitis: a case report

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is characterized by excessive activation of the immune system due to infection, autoimmune diseases, or malignancy. As an aggressive and life-threatening clinical syndrome, HLH secondary to peritoneal dialysis associated peritonitis (PDAP) has never been reported.

CASE PRESENTATION

A 34-year-old female peritoneal dialysis (PD) patient was hospitalized for fever, progressively multi-organ damage (including cytopenias, abnormalities of coagulation and liver enzyme) after an episode of organism-specific peritonitis. She was refractory to the broad-spectrum antimicrobial agent. Further tests found hemophagocytosis on the bone marrow examination, and extremely high level of sIL2-R and impaired activity of NK cell. The diagnosis of HLH was eventually established. After HLH-specific therapy, this patient recovered and discharged.

CONCLUSIONS

The present case suggests that clinicians should to be aware of HLH in those patients apparently suspected with refractory or relapsing peritonitis, especially those accompanied with persist fever, hyperferritinemia, and cytopenias. HLH-specific therapy and supportive care should be applied without delay.

Deficiency of perforin and hCNT1, a novel inborn error of pyrimidine metabolism, associated with a rapidly developing lethal phenotype due to multi-organ failure

Pyrimidine nucleotides are essential for a vast number of cellular processes and dysregulation of pyrimidine metabolism has been associated with a variety of clinical abnormalities. Inborn errors of pyrimidine metabolism affecting enzymes in the pyrimidine de novo and degradation pathway have been identified but no patients have been described with a deficiency in proteins affecting the cellular import of ribonucleosides. In this manuscript, we report the elucidation of the genetic basis of the observed uridine-cytidineuria in a patient presenting with fever, hepatosplenomegaly, persistent lactate acidosis, severely disturbed liver enzymes and ultimately multi-organ failure. Sequence analysis of genes encoding proteins directly involved in the metabolism of uridine and cytidine showed two variants c.1528C > T (p.R510C) and c.1682G > A (p.R561Q) in SLC28A1, encoding concentrative nucleotide transporter 1 (hCNT1). Functional analysis showed that these variants affected the three-dimensional structure of hCNT1, altered glycosylation and decreased the half-life of the mutant proteins which resulted in impaired transport activity. Co-transfection of both variants, mimicking the trans disposition of c.1528C > T (p.R510C) and c.1682G > A (p.R561Q) in the patient, significantly impaired hCNT1 biological function. Whole genome sequencing identified two pathogenic variants c.50delT; p.(Leu17Argfs*34) and c.853_855del; p.(Lys285del) in the PRF1 gene, indicating that our patient was also suffering from Familial Hemophagocytic Lymphohistiocytosis type 2. The identification of two co-existing monogenic defects might have resulted in a blended phenotype. Thus, the clinical presentation of isolated hCNT1 deficiency remains to be established.

Epstein-Barr Virus-Associated T and NK-Cell Lymphoproliferative Diseases

EBV-associated T and NK-cell lymphoproliferative diseases (EBV-T/NK LPDs) are characterized by the transformation and proliferation of EBV-infected T or NK cells. The 2016 revised World Health Organization classification recognizes the following EBV-positive lymphoproliferative disorders (LPD): chronic active EBV infection (CAEBV) of T- and NK-cell type (cutaneous and systemic forms), systemic EBV-positive T-cell lymphoma of childhood, aggressive NK-cell leukemia, extranodal NK/T-cell lymphoma, nasal type, and the new provisional entity primary EBV-positive nodal T/NK-cell lymphoma. EBV-associated hemophagocytic lymphohistiocytosis (HLH), although not included in the WHO classification because it is a reactive, inflammatory disease, is included in this review because it can be life-threatening and may have overlapping features with other EBV+ T/NK LPDs. EBV+ T/NK LPDs are rare diseases difficult to diagnose and manage properly, because some LPDs have unusual presentations, and discrepancies between clinical and histological findings might be encountered. Furthermore, EBV+ T/NK disorders share some clinico-pathological features, and may evolve into other categories during the clinical course, including malignant transformation of CAEBV. Here, we review the EBV+ T/NK LPDs in terms of their definitions, clinical features, histology, immunophenotype, molecular findings, and pathogenesis. This review aims to increase our understanding and awareness of the differential diagnosis among the different EBV+ T/NK LPDs. New insights into the genetic characteristics of these disorders will also be discussed.

Pembrolizumab-induced Autoimmune Hemolytic Anemia and Hemophagocytic Lymphohistiocytosis in Non-small Cell Lung Cancer

We herein report a 78-year old man with squamous cell carcinoma of the lungs treated with pembrolizumab. At 10 days after the administration of pembrolizumab, he showed progressive anemia and increased levels of bilirubin. Because the findings of a direct coombs test and cold hemagglutinin were positive, we diagnosed the patient with autoimmune hemolytic anemia and treated him with prednisolone. Subsequently, he was admitted to our hospital owing to fatigue, a high fever, and jaundice. His clinical findings met the diagnostic criteria of hemophagocytic lymphohistiocytosis, and he was rescued with a high dose of glucocorticoids. Marked tumor regression was obtained and has been maintained since then.

Haploidentical hematopoietic stem cell transplantation using reduced-intensity conditioning for pediatric patients with familial hemophagocytic lymphohistiocytosis

IMPORTANCE

Allogeneic hematopoietic stem cell transplantation (HSCT) is considered to be the only curative treatment for familial hemophagocytic lymphohistiocytosis (FHLH). Treatment of pediatric FHLH with reduced-intensity conditioning (RIC)-based haploidentical donor (HID) HSCT has been rarely reported.

OBJECTIVE

To investigate outcomes and adverse events in patients with FHLH who received HID-HSCT.

METHODS

We conducted a retrospective study of five patients, including three with mutations in PRF1 and two with XIAP deficiency. Four of the five donors were heterozygous for these mutations. The conditioning regimen included fludarabine, cyclophosphamide, and antithymocyte globulin, with or without low-dose irradiation. Unmanipulated mobilized bone marrow and peripheral blood stem cells were used as the grafts.

RESULTS

All five patients were successfully engrafted. Four patients survived, and one patient died. All exhibited complete response (CR) after HSCT. All of the patients who survived exhibited CR to FHLH without severe regimen-related complications at a median of 29.5 months (range: 23-34 months) after HSCT. Four of the five patients had mixed donor chimerism. Three patients had 17% to 87% mixed donor chimerism but remained free of disease. Four patients received donor lymphocyte infusion (DLI), which improved the level of mixed donor chimerism. One patient experienced a decrease in donor chimerism to 1% and relapsed; Four patients developed acute graft-versus-host disease (GvHD) (grade I or II), and one patient developed grade IV GvHD.

INTERPRETATION

HID-HSCT with RIC can be considered for treatment for patients with FHLH, but the conditions and DLI regimens need to be optimized for long-term use, and more prospective studies should be conducted.

Risk factors affecting outcome of unrelated cord blood transplantation for children with familial haemophagocytic lymphohistiocytosis

Allogeneic haematopoietic stem cell transplantation is still the only available curative option for Familial Haemophagocytic Lymphohistiocytosis (FHLH). Most studies report outcomes after bone marrow or peripheral blood stem cell transplantation. We analysed the outcomes of 118 children with FHLH undergoing single-unit umbilical cord blood transplantation performed from 1996 to 2014. Myeloablative conditioning regimen was given to 90% of the patients, and was mostly busulfan-based (n = 81, 76%), including anti-thymocyte globulin or alemtuzumab (n = 102, 86%). The cumulative incidence of Day 60 neutrophil engraftment was 85%; and that of non-relapse mortality and acute graft-versus-host disease (GvHD) was 21% and 33% at 100 days, respectively. The 6-year cumulative incidence of chronic GvHD was 17% and the 6-year probability of overall survival was 55%. In multivariate analysis, children receiving a graft with a total nucleated cell dose greater than 9·9 × 10⁷ /kg had a better overall survival (hazard ratio [HR]: 0·49, 95% CI: 0·27-0·88, P = 0·02). Degree of human leucocyte antigen (HLA) matching was associated with improved disease-free survival (5/6 vs. 6/6 HR: 2·11, 95% confidence interval [CI]: 1·01-4·4, P = 0·05 and ≤4/6 vs. 6/6, HR: 2·82, CI: 1·27-6·23, P = 0·01). Umbilical cord blood transplantation with a high cell dose and good HLA match is a suitable alternative option to haematopoietic stem cell transplantation in children with FHLH who lack a HLA-matched donor.

Disruption of IL-33 Signaling Limits Early CD8+ T Cell Effector Function Leading to Exhaustion in Murine Hemophagocytic Lymphohistiocytosis

Danger signals mediated through ST2, the interleukin-33 (IL-33) receptor, amplify CD8⁺ T cell-mediated inflammation in the murine model of familial hemophagocytic lymphohistiocytosis type 2 (FHL2), and blockade of ST2 provides a potential therapeutic strategy in this disease. However, the long-term effects of disrupting IL-33/ST2 signaling on the CD8⁺ T cell compartment are unknown. Here, we examined the evolution of the T cell response in murine FHL type 2 in the absence of ST2 signaling and found that CD8⁺ T cells gradually undergo exhaustion, similar to a related nonfatal FHL model. ST2 inhibition indirectly promotes CD8⁺ T cell exhaustion, and in contrast to other forms of FHL, reversal of exhaustion does not affect mortality. Disruption of IL-33 signaling exerts a more significant impact on the CD8⁺ T cell compartment early in the course of disease by intrinsically limiting CD8⁺ T cell proliferative and cytokine production capacity. Our data thus suggest that while ST2 blockade ultimately enables the development of CD8⁺ T cell exhaustion in late-stage murine FHL2, exhaustion is merely an effect, rather than the cause, of extended survival in these mice. The acute impact of ST2 inhibition on both the quantity and quality of the effector CD8⁺ T cell response more likely underlies the protective benefits of this treatment. This study provides evidence that redefines the relationship between CD8⁺ T cell exhaustion and mortality in murine FHL and supports the therapeutic use of ST2 blockade during the acute stage of disease.

Hepatobiliary Dysfunction and Disseminated Intravascular Coagulation Increase Risk of Mortality in Pediatric Hemophagocytic Lymphohistiocytosis

OBJECTIVES

Hemophagocytic lymphohistiocytosis poses significant challenges due to limited tools to guide clinical decisions in a population at high risk of death. We sought to assess whether disseminated intravascular coagulation and hepatobiliary dysfunction, significant comorbidities seen in critical care settings, would identify hemophagocytic lymphohistiocytosis patients with increased risk of mortality.

DESIGN

Retrospective chart review.

SETTING

Single-center PICU.

PATIENTS

All patients admitted to a tertiary care children's hospital diagnosed with hemophagocytic lymphohistiocytosis from 2005 to 2012.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Forty-three patients were diagnosed with hemophagocytic lymphohistiocytosis with median age of 61 months. The 5-year overall survival was 51% (22/43). Univariate analyses revealed ferritin levels greater than 10,000 (ng/mL), international normalized ratio greater than 1.5, or platelet counts less than 100,000/µL at initiation of dexamethasone were individually associated with mortality. Development of disseminated intravascular coagulation, hepatobiliary dysfunction, or both increased the likelihood of death in hemophagocytic lymphohistiocytosis patients (relative risk; 95% CI) (6; 1.4-34; p < 0.05), (4.1; 1.8-10; p < 0.05), and (7.5; 1.8-42; p < 0.05). Of 12 autopsies performed, 75% had at least one active infection, 66% had chronic lymphopenia, 50% had lymphocyte depletion in the spleen, thymus, or bone marrow, 42% had evidence of microvascular thrombosis, and 92% had evidence of hepatocellular injury.

CONCLUSIONS

Hemophagocytic lymphohistiocytosis continues to have high mortality with hemophagocytic lymphohistiocytosis-1994/2004 (dexamethasone/etoposide), the current standard of care for all children with hemophagocytic lymphohistiocytosis. Hemophagocytic lymphohistiocytosis patients who developed disseminated intravascular coagulation, hepatobiliary dysfunction, or both had higher risk of death with mortalities of 60%, 77%, and 77%, respectively. Phenotypic classifications are urgently needed to guide individualized treatment strategies to improve outcomes for children with hemophagocytic lymphohistiocytosis.

T-cell gene therapy for perforin deficiency corrects cytotoxicity defects and prevents hemophagocytic lymphohistiocytosis manifestations

BACKGROUND

Mutations in the perforin 1 (PRF1) gene account for up to 58% of familial hemophagocytic lymphohistiocytosis syndromes. The resulting defects in effector cell cytotoxicity lead to hypercytokinemia and hyperactivation with inflammation in various organs.

OBJECTIVE

We sought to determine whether autologous gene-corrected T cells can restore cytotoxic function, reduce disease activity, and prevent hemophagocytic lymphohistiocytosis (HLH) symptoms in in vivo models.

METHODS

We developed a gammaretroviral vector to transduce murine CD8 T cells in the Prf-/- mouse model. To verify functional correction of Prf-/- CD8 T cells in vivo, we used a lymphocytic choriomeningitis virus (LCMV) epitope-transfected murine lung carcinoma cell tumor model. Furthermore, we challenged gene-corrected and uncorrected mice with LCMV. One patient sample was transduced with a PRF1-encoding lentiviral vector to study restoration of cytotoxicity in human cells.

RESULTS

We demonstrated efficient engraftment and functional reconstitution of cytotoxicity after intravenous administration of gene-corrected Prf-/- CD8 T cells into Prf-/- mice. In the tumor model infusion of Prf-/- gene-corrected CD8 T cells eliminated the tumor as efficiently as transplantation of wild-type CD8 T cells. Similarly, mice reconstituted with gene-corrected Prf-/- CD8 T cells displayed complete protection from the HLH phenotype after infection with LCMV. Patients' cells showed correction of cytotoxicity in human CD8 T cells after transduction.

CONCLUSION

These data demonstrate the potential application of T-cell gene therapy in reconstituting cytotoxic function and protection against HLH in the setting of perforin deficiency.

Treatment dilemmas in asymptomatic children with primary hemophagocytic lymphohistiocytosis

Asymptomatic carriers (ACs) of pathogenic biallelic mutations in causative genes for primary hemophagocytic lymphohistiocytosis (HLH) are at high risk of developing life-threatening HLH, which requires allogeneic hematopoietic stem cell transplantation (HSCT) to be cured. There are no guidelines on the management of these asymptomatic patients. We analyzed the outcomes of pairs of index cases (ICs) and subsequently diagnosed asymptomatic family members carrying the same genetic defect. We collected data from 22 HSCT centers worldwide. Sixty-four children were evaluable. ICs presented with HLH at a median age of 16 months. Seven of 32 ICs died during first-line therapy, and 2 are alive after chemotherapy only. In all, 23/32 underwent HSCT, and 16 of them are alive. At a median follow-up of 36 months from diagnosis, 18/32 ICs are alive. Median age of ACs at diagnosis was 5 months. Ten of 32 ACs activated HLH while being observed, and all underwent HSCT: 6/10 are alive and in complete remission (CR). 22/32 ACs remained asymptomatic, and 6/22 have received no treatment and are in CR at a median follow-up of 39 months. Sixteen of 22 underwent preemptive HSCT: 15/16 are alive and in CR. Eight-year probability of overall survival (pOS) in ACs who did not have activated HLH was significantly higher than that in ICs (95% vs 45%; P = .02), and pOS in ACs receiving HSCT before disease activation was significantly higher than in ACs receiving HSCT after HLH activation (93% vs 64%; P = .03). Preemptive HSCT in ACs proved to be safe and should be considered.

A prospective quality improvement initiative in adult hemophagocytic lymphohistiocytosis to improve testing and a framework to facilitate trigger identification and mitigate hemorrhage from retrospective analysis

Hemophagocytic lymphohistiocytosis (HLH) is a highly fatal, hyperinflammatory syndrome in adults triggered by an underlying illness in most cases. As such, suspicion of HLH dictates further investigation to identify the HLH trigger and determine treatment. HLH is clinically challenging due to diverse presentations and underlying triggers, provider unfamiliarity, and bleeding complications. Clinically, we observed diagnostic error from incorrect testing and cognitive biases (interleukin-2 confused with soluble interleukin-2 receptor and natural killer cell quantification confused with functional assays).This study reports our single institutional experience with adult HLH with the aim to reduce erroneous testing with a quality improvement (QI) project, and to facilitate trigger discovery and mitigate hemorrhage. Provider education on HLH testing was the prospective intervention, followed by mistaken test removal. HLH triggers and diagnostic utility were determined by retrospective chart review. Risk factors for hemorrhage were determined by multivariable analysis.Erroneous HLH testing was reduced from 74% to 24% of patients (P < .001) by the QI intervention. These changes were projected to save $11,700 yearly. The majority (64%) of patients evaluated for HLH were on non-hematology/oncology services, highlighting the need for vigilance in hematology consultation. Sixty-three patients met classic HLH-2004 criteria for HLH. Malignancy (38%), infection (27%), Epstein-Barr virus (EBV) (14%), or autoimmune disease (8%) triggered most HLH cases. HLH triggers were most commonly identified by serologic testing (27%) and bone marrow biopsy (19%). Biopsy of other affected organs based on PET-CT imaging after unsuccessful initial diagnostic measures was helpful, and focal fluorodeoxyglucose uptake was predictive of an underlying malignancy (likelihood ratio 8.3, P = .004). Major hemorrhage occurred in 41% of patients. On multivariable analysis the odds ratios (OR) for major hemorrhage were increased for patients with intensive care unit level care (OR 10.47, P = .005), and disseminated intravascular coagulation in the first week of admission (OR 10.53, P = .04).These data are incorporated into a framework to encourage early HLH recognition with the HScore, facilitate trigger identification, identify those at risk for hemorrhage, and minimize low-yield or erroneous testing.

An effective diagnostic index for lymphoma-associated hemophagocytic syndrome

BACKGROUND

Lymphoma-associated hemophagocytic syndrome (LAHS) is a highly fatal immune disorder. Poor prognosis is partly attributed to under diagnosis or delayed diagnosis.

AIM

Early identification of LAHS patients based on the laboratory findings could improve the outcomes.

DESIGN

Retrospective observational cross-sectional study.

METHODS

From January 2011 to June 2016, 282 adult patients with hemophagocytosis in bone marrow were enrolled, and 114 hemophagocytic lymphohistiocytosis (HLH) patients with definite underlying cause were finally included for analysis. The HLH patients were further divided into LAHS (76 out of 114) and non-malignancy-associated HLH (38 out of 114) groups.

RESULTS

Compared to non-malignancy-associated HLH, LAHS patients had significantly elevated lactate dehydrogenase (LDH) levels, increased thickness of spleen, higher proportion of patients with lymphadenopathy and significantly decreased peripheral blood cell count. In multivariate logistic regression model analysis, thickness of spleen ≥5 cm (OR = 17.9, 95%CI 1.35-236.6; P = 0.028), IL-6 level ≥55.1 pg/ml (OR = 12.01, 95%CI 1.03-138.9; P = 0.047) and IL-10 level ≥425.9 pg/ml (OR = 51.18, 95%CI 2.53-1035.1; P = 0.010) were independent predictors of LAHS diagnosis. Based on the regression parameters, we established a diagnostic index with weighted risk scores of 1 assigned to thickness of spleen and IL-6 level respectively, and a score of 3 assigned to IL-10 level. A diagnostic index ≥ 2 points had the best AUC value (0.889) with 84.2% of sensitivity and 93.7% of specificity for predicting LAHS.

CONCLUSIONS

LAHS can be considered when HLH patients have a diagnostic index ≥2 points, so actively looking for evidence of lymphoma and effective chemotherapy may be necessary.

Hemophagocytic Lymphohistiocytosis in the Elderly

Hemophagocytic lymphohistiocytosis (HLH) is a rare disease of massive, dysregulated cytokine release and secondary multiorgan failure and is associated with high mortality. Primary HLH occurs predominately in infants and young children with a genetic predisposition. Acquired HLH is less well characterized and usually occurs in younger adults in the setting of severe inflammation triggered by infection or malignancy. Little is known about the disease in elderly. We report 3 patients >50 years old who presented with multiorgan failure and shock without an identifiable source and were ultimately diagnosed with acquired HLH. We performed a literature review of HLH in adults >50 years of age and identified an additional 68 cases. Mean age was 62 years, with male predominance. Most cases were triggered by infection (49%) followed by malignancy (27%). Nineteen patients were treated with the HLH-94 protocol, 11 received corticosteroids and the remainder received non-HLH specific interventions. Overall mortality was 62%.

Severe hemophagocytic lymphohistiocytosis in a melanoma patient treated with ipilimumab + nivolumab

BACKGROUND

Treatment of metastatic melanoma patients with immune checkpoint inhibitors is an important standard of care. Side effects are due to immune activation, can affect virtually all organ systems, and are occasionally severe. Although hematologic toxicity has been reported, we present a case of hemophagocytic lymphohistiocytosis (HLH) due to immune checkpoint inhibitor therapy.

CASE PRESENTATION

A patient with metastatic melanoma was treated with one course of ipilimumab + nivolumab and presented 3 weeks later with severe anemia and hyperferritinemia. A bone marrow biopsy revealed necrotic tumor cells, infiltrating T cells, and hemophagocytosis. The patient was treated with high-dose steroids; 12 months later, the patient remains off all therapy and in complete remission of both HLH and metastatic melanoma.

CONCLUSIONS

The hemophagocytic syndromes are attributable to dysregulated immune activation and share pathophysiologic mechanisms with immune activation from checkpoint inhibitors. Increasing use of regimens that include immune checkpoint inhibition require vigilant monitoring for immune-activating side effects as they can occasionally be life threatening, as in this case of HLH.

Recycling endosomes in human cytotoxic T lymphocytes constitute an auxiliary intracellular trafficking pathway for newly synthesized perforin

Although cytotoxic T lymphocytes (CTLs) store perforin within cytoplasmic secretory granules for immediate use, perforin is synthesized anew within hours of TCR stimulation. Previously, we observed new perforin protein at an immunologic synapse independent of secretory lysosomes; herein, we aimed to determine how new perforin transits to the synapse if not via lytic granules. We analyzed antigen-specific human CTLs via imaging flow cytometry and high-resolution confocal microscopy, with attention to intracellular trafficking components and new perforin. The recycling endosome compartments identified by rab8, rab11a, rab4, and rab37 co-localized with new perforin, as well as the SNAREs vti1b and VAMP4. After ablating the function of the recycling endosome pathway, we observed a relative accumulation of new perforin in rab8 vesicles. The recycling endosome pathway may serve as an auxiliary intracellular route for the delivery of new perforin to an immunologic synapse in order to perpetuate a cytotoxic response.

Atteinte rénale du syndrome d’activation macrophagique

Le syndrome d’activation macrophagique (SAM) ou syndrome hémophagocytaire est une pathologie compliquant soit certains déficits immunitaires d’origine génétique, soit certaines maladies hématologiques (essentiellement des lymphomes non hodgkiniens), infectieuses (herpèsvirus, bactéries, parasites) ou auto-immunes (lupus, maladie de Still). Il se caractérise par une suractivation aiguë du système immunitaire et plus particulièrement des lymphocytes T cytotoxiques et des cellules histiocytaires/macrophagiques, déclenchant une production massive de cytokines pro-inflammatoires avec fièvre, pancytopénie, organomégalie, altérations du bilan hépatique et de la coagulation. Une défaillance multiviscérale est fréquente, nécessitant la prise en charge en réanimation et mettant souvent en jeu le pronostic vital, avec une mortalité qui reste dans certains cas à près de 50 %. Le SAM implique souvent le rein, par le biais d’une nécrose tubulaire aiguë, d’une néphropathie interstitielle inflammatoire ou d’une glomérulopathie sévère, responsable de syndrome néphrotique. La mise en évidence de ce syndrome n’est pas toujours facile chez un patient avec un tableau de sepsis ou de choc septique, mais elle peut guider la prise en charge thérapeutique, notamment l’initiation d’un traitement par chimiothérapie ou immunosuppresseurs, selon l’étiologie identifiée.

Comprehensive molecular diagnosis of Epstein-Barr virus-associated lymphoproliferative diseases using next-generation sequencing

Epstein-Barr virus (EBV) is associated with several life-threatening diseases, such as lymphoproliferative disease (LPD), particularly in immunocompromised hosts. Some categories of primary immunodeficiency diseases (PIDs) including X-linked lymphoproliferative syndrome (XLP), are characterized by susceptibility and vulnerability to EBV infection. The number of genetically defined PIDs is rapidly increasing, and clinical genetic testing plays an important role in establishing a definitive diagnosis. Whole-exome sequencing is performed for diagnosing rare genetic diseases, but is both expensive and time-consuming. Low-cost, high-throughput gene analysis systems are thus necessary. We developed a comprehensive molecular diagnostic method using a two-step tailed polymerase chain reaction (PCR) and a next-generation sequencing (NGS) platform to detect mutations in 23 candidate genes responsible for XLP or XLP-like diseases. Samples from 19 patients suspected of having EBV-associated LPD were used in this comprehensive molecular diagnosis. Causative gene mutations (involving PRF1 and SH2D1A) were detected in two of the 19 patients studied. This comprehensive diagnosis method effectively detected mutations in all coding exons of 23 genes with sufficient read numbers for each amplicon. This comprehensive molecular diagnostic method using PCR and NGS provides a rapid, accurate, low-cost diagnosis for patients with XLP or XLP-like diseases.

The genetic nomenclature of recessive cerebellar ataxias

The recessive cerebellar ataxias are a large group of degenerative and metabolic disorders, the diagnostic management of which is difficult because of the enormous clinical and genetic heterogeneity. Because of several limitations, the current classification systems provide insufficient guidance for clinicians and researchers. Here, we propose a new nomenclature for the genetically confirmed recessive cerebellar ataxias according to the principles and criteria laid down by the International Parkinson and Movement Disorder Society Task Force on Classification and Nomenclature of Genetic Movement Disorders. We apply stringent criteria for considering an association between gene and phenotype to be established. The newly proposed list of recessively inherited cerebellar ataxias includes 62 disorders that were assigned an ATX prefix, followed by the gene name, because these typically present with ataxia as a predominant and/or consistent feature. An additional 30 disorders that often combine ataxia with a predominant or consistent other movement disorder received a double prefix (e.g., ATX/HSP). We also identified a group of 89 entities that usually present with complex nonataxia phenotypes, but may occasionally present with cerebellar ataxia. These are listed separately without the ATX prefix. This new, transparent and adaptable nomenclature of the recessive cerebellar ataxias will facilitate the clinical recognition of recessive ataxias, guide diagnostic testing in ataxia patients, and help in interpreting genetic findings. © 2018 International Parkinson and Movement Disorder Society.

Genetic variant spectrum in 265 Chinese patients with hemophagocytic lymphohistiocytosis: Molecular analyses of PRF1, UNC13D, STX11, STXBP2, SH2D1A, and XIAP

Hemophagocytic lymphohistiocytosis (HLH) is a rare life-threatening hyperinflammatory disease. This study aimed to investigate the frequencies and distributions of inherited variants in PRF1, UNC13D, STX11, STXBP2, SH2D1A, and XIAP genes in Chinese patients with HLH. A total of 265 patients diagnosed with HLH from January, 2010 to December, 2016 were recruited and analyzed for the 6 genes. Genetic variants were observed in 87 (32.83%) patients. 36 (13.58%) exhibited variants in UNC13D, 18 (6.79%) exhibited PRF1 variants, 10 (3.77%) had variants in XIAP, 9 (3.40%) exhibited variants in STXBP2, 6 (2.26%) carried variants in SH2D1A, 1 (0.38%) had STX11 variant, and 7 (2.64%) exhibited digenic variants. Monoallelic variants were the most common, which accounted for 49.43% of all cases with variants. All variants were confirmed to be germline-derived. The present study describes a distinct variant spectrum in Chinese patients with HLH, whereby UNC13D is the most frequently mutated gene with missense variants that are the most common molecular defects. The variant profile of Chinese HLH patients is quite different from that of Western cohorts but similar to that of Korean patients, yet showing its own uniqueness. This racial difference shows the role of genetic background in the occurrence of HLH.

Resistance of HIV-infected macrophages to CD8+ T lymphocyte-mediated killing drives activation of the immune system

CD4⁺ T lymphocytes are the principal target of human immunodeficiency virus (HIV), but infected macrophages also contribute to viral pathogenesis. The killing of infected cells by CD8⁺ cytotoxic T lymphocytes (CTLs) leads to control of viral replication. Here we found that the killing of macrophages by CTLs was impaired relative to the killing of CD4⁺ T cells by CTLs, and this resulted in inefficient suppression of HIV. The killing of macrophages depended on caspase-3 and granzyme B, whereas the rapid killing of CD4⁺ T cells was caspase independent and did not require granzyme B. Moreover, the impaired killing of macrophages was associated with prolonged effector cell-target cell contact time and higher expression of interferon-γ by CTLs, which induced macrophage production of pro-inflammatory chemokines that recruited monocytes and T cells. Similar results were obtained when macrophages presented other viral antigens, suggestive of a general mechanism for macrophage persistence as antigen-presenting cells that enhance inflammation and adaptive immunity. Inefficient killing of macrophages by CTLs might contribute to chronic inflammation, a hallmark of chronic disease caused by HIV.

Molecular Classification of Primary Immunodeficiencies of T Lymphocytes

Proper regulation of the immune system is required for protection against pathogens and preventing autoimmune disorders. Inborn errors of the immune system due to inherited or de novo germline mutations can lead to the loss of protective immunity, aberrant immune homeostasis, and the development of autoimmune disease, or combinations of these. Forward genetic screens involving clinical material from patients with primary immunodeficiencies (PIDs) can vary in severity from life-threatening disease affecting multiple cell types and organs to relatively mild disease with susceptibility to a limited range of pathogens or mild autoimmune conditions. As central mediators of innate and adaptive immune responses, T cells are critical orchestrators and effectors of the immune response. As such, several PIDs result from loss of or altered T cell function. PID-associated functional defects range from complete absence of T cell development to uncontrolled effector cell activation. Furthermore, the gene products of known PID causal genes are involved in diverse molecular pathways ranging from T cell receptor signaling to regulators of protein glycosylation. Identification of the molecular and biochemical cause of PIDs can not only guide the course of treatment for patients, but also inform our understanding of the basic biology behind T cell function. In this chapter, we review PIDs with known genetic causes that intrinsically affect T cell function with particular focus on perturbations of biochemical pathways.

Characterization of a large UNC13D gene duplication in a patient with familial hemophagocytic lymphohistiocytosis type 3

Familial hemophagocytic lymphohistiocytosis (FHL) type 3 is a life-threatening immune dysregulation syndrome caused by mutations in the UNC13D gene, encoding the munc13-4 protein, which is important for function of cytotoxic lymphocytes. FHL3 accounts for 30-40% of FHL cases, and more than 100 mutations in the UNC13D gene have been described to date. We describe the first case of FHL3 carrying an intragenic duplication of UNC13D, apparently mediated by recombination of Alu elements. NK cell degranulation and munc13-4 protein expression assays are useful for early identification of such mutations, which may be missed by analysis of genomic DNA alone.

Human CTL-based functional analysis shows the reliability of a munc13-4 protein expression assay for FHL3 diagnosis

Familial hemophagocytic lymphohistiocytosis (FHL) is the major form of hereditary hemophagocytic lymphohistiocytosis (HLH); as such, it requires prompt and accurate diagnosis. We previously reported that FHL type 3 (FHL3) can be rapidly screened by detecting munc13-4 expression in platelets using flow cytometry; however, the reliability of the munc13-4 expression assay for FHL3 diagnosis is unclear. Regardless of the type of UNC13D mutation, all reported FHL3 cases examined for the munc13-4 protein showed significantly reduced expression. However, the translated munc13-4 protein of some reportedly disease-causing UNC13D missense variants has not been assessed in terms of expression or function; therefore, their clinical significance remains unclear. The aim of this study was to determine the reliability of a munc13-4 expression assay for screening FHL3. Between 2011 and 2016, 108 HLH patients were screened by this method in our laboratory, and all 15 FHL3 patients were diagnosed accurately. To further elucidate whether munc13-4 expression analysis can reliably identify FHL3 patients harboring missense mutations in UNC13D, we developed an alloantigen-specific cytotoxic T lymphocyte (CTL) line and a CTL line immortalized by Herpesvirus saimiri derived from FHL3 patients. We then performed a comprehensive functional analysis of UNC13D variants. Transient expression of UNC13D complementary DNA constructs in these cell lines enabled us to determine the pathogenicity of the reported UNC13D missense variants according to expression levels of their translated munc13-4 proteins. Taken together with previous findings, the results presented herein show that the munc13-4 protein expression assay is a reliable tool for FHL3 screening.

Macrophage Activation Syndrome

Hemophagocytic lymphohistiocytosis (HLH), or termed macrophage activation syndrome (MAS) when associated with rheumatic disorders, is a frequently fatal complication of infections, rheumatic disorders, and hematopoietic malignancies. Clinically, HLH/MAS is a life-threatening condition that is usually diagnosed among febrile hospitalized patients (children and adults) who commonly present with unremitting fever and a shock-like multiorgan dysfunction scenario. Laboratory studies reveal pancytopenia, elevated liver enzymes, elevated markers of inflammation (ESR, CRP), hyperferritinemia, and features of coagulopathy. In about 60% of cases, excess hemophagocytosis (macrophages/histiocytes engulfing other hematopoietic cell types) is noted on biopsy specimens from the bone marrow, liver, lymph nodes, and other organs. HLH/MAS has been hypothesized to occur when a threshold level of inflammation has been achieved, and genetic and environmental risk factors are believed to contribute to the hyperinflammatory state. A broad variety of infections, from viruses to fungi to bacteria, have been identified as triggers of HLH/MAS, either in isolation or in addition to an underlying inflammatory disease state. Certain infections, particularly by members of the herpesvirus family, are the most notorious triggers of HLH/MAS. Treatment for infection-triggered MAS requires therapy for both the underlying infection and dampening of the hyperactive immune response.

Features, Treatment, and Outcomes of Macrophage Activation Syndrome in Childhood-Onset Systemic Lupus Erythematosus

OBJECTIVE

To describe the features and treatment of macrophage activation syndrome (MAS) in a single-center cohort of patients with childhood-onset systemic lupus erythematosus (SLE), and to compare childhood-onset SLE manifestations and outcomes between those with and those without MAS.

METHODS

We included all patients with childhood-onset SLE followed up at The Hospital for Sick Children from 2002 to 2012, and identified those also diagnosed as having MAS. Demographic, clinical, and laboratory features of MAS and SLE, medication use, hospital and pediatric intensive care unit (PICU) admissions, as well as damage indices and mortality data were extracted from the Lupus database. Student's t-tests and Fisher's exact tests were used to compare continuous and categorical variables, respectively. We calculated incidence rate ratios of hospital and PICU admissions comparing patients with and those without MAS, using Poisson models. Kaplan-Meier survival analysis was used to examine the time to disease damage accrual.

RESULTS

Of the 403 patients with childhood-onset SLE, 38 (9%) had MAS. The majority (68%) had concomitant MAS and SLE diagnoses. Fever was the most common MAS clinical feature. The frequency of renal and central nervous system disease, hospital admissions, the average daily dose of steroids, and time to disease damage were similar between those with and those without MAS. We observed a higher mortality rate among those with MAS (5%) than those without MAS (0.2%) (P = 0.02).

CONCLUSION

MAS was most likely to develop concomitantly with childhood-onset SLE diagnosis. The majority of the MAS patients were successfully treated with corticosteroids with no MAS relapses. Although the numbers were small, there was a higher risk of death associated with MAS compared to SLE without MAS.

Allogeneic hematopoietic stem cell transplantation is associated with cure and durable remission of late-onset primary isolated central nervous system hemophagocytic lymphohistiocytosis

Primary isolated CNS presentation of HLH is exceedingly rare and typically associated with significant morbidity and mortality. We describe an adolescent patient with late-onset, primary isolated CNS HLH and a compound heterozygous PRF1 mutation (c50delT (p.L17 fs); c.1229G>C (p.R410P)), not previously reported with this phenotype. He was successfully treated with allogeneic HSCT following a reduced-intensity conditioning regimen, despite a high pre-HSCT comorbidity index. Two years after transplant, he is alive and in disease remission. While patients with systemic HLH and active CNS disease have relatively poorer outcomes, a high index of suspicion may aid with early diagnosis of primary isolated CNS HLH; prompt treatment with HSCT may be associated with improved cure and durable remission of this rare disease.

Primary hemophagocytic lymphohistiocytosis in adults: the utility of family surveys in a single-center study from China

Background

This study investigated the clinical characteristics of primary hemophagocytic lymphohistiocytosis (HLH) in adults, including immunological markers, pedigree findings, and conditions of allogeneic hematopoietic stem cell transplantation (Allo-HSCT).

Methods

The study included clinical data of 18 adult patients with primary HLH treated in our center from June 2010 to January 2017.

Results

Of these 18 cases, pathogenic variants were found in the following genes: PRF1 (n = 11), UNC13D (n = 5), SH2D1A (n = 2), RAB27a (n = 1), and LYST (n = 2). One patient had pathogenic variants in both PRF1 and UNC13D genes, one patient had pathogenic variants in both LYST and UNC13D genes and another patient had pathogenic variants in both PRF1 and SH2D1A genes. Additionally, 3 of the 18 cases involved homozygous pathogenic variants, while 2 cases involved hemizygous pathogenic variants. The remaining 13 cases involved compound heterozygous pathogenic variants. The natural killer (NK) cell activity test was conducted in all 18 cases where 14(77.8%)patients showed reduction in NK cell activity. Furthermore, this article presents 3 representative results of the pedigree findings from 12 patients who underwent family surveys. The 8 patients who underwent Allo-HSCT had a median survival of 27.2 months, as compared with the median survival of 7 months for the10 patients who did not undergo Allo-HSCT, a significant difference between the two groups of patients (p = 0.006).

Conclusion

PRF1 was one of the most commonly mutated gene in adult patients with primary HLH. Family surveys and immunological markers were important for the HLH diagnosis and the selection of an appropriate donor. Allo-HSCT was an effective therapy for adult primary HLH.

Interleukin-18 diagnostically distinguishes and pathogenically promotes human and murine macrophage activation syndrome

Hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) are life-threatening hyperferritinemic systemic inflammatory disorders. Although profound cytotoxic impairment causes familial HLH (fHLH), the mechanisms driving non-fHLH and MAS are largely unknown. MAS occurs in patients with suspected rheumatic disease, but the mechanistic basis for its distinction is unclear. Recently, a syndrome of recurrent MAS with infantile enterocolitis caused by NLRC4 inflammasome hyperactivity highlighted the potential importance of interleukin-18 (IL-18). We tested this association in hyperferritinemic and autoinflammatory patients and found a dramatic correlation of MAS risk with chronic (sometimes lifelong) elevation of mature IL-18, particularly with IL-18 unbound by IL-18 binding protein, or free IL-18. In a mouse engineered to carry a disease-causing germ line NLRC4^T337S mutation, we observed inflammasome-dependent, chronic IL-18 elevation. Surprisingly, this NLRC4^T337S-induced systemic IL-18 elevation derived entirely from intestinal epithelia. NLRC4^T337S intestines were histologically normal but showed increased epithelial turnover and upregulation of interferon-γ-induced genes. Assessing cellular and tissue expression, classical inflammasome components such as Il1b, Nlrp3, and Mefv predominated in neutrophils, whereas Nlrc4 and Il18 were distinctly epithelial. Demonstrating the importance of free IL-18, Il18 transgenic mice exhibited free IL-18 elevation and more severe experimental MAS. NLRC4^T337S mice, whose free IL-18 levels were normal, did not. Thus, we describe a unique connection between MAS risk and chronic IL-18, identify epithelial inflammasome hyperactivity as a potential source, and demonstrate the pathogenicity of free IL-18. These data suggest an IL-18-driven pathway, complementary to the cytotoxic impairment of fHLH, with potential as a distinguishing biomarker and therapeutic target in MAS.

Epstein-Barr Virus and Hemophagocytic Lymphohistiocytosis

Epstein–Barr virus (EBV) is a ubiquitous virus that infects nearly all people worldwide without serious sequela. However, for patients who have genetic diseases which predispose them to the development of hemophagocytic lymphohistiocytosis (HLH), EBV infection is a life-threatening problem. As a part of a themed collection of articles on EBV infection and human primary immune deficiencies, we will review key concepts related to the understanding and treatment of HLH.

Perforin gene variation influences survival in childhood acute lymphoblastic leukemia

Although a growing body of data links mutations in the perforin gene with increased susceptibility to hematologic malignancies, no studies discuss their influence on the clinical course of such diseases. The present study examines the impact of perforin gene variation on the clinical outcome in acute lymphoblastic leukemia (ALL) patients. The study enrolled 312 children aged 1-18 years, treated for ALL. PRF1 gene variants were analyzed through direct DNA sequencing. Variation in rs885822 was found to be associated with overall survival: patients carrying the GG genotype demonstrated a significantly increased risk of death compared to those carrying the A allele, independently of ALL risk groups (HR 3.13, 95%CI 1.16-7.8, p = 0.014). The effect was even more pronounced in high-risk ALL patients (p = 0.006). On the other hand, the presence of the rs35947132 minor A allele was slightly protective with regard to overall prognosis (p = 0.047). No differences in relapse-free survival were observed with regard to genotypes. The results of the study may imply that perforin gene variation has a role in modifying mortality in childhood ALL.

Non-neoplastic histiocytic and dendritic cell disorders in lymph nodes

Benign and malignant proliferations of histiocytes and dendritic cells may be encountered in lymph nodes. Reactive histiocytic and dendritic cell infiltrates occur in response to diverse stimuli and in addition to causing lymphadenopathy, may be present unexpectedly in lymph nodes excised for other indications. This review summarizes the pathogenesis and histopathological features of the various non-neoplastic histiocytic and dendritic cell infiltrates that can occur in lymph nodes.

Two Brothers with Atypical UNC13D-Related Hemophagocytic Lymphohistiocytosis Characterized by Massive Lung and Brain Involvement

Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal hyperinflammatory condition. Variants in different genes have been associated with the familial forms of the syndrome (FHL), usually presenting within the first 2 years of life. Due to increasing awareness of the signs and symptoms of HLH and a better understanding of the genetic basis of the disease, FHL has been increasingly diagnosed in patients presenting beyond infancy. Here, we report on two brothers with atypical, late-onset HLH in which whole exome sequencing revealed a homozygous pathogenic UNC13D variant. In the first brother, the clinical phenotype was dominated by a massive lung involvement. In the second brother a progressive neurological deterioration was observed. In both cases, the clinical manifestations at symptom onset were misleading, making the diagnosis difficult to achieve. This report expands the spectrum of clinical presentations of FLH3. Moreover, it highlights the importance to warn clinicians to keep a high level of suspicion in patients presenting with fever, cytopenia, splenomegaly of unknown origin, and unresponsiveness to conventional treatment even beyond early childhood. Moreover, this report emphasizes that insidious neurologic symptoms may represent the initial or sole presenting sign of FHL, even in the absence of peripheral signs of activation.

Human perforin gene variation is geographically distributed

Background

Deleterious mutations in PRF1 result in lethal, childhood disease, familial hemophagocytic lymphohistiocytosis type 2 (FHL 2). However, not all mutations in PRF1 are deleterious and result in FHL 2. Currently, these nondeleterious mutations are being investigated in the onset of numerous disorders, such as lymphomas and diabetes. Yet, there is still an overwhelmingly large amount of PRF1 mutations that are not associated with disease.

Methods

We conducted a post hoc analysis of the PRF1 mutations in the coding region using the recently published Exome Aggregation Consortium genomes, Leiden Open Variation Database, NCBI SNP database, and primary literature to better understand PRF1 variation in the human population.

Results

This study catalogs 460 PRF1 mutations in the coding region, and demonstrates PRF1 is more variant then previously predicted. We identify key PRF1 mutations with high allelic frequency and are only found in certain populations. Additionally, we define PRF1SNVs are geographically distributed.

Conclusions

This study concludes with a novel hypothesis that nondeleterious mutation in PRF1, which decreases perforin expression and/or activity, may be an example of selective advantage in the context of environmental stressors prevalent near the equator. Our studies illustrate how perforin deficiency can be protective from injuries resulting in blood–brain barrier (BBB) disruption.

Germline cytotoxic lymphocytes defective mutations in Chinese patients with lymphoma

Certain patients with lymphoma may harbor mutations in perforin 1 (PRF1), unc-13 homolog D (UNC13D), syntaxin 11 (STX11), STXBP2 (syntaxin binding protein 2) or SH2 domain containing 1A (SH2D1A), which causes functional defects of cytotoxic lymphocytes. Data regarding the association between genetic defects and the development of lymphoma in Chinese patients are limited to date. In the present study, 90 patients with lymphoma were analyzed for UNC13D, PRF1, STXBP2, STX11, SH2D1A and X-linked inhibitor of apoptosis. Mutations were observed in 24 (26.67%) patients; 16 patients exhibited mutations in UNC13D, 7 exhibited PRF1 mutations, and 1 exhibited monoallelic mutation in STX11. UNC13D c.2588G>A/p.G863D mutation was detected in 9 patients (10.00%) and in 4/210 controls (1.90%). This mutation was predicted to be pathogenic and it predominantly existed in the Chinese population. These findings suggest that impaired cytotoxic machinery may represent a predisposing factor for the development of lymphoma. Furthermore, these data describe a distinct mutation spectrum in Chinese patients with lymphoma, whereby UNC13D is the most frequently mutated gene. In addition, these findings suggest UNC13D c.2588G>A mutation is a founder mutation in Chinese patients.

Confirmed efficacy of etoposide and dexamethasone in HLH treatment: long-term results of the cooperative HLH-2004 study

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome comprising familial/genetic HLH (FHL) and secondary HLH. In the HLH-94 study, with an estimated 5-year probability of survival (pSu) of 54% (95% confidence interval, 48%-60%), systemic therapy included etoposide, dexamethasone, and, from week 9, cyclosporine A (CSA). Hematopoietic stem cell transplantation (HSCT) was indicated in patients with familial/genetic, relapsing, or severe/persistent disease. In HLH-2004, CSA was instead administered upfront, aiming to reduce pre-HSCT mortality and morbidity. From 2004 to 2011, 369 children aged <18 years fulfilled HLH-2004 inclusion criteria (5 of 8 diagnostic criteria, affected siblings, and/or molecular diagnosis in FHL-causative genes). At median follow-up of 5.2 years, 230 of 369 patients (62%) were alive (5-year pSu, 61%; 56%-67%). Five-year pSu in children with (n = 168) and without (n = 201) family history/genetically verified FHL was 59% (52%-67%) and 64% (57%-71%), respectively (familial occurrence [n = 47], 58% [45%-75%]). Comparing with historical data (HLH-94), using HLH-94 inclusion criteria, pre-HSCT mortality was nonsignificantly reduced from 27% to 19% (P = .064 adjusted for age and sex). Time from start of therapy to HSCT was shorter compared with HLH-94 (P =020 adjusted for age and sex) and reported neurological alterations at HSCT were 22% in HLH-94 and 17% in HLH-2004 (using HLH-94 inclusion criteria). Five-year pSu post-HSCT overall was 66% (verified FHL, 70% [63%-78%]). Additional analyses provided specific suggestions on potential pre-HSCT treatment improvements. HLH-2004 confirms that a majority of patients may be rescued by the etoposide/dexamethasone combination but intensification with CSA upfront, adding corticosteroids to intrathecal therapy, and reduced time to HSCT did not improve outcome significantly.

Substituted arylsulphonamides as inhibitors of perforin-mediated lysis

The structure-activity relationships for a series of arylsulphonamide-based inhibitors of the pore-forming protein perforin have been explored. Perforin is a key component of the human immune response, however inappropriate activity has also been implicated in certain auto-immune and therapy-induced conditions such as allograft rejection and graft versus host disease. Since perforin is expressed exclusively by cells of the immune system, inhibition of this protein would be a highly selective strategy for the immunosuppressive treatment of these disorders. Compounds from this series were demonstrated to be potent inhibitors of the lytic action of both isolated recombinant perforin and perforin secreted by natural killer cells in vitro. Several potent and soluble examples were assessed for in vivo pharmacokinetic properties and found to be suitable for progression to an in vivo model of transplant rejection.

Advances in immunopathogenesis of macrophage activation syndrome during rheumatic inflammatory diseases: toward new therapeutic targets?

INTRODUCTION

Macrophage activation syndrome (MAS) is a severe, hyperinflammatory life-threatening syndrome, generally complicating different rheumatic diseases. Despite the severity of the disease, little is known about the pathogenic mechanisms and, thus, possible targeted therapies in the management of these patients. Areas covered: In this review, we aimed to update the current pathogenic knowledge of MAS, during rheumatic diseases, focusing mainly on immunologic abnormalities and on new possible therapeutic strategies. Expert commentary: The difficult pathogenic scenario of MAS, in which genetic defects, predisposing diseases, and triggers are mixed together with the high mortality rate, make it difficult to manage these patients. Although most efforts have been focused on investigating the disease in children, in recent years, several studies are trying to elucidate the possible pathogenic mechanism in adult MAS patients. In this context, genetic and immunological studies might lead to advances in the knowledge of pathogenic mechanisms and possible new therapeutic targets. In the future, the results of ongoing clinical trials are awaited in order to improve the management and, thus, the survival of these patients.

Hemophagocytic syndrome: primary forms and predisposing conditions

Hemophagocytic lymphohistiocytosis (HLH, also referred to a hemophagocytic syndrome) is a life-threatening condition in which uncontrolled activation of lymphocytes and macrophages, and thus the secretion of large amounts of inflammatory cytokines, leads to a severe hyperinflammatory state. Over the last few decades, researchers have characterized primary forms of HLH caused by genetic defects that impair lymphocytes' cytotoxic machinery. Other genetic causes of HLH not related to impaired cytotoxicity have also recently been identified. Furthermore, the so-called 'acquired' forms of HLH are encountered in the context of severe infections, autoimmune and autoinflammatory diseases, malignancy, and metabolic disorders, and may also be associated with primary immunodeficiencies. This implies that a variety of disease mechanisms can lead to HLH. Today's research seeks to gain a better understanding of the various pathogenetic and environmental factors that converge to induce HLH.

Regulation of perforin activation and pre-synaptic toxicity through C-terminal glycosylation

Perforin is a highly cytotoxic pore-forming protein essential for immune surveillance by cytotoxic lymphocytes. Prior to delivery to target cells by exocytosis, perforin is stored in acidic secretory granules where it remains functionally inert. However, how cytotoxic lymphocytes remain protected from their own perforin prior to its export to secretory granules, particularly in the Ca²⁺-rich endoplasmic reticulum, remains unknown. Here, we show that N-linked glycosylation of the perforin C-terminus at Asn549 within the endoplasmic reticulum inhibits oligomerisation of perforin monomers and thus protects the host cell from premature pore formation. Subsequent removal of this glycan occurs through proteolytic processing of the C-terminus within secretory granules and is imperative for perforin activation prior to secretion. Despite evolutionary conservation of the C-terminus, we found that processing is carried out by multiple proteases, which we attribute to the unstructured and exposed nature of the region. In sum, our studies reveal a post-translational regulatory mechanism essential for maintaining perforin in an inactive state until its secretion from the inhibitory acidic environment of the secretory granule.

An Overview of Hemophagocytic Lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening syndrome characterized by a dysregulated hyperinflammatory response associated with aberrant activation of lymphocytes and macrophages that results in hypercytokinemia. It is classically divided into two types: (1) primary or familial HLH and (2) secondary HLH. Familial HLH is generally an autosomal recessive condition, whereas secondary HLH is usually associated with infectious diseases, autoinflammatory and autoimmune diseases (where it is more commonly known as macrophage activation syndrome), malignancy, immunosuppression, hematopoietic stem cell transplantation, organ transplantation, HIV infection, and metabolic diseases. Although its clinical presentation is often similar to bacterial sepsis or systemic inflammatory response syndrome, HLH can be life-threatening. As such, it is imperative to recognize and diagnose HLH in a timely manner to optimize care. [Pediatr Ann. 2017;46(8):e309-e313.].

The cytotoxic T lymphocyte immune synapse at a glance

The immune synapse provides an important structure for communication with immune cells. Studies on immune synapses formed by cytotoxic T lymphocytes (CTLs) highlight the dynamic changes and specialised mechanisms required to facilitate focal signalling and polarised secretion in immune cells. In this Cell Science at a Glance article and the accompanying poster, we illustrate the different steps that reveal the specialised mechanisms used to focus secretion at the CTL immune synapse and allow CTLs to be such efficient and precise serial killers.

Finding a Balance between Protection and Pathology: The Dual Role of Perforin in Human Disease

Perforin is critical for controlling viral infection and tumor surveillance. Clinically, mutations in perforin are viewed as unfavorable, as lack of this pore-forming protein results in lethal, childhood disease, familial hemophagocytic lymphohistiocytosis type 2 (FHL 2). However, many mutations in the coding region of PRF1 are not yet associated with disease. Animal models of viral-associated blood–brain barrier (BBB) disruption and experimental cerebral malaria (ECM) have identified perforin as critical for inducing pathologic central nervous system CNS vascular permeability. This review focuses on the role of perforin in both protecting and promoting human disease. It concludes with a novel hypothesis that diversity observed in the PRF1 gene may be an example of selective advantage that protects an individual from perforin-mediated pathology, such as BBB disruption.

Disrupted apical exocytosis of cargo vesicles causes enteropathy in FHL5 patients with Munc18-2 mutations

Familial hemophagocytic lymphohistiocytosis 5 (FHL5) is an autosomal recessive disease caused by mutations in STXBP2, coding for Munc18-2, which is required for SNARE-mediated membrane fusion. FHL5 causes hematologic and gastrointestinal symptoms characterized by chronic enteropathy that is reminiscent of microvillus inclusion disease (MVID). However, the molecular pathophysiology of FHL5-associated diarrhea is poorly understood. Five FHL5 patients, including four previously unreported patients, were studied. Morphology of duodenal sections was analyzed by electron and fluorescence microscopy. Small intestinal enterocytes and organoid-derived monolayers displayed the subcellular characteristics of MVID. For the analyses of Munc18-2-dependent SNARE-protein interactions, a Munc18-2 CaCo2-KO model cell line was generated by applying CRISPR/Cas9 technology. Munc18-2 is required for Slp4a/Stx3 interaction in fusion of cargo vesicles with the apical plasma membrane. Cargo trafficking was investigated in patient biopsies, patient-derived organoids, and the genome-edited model cell line. Loss of Munc18-2 selectively disrupts trafficking of certain apical brush-border proteins (NHE3 and GLUT5), while transport of DPPIV remained unaffected. Here, we describe the molecular mechanism how the loss of function of Munc18-2 leads to cargo-selective mislocalization of brush-border components and a subapical accumulation of cargo vesicles, as it is known from the loss of polarity phenotype in MVID.