Perforin gene defects in familial hemophagocytic lymphohistiocytosis

Patients and mice with deficiency in the SNARE protein SYNTAXIN-11 have a secondary B cell defect

SYNTAXIN-11 (STX11) is a SNARE protein that mediates the fusion of cytotoxic granules with the plasma membrane at the immunological synapses of CD8 T or NK cells. Autosomal recessive inheritance of deleterious STX11 variants impairs cytotoxic granule exocytosis, causing familial hemophagocytic lymphohistiocytosis type 4 (FHL-4). In several FHL-4 patients, we also observed hypogammaglobulinemia, elevated frequencies of naive B cells, and increased double-negative DN2:DN1 B cell ratios, indicating a hitherto unrecognized role of STX11 in humoral immunity. Detailed analysis of Stx11-deficient mice revealed impaired CD4 T cell help for B cells, associated with disrupted germinal center formation, reduced isotype class switching, and low antibody avidity. Mechanistically, Stx11-/- CD4 T cells exhibit impaired membrane fusion leading to reduced CD107a and CD40L surface mobilization and diminished IL-2 and IL-10 secretion. Our findings highlight a critical role of STX11 in SNARE-mediated membrane trafficking and vesicle exocytosis in CD4 T cells, important for successful CD4 T cell-B cell interactions. Deficiency in STX11 impairs CD4 T cell-dependent B cell differentiation and humoral responses.

Hemophagocytic Lymphohistiocytosis in a Remote Kidney Transplant Recipient Triggered by HSV Infection With Complete Recovery: An Educational Case Report

Rationale

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening disease characterized by excessive immune activation. It is more commonly seen in children but increasingly recognized in adults. Primary HLH relies on a genetic predisposition, whereas secondary HLH develops in the context of infections, malignancies, or autoimmune diseases. Hemophagocytic lymphohistiocytosis has been rarely described in patients on immunosuppressive therapy after kidney transplant. Here, we describe a case of HLH in a patient with a remote history of kidney transplant, triggered by a viral infection.

Presenting Concerns

A 45-year-old female, with a kidney transplant in 2009 for IgA nephropathy, presented with fever, vomiting, and back pain of 1-week duration. She was on triple immunosuppression consisting of daily doses of prednisone 5 mg, azathioprine 100 mg, and tacrolimus extended release 1 mg, and a baseline creatinine of 130 µmol/L.

Diagnosis

Initial investigations showed anemia, leukopenia, elevated serum creatinine, transaminitis, and markedly increased ferritin of 67 600 µg/L which prompted a bone marrow biopsy to rule out HLH. The bone marrow showed an increased proportion of CD68+ cells (macrophages) with more than 5 in 1000 hemophagocytic macrophages. Her soluble IL-2 receptor (CD25) level was 3406 pg/mL (606-2299 pg/mL) which was mildly elevated. She fulfilled 4 of the 8 criteria for HLH and with an H score was 223 which suggested a diagnosis of HLH with 96.9% probability. An extensive secondary workup for possible triggers for HLH led to a swab from genital ulcers that was positive for herpes simplex virus (HSV) type 2. The polymerase chain reaction (PCR) in the blood for HSV type 2 was also positive.

Interventions

Given the diagnosis of HSV type 2 as the putative trigger for HLH, she was started on parenteral acyclovir for 2 weeks followed by oral valacyclovir for 2 more weeks. In the context of infection, the azathioprine was stopped while low-dose steroid and tacrolimus were continued.

Outcomes

With the initiation of treatment for HSV infection, leukopenia, creatinine, and transaminases improved along with ferritin levels. At her 6-month follow-up, her blood counts and liver enzymes had normalized, and ferritin was 566 µg/L.

Teaching points

Hemophagocytic lymphohistiocytosis is a rare disease in kidney transplant recipients with a high mortality rate. It can occur even in remote kidney transplant recipients so a high degree of suspicion is necessary to lead to a prompt diagnosis. Infections are common triggers for secondary HLH. Early identification and treatment of the triggering infection may improve outcomes.

Genetic background of primary and familial HLH in Qatar: registry data and population study

Background

Familial hemophagocytic lymphohistiocytosis (FHLH) is an inherited life-threatening disease. Five types are identified, with the addition of congenital immunodeficiency syndromes in which HLH is a typical manifestation. The literature on this disease is very scarce in the Middle East, with only a few scattered reports.

Methods

We report detailed demographic, clinical, and genomic data from 28 patients diagnosed with primary and familial HLH over the last decade in Qatar. An evaluation was performed of allele frequencies of deleterious variants from 12 primary and familial HLH causative genes on the Qatar Genome Programme (QGP) cohort of 14,669 Qatari individuals.

Results

The genetic diagnosis was obtained in 15 patients, and four novel mutations in Perforin 1 (PRF1), UNC13D, LYST, and RAB27A genes were found. We identified 22,945 low/high/moderate/modifier impact variants significantly enriched in the QGP in those 12 genes. The variants rs1271079313 in PRF1 and rs753966933 in RAB27A found in our patient cohort were significantly more prevalent in the QGP compared to the Genome Aggregation Database (gnomAD) database, with a high carrier frequency in the Qatari population.

Conclusions

We established the first primary and familial HLH Registry in the Gulf Region and identified novel possibly pathogenic variants present at higher frequency in the Qatari population, which could be used for screening purposes. Raising awareness about primary and familial HLH and implementing screening activities in the Qatari highly inbred population could stem into more comprehensive premarital and prenatal evaluations and faster diagnosis.

New discoveries in the genetics and genomics of systemic juvenile idiopathic arthritis

INTRODUCTION

Systemic juvenile idiopathic arthritis (sJIA) is a severe inflammatory condition with onset in childhood. It is sporadic, but elements of its stereotypical innate immune responses are likely genetically encoded by both common variants with small effect sizes and rare variants with larger effects.

AREAS COVERED

Genomic investigations have defined the unique genetic architecture of sJIA. Identification of the class II HLA locus as the strongest sJIA risk factor for the first time brought attention to T lymphocytes and adaptive immune mechanisms in sJIA. The importance of the human leukocyte antigen (HLA) locus was reinforced by recognition that HLA-DRB1*15 alleles are strongly associated with development of drug reactions and sJIA-associated lung disease (sJIA-LD). At the IL1RN locus, genetic variation relates to both risk of sJIA and may also predict non-response to anakinra. Finally, rare genetic variants may have critical roles in disease complications, such as homozygous LACC1 mutations in families with an sJIA-like illness, and hemophagocytic lymphohistiocytosis (HLH) gene variants in some children with macrophage activation syndrome (MAS).

EXPERT OPINION

Genetic and genomic analysis of sJIA holds great promise for both basic discovery of the course and complications of sJIA, and may help guide personalized medicine and therapeutic decision-making.

Heterogeneity of macrophage activation syndrome and treatment progression

Macrophage activation syndrome (MAS) is a rare complication of autoimmune inflammatory rheumatic diseases (AIIRD) characterized by a progressive and life-threatening condition with features including cytokine storm and hemophagocytosis. Predisposing factors are typically associated with microbial infections, genetic factors (distinct from typical genetically related hemophagocytic lymphohistiocytosis (HLH)), and inappropriate immune system overactivation. Clinical features include unremitting fever, generalized rash, hepatosplenomegaly, lymphadenopathy, anemia, worsening liver function, and neurological involvement. MAS can occur in various AIIRDs, including but not limited to systemic juvenile idiopathic arthritis (sJIA), adult-onset Still's disease (AOSD), systemic lupus erythematosus (SLE), Kawasaki disease (KD), juvenile dermatomyositis (JDM), rheumatoid arthritis (RA), and Sjögren's syndrome (SS), etc. Although progress has been made in understanding the pathogenesis and treatment of MAS, it is important to recognize the differences between different diseases and the various treatment options available. This article summarizes the cell types and cytokines involved in MAS-related diseases, the heterogeneity, and treatment options, while also comparing it to genetically related HLH.

Dengue-Associated Hemophagocytic Lymphohistiocytosis: A Narrative Review of Its Identification and Treatment

Dengue's lack of specific treatments beyond supportive care prompts a focus on uncovering additional pathophysiological factors. Dengue-associated hemophagocytic lymphohistiocytosis (HLH), characterized by dysregulated macrophage activation and cytokine storm, remains underexplored despite its potential to worsen disease severity and mortality. While rare, dengue-associated HLH disproportionately affects severe cases, significantly impacting mortality rates. To mitigate high mortality, early identification and familiarity with dengue-associated HLH are imperative for prompt treatment by clinicians. This narrative review therefore aims to examine the current clinical and therapeutic knowledge on dengue-associated HLH, and act as a resource for clinicians to improve their management of HLH associated with severe dengue. Dengue-associated HLH should be considered for all cases of severe dengue and may be suspected based on the presence of prolonged or recurrent fever for >7 days, or anemia without intravascular hemolysis or massive bleeding. Diagnosis relies on fulfilling at least five of the eight HLH-2004 criteria. Treatment predominantly involves short courses (3-4 days) of high-dose steroids (e.g., dexamethasone 10 mg/m2), with additional therapies considered in more severe presentations. Notably, outcomes can be favorable with steroid therapy alone.

Hemophagocytic lymphohistiocytosis and macrophage activation syndrome: two rare sides of the same devastating coin

Hemophagocytic lymphohistiocytosis (HLH) is a rare genetic hyperinflammatory syndrome that occurs early in life. Macrophage activation syndrome (MAS) usually refers to a secondary form of HLH associated with autoimmunity, although there are other causes of secondary HLH, such as infections and malignancy. In this article, we reviewed the concepts, epidemiology, clinical and laboratory features, diagnosis, differential diagnosis, prognosis, and treatment of HLH and MAS. We also reviewed the presence of MAS in the most common autoimmune diseases that affect children. Both are severe diseases that require prompt diagnosis and treatment to avoid morbidity and mortality.

Sequential haplo-identical conditioning transplant regimen for pediatric patients with relapsed or refractory hemophagocytic lymphohistiocytosis

Allogeneic hematopoietic stem cell transplantation (HSCT) currently stands as the sole remedy for individuals afflicted with hemophagocytic lymphohistiocytosis (HLH). In this study, we retrospectively evaluated how pediatric patients with relapsed or refractory (R/R) HLH responded to our institution's cocktail conditioning regimen. The disease was diagnosed according to criteria applicable to patients with familial/genetic, relapsing, or severe/persistent HLH. All donors were HLA haplo-identical family donors. In our cohort, sixty-five patients (P-HLH), including 28 with familial/genetic HLH, 36 with secondary HLH, and 1 with an unknown cause, underwent haplo-identical family donor HSCT. The conditioning regimen consisted of intravenous administration of etoposide (VP-16), busulfan, fludarabine, rabbit anti-human thymocyte globulin (r-ATG), and cyclophosphamide (Cy). Tacrolimus and mycophenolate mofetil were used for graft-versus-host disease (GvHD) prevention. We observed that the median time for neutrophil recovery was 11 days (range, 8-24), and for platelet counts to exceed 20 × 109/L, it was 14 days (range, 7-130). There were 5 patients (7.7%) who experienced grades III to IV acute GvHD, and 6 patients (9.2%) developed extensive chronic GvHD. The estimated 3- and 5-year overall survival rates were 78.1% (95% CI, 65.8-84.6%) and 74.9% (95% CI, 61.2-84.4%), respectively. The estimated 3- and 5-year event-free survival rates were 73.5% (95% CI, 60.8-82.6%) and 70.3% (95% CI, 56.4-80.5%), respectively. Our findings demonstrate that our innovative conditioning regimen is both effective and safe, offering valuable insights for healthcare professionals evaluating the merits of existing therapies.

Hemophagocytic Lymphohistiocytosis (HLH) Flare Following the COVID-19 Vaccine: A Case Report

Hemophagocytic lymphohistiocytosis (HLH) is a rare hyperinflammatory state that leads to overactivation of the immune system due to underlying disease. It can lead to multiorgan failure and death if not treated properly. HLH after vaccination is rare but has been reported in a few cases. Here, we present a case of a patient who developed HLH after she received the COVID-19 vaccine. Workup was done to find the underlying cause of her symptoms. However, as all investigations yielded negative results, the close temporal association with the COVID-19 vaccine suggested that the vaccine might have been the causative factor. She was treated appropriately with steroids and discharged with follow-up appointments. The exact pathogenesis of HLH caused by COVID vaccine is unknown, but it is likely related to the inflammatory response caused by the vaccine in the body. The treatment of HLH depends on the treatment of underlying conditions causing the HLH. Very few cases have been reported in the literature regarding HLH caused by COVID vaccine. Immediate recognition and treatment are imperative for improved prognosis and improved chances of survival.

Hemophagocytic lymphohistiocytosis: A disorder of T cell activation, immune regulation, and distinctive immunopathology

Hemophagocytic lymphohistiocytosis (HLH) is a disorder that has been recognized since the middle of the last century. In recent decades, increasing understanding of the genetic roots and pathophysiology of HLH has led to improved diagnosis and treatment of this once universally fatal disorder. HLH is best conceptualized as a maladaptive state of excessive T cell activation driving life-threatening myeloid cell activation, largely via interferon-gamma (IFN-γ). In familial forms of HLH (F-HLH), inherited defects of lymphocyte cytotoxic biology underlie excessive T cell activation, demonstrating the importance of the perforin/granzyme pathway as a negative feedback loop limiting acute T cell activation in response to environmental factors. HLH occurring in other contexts and without apparent inherited genetic predisposition remains poorly understood, though it may share some downstream aspects of pathophysiology including excessive IFN-γ action and activation of innate immune effectors. Iatrogenic forms of HLH occurring after immune-activating therapies for cancer are providing new insights into the potential toxicities of inadequately controlled T cell activation. Diagnosing HLH increasingly relies on context-specific measures of T cell activation, IFN-γ activity, and inflammation. Treatment of HLH largely relies on cytotoxic chemotherapy, though targeted therapies against T cells, IFN-γ, and other cytokines are increasingly utilized.

Guardians of immunity: NK cell-mediated defense in COVID-19 and post-COVID scenarios

The COVID-19 pandemic has left a lasting impact on global health, challenging communities, healthcare systems, and researchers worldwide. As we navigate this unprecedented crisis, this paper embarks on a multifaceted exploration of the pivotal role played by natural killer (NK) cells in the context of COVID-19. A significant portion of this paper is devoted to dissecting the nuanced role that NK cells assume in the context of COVID-19. From the initial acute infection to post-recovery immunity, NK cells emerge as critical players. We scrutinize the activation and dysregulation of NK cells during SARS-CoV-2 infection, shedding light on their potential contribution to disease severity. Moreover, we explore the fascinating landscape of post-COVID immunity, where NK cells are known to interact with adaptive immune responses, providing a foundation for long-term protection. In light of their central role, we investigate therapeutic strategies targeting NK cells in COVID-19 management, presenting an overview of current research efforts and their promise in mitigating disease progression. Lastly, we draw attention to research gaps, emphasizing the need for further investigation into NK cell dynamics during COVID-19. These gaps represent opportunities for advancing our understanding of NK cell biology and, by extension, enhancing our strategies for combating this global health crisis. This comprehensive exploration not only highlights the intricate interplay between NK cells and the COVID-19 pandemic but also underscores the importance of these innate immune warriors in shaping both the acute response and long-term immunity, ultimately contributing to the broader discourse surrounding the pandemic's pathophysiology and therapeutic approaches.

Human genetic errors of immunity illuminate an adaptive arsenal model of rapid defenses

New discoveries in the field of human monogenic immune diseases highlight critical genes and pathways governing immune responses. Here, I describe how the ~500 currently defined human inborn errors of immunity help shape what I propose is an 'adaptive arsenal model of rapid defenses', emphasizing the set of immunological defenses poised for rapid responses in the natural environment. This arsenal blurs the lines between innate and adaptive immunity and is established through molecular relays between cell types, often traversing from sensors (pathogen detection) to intermediates to executioners (pathogen clearance) via soluble factors. Predictions and missing information based on the adaptive arsenal model are discussed, as are emergent and outstanding questions fundamental to advances in the field.

Antigen-specific age-related memory CD8 T cells induce and track Alzheimer's-like neurodegeneration

Cerebral (Aβ) plaque and (pTau) tangle deposition are hallmarks of Alzheimer's disease (AD), yet are insufficient to confer complete AD-like neurodegeneration experimentally. Factors acting upstream of Aβ/pTau in AD remain unknown, but their identification could enable earlier diagnosis and more effective treatments. T cell abnormalities are emerging AD hallmarks, and CD8 T cells were recently found to mediate neurodegeneration downstream of tangle deposition in hereditary neurodegeneration models. The precise impact of T cells downstream of Aβ/fibrillar pTau, however, appears to vary depending on the animal model used. Our prior work suggested that antigen-specific memory CD8 T (" hi T") cells act upstream of Aβ/pTau after brain injury. Here we examine whether hi T cells influence sporadic AD-like pathophysiology upstream of Aβ/pTau. Examining neuropathology, gene expression, and behavior in our hi T mouse model we show that CD8 T cells induce plaque and tangle-like deposition, modulate AD-related genes, and ultimately result in progressive neurodegeneration with both gross and fine features of sporadic human AD. T cells required Perforin to initiate this pathophysiology, and IFNγ for most gene expression changes and progression to more widespread neurodegenerative disease. Analogous antigen-specific memory CD8 T cells were significantly elevated in the brains of human AD patients, and their loss from blood corresponded to sporadic AD and related cognitive decline better than plasma pTau-217, a promising AD biomarker candidate. Our work is the first to identify an age-related factor acting upstream of Aβ/pTau to initiate AD-like pathophysiology, the mechanisms promoting its pathogenicity, and its relevance to human sporadic AD.

Significance Statement

This study changes our view of Alzheimer's Disease (AD) initiation and progression. Mutations promoting cerebral beta-amyloid (Aβ) deposition guarantee rare genetic forms of AD. Thus, the prevailing hypothesis has been that Aβ is central to initiation and progression of all AD, despite contrary animal and patient evidence. We show that age-related T cells generate neurodegeneration with compelling features of AD in mice, with distinct T cell functions required for pathological initiation and neurodegenerative progression. Knowledge from these mice was applied to successfully predict previously unknown features of human AD and generate novel tools for its clinical management.

Hemophagocytic Lymphohistiocytosis in Adolescents and Young Adults: Genetic Predisposition and Secondary Disease

Hemophagocytic lymphohistiocytosis (HLH) is a disorder of impaired immune regulation resulting in hyperinflammation that is ultimately fatal if not treated. HLH is categorized into familial disease, caused by genetic mutations affecting the function of cytotoxic T lymphocytes and natural killer cells, and secondary disease, triggered by infections, malignancies, rheumatologic disorders, or immune deficiency. Adolescent and young adults with HLH represent a unique population with specific diagnostic challenges. Here we review the diagnostic criteria, possible etiologies, pathophysiology, and management of HLH with focus on the adolescent population.

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.

Inflamed-HLH, MAS, or something else?

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of excessive and maladaptive inflammation. Primary HLH is most frequently encountered in young children, and, without timely recognition and therapy, can lead to multiorgan failure and death. It is most often diagnosed using the HLH-2004 criteria and by identifying pathological mutations. However, the HLH-2004 criteria are not specific for HLH, and patients can easily fulfill these diagnostic criteria in other proinflammatory states in which HLH-therapy would not be indicated, including hematologic malignancies, infections, and rheumatologic disease. Therefore, great care must be taken to ensure that the specific disease associated with features of HLH is accurately recognized, as consequences of improper treatment can be catastrophic. We propose a diagnostic pathway for patients for whom HLH is on the differential (visual abstract). Importantly, in situations in which the initial diagnostic workup is equivocal or unrevealing, reevaluation for occult malignancy, infection, or rheumatologic disease would be prudent, as occult presentations may be missed on primary evaluation. Temporizing medications can be used in critically ill patients while awaiting secondary evaluation. By using this framework, clinicians will be able to more reliably discern primary HLH from other pro-inflammatory states and thus provide timely, appropriate disease-specific therapy.

The opposing effects of two gene defects in STX11 and SLP76 on the disease in a patient with an inborn error of immunity

BACKGROUND

Inborn errors of immunity are mostly monogenic. However, disease phenotype and outcome may be modified by the coexistence of a second gene defect.

OBJECTIVE

We sought to identify the genetic basis of the disease in a patient who experienced bleeding episodes, pancytopenia, hepatosplenomegaly, and recurrent pneumonia that resulted in death.

METHODS

Genetic analysis was done using next-generation sequencing. Protein expression and phosphorylation were determined by immunoblotting. T-cell proliferation and F-actin levels were studied by flow cytometry.

RESULTS

The patient harbored 2 homozygous deletions in STX11 (c.369_370del, c.374_376del; p.V124fs60∗) previously associated with familial hemophagocytic lymphohistiocytosis and a novel homozygous missense variant in SLP76 (c.767C>T; p.T256I) that resulted in an approximately 85% decrease in SLP76 levels and absent T-cell proliferation. The patient's heterozygous family members showed an approximately 50% decrease in SLP76 levels but normal immune function. SLP76-deficient J14 Jurkat cells did not express SLP76 and had decreased extracellular signal-regulated kinase signaling, basal F-actin levels, and polymerization following T-cell receptor stimulation. Reconstitution of J14 cells with T256I mutant SLP76 resulted in low protein expression and abnormal extracellular signal-regulated kinase phosphorylation and F-actin polymerization after T-cell receptor activation compared with normal expression and J14 function when wild-type SLP76 was introduced.

CONCLUSIONS

The hypomorphic mutation in SLP76 tones down the hyperinflammation due to STX11 deletion, resulting in a combined immunodeficiency that overshadows the hemophagocytic lymphohistiocytosis phenotype. To our knowledge, this study represents the first report of the opposing effects of 2 gene defects on the disease in a patient with an inborn error of immunity.

Perforin and granzyme A release as novel tool to measure NK cell activation in chickens

Natural killer (NK) cells are cytotoxic lymphocytes that are present in the circulation but also in many organs including spleen and gut, where they play an important role in the defense against infections. Interaction of NK cells with target cells leads to degranulation, which results in the release of perforin and granzymes in the direct vicinity of the target cell. Chicken NK cells have many characteristics similar to their mammalian counterparts and based on similarities with studies on human NK cells, surface expression of CD107 was always presumed to correlate with granule release. However, proof of this degranulation or in fact the actual presence of perforin (PFN) and granzyme A (GrA) in chicken NK cells and their release upon activation is lacking. Therefore, the purpose of the present study was to determine the presence of perforin and granzyme A in primary chicken NK cells and to measure their release upon degranulation, as an additional tool to study the function of chicken NK cells. Using human specific antibodies against PFN and GrA in fluorescent and confocal microscopy resulted in staining in chicken NK cells. The presence of PFN and GrA was also confirmed by Western blot analyses and its gene expression by PCR. Stimulation of NK cells with the pectin SPE6 followed by flow cytometry resulted in reduced levels of intracellular PFN and GrA, suggesting release of PFN and GrA. Expression of PFN and GrA reversely correlated with increased surface expression of the lysosomal marker CD107. Finally it was shown that the supernatant of activated NK cells, containing the NK cell granule content including PFN and GrA, was able to kill Escherichia coli. This study correlates PFN and GrA release to activation of chicken NK cells and establishes an additional tool to study activity of cytotoxic lymphocytes in chickens.

Complementary HLH susceptibility factors converge on CD8 T-cell hyperactivation

Hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) are life-threatening hyperinflammatory syndromes. Familial HLH is caused by genetic impairment of granule-mediated cytotoxicity (eg, perforin deficiency). MAS is linked to excess activity of the inflammasome-activated cytokine interleukin-18 (IL-18). Though individually tolerated, mice with dual susceptibility (Prf1⁻/⁻Il18tg; DS) succumb to spontaneous, lethal hyperinflammation. We hypothesized that understanding how these susceptibility factors synergize would uncover key pathomechanisms in the activation, function, and persistence of hyperactivated CD8 T cells. In IL-18 transgenic (Il18tg) mice, IL-18 effects on CD8 T cells drove MAS after a viral (lymphocytic choriomeningitis virus), but not innate (toll like receptor 9), trigger. In vitro, CD8 T cells also required T-cell receptor (TCR) stimulation to fully respond to IL-18. IL-18 induced but perforin deficiency impaired immunoregulatory restimulation-induced cell death (RICD). Paralleling hyperinflammation, DS mice displayed massive postthymic oligoclonal CD8 T-cell hyperactivation in their spleens, livers, and bone marrow as early as 3 weeks. These cells increased proliferation and interferon gamma production, which contrasted with increased expression of receptors and transcription factors associated with exhaustion. Broad-spectrum antibiotics and antiretrovirals failed to ameliorate the disease. Attempting to genetically "fix" TCR antigen-specificity instead demonstrated the persistence of spontaneous HLH and hyperactivation, chiefly on T cells that had evaded TCR fixation. Thus, drivers of HLH may preferentially act on CD8 T cells: IL-18 amplifies activation and demand for RICD, whereas perforin supplies critical immunoregulation. Together, these factors promote a terminal CD8 T-cell activation state, combining features of exhaustion and effector function. Therefore, susceptibility to hyperinflammation may converge on a unique, unrelenting, and antigen-dependent state of CD8 T-cell hyperactivation.

CD8+ T-cells target the Crimean-Congo haemorrhagic fever virus Gc protein to control the infection in wild-type mice

BACKGROUND

Crimean-Congo haemorrhagic fever (CCHF) is a serious viral hemorrhagic fever caused by the CCHF virus (CCHFV). Spread by the bites of infected ticks or handling of viremic livestock, human disease is characterized by a non-specific febrile illness that can rapidly progress to fatal hemorrhagic disease. No vaccines or antivirals are available. Case fatality rates can vary but can be higher than 30%, although sub-clinical infections are often unrecognized and unreported. Yet, while most humans infected with CCHFV will survive the infection, often with little-to-no symptoms, the host responses that control the infection are unknown.

METHODS

Here we investigated the role of cellular immunity in control of CCHFV infection in an immunocompetent mouse model.

FINDINGS

We found that CD8+ T-cells are crucial for efficient control of the acute infection and rapidly acquired CCHFV-specific antiviral effector functions such as production of antiviral cytokines and degranulating in response to CCHFV peptides. We further identified the minimal CD8+ T-cell epitopes in the viral Gc proteins and that infection of mice lacking IFNγ resulted in worsened disease and higher viral loads.

INTERPRETATION

Together our data suggest that CD8+ T-cells are important for control of acute CCHFV infection likely through production of antiviral cytokines.

FUNDING

This work was supported by the Intramural Research Program of the NIH.

Hemophagocytic lymphohistiocytosis with a hemizygous PRF1 c.674G>A mutation

Hemophagocytic lymphohistiocytosis(HLH) is a rare highly-fatal disease presenting with fever, hepatosplenomegaly, and pancytopenia and has a poor prognosis. Homozygous or semi-zygous or complex heterozygous variants can cause familial HLH and heterozygous carriers are frequently seen in secondary HLH. A 42-year-old male patient was admitted to the hospital for persistent fever, fatigue, and splenomegaly. Investigations revealed hypertriglyceridemia, hyperlactatemia dehydrogenaseemia, hyperferritinemia, and elevated levels of soluble cluster of differentiation 25. We found a heterozygous mutation of PRF1: c.674G>A (p.R225Q) through next-generation sequencing technology of hemophagocytic-lymphohistiocytosis-related genes. After a brief remission with dexamethasone and etoposide-based therapy, the disease relapsed quickly, and an allogeneic hematopoietic stem cell transplant was performed to achieve complete remission. To date, the patient's condition was in complete remission. Our study detected a rare missense mutation in the PRF1 gene in a patient with HLH disease and the c.674G>A mutation may be rated as a possible pathogenic variant.

Hemophagocytic lymphohistiocytosis: A scourge for the physician and bane to the bone marrow

Background

Hemophagocytic lymphohistiocytosis (HLH) is a condition characterized by hyperinflammation. It can occur due to primary genetic defect or secondary to other etiology such as infection and rheumatological conditions. Clinical features include fever, cytopenia, organomegaly and several laboratory abnormalities. It can be a life-threatening condition secondary to worsening cytopenia and multiorgan dysfunction.

Aims and Objectives

To study the clinical profile of HLH in a tertiary care hospital in Southern India.

Materials and Methods

Our study has reviewed nine cases of HLH among adult patients presented over 5 years (2017-2022).

Results

The majority of our cases were secondary to infection and had a hospital stay over two weeks and with a good response to steroid and immunomodulators.

Conclusion

We would like to stress upon the importance of awareness of such a condition so that there can be early suspicion and workup including bone marrow examination, enabling early initiating of specific therapy for this fatal condition.

First case of very late-onset FHL2 in Spain with two variants in the PRF1 gene

Hemophagocytic lymphohistiocytosis (HLH) is a rare but fatal disorder characterized by the proliferation and infiltration of macrophages and hyperactivated T lymphocytes that escape from the physiological control pathways and favour the existence of an environment of excessive inflammation and tissue destruction. HLH has been classified into two types: a primary or familial autosomal recessive form, caused by mutations in genes encoding proteins involved in the granule-dependent cytotoxic pathway (familial hemophagocytic lymphohistiocytosis [FHL] types 1-5); and other secondary or acquired form, generally associated with infections, malignancy, autoimmune diseases, metabolic disorders or primary immunodeficiencies. Since the first familial hemophagocytic lymphohistiocytosis-2 (FHL2) causative mutation in the PRF1 gene was described in 1999, more than 200 mutations have been identified to date. Here, we report the first case of very late-onset FHL2 in a Spanish 72-year-old female with splenomegaly, hypertriglyceridemia, hypofibrinogenemia, pancytopenia and marrow hemophagocytosis harbouring in heterozygosity two PRF1 variants proposed as causative in this study. The heterozygous mutation c.445G>A (p.Gly149Ser) identified in the exon 2 results in a missense mutation previously described as a probable pathogenic variant associated with the development of FHL2. Affecting the same exon, c.272C>T (p.Ala91Val) is the most prevalent variant of this gene. Although it was initially classified as benign, recent studies support its potential pathogenic role, considering it a variant of uncertain significance associated with a risk of developing FHL2. The genetic confirmation of FHL made possible an adequate counselling to the patient and direct relatives and provided important information for her control and follow-up.

Surface plasmon resonance and microscale thermophoresis approaches for determining the affinity of perforin for calcium ions

Perforin is a pore-forming protein that plays a crucial role in the immune system by clearing virus-infected or tumor cells. It is released from cytotoxic granules of immune cells and forms pores in targeted lipid membranes to deliver apoptosis-inducing granzymes. It is a very cytotoxic protein and is therefore adapted not to act in producing cells. Its activity is regulated by the requirement for calcium ions for optimal activity. However, the exact affinity of perforin for calcium ions has not yet been determined. We conducted a molecular dynamics simulation in the absence or presence of calcium ions that showed that binding of at least three calcium ions is required for stable perforin binding to the lipid membrane. Biophysical studies using surface plasmon resonance and microscale thermophoresis were then performed to estimate the binding affinities of native human and recombinant mouse perforin for calcium ions. Both approaches showed that mouse perforin has a several fold higher affinity for calcium ions than that of human perforin. This was attributed to a particular residue, tryptophan at position 488 in mouse perforin, which is replaced by arginine in human perforin. This represents an additional mechanism to control the activity of human perforin.

[Clinical characteristics of primary hemophagocytic lymphohistiocytosis associated with perforin gene deficiency: a single-center retrospective study]

Objective: This study aimed to investigate the clinical characteristics of patients diagnosed with primary hemophagocytic lymphohistiocytosis (pHLH) associated with perforin gene deficiency. Methods: We retrospectively analyzed the clinical data of 16 pHLH patients associated with perforin gene deficiency at Beijing Friendship Hospital, Capital Medical University, from April 2014 to August 2021. The mutation sites, mutation types, family history, clinical characteristics, and prognosis of the patients were assessed. Results: A total of 16 patients, including ten males and six females, with a median onset age of 17.5 years (range: 4-42 years), were enrolled in this study. Sixteen different mutations were identified, consisting of 11 missense mutations, one nonsense mutation, two frameshift mutations, and two in-frame mutations. All patients harbored at least one deleterious missense mutation, with the most common mutation sites being c.1349C>T (p.T450M) and c.503G>A (p.S168N). Decreased natural killer (NK) cell activity was observed in 11 patients, reduced perforin protein expression in ten patients, concurrent Epstein-Barr virus (EBV) infection at onset in eight patients, a family history in two patients, and central nervous system involvement in four patients. Eleven cases underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT), with eight cases surviving. The median survival time of non-transplanted patients was eight months (range: 4-18 months), while that of transplanted patients was reported as "not reached". Conclusions: Emphasizing the diagnosis of pHLH in adults with perforin gene deficiency. In addition, it should be noted that EBV infection can potentially act as a triggering factor in such disease, and allo-HSCT exerts a substantial effect on the prognosis of patients.

Secondary haemophagocytic lymphohistiocytosis in a patient with new-onset systemic lupus erythematosus: the challenges of timely diagnosis and successful treatment

Haemophagocytic lymphohistiocytosis (HLH) is an immune-mediated disease driven by abnormal macrophage activation and regulatory cell dysfunction. HLH can be primary due to genetic mutations or secondary due to infection, malignancy or autoimmune conditions. We describe a woman in her early 30s who developed HLH while being treated for newly diagnosed systemic lupus erythematosus (SLE) complicated by lupus nephritis as well as concomitant cytomegalovirus (CMV) reactivation from a dormant infection. The trigger for this secondary form of HLH may have been either aggressive SLE and/or CMV reactivation. Despite prompt treatment with immunosuppressive therapies for SLE consisting of high-dose corticosteroids, mycophenolate mofetil, tacrolimus, etoposide for HLH and ganciclovir for CMV infection, the patient developed multiorgan failure and passed away. We demonstrate the difficulty in identifying a specific cause for secondary HLH when multiple conditions are present (SLE and CMV) and the fact that, despite aggressive treatment for both conditions, the mortality for HLH remains high.

Effects of a Small-Molecule Perforin Inhibitor in a Mouse Model of CD8 T Cell-Mediated Neuroinflammation

BACKGROUND AND OBJECTIVES

Alteration of the blood-brain barrier (BBB) at the interface between blood and CNS parenchyma is prominent in most neuroinflammatory diseases. In several neurologic diseases, including cerebral malaria and Susac syndrome, a CD8 T cell-mediated targeting of endothelial cells of the BBB (BBB-ECs) has been implicated in pathogenesis.

METHODS

In this study, we used an experimental mouse model to evaluate the ability of a small-molecule perforin inhibitor to prevent neuroinflammation resulting from cytotoxic CD8 T cell-mediated damage of BBB-ECs.

RESULTS

Using an in vitro coculture system, we first identified perforin as an essential molecule for killing of BBB-ECs by CD8 T cells. We then found that short-term pharmacologic inhibition of perforin commencing after disease onset restored motor function and inhibited the neuropathology. Perforin inhibition resulted in preserved BBB-EC viability, maintenance of the BBB, and reduced CD8 T-cell accumulation in the brain and retina.

DISCUSSION

Therefore, perforin-dependent cytotoxicity plays a key role in the death of BBB-ECs inflicted by autoreactive CD8 T cells in a preclinical model and potentially represents a therapeutic target for CD8 T cell-mediated neuroinflammatory diseases, such as cerebral malaria and Susac syndrome.

Immune Effector Cell-Associated Hemophagocytic Lymphohistiocytosis-Like Syndrome

T cell-mediated hyperinflammatory responses, such as cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS), are now well-established toxicities of chimeric antigen receptor (CAR) T cell therapy. As the field of CAR T cells advances, however, there is increasing recognition that hemophagocytic lymphohistiocytosis (HLH)-like toxicities following CAR T cell infusion are occurring broadly across patient populations and CAR T cell constructs. Importantly, these HLH-like toxicities are often not as directly associated with CRS and/or its severity as initially described. This emergent toxicity, however ill-defined, is associated with life-threatening complications, creating an urgent need for improved identification and optimal management. With the goal of improving patient outcomes and formulating a framework to characterize and study this HLH-like syndrome, we established an American Society for Transplantation and Cellular Therapy panel composed of experts in primary and secondary HLH, pediatric and adult HLH, infectious disease, rheumatology and hematology, oncology, and cellular therapy. Through this effort, we provide an overview of the underlying biology of classical primary and secondary HLH, explore its relationship with similar manifestations following CAR T cell infusions, and propose the term "immune effector cell-associated HLH-like syndrome (IEC-HS)" to describe this emergent toxicity. We also delineate a framework for identifying IEC-HS and put forward a grading schema that can be used to assess severity and facilitate cross-trial comparisons. Additionally, given the critical need to optimize outcomes for patients experiencing IEC-HS, we provide insight into potential treatment approaches and strategies to optimize supportive care and delineate alternate etiologies that should be considered in a patient presenting with IEC-HS. By collectively defining IEC-HS as a hyperinflammatory toxicity, we can now embark on further study of the pathophysiology underlying this toxicity profile and make strides toward a more comprehensive assessment and treatment approach.

Approaching hemophagocytic lymphohistiocytosis

Hemophagocytic Lymphohistiocytosis (HLH) is a rare clinical condition characterized by sustained but ineffective immune system activation, leading to severe and systemic hyperinflammation. It may occur as a genetic or sporadic condition, often triggered by an infection. The multifaceted pathogenesis results in a wide range of non-specific signs and symptoms, hampering early recognition. Despite a great improvement in terms of survival in the last decades, a considerable proportion of patients with HLH still die from progressive disease. Thus, prompt diagnosis and treatment are crucial for survival. Faced with the complexity and the heterogeneity of syndrome, expert consultation is recommended to correctly interpret clinical, functional and genetic findings and address therapeutic decisions. Cytofluorimetric and genetic analysis should be performed in reference laboratories. Genetic analysis is mandatory to confirm familial hemophagocytic lymphohistiocytosis (FHL) and Next Generation Sequencing is increasingly adopted to extend the spectrum of genetic predisposition to HLH, though its results should be critically discussed with specialists. In this review, we critically revise the reported laboratory tools for the diagnosis of HLH, in order to outline a comprehensive and widely available workup that allows to reduce the time between the clinical suspicion of HLH and its final diagnosis.

Lytic granule exocytosis at immune synapses: lessons from neuronal synapses

Regulated exocytosis is a central mechanism of cellular communication. It is not only the basis for neurotransmission and hormone release, but also plays an important role in the immune system for the release of cytokines and cytotoxic molecules. In cytotoxic T lymphocytes (CTLs), the formation of the immunological synapse is required for the delivery of the cytotoxic substances such as granzymes and perforin, which are stored in lytic granules and released via exocytosis. The molecular mechanisms of their fusion with the plasma membrane are only partially understood. In this review, we discuss the molecular players involved in the regulated exocytosis of CTL, highlighting the parallels and differences to neuronal synaptic transmission. Additionally, we examine the strengths and weaknesses of both systems to study exocytosis.

The Multifaceted Immunology of Cytokine Storm Syndrome

Cytokine storm syndromes (CSSs) are potentially fatal hyperinflammatory states that share the underpinnings of persistent immune cell activation and uninhibited cytokine production. CSSs can be genetically determined by inborn errors of immunity (i.e., familial hemophagocytic lymphohistiocytosis) or develop as a complication of infections, chronic inflammatory diseases (e.g., Still disease), or malignancies (e.g., T cell lymphoma). Therapeutic interventions that activate the immune system such as chimeric Ag receptor T cell therapy and immune checkpoint inhibition can also trigger CSSs in the setting of cancer treatment. In this review, the biology of different types of CSSs is explored, and the current knowledge on the involvement of immune pathways and the contribution of host genetics is discussed. The use of animal models to study CSSs is reviewed, and their relevance for human diseases is discussed. Lastly, treatment approaches for CSSs are discussed with a focus on interventions that target immune cells and cytokines.

Coronavirus Does It Again: Post-COVID-19 Hemophagocytic Lymphohistiocytosis (HLH)

Hemophagocytic lymphohistiocytosis (HLH) is a hematological disorder that results from an uncontrolled activation of the immune system, which can then lead to multisystem organ failure. Given the nonspecific nature of this illness, it can go undetected for too long, thereby causing permanent damage to organ systems. In adults, HLH has been associated with a number of infectious etiologies, particularly viral infections. Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to a global pandemic and has been associated with acute respiratory distress syndrome (ARDS). Among its other manifestations, COVID-19 has also been linked to HLH. In this report, we describe a case of a male patient who presented with multisystem organ failure and was found to have HLH. Since no clear etiology for his HLH could be elicited, it was determined to be a result of his recent COVID-19 infection.

Mortality and Associated Causes in Hemophagocytic Lymphohistiocytosis: A Multiple-Cause-of-Death Analysis in France

Hemophagocytic lymphohistiocytosis (HLH) is a severe hyperinflammatory syndrome with an overall mortality rate of 40%. A multiple-cause-of-death analysis allows for the characterization of mortality and associated causes over an extended period. Death certificates, collected between 2000 and 2016 by the French Epidemiological Centre for the Medical Causes of Death (CepiDC, Inserm), containing the ICD10 codes for HLH (D76.1/2), were used to calculate HLH-related mortality rates and to compare them with the general population (observed/expected ratios, O/E). HLH was mentioned in 2072 death certificates as the underlying cause of death (UCD, n = 232) or as a non-underlying cause of death (NUCD, n = 1840). The mean age at death was 62.4 years. The age-standardized mortality rate was 1.93/million person-years and increased over the study period. When HLH was an NUCD, the most frequently associated UCDs were hematological diseases (42%), infections (39.4%), and solid tumors (10.4%). As compared to the general population, HLH decedents were more likely to have associated CMV infections or hematological diseases. The increase in mean age at death over the study period indicates progress in diagnostic and therapeutic management. This study suggests that the prognosis of HLH may be at least partially related to coexisting infections and hematological malignancies (either as causes of HLH or as complications).

Dendritic cells in inborn errors of immunity

Dendritic cells (DCs) are crucial cells for initiating and maintaining immune response. They play critical role in homeostasis, inflammation, and autoimmunity. A number of molecules regulate their functions including synapse formation, migration, immunity, and induction of tolerance. A number of IEI are characterized by mutations in genes encoding several of these molecules resulting in immunodeficiency, inflammation, and autoimmunity in IEI. Currently, there are 465 Inborn errors of immunity (IEI) that have been grouped in 10 different categories. However, comprehensive studies of DCs have been reported in only few IEI. Here we have reviewed biology of DCs in IEI classified according to recently published IUIS classification. We have reviewed DCs in selected IEI in each group category and discussed in depth changes in DCs where significant data are available regarding role of DCs in clinical and immunological manifestations. These include severe immunodeficiency diseases, antibody deficiencies, combined immunodeficiency with associated and syndromic features, especially disorders of synapse formation, and disorders of immune regulation.

The hyperinflammatory spectrum: from defects in cytotoxicity to cytokine control

Cytotoxic lymphocytes kill target cells through polarized release of the content of cytotoxic granules towards the target cell. The importance of this cytotoxic pathway in immune regulation is evidenced by the severe and often fatal condition, known as hemophagocytic lymphohistiocytosis (HLH) that occurs in mice and humans with inborn errors of lymphocyte cytotoxic function. The clinical and preclinical data indicate that the damage seen in severe, virally triggered HLH is due to an overwhelming immune system reaction and not the direct effects of the virus per se. The main HLH-disease mechanism, which links impaired cytotoxicity to excessive release of pro-inflammatory cytokines is a prolongation of the synapse time between the cytotoxic effector cell and the target cell, which prompts the former to secrete larger amounts of cytokines (including interferon gamma) that activate macrophages. We and others have identified novel genetic HLH spectrum disorders. In the present update, we position these newly reported molecular causes, including CD48-haploinsufficiency and ZNFX1-deficiency, within the pathogenic pathways that lead to HLH. These genetic defects have consequences on the cellular level on a gradient model ranging from impaired lymphocyte cytotoxicity to intrinsic activation of macrophages and virally infected cells. Altogether, it is clear that target cells and macrophages may play an independent role and are not passive bystanders in the pathogenesis of HLH. Understanding these processes which lead to immune dysregulation may pave the way to novel ideas for medical intervention in HLH and virally triggered hypercytokinemia.

Beyond target cell death - Granzyme serine proteases in health and disease

Granzymes are a family of small (∼32 kDa) serine proteases with a range of substrate specificities that are stored in, and released from, the cytoplasmic secretory vesicles ('granules') of cytotoxic T lymphocytes and natural killer cells. Granzymes are not digestive proteases but finely tuned processing enzymes that target their substrates in specific ways to activate various signalling pathways, or to inactivate viral proteins and other targets. Great emphasis has been placed on studying the pro-apoptotic functions of granzymes, which largely depend on their synergy with the pore-forming protein perforin, on which they rely for penetration into the target cell cytosol to access their substrates. While a critical role for granzyme B in target cell apoptosis is undisputed, both it and the remaining granzymes also influence a variety of other biological processes (including important immunoregulatory functions), which are discussed in this review. This includes the targeting of many extracellular as well as intracellular substrates, and can also lead to deleterious outcomes for the host if granzyme expression or function are dysregulated or abrogated. A final important consideration is that granzyme repertoire, biochemistry and function vary considerably across species, probably resulting from the pressures applied by viruses and other pathogens across evolutionary time. This has implications for the interpretation of granzyme function in preclinical models of disease.

Hemophagocytic lymphohistiocytosis as an etiology of bone marrow failure

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of multiorgan system dysfunction that is caused by hypercytokinemia and persistent activation of cytotoxic T lymphocytes and macrophages. A nearly ubiquitous finding and a diagnostic criterion of HLH is the presence of cytopenias in ≥ 2 cell lines. The mechanism of cytopenias in HLH is multifactorial but appears to be predominantly driven by suppression of hematopoiesis by pro-inflammatory cytokines and, to some extent, by consumptive hemophagocytosis. Recognition of cytopenias as a manifestation of HLH is an important consideration for patients with bone marrow failure of unclear etiology.

An Evidence-Based Guideline Improves Outcomes for Patients With Hemophagocytic Lymphohistiocytosis and Macrophage Activation Syndrome

OBJECTIVE

To compare clinical outcomes in children with hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) who were managed before and after implementation of an evidence-based guideline (EBG).

METHODS

A management algorithm for MAS-HLH was developed at our institution based on literature review, expert opinion, and consensus building across multiple pediatric subspecialties. An electronic medical record search retrospectively identified hospitalized patients with MAS-HLH in the pre-EBG (October 15, 2015, to December 4, 2017) and post-EBG (January 1, 2018, to January 21, 2020) time periods. Predetermined outcome metrics were evaluated in the 2 cohorts.

RESULTS

After the EBG launch, 57 children were identified by house staff as potential patients with MAS-HLH, and rheumatology was consulted for management. Ultimately, 17 patients were diagnosed with MAS-HLH by the treating team. Of these, 59% met HLH 2004 criteria, and 94% met 2016 classification criteria for MAS complicating systemic juvenile idiopathic arthritis. There was a statistically significant reduction in mortality from 50% before implementation of the EBG to 6% in the post-EBG cohort (P = 0.02). There was a significant improvement in time to 50% reduction in C-reactive protein level in the post-EBG vs pre-EBG cohorts (log-rank P < 0.01). There were trends toward faster time to MAS-HLH diagnosis, faster initiation of immunosuppressive therapy, shorter length of hospital stay, and more rapid normalization of MAS-HLH-related biomarkers in the patients post-EBG.

CONCLUSION

While the observed improvements may be partially attributed to advances in treatment of MAS-HLH that have accumulated over time, this analysis also suggests that a multidisciplinary treatment pathway for MAS-HLH contributed meaningfully to favorable patient outcomes.

Comparing the Cytokine Storms of COVID-19 and Pandemic Influenza

Emerging respiratory viruses are major health threats due to their potential to cause massive outbreaks. Over the past 2 years, the coronavirus disease 2019 (COVID-19) pandemic has caused millions of cases of severe infection and deaths worldwide. Although natural and vaccine-induced protective immune mechanisms against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been increasingly identified, the factors that determine morbimortality are less clear. Comparing the immune signatures of COVID-19 and other severe respiratory infections such as the pandemic influenza might help dissipate current controversies about the origin of their severe manifestations. As such, identifying homologies in the immunopathology of both diseases could provide targets for immunotherapy directed to block shared pathogenic mechanisms. Meanwhile, finding unique characteristics that differentiate each infection could shed light on specific immune alterations exploitable for diagnostic and individualized therapeutics for each case. In this study, we summarize immunopathological aspects of COVID-19 and pandemic influenza from the perspective of cytokine storms as the driving force underlying morbidity. Thereby, we analyze similarities and differences in the cytokine profiles of both infections, aiming to bring forward those molecules more attractive for translational medicine and drug development.

Role of Genetic Polymorphism Present in Macrophage Activation Syndrome Pathway in Post Mortem Biopsies of Patients with COVID-19

COVID-19 is a viral disease associated with an intense inflammatory response. Macrophage Activation Syndrome (MAS), the complication present in secondary hemophagocytic lymphohistiocytosis (sHLH), shares many clinical aspects observed in COVID-19 patients, and investigating the cytolytic function of the responsible cells for the first line of the immune response is important. Formalin-fixed paraffin-embedded lung tissue samples obtained by post mortem necropsy were accessed for three groups (COVID-19, H1N1, and CONTROL). Polymorphisms in MAS cytolytic pathway (PRF1; STX11; STXBP2; UNC13D and GZMB) were selected and genotyping by TaqMan^® assays (Thermo Fisher Scientific, MA, USA) using Real-Time PCR (Applied Biosystems, MA USA). Moreover, immunohistochemistry staining was performed with a monoclonal antibody against perforin, CD8+ and CD57+ proteins. Histopathological analysis showed high perforin tissue expression in the COVID-19 group; CD8+ was high in the H1N1 group and CD57+ in the CONTROL group. An association could be observed in two genes related to the cytolytic pathway (PRF1 rs885822 G/A and STXBP2 rs2303115 G/A). Furthermore, PRF1 rs350947132 was associated with increased immune tissue expression for perforin in the COVID-19 group. The genotype approach could help identify patients that are more susceptible, and for this reason, our results showed that perforin and SNPs in the PRF1 gene can be involved in this critical pathway in the context of COVID-19.

Case report and literature review: Hemophagocytic lymphohistiocytosis in a pregnant woman with systemic lupus erythematosus with Syntaxin 11 gene defect

Hemophagocytic lymphohistiocytosis is an extremely rare occurrence during pregnancy. Early recognition of its signs and symptoms is critical for early intervention, and delays in diagnosis may be life-threatening. A 23-year-old nulliparous woman presented with a persistent fever as high as 39°C with bilateral edema of the lower limbs at 24 weeks of gestation. Typical laboratory findings included pancytopenia, high triglycerides, ferritin, transaminases, bilirubin, and hypoproteinemia. Active systemic lupus erythematosus was diagnosed using an autoimmune work-up and a Systemic Lupus Erythematosus Disease Activity Index 2000 score of 17 points. Her bone marrow aspirate revealed prominent hemophagocytosis; hence, HLH was confirmed. Genetic tests showed mutations in Syntaxin 11 mutations. Considering the potential impact of drugs on the fetus, the patient and her family members chose to terminate the pregnancy through medical induction of labor. Afterwards, her condition improved with immunosuppressive therapy.

Fatal Acute Heart Failure in the Course of Macrophage Activation Syndrome: Case Report and Literature Review

Macrophage activation syndrome is a severe and potentially fatal condition in rheumatology. It can involve many different organs and systems, including the cardiovascular system, but heart failure due to its course is a relatively rare occurrence. In the following paper, we present a case of a young woman with newly diagnosed systemic lupus erythematosus who, in the span of two months, developed macrophage activation syndrome and acute heart failure, which caused her death. We analyze potential causes that may have led to that outcome, and present a brief review of the current literature concerning different macrophage groups in the heart and their potential involvement in the development of heart failure.

Locked and Loaded: Mechanisms Regulating Natural Killer Cell Lytic Granule Biogenesis and Release

NK cell-mediated cytotoxicity is a critical element of our immune system required for protection from microbial infections and cancer. NK cells bind to and eliminate infected or cancerous cells via direct secretion of cytotoxic molecules toward the bound target cells. In this review, we summarize the current understanding of the molecular regulations of NK cell cytotoxicity, focusing on lytic granule development and degranulation processes. NK cells synthesize apoptosis-inducing proteins and package them into specialized organelles known as lytic granules (LGs). Upon activation of NK cells, LGs converge with the microtubule organizing center through dynein-dependent movement along microtubules, ultimately polarizing to the cytotoxic synapse where they subsequently fuse with the NK plasma membrane. From LGs biogenesis to degranulation, NK cells utilize several strategies to protect themselves from their own cytotoxic molecules. Additionally, molecular pathways that enable NK cells to perform serial killing are beginning to be elucidated. These advances in the understanding of the molecular pathways behind NK cell cytotoxicity will be important to not only improve current NK cell-based anti-cancer therapies but also to support the discovery of additional therapeutic opportunities.

Cytolytic CD4+ and CD8+ Regulatory T-Cells and Implications for Developing Immunotherapies to Combat Graft-Versus-Host Disease

Regulatory T-cells (Treg) are critical for the maintenance of immune homeostasis and tolerance induction. While the immunosuppressive mechanisms of Treg have been extensively investigated for decades, the mechanisms responsible for Treg cytotoxicity and their therapeutic potential in regulating immune responses have been incompletely explored and exploited. Conventional cytotoxic T effector cells (Teffs) are known to be important for adaptive immune responses, particularly in the settings of viral infections and cancer. CD4+ and CD8+ Treg subsets may also share similar cytotoxic properties with conventional Teffs. Cytotoxic effector Treg (cyTreg) are a heterogeneous population in the periphery that retain the capacity to suppress T-cell proliferation and activation, induce cellular apoptosis, and migrate to tissues to ensure immune homeostasis. The latter can occur through several cytolytic mechanisms, including the Granzyme/Perforin and Fas/FasL signaling pathways. This review focuses on the current knowledge and recent advances in our understanding of cyTreg and their potential application in the treatment of human disease, particularly Graft-versus-Host Disease (GVHD).

Tuberculosis-associated hemophagocytic lymphohistiocytosis misdiagnosed as systemic lupus erythematosus: A case report

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is a rare disorder with rapid progression and high mortality. HLH occurs mostly due to infection, malignant tumors, and immune disorders. Among infections that cause HLH, viral infections, especially Epstein-Barr virus infections, are common, whereas tuberculosis is rare. Tuberculosis-associated HLH has a wide range of serological and clinical manifestations that are similar to those of systemic lupus erythematosus (SLE).

CASE SUMMARY

This study describes a case of tuberculosis-associated HLH misdiagnosed as SLE because of antinuclear antibody (ANA), Smith (Sm) antibody and lupus anticoagulant positivity; leukopenia; thrombocytopenia; pleural effusion; decreased C3, quantitatively increased 24 h urinary protein and fever. The patient was initially treated with glucocorticoids, which resulted in peripheral blood cytopenia and symptom recurrence. Then, caseating granulomas and hemophagocytosis were observed in her bone marrow. She was successfully treated with conventional category 1 antituberculous drugs. In addition, we reviewed the literature on tuberculosis-associated HLH documented in PubMed, including all full-text articles published in English from December 2009 to December 2019, and summarized the key points, including the epidemiology, clinical manifestations, diagnosis, and treatment of tuberculosis-associated HLH and the differences of the present case from previous reports.

CONCLUSION

Tuberculosis should be considered in patients with fever or respiratory symptoms. Antituberculous drugs are important for treating tuberculosis-associated HLH.

Hemophagocytic lymphohistiocytosis: a rare disease unveiling the diagnosis of EBV-related large B cell lymphoma in a patient with HIV

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is a rare disease resulting from the overactivation of the immune system due to under regulation of cytotoxic lymphocytes, macrophages and natural killer (NK) cells. HLH is associated with malignancies, infections, autoimmune disorders and rarely AIDS and is rapidly fatal.

CASE PRESENTATION

This case report identified a 53 year old male with acquired immunodeficiency syndrome (AIDS) who presented with neutropenic fever of unknown origin. He had two previous hospitalizations prior to the hospitalization diagnosing HLH. The first led to a diagnosis of drug fevers in the setting of treatment for thrombotic thrombocytopenic purpura and subsequent hospitalization led to empiric treatment of hospital acquired pneumonia after workup for intermittent fevers was negative. He was discharged but readmitted 10 days after for recurrence of neutropenic fevers. During this final hospitalization, he was found to have elevated liver enzymes, ferritin, triglycerides and soluble IL-2 receptor with persistent fevers, new splenomegaly and bicytopenia meeting the 2004 HLH criteria. Bone marrow biopsy confirmed the diagnosis of HLH as well as EBV associated large B-cell lymphoma. The patient improved on treatment with steroids, rituximab, tocilizumab, and chemotherapy but ultimately passed away due to refractory septic shock from multi-drug resistant Klebsiella pneumoniae.

CONCLUSION

This novel case highlights a patient diagnosed with HLH in the setting of several risk factors for the disease, including AIDS, B-cell lymphoma and EBV. Additionally, this case highlights the importance of early consideration of HLH in the setting of neutropenic fever without clear infectious etiology and search for malignancy associated reasons for HLH especially in immunocompromised patients.

ALPS, FAS, and beyond: from inborn errors of immunity to acquired immunodeficiencies

Autoimmune lymphoproliferative syndrome (ALPS) is a primary immune regulatory disorder characterized by benign or malignant lymphoproliferation and autoimmunity. Classically, ALPS is due to mutations in FAS and other related genes; however, recent research revealed that other genes could be responsible for similar clinical features. Therefore, ALPS classification and diagnostic criteria have changed over time, and several ALPS-like disorders have been recently identified. Moreover, mutations in FAS often show an incomplete penetrance, and certain genotypes have been associated to a dominant or recessive inheritance pattern. FAS mutations may also be acquired or could become pathogenic when associated to variants in other genes, delineating a possible digenic type of inheritance. Intriguingly, variants in FAS and increased TCR αβ double-negative T cells (DNTs, a hallmark of ALPS) have been identified in multifactorial autoimmune diseases, while FAS itself could play a potential role in carcinogenesis. These findings suggest that alterations of FAS-mediated apoptosis could trespass the universe of inborn errors of immunity and that somatic mutations leading to ALPS could only be the tip of the iceberg of acquired immunodeficiencies.

T Lymphocyte and CAR-T Cell-Derived Extracellular Vesicles and Their Applications in Cancer Therapy

Extracellular vesicles (EV) are a very diverse group of cell-derived vesicles released by almost all kind of living cells. EV are involved in intercellular exchange, both nearby and systemically, since they induce signals and transmit their cargo (proteins, lipids, miRNAs) to other cells, which subsequently trigger a wide variety of biological responses in the target cells. However, cell surface receptor-induced EV release is limited to cells from the immune system, including T lymphocytes. T cell receptor activation of T lymphocytes induces secretion of EV containing T cell receptors for antigen and several bioactive molecules, including proapoptotic proteins. These EV are specific for antigen-bearing cells, which make them ideal candidates for a cell-free, EV-dependent cancer therapy. In this review we examine the generation of EV by T lymphocytes and CAR-T cells and some potential therapeutic approaches of these EV.

Clinical spectrum and therapeutic management of systemic lupus erythematosus-associated macrophage activation syndrome: a study of 20 Moroccan adult patients

OBJECTIVE

The objective of this study was to describe the clinical and laboratory manifestations, triggers factors, treatment, and outcome of MAS complicating SLE.

METHODS

We retrospectively analyzed the medical records of adult patients with SLE for a period of 8 years (2009-2016) and identified patients who had developed MAS. We conducted statistical analysis to identify factors associated with MAS.

RESULTS

Among 208 consecutive lupus patients, 20 patients (19 women) were identified having MAS. The mean age of patients was 35.4 ± 10 years. MAS revealed lupus in 7 patients. In the others, the delay between diagnosis of SLE and MAS was 33,3 months. All cases required hospital admission, and 2 patients were admitted to the intensive care unit. An anemia (hemoglobin < 10 g/dL) was found in all patients. A thrombopenia was observed in 19 (95%) cases. Hypertriglyceridemia and hyperferritinemia were present in all patients. All patients had anti-nuclear antibodies and anti-double-stranded DNA antibodies. Bone marrow aspiration showed hemophagocytosis in 15 (94%) cases. The mean SLEDAI was 20.95 corresponding to an SLE of a very high activity. The mean H-Score was 233.85. MAS was associated with a lupus flare in 13 patients. Documented bacterial infections, viral infections, and a breast cancer were respectively diagnosed in 4, 3, and 1 cases respectively. The corticosteroids were administered in all patients. Intravenous cyclophosphamide was used together with corticosteroids in 6 patients, mycophenolate mofetil in 2 cases and azathioprine in 2 cases. Intravenous immunoglobulin was given in 4 cases, etoposide in one case and rituximab was used as the third line treatment in one patient. All infectious episodes were also treated by broad spectrum antibiotics. All patients had a good outcome without any mortality at the management, with a mean follow-up of 24 months. The clinical parameters significantly associated with MAS were fever (p = 0,001), splenomegaly (p < 0.0001), lymphadenopathy (p < 0.0001), oral and/or nasopharyngeal ulceration (p = 0.04), arthritis (p = 0.017), and pulmonary signs (p = 0.003). Laboratory parameters associated with MAS were anemia (p < 0.0001), thrombopenia (p < 0.0001), hyperferritinemia (p < 0.0001), hypertriglyceridemia (p < 0.0001), SLEDAI (p < 0.0001), and H-Score (p < 0.0001). Receiver operating characteristic (ROC) analysis identified optimal cutoff values of ferritin (> 695 ng/mL) and SLEDAI (> 13.5) to predict the occurrence of MAS in SLE.

CONCLUSION

MAS was observed in 9.62% Moroccan adult patients with SLE. SLE flare and infection were the common triggers of MAS in our study. Our study indicates that the occurrence of unexplained fever, splenomegaly, lymphadenopathy, profound cytopenia, hyperferritinemia, hypertriglyceridemia, high SLEDAI, and H-Score should raises the possibility of the diagnosis of MAS in SLE patients. Early diagnosis and urgent therapeutic management improves the overall prognosis. Key Points • Macrophage activation syndrome (MAS) is an underdiagnosed complication of systemic lupus erythematosus (SLE). The prevalence of this complication in this study is nearly 10%. • The diagnosis of MAS represents a major challenge for clinicians, as it could mimic a SLE flare up or be confused with infections. Validated diagnostic criteria for MAS in adults secondary to SLE are urgently needed. • In this study, the H-score calculate the individual risk of adult patients having reactive MAS. The cut-off value for the H-score was 190.5 (sensitivity 96.7%, specificity 97.6%). • The prognosis of MAS with SLE is good in our study. However, in the literature MAS may be a fatal condition in SLE patients. Prospective studies are necessary to confirm these results.