Familial Hemophagocytic Lymphohistiocytosis Research Articles

Familial haemophagocytic lymphohistiocytosis

Haemophagocytic lymphohistiocytosis (HLH) is a rare, but potentially fatal, disease that occurs when normal histiocytes and lymphocytes become overactive and commonly occurs in infancy. Two forms of the disease have been described: primary and secondary. This article reports twins who were less than 2 years old at the time of presentation and who had clinical symptoms of primary (familial) HLH, which was diagnosed by a contributory pathological bone marrow test.

Syntaxin 11 is required for NK and CD8+ T‐cell cytotoxicity and neutrophil degranulation

Syntaxin 11 (STX11) controls vesicular trafficking and is a key player in exocytosis. Since Stx11 mutations are causally associated with a familial hemophagocytic lymphohistio-cytosis, we wanted to clarify whether STX11 is functionally important for key immune cell populations. This was studied in primary cells obtained from newly generated Stx11(-/-) mice. Our data revealed that STX11 is not only widely expressed in different immune cells, but also induced upon LPS or IFN-γ treatment. However, Stx11 deficiency does not affect macrophage phagocytic function and cytokine secretion, mast cell activation, or antigen presentation by DCs. Instead, STX11 selectively controls lymphocyte cytotoxicity in NK and activated CD8(+) T cells and degranulation in neutrophils. Stx11(-/-) NK cells and CTLs show impaired degranulation, despite a comparable activation, maturation and expression of the complex-forming partners MUNC18-2 and VTI1B. In addition, Stx11(-/-) CTLs and NK cells produce abnormal levels of IFN-γ. Since functional reconstitution rescues the defective phenotype of Stx11(-/-) CTLs, we suggest a direct, specific and key role of STX11 in controlling lymphocyte cytotoxicity, cytokine production and secretion. Finally, we show that these mice are a very useful tool for dissecting the role of STX11 in vesicular trafficking and secretion.

MUNC13-4 Protein Regulates the Oxidative Response and Is Essential for Phagosomal Maturation and Bacterial Killing in Neutrophils

Neutrophils use diverse mechanisms to kill pathogens including phagocytosis, exocytosis, generation of reactive oxygen species (ROS), and neutrophil extracellular traps. These mechanisms rely on their ability to mobilize intracellular organelles and to deliver granular cargoes to specific cellular compartments or into the extracellular milieu, but the molecular mechanisms regulating vesicular trafficking in neutrophils are not well understood. MUNC13-4 is a RAB27A effector that coordinates exocytosis in hematopoietic cells, and its deficiency is associated with the human immunodeficiency familial hemophagocytic lymphohistiocytosis type 3. In this work, we have established an essential role for MUNC13-4 in selective vesicular trafficking, phagosomal maturation, and intracellular bacterial killing in neutrophils. Using neutrophils from munc13-4 knock-out (KO) mice, we show that MUNC13-4 is necessary for the regulation of p22(phox)-expressing granule trafficking to the plasma membrane and regulates extracellular ROS production. MUNC13-4 was also essential for the regulation of intracellular ROS production induced by Pseudomonas aeruginosa despite normal trafficking of p22(phox)-expressing vesicles toward the phagosome. Importantly, in the absence of MUNC13-4, phagosomal maturation was impaired as observed by the defective delivery of azurophilic granules and multivesicular bodies to the phagosome. Significantly, this mechanism was intact in RAB27A KO neutrophils. Intracellular bacterial killing was markedly impaired in MUNC13-4 KO neutrophils. MUNC13-4-deficient cells showed a significant increase in neutrophil extracellular trap formation but were unable to compensate for the impaired bacterial killing. Altogether, these findings characterize novel functions of MUNC13-4 in the innate immune response of the neutrophil and have direct implications for the understanding of immunodeficiencies in patients with MUNC13-4 deficiency.

Founder effects in two predominant intronic mutations of UNC13D, c.118-308C>T and c.754-1G>C underlie the unusual predominance of type 3 familial hemophagocytic lymphohistiocytosis (FHL3) in Korea

Familial hemophagocytic lymphohistiocytosis (familial HLH or FHL) is a potentially fatal autosomal recessive disorder. Our previous study demonstrated that UNC13D mutations (FHL3) account for ~90 % of FHL in Korea with recurrent splicing mutation c.754-1G>C (IVS9-1G>C). Notably, half of the FHL3 patients had a monoallelic mutation of UNC13D. Deep intronic mutations in UNC13D were recently reported in patients of European descent. In this study, we performed targeted mutation analyses for deep intronic mutations and investigated on the founder effect in FHL3 in Korean patients. The study patients were 72 children with HLH including those with FHL3 previously reported to have a monoallelic UNC13D mutation. All patients were recruited from the Korean Registry of Hemophagocytic Lymphohistiocytosis. In addition to conventional sequencing of FHL2-4, targeted tests for c.118-308C>T and large intronic rearrangement mutations of UNC13D were performed. Haplotype analysis was performed for founder effects using polymorphic markers in the FHL3 locus. FHL mutations were detected in 20 patients (28 %). Seventeen patients had UNC13D mutations (FHL3, 85 %) and three had PRF1 mutations (FHL2, 15 %). UNC13D:c.118-308C>T was detected in ten patients, accounting for 38 % of all mutant alleles of UNC13D, followed by c.754-1G>C (26 %). Haplotype analyses revealed significantly shared haplotypes in both c.118-308C>T and c.754-1G>C, indicating the presence of founder effects. The deep intronic mutation UNC13D:c.118-308C>T accounts for the majority of previously missing mutations and is the most frequent mutation in FHL3 in Korea. Founder effects of two recurrent intronic mutations of UNC13D explain the unusual predominance of FHL3 in Korea.

Cytokine Environement Analysis During Allogeneic Hematopoietic Stem Cell Transplantation for Inherited Diseases

AbstractAbstract 4484Hematopoietic stem cell transplantation (HSCT) is the treatment for an increasing number of inherited diseases. Graft rejection and acute Graft Versus Host Disease (GVHD) are known to be the two major complications of this procedure. A high frequency of graft rejection is observed particularly in patients with inflammatory conditions associated with congenital metabolic diseases, IFN-gR1 deficiency, familial hemophagocytic lymphohistiocytosis. GVHD results from immunological attack on target recipient organs (skin, liver and gut) by donor allogeneic T cells that are transferred along with the allograft. A better understanding of the patients' inflammatory environment in the course of HSCT may allow for the establishment of predictive markers for the occurrence of engraftment or GVHD and the improvement of conditioning regimens and post-transplant immunosuppressive therapy. Methods:All pediatric patients treated in the Department of Immuno-Hematology at the Necker Hospital who received allogeneic HSCT after full intensity conditioning regimen for nonmalignant disorders including inherited immunodeficiencies, metabolic diseases or hemoglobinopathies are eligible for inclusion.Plasma samples are collected before conditioning (day-15), at the time of transplant (day 0), at day+15 and day+30 post-HSCT.Validated markers of GVHD (Elafin, Reg3α, and ST2) as well as pro-inflammatory, anti-inflammatory, and angiogenic cytokines were analyzed, respectively, using sequential enzyme-linked immunosorbent assays and Luminex technology, which enables the determination of large numbers of cytokines in very small amounts of childrens’ plasma. Engraftment was assessed on the presence of full donor chimerism, GVHD upon clinical, biological and histopathological data. Results:From April 2011 to March 2012, 15 patients were included (8 males and 7 females with an age ranging from 4 months to 9 years). Five patients presented with severe combined immunodeficiencies, three with chronic granulomatous disease, five with metabolic diseases (three Hurler and two osteopetrosis), one with congenital aplastic anemia and one with sickle cell diseaseConditioning regimen consisted of Busulfan/Fludarabin/ATG for ten patients, Busulfan/Fludarabin/Thiotepa/ATG for four patients and Busulfan/Cyclophosphamid/ATG in one. Donors were matched unrelated (n=6), 4 matched related (n=4), haplo-identical (n=4), and with intrafamilial mismatched donor (n=1). Acute graft rejection was observed in 2 of 15 patients and sustained engraftment in 13 of 15. Acute GVHD was observed in 6 of 15 patient occurring between day+10 and day+45 [grade 1 (n=1), grade 3 (n=3) and grade 4 (n=2)].At day+30, we found significantly higher plasma concentrations of IFNγ, TNFα, ST2, and VEGF in patients with GVHD as compared to patients without GVHD. TNFα was the only cytokine for which the plasma concentrations was already significantly higher at day+15 in patients with GVHD versus patients without GVHD. No statistically significant differences in plasma concentrations of IL-4, IL-6, TGFβ, IL-7, IL-8, IL-12, IL-13 and IL-17 were observed.The cytokine that appeared to differentiate patients with GVHD and patients without GVHD the most was IFN-α2 which had plasma concentrations that were consistently and significantly higher in patients without GVHD as compared to patients with GVHD from day-15 to day+15. Conclusion:These results confirm the Th1 associated profile of acute GVHD and the importance of endothelial dysfunction in GVHD, as suggested by increased concentrations of ST2 and VEGF in patients with GVHD. The potential forIFN-α2 as a predictive marker of GVHD in our population needs further confirmation through additional inclusions. A larger population is also needed to determine if a specific cytokine milieu is associated with other common HSCT complications seen in our population such as graft rejection and vascular complications such as sinusoidal obstructive syndrome of the liver and pulmonary arterial hypertension. Disclosures:No relevant conflicts of interest to declare.

Temporal Secretion of α-Granular Products: Insights into the Mechanisms of Release Reaction

Abstract SCI-36Upon activation, platelets secrete numerous molecules that affect the local vascular microenvironment. Many of these components are important for hemostasis; however, others play key roles in the sequelae of thrombosis, such as angiogenesis, inflammation, and wound repair. These molecules are stored in three general types of platelet granules: dense, α, and lysosome. Analysis of platelet exocytosis shows that there is a direct correlation between agonist potency (thrombin > convulxin > PAR1 agonist > PAR4 agonist) and the extent and rate of content release. Release from dense granules is most rapid, while lysosome content release is the slowest; release of α-granule contents is heterogeneous. Detailed analysis of α-granule cargo release identified three kinetic classes of release events that differ in their rate. The content released in each of these three classes appeared to be random. Mechanistically, secretion from each granule requires integral membrane proteins called soluble NSF attachment protein receptors (SNAREs). v-SNAREs (vesicle-associated membrane proteins [VAMPs] from the granules) and heterodimeric t-SNAREs (syntaxins and SNAP-23 from the plasma membrane) form a trans-membrane, trimeric complex that mediates fusion and content release. How and where the SNAREs interact is controlled by regulatory proteins that in turn are affected during platelet activation. By analyzing platelet secretion from knockout mice and patients with familial hemophagocytic lymphohistiocytosis (FHL), it has been possible to identify the machinery required for each granule secretion event. Platelets contain four v-SNAREs (VAMP-2, −3, −7, and −8), but only VAMP-8 is required for content release. Platelets contain six t-SNAREs (syntaxin 2, 4, 7, 11, 13, and SNAP-23). Deletion of only syntaxin 11 in patients with FHL4 is sufficient to diminish platelet secretion. SNAP-23 is regulated by phosphorylation on Ser 95 by IκB kinase (IKK). This is important for SNARE complex formation, membrane fusion, and secretion. Intriguingly, mice treated with IKK inhibitors or genetically engineered with a platelet-specific deletion of Ikkb show increased tail-bleeding times. A number of syntaxin regulators have been identified in platelets. MUNC18b is a syntaxin 11 chaperone that is essential for platelet secretion in FHL5 patients. MUNC13 proteins, which facilitate t-SNARE/v-SNARE binding, are also important for platelet granule release. Deletion of Munc13-4 results in a significant platelet secretion defect and a robust bleeding diathesis in mice. Biochemical analysis shows that MUNC13-4 is a docking/tethering factor required to increase the efficacy of membrane fusion. Both MUNC18b and MUNC13-4 appear to be limiting in platelets, suggesting that they might be useful therapeutic targets. A greater understanding of platelet exocytosis is unfolding. This knowledge will undoubtedly lead to the development of better antithrombotic drugs. This work is supported by HL56652 and HL091893 from the National Institutes of Health. Disclosures:No relevant conflicts of interest to declare.

Outcome of Adult Patients with Hemophagocytic Syndrome: A Tertiary Care Center Experience

AbstractAbstract 1040 Introduction:Hemophagocytic syndrome (HPS) is a rare disorder characterized by fever, splenomegaly, cytopenias, hypofibrinogenemia, hyperferritinemia and hemophagocytosis in the bone marrow or lymph nodes. It is caused by pathologic activation of the immune system, and manifests clinically with signs and symptoms related to extreme inflammation. Primary HPS or familial hemophagocytic lymphohistiocytosis (HLH) occurs predominantly in children (<18 years) due to inherited defects in natural killer and cytotoxic T-cell function. Secondary HPS generally occurs in adults (>18 years) and is precipitated by autoimmune disorders, malignancy and a variety of infections. The results of HLH-94 trial, the largest prospective study in pediatric patients with HLH, reported an estimated 5-year survival of 54%. There is a paucity of information about HPS in adult patients. Methods:Records of all adult (≥ 18 years) patients with a diagnosis of “hemophagocytosis“ or “hemophagocytic syndrome” presenting from January 1996 through December 2011 at Mayo Clinic were reviewed. Our hematopathology database was also analyzed for patients bearing a diagnosis of HPS. Out of a total of 127 patients identified in the database, 50 adult patients were diagnosed to have HPS as per the diagnostic criteria of the HLH-1994 trial (for patients seen prior to 2004), and HLH-2004 trial (for patients seen after 2004). This study was approved by the Institutional Review Board at Mayo Clinic. Results:Baseline characteristics of all patients are shown in Table 1. The median time to diagnosis from the onset of symptoms was 38 days (4–158 days). Secondary HPS was diagnosed in 46 (92%) patients. The causes of secondary HPS are shown in Table 2. Twenty (40%) patients were treated with etoposide containing regimen, 26 (52%) were treated with therapeutic agents directed specifically to the underlying precipitating disease, and 4 (8%) patients did not receive any treatment. No patient in our study underwent a stem cell transplant (SCT). After a median follow-up of 43 months, 36 (72%) patients have died. The causes of death were infection (47%), malignancy (42%), bleeding (8%) and unknown (3%). The median overall survival (OS) for the entire cohort was 1.5 months (95% CI, 0.7–4.5 months). The median OS for patients with malignancy- related HPS was 0.8 months (95% CI, 0.4–2.4 months) compared to 11 months (95% CI, 0.7-not reached) for patients with non-malignancy related HPS (p-value:0.006; Figure). On univariableanalysis, factors associated with a worse survival were serum albumin <2 g/dL (hazard ratio, 8.3), malignancy-related HPS (hazard ratio, 7.3) and serum creatinine >1.3 mg/dL (hazard ratio, 3.8). Conclusion:In this large series of adult HPS patients treated at a single tertiary care center, most cases are secondary, and are associated with a worse survival compared to historical outcomes reported for children enrolled on the HLH-94 trial. This is likely related to a marked delay in referral to our institution, and high early mortality precluding consideration of SCT. Adult patients with malignancy- related HPS in this study had a markedly inferior outcome compared to patients with non-malignancy related HPS.Table 1Characteristic(Range) or [%]Total Number of patients50Median Age, years49 (18–87)Males33 [66]Median hemoglobin, gm/dL9 (6.2–13.7)Median total WBC (x109/L)1.8 (0.2–43.5)Median absolute neutrophil (x109/L)1.2 (0–33.6)Median platelet (x109/L)55 (6–288)Median aspartate aminotransferase (U/L)111 (10–9450)Median total bilirubin (mg/dL)1.9 (0.3–25.6)Median lactate dehydrogenase (U/L)472 (90–9290)Serum triglycerides (mg/dL)Median252 (68–831)>26514 [28]<26520 [40]Not available16 [32]Serum fibrinogen (mg/dL)Median160 (50–585)<15022 [44]>15022 [44]Not available6 [12]Serum ferritin (ng/mL)Median8400 (372–140,690)<5001 [2]501–300016 [32]>300124 [48]Not available9 [18]Table 2Etiology of Secondary HPSTotal Number of Patients = 46 (%)MalignancyTotal23 (46)T-cell lymphoma14B-cell lymphoma5Hodgkin's lymphoma1Myeloid neoplasm1Solid organ1Other (systemic histiocytosis)1InfectionTotal19 (38)Ebstein Barr virus7Cytomegalovirus3Nonspecific viral infection3Histoplasmosis3Bacterial2Blastomycosis1AutoimmuneTotal4 (8) [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Functional impact of A91V mutation of the PRF1 perforin gene

Perforin (PRF1) gene mutations have been associated with Familial Hemophagocytic Lymphohistiocytosis type 2 (FHL2). Substitution p.A91V (c.272C>T) in exon 2 was first described as a neutral polymorphism. Nonetheless, recent clinical evidence and functional assays, suggest a potential pathogenic role for p.A91V, especially in compound heterozygous individuals. Moreover, p.A91V homozygosity has been linked to various pathological states including FHL and lymphocytic leukaemias. In the present report we evaluated the impact of this mutation in a compound heterozygous A91V/G149S 31 year-old asymptomatic female. Functional assays revealed low perforin expression levels, as well as an impaired NK cell-mediated cytotoxicity, partially reconstituted after incubation with IL-2. These results support that p.A91V mutation, associated to another mutated PRF1 allele, may potentially predispose seemingly healthy carriers to suffer a milder FHL2 clinical phenotype, including later onset of the disease. Thus, clinical monitoring of p.A91V carrier individuals bearing another mutation in PRF1 is warranted.

Syntaxin-11, but not syntaxin-2 or syntaxin-4, is required for platelet secretion

AbstractThe platelet release reaction plays a critical role in thrombosis and contributes to the events that follow hemostasis. Previous studies have shown that platelet secretion is mediated by Soluble NSF Attachment Protein Receptor (SNARE) proteins from granule and plasma membranes. The SNAREs form transmembrane complexes that mediate membrane fusion and granule cargo release. Although VAMP-8 (v-SNARE) and SNAP-23 (a t-SNARE class) are important for platelet secretion, the identity of the functional syntaxin (another t-SNARE class) has been controversial. Previous studies using anti-syntaxin Abs in permeabilized platelets have suggested roles for both syntaxin-2 and syntaxin-4. In the present study, we tested these conclusions using platelets from syntaxin-knockout mouse strains and from a Familial Hemophagocytic Lymphohistiocytosis type 4 (FHL4) patient. Platelets from syntaxin-2 and syntaxin-4 single- or double-knockout mice had no secretion defect. Platelets from a FHL4 patient deficient in syntaxin-11 had a robust defect in agonist-induced secretion although their morphology, activation, and cargo levels appeared normal. Semiquantitative Western blotting showed that syntaxin-11 is the more abundant syntaxin in both human and murine platelets. Coimmunoprecipitation experiments showed that syntaxin-11 can form SNARE complexes with both VAMP-8 and SNAP-23. The results of the present study indicate that syntaxin-11, but not syntaxin-2 or syntaxin-4, is required for platelet exocytosis.

Munc18b/STXBP2 is required for platelet secretion

AbstractPlatelets are vital for hemostasis because they release their granule contents in response to vascular damage. Platelet exocytosis is mediated by soluble N-ethylmaleimide–sensitive factor attachment protein receptors (SNAREs), whose interactions are governed by regulators, eg, Sec/Munc18 proteins. These proteins chaperone syntaxin t-SNAREs and are required for exocytosis. Platelets contain 3 Munc18 isoforms: Munc18a, Munc18b, and Munc18c. We report that Munc18b is the major isoform and is required for platelet secretion. Familial hemophagocytic lymphohistiocytosis type 5 (FHL5) is caused by defects in the Munc18b/STXBP2 gene. We confirm a previous report showing that platelets from FHL5 patients have defective secretion. Serotonin, ADP/ATP, and platelet factor 4 release was profoundly affected in the 2 biallelic patients and partially in a heterozygous patient. Release of lysosomal contents was only affected in the biallelic platelets. Platelets from the FHL5 biallelic patients showed decreased Munc18b and syntaxin-11 levels were significantly reduced; other syntaxins were unaffected. Munc18b formed complexes with syntaxin-11, SNAP-23, and vesicle-associated membrane protein-8 in human platelets. Other potential secretion regulators, Munc13-4 and Rab27, were also found associated. These data demonstrate a key role for Munc18b, perhaps as a limiting factor, in platelet exocytosis and suggest that it regulates syntaxin-11.

Familial Hemophagocytic Lymphohistiocytosis May Present during Adulthood: Clinical and Genetic Features of a Small Series

Familial Hemophagocytic lymphohistiocytosis (FHL) is a rare immune deficiency with defective cytotoxic function. The age at onset is usually young and the natural course is rapidly fatal if untreated. A later onset of the disease has been sporadically reported even in adolescents and adults. We report the results of our retrospective data collection of all cases diagnosed with FHL at an age of 18 years or older and enrolled in the Italian Registry of HLH. All cases were diagnosed with FHL based on evidence of genetic defect in one FHL-related gene. A total of 11 patients were diagnosed with FHL. They were 9 males and 2 females, from 10 unrelated families; their age ranged between 18 and 43 years (median, 23 years). Family history was unremarkable in eight families at the time of the diagnosis. Their genetic diagnoses are: FHL2 (n = 6), FHL3 (n = 2), FHL5 (n = 1), XLP1 (n = 2). Clinical, molecular and functional data are described. These data confirm that FHL may present beyond the pediatric age and up to the fifth decade. FHL2 due to perforin defect is the most frequently reported subtype. Adult specialists should consider FHL in the differential diagnosis of patients with cytopenia and liver or central nervous system disorders, especially when a lymphoproliferative disease is suspected but eventually not confirmed. FHL may turn to be fatal within a short time course even in adults. This risk, together with the continuous improvement in the transplant technique, especially in the area of transplant from matched unrelated donor, resulting in reduced treatment related mortality, might suggest a wider use of SCT in this population. Current diagnostic approach allows prompt identification of patients by flow-cytometry screening, then confirmed by the genetic study, and treatment with chemo-immunotherapy followed by stem cell transplantation.

Treatment of Familial Hemophagocytic Lymphohistiocytosis with Third-Party Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSCs) represent an attractive tool for cellular therapies on grounds of their immunomodulatory and regenerative properties. Here, we report the first case of familial hemophagocytic lymphohistiocytosis (FHL) treated with MSCs. This rare autosomal recessive disorder is characterized by hyperinflammation that results from a failure of natural control mechanisms to terminate immune responses. Crosstalk between innate (macrophages) and adaptive (T cells) immunity is heavily altered. Immunochemotherapy is only temporarily effective in the control of FHL, and the outcome is usually fatal unless the patient undergoes allogeneic stem cell transplantation. Our hypothesis was that the application of MSCs could be effective in the treatment of FHL, since MSCs possess a broad repertoire of immunomodulating mechanisms impacting both innate and adaptive immunity pathways. In fact, the adoptive transfer of third-party MSCs transiently controlled the extreme immunological deterioration in the described patient who was otherwise not responsive to standard treatment, including repetitive chemotherapy. If these transient effects of MSCs can be confirmed in future-controlled clinical trials, adoptive MSC therapy could represent a salvage agent in FHL acting as a bridge to definitive treatment with stem cell transplantation.

Distinct mutations in STXBP2 are associated with variable clinical presentations in patients with familial hemophagocytic lymphohistiocytosis type 5 (FHL5)

AbstractFamilial hemophagocytic lymphohistiocytosis (FHL) is a genetically determined hyperinflammatory syndrome caused by uncontrolled immune response mediated by T-lymphocytes, natural killer (NK) cells, and macrophages. STXBP2 mutations have recently been associated with FHL5. To better characterize the genetic and clinical spectrum of FHL5, we analyzed a cohort of 185 patients with suspected FHL for mutations in STXBP2. We detected biallelic mutations in 37 patients from 28 families of various ethnic origins. Missense mutations and mutations affecting 1 of the exon 15 splice sites were the predominant changes detectable in this cohort. Patients with exon 15 splice-site mutations (n = 13) developed clinical manifestations significantly later than patients with other mutations (median age, 4.1 year vs 2 months) and showed less severe impairment of degranulation and cytotoxic function of NK cells and CTLs. Patients with FHL5 showed several atypical features, including sensorineural hearing deficit, abnormal bleeding, and, most frequently, severe diarrhea that was only present in early-onset disease. In conclusion, we report the largest cohort of patients with FHL5 so far, describe an extended disease spectrum, and demonstrate for the first time a clear genotype-phenotype correlation.

Novel STXBP2 Mutation Causing Familial Hemophagocytic Lymphohistiocytosis

Familial Hemophagocytic Lymphohistiocytosis (FHL) is a rare autosomal recessive disorder. Diagnosis is established in presence of genetic mutation or positive family history in one of the siblings. Common genetic mutations associated with FHL are mutations in gene PRF1 (also known as FHL 2), UNC13D (FHL 3) and STX11 (FHL 4). Recently mutation in STXBP2 encoding syntaxin binding protein 2 (Munc 18 -2) has been found to be associated with FHL type 5. Here we describe the first reported Indian patient with homozygous mutation in STX BP2 gene (c1697 G > A resulting in amino acid change p.G566D) causing FHL 5.

Epitope specificity of memory CD8+ T cells dictates vaccination-induced mortality in LCMV-infected perforin-deficient mice.

Perforin-deficient (PKO) mice serve as models for familial hemophagocytic lympho-histiocytosis, a uniformly fatal disease associated with viral infection of perforin-deficient humans. Naïve perforin-deficient BALB/c mice survive while vaccinated PKO mice containing virus-specific memory CD8(+) T cells rapidly succumb to lymphocytic choriomeningitis virus (LCMV) infection. Thus, vaccination converts a nonlethal persistent infection into a fatal disease mediated by virus-specific memory CD8(+) T cells. Here, we determine the extent to which vaccination-induced mortality in PKO mice following LCMV challenge is due to differences in vaccine modalities, the quantity or epitope specificity of memory CD8(+) T cells. We show that LCMV-induced mortality in immune PKO mice is independent of vaccine modalities and that the starting number of memory CD8(+) T cells specific to the immunodominant epitope NP(118-126) dictates the magnitude of secondary CD8(+) T-cell expansion, the inability to regulate production of CD8(+) T-cell-derived IFN-γ, and mortality in the vaccinated PKO mice. Importantly, mortality is determined by the epitope specificity of memory CD8(+) T cells and the associated degree of functional exhaustion and cytokine dysregulation but not the absolute magnitude of CD8(+) T-cell expansion. These data suggest that deeper understanding of the parameters that influence the outcome of vaccine-induced diseases would aid rational vaccine design to minimize adverse outcomes after infection.

Functional significance of Syntaxin 8 in Cytotoxic T Lymphocyte cytotoxicity (122.3)

Abstract Cytotoxic T Lymphocytes (CTLs) are activated CD8+ T cells which identify and kill pathogen infected, tumor and nonself cells by FAS ligand expression and by secretion of perforin and granzymes from lytic granules specifically at the immunological synapse (IS). This prevents killing of healthy bystander cells. Therefore at the time of killing these cytotoxic molecules are to be delivered to the IS. SNAREs are membrane associated proteins involved in vesicle transport, docking and fusion. Mutations of these proteins can cause diseases like Familial Hemophagocytic Lymphohistiocytosis. We have shown previously that Vti1b is required for docking of lytic granules at the IS. We also found that Vti1b and Syntaxin 8 (Stx8) colocalize with perforin in human CTLs. Further experiments showed that Stx8 partially colocalized with Vti1b. To elucidate the role of SNAREs in CTL cytotoxicity, siRNA were used to downregulate their expression. Stx8 downregulation did not impair the IS formation as CD3 accumulation at the IS was unaffected. We have previously shown that the killing capacity of CTLs is impaired by Vti1b downregulation. Here, Stx8 downregulated CTLs used in real time killing assay showed reduction in killing. Cycloheximide treatment of control and Stx8 downregulated CTLs showed that Stx8 is required for killing by perforin secretion. This conclusion is also supported by our preliminary ELISA data, which shows reduced perforin secretion in Stx8 downregulated CTLs.

Neonatal Liver Failure

Neonatal liver failure (NLF) is a rare but often fatal event. It is defined as a presence of significant synthetic liver dysfunction in infant less than 3 months of age. Most common etiologies of AL F are indeterminate (38%), neonatal hemochromatosis (13.6%), and herpes simplex virus infection (12.8%). In most recent report of ALF study group spontaneous survival occurred in 60% of the infants. 16% of infants underwent liver transplantation, and 24% died without undergoing liver transplantation. Early detection, careful supportive care and prompt diagnostic workup can improve chances of survival. Liver transplant offers hope for severely ill, with a long term survival of exceeding 60% in infants with acute liver failure. Yet in some disorders like familial hemophagocytic lymphohistiocytosis and mitochondrial DNA depletion syndrome liver transplant will not be therapeutic or appropriate. Liver transplant in infants with undetermined etiology remains controversial.

IL-15 restores defective NK anti-fungal activity in a primary Hemophagocytic lymphohistiocytosis Patient (164.1)

Abstract Hemophagocytic lymphohistiocytosis (HLH) is a rare yet potentially fatal clinical syndrome caused by various congenital defects that result in defective perforin-dependent cytotoxicity of NK cells. This leads to increased T cell activation and proliferation and excessive cytokine production including IL-1, IL-6, IFN-γ, TNF-α and GM-CSF that causes sustained activation of macrophages that is manifest as extensive inflammation and tissue damage. One study showed that 50% of deaths from familial HLH were due to invasive fungal infections. We sought to investigate whether NK cells from a patient with HLH have defective anti-fungal activity and seek a potential therapeutic approach. NK cells (CD56+/CD3-) were isolated from a two-month-old boy with c1090-1091del of the perforin gene resulting in p.Leu364&amp;gt;Stop consistent with the FHL-2 form of HLH. Defective NK killing was observed for both Cryptococcus neoformans and Candida albicans. Remarkably, the defective anti-Candida activity of NK cells could be restored within 24 hours by IL-15 treatment that was similar to the enhanced anti-Candida activity of NK cells from healthy donors. We speculate that IL-15 enhances antifungal activity by stimulating NK cells to employ an alternate microbicidal effector mechanism. This result is the first to show that IL-15 can restore defective cytotoxic activity of NK cells from an HLH patient, and further studies might be considered to explore the mechanism and potential form of immunotherapy.

Function of Syntaxin11 in cytotoxic T lymphocytes (121.9)

Abstract Cytotoxic T Lymphocytes (CTLs) form immunological synapses (IS) with antigen presenting cells to kill them. Killing requires the fusion of lytic granules at the IS to release the containing cytotoxic molecules (perforin and granzymes). The fusion process is mediated by SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptor) proteins. Since mutations within the coding region of syntaxin11 lead to Familial Hemophagocytic Lymphohistiocytosis (FHL4), an immune disorder caused by impaired granule exocytosis. We have investigated the contribution of syntaxin11 to lytic granule release. Using CD3 specific antibodies as a marker for a functional IS, we show that syntaxin11 accumulates at the IS in CTLs. Syntaxin11 was also co-localized with Munc18-2, a docking factor in agreement with the role of Munc18-2 as a syntaxin chaperone in other cell types. Using high resolution nanoscopy (structured illumination microscopy) we determined the subcellular localization of syntaxin11 in CTLs with a syntaxin11 specific antibody. Syntaxin11 was associated with recycling endosomes and mannose 6-phosphate receptor (M6PR) positive compartments. Functional assays using Syntaxin11 specific siRNA (knockdown studies) show a reduction in degranulation and killing efficiency in contrast to control siRNA transfected CTLs. These results support the conclusion that syntaxin11 is required for lytic granule exocytosis.

Reduced‐intensity conditioning in unrelated donor cord blood transplantation for familial hemophagocytic lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis (FHL) is a disorder of immune homeostasis characterized by fever, cytopenias, hepatosplenomegaly, and coagulopathy. We studied the outcomes of 13 FHL patients who underwent the first unrelated cord blood transplantation (UCBT) after non-myeloablative conditionings. The major regimen consisted of fludarabine (FLU; n = 12)+melphalan (MEL; n = 11)± low-dose total body irradiation (TBI 2-4 Gy; n = 6). The median age at presentation and period to UCBT were 6 and 5 months, respectively. Central nervous system (CNS) disease developed in one infant at diagnosis, and in two others until UCBT. HLH activity was controlled in all but one at the time of UCBT. Ten patients had early engraftment on median day 21 with no grade >2 treatment-related toxicity and two controllable grade >2 acute GVHD. Two patients with early rejection successfully underwent subsequent UCBT after myeloablative conditioning. Two others had late graft failure following mixed donor chimerism. Two deaths occurred from HLH; early liver failure and late CNS disease. Of 11 FLU+MEL-conditioned patients, the frequency of disease-free complete engraftment was higher for MEL (≥120 mg/m(2) )+TBI, or high-dose MEL (180 mg/m(2) ) than for others (83% vs. 25%, p = 0.036). The FLU+MEL-based non-myeloablative regimen was acceptable for FHL infants undergoing UCBT, although further studies will be needed for confirmation.