X-linked lymphoproliferative disease due to SAP/SH2D1A deficiency: a multicenter study on the manifestations, management and outcome of the disease. Blood. 2011;117:53-62. [PMID: 20926771 DOI: 10.1182/blood-2010-06-284935]

Hemophagocytic lymphohistiocytosis: Recent progress in the pathogenesis, diagnosis and treatment

Hemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory syndrome that develops as a primary (familial/hereditary) or secondary (non-familial/hereditary) disease characterized in the majority of the cases by hereditary or acquired impaired cytotoxic T-cell (CTL) and natural killer responses. The molecular mechanisms underlying impaired immune homeostasis have been clarified, particularly for primary diseases. Familial HLH (familial hemophagocytic lymphohistiocytosis type 2-5, Chediak-Higashi syndrome, Griscelli syndrome type 2, Hermansky-Pudlak syndrome type 2) develops due to a defect in lytic granule exocytosis, impairment of (signaling lymphocytic activation molecule)-associated protein, which plays a key role in CTL activity [e.g., X-linked lymphoproliferative syndrome (XLP) 1], or impairment of X-linked inhibitor of apoptosis, a potent regulator of lymphocyte homeostasis (e.g., XLP2). The development of primary HLH is often triggered by infections, but not in all. Secondary HLH develops in association with infection, autoimmune diseases/rheumatological conditions and malignancy. The molecular mechanisms involved in secondary HLH cases remain unknown and the pathophysiology is not the same as primary HLH. For either primary or secondary HLH cases, immunosuppressive therapy should be given to control the hypercytokinemia with steroids, cyclosporine A, or intravenous immune globulin, and if primary HLH is diagnosed, immunochemotherapy with a regimen containing etoposide or anti-thymocyte globulin should be started. Thereafter, allogeneic hematopoietic stem-cell transplantation is recommended for primary HLH or secondary refractory disease (especially EBV-HLH).

XLP: clinical features and molecular etiology due to mutations in SH2D1A encoding SAP

X-linked lymphoproliferative disease (XLP) is a rare primary immunodeficiency affecting approximately 1-2 per 1 million males. A key feature of XLP is the exquisite sensitivity of affected individuals to disease induced following EBV infection. However, patients can also develop hypogammaglobulinemia and B-cell lymphoma independently of exposure to EBV. XLP is caused by loss-of function mutations in SH2D1A, which encodes the intracellular adaptor molecule SAP. SAP is predominantly expressed in T cells and NK cells, and functions to regulate signal transduction pathways downstream of the SLAM family of surface receptors to control CD4+ T cell (and by extension B cells), CD8+ T cell and NK cell function, as well as the development of NKT cells. The study of XLP had shed substantial light on the requirements for lymphocyte differentiation and immune regulation, which in turn have the potential to be translated into novel treatments for not only XLP patients but individuals affected by EBV-induced disease, impaired humoral immunity and malignancy.

Lentiviral vectors for the treatment of primary immunodeficiencies

In the last years important progress has been made in the treatment of several primary immunodeficiency disorders (PIDs) with gene therapy. Hematopoietic stem cell (HSC) gene therapy indeed represents a valid alternative to conventional transplantation when a compatible donor is not available and recent success confirmed the great potential of this approach. First clinical trials performed with gamma retroviral vectors were promising and guaranteed clinical benefits to the patients. On the other hand, the outcome of severe adverse events as the development of hematological abnormalities highlighted the necessity to develop a safer platform to deliver the therapeutic gene. Self-inactivating (SIN) lentiviral vectors (LVVs) were studied to overcome this hurdle through their preferable integration pattern into the host genome. In this review, we describe the recent advancements achieved both in vitro and at preclinical level with LVVs for the treatment of Wiskott-Aldrich syndrome (WAS), chronic granulomatous disease (CGD), ADA deficiency (ADA-SCID), Artemis deficiency, RAG1/2 deficiency, X-linked severe combined immunodeficiency (γchain deficiency, SCIDX1), X-linked lymphoproliferative disease (XLP) and immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome.

Diagnosing XLP1 in patients with hemophagocytic lymphohistiocytosis

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening, heterogeneous, hyperinflammmatory disorder. Prompt identification of inherited forms resulting from mutation in genes involved in cellular cytotoxicity can be crucial. X-linked lymphoproliferative disease 1 (XLP1), due to mutations in SH2D1A (Xq25) encoding signaling lymphocyte activation molecule-associated protein (SAP), may present with HLH. Defective SAP induces paradoxical inhibitory function of the 2B4 coreceptor and impaired natural killer (NK) (and T) cell response against EBV-infected cells.

OBJECTIVE

To characterize a cohort of patients with HLH and XLP1 for SAP expression and 2B4 function in lymphocytes, proposing a rapid diagnostic screening to direct mutation analysis.

METHODS

We set up rapid assays for 2B4 function (degranulation or (51)Cr-release) to be combined with intracellular SAP expression in peripheral blood NK cells. We studied 12 patients with confirmed mutation in SH2D1A and some family members.

RESULTS

The combined phenotypic/functional assays allowed efficient and complete diagnostic evaluation of all patients with XLP1, thus directing mutation analysis and treatment. Nine cases were SAP(-), 2 expressed SAP with mean relative fluorescence intensity values below the range of healthy controls (SAP(dull)), and 1, carrying the R55L mutation, was SAP(+). NK cells from all patients showed inhibitory 2B4 function and defective killing of B-EBV cells. Carriers with SH2D1A mutations abolishing SAP expression and low percentage of SAP(+) cells showed neutral 2B4 function at the polyclonal NK cell level. Three novel SH2D1A mutations have been identified.

CONCLUSIONS

Study of SAP expression is specific but may have insufficient sensitivity for screening XLP1 as a single tool. Combination with 2B4 functional assay allows identification of all cases.

Epstein-Barr virus induced hemophagocytic lymphohistiocytosis in X-linked lymphoproliferative disease

X-linked lymphoproliferative disease (XLP) is a rare, often fatal genetic disorder characterized by extreme vulnerability to Epstein-Barr virus (EBV). EBV-induced hemophagocytic lymphohistiocytosis (HLH) is a known presentation in XLP. In EBV-induced HLH in XLP, the brain imaging findings in the acute phase include a non specific pattern. In this report, we highlight the magnetic resonance imaging and magnetic resonance spectroscopy findings in a child with EBV induced HLH in XLP.

Reduced-intensity conditioning hematopoietic cell transplantation is an effective treatment for patients with SLAM-associated protein deficiency/X-linked lymphoproliferative disease type 1

X-linked lymphoproliferative disease type 1 (XLP1) is a rare immune deficiency caused by mutations in SH2D1A. Allogeneic hematopoietic cell transplantation (HCT) is often performed because of the morbidity and mortality associated with XLP1. There is limited experience using reduced-intensity conditioning (RIC) regimens for these patients. Here we report our 8-year single-center experience. Sixteen consecutive patients diagnosed with XLP1 underwent allogeneic HCT between 2006 and 2013 after a RIC regimen consisting of alemtuzumab, fludarabine, and melphalan. Patient phenotypes included hemophagocytic lymphohistiocytosis (HLH) after Epstein-Barr virus (n = 5) or human herpesvirus 6 (n = 1), macrophage activation syndrome (n = 1), interstitial pneumonitis and encephalitis (n = 1), B cell lymphoma (n = 8), and hypogammaglobulinemia (n = 2). One patient was asymptomatic. Fourteen of 16 patients received 8/8 HLA-matched unrelated or related bone marrow grafts, whereas 2 patients received mismatched unrelated grafts. Acute graft-versus-host disease (GVHD) prophylaxis consisted of methylprednisolone and cyclosporine in all but 1 patient, who additionally received methotrexate. All patients had hematopoietic recovery. There were no cases of hepatic veno-occlusive disease or pulmonary hemorrhage. One patient (6%) developed acute GVHD and later also developed chronic GVHD (6%). Five patients (31%) developed mixed chimerism. Only 1 patient with mixed chimerism (6%) experienced a decline of donor chimerism to less than 50% but returned to full donor chimerism after infusion of donor lymphocytes and a CD34(+) selected stem cell boost. Infectious complications were frequent, particularly viral reactivation. One-year survival estimated by Kaplan-Meier analysis was 80%, with long-term survival estimated at 71%. Survival was similar for patients with or without a history of HLH (86% versus 75%, respectively, P = .70). There were no occurrences of lymphoma or HLH after HCT. RIC HCT with alemtuzumab, fludarabine, and melphalan is an effective treatment for patients with XLP1, offering good survival rates regardless of prior disease manifestations, including HLH.

X-linked lymphoproliferative syndromes and related autosomal recessive disorders

PURPOSE OF REVIEW

X-linked lymphoproliferative (XLP) syndromes and related autosomal disorders are severe primary immune deficiencies triggered by infection with Epstein-Barr virus (EBV), the causative agent of infectious mononucleosis. Recent findings reviewed herein provided key new insights into the genetic and immunological basis of these diseases. They also improved our comprehension of the immunological mechanisms controlling EBV infection.

RECENT FINDINGS

Mutations of an X-linked gene, SH2D1A, which encodes the signaling lymphocytic activation molecule (SLAM)-associated protein (SAP), are responsible for most cases of XLP disorders. More recently, other genetic causes for XLP syndromes and autosomal recessive variants of this disease were elucidated. Mutations in genes such as XIAP, ITK, and CD27 were identified. The clinical manifestations and immunological defects seen in these patients were characterized.

SUMMARY

The similarities and differences in immunological defects and clinical manifestations between XLP syndromes and related autosomal recessive disorders enabled important new insights into the pathogenesis of these diseases. They also helped our comprehension of the mechanisms implicated in the control of EBV infection. They suggested that CD8+ T cells, natural killer (NK) cells, and NKT cells are critically involved.

Familial hemophagocytic lymphohistiocytosis: when rare diseases shed light on immune system functioning

The human immune system depends on the activity of cytotoxic T lymphocytes (CTL), natural killer (NK) cells, and NKT cells in order to fight off a viral infection. Understanding the molecular mechanisms during this process and the role of individual proteins was greatly improved by the study of familial hemophagocytic lymphohistiocytosis (FHL). Since 1999, genetic sequencing is the gold standard to classify patients into different subgroups of FHL. The diagnosis, once based on a clinical constellation of abnormalities, is now strongly supported by the results of a functional flow-cytometry screening, which directs the genetic study. A few additional congenital immune deficiencies can also cause a resembling or even identical clinical picture to FHL. As in many other rare human disorders, the collection and analysis of a relatively large number of cases in registries is crucial to draw a complete picture of the disease. The conduction of prospective therapeutic trials allows investigators to increase the awareness of the disease and to speed up the diagnostic process, but also provides important functional and genetic confirmations. Children with confirmed diagnosis may undergo hematopoietic stem cell transplantation, which is the only cure known to date. Moreover, detailed characterization of these rare patients helped to understand the function of individual proteins within the exocytic machinery of CTL, NK, and NKT cells. Moreover, identification of these genotypes also provides valuable information on variant phenotypes, other than FHL, associated with biallelic and monoallelic mutations in the FHL-related genes. In this review, we describe how detailed characterization of patients with genetic hemophagocytic lymphohistiocytosis has resulted in improvement in knowledge regarding contribution of individual proteins to the functional machinery of cytotoxic T- and NK-cells. The review also details how identification of these genotypes has provided valuable information on variant phenotypes.

Stem cell transplantation for primary immune deficiency

PURPOSE OF REVIEW

In this article, we summarize the recent advances in treating primary immune deficiency (PID) disorders by stem cell transplantation (SCT); we have focused on articles published in the past 2 years since the last major review of SCT for PID.

RECENT FINDINGS

Analyses of the outcomes of SCT for PID by specific molecular defect have clarified which conditions are receptive to unconditioned transplants and which require more myeloablative conditioning. Improved outcomes for 'difficult' conditions [adenosine deaminase-severe combined immunodeficiency (ADA-SCID), major histocompatibility complex class II deficiency] and potential advantages of using cord blood as a stem cell source have also been described. Newborn screening for SCID identifies well babies with SCID: the optimal SCT protocol for such young infants remains to be determined. Reduced toxicity conditioning has been successfully used to treat conditions such as Wiskott-Aldrich syndrome and chronic granulomatous disease, offering curative engraftment with reduced transplant-related mortality. Similarly, treating children with familial hemophagocytic lymphohistiocytosis using reduced intensity conditioning SCT results in much improved outcomes. Advances in next generation sequencing have identified new diseases amenable to SCT, such as DOCK8 deficiency, resulting in improved quality of life and protection from malignancy.

SUMMARY

Recent studies suggest that further improvements in treating PID with SCT are possible with a greater understanding of the genetics and immunobiology of these diseases, facilitating the matching of donor type and conditioning regimens, or indeed alternative therapies (such as gene therapy) to specific PID disorders.

Hemophagocytic syndromes--an update

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome and not an independent disease. HLH represents the extreme end of a severe uncontrolled hyperinflammatory reaction that can occur in many underlying conditions. Genetic forms of HLHs are due to defects in transport, processing and function of cytotoxic granules in natural killer cells and cytotoxic T lymphocytes, and are not restricted to manifestation in childhood. Acquired forms of HLH are encountered in infections, autoinflammatory and autoimmune diseases, malignancies, acquired immune deficiency. Functional tests allow for differentiation between genetic and acquired HLH. Treatment aims at suppressing hypercytokinemia and eliminating activated and infected cells. It includes immunomodulatory and immunosuppressive agents, cytostatics, T-cell and cytokine antibodies. In genetic HLH cure can only be achieved with hematopoietic stem cell transplantation. Reduced-intensity conditioning regimens have considerably improved survival.

[Infections by Epstein-Barr virus and cytomegalovirus]

Infections by Epstein-Barr virus is the most common cause of infectious mononucleosis. We describe the diagnosis and different serological patterns, as well as its major complications related to the development of malignancies, lymphoproliferative disorders and autoimmune diseases. There is no effective treatment. Cytomegalovirus is the second cause of mononucleosis syndrome and the first of congenital infection in our environment. It has an high morbidity and mortality in immunocompromised patients, mainly solid organ transplants, bone marrow and coinfection by human immunodeficiency virus. Its treatment is based on antivirals, mainly ganciclovir and valganciclovir. We describe its management, adverse effects, new drugs and prophylaxis.

Cellular immune controls over Epstein-Barr virus infection: new lessons from the clinic and the laboratory

Epstein-Barr virus (EBV), a human herpesvirus with potent B cell growth transforming ability, induces multiple cellular immune responses in the infected host. How these host responses work together to prevent virus pathogenicity, and how immune imbalance predisposes to disease, remain poorly understood. Here, we describe three ongoing lines of enquiry that are shedding new light on these issues. These focus on: (i) patients with infectious mononucleosis or its fatal equivalent, X-linked lymphoproliferative disease; (ii) EBV infection in a range of new, genetically defined, primary immune deficiency states; and (iii) experimental infection in two complementary animal models, the rhesus macaque and the human haemopoietic stem cell reconstituted mouse.

XLP1 inhibitory effect by 2B4 does not affect DNAM-1 and NKG2D activating pathways in NK cells

X-linked lymphoproliferative disease 1 (XLP1) is a rare congenital immunodeficiency caused by SH2D1A (Xq25) mutations resulting in lack or dysfunction of SLAM-associated protein adaptor molecule. In XLP1 patients, upon ligand (CD48) engagement, 2B4 delivers inhibitory signals that impair the cytolytic activity of NK (and T) cells. This causes the selective inability to control EBV infections and the occurrence of B-cell lymphomas. Here, we show that in the absence of SLAM-associated protein, co-engagement of 2B4 with different activating receptors, either by antibodies or specific ligands on target cells, inhibits different ITAM-dependent signaling pathways including activating killer Ig-like receptors. In XLP1 NK cells, 2B4 affected both the cytolytic and IFN-γ production capabilities, functions that were restored upon disruption of the 2B4/CD48 interactions. Notably, we provide evidence that 2B4 dysfunction does not affect the activity of DNAM-1 and NKG2D triggering receptors. Thus, while CD48(+) B-EBV and lymphoma B cells devoid of NKG2D and DNAM-1 ligands were resistant to lysis, the preferential usage of these receptors allowed XLP1 NK cells to kill lymphomas that expressed sufficient amounts of the specific ligands. The study sheds new light on the XLP1 immunological defect and on the cross-talk of inhibitory 2B4 with triggering NK (and T) receptors.

Clinical flow cytometric screening of SAP and XIAP expression accurately identifies patients with SH2D1A and XIAP/BIRC4 mutations

INTRODUCTION

X-linked lymphoproliferative disease is caused by mutations in two genes, SH2D1A and XIAP/BIRC4. Flow cytometric methods have been developed to detect the gene products, SAP and XIAP. However, there is no literature describing the accuracy of flow cytometric screening performed in a clinical lab setting.

METHODS

We reviewed the clinical flow cytometric testing results for 656 SAP and 586 XIAP samples tested during a 3-year period. Genetic testing was clinically performed as directed by the managing physician in 137 SAP (21%) and 115 XIAP (20%) samples. We included these samples for analyses of flow cytometric test accuracy.

RESULTS

SH2D1A mutations were detected in 15/137 samples. SAP expression was low in 13/15 (sensitivity 87%, CI 61-97%). Of the 122 samples with normal sequencing, SAP was normal in 109 (specificity 89%, CI 82-94%). The positive predictive values (PPVs) and the negative predictive values (NPVs) were 50% and 98%, respectively. XIAP/BIRC4 mutations were detected in 19/115 samples. XIAP expression was low in 18/19 (sensitivity 95%, CI 73-100%). Of the 96 samples with normal sequencing, 59 had normal XIAP expression (specificity 61%, CI 51-71%). The PPVs and NPVs were 33% and 98%, respectively. Receiver-operating characteristic analysis was able to improve the specificity to 75%.

CONCLUSION

Clinical flow cytometric screening tests for SAP and XIAP deficiencies offer good sensitivity and specificity for detecting genetic mutations, and are characterized by high NPVs. We recommend these tests for patients suspected of having X-linked lymphoproliferative disease type 1 (XLP1) or XLP2.

Clinical and genetic features of 5 Chinese patients with X-linked lymphoproliferative syndrome

In this study, we report the clinical and genetic features of Chinese patients with X-linked lymphoproliferative syndrome (XLP). Male patients with fulminant infectious mononucleosis (FIM), Epstein-Barr virus (EBV)-associated hemophagocytic lymphohistiocytosis (HLH) or persistent EBV viremia were enrolled in this study. Direct sequencing was used to detect SH2D1A/XIAP gene mutations. The patients' clinical features were assessed by retrieval of data from medical records. Twenty-one male patients with FIM, EBV-associated HLH or persistent EBV viremia were evaluated. Four patients had SH2D1A mutations, and one patient had an XIAP mutation. All five of these patients had symptoms of HLH and EBV infection. Among the five patients, the youngest one was only 1 month old at onset. One patient exhibited hypogammaglobulinemia. Of four patients evaluated for immunological function, all exhibited reduced CD4/CD8 ratios. Three patients had rapid disease progression and died. One patient received haematopoietic stem cell transplantation and is well. The overall clinical phenotypes of Chinese patients with XLP matched previous reports. For patients with severe EBV-associated HLH, our results indicate the need to examine the possibility of XLP.

Graded defects in cytotoxicity determine severity of hemophagocytic lymphohistiocytosis in humans and mice

Primary hemophagocytic lymphohistiocytosis (HLH) is a life-threatening disease of hyperinflammation resulting from immune dysregulation due to inherited defects in the cytolytic machinery of natural killer and T cells. In humans, mutations in seven genes encoding proteins involved in cytolytic effector functions have so far been identified that predispose to HLH. However, although most affected patients develop HLH eventually, disease onset and severity are highly variable. Due to the genetic heterogeneity and variable time and nature of disease triggers, the immunological basis of these variations in HLH progression is incompletely understood. Several murine models of primary HLH have been established allowing to study HLH pathogenesis under more defined conditions. Here we directly compare the clinical HLH phenotype in six HLH-prone mouse strains with defects in the granule-dependent cytotoxic pathway. A severity gradient of HLH manifestations could be identified that is defined by the genetically determined residual lytic activity of cytotoxic T lymphocytes (CTL) and their ability to control lymphocytic choriomeningitis virus, which was used as a trigger for disease induction. Importantly, analysis of cohorts of HLH patients with severe bi-allelic mutations in the corresponding genes yielded a similar severity gradient in human HLH as reflected by the age at disease onset. Our findings define HLH as a threshold disease determined by subtle differences in the residual lytic activity of CTL.

Challenges and opportunities for international cooperative studies in pediatric hematopoeitic cell transplantation: priorities of the Westhafen Intercontinental Group

More than 20% of allogeneic hematopoietic cell transplantations (HCTs) are performed in children and adolescents at a large number of relatively small centers. Unlike adults, at least one-third of HCTs in children are performed for rare, nonmalignant indications. Clinical trials to improve HCT outcomes in children have been limited by small numbers and these pediatric-specific features. The need for a larger number of pediatric HCT centers to participate in trials has led to the involvement of international collaborative groups. Representatives of the Pediatric Blood and Marrow Transplant Consortium, European Group for Blood and Marrow Transplantation's Pediatric Working Group, International Berlin-Frankfurt-Munster (iBFm) Stem Cell Transplantation Committee, and Children's Oncology Group's Hematopoietic Stem Cell Transplantation Discipline Committee met on October 3, 2012, in Frankfurt, Germany to develop a consensus on the highest priorities in pediatric HCT. In addition, it explored the creation of an international consortium to develop studies focused on HCT in children and adolescents. This meeting led to the creation of an international HCT network, dubbed the Westhafen Intercontinental Group, to develop worldwide priorities and strategies to address pediatric HCT issues. This review outlines the priorities of need as identified by this consensus group.

Lymphoma and cerebral vasculitis in association with X-linked lymphoproliferative disease

Lymphoma is seen in up to 30% of patients with X-linked lymphoproliferative disease (XLP), but cerebral vasculitis related with XLP after cure of Burkitt lymphoma is rarely reported. We describe a case of a 5-year-old boy with XLP who developed cerebral vasculitis two years after cure of Burkitt lymphoma. He had Burkitt lymphoma at the age of 3 years and received chemotherapy (non-Hodgkin's lymphoma-Berlin-Frankfurt-Milan-90 protocol plus rituximab), which induced complete remission over the following two years. At the age of 5 years, the patient first developed headache, vomiting, and then intellectual and motorial retrogression. His condition was not improved after anti-infection, dehydration, or dexamethasone therapy. No tumor cells were found in his cerebrospinal fluid. Magnetic resonance imaging showed multiple non-homogeneous, hypodense masses along the bilateral cortex. Pathology after biopsy revealed hyperplasia of neurogliocytes and vessels, accompanied by lymphocyte infiltration but no tumor cell infiltration. Despite aggressive treatment, his cognition and motor functions deteriorated in response to progressive cerebral changes. The patient is presently in a vegetative state. We present this case to inform clinicians of association between lymphoma and immunodeficiency and explore an optimal treatment for lymphoma patients with compromised immune system.

Primary immunodeficiencies predisposed to Epstein-Barr virus-driven haematological diseases

Epstein-Barr virus (EBV), a ubiquitous human herpesvirus, maintains lifelong subclinical persistent infections in humans. In the circulation, EBV primarily infects the B cells, and protective immunity is mediated by EBV-specific cytotoxic T cells (CTLs) and natural killer (NK) cells. However, EBV has been linked to several devastating diseases, such as haemophagocytic lymphohistiocytosis (HLH) and lymphoproliferative diseases in the immunocompromised host. Some types of primary immunodeficiencies (PIDs) are characterized by the development of EBV-associated complications as their predominant clinical feature. The study of such genetic diseases presents an ideal opportunity for a better understanding of the biology of the immune responses against EBV. Here, we summarize the range of PIDs that are predisposed to EBV-associated haematological diseases, describing their clinical picture and pathogenetic mechanisms.

Advances in understanding the pathogenesis of HLH

Haemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory disorder resulting from immune dysfunction reflecting either primary immune deficiency or acquired failure of normal immune homeostasis. Familial HLH includes autosomal recessive and X-linked disorders characterized by uncontrolled activation of T cells and macrophages and overproduction of inflammatory cytokines, secondary to defects in genes encoding proteins involved in granule-dependent cytolytic pathways. In older children and adults, HLH is associated more often with infections, malignancies, autoimmune diseases, and acquired immune deficiencies. HLH, macrophage activation syndrome, sepsis, and systemic inflammatory response syndrome are different clinical entities that probably represent a common immunopathological state, termed cytokine storm. These conditions may be clinically indistinguishable; all include massive inflammatory response, elevated serum cytokine levels, multi-organ involvement, haemophagocytic macrophages, and often death. Tissues of haematopoietic and lymphoid function are directly involved; other organs are secondarily damaged by circulating cytokines and chemokines. Haemophagocytic disorders are now increasingly diagnosed in the context of severe inflammatory reactions to viruses, malignancies and systemic connective tissue diseases. Many of these cases may reflect underlying genetic predispositions to HLH. The detection of gene defects has contributed considerably to our understanding of HLH, but the mechanisms leading to acquired HLH have yet to be fully determined.

Treatment of Epstein Barr virus-induced haemophagocytic lymphohistiocytosis with rituximab-containing chemo-immunotherapeutic regimens

Haemophagocytic lymphohistiocytosis (HLH) is a life threatening complication of Epstein-Barr virus (EBV) infection. The anti-CD20 antibody rituximab depletes B cells, leading to improved outcomes for patients with EBV-associated B-lymphoproliferative disorders. To gather data on the use of rituximab in EBV-HLH, we performed a retrospective investigation involving 42 EBV-HLH patients who had received treatment with rituximab-containing regimens. On average, patients received 3 rituximab infusions (range 1-10) at a median dose of 375 mg/m(2) . In all patients, rituximab was administered with other HLH-directed medications, including steroids, etoposide and/or ciclosporin. Rituximab-containing regimens appeared well tolerated and improved clinical status in 43% of patients. Examination of laboratory data obtained prior to and within 2-4 weeks after the first rituximab dose revealed significant reductions in EBV load (median load pre-rituximab: 114,200 copies/ml, median post-rituximab: 225 copies/ml, P = 0.0001) and serum ferritin levels (median ferritin pre-rituximab: 4260 μg/l, median post-rituximab: 1149 μg/l, P = 0.001). Thus, when combined with conventional HLH-directed therapies, rituximab improves symptoms, reduces viral load and diminishes inflammation. These data support the incorporation of rituximab into future prospective clinical trials for patients with EBV-HLH.

Hemophagocytic lymphohistiocytosis: pathogenesis and treatment

Hemophagocytic lymphohistiocytosis (HLH) is not an independent disease but rather a life-threatening clinical syndrome that occurs in many underlying conditions and in all age groups. HLH is the consequence of a severe, uncontrolled hyperinflammatory reaction that in most cases is triggered by an infectious agent. Persistent stimulation of lymphocytes and histiocytes results in hypercytokinemia, leading to the characteristic symptoms of HLH. Genetic defects in familial HLH and in immunodeficiency syndromes associated with albinism affect the transport, processing, and function of cytotoxic granules in natural killer cells and cytotoxic T lymphocytes. This leads to defective killing of target cells and a failure to contract the immune response. The defects are increasingly found also in adolescents and adults. Acquired HLH occurs in autoinflammatory and autoimmune diseases (macrophage activation syndrome) and in patients with iatrogenic immunosuppression or with malignancies, but also in otherwise healthy persons with infections. Treatment of HLH aims at suppressing hypercytokinemia and eliminating the activated and infected cells. In genetic HLH, hematopoietic stem cell transplantation (HSCT) is needed for the correction of the immune defect. Treatment modalities include immunosuppressive, immunomodulatory, and cytostatic drugs; T-cell antibodies; and anticytokine agents. Using immunochemotherapy, familial HLH, which had been invariably fatal, has become a curable disease with more than 50% survivors. Reduced intensity conditioning for HSCT, which is associated with less transplantation-related mortality, will further improve cure rates.

SAP gene transfer restores cellular and humoral immune function in a murine model of X-linked lymphoproliferative disease

X-linked lymphoproliferative disease (XLP1) arises from mutations in the gene encoding SLAM-associated protein (SAP) and leads to abnormalities of NKT-cell development, NK-cell cytotoxicity, and T-dependent humoral function. Curative treatment is limited to allogeneic hematopoietic stem cell (HSC) transplantation. We tested whether HSC gene therapy could correct the multilineage defects seen in SAP(-/-) mice. SAP(-/-) murine HSCs were transduced with lentiviral vectors containing either SAP or reporter gene before transplantation into irradiated recipients. NKT-cell development was significantly higher and NK-cell cytotoxicity restored to wild-type levels in mice receiving the SAP vector in comparison to control mice. Baseline immunoglobulin levels were significantly increased and T-dependent humoral responses to NP-CGG, including germinal center formation, were restored in SAP-transduced mice.We demonstrate for the first time that HSC gene transfer corrects the cellular and humoral defects in SAP(-/-) mice providing proof of concept for gene therapy in XLP1.

Diagnostic evaluation of patients with suspected haemophagocytic lymphohistiocytosis

Haemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome characterized by severely disturbed immune homeostasis. It can affect all age groups. Diagnostic evaluation of the patient with suspected HLH has to address three main questions: (i) does the patient have HLH? There is no simple diagnostic test, but a number of clinical and laboratory criteria define this clinical syndrome. (ii) Can a trigger be identified? A variety of infections, malignant or autoimmune diseases can contribute to the disturbed immune homeostasis with important consequences for treatment. (iii) Does the patient suffer from a genetic disease predisposing to HLH? Recent advances in the understanding of the genetic and pathophysiological basis of HLH have enabled a better and more rapid answer to this question, which is relevant for prognosis and the decision to perform haematopoietic stem cell transplantation. This review summarizes the current diagnostic approach to the patient with HLH.

Allogeneic hematopoietic cell transplantation for XIAP deficiency: an international survey reveals poor outcomes

There have been no studies on patient outcome after allogeneic hematopoietic cell transplantation (HCT) in patients with X-linked inhibitor of apoptosis (XIAP) deficiency. To estimate the success of HCT, we conducted an international survey of transplantation outcomes. Data were reported for 19 patients. Seven patients received busulfan-containing myeloablative conditioning (MAC) regimens. Eleven patients underwent reduced intensity conditioning (RIC) regimens predominantly consisting of alemtuzumab, fludarabine, and melphalan. One patient received an intermediate-intensity regimen. Survival was poor in the MAC group, with only 1 patient surviving (14%). Most deaths were from transplantation-related toxicities, including venoocclusive disease and pulmonary hemorrhage. Of the 11 patients who received RIC, 6 are currently surviving at a median of 570 days after HCT (55%). Preparative regimen and HLH activity affected outcomes, and of RIC patients reported to be in remission from HLH, survival is 86% (P = .03). We conclude that MAC regimens should not be used for patients with XIAP deficiency. It is possible that the loss of XIAP and its antiapoptotic functions contributes to the high incidence of toxicities observed with MAC regimens. RIC regimens should be pursued with caution and, if possible, efforts should be made to ensure HLH remission before HCT in these patients.

Clinical features and outcome of X-linked lymphoproliferative syndrome type 1 (SAP deficiency) in Japan identified by the combination of flow cytometric assay and genetic analysis

OBJECTIVE

X-linked lymphoproliferative syndrome (XLP) type 1 is a rare immunodeficiency, which is caused by mutations in SH2D1A gene. The prognosis of XLP is very poor, and hematopoietic stem cell transplantation (HSCT) is the only curative therapy. We characterized the clinical features and outcome of Japanese patients with XLP-1.

METHODS

We used a combination of flow cytometric analysis and genetic analysis to identify XLP-1 and reviewed the patient characteristics and survival with HSCT.

RESULTS

We identified 33 patients from 21 families with XLP-1 in Japan. Twenty-one of the patients (65%) who did not undergo a transplant died of the disease and complications. Twelve patients underwent HSCT, and 11 of these (92%) survived.

CONCLUSION

We described the clinical characteristics and outcomes of Japanese patients with XLP-1, and HSCT was the only curative therapy for XLP-1. The rapid and accurate diagnosis of XLP with the combination of flow cytometric assay and genetic analysis is important.

SAP and XIAP deficiency in hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a multisystem inflammatory disorder due to cytokine overproduction from excessively activated lymphocytes and macrophages. HLH has been divided into two subgroups: primary HLH and secondary HLH. Primary HLH includes PRF1, UNC13D, STX11, STXBP2, RAB27A, LYST, SH2D1A and XIAP gene mutations; and secondary HLH is associated with infections, malignancies and autoimmune diseases. Among primary HLH-related genes, SH2D1A and XIAP are genetically responsible for X-linked lymphoproliferative syndrome (XLP) due to signaling-lymphocytic-activation-molecule-associated protein (SAP) and XIAP deficiencies, respectively. XLP is characterized by extreme vulnerability to Epstein-Barr virus infection. The major clinical manifestations of XLP consist of HLH (60%), lymphoproliferative disorder (30%) and dysgammaglobulinemia (30%). Analysis of clinical phenotypes of XLP patients suggests that XLP predominantly shows familial HLH phenotypes, whereas some XLP patients present sporadic HLH. For many decades, clinicians and investigators have been concerned with possible XLP in young boys presenting with Epstein-Barr-virus-associated HLH. This review aims to describe the new knowledge about XLP and to draw the attention of the pediatrician to XLP, which should be differentiated from other forms of HLH.

Positive and negative signaling through SLAM receptors regulate synapse organization and thresholds of cytolysis

X-linked lymphoproliferative syndrome, characterized by fatal responses to Epstein-Barr virus infection, is caused by mutations affecting the adaptor SAP, which links SLAM family receptors to downstream signaling. Although cytotoxic defects in SAP-deficient T cells are documented, the mechanism remains unclear. We show that SAP-deficient murine CD8(+) T cells exhibited normal cytotoxicity against fibrosarcoma targets, yet had impaired adhesion to and killing of B cell and low-avidity T cell targets. SAP-deficient cytotoxic lymphocytes showed specific defects in immunological synapse organization with these targets, resulting in inefficient actin clearance. In the absence of SAP, signaling through the SLAM family members Ly108 and 2B4 resulted in increased recruitment of the SHP-1 phosphatase, associated with altered SHP-1 localization and decreased activation of Src kinases at the synapse. Hence, SAP and SLAM receptors regulate positive and negative signals required for organizing the T cell:B cell synapse and setting thresholds for cytotoxicity against distinct cellular targets.

Familial and acquired hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening syndrome in which an uncontrolled and ineffective immune response, triggered in most cases by infectious agents, leads to severe hyperinflammation. Familial forms of HLH (FHL), which are increasingly found also in adolescents and adults, are due to genetic defects leading to impaired function of natural killer cells and cytotoxic T cells. These mutations occur either in the perforin gene or in genes important for the exocytosis of cytotoxic granules. Cytotoxic granules contain perforin and granzymes, which induce apoptosis upon entering (infected) target cells. Additionally, perforin is important for the downregulation of the immune response. Acquired forms of HLH are encountered in association with (usually) viral infections, autoinflammatory/autoimmune diseases, malignant diseases, and acquired immune deficiency states (e.g., after organ transplantation). Treatment of HLH includes immune-suppressive and immune-modulatory agents, cytostatic drugs, and biological response modifiers. For patients with FHL, stem cell transplantation is indicated and can be curative.

Expansion of somatically reverted memory CD8+ T cells in patients with X-linked lymphoproliferative disease caused by selective pressure from Epstein-Barr virus

In patients with XLP, a primary immunodeficiency caused by mutations in SH2D1A, EBV infection can lead to somatic reversion of the disease-causing mutation selectively in effector memory CD8 T cells; reverted CD8 cells are better able to respond to and kill EBV-infected cells.

Patients with the primary immunodeficiency X-linked lymphoproliferative disease (XLP), which is caused by mutations in SH2D1A, are highly susceptible to Epstein-Barr virus (EBV) infection. Nonetheless, some XLP patients demonstrate less severe clinical manifestations after primary infection. SH2D1A encodes the adaptor molecule SLAM-associated protein (SAP), which is expressed in T and natural killer cells and is required for cytotoxicity against B cells, the reservoir for EBV. It is not known why the clinical presentation of XLP is so variable. In this study, we report for the first time the occurrence of somatic reversion in XLP. Reverted SAP-expressing cells resided exclusively within the CD8⁺ T cell subset, displayed a CD45RA⁻CCR7⁻ effector memory phenotype, and were maintained at a stable level over time. Importantly, revertant CD8⁺ SAP⁺ T cells, but not SAP⁻ cells, proliferated in response to EBV and killed EBV-infected B cells. As somatic reversion correlated with EBV infection, we propose that the virus exerts a selective pressure on the reverted cells, resulting in their expansion in vivo and host protection against ongoing infection.

Characterization of Ly108 in the thymus: evidence for distinct properties of a novel form of Ly108

Ly108 (CD352) is a member of the signaling lymphocyte activation molecule (SLAM) family of receptors that signals through SLAM-associated protein (SAP), an SH2 domain protein that can function by the recruitment of Src family kinases or by competition with phosphatases. Ly108 is expressed on a variety of hematopoietic cells, with especially high levels on developing thymocytes. We find that Ly108 is constitutively tyrosine phosphorylated in murine thymi in a SAP- and Fyn kinase-dependent manner. Phosphorylation of Ly108 is rapidly lost after thymocyte disaggregation, suggesting dynamic contact-mediated regulation of Ly108. Similar to recent reports, we find at least three isoforms of Ly108 mRNA and protein in the thymus, which are differentially expressed in the thymi of C57BL/6 and 129S6 mice that express the lupus-resistant and lupus-prone haplotypes of Ly108, respectively. Notably, the recently described novel isoform Ly108-H1 is not expressed in mice having the lupus-prone haplotype of Ly108, but is expressed in C57BL/6 mice. We further provide evidence for differential phosphorylation of these isoforms; the novel Ly108-H1does not undergo tyrosine phosphorylation, suggesting that it functions as a decoy isoform that contributes to the reduced overall phosphorylation of Ly108 seen in C57BL/6 mice. Our study suggests that Ly108 is dynamically regulated in the thymus, shedding light on Ly108 isoform expression and phosphorylation.

The expanding spectrum of hemophagocytic lymphohistiocytosis

PURPOSE OF REVIEW

Hemophagocytic lymphohistiocytosis (HLH) is more widely recognized by clinicians. No longer viewed as a disorder of young children, adult patients are now being identified and treated. In this review, I summarize clinical features of patients with recently identified genetic causes, discuss a new paradigm for understanding the clinical evolution of HLH, and update current results with hematopoietic cell transplantation.

RECENT FINDINGS

The list of genetic defects underlying HLH continues to grow. Among the autosomal recessive defects underlying HLH, we add STX11 (Syntaxin 11) - a snare protein, and MUNC18-2 (also known as STXBP2 - Syntaxin-binding protein). These two proteins now join MUNC 13-4 as components of the degranulation machinery in cytotoxic lymphocytes, responsible for the delivery of Perforin and Granzyme B to selectively kill target cells. The mechanism of action in the newest X-linked disorder associated with HLH, XIAP deficiency (also termed XLP 2), is currently unknown. Treatment of HLH has also improved in recent years, at least in experienced centers where a significant number of patients are seen. Clinicians who are familiar with the dynamic evolution of the disease are learning how to modify treatment when initial or continuation therapy fails to achieve a stable clinical status, preferably clinical remission. Use of reduced intensity conditioning protocols pretransplant has resulted in superior short-term and long-term survival rates of greater than 85%.

SUMMARY

Substantial progress continues to be made in exploring the complex cause and pathophysiology of HLH. Hand in hand, a greater recognition of the condition has led to improved treatments.

Skin lesions in a boy with X-linked lymphoproliferative disorder: comparison of 5 SH2D1A deletion cases

SH2D1A gene defects are the cause of X-linked lymphoproliferative disorder (XLP-1), a rare condition characterized by severe immune dysregulation. We present a patient lacking the typical symptoms of XLP-1, but experiencing a severe unusual skin condition encompassing features of dermatosclerosis and vesiculobullous skin disease. A maternal cousin of the patient was diagnosed with XLP-1 and found to carry a deletion of the SH2D1A gene. SH2D1A deletion was also identified in our patient, which offered a possible explanation for his skin symptoms. Subsequent analysis showed that the deletion in both cousins was identical and involved the whole SH2D1A gene and a part of the adjacent ODZ1 gene. High phenotypic variability of XLP-1 observed in this family prompted us to analyze the genotype-phenotype correlation of 2 different-sized deletions involving SH2D1A and ODZ1 in 5 patients from 2 families, and we report the clinical and laboratory data on these individuals. Our findings illustrate the wide clinical variability of XLP-1, both inter- and intrafamilial, which may complicate the diagnosis of this condition. The comparison of phenotypes of our patients argues against a strong involvement of the ODZ1 gene in the skin disorder and other symptoms observed in our index patient. His hitherto not described severe skin condition extends the phenotypic range of XLP-1.

A prospective evaluation of degranulation assays in the rapid diagnosis of familial hemophagocytic syndromes

Familial hemophagocytic lymphohistiocytosis (FHL) is a life-threatening disorder of immune regulation caused by defects in lymphocyte cytotoxicity. Rapid differentiation of primary, genetic forms from secondary forms of hemophagocytic lymphohistiocytosis (HLH) is crucial for treatment decisions. We prospectively evaluated the performance of degranulation assays based on surface up-regulation of CD107a on natural killer (NK) cells and cytotoxic T lymphocytes in a cohort of 494 patients referred for evaluation for suspected HLH. Seventy-five of 77 patients (97%) with FHL3-5 and 11 of 13 patients (85%) with Griscelli syndrome type 2 or Chediak-Higashi syndrome had abnormal resting NK-cell degranulation. In contrast, NK-cell degranulation was normal in 14 of 16 patients (88%) with X-linked lymphoproliferative disease and in 8 of 14 patients (57%) with FHL2, who were identified by diminished intracellular SLAM-associated protein (SAP), X-linked inhibitor of apoptosis protein (XIAP), and perforin expression, respectively. Among 66 patients with a clinical diagnosis of secondary HLH, 13 of 59 (22%) had abnormal resting NK-cell degranulation, whereas 0 of 43 had abnormal degranulation using IL-2-activated NK cells. Active disease or immunosuppressive therapy did not impair the assay performance. Overall, resting NK-cell degranulation below 5% provided a 96% sensitivity for a genetic degranulation disorder and a specificity of 88%. Therefore, degranulation assays allow a rapid and reliable classification of patients, benefiting treatment decisions.

Monogenic autoimmunity

Monogenic autoimmune syndromes provide a rare yet powerful glimpse into the fundamental mechanisms of immunologic tolerance. Such syndromes reveal not only the contribution of an individual breakpoint in tolerance but also patterns in the pathogenesis of autoimmunity. Disturbances in innate immunity, a system built for ubiquitous sensing of danger signals, tend to generate systemic autoimmunity. For example, defects in the clearance of self-antigens and chronic stimulation of type 1 interferons lead to the systemic autoimmunity seen in C1q deficiency, SPENCDI, and AGS. In contrast, disturbances of adaptive immunity, which is built for antigen specificity, tend to produce organ-specific autoimmunity. Thus, the loss of lymphocyte homeostasis, whether through defects in apoptosis, suppression, or negative selection, leads to organ-specific autoimmunity in ALPS, IPEX, and APS1. We discuss the unique mechanisms of disease in these prominent syndromes as well as how they contribute to the spectrum of organ-specific or systemic autoimmunity. The continued study of rare variants in autoimmune disease will inform future investigations and treatments directed at rare and common autoimmune diseases alike.

Familial hemophagocytic lymphohistiocytosis: a model for understanding the human machinery of cellular cytotoxicity

Cytotoxic T lymphocytes, natural killer cells, and NKT cells are effector cells able to kill infected cells. In some inherited human disorders, a defect in selected proteins involved in the cellular cytotoxicity mechanism results in specific clinical syndromes, grouped under the name of familial hemophagocytic lymphohistiocytosis. Recent advances in genetic studies of these patients has allowed the identification of different genetic subsets. Additional genetic immune deficiencies may also induce a similar clinical picture. International cooperation and prospective trials resulted in refining the diagnostic and therapeutic approach to these rare diseases with improved outcome but also with improved knowledge of the mechanisms underlying granule-mediated cellular cytotoxicity in humans.

Familial hemophagocytic lymphohistiocytosis type 3 (FHL3) caused by deep intronic mutation and inversion in UNC13D

Familial hemophagocytic lymphohistiocytosis (FHL) is an autosomal recessive, often-fatal hyperinflammatory disorder. Mutations in PRF1, UNC13D, STX11, and STXBP2 are causative of FHL2, 3, 4, and 5, respectively. In a majority of suspected FHL patients from Northern Europe, sequencing of exons and splice sites of such genes required for lymphocyte cytotoxicity revealed no or only monoallelic UNC13D mutations. Here, in 21 patients, we describe 2 pathogenic, noncoding aberrations of UNC13D. The first is a point mutation localized in an evolutionarily conserved region of intron 1. This mutation selectively impairs UNC13D transcription in lymphocytes, abolishing Munc13-4 expression. The second is a 253-kb inversion straddling UNC13D, affecting the 3′-end of the transcript and likewise abolishing Munc13-4 expression. Carriership of the intron 1 mutation was found in patients across Europe, whereas carriership of the inversion was limited to Northern Europe. Notably, the latter aberration represents the first description of an autosomal recessive human disease caused by an inversion. These findings implicate an intronic sequence in cell-type specific expression of Munc13-4 and signify variations outside exons and splice sites as a common cause of FHL3. Based on these data, we propose a strategy for targeted sequencing of evolutionary conserved noncoding regions for the diagnosis of primary immunodeficiencies.

Reduced-intensity conditioning haematopoietic cell transplantation for haemophagocytic lymphohistiocytosis: an important step forward

Haemophagocytic lymphohistiocytosis (HLH) is a life-threatening immunodeficiency characterized by severe systemic hyper-inflammatory responses to infectious or other triggers of the immune system. In many patients, the underlying cause of HLH is a genetic defect leading to defective CD8(+) T cell and natural killer cell granule-mediated cytotoxicity. The treatment of HLH consists principally of immune suppression followed by allogeneic haematopoietic cell transplantation (HCT) to cure the underlying defect and prevent relapse of HLH. Initial treatment regimens consist of steroids coupled with either etoposide or antithymocyte globulin, ± ciclosporin. Complete responses are observed in only 50-75% of patients and even after a complete response, relapse and death still occur. The only definitive, long-term cure for patients with genetic forms of HLH is allogeneic HCT. Unfortunately, allogeneic HCT for patients with HLH is often complicated by critical illness, extensive organ involvement, active infections, or refractory HLH. For these reasons, patients are unusually prone to developing transplant-related toxicities and complications. In recent years, great strides have been made with regard to the care and transplantation of patients with HLH. Here we review the current state of the treatment of patients with HLH with allogeneic HCT, highlighting the important steps forward that have been made with reduced-intensity conditioning.

SLAM family receptors and SAP adaptors in immunity

The signaling lymphocyte activation molecule (SLAM)-associated protein, SAP, was first identified as the protein affected in most cases of X-linked lymphoproliferative (XLP) syndrome, a rare genetic disorder characterized by abnormal responses to Epstein-Barr virus infection, lymphoproliferative syndromes, and dysgammaglobulinemia. SAP consists almost entirely of a single SH2 protein domain that interacts with the cytoplasmic tail of SLAM and related receptors, including 2B4, Ly108, CD84, Ly9, and potentially CRACC. SLAM family members are now recognized as important immunomodulatory receptors with roles in cytotoxicity, humoral immunity, autoimmunity, cell survival, lymphocyte development, and cell adhesion. In this review, we cover recent findings on the roles of SLAM family receptors and the SAP family of adaptors, with a focus on their regulation of the pathways involved in the pathogenesis of XLP and other immune disorders.