Molecular and cellular pathogenesis of X-linked lymphoproliferative disease

Diagnostic tests for primary immunodeficiency disorders: Classic and genetic testing

Primary immunodeficiency diseases encompass a variety of genetic conditions characterized by a compromised immune system and typically results in increased susceptibility to infection. In fact, they also manifest as autoimmunity, autoinflammation, atopic diseases, and malignancy. Currently, the number of recognized monogenic primary immunodeficiency disorders is set at ∼500 different entities, owing to the exponential use of unbiased genetic testing for disease discovery. In addition, the prevalence of secondary immunodeficiency has also been on the rise due to the increased use of immunosuppressive drugs to treat diseases based on immune dysregulation, an increase in the number of individuals undergoing hematopoietic stem cell transplantation, and other chronic medical conditions, including autoimmunity. Although the clinical symptoms of immunodeficiency disorders are broad, an early diagnosis and tailored management strategies are essential to mitigate the risk of infections and prevent disease-associated morbidity. Generally, the medical history and physical examination can provide useful information that can help delineate the possibility of immune defects. In turn, this makes it feasible to select focused laboratory tests that identify immunodeficiency disorders based on the specific immune cells and their functions or products that are affected. Laboratory evaluation involves quantitative and functional classic testing (e.g., leukocyte counts, serum immunoglobulin levels, specific antibody titers in response to vaccines, and enumeration of lymphocyte subsets) as well as genetic testing (e.g., individual gene evaluation via Sanger sequencing or unbiased evaluation based on next-generation sequencing). However, in many cases, a diagnosis also requires additional advanced research techniques to validate genetic or other findings. This article updates clinicians about available laboratory tests for evaluating the immune system in patients with primary immunodeficiency disorders. It also provides a comprehensive list of testing options, organized based on different components of host defense.

Cytokine Storm Syndromes Associated with Epstein-Barr Virus

Epstein-Barr virus (EBV) is a ubiquitous and predominantly B cell tropic virus. One of the most common viruses to infect humans, EBV, is best known as the causative agent of infectious mononucleosis (IM). Although most people experience asymptomatic infection, EBV is a potent immune stimulus and as such it elicits robust proliferation and activation of the B-lymphocytes it infects as well as the immune cells that respond to infection. In certain individuals, such as those with inherited or acquired defects affecting the immune system, failure to properly control EBV leads to the accumulation of EBV-infected B cells and EBV-reactive immune cells, which together contribute to the development of often life-threatening cytokine storm syndromes (CSS). Here, we review the normal immune response to EBV and discuss several CSS associated with EBV, such as chronic active EBV infection, hemophagocytic lymphohistiocytosis, and post-transplant lymphoproliferative disorder. Given the critical role for cytokines in driving inflammation and contributing to disease pathogenesis, we also discuss how targeting specific cytokines provides a rational and potentially less toxic treatment for EBV-driven CSS.

Genetics of Primary Hemophagocytic Lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) constitutes a rare, potentially life-threatening hyperinflammatory immune dysregulation syndrome that can present with a variety of clinical signs and symptoms, including fever, hepatosplenomegaly, and abnormal laboratory and immunological findings such as cytopenias, hyperferritinemia, hypofibrinogenemia, hypertriglyceridemia, elevated blood levels of soluble CD25 (interleukin (IL)-2 receptor α-chain), or diminished natural killer (NK)-cell cytotoxicity (reviewed in detail in Chapter 11 of this book). While HLH can be triggered by an inciting event (e.g., infections), certain monogenic causes have been associated with a significantly elevated risk of development of HLH, or recurrence of HLH in patients who have recovered from their disease episode. These monogenic predisposition syndromes are variably referred to as "familial" (FHL) or "primary" HLH (henceforth referred to as "pHLH") and are the focus of this chapter. Conversely, secondary HLH (sHLH) often occurs in the absence of monogenic etiologies that are commonly associated with pHLH and can be triggered by infections, malignancies, or rheumatological diseases; these triggers and the genetics associated with sHLH are discussed in more detail in other chapters in this book.

Approaching hemophagocytic lymphohistiocytosis

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

Cytokine Storm Syndromes in Pediatric Patients

Cytokine storm syndromes (CSS) represent a diverse group of disorders characterized by severe overactivation of the immune system. In the majority of patients, CSS arise from a combination of host factors, including genetic risk and predisposing conditions, and acute triggers such as infections. CSS present differently in adults than in children, who are more likely to present with monogenic forms of these disorders. Individual CSS are rare, but in aggregate represent an important cause of severe illness in both children and adults. We present 3 rare, illustrative cases of CSS in pediatric patients that describe the spectrum of CSS.

Human natural killer cells: Form, function, and development

Human natural killer (NK) cells are innate lymphoid cells that mediate important effector functions in the control of viral infection and malignancy. Their ability to distinguish "self" from "nonself" and lyse virally infected and tumorigenic cells through germline-encoded receptors makes them important players in maintaining human health and a powerful tool for immunotherapeutic applications and fighting disease. This review introduces our current understanding of NK cell biology, including key facets of NK cell differentiation and the acquisition and execution of NK cell effector function. Further, it addresses the clinical relevance of NK cells in both primary immunodeficiency and immunotherapy. It is intended to provide an up-to-date and comprehensive overview of this important and interesting innate immune effector cell subset.

Allosteric inhibition of SHP2 rescues functional T-cell abnormalities in SAP deficiency

BACKGROUND

X-linked lymphoproliferative disease (XLP) is a primary immunodeficiency arising from SH2D1A mutations leading to loss of SLAM-associated protein (SAP). SAP is an intracellular adaptor protein that binds to SLAM family receptors and is expressed in specific lymphoid lineages. In T cells, SAP relays activatory signals from the T-cell receptor but in its absence SH2 containing protein tyrosine phosphase-1 (SHP1), SH2 containing protein tyrosine phosphase-2 (SHP2), and SH2 containing inositol 5'-phosphatase proteins (SHIP) induce T-cell inhibitory signals leading to abnormal T-cell responses. This results in severe clinical manifestations including immune dysregulation, dysgammaglobulinemia, lymphoma, and hemophagocytic lymphohistiocytosis. Current treatment relies on supportive therapies including immunoglobulin replacement and symptom-directed therapy, with hematopoietic stem cell transplant offering the only curative option.

OBJECTIVES

As most XLP symptoms are due to defective T-cell function, this study investigated whether inhibition of SHP2 can restore cellular function in the absence of SAP.

METHODS

Healthy donor and XLP patient T cells were activated with anti-CD3/CD28 in T-cell media supplemented with a SHP2 inhibitor (RMC-4550 in vitro for 24 hours) and functional assays were performed to assess follicular T_H (T_FH) cell function, CD8 cytotoxicity, and sensitivity to restimulation-induced cell death. Additionally, SAP-deficient (SAP^y/-) mice were treated with RMC-4550 before T-cell mediated challenge with 4-hydroxy-3-nitrophenylacetly conjugated chicken gammaglobulin and subsequent assessment of humoral immunity analyzing T_FH cell population, germinal center formation, and antigen-dependent immunoglobulin secretion.

RESULTS

This study shows that the use of RMC-4550 restores T-cell function in XLP patient cells and a SAP^y/- model, demonstrating restoration of T_FH cell function through immunoglobulin and cytokine secretion analysis alongside rescue of cytotoxicity and restimulation-induced cell death.

CONCLUSIONS

These data suggest that SHP2 inhibitors could offer a novel and effective targeted treatment approach for patients with XLP.

Epstein Barr virus-mediated transformation of B cells from XIAP-deficient patients leads to increased expression of the tumor suppressor CADM1

X-linked lymphoproliferative disease (XLP) is either caused by loss of the SLAM-associated protein (SAP; XLP-1) or the X-linked inhibitor of apoptosis (XIAP; XLP-2). In both instances, infection with the oncogenic human Epstein Barr virus (EBV) leads to pathology, but EBV-associated lymphomas only emerge in XLP-1 patients. Therefore, we investigated the role of XIAP during B cell transformation by EBV. Using humanized mice, IAP inhibition in EBV-infected mice led to a loss of B cells and a tendency to lower viral titers and lymphomagenesis. Loss of memory B cells was also observed in four newly described patients with XIAP deficiency. EBV was able to transform their B cells into lymphoblastoid cell lines (LCLs) with similar growth characteristics to patient mothers' LCLs in vitro and in vivo. Gene expression analysis revealed modest elevated lytic EBV gene transcription as well as the expression of the tumor suppressor cell adhesion molecule 1 (CADM1). CADM1 expression on EBV-infected B cells might therefore inhibit EBV-associated lymphomagenesis in patients and result in the absence of EBV-associated malignancies in XLP-2 patients.

Modulation of TCR signalling components occurs prior to positive selection and lineage commitment in iNKT cells

iNKT cells play a critical role in controlling the strength and character of adaptive and innate immune responses. Their unique functional characteristics are induced by a transcriptional program initiated by positive selection mediated by CD1d expressed by CD4⁺CD8⁺ (double positive, DP) thymocytes. Here, using a novel Vα14 TCR transgenic strain bearing greatly expanded numbers of CD24^hiCD44^loNKT cells, we examined transcriptional events in four immature thymic iNKT cell subsets. A transcriptional regulatory network approach identified transcriptional changes in proximal components of the TCR signalling cascade in DP NKT cells. Subsequently, positive and negative selection, and lineage commitment, occurred at the transition from DP NKT to CD4 NKT. Thus, this study introduces previously unrecognised steps in early NKT cell development, and separates the events associated with modulation of the T cell signalling cascade prior to changes associated with positive selection and lineage commitment.

Improved transplant outcomes with myeloablative conditioning for hemophagocytic lymphohistiocytosis in HLA-matched and mismatched donors: a national multicenter retrospective study

We report the results of national retrospective study of 45 children with hemophagocytic lymphohistiocytosis (HLH) who underwent allogeneic hematopoietic stem-cell transplantation (HSCT) in Israel between the years 2000-2018. Donors were either HLA-matched (n = 26), partially mismatched (n = 7), haploidentical (n = 8), or cord-blood (n = 4). Myeloablative conditioning (MAC) was used in 20 procedures, and reduced-intensity conditioning (RIC) in 25. Forty-two patients engrafted, two had primary graft failure (one successfully retransplanted), one died prior to engraftment, and two developed secondary graft failure. Of the eight patients who had mixed donor chimerism at day 30 (5-95%), five achieved stable mixed or full donor chimerism. The 5-year probabilities of overall survival and event-free survival (EFS) were 86% and 82%, respectively. Five-year EFS was lower for patients receiving RIC compared to MAC (72% vs. 100%, p = 0.018) and following alternative-donor transplant (68% vs. 92% for HLA-matched donors, p = 0.034), mostly due to increased transplant-related mortality (TRM). Thus, both HLA-matched and alternative donor transplant procedures may benefit form a myeloablative conditioning regimen.

Diacylglycerol Kinase alpha in X Linked Lymphoproliferative Disease Type 1

Diacylglycerol kinases are intracellular enzymes that control the balance between the secondary messengers diacylglycerol and phosphatidic acid. DGKα and DGKζ are the prominent isoforms that restrain the intensity of T cell receptor signalling by metabolizing PLCγ generated diacylglycerol. Thus, their activity must be tightly controlled to grant cellular homeostasis and refine immune responses. DGKα is specifically inhibited by strong T cell activating signals to allow for full diacylglycerol signalling which mediates T cell response. In X-linked lymphoproliferative disease 1, deficiency of the adaptor protein SAP results in altered T cell receptor signalling, due in part to persistent DGKα activity. This activity constrains diacylglycerol levels, attenuating downstream pathways such as PKCθ and Ras/MAPK and decreasing T cell restimulation induced cell death. This is a form of apoptosis triggered by prolonged T cell activation that is indeed defective in CD8⁺ cells of X-linked lymphoproliferative disease type 1 patients. Accordingly, inhibition or downregulation of DGKα activity restores in vitro a correct diacylglycerol dependent signal transduction, cytokines production and restimulation induced apoptosis. In animal disease models, DGKα inhibitors limit CD8⁺ expansion and immune-mediated tissue damage, suggesting the possibility of using inhibitors of diacylglycerol kinase as a new therapeutic approach.

Signaling pathways involved in the T-cell-mediated immunity against Epstein-Barr virus: Lessons from genetic diseases

Primary immunodeficiencies (PIDs) provide researchers with unique models to understand in vivo immune responses in general and immunity to infections in particular. In humans, impaired immune control of Epstein-Barr virus (EBV) infection is associated with the occurrence of several different immunopathologic conditions; these include non-malignant and malignant B-cell lymphoproliferative disorders, hemophagocytic lymphohistiocytosis (HLH), a severe inflammatory condition, and a chronic acute EBV infection of T cells. Studies of PIDs associated with a predisposition to develop severe, chronic EBV infections have led to the identification of key components of immunity to EBV - notably the central role of T-cell expansion and its regulation in the pathophysiology of EBV-associated diseases. On one hand, the defective expansion of EBV-specific CD8 T cells results from mutations in genes involved in T-cell activation (such as RASGRP1, MAGT1, and ITK), DNA metabolism (CTPS1) or co-stimulatory pathways (CD70, CD27, and TNFSFR9 (also known as CD137/4-1BB)) leads to impaired elimination of proliferating EBV-infected B cells and the occurrence of lymphoma. On the other hand, protracted T-cell expansion and activation after the defective killing of EBV-infected B cells is caused by genetic defects in the components of the lytic granule exocytosis pathway or in the small adapter protein SH2D1A (also known as SAP), a key activator of T- and NK cell-cytotoxicity. In this setting, the persistence of EBV-infected cells results in HLH, a condition characterized by unleashed T-cell and macrophage activation. Moreover, genetic defects causing selective vulnerability to EBV infection have highlighted the role of co-receptor molecules (CD27, CD137, and SLAM-R) selectively involved in immune responses against infected B cells via specific T-B cell interactions.

Flow Cytometry Contributions for the Diagnosis and Immunopathological Characterization of Primary Immunodeficiency Diseases With Immune Dysregulation

Almost 70 years after establishing the concept of primary immunodeficiency disorders (PIDs), more than 320 monogenic inborn errors of immunity have been identified thanks to the remarkable contribution of high-throughput genetic screening in the last decade. Approximately 40 of these PIDs present with autoimmune or auto-inflammatory symptoms as the primary clinical manifestation instead of infections. These PIDs are now recognized as diseases of immune dysregulation. Loss-of function mutations in genes such as FOXP3, CD25, LRBA, IL-10, IL10RA, and IL10RB, as well as heterozygous gain-of-function mutations in JAK1 and STAT3 have been reported as causative of these disorders. Identifying these syndromes has considerably contributed to expanding our knowledge on the mechanisms of immune regulation and tolerance. Although whole exome and whole genome sequencing have been extremely useful in identifying novel causative genes underlying new phenotypes, these approaches are time-consuming and expensive. Patients with monogenic syndromes associated with autoimmunity require faster diagnostic tools to delineate therapeutic strategies and avoid organ damage. Since these PIDs present with severe life-threatening phenotypes, the need for a precise diagnosis in order to initiate appropriate patient management is necessary. More traditional approaches such as flow cytometry are therefore a valid option. Here, we review the application of flow cytometry and discuss the relevance of this powerful technique in diagnosing patients with PIDs presenting with immune dysregulation. In addition, flow cytometry represents a fast, robust, and sensitive approach that efficiently uncovers new immunopathological mechanisms underlying monogenic PIDs.

Rare cause of Hemophagocytic Lymphohistiocytosis due to mutation in PRF1 and SH2D1A genes in two children - a case report with a review

Background

Hemophagocytic Lymphohistiocytosis (HLH) is a rare, complex, life-threatening hyper-inflammatory condition due to over activation of lymphocytes mediated secretory cytokines in the body. It occurs as a primary HLH due to genetic defect that mostly occurs in the childhood and associated with early neonatal death. Secondary HLH is triggered by secondary to infection and can occur at any age.

Case presentation

The current report presents two cases of HLH. Case 1, three-months-old boy born to second degree consanguineous parents was clinically suspected with HLH. A pathogenic variant in exon 2 of PRF1 gene [c.386G > C (p.Trp129Ser); FLH-type2] was detected. The parents and the fetus under investigation were shown to be heterozygous carriers, while Case-1 was homozygous for the said variant. Case 2, a one and half-year old male child referred for work-up was born to non-consanguineous young parents. His HLH suspicion was in accordance with HLH-2004 Revised diagnostic guidelines (fulfilling 5/8 criteria). Molecular study revealed hemizygous likely pathogenic variant c.138-3C > G in intron 1 of SH2D1A gene. Both the mother and younger sister were confirmed to be the carrier of the same variant.

Conclusion

This study has represented two rare cases of HLH carrying missense variant in PRF1 and splice site variant in SH2D1A gene. Detailed molecular analysis has helped the families with precise genetic counselling and prenatal diagnosis during subsequent pregnancy. It is advocated that male patients presenting with EBV-associated HLH may be screened for XLP that may lead to early diagnosis and therapeutic implication if any.

Electronic supplementary material

The online version of this article (10.1186/s12887-019-1444-4) contains supplementary material, which is available to authorized users.

T follicular-like helper cells in the peripheral blood of patients with primary Sjögren's syndrome

Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease characterized by exocrine gland dysfunction, mainly causing sicca symptoms. B cells have a prominent role in SS, and the T follicular helper (TFH ) cells provide B cells with survival and specialization signals in germinal centres. Here, we investigate peripheral TFH cells in pSS. Sixteen pSS patients and healthy controls were enrolled in the study, with 13 women and 3 men in each group. Whole blood was collected and separated into PBMC and plasma, followed by cryopreservation. Plasma samples were analysed for Ro52, Ro60 and La48 autoantibodies by indirect ELISA. For flow cytometric analysis, we defined 4 subsets of TFH-like cells within the CD3+ CD4+ CXCR5+ population, namely the ICOS- PD-1- , ICOS- PD-1+ , ICOS+ PD-1- and ICOS+ PD-1+ ("TFH") cells. We also investigated 4 CD19+ B cell subsets, the CD20+ CD27+ CD38- memory B cells, CD20+ CD27+ CD38+ memory B cells, CD20- CD27+ CD38++ CD138- plasmablasts and CD20- CD27+ CD38++ CD138+ plasma cells. We observed higher fractions of ICOS+ PD-1- cells, ICOS+ PD-1+ ("TFH ") cells and plasmablasts in pSS patients compared to controls, and lower frequencies of both types of memory B cells. The number of TFH cells correlated positively with the levels of plasmablasts and plasma cells in the pSS patients, but not in the controls. The pSS patients were stratified according to Ro52/Ro60/La48 serology, and a positive association was found between autoantibody levels and increased level of TFH cells, plasmablasts and plasma cells and lowered levels of memory B cells. We observed a higher response to Ro/La stimulation in pSS patients compared to controls of the memory B cells, although only significantly for the CD38- memory B cells. Overall, a pathological relation between the ICOS+ T follicular-like helper cells and B cells in pSS was observed, but further work should be conducted to explore their overall impact upon disease progression.

The SLAM family receptors: Potential therapeutic targets for inflammatory and autoimmune diseases

The signaling lymphocytic activation molecule (SLAM) family is comprised of nine distinct receptors (SLAMF1 through SLAMF9) that are expressed on hematopoietic cells. All of these receptors, with the exception of SLAMF4, are homotypic by nature as downstream signaling occurs when hematopoietic cells that express the same SLAM receptor interact. The SLAM family receptor function is largely controlled via SLAM associated protein (SAP) family adaptors. The SAP family adaptors consist of SAP, Ewing sarcoma associated transcript (EAT)-2, and EAT-2-related transducer (ERT). These adaptors associate with the cytoplasmic domain of the SLAM family receptors through phosphorylated tyrosines. Defects in SLAM family members and SAP adaptors have been implicated in causing immune deficiencies. This is exemplified in patients with X-linked lymphoproliferative (XLP) disease, where SAP undergoes a loss of function mutation. Furthermore, evidence has been accumulating that SLAM family members are potential targets for inflammatory and autoimmune diseases. This review will discuss the structure and function of the SLAM family receptors and SAP family adaptors, their role in immune regulation, and potential approaches to target this family of receptors therapeutically.

Flow Cytometric Evaluation of Primary Immunodeficiencies

Primary immunodeficiency diseases are genetic disorders that mostly cause susceptibility to infections and are sometimes associated with autoimmune and malignant diseases. For early detection and management of these diseases, flow cytometric procedures allow an encompassing assessment of cellular phenotypes and cellular functions. State-of-the art cytometry is based today on 8- to 10-color staining and includes an assessment of lineage maturation and functional markers.

X-Linked Lymphoproliferative Disease Type 1: A Clinical and Molecular Perspective

X-linked lymphoproliferative disease (XLP) was first described in the 1970s as a fatal lymphoproliferative syndrome associated with infection with Epstein–Barr virus (EBV). Features include hemophagocytic lymphohistiocytosis (HLH), lymphomas, and dysgammaglobulinemias. Molecular cloning of the causative gene, SH2D1A, has provided insight into the nature of disease, as well as helped characterize multiple features of normal immune cell function. Although XLP type 1 (XLP1) provides an example of a primary immunodeficiency in which patients have problems clearing primarily one infectious agent, it is clear that XLP1 is also a disease of severe immune dysregulation, even independent of EBV infection. Here, we describe clinical features of XLP1, how molecular and biological studies of the gene product, SAP, and the associated signaling lymphocyte activation molecule family receptors have provided insight into disease pathogenesis including specific immune cell defects, and current therapeutic approaches including the potential use of gene therapy. Together, these studies have helped change the outcome of this once almost uniformly fatal disease.

Molecular Classification of Primary Immunodeficiencies of T Lymphocytes

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

Non-neoplastic histiocytic and dendritic cell disorders in lymph nodes

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

Mucosal-Associated Invariant T Cells in Regenerative Medicine

Although antibiotics to inhibit bacterial growth and small compounds to interfere with the productive life cycle of human immunodeficiency virus (HIV) have successfully been used to control HIV infection, the recent emergence of the drug-resistant bacteria and viruses poses a serious concern for worldwide public health. Despite intensive scrutiny in developing novel antibiotics and drugs to overcome these problems, there is a dilemma such that once novel antibiotics are launched in markets, sooner or later antibiotic-resistant strains emerge. Thus, it is imperative to develop novel methods to avoid this vicious circle. Here, we discuss the possibility of using induced pluripotent stem cell (iPSC)-derived, innate-like T cells to control infection and potential application of these cells for cancer treatment. Mucosal-associated invariant T (MAIT) cells belong to an emerging family of innate-like T cells that link innate immunity to adaptive immunity. MAIT cells exert effector functions without priming and clonal expansion like innate immune cells and relay the immune response to adaptive immune cells through production of relevant cytokines. With these characteristics, MAIT cells are implicated in a wide range of human diseases such as autoimmune, infectious, and metabolic diseases, and cancer. Circulating MAIT cells are often depleted by these diseases and often remain depleted even after appropriate remedy because MAIT cells are susceptible to activation-induced cell death and poor at proliferation in vivo, which threatens the integrity of the immune system. Because MAIT cells have a pivotal role in human immunity, supplementation of MAIT cells into immunocompromised patients suffering from severe depletion of these cells may help recapitulate or recover immunocompetence. The generation of MAIT cells from human iPSCs has made it possible to procure MAIT cells lost from disease. Such technology creates new avenues for cell therapy and regenerative medicine for difficult-to-cure infectious diseases and cancer and contributes to improvement of our welfare.

Characterization of a novel disease-causing mutation in exon 1 of SH2D1A gene through amplicon sequencing: a case report on HLH

BACKGROUND

Hemophagocytic lymphohistocytosis (HLH) is a rare but fatal hyperinflammatory syndrome caused by uncontrolled proliferation of activated macrophages and T lymphocytes secreting high amounts of inflammatory cytokines. Genetic defect is a common cause of HLH. HLH is complicated to be diagnosed as there are many common symptoms with other disorders.

CASE PRESENTATION

Here we report on an HLH case caused by 1 bp deletion in gene SH2D1A. Patient was a 3-years-old boy and had fever for more than 8 days. Splenomegaly and hemophagocytosis in bone marrow were observed in examination. The results of the blood analysis suggested the diagnosis of HLH. Genetic test based on high throughput amplicon sequencing was then conducted by targeting all six known HLH-causing genes simultaneously. It took only one single day to accomplish the amplicon sequencing library preparation, sequencing and data analysis. Finally, a novel 1 bp deletion in gene SH2D1A was discovered. The result was also confirmed by Sanger sequencing. The result of the genetic test served as a good basis for further diagnosis of HLH.

CONCLUSION

This is the first case that the disease-causing genetic defect of HLH was quickly determined by high throughput amplicon sequencing. This diagnosis was also confirmed by Sanger sequencing and cross-validated by blood analysis and other clinical criteria. This case suggests that genetic test based on amplicon sequencing is a powerful tool for diagnosis of HLH and other diseases caused by genetic defect.

Primary/Congenital Immunodeficiency: 2015 SH/EAHP Workshop Report-Part 5

OBJECTIVES

The 2015 Workshop of the Society for Hematopathology/European Association for Haematopathology aimed to review primary immunodeficiency and related lymphoproliferations.

METHODS

Primary immunodeficiencies were divided into immune dysregulation, DNA repair defects, low immunoglobulins, and combined immunodeficiencies.

RESULTS

Autoimmune lymphoproliferative syndrome (ALPS) is a prototypical immune dysregulation-type immunodeficiency, with defects in T-cell signaling or apoptosis, expansion of T-cell subsets, and predisposition to hemophagocytic lymphohistiocytosis. DNA repair defects directly predispose to malignancy. Low immunoglobulin immunodeficiencies such as common variable immunodeficiency (CVID) have underlying T-cell repertoire abnormalities predisposing to autoimmunity and B-cell lymphoproliferations. The full spectrum of B-cell lymphoproliferative disorders occurs in primary immunodeficiency.

CONCLUSIONS

Lymphoproliferations in primary immunodeficiency mirror those in other immunodeficiency settings, with monomorphic B- and sometimes T lymphoproliferative disorders enriched in DNA repair defects. Distinctive T-cell subset expansions in ALPS, CVID, and related entities can mimic lymphoma, and recognition of double-negative T-cell or cytotoxic T-cell expansions is key to avoid overdiagnosis.

2B4-SAP signaling is required for the priming of naive CD8+ T cells by antigen-expressing B cells and B lymphoma cells

Mutations in SH2D1A gene that encodes SAP (SLAM-associated protein) result in X-linked lymphoproliferative disease (XLP), a rare primary immunodeficiency disease defined by exquisite sensitivity to the B-lymphotropic Epstein-Barr virus (EBV) and B cell lymphomas. However, the precise mechanism of how the loss of SAP function contributes to extreme vulnerability to EBV and the development of B cell lymphomas remains unclear. Here, we investigate the hypothesis that SAP is critical for CD8⁺ T cell immune surveillance of antigen (Ag)-expressing B cells or B lymphoma cells under conditions of defined T cell receptor (TCR) signaling. Sh2d1a^-/- CD8⁺ T cells exhibited greatly diminished proliferation relative to wild type when Ag-presenting-B cells or -B lymphoma cells served as the primary Ag-presenting cell (APC). By contrast, Sh2d1a^-/- CD8⁺ T cells responded equivalently to wild-type CD8⁺ T cells when B cell-depleted splenocytes, melanoma cells or breast carcinoma cells performed Ag presentation. Through application of signaling lymphocyte activation molecule (SLAM) family receptor blocking antibodies or SLAM family receptor-deficient CD8⁺ T cells and APCs, we found that CD48 engagement on the B cell surface by 2B4 is crucial for initiating SAP-dependent signaling required for the Ag-driven CD8⁺ T cell proliferation and differentiation. Altogether, a pivotal role for SAP in promoting the expansion and differentiation of B cell-primed viral-specific naive CD8⁺ T cells may explain the selective immune deficiency of XLP patients to EBV and B cell lymphomas.

How genetic testing can lead to targeted management of XIAP deficiency-related inflammatory bowel disease

X-linked lymphoproliferative disease type 2 (XLP-2, OMIM 300635) is a primary immunodeficiency caused by the loss of X chromosome-linked inhibitor of apoptosis (XIAP), the X-linked inhibitor of apoptosis gene at Xq25. XLP-2 individuals are susceptible to several specific and potentially fatal infections, such as Epstein-Barr virus (EBV). Children with XIAP-related XLP-2 may present with either familial hemophagocytic lymphohistiocytosis, often triggered in response to EBV infection, or with a treatment-refractory severe pediatric form of inflammatory bowel disease (IBD) that might be diagnosed as Crohn disease. However, this monogenic cause of IBD is distinct from adult Crohn disease (a polygenic and multifactorial disease) in its etiology and responsiveness to therapy. XLP-2 and the associated IBD symptoms are managed by a reduced-intensity conditioning regimen with an allogeneic hematopoietic stem cell transplantation that causes resolution of gastrointestinal symptoms. Exome sequencing has enabled identification of XIAP-deficient diseased individuals and has altered their morbidity by providing potentially lifesaving strategies in a timely and effective manner. Here, we summarize XLP-2 IBD treatment history and patient morbidity/mortality since its original identification in 2006. Since XLP-2 is rare, cases are probably undergiagnosed or misdiagnosed. Consideration of XLP-2 in children with severe symptoms of IBD can prevent serious morbidities and mortality, avoid unnecessary procedures, and expedite specific targeted therapy.Genet Med 19 2, 133-143.

Current Updates on Classification, Diagnosis and Treatment of Hemophagocytic Lymphohistiocytosis (HLH)

Hemophagocytic lymphohistiocytosis (HLH) is a life threatening hyperinflammatory syndrome characterized by excessive activation of macrophages and T cells resulting from defective cytotoxicity. Severe hyperinflammation caused by uncontrolled proliferation of activated lymphocytes and histiocytes (macrophages) secreting high amounts of inflammatory cytokines threatens the life of the patient and may lead to death unless arrested by appropriate treatment. HLH can be caused either by certain underlying genetic diseases (familial HLH), or may also occur due to particular triggers in patients with no known inherited disorder (acquired HLH). Due to life threatening nature of the disease, early diagnosis and initiation of immunosuppressive therapy is extremely important. HLH diagnosis is based on constellation of clinical manifestations and laboratory parameters which often overlap with those of severe infection or sepsis. Identification of patients with familial HLH and their underlying genetic defects requires specialized laboratory tests and is important for predicting relapses and planning early therapeutic hematopoietic stem cell transplantation (HSCT). A high suspicion and thorough clinical, immunological and genetic work-up is required for diagnosis of HLH. Prompt initiation of adequate treatment is essential for the survival. Substantial progress has been made in exploring the complex cause and pathophysiology of HLH and also in management of HLH patients.

The intersection of immune deficiency and autoimmunity

PURPOSE OF REVIEW

Immune deficiency and autoimmunity have been recognized as cotravelers for decades. This clinically oriented review brings together our evolving mechanistic understanding to highlight associations of particular relevance to rheumatologists.

RECENT FINDINGS

Conceptually, all autoimmunity derives from a loss of tolerance. This distinguishes it from autoinflammation in which the innate immune system is dysregulated without necessarily affecting tolerance. Studies have demonstrated the profound effects of signaling defects, apoptotic pathways and the ramifications of homeostatic proliferation on tolerance. This foundation has translated into an improved understanding of the specific associations of autoimmune diseases with immune deficiencies. This important foundation paves the way for personalized treatment strategies.

SUMMARY

This review identifies critical mechanisms important to conceptualize the association of primary immune deficiencies and autoimmunity. It highlights a growing appreciation of the hidden single gene defects affecting T-cells within the group of patients with early-onset pleomorphic autoimmunity.

T cell immunodeficiency

T cell immunodeficiency can occur as one of a group of primary disorders or develop secondary to chronic infection, illness or drug therapy. Primary T cell disorders are rare, accounting for approximately 11% of reported primary immunodeficiencies, and generally present in infancy or early childhood. Early recognition is very important as many of these patients will require bone marrow transplantation prior to the onset of severe infection or other complications. Because of their rarity, these infants usually present to clinicians who have little or no prior experience of these conditions, and therefore laboratory-based clinicians with knowledge of the key laboratory/pathological abnormalities and clinical features have a valuable role in identifying the possibility of immunodeficiency. Secondary T cell deficiency is a cardinal feature of HIV infection and the specific susceptibility to infectious micro-organisms is highlighted. The possibility of T cell immunodeficiency should be considered in any patient presenting with unusual or severe viral, fungal or protozoal infection.

A mutation in X-linked inhibitor of apoptosis (G466X) leads to memory inflation of Epstein-Barr virus-specific T cells

Mutations in the X-linked inhibitor of apoptosis (XIAP) gene have been associated with XLP-like disease, including recurrent Epstein-Barr virus (EBV)-related haemophagocytic lymphohystiocytosis (HLH), but the immunopathogenic bases of EBV-related disease in XIAP deficiency is unknown. We present the first analysis of EBV-specific T cell responses in functional XIAP deficiency. In a family of patients with a novel mutation in XIAP (G466X) leading to a late-truncated protein and varying clinical features, we identified gradual hypogammaglobulinaemia and large expansions of T cell subsets, including a prominent CD4(+) CD8(+) population. Extensive ex-vivo analyses showed that the expanded T cell subsets were dominated by EBV-specific cells with conserved cytotoxic, proliferative and interferon (IFN)-γ secretion capacity. The EBV load in blood fluctuated and was occasionally very high, indicating that the XIAP(G466X) mutation could impact upon EBV latency. XIAP deficiency may unravel a new immunopathogenic mechanism in EBV-associated disease.

Laboratory diagnosis of primary immunodeficiencies

Primary immune deficiency disorders represent a highly heterogeneous group of disorders with an increased propensity to infections and other immune complications. A careful history to delineate the pattern of infectious organisms and other complications is important to guide the workup of these patients, but a focused laboratory evaluation is essential to the diagnosis of an underlying primary immunodeficiency. Initial workup of suspected immune deficiencies should include complete blood counts and serologic tests of immunoglobulin levels, vaccine titers, and complement levels, but these tests are often insufficient to make a diagnosis. Recent advancements in the understanding of the immune system have led to the development of novel immunologic assays to aid in the diagnosis of these disorders. Classically utilized to enumerate lymphocyte subsets, flow cytometric-based assays are increasingly utilized to test immune cell function (e.g., neutrophil oxidative burst, NK cytotoxicity), intracellular cytokine production (e.g., TH17 production), cellular signaling pathways (e.g., phosphor-STAT analysis), and protein expression (e.g., BTK, Foxp3). Genetic testing has similarly expanded greatly as more primary immune deficiencies are defined, and the use of mass sequencing technologies is leading to the identification of novel disorders. In order to utilize these complex assays in clinical care, one must have a firm understanding of the immunologic assay, how the results are interpreted, pitfalls in the assays, and how the test affects treatment decisions. This article will provide a systematic approach of the evaluation of a suspected primary immunodeficiency, as well as provide a comprehensive list of testing options and their results in the context of various disease processes.

The adaptor protein SAP regulates type II NKT-cell development, cytokine production, and cytotoxicity against lymphoma

CD1d-restricted NKT cells represent a unique lineage of immunoregulatory T cells that are divided into two groups, type I and type II, based on their TCR usage. Because there are no specific tools to identify type II NKT cells, little is known about their developmental requirements and functional regulation. In our previous study, we showed that signaling lymphocytic activation molecule associated protein (SAP) is essential for the development of type II NKT cells. Here, using a type II NKT-cell TCR transgenic mouse model, we demonstrated that CD1d-expressing hematopoietic cells, but not thymic epithelial cells, meditate efficient selection of type II NKT cells. Furthermore, we showed that SAP regulates type II NKT-cell development by controlling early growth response 2 protein and promyelocytic leukemia zinc finger expression. SAP-deficient 24αβ transgenic T cells (24αβ T cells) exhibited an immature phenotype with reduced Th2 cytokine-producing capacity and diminished cytotoxicity to CD1d-expressing lymphoma cells. The impaired IL-4 production by SAP-deficient 24αβ T cells was associated with reduced IFN regulatory factor 4 and GATA-3 induction following TCR stimulation. Collectively, these data suggest that SAP is critical for regulating type II NKT cell responses. Aberrant responses of these T cells may contribute to the immune dysregulation observed in X-linked lymphoproliferative disease caused by mutations in SAP.

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.

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.

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.

SAP facilitates recruitment and activation of LCK at NTB-A receptors during restimulation-induced cell death

Upon TCR restimulation, activated, cycling T cells can undergo a self-regulatory form of apoptosis known as restimulation-induced cell death (RICD). We previously demonstrated that RICD is impaired in T cells from patients with X-linked lymphoproliferative disease, which lack SLAM-associated protein (SAP) expression. Both SAP and the specific SLAM receptor NK, T, and B cell Ag (NTB-A) are required for RICD, but the mechanism by which these molecules promote a strong, proapoptotic signal through the TCR remains unclear. In this article, we show that the Src-family kinase LCK, but not FYN, associates with NTB-A in activated human T cells. This association increased after TCR restimulation in a SAP-dependent manner, requiring both immunoreceptor tyrosine-based switch motifs in the NTB-A cytoplasmic tail. Both NTB-A-associated LCK phosphorylation and kinase activity were enhanced in restimulated T cells, amplifying proximal TCR signaling. In contrast, TCR-induced LCK association with NTB-A, as well as phosphorylation and kinase activity, was reduced in T cells from patients with X-linked lymphoproliferative disease or normal T cells transfected with SAP-specific small interfering RNA, consistent with RICD resistance. Collectively, our data reveal how SAP nucleates a previously unknown signaling complex involving NTB-A and LCK to potentiate RICD of activated human T cells.

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.

The adaptor protein SAP directly associates with PECAM-1 and regulates PECAM-1-mediated-cell adhesion in T-like cell lines

SAP is a small cytosolic adaptor protein expressed in hematopoietic lineages whose main function is to regulate intracellular signaling pathways induced by the triggering of members of the SLAM receptor family. In this paper, we have identified the adhesion molecule PECAM-1 as a new partner for SAP in a conditional yeast two-hybrid screen. PECAM-1 is an immunoglobulin-like molecule expressed by endothelial cells and leukocytes, which possesses both pro- and anti-inflammatory properties. However, little is known about PECAM-1 functions in T cells. We show that SAP directly and specifically interacts with the cytosolic tyrosine 686 of PECAM-1. We generated different T-like cell lines in which SAP or PECAM-1 are expressed or down modulated and we demonstrate that a diminished SAP expression correlates with a diminished PECAM-1-mediated adhesion. Although SAP has mainly been shown to associate with SLAM receptors, we evidence here that SAP is a new actor downstream of PECAM-1.

Signaling lymphocytic activation molecule (SLAM)/SLAM-associated protein pathway regulates human B-cell tolerance

BACKGROUND

Signaling lymphocytic activation molecule (SLAM)-associated protein (SAP) can mediate the function of SLAM molecules, which have been proposed to be involved in the development of autoimmunity in mice.

OBJECTIVE

We sought to determine whether the SLAM/SAP pathway regulates the establishment of human B-cell tolerance and what mechanisms of B-cell tolerance could be affected by SAP deficiency.

METHODS

We tested the reactivity of antibodies isolated from single B cells from SAP-deficient patients with X-linked lymphoproliferative disease (XLP). The expressions of SAP and SLAM family members were assessed in human bone marrow-developing B cells. We also analyzed regulatory T (Treg) cell function in patients with XLP and healthy control subjects.

RESULTS

We found that new emigrant/transitional B cells from patients with XLP were enriched in autoreactive clones, revealing a defective central B-cell tolerance checkpoint in the absence of functional SAP. In agreement with a B cell-intrinsic regulation of central tolerance, we identified SAP expression in a discrete subset of bone marrow immature B cells. SAP colocalized with SLAMF6 only in association with clustered B-cell receptors likely recognizing self-antigens, suggesting that SLAM/SAP regulate B-cell receptor-mediated central tolerance. In addition, patients with XLP displayed defective peripheral B-cell tolerance, which is normally controlled by Treg cells. Treg cells in patients with XLP seem functional, but SAP-deficient T cells were resistant to Treg cell-mediated suppression. Indeed, SAP-deficient T cells were hyperresponsive to T-cell receptor stimulation, which resulted in increased secretion of IL-2, IFN-γ, and TNF-α.

CONCLUSIONS

SAP expression is required for the counterselection of developing autoreactive B cells and prevents their T cell-dependent accumulation in the periphery.

Frequent mutations in SH2D1A (XLP) in males presenting with high-grade mature B-cell neoplasms

X-linked lymphoproliferative syndrome (XLP) is caused by mutations in SH2D1A, and is associated with overwhelming infectious mononucleosis, aplastic anemia, hypogammaglobulinemia, and B-cell lymphomas. However, the frequency of SH2D1A mutations in males who present with B NHL is unknown. Five cases of XLP were diagnosed among 158 males presenting with B NHL (approximately 3.2%). Four of the patients had two episodes of B NHL and one had a single episode of B NHL followed by aggressive infectious mononucleosis. Prospective screening for XLP in males with B-cell lymphoma at the time of initial diagnosis should be considered.

Innate immune responses against Epstein Barr virus infection

EBV persists life-long in >95% of the human adult population. Whereas it is perfectly immune-controlled in most infected individuals, a minority develops EBV-associated diseases, primarily malignancies of B cell and epithelial cell origin. In recent years, it has become apparent that the course of primary infection determines part of the risk to develop EBV-associated diseases. Particularly, the primary symptomatic EBV infection or IM, which is caused by exaggerated T cell responses, resulting in EBV-induced lymphocytosis, predisposes for EBV-associated diseases. The role of innate immunity in the development of IM remains unknown. Therefore, it is important to understand how the innate immune response to this virus differs between symptomatic and asymptomatic primary EBV infection. Furthermore, the efficiency of innate immune compartments might determine the outcome of primary infection and could explain why some individuals are susceptible to IM. We will discuss these aspects in this review with a focus on intrinsic immunity in EBV-infected B cells, as well as innate immune responses by DCs and NK cells, which constitute promising immune compartments for the understanding of early immune control against EBV and potential targets for EBV-specific immunotherapies.

CD84 is a survival receptor for CLL cells

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of CD5+ B lymphocytes in peripheral blood, lymphoid organs and bone marrow. The main feature of the disease is accumulation of the malignant cells due to decreased apoptosis. CD84 belongs to the signaling lymphocyte activating molecule family of immunoreceptors, and has an unknown function in CLL cells. Here, we show that the expression of CD84 is significantly elevated from the early stages of the disease, and is regulated by macrophage migration inhibitory factor and its receptor, CD74. Activation of cell surface CD84 initiates a signaling cascade that enhances CLL cell survival. Both downmodulation of CD84 expression and its immune-mediated blockade induce cell death in vitro and in vivo. In addition, analysis of samples derived from an on-going clinical trial, in which human subjects were treated with humanized anti-CD74 (milatuzumab), shows a decrease in CD84 messenger RNA and protein levels in milatuzumab-treated cells. This downregulation was correlated with reduction of Bcl-2 and Mcl-1 expression. Thus, our data show that overexpression of CD84 in CLL is an important survival mechanism that appears to be an early event in the pathogenesis of the disease. These findings suggest novel therapeutic strategies based on the blockade of this CD84-dependent survival pathway.