Clinical and immunological overlap between autoimmune lymphoproliferative syndrome and common variable immunodeficiency

Non-apoptotic FAS signaling controls mTOR activation and extrafollicular maturation in human B cells

Defective FAS (CD95/Apo-1/TNFRSF6) signaling causes autoimmune lymphoproliferative syndrome (ALPS). Hypergammaglobulinemia is a common feature in ALPS with FAS mutations (ALPS-FAS), but paradoxically, fewer conventional memory cells differentiate from FAS-expressing germinal center (GC) B cells. Resistance to FAS-induced apoptosis does not explain this phenotype. We tested the hypothesis that defective non-apoptotic FAS signaling may contribute to impaired B cell differentiation in ALPS. We analyzed secondary lymphoid organs of patients with ALPS-FAS and found low numbers of memory B cells, fewer GC B cells, and an expanded extrafollicular (EF) B cell response. Enhanced mTOR activity has been shown to favor EF versus GC fate decision, and we found enhanced PI3K/mTOR and BCR signaling in ALPS-FAS splenic B cells. Modeling initial T-dependent B cell activation with CD40L in vitro, we showed that FAS competent cells with transient FAS ligation showed specifically decreased mTOR axis activation without apoptosis. Mechanistically, transient FAS engagement with involvement of caspase-8 induced nuclear exclusion of PTEN, leading to mTOR inhibition. In addition, FASL-dependent PTEN nuclear exclusion and mTOR modulation were defective in patients with ALPS-FAS. In the early phase of activation, FAS stimulation promoted expression of genes related to GC initiation at the expense of processes related to the EF response. Hence, our data suggest that non-apoptotic FAS signaling acts as molecular switch between EF versus GC fate decisions via regulation of the mTOR axis and transcription. The defect of this modulatory circuit may explain the observed hypergammaglobulinemia and low memory B cell numbers in ALPS.

Common Variable Immunodeficiency: More Pathways than Roads to Rome

Fifty years have elapsed since the term common variable immunodeficiency (CVID) was introduced to accommodate the many and varied antibody deficiencies being identified in patients with suspected inborn errors of immunity (IEIs). Since then, how the term is understood and applied for diagnosis and management has undergone many revisions, though controversy persists on how exactly to define and classify CVID. Many monogenic disorders have been added under its aegis, while investigations into polygenic, epigenetic, and somatic contributions to CVID susceptibility have gained momentum. Expansion of the overall IEI landscape has increasingly revealed genotypic and phenotypic overlap between CVID and various other immunological conditions, while increasingly routine genotyping of CVID patients continues to identify an incredible diversity of pathophysiological mechanisms affecting even single genes. Though many questions remain to be answered, the lessons we have already learned from CVID biology have greatly informed our understanding of adaptive, but also innate, immunity.

Inborn errors of immunity and immunodeficiencies: antibody-mediated pathology and autoimmunity as a consequence of impaired immune reactions

B cell tolerance to self-antigen is an active process that requires the temporal and spatial integration of signals of defined intensity. In common variable immune deficiency disorders (CVID), CTLA-4 deficiency, autoimmune lymphoproliferative syndrome (ALPS), or in collagen VII deficiency, genetic defects in molecules regulating development, activation, maturation and extracellular matrix composition alter the generation of B cells, resulting in immunodeficiency. Paradoxically, at the same time, the defective immune processes favor autoantibody production and immunopathology through impaired establishment of tolerance. The development of systemic autoimmunity in the framework of defective BCR signaling is relatively unusual in genetic mouse models. In sharp contrast, such reduced signaling in humans is clearly linked to pathological autoimmunity. The molecular mechanisms by which tolerance is broken in these settings are only starting to be explored resulting in novel therapeutic interventions. For instance, in CTLA-4 deficiency, homeostasis can be restored by CTLA-4 Ig treatment. Following this example, the identification of the molecular targets causing the reduced signals and their restoration is a visionary way to reestablish tolerance and develop novel therapeutic avenues for immunopathologies. This article is protected by copyright. All rights reserved.

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

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

Cellular and molecular mechanisms breaking immune tolerance in inborn errors of immunity

In addition to susceptibility to infections, conventional primary immunodeficiency disorders (PIDs) and inborn errors of immunity (IEI) can cause immune dysregulation, manifesting as lymphoproliferative and/or autoimmune disease. Autoimmunity can be the prominent phenotype of PIDs and commonly includes cytopenias and rheumatological diseases, such as arthritis, systemic lupus erythematosus (SLE), and Sjogren's syndrome (SjS). Recent advances in understanding the genetic basis of systemic autoimmune diseases and PIDs suggest an at least partially shared genetic background and therefore common pathogenic mechanisms. Here, we explore the interconnected pathogenic pathways of autoimmunity and primary immunodeficiency, highlighting the mechanisms breaking the different layers of immune tolerance to self-antigens in selected IEI.

Immunologic evaluation and genetic defects of apoptosis in patients with autoimmune lymphoproliferative syndrome (ALPS)

Apoptosis plays an important role in controlling the adaptive immune response and general homeostasis of the immune cells, and impaired apoptosis in the immune system results in autoimmunity and immune dysregulation. In the last 25 years, inherited human diseases of the Fas-FasL pathway have been recognized. Autoimmune lymphoproliferative syndrome (ALPS) is an inborn error of immunity, characterized clinically by nonmalignant and noninfectious lymphoproliferation, autoimmunity, and increased risk of lymphoma due to a defect in lymphocyte apoptosis. The laboratory hallmarks of ALPS are an elevated percentage of T-cell receptor αβ double negative T cells (DNTs), elevated levels of vitamin B12, soluble FasL, IL-10, IL-18 and IgG, and defective in vitro Fas-mediated apoptosis. In order of frequency, the genetic defects associated with ALPS are germinal and somatic ALPS-FAS, ALPS-FASLG, ALPS-CASP10, ALPS-FADD, and ALPS-CASP8. Partial disease penetrance and severity suggest the combination of germline and somatic FAS mutations as well as other risk factor genes. In this report, we summarize human defects of apoptosis leading to ALPS and defects that are known as ALPS-like syndromes that can be clinically similar to, but are genetically distinct from, ALPS. An efficient genetic and immunological diagnostic approach to patients suspected of having ALPS or ALPS-like syndromes is essential because this enables the establishment of specific therapeutic strategies for improving the prognosis and quality of life of patients.

Evans Syndrome in Childhood: Long Term Follow-Up and the Evolution in Primary Immunodeficiency or Rheumatological Disease

Evans syndrome (ES) is a rare but challenging condition, characterized by recurrent and refractory cytopenia episodes. Recent discoveries highlighted that an appropriate diagnostic workup is fundamental to identify an underlying immune dysregulation such as primary immunodeficiencies or a rheumatological disease. We hereby describe clinical features and laboratory results of 12 pediatric patients affected by ES referred to the Pediatric Onco-Hematology Unit of Bologna. Patients experienced a median of four acute episodes of cytopenia with 9 years as median age at the onset of symptoms. In 8/12 (67%) patients an underlying etiology, primary immunodeficiencies, or rheumatological disease was identified. In 4/12 children, other immune manifestations were associated (Thyroiditis, Celiac disease, Psoriasis, Vitiligo, Myositis, Membranoproliferative Glomerulonephritis). ES remained the primary diagnosis in four patients (33%). At a median follow-up time of 4 years, 5/12 (42%) patients revealed a chronic ITP, partially responsive to second line therapy. Immunoglobulin Replacement Therapy (IRT) was effective with a good hematological values control in three patients with a secondary ES (ALPS, CVID, and a patient with Rubinstein Taybi Syndrome and a progressive severe B cell deficiency with hypogammaglobulinemia). Our experience highlights that, in pediatric patients, ES is often only the first manifestation of an immunological or rheumatological disease, especially when cytopenias are persistent or resistant to therapy, with an early-onset or when are associated with lymphadenopathy.

The Autoimmune Lymphoproliferative Syndrome with Defective FAS or FAS-Ligand Functions

The autoimmune lymphoproliferative syndrome (ALPS) is a non-malignant and non-infectious uncontrolled proliferation of lymphocytes accompanied by autoimmune cytopenia. The genetic etiology of the ALPS was described in 1995 by the discovery of the FAS gene mutations. The related apoptosis defect accounts for the accumulation of autoreactive lymphocytes as well as for specific clinical and biological features that distinguish the ALPS-FAS from other monogenic defects of this apoptosis pathway, such as FADD and CASPASE 8 deficiencies. The ALPS-FAS was the first description of a monogenic cause of autoimmunity, but its non-Mendelian expression remained elusive until the description of somatic and germline mutations in ALPS patients. The recognition of these genetic diseases brought new information on the role of this apoptotic pathway in controlling the adaptive immune response in humans.

Dysregulation of Innate Lymphoid Cells in Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is the most prevalent symptomatic primary immune deficiency. With widespread use of immunoglobulin replacement therapy, non-infectious complications, such as autoimmunity, chronic intestinal inflammation, and lung disease, have replaced infections as the major cause of morbidity and mortality in this immune deficiency. The pathogenic mechanisms that underlie the development of these complications in CVID are not known; however, there have been numerous associated laboratory findings. Among the most intriguing of these associations is elevation of interferon signature genes in CVID patients with inflammatory/autoimmune complications, as a similar gene expression profile is found in systemic lupus erythematosus and other chronic inflammatory diseases. Linked with this heightened interferon signature in CVID is an expansion of circulating IFN-γ-producing innate lymphoid cells. Innate lymphoid cells are key regulators of both protective and pathogenic immune responses that have been extensively studied in recent years. Further exploration of innate lymphoid cell biology in CVID may uncover key mechanisms underlying the development of inflammatory complications in these patients and may inspire much needed novel therapeutic approaches.

Evans Syndrome as First Manifestation of Primary Immunodeficiency in Clinical Practice

BACKGROUND

Evans syndrome (ES) is a rare immune disorder in children, manifested by simultaneous or sequential autoimmune cytopenias (ACs) of unknown cause and having a chronic course with periods of exacerbation and remission. Some primary immunodeficiencies (PIDs) may present with autoimmune manifestations without infections, masking suspicion of them. The PIDs that can typically manifest as ES are autoimmune lymphoproliferative syndrome and common variable immunodeficiency (CVID).

MATERIALS AND METHODS

Review of clinical charts and laboratory results of pediatric patients followed-up in the outpatient clinic of PID with a diagnosis of ES and humoral immunodeficiency.

RESULTS

Three pediatric patients, a boy and 2 girls, presented with corticosteroid-dependent ES. In the diagnostic approach, autoimmune lymphoproliferative syndrome was ruled out, and during follow-up, patients showed laboratory signs of humoral immune deficiency and were diagnosed with CVID. After initiating the recommended treatment for CVID with AC, patients improved without new exacerbations.

CONCLUSIONS

These cases highlight the importance of detection of possible PID in the context of ES and the establishment of CVID treatment to control AC.

The autoimmune conundrum in common variable immunodeficiency disorders

PURPOSE OF REVIEW

Autoimmune and inflammatory manifestations are the biggest clinical challenge in the care of patients with common variable immunodeficiency (CVID). The increasing pathogenic knowledge and potential therapeutic implications require a new evaluation of the status quo. (Figure is included in full-text article.)

RECENT FINDINGS

The conundrum of the simultaneous manifestation of primary immunodeficiency and autoimmune disease (AID) is increasingly elucidated by newly discovered genetic defects. Thus, cytotoxic T lymphocyte-associated antigen 4 or caspase-9 deficiency presenting with CVID-like phenotypes reiterate concepts of immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome and autoimmune lymphoproliferative syndrome. Activating signaling defects downstream of antigen or cytokine receptors are often associated with loss-of-tolerance in the affected patients. Increasingly, forms of combined immunodeficiency are discovered among CVID-like patients. Although different autoimmune manifestations often coincide in the same patient their immunopathology varies. Treatment of AID in CVID remains a challenge, but based on a better definition of the immunopathology first attempts of targeted treatment have been made.

SUMMARY

The increasing comprehension of immunological concepts promoting AID in CVID will allow better and in some cases possibly even targeted treatment. A genetic diagnosis therefore becomes important information in this group of patients, especially in light of the fact that some patients might require hematopoietic stem cell transplantation because of their underlying immunodeficiency.

Autoimmune and Lymphoproliferative Complications of Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is frequently complicated by the development of autoimmune and lymphoproliferative diseases. With widespread use of immunoglobulin replacement therapy, autoimmune and lymphoproliferative complications have replaced infection as the major cause of morbidity and mortality in CVID patients. Certain CVID complications, such as bronchiectasis, are likely to be the result of immunodeficiency and are associated with infection susceptibility. However, other complications may result from immune dysregulation rather than immunocompromise. CVID patients develop autoimmunity, lymphoproliferation, and granulomas in association with distinct immunological abnormalities. Mutations in transmembrane activator and CAML interactor, reduction of isotype-switched memory B cells, expansion of CD21 low B cells, heightened interferon signature expression, and retained B cell function are all associated with both autoimmunity and lymphoproliferation in CVID. Further research aimed to better understand that the pathological mechanisms of these shared forms of immune dysregulation may inspire therapies beneficial for multiple CVID complications.

Pulmonary Manifestations of the Autoimmune Lymphoproliferative Syndrome. A Retrospective Study of a Unique Patient Cohort

RATIONALE

Patients with autoimmune lymphoproliferative syndrome (ALPS), a disorder of impaired lymphocyte apoptosis, often undergo radiographic chest imaging to evaluate the presence and progression of lymphadenopathy. These images often lead to parenchymal and interstitial lung findings of unclear clinical significance.

OBJECTIVES

To characterize the pulmonary findings associated with ALPS and to determine if lung abnormalities present on computed tomographic (CT) imaging of the chest correlate with infection or functional status.

METHODS

Patients with lung abnormalities observed on chest CT scans were retrospectively identified from the largest known ALPS cohort. Lung computed tomography findings were characterized and correlated with medical records, bronchoalveolar lavage, biopsy, and lung function.

MEASUREMENTS AND MAIN RESULTS

CT images of the chest were available for 234 (92%) of 255 of the patients with ALPS. Among patients with a chest CT scan, 18 (8%) had lung abnormalities on at least one CT scan. Fourteen (78%) of those 18 were classified as having ALPS with undetermined genetic defect. Most patients (n = 16 [89%]) with lung lesions were asymptomatic. However, two (11%) of them had associated dyspnea and/or desaturation on room air. Immunosuppressive treatment was administered for lung disease in nine (50%) cases, and all were followed for clinical outcomes.

CONCLUSIONS

Patients with ALPS can develop chest radiographic findings with protean manifestations that may mimic pulmonary infection. Management of patients with ALPS with incidental lung lesions identified by CT imaging should be guided by clinical correlation. Symptomatic patients may benefit from chest CT imaging and lesion biopsy to exclude infection and guide administration of immunosuppressive therapy.

Disturbed B-lymphocyte selection in autoimmune lymphoproliferative syndrome

Fas is a transmembrane receptor involved in the maintenance of tolerance and immune homeostasis. In murine models, it has been shown to be essential for deletion of autoreactive B cells in the germinal center. The role of Fas in human B-cell selection and in development of autoimmunity in patients carrying FAS mutations is unclear. We analyzed patients with either a somatic FAS mutation or a germline FAS mutation and somatic loss-of-heterozygosity, which allows comparing the fate of B cells with impaired vs normal Fas signaling within the same individual. Class-switched memory B cells showed: accumulation of FAS-mutated B cells; failure to enrich single V, D, J genes and single V-D, D-J gene combinations of the B-cell receptor variable region; increased frequency of variable regions with higher content of positively charged amino acids; and longer CDR3 and maintenance of polyreactive specificities. Importantly, Fas-deficient switched memory B cells showed increased rates of somatic hypermutation. Our data uncover a defect in B-cell selection in patients with FAS mutations, which has implications for the understanding of the pathogenesis of autoimmunity and lymphomagenesis of autoimmune lymphoproliferative syndrome.

The Incidence and Prevalence of Common Variable Immunodeficiency Disease in Taiwan, A Population-Based Study

Common variable immunodeficiency (CVID) is one of the primary immunodeficiency diseases that occur in both children and adults. We present here a nationwide, population-based epidemiological study of CVID across all ages in Taiwan during 2002–2011. Using the International Classification of Diseases, Ninth Revision code 279.06, cases of CVID were identified from Taiwan's National Health Insurance Research Database from January 2002 to December 2011. Age- and sex-specific incidence and prevalence rates were calculated. A total of 47 new cases of CVID during 2002–2011 were identified. Total prevalence rose from 0.13 per 100,000 in 2002 to 0.28 per 100,000 in 2011. The annual incidence rate during 2002–2011 was 0.019 per 100,000. Cases were equally distributed between males and females and males mostly occurred in younger patients. This nationwide population-based study showed that the incidence and prevalence of CVID in Taiwan were lower than that in Western countries.

Progression of Common Variable Immunodeficiency Interstitial Lung Disease Accompanies Distinct Pulmonary and Laboratory Findings

BACKGROUND

Common variable immunodeficiency may be complicated by interstitial lung disease, which leads to worsened morbidity and mortality in some. Although immunomodulatory treatment has efficacy, choice of patient, duration of treatment, and long-term follow-up are not available. Interstitial lung disease appears stable in certain instances, so it is not known whether all patients will develop progressive disease or require immunomodulatory therapy.

OBJECTIVE

This study aims to determine if all common variable immunodeficiency patients with interstitial lung disease have physiological worsening, and if clinical and/or laboratory parameters may correlate with disease progression.

METHODS

A retrospective review of medical records at Mount Sinai Medical Center in New York was conducted for referred patients with common variable immunodeficiency, CT scan-confirmed interstitial lung disease, and periodic pulmonary function testing covering 20 or more months before immunomodulatory therapy. Fifteen patients were identified from the retrospective review and included in this study.

RESULTS

Of the 15 patients with common variable immunodeficiency, 9 had physiological worsening of interstitial lung disease adapted from consensus guidelines, associated with significant reductions in forced expiratory volume in 1 second, forced vital capacity, and diffusion capacity of the lung for carbon monoxide. Those with progressive lung disease also had significantly lower mean immunoglobulin G levels, greater increases and highest levels of serum immunoglobulin M (IgM), and more significant thrombocytopenia.

CONCLUSION

Interstitial lung disease resulted in physiological worsening in many, but not all subjects, and was associated with suboptimal immunoglobulin G replacement. Those with worsening pulmonary function tests, elevated IgM, and severe thrombocytopenic episodes appear to be at highest risk for progressive disease. Such patients may benefit from immunomodulatory treatment.

Immunodeficiencies with hypergammaglobulinemia: a review

Primary immunodeficiencies (PID) can present with recurrent infections, autoimmunity, inflammation, or malignancy and each of these conditions can be associated with elevated immunoglobulin. A high level of immunoglobulin G (IgG) is an uncommon finding, especially in pediatrics, and does not rule out primary immunodeficiency. Deficiencies in varied aspects of immune response have been described with high IgG. Reported PID conditions with elevated IgG include defects in humoral, cellular, and innate immunity. Some of these immunodeficiencies can have fatal outcomes, some require hematopoetic stem cell transplantation, and some require systemic medications. The mechanisms driving elevated IgG are not well understood, but in some cases abnormal cytokine production has been proposed. The evaluation of a patient with high IgG is guided by the patient's history and a physical examination, with special attention to autoimmunity in pediatrics and malignancy and liver disease in adults. In the setting of autoimmunity, chronic gastrointestinal disease, or chronic infections, the measurement of specific antibodies to evaluate the function of the IgG should be considered. An increased appreciation of elevation in IgG reflecting immune dysregulation may lead to earlier PID diagnoses.

Autoimmune lymphoproliferative syndrome-like disease in patients with LRBA mutation

Mutations in LPS-responsive and beige-like anchor (LRBA) gene were recently described in patients with combined immunodeficiency, enteropathy and autoimmune cytopenia. Here, we extend the clinical and immunological phenotypic spectrum of LRBA associated disorders by reporting on three patients from two unrelated families who presented with splenomegaly and lymphadenopathy, cytopenia, elevated double negative T cells and raised serum Fas ligand levels resembling autoimmune lymphoproliferative syndrome (ALPS) and one asymptomatic patient. Homozygous loss of function mutations in LRBA were identified by whole exome analysis. Similar to ALPS patients, Fas mediated apoptosis was impaired in LRBA deficient patients, while apoptosis in response to stimuli of the intrinsic mitochondria mediated apoptotic pathway was even enhanced. This manuscript illustrates the phenotypic overlap of other primary immunodeficiencies with ALPS-like disorders and strongly underlines the necessity of genetic diagnosis in order to provide early correct diagnosis and subsequent care.

A mutation in caspase-9 decreases the expression of BAFFR and ICOS in patients with immunodeficiency and lymphoproliferation

Lymphocyte apoptosis is mainly induced by either death receptor-dependent activation of caspase-8 or mitochondria-dependent activation of caspase-9. Mutations in caspase-8 lead to autoimmunity/lymphoproliferation and immunodeficiency. This work describes a heterozygous H237P mutation in caspase-9 that can lead to similar disorders. H237P mutation was detected in two patients: Pt1 with autoimmunity/lymphoproliferation, severe hypogammaglobulinemia and Pt2 with mild hypogammaglobulinemia and Burkitt lymphoma. Their lymphocytes displayed defective caspase-9 activity and decreased apoptotic and activation responses. Transfection experiments showed that mutant caspase-9 display defective enzyme and proapoptotic activities and a dominant-negative effect on wild-type caspase-9. Ex vivo analysis of the patients' lymphocytes and in vitro transfection experiments showed that the expression of mutant caspase-9 correlated with a downregulation of BAFFR (B-cell-activating factor belonging to the TNF family (BAFF) receptor) in B cells and ICOS (inducible T-cell costimulator) in T cells. Both patients carried a second inherited heterozygous mutation missing in the relatives carrying H237P: Pt1 in the transmembrane activator and CAML interactor (TACI) gene (S144X) and Pt2 in the perforin (PRF1) gene (N252S). Both mutations have been previously associated with immunodeficiencies in homozygosis or compound heterozygosis. Taken together, these data suggest that caspase-9 mutations may predispose to immunodeficiency by cooperating with other genetic factors, possibly by downregulating the expression of BAFFR and ICOS.

Approaches to Managing Autoimmune Cytopenias in Novel Immunological Disorders with Genetic Underpinnings Like Autoimmune Lymphoproliferative Syndrome

Autoimmune lymphoproliferative syndrome (ALPS) is a rare disorder of apoptosis. It is frequently caused by mutations in FAS (TNFRSF6) gene. Unlike most of the self-limiting autoimmune cytopenias sporadically seen in childhood, multi lineage cytopenias due to ALPS are often refractory, as their inherited genetic defect is not going to go away. Historically, more ALPS patients have died due to overwhelming sepsis following splenectomy to manage their chronic cytopenias than due to any other cause, including malignancies. Hence, current recommendations underscore the importance of avoiding splenectomy in ALPS, by long-term use of corticosteroid-sparing immunosuppressive agents like mycophenolate mofetil and sirolimus. Paradigms learnt from managing ALPS patients in recent years is highlighted here and can be extrapolated to manage refractory cytopenias in patients with as yet undetermined genetic bases for their ailments. It is also desirable to develop international registries for children with rare and complex immune problems associated with chronic multilineage cytopenias in order to elucidate their natural history and long-term comorbidities due to the disease and its treatments.

Autoimmune and other cytopenias in primary immunodeficiencies: pathomechanisms, novel differential diagnoses, and treatment

Autoimmunity and immune dysregulation may lead to cytopenia and represent key features of many primary immunodeficiencies (PIDs). Especially when cytopenia is the initial symptom of a PID, the order and depth of diagnostic steps have to be performed in accordance with both an immunologic and a hematologic approach and will help exclude disorders such as systemic lupus erythematosus, common variable immunodeficiency, and autoimmune lymphoproliferative syndromes, hemophagocytic disorders, lymphoproliferative diseases, and novel differential diagnoses such as MonoMac syndrome (GATA2 deficiency), CD27 deficiency, lipopolysaccharide-responsive beige-like anchor (LRBA) deficiency, activated PI3KD syndrome (APDS), X-linked immunodeficiency with magnesium defect (MAGT1 deficiency), and others. Immunosuppressive treatment often needs to be initiated urgently, which impedes further relevant immunologic laboratory analyses aimed at defining the underlying PID. Awareness of potentially involved disease spectra ranging from hematologic to rheumatologic and immunologic disorders is crucial for identifying a certain proportion of PID phenotypes and genotypes among descriptive diagnoses such as autoimmune hemolytic anemia, chronic immune thrombocytopenia, Evans syndrome, severe aplastic anemia/refractory cytopenia, and others. A synopsis of pathomechanisms, novel differential diagnoses, and advances in treatment options for cytopenias in PID is provided to facilitate multidisciplinary management and to bridge different approaches.

Defective anti-polysaccharide response and splenic marginal zone disorganization in ALPS patients

Autoimmune lymphoproliferative syndrome (ALPS) caused by impaired FAS-mediated apoptosis of lymphocytes is characterized by lymphoproliferation, autoimmunity, but also an increased risk of invasive bacterial infection, notably following splenectomy. We surveyed a cohort of 100 ALPS patients (including 33 splenectomized) and found that 12 (10 splenectomized) had experienced 23 invasive bacterial infections mainly caused by Streptococcus pneumoniae. This vulnerability was associated with evidence of defective B-cell function characterized by low serum immunoglobulin (Ig) M, low IgM antibody production in response to S pneumoniae following nonconjugated immunization, and low blood memory B-cells counts (including marginal zone [MZ] B-cell counts). This immunodeficiency strongly correlated with intensity of lymphoproliferation. Spleen sections from 9 ALPS patients revealed double-negative T-cell (DN-T) infiltration of the MZ, which was depleted of B cells. MZ in ALPS patients contained an abnormally thick layer of MAdCAM-1((+)) stromal cells and an excess of DN-Ts. DN-Ts were shown to express MAdCAM-1 ligand, the α4β7 integrin. These observations suggest that accumulating DN-Ts are trapped within stromal cell meshwork and interfere with correct localization of MZ B cells. Similar observations were made in spleens of fas-deficient mice. Our data revealed an unexpected mechanism by which ALPS results in anti-polysaccharide IgM antibody production-specific defect. Splenectomy should be avoided.

[Advances in the knowledge and management of autoimmune lymphoproliferative syndrome]

Autoimmune lymphoproliferative syndrome (ALPS) represents a failure of apoptotic mechanisms to maintain lymphocyte homeostasis. ALPS often manifest in childhood with cytopenias, chronic non-malignant lymphoproliferation and autoimmune complications. A number of new insights have improved the understanding of the genetics and biology of ALPS. The treatment of the disease has changed and mycophenolate mofetil and sirolimus have been demonstrated to have marked activity against the disease, improving quality of life for many patients. These will be discussed in this review.

Sequential decisions on FAS sequencing guided by biomarkers in patients with lymphoproliferation and autoimmune cytopenia

Clinical and genetic heterogeneity renders confirmation or exclusion of autoimmune lymphoproliferative syndrome difficult. To re-evaluate and improve the currently suggested diagnostic approach to patients with suspected FAS mutation, the most frequent cause of autoimmune lymphoproliferative syndrome, we prospectively determined 11 biomarkers in 163 patients with splenomegaly or lymphadenopathy and presumed or proven autoimmune cytopenia(s). Among 98 patients sequenced for FAS mutations in CD3(+)TCRα/β(+)CD4(-)CD8(-) "double negative" T cells, 32 had germline and six had somatic FAS mutations. The best a priori predictor of FAS mutations was the combination of vitamin B12 and soluble FAS ligand (cut-offs 1255 pg/mL and 559 pg/mL, respectively), which had a positive predictive value of 92% and a negative predictive value of 97%. We used these data to develop a web-based probability calculator for FAS mutations using the three most discriminatory biomarkers (vitamin B12, soluble FAS ligand, interleukin-10) of the 11 tested. Since more than 60% of patients with lymphoproliferation and autoimmune cytopenia(s) in our cohort did not harbor FAS mutations, 15% had somatic FAS mutations, and the predictive value of double-negative T-cell values was rather low (positive and negative predictive values of 61% and 77%, respectively), we argue that the previously suggested diagnostic algorithm based on determination of double-negative T cells and germline FAS sequencing, followed by biomarker analysis, is not efficient. We propose vitamin B12 and soluble FAS ligand assessment as the initial diagnostic step with subsequent decision on FAS sequencing supported by a probability-calculating tool.

Common variable immunodeficiency unmasked by treatment of immune thrombocytopenic purpura with Rituximab

Background

Hypogammaglobulinemia may be part of several different immunological or malignant conditions, and its origin is not always obvious. Furthermore, although autoimmune cytopenias are known to be associated with common variable immunodeficiency (CVID) and even may precede signs of immunodeficiency, this is not always recognized. Despite novel insight into the molecular immunology of common variable immunodeficiency, several areas of uncertainty remain. In addition, the full spectrum of immunological effects of the B cell depleting anti-CD20 antibody Rituximab has not been fully explored. To our knowledge this is the first report of development of CVID in a patient with normal immunoglobulin prior to Rituximab treatment.

Case presentation

Here we describe the highly unusual clinical presentation of a 34-year old Caucasian male with treatment refractory immune thrombocytopenic purpura and persistent lymphadenopathy, who was splenectomized and received multiple courses of high-dose corticosteroid before treatment with Rituximab resulted in a sustained response. However, in the setting of severe pneumococcal meningitis, hypogammaglobulinemia was diagnosed. An extensive immunological investigation was performed in order to characterize his immune status, and to distinguish between a primary immunodeficiency and a side effect of Rituximab treatment. We provide an extensive presentation and discussion of the literature on the basic immunology of CVID, the mechanism of action of Rituximab, and the immunopathogenesis of hypogammaglobulinemia observed in this patient.

Conclusions

We suggest that CVID should be ruled out in any patient with immune cytopenias in order to avoid diagnostic delay. Likewise, we stress the importance of monitoring immunoglobulin levels before, during, and after Rituximab therapy to identify patients with hypogammaglobulinemia to ensure initiation of immunoglobulin replacement therapy in order to avoid life-threatening invasive bacterial infections. Recent reports indicate that Rituximab is not contra-indicated for the treatment of CVID-associated thrombocytopenia, however concomitant immunoglobulin substitution therapy is of fundamental importance to minimize the risk of infections. Therefore, lessons can be learned from this case report by clinicians caring for patients with immunodeficiencies, haematological diseases or other autoimmune disorders, particularly, when Rituximab treatment may be considered.

Cytopenia and autoimmune diseases: a vicious cycle fueled by mTOR dysregulation in hematopoietic stem cells

A long-standing but poorly understood defect in autoimmune diseases is dysfunction of the hematopoietic cells. Leukopenia is often associated with systemic lupus erythematous (SLE) and other autoimmune diseases. In addition, homeostatic proliferation of T cells, which is a host response to T-cell lymphopenia, has been implicated as potential cause of rheumatoid arthritis (RA) in human and experimental models of autoimmune diabetes in the NOD mice and the BB rats. Conversely, successful treatments of aplastic anemia by immune suppression suggest that the hematologic abnormality may have a root in autoimmune diseases. Traditionally, the link between autoimmune diseases and defects in hematopoietic cells has been viewed from the prism of antibody-mediated hemolytic cytopenia. While autoimmune destruction may well be part of pathogenesis of defects in hematopoietic system, it is worth considering the hypothesis that either leukopenia or pancytopenia may also result directly from defective hematopoietic stem cells (HSC). We have recently tested this hypothesis in the autoimmune Scurfy mice which has mutation Foxp3, the master regulator of regulatory T cells. Our data demonstrated that due to hyperactivation of mTOR, the HSC in the Scurfy mice are extremely poor in hematopoiesis. Moreover, rapamycin, an mTOR inhibitor rescued HSC defects and prolonged survival of the Scurfy mice. Our data raised the intriguing possibility that targeting mTOR dysregulation in the HSC may help to break the vicious cycle between cytopenia and autoimmune diseases.

A rapid ex vivo clinical diagnostic assay for fas receptor-induced T lymphocyte apoptosis

Deleterious mutations in genes involved in the Fas apoptosis pathway lead to Autoimmune Lymphoproliferative Syndrome (ALPS). Demonstration of an apoptosis defect is critical for the diagnosis and study of ALPS. The traditional in vitro apoptosis assay, however, requires a week of experimental procedures. Here, we show that defects in Fas-induced apoptosis in PBMCs can be evaluated directly ex vivo using multicolor flow cytometry to analyze the apoptosis of effector memory T cells, a Fas-sensitive subset of PBMCs. This method allowed us to sensitively quantify defective apoptosis in ALPS patients within a few hours. Some ALPS patients (ALPS-sFAS) without germline mutations have somatic mutations in Fas specifically in double-negative αβ T cells (DNTs), an unusual lymphocyte population that is characteristically expanded in ALPS. Since DNTs have been notoriously difficult to culture, defective apoptosis has not been previously demonstrated for ALPS-sFAS patients. Using our novel ex vivo apoptosis assay, we measured Fas-induced apoptosis of DNTs for the first time and found that ALPS-sFAS patients had significant apoptosis defects in these cells compared to healthy controls. Hence, this rapid apoptosis assay can expedite the diagnosis of new ALPS patients, including those with somatic mutations, and facilitate clinical and molecular investigation of these diseases.

Common variable immunodeficiency: crossroads between infections, inflammation and autoimmunity

Common variable immunodeficiency is a collection of diseases characterized by primary hypogammaglobulinemia. The causes of CVID are extremely heterogeneous and may affect virtually every pathway linked to B cell development and function. Clinical manifestations of CVID mainly include recurrent bacterial infections, but autoimmune, gastrointestinal, lymphoproliferative, granulomatous, and malignant disorders have also been frequently reported as associated conditions. We aimed to focus on the state of the art of the relationship between infections, inflammation and autoimmunity in CVID.

Autoimmune cytopenias in common variable immunodeficiency

Common variable immunodeficiency (CVID) is a humoral immunodeficiency whose primary diagnostic features include hypogammaglobulinemia involving two or more immunoglobulin isotypes and impaired functional antibody responses in the majority of patients. While increased susceptibility to respiratory and other infections is a common thread that binds a large cross-section of CVID patients, the presence of autoimmune complications in this immunologically and clinically heterogeneous disorder is recognized in up to two-thirds of patients. Among the autoimmune manifestations reported in CVID (20–50%; Chapel et al., 2008; Cunningham-Rundles, 2008), autoimmune cytopenias are by far the most common occurring variably in 4–20% (Michel et al., 2004; Chapel et al., 2008) of these patients who have some form of autoimmunity. Association of autoimmune cytopenias with granulomatous disease and splenomegaly has been reported. The spectrum of autoimmune cytopenias includes thrombocytopenia, anemia, and neutropenia. While it may seem paradoxical “prima facie” that autoimmunity is present in patients with primary immune deficiencies, in reality, it could be considered two sides of the same coin, each reflecting a different but inter-connected facet of immune dysregulation. The expansion of CD21 low B cells in CVID patients with autoimmune cytopenias and other autoimmune features has also been previously reported. It has been demonstrated that this unique subset of B cells is enriched for autoreactive germline antibodies. Further, a correlation has been observed between various B cell subsets, such as class-switched memory B cells and plasmablasts, and autoimmunity in CVID. This review attempts to explore the most recent concepts and highlights, along with treatment of autoimmune hematological manifestations of CVID.

Pathogenesis of autoimmunity in common variable immunodeficiency

Common variable immunodeficiency (CVID) presents in up to 25% of patients with autoimmune (AI) manifestations. Given the frequency and early onset in some patients with CVID, AI dysregulation seems to be an integral part of the immunodeficiency. Antibody-mediated AI cytopenias, most often affecting erythrocytes and platelets make up over 50% of these patients. This seems to be distinct from mainly cell-mediated organ-specific autoimmunity. Some patients present like patients with AI lymphoproliferative syndrome. Interestingly, in the majority of patients with AI cytopenias the immunological examination reveals a dysregulated B and T cell homeostasis. These phenotypic changes are associated with altered signaling through the antigen receptor which may well be a potential risk factor for disturbed immune tolerance as has been seen in STIM1 deficiency. In addition, elevated B cell-activating factor serum levels in CVID patients may contribute to survival of autoreactive B cells. Of all genetic defects associated with CVID certain alterations in TACI, CD19, and CD81 deficiency have most often been associated with AI manifestations. In conclusion, autoimmunity in CVID offers opportunities to gain insights into general mechanisms of human autoimmunity.

[Primary immunodeficiencies presenting with autoimmune cytopenias in adults]

Although primary immunodeficiencies (PID) are typically marked by increased susceptibility to infections, autoimmune manifestations have increasingly been recognized as an important component of several forms of PID. Here, we discuss two forms of PID in which autoimmune cytopenias are particularly common and may be the first manifestation of the disease in adults: autoimmune lymphoproliferative syndrome (ALPS) and common variable immunodeficiency (CVID). Approximately one fifth of patients with CVID develop autoimmune diseases, and immune thrombocytopenic purpura (ITP) and autoimmune hemolytic anemia (AHA) are the most common. Since autoimmune cytopenias frequently precede the diagnosis of CVID, testing for immunoglobulin levels should be performed in patients diagnosed with AITP and AHA. Patients with CVID in association with autoimmune cytopenias have a "particular phenotype" with lower susceptibility to infection and higher susceptibility to autoimmune manifestations and, for patients with AHA, a more frequent development of splenomegaly and lymphoma. Corticosteroids and high doses of intravenous immunoglobulins (IVIg) seem to have the same efficacy as in idiopathic AITP and AHA. Splenectomy and rituximab are as effective as in idiopathic autoimmune cytopenias but are associated with an increased risk of severe infection and should, in our opinion, be considered only for those rare patients with "refractory diseases". The course and outcome of autoimmune cytopenias is not affected by supportive IVIg therapy. Autoimmune destruction of blood cells affects over 70% of ALPS patients. The median age of first presentation is 24 months of age, but with increasing awareness of this condition, adults with autoimmune cytopenias are now being diagnosed more frequently. Testing for ALPS should therefore be considered in young adults with unexplained Evan's syndrome. Patients usually respond to immunosuppressive medications, including corticosteroids. Unlike many patients with idiopathic autoimmune cytopenias, the cytopenias in patients with ALPS typically do not respond to IVIg. After corticosteroids, the immunosuppressive drug that is the most studied in ALPS patients is mycophenolate mofetyl. Rituximab and splenectomy are relatively contraindicated in ALPS because of an increase risk of severe infection and should be reserved for patients who fail all other therapies.

Autoimmunity, intestinal lymphoid hyperplasia, and defects in mucosal B-cell homeostasis in patients with PTEN hamartoma tumor syndrome

The Phosphatase And Tensin Homolog Deleted On Chromosome 10 (PTEN) regulates the phosphoinositol-3-kinase (PI3K)-AKT signaling pathway. In a series of 34 patients with PTEN mutations, we described gastrointestinal lymphoid hyperplasia, extensive hyperplastic tonsils, thymus hyperplasia, autoimmune lymphocytic thyroiditis, autoimmune hemolytic anemia, and colitis. Functional analysis of the gastrointestinal mucosa-associated lymphoid tissue revealed increased signaling via the PI3K-AKT pathway, including phosphorylation of S6 and increased cell proliferation, but also reduced apoptosis of CD20(+)CD10(+) B cells. Reduced activity of PTEN therefore affects homeostasis of human germinal center B cells by increasing PI3K-AKT signaling via mammalian target of rapamycin as well as antiapoptotic signals.

Antiviral and regulatory T cell immunity in a patient with stromal interaction molecule 1 deficiency

Stromal interaction molecule 1 (STIM1) deficiency is a rare genetic disorder of store-operated calcium entry, associated with a complex syndrome including immunodeficiency and immune dysregulation. The link from the molecular defect to these clinical manifestations is incompletely understood. We report two patients with a homozygous R429C point mutation in STIM1 completely abolishing store-operated calcium entry in T cells. Immunological analysis of one patient revealed that despite the expected defect of T cell proliferation and cytokine production in vitro, significant antiviral T cell populations were generated in vivo. These T cells proliferated in response to viral Ags and showed normal antiviral cytotoxicity. However, antiviral immunity was insufficient to prevent chronic CMV and EBV infections with a possible contribution of impaired NK cell function and a lack of NKT cells. Furthermore, autoimmune cytopenia, eczema, and intermittent diarrhea suggested impaired immune regulation. FOXP3-positive regulatory T (Treg) cells were present but showed an abnormal phenotype. The suppressive function of STIM1-deficient Treg cells in vitro, however, was normal. Given these partial defects in cytotoxic and Treg cell function, impairment of other immune cell populations probably contributes more to the pathogenesis of immunodeficiency and autoimmunity in STIM1 deficiency than previously appreciated.

How I treat autoimmune lymphoproliferative syndrome

Autoimmune lymphoproliferative syndrome (ALPS) represents a failure of apoptotic mechanisms to maintain lymphocyte homeostasis, permitting accumulation of lymphoid mass and persistence of autoreactive cells that often manifest in childhood with chronic nonmalignant lymphadenopathy, hepatosplenomegaly, and recurring multilineage cytopenias. Cytopenias in these patients can be the result of splenic sequestration as well as autoimmune complications manifesting as autoimmune hemolytic anemia, immune-mediated thrombocytopenia, and autoimmune neutropenia. More than 300 families with hereditary ALPS have now been described; nearly 500 patients from these families have been studied and followed worldwide over the last 20 years by our colleagues and ourselves. Some of these patients with FAS mutations affecting the intracellular portion of the FAS protein also have an increased risk of B-cell lymphoma. The best approaches to diagnosis, follow-up, and management of ALPS, its associated cytopenias, and other complications resulting from infiltrative lymphoproliferation and autoimmunity are presented.

T and B lymphocyte abnormalities in bone marrow biopsies of common variable immunodeficiency

In common variable immunodeficiency (CVID) defects in early stages of B-cell development, bone marrow (BM) plasma cells and T lymphocytes have not been studied systematically. Here we report the first morphologic and flow cytometric study of B- and T-cell populations in CVID BM biopsies and aspirates. Whereas the hematopoietic compartment showed no major lineage abnormalities, analysis of the lymphoid compartment exhibited major pathologic alterations. In 94% of the patients, BM plasma cells were either absent or significantly reduced and correlated with serum immunoglobulin G levels. Biopsies from CVID patients had significantly more diffuse and nodular CD3(+) T lymphocyte infiltrates than biopsies from controls. These infiltrates correlated with autoimmune cytopenia but not with other clinical symptoms or with disease duration and peripheral B-cell counts. Nodular T-cell infiltrates correlated significantly with circulating CD4(+)CD45R0(+) memory T cells, elevated soluble IL2-receptor and neopterin serum levels indicating an activated T-cell compartment in most patients. Nine of 25 patients had a partial block in B-cell development at the pre-B-I to pre-B-II stage. Because the developmental block correlates with lower transitional and mature B-cell counts in the periphery, we propose that these patients might form a new subgroup of CVID patients.