Genetic defects in common variable immunodeficiency

Role of rare immune cells in common variable immunodeficiency

Common variable immunodeficiency disorder (CVID) is a heterogeneous disorder and the most common symptomatic antibody deficiency disease characterized with hypogammaglobulinemia and a broad range of clinical manifestations. Multiple genetic, epigenetic, and immunological defects are involved in the pathogenesis of CVID. These immunological defects include abnormalities in the number and/or function of B lymphocytes, T lymphocytes, and other rare immune cells. Although some immune cells have a relatively lower proportion among total immune subsets in the human body, they could have important roles in the pathogenesis of immunological disorders like CVID. To the best of our knowledge, this is the first review that described the role of rare immune cells in the pathogenesis and clinical presentations of CVID.

Age-stratified pediatric reference values of lymphocytes in the Moroccan population

The number of circulating lymphocytes is altered in a number of diseases including either increase (lymphocytosis) or decrease (lymphocytopenia). Therefore, the assessment of total blood lymphocyte numbers and the relative distribution of lymphocyte subsets is a critical front-line tool in the clinical diagnosis of a number of diseases, including pediatric diseases and disorders. However, the interpretation of this data requires comparison of patient's results to reliable reference values. Blood lymphocyte subpopulation numbers are also subject to genetic polymorphisms, immunogenic and environmental factors and vary greatly between populations. While the best practice reference values should be established within local representative populations of healthy subjects, to date, Caucasian reference values are used in Morocco due to the absence of indigenous reference values. Potential differences in blood lymphocyte subpopulation reference values between Caucasian versus Moroccan populations can adversely affect the diagnosis of pediatric and childhood diseases and disorders such as primary immunodeficiency (PID) in Morocco.

OBJECTIVE

The aim of this study was to establish the age-stratified normal reference values of blood lymphocyte subsets for the pediatric Moroccan population.

METHODS

We measured the concentration of lymphocyte subpopulations by flow cytometry from 83 Moroccan healthy subjects stratified into 5 age groups of 0-1, 1-2, 2-6, 6-12 and > 12-18 (adult).

RESULTS

The absolute and relative amounts of the main lymphocyte subsets of T-cells, B cells and Natural Killer (NK) cells were measured and compared to previously described reference values from Cameroonian, Turkish, American and Dutch populations. Additionally, we also observed an age-related decline in the absolute population sizes of lymphocyte subsets within our study group. Relative proportions of CD3+CD4+ helper T lymphocytes decreased with increasing age and by 12 years-adult age, both proportions of CD3+CD4+ helper T lymphocytes and CD3+CD8+ cytotoxic T lymphocytes, as well as CD3-CD19+ B lymphocytes were also decreased. Finally, we compared the median values and range of our Moroccan study group with that of published results from Cameroon, Turkey, USA and Netherlands and observed significant differences in median and mean values of absolute number and relative proportions of lymphocyte subsets especially at 0-1 years and 1-2 years age groups. Above age 12 years, the Moroccan values were lower. For NK cells, the Moroccan values are also lower.

CONCLUSIONS

The results of this study have a significant impact in improving the threshold values of the references intervals routinely used in the diagnosis of paediatric diseases such as PIDs or mother-to-child transmitted HIV within the Moroccan population.

Human inborn errors of immunity caused by defects of receptor and proteins of cellular membrane

Inborn errors of immunity are diseases of the immune system resulting from mutations that alter the expression of encoded proteins or molecules. Total updated number of these disorders is currently 406, with 430 different identified gene defects involved. Studies of the underlying mechanisms have contributed in better understanding the pathophysiology of the diseases, but also the complexity of the biology of innate and adaptive immune system and its interaction with microbes. In this review we present and briefly discuss Inborn Errors of Immunity caused by defects in genes encoding for receptors and protein of cellular membrane, including cytokine receptors, T cell antigen receptor (TCR) complex, cellular surface receptors or receptors signaling causing predominantly antibody deficiencies, co-stimulatory receptors and others. These alterations impact many biological processes of immune-system cells, including development, proliferation, activation and down-regulation of the immunological response, and result in a variety of diseases that present with distinct clinical features or with overlapping signs and symptoms.

Whole exome sequencing identifies compound heterozygous variants of CR2 gene in monozygotic twin patients with common variable immunodeficiency

Objectives:

A pair of female Malay monozygotic twins who presented with recurrent upper respiratory tract infections, hepatosplenomegaly, bronchiectasis and bicytopenia were recruited in this study. Both patients were suspected with primary immunodeficiency diseases. However, the definite diagnosis was not clear due to complex disease phenotypes. The objective of this study was to identify the causative gene mutation in these patients.

Methods:

Lymphocyte subset enumeration test and whole exome sequencing were performed.

Results:

We identified a compound heterozygous CR2 mutation (c.1916G>A and c.2012G>A) in both patients. These variants were then confirmed using Sanger sequencing.

Conclusion:

Whole exome sequencing analysis of the monozygotic twins revealed compound heterozygous missense mutations in CR2.

Immunological features in pediatric patients with recurrent and severe infection: Identification of Primary Immunodeficiency Diseases in Merida, Venezuela

INTRODUCTION AND OBJECTIVES

Primary immunodeficiency diseases (PIDs) are disorders associated mainly with recurrent and severe infection and an increase in susceptibility to autoimmune conditions and cancer. In Venezuela, PIDs are underdiagnosed and there is usually a delay in their diagnosis. Hence there are no data concerning the frequency and type of PIDs that occur. The aim of this study was to identify and quantify the types of PIDs that occur in Merida, a population within Venezuela.

PATIENTS OR MATERIALS AND METHODS

Following an informative program designed to alert local health professionals to the warning signs for PIDs, patients with a history of recurrent infections were referred to the Instituto de Inmunologia Clinica, Universidad de Los Andes.

RESULTS AND CONCLUSIONS

During the three-year period January 2014 to January 2017, thirty-two cases of PIDs were identified in pediatric patients, and 17 different types of PIDs, were identified. Predominantly antibody deficiencies were most frequent (40.6%), followed by immunodeficiencies affecting cellular and humoral immunity (21.8%), congenital defects of phagocyte (18.7%), CID with associated or syndromic features (9.3%), defects in intrinsic and innate immunity (6.4%) and diseases of immune dysregulation (3.2%). These results have important implications not only to the future approach for management of patients in our regions, but add important knowledge concerning PIDs in Latin America and worldwide.

Familial inheritance and screening of first-degree relatives in common variable immunodeficiency and immunoglobulin A deficiency patients

Common variable immunodeficiency (CVID) and immunoglobulin A deficiency (IgAD) are the most prevalent primary immunodeficiency disorders. High rates of familial inheritance have been described in CVID and IgAD, but it is unknown in different ethnic populations. We aimed to determine the prevalence of familial cases and whether they showed more severe clinical characteristics than sporadic ones in Turkish patients. A total of 40 CVID and 70 IgAD patients and their 251 first-degree relatives (FDRs) were evaluated. Demographic, clinical, and laboratory data were reviewed. A familial case was defined as a patient with at least one affected FDR (A-FDR). The rate of parental consanguinity was 19.1%. There were 37 familial cases (37/110) (33.6%) with at least one A-FDR. There were 48 A-FDRs who had immunoglobulins lower than age-related normals (48/251) (19.1%). Pulmonary infections were significantly higher in familial cases. To our knowledge, this study includes the highest number of CVID/IgAD patients and their FDRs in literature. Familial cases are at least 30% of the IgAD and CVID patients, and they have more frequent lower respiratory tract infections than sporadic ones, so these patients have to be evaluated depending on their being familial or sporadic for better management. The risk of carrying any immunologic alterations in relatives of patients with IgAD and CVID is approximately 20%. Although most A-FDRs are asymptomatic, considering the risk of progression to CVID by age, we highly recommend routine screening for FDRs.

Neutropenia in Patients with Common Variable Immunodeficiency: a Rare Event Associated with Severe Outcome

BACKGROUND

Common variable immunodeficiency (CVID) is characterized by infections and hypogammaglobulinemia. Neutropenia is rare during CVID.

METHODS

The French DEFI study enrolled patients with primary hypogammaglobulinemia. Patients with CVID and neutropenia were retrospectively analyzed.

RESULTS

Among 473 patients with CVID, 16 patients displayed neutropenia (lowest count [0-1400]*10⁶/L). Sex ratio (M/F) was 10/6. Five patients died during the follow-up (11 years) with an increased percentage of deaths compared to the whole DEFI group (31.3 vs 3.4%, P < 0.05). Neutropenia was diagnosed for 10 patients before 22 years old. The most frequent symptoms, except infections, were autoimmune cytopenia, i.e., thrombopenia or anemia (11/16). Ten patients were affected with lymphoproliferative diseases. Two patients were in the infection only group and the others belonged to one or several other CVID groups. The median level of IgG was 2.6 g/L [0.35-4.4]. Most patients presented increased numbers of CD21^low CD38^low B cell, as already described in CVID autoimmune cytopenia group. Neutropenia was considered autoimmune in 11 cases. NGS for 52 genes of interest was performed on 8 patients. No deleterious mutations were found in LRBA, CTLA4, and PIK3. More than one potentially damaging variant in other genes associated with CVID were present in most patients arguing for a multigene process.

CONCLUSION

Neutropenia is generally associated with another cytopenia and presumably of autoimmune origin during CVID. In the DEFI study, neutropenia is coupled with more severe clinical outcomes. It appears as an "alarm bell" considering patients' presentation and the high rate of deaths. Whole exome sequencing diagnosis should improve management.

Killer-cell immunoglobulin-like receptor and human leukocyte antigen-C genes in common variable immunodeficiency

BACKGROUND

We aimed herein to investigate the killer-cell immunoglobulin-like receptor (KIR) genes and human leukocyte antigen (HLA)-C alleles in patients with common variable immunodeficiency (CVID), and to reveal their differences from those in healthy population.

METHODS

In all, 18 patients who have been diagnosed with CVID and 15 living donors of kidney transplant recipients were enrolled in the study. Polymerase chain reaction-sequence-specific primer (PCR-SSP) typing method was used in molecular genetic analysis. The frequencies of the genes in the study groups were statistically compared with each other using chi-square or Fisher exact tests, whichever were appropriate.

RESULTS

Although there was no significant difference between both study groups with respect to distribution of KIR and HLA-C2 group genes, HLA-Cw7 allele frequency in patients with CVID was significantly lower than that in healthy population (P = 0.008).

CONCLUSION

This present study results support that HLA-Cw7 allele, an inhibitor of KIR ligand, may play a role in the pathogenesis of CVID.

Genetic defects and the role of helper T-cells in the pathogenesis of common variable immunodeficiency

Common variable immunodeficfiiency (CVID) is a primary immunodeficiency syndrome representing a heterogeneous set of disorders resulting mostly in antibody deficiency and recurrent infections. However, inflammatory and autoimmune disorders and some kinds of malignancies are frequently reported as a part of the syndrome. Although it is one of the most widespread primary immunodeficiency, only recently some genetic defects in CVID have been identified. Mutations have been detected in inducible T-cell costimulator (ICOS), transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI), B-cell activating factor-receptor (BAFF-R), B-cell receptor complex (CD19, CD21 and CD81) and CD20. On the other hand, recent studies have shown a decrease in T-helper-17 cells frequency and their characteristic cytokines in CVID patients and this emphasis on the vital role of the T-cells in immunopathogenesis of the CVID. Furthermore, in the context of autoimmune diseases accompanying CVID, interleukin 9 has recently attracted a plenty of considerations. However, the list of defects is expanding as exact immunologic pathways and genetic disorders in CVID are not yet defined. In this review, we have a special focus on the immunopathogenesis of CVID, recent advances in understanding the underlying etiology and genetics for patients.

Immunophenotypic Analysis of B Lymphocytes in Patients with Common Variable Immunodeficiency: Identification of CD23 as a Useful Marker in the Definition of the Disease

Common variable immunodeficiency (CVID) is a primary immunodeficiency characterized by the failure of B lymphocytes differentiation leading to deficient immunoglobulins secretion. The identified genetic defects account only for a minority of cases. The importance of B cells immunophenotyping in the classification of CVID is known. This procedure can identify alterations on the cell surface molecules expression that could explain some immunological disorders characteristic of CVID. Moreover, some immunophenotypical aspects can correlate with clinical features of the disease. We used this procedure to analyze a cohort of 23 patients affected by CVID, in order to identify the novel alterations of B cells and to find the possible correlations with clinical features. Circulating B cells were studied by flow cytometry incubating whole blood with specific antibodies for B cell surface molecules including CD27, IgM, IgD, CD21, and CD23. We compared the population of “switched memory” IgD− CD27+ B lymphocytes with the population of “switched memory” IgM− IgD− CD23− CD27+ B cells. These last B cells were reduced in patients compared to healthy controls; moreover, IgM− IgD− CD23− CD27+ B cells were lower than IgD− CD27+ B cells in patients with CVID. The reduction of this subset of B lymphocytes correlates more tightly than IgD− CD27+ B cells with lymphadenopathy and airways infections. In conclusion, our findings may help in better identifying patients with CVID.

Three different classifications, B lymphocyte subpopulations, TNFRSF13B (TACI), TNFRSF13C (BAFF-R), TNFSF13 (APRIL) gene mutations, CTLA-4 and ICOS gene polymorphisms in Turkish patients with common variable immunodeficiency

B lymphocyte subpopulations, previously defined classification schemes (Freiburg, Paris, EuroClass), TNFRSF13B (TACI), TNFRSF13C (BAFF-R), TNFSF13 (APRIL) gene mutations, CTLA-4 and ICOS gene polymorphisms were analyzed in 25 common variable immunodeficiency (CVID) patients and 25 healthy controls. Patients were also divided into two subgroups due to some disease severity criteria. SG (severe disease group) (n:11) included patients who have splenomegaly and/or granulomatous diseases and/or bronchiectasis and/or lower baseline IgG values (<270 mg/dl). MG (moderate disease group) (n:14) patients diagnosed as having ESID/PAGID criteria but does not fulfill SG inclusion criteria. The onset of infectious symptoms and age at diagnosis were 50.0 ± 45.7 and 78.5 ± 54.5 months, respectively. Parental consanguinity rate was 54.5% in SG and 7.1% in MG. Switched-memory B cells (CD19 + 27 + IgD-IgM-) showed significant decrease in CVID patients and these cells were also significantly lower in SG compared to MG. CVID patients had significantly higher percentages of CD19 + κ + B cells and CD19 + λ + B cells than healthy controls. Freiburg classification: 87.5% of patients (n:21) were in group I and 12.5% were in Group II. Eighteen (75%) CVID patients with a low percentage of CD21(low) B cells were in Group Ib while three patients classified as Group Ia. The significantly lower levels of IgG and IgA in Group Ia is a novel finding. The percentages of patients for Paris Classification groups MB0, MB1, MB2 were 88%, 4% and 8%, respectively. There was a significant increase of splenomegaly, lymphadenopathy and autoimmune cytopenia in Group MB0. EuroClass: 45.8% of patients were smB+ and 54.2% were smB-. Splenomegaly and lymphadenopathy were significantly higher in smB- group. TACI: One patient carried heterozygous C104R mutation which was known as disease causing. APRIL: G67R and N96S SNPs were detected in most of the patients and healthy controls. BAFF-R: P21R/H159Y compound heterozygous mutation (n:1) and P21R heterozygous mutations (n:3) were detected. +49 A > G changes in exon 1 of CTLA-4 gene: GG and AG genotypes increase the risk of CVID development 1.32 and 2.18 fold, respectively. 1564 T > C polymorphisms on 3'UTR region in exon 2 of ICOS gene was not found to be significantly different in CVID patients. CVID classifications were not helpful in determining the genetic etiology of CVID.

B cell responses to CpG correlate with CXCL16 expression levels in common variable immunodeficiency

Broad Toll-like receptor 9 (TLR9) signalling defects after CpG in vitro stimulation have been described in common variable immunodeficiency (CVID). CXCL16, a surface receptor, was recently shown to influence cell responses to CpG. We evaluated the expression and function of CXCL16 on B cells from healthy controls and CVID patients. We report that CXCL16 is normally expressed on B cells throughout peripheral maturation. Decreased B cell expression of CXCL16 was observed in a subgroup of CVID patients that correlated with defective in vitro responses to CpG (such as upregulation of CD69, CD86, AICDA, IL-6, and TLR9). Our data suggest that expression levels of a surface receptor, namely, CXCL16, correlate with B cell responses mediated by TLR9 in common variable immunodeficiency.

Primary cutaneous actinomycosis caused by Actinomyces bovis in a patient with common variable immunodeficiency

Actinomycosis is a chronic, suppurative granulomatous disease caused by the genus Actinomyces. This report is an interesting case of primary cutaneous actinomycosis (PCA) in a patient with common variable immunodeficiency (CVI) affecting the fingernails. The patient was successfully treated with penicillin G, cefazolin and metronidazole as well as surgical debridement of the infected tissues. In a 4-year follow-up period, no recurrence was observed. Primary cutaneous actinomycosis is a rare disease and the diagnosis needs a high index of clinical suspicion with attention to the history of skin implantation of the organism.

Altered spectrum of somatic hypermutation in common variable immunodeficiency disease characteristic of defective repair of mutations

Pathogenic common variable immunodeficiency diseases (CVID) are genetic, usually inherited diseases for which a limited number of genetic defects have been implicated. As CVID presents with a wide range of clinical characteristics, there are likely diverse and for the most part unidentified genetic causes. In some individuals, defects in somatic hypermutation (SHM) have been suggested as the underlying cause of CVID. To address the mechanisms of SHM defects in CVID, we conducted a comprehensive mutational analysis of immunoglobulin heavy chain sequences from CVID patients. We identified several remarkably specific alterations in the spectra of SHM in comparison to healthy individuals. We provide evidence that some CVID cases are associated with defective repair of AID-induced mutations by the DNA mismatch repair (MMR) machinery. Our findings together with reports of increased chromosomal radiosensitivity and associated lymphoproliferative disorders amongst CVID patients, suggest that altered DNA damage repair may be a cause of CVID.

Analysis of TACI mutations in CVID & RESPI patients who have inherited HLA B*44 or HLA*B8

Background

Recent reports have suggested that Common Variable Immunodeficieny (CVID) can present as an autosomal dominant trait dependent on the inheritance of a set of uncommon mutations/alleles of TACI (transmembrane activator and calcium-modulator and cyclophilin ligand interactor) involving exons 3 or 4. Penetrance, however, appears to be incomplete. Among our clinic population, the greatest genetic linkage for CVID is to the major histocompatibility complex (MHC) on chromosome 6. The majority of our patients have inherited HLA *DQ2, *DR7, *DR3(17), *B8, and/or *B44. Of these, HLA*B44 was present in almost half of the patients and was thus the most common susceptibility allele. HLA *B44 was also found to be over-represented among patients who presented to our clinic with adult-onset recurrent sinopulmonary infections (RESPI) and normal serum immunoglobulin levels, a cohort that included first and second degree relatives of patients with CVID. One of the two original reports of the association between TACI and CVID also reported Human Leukocyte Antigen (HLA) haplotypes. Of 13 affected subjects, nine had inherited HLA *B8 and six had inherited HLA B44. This raised the possibility that TACI mutations might synergize with MHC class I alleles to enhance susceptibility to humoral immune deficiency.

Methods

We identified 63 CVID patients irrespective of HLA status and 13 RESPI patients who had inherited HLA*B44. To evaluate for mutations in the gene for TACI, we PCR amplified and sequenced TACI exons 3 and 4 from these patients.

Results

Of the 76 patients, eleven proved heterozygous for a previously reported, silent T->G polymorphism [rs35062843] at proline 97 in exon 3. However, none of the 13 RESPI patients and only one of the 63 CVID patients inherited a TACI allele previously associated with CVID. This patient was heterozygous for the TACI A181E allele (exon 4). She did not carry *DQ2, *DR7, *DR3(17), *B8, or *B44.

Conclusion

These findings suggest that TACI mutations are unlikely to play a critical role in creating susceptibility to CVID among patients with previously recognized MHC class I and class II susceptibility alleles.

Supported by NIH/USIDNET N01-AI30070, NIH R21 AI079741 and NIH M01-RR00032

Common variable immunodeficiency (CVID): case report and review of the literature

Common variable immunodeficiency (CVID) is an immunodeficiency disease characterized by diminished ability to produce immunoglobulins. CVID has an estimated incidence of 1:10,000 to 1:200,000 (male:female 1:1) and usually presents in the second and third decade, although it also has a peak of incidence in childhood. The exact pathophysiology remains unclear. CVID can be associated with autoimmune, granulomatous and gastrointestinal diseases and patients have a predisposition to malignancies (especially non-Hodgkin lymphoma). Since different organ systems can be affected, all clinicians need to be aware of this entity, especially when confronted with patients with recurrent infections and/or multiple autoimmune diseases.

Recent developments related to the laboratory diagnosis of primary immunodeficiency diseases

PURPOSE OF REVIEW

The rapid increases in newly recognized primary immunodeficiency diseases (PIDs), including their clinical, genetic and laboratory-associated abnormalities, make staying abreast of the latest developments a challenge. This review provides an overview of current information directly and indirectly related to the laboratory diagnosis of PIDs.

RECENT FINDINGS

The latest classification and several prevalence studies provide the framework for understanding the breadth, categories and incidence rates of over 120 recognized disease entities. The latter is followed by reviews of new information related to specific PIDs including new tests, new genetic associations and newly discovered laboratory-based abnormalities. The final section presents new PIDs and a discussion of the future potential of array-based technologies in the diagnosis of PIDs.

SUMMARY

The information provided in this review will allow a new appreciation of previously underestimated PIDs' prevalence rates and the delay in their diagnosis. Understanding the molecular causes of PIDs will lead to earlier diagnoses and new targets for improved therapeutic intervention. The presentation of new diagnostic tests should encourage other laboratories to assess their potential in their own laboratories. Ultimately, this information will lead to an increase in the understanding of novel laboratory parameters associated with specific PID and should improve the time required to attain an accurate diagnosis.

Genetic polymorphism study of regulatory B cell molecules and cellular immunity function in an adult patient with Common Variable Immunodeficiency

A 43 year old female patient presented for recurrent bacterial lower respiratory infections. A research for immunodeficiency status revealed total hypogammaglobulinemia, reduced IgG1, IgG2, IgG3 subclass levels, and low number of B lymphocytes (CD19+). Common Variable Immunodeficiency (CVID) 11.2 category was diagnosed according to recent criteria of primary immunodeficiencies (PID). Further immunological study consisting of genetic polymorphism of genes relating to differentiation, activation and function of B cells (ICOS, BAFF receptor BCMA and TACI) was performed, which did not reveal any related mutations. T cell parameters and Th1/Th2 cytokine network did not show any disturbances. It is postulated that probable endstage B cell differentiation defects should be investigated. The patient receives IVIGs replacement thereafter and the rate and severity of infections have significantly improved.

Homologous recombination is necessary for normal lymphocyte development

Primary immunodeficiencies are rare but serious diseases with diverse genetic causes. Accumulating evidence suggests that defects in DNA double-strand break (DSB) repair can underlie many of these syndromes. In this context, the nonhomologous end joining pathway of DSB repair is absolutely required for lymphoid development, but possible roles for the homologous recombination (HR) pathway have remained more controversial. While recent evidence suggests that HR may indeed be important to suppress lymphoid transformation, the specific relationship of HR to normal lymphocyte development remains unclear. We have investigated roles of the X-ray cross-complementing 2 (Xrcc2) HR gene in lymphocyte development. We show that HR is critical for normal B-cell development, with Xrcc2 nullizygosity leading to p53-dependent early S-phase arrest. In the absence of p53 (encoded by Trp53), Xrcc2-null B cells can fully develop but show high rates of chromosome and chromatid fragmentation. We present a molecular model wherein Xrcc2 is important to preserve or restore replication forks during rapid clonal expansion of developing lymphocytes. Our findings demonstrate a key role for HR in lymphoid development and suggest that Xrcc2 defects could underlie some human primary immunodeficiencies.