Prediction of persistent immunodeficiency in the DiGeorge anomaly

DiGeorge Syndrome Diagnosed at Age 38: Challenges in Low-resource Settings and Implications of a Missed Diagnosis

22q11.2 deletion syndrome (22.q11.2 DS) is a genetic syndrome resulting from a microdeletion on chromosome 22. It has a diverse array of manifestations, and most cases are diagnosed early in childhood. We present the case of a 38-year-old female born in a developing country who presented to our clinic to establish care for a history of primary hypothyroidism. She was clinically and biochemically euthyroid on thyroid supplementation. She was also noted to have hypocalcemia in the setting of low PTH, for which the patient was previously prescribed calcitriol. Given a history of cleft palate, abnormal facial features, mild recurrent sinopulmonary infections, and her endocrine history (including short stature with height in the 6th percentile), genetic testing was obtained. She was diagnosed with a heterozygous whole gene deletion of the TBX1 gene. Additional genetic evaluation demonstrated a 2.6-Mb microdeleted segment of the 22a11.2 region encompassing 62 genes. The patient was referred to cardiology for evaluation of cardiac involvement given a history of tachyarrhythmia. This case highlights challenges in diagnosis and the implications of a delayed diagnosis of 22.q11.2 DS.

Syndromic and non-syndromic etiologies causing neonatal hypocalcemic seizures

BACKGROUND

The diagnosis of neonatal hypocalcemic seizures (HS) in newborns is made based on clinical signs and serum calcium level. Their etiology is broad and diverse, and timely detection and initiation of treatment is essential.

METHODS

We retrospectively reviewed 1029 patients admitted to the neonatal intensive care unit. Neonatal HS were diagnosed in 16 patients, and we compared etiologies and clinical outcomes, including clinical seizures and neurodevelopment at least over 1 year old.

RESULTS

The etiologies can be broadly categorized into 5 syndromic and 11 non-syndromic neonatal HS. Syndromic neonatal HS included 3 Digeorge syndrome, 1 Kleefstra syndrome and 1 Alström syndrome. Non-syndromic neonatal HS included 8 vitamin D deficiency, 1 hypoparathyroidism, and 2 hypoxic-ischemic encephalopathy. Patients with syndromic neonatal HS were found to have worse clinical outcomes than those with nonsyndromic HS. In eight patients with vitamin D deficiency, neurodevelopment was normal. Five of five patients (100%) with syndromic HS used two or more antiseizure drugs. However, among patients with non-syndromic neonatal HS, only one of 11 (9.1%) used more than one drug (p = 0.001).

CONCLUSION

This finding highlighted that syndromic hypocalcemic seizures in newborns have worse neurodevelopmental outcomes and are more often difficult to manage, and would benefit from a genetic diagnostic approach.

Clinical and immunological features in a cohort of patients with partial DiGeorge syndrome followed at a single center

DiGeorge syndrome (DGS) is a primary immunodeficiency characterized by various degrees of T-cell deficiency. In partial DGS (pDGS), other risk factors could predispose to recurrent infections, autoimmunity, and allergy. The aim of this study was to assess the effect of different factors in the development of infections, autoimmunity, and/or allergy in patients with pDGS. We studied 467 pDGS patients in follow-up at Great Ormond Street Hospital. Using a multivariate approach, we observed that palatal anomalies represent a risk factor for the development of recurrent otitis media with effusion. Gastroesophageal reflux/dysphagia and asthma/rhinitis represent a risk factor for the development of recurrent upper respiratory tract infections. Allergy and autoimmunity were associated with persistently low immunoglobulin M levels and lymphopenia, respectively. Patients with autoimmunity showed lower levels of CD3⁺, CD3⁺CD4⁺, and naïve CD4⁺CD45RA⁺CD27⁺ T lymphocytes compared with pDGS patients without autoimmunity. We also observed that the physiological age-related decline of the T-cell number was slower in pDGS patients compared with age-matched controls. The age-related recovery of the T-cell number depended on a homeostatic peripheral proliferation of T cells, as suggested by an accelerated decline of the naïve T lymphocytes in pDGS as well as a more skewed T-cell repertoire in older pDGS patients. These evidences suggest that premature CD4⁺ T-cell aging and lymphopenia induced spontaneous peripheral T-cell proliferation might contribute to the pathogenesis of autoimmunity in patients with pDGS. Infections in these patients represent, in most of the cases, a complication of anatomical or gastroenterological anomalies rather than a feature of the underlying immunodeficiency.

Thymic output: Assessment of CD4+ recent thymic emigrants and T-Cell receptor excision circles in infants

BACKGROUND

CD4⁺ recent thymic emigrants (CD4⁺ RTEs) constitute a subset of T cells recently generated in the thymus and exported into peripheral blood. CD4⁺ RTEs have increased copy numbers of T-cell receptor excision circles (TREC). They are characterized by the expression of CD31 on naïve CD4 T-cells. We aimed to validate a flow-cytometry assay to enumerate CD4⁺ RTEs and assess its performance in relation to TREC measurement.

METHODS

CD4⁺ RTEs cell count in peripheral blood was measured to determine sample stability, precision, linearity, and to establish reference ranges. TRECs were measured using qPCR assay performed with DNA isolated from peripheral blood. CD4⁺ RTEs, TRECs, and flow cytometry results for major T-cell markers were assessed in 50 infants less than 2 years of age.

RESULTS

Inter-and intra-assay precisions (% CV) were 1.5-12.2 and 1.5-7.0, respectively. Linearity studies showed that the results are linear over a range of 0.7 to 403.0 CD4⁺ RTEs/μL of blood. There was 84% agreement (42 of 50) between CD4⁺ RTEs and TRECs qualitative results for the infant samples. CD4⁺ RTEs reference ranges in 17 healthy children was in agreement with published data, while that of the healthy adults were 51-609 cells/μL of blood.

CONCLUSION

The validation results provide acceptable measures of the CD4⁺ RTEs test performance within CAP/CLIA frameworks. CD4⁺ RTEs and TRECs assays show high agreement in the infant population. The CD4⁺ RTEs test can be used as a confirmation for the TREC results along with or as an alternative to T-cell phenotyping in infants with repeatedly low TRECs concentrations. © 2015 International Clinical Cytometry Society.

The diverse clinical features of chromosome 22q11.2 deletion syndrome (DiGeorge syndrome)

A 2-year-old boy with chromosome 22q11.2 deletion syndrome was referred for recurrent sinopulmonary infections. He was diagnosed shortly after birth by a fluorescence in situ hybridization test that was performed due to interrupted aortic arch type B. He had no hypocalcemia, and his recovery from cardiac repair was uneventful. He had difficulty feeding and gained weight slowly, but, otherwise, there were no concerns during his first year of life. At 15 months of age, he began to develop significant otitis media and bronchitis. He was hospitalized once for pneumonia at 18 months of age and has never been off antibiotics for more than 1 week since then. He has not had any previous immunologic evaluation. Recurrent sinopulmonary infections in a child with chromosome 22q11.2 deletion syndrome can have the same etiologies as in any other child. Atopy, anatomic issues, cystic fibrosis, and new environmental exposures could be considered in this setting. Early childhood can be problematic for patients with chromosome 22q11.2 deletion syndrome due to unfavorable drainage of the middle ear and sinuses. Atopy occurs at a higher frequency in 22q11.2 deletion syndrome, and these children also have a higher rate of gastroesophageal reflux and aspiration than the general population. As would be appropriate for any child who presents with recurrent infections at 2 years of age, an immunologic evaluation should be performed. In this review, we will highlight recent findings and new data on the management of children and adults with chromosome 22q11.2 deletion syndrome.

Thymus transplantation restores the repertoires of forkhead box protein 3 (FoxP3)+ and FoxP3- T cells in complete DiGeorge anomaly

The development of T cells with a regulatory phenotype after thymus transplantation has not been examined previously in complete DiGeorge anomaly (cDGA). Seven athymic infants with cDGA and non-maternal pretransplantation T cell clones were assessed. Pretransplantation forkhead box protein 3 (Foxp3)(+) T cells were detected in five of the subjects. Two subjects were studied in greater depth. T cell receptor variable β chain (TCR-Vβ) expression was assessed by flow cytometry. In both subjects, pretransplantation FoxP3(+) and total CD4(+) T cells showed restricted TCR-Vβ expression. The development of naive T cells and diverse CD4(+) TCR-Vβ repertoires following thymic transplantation indicated successful thymopoiesis from the thymic tissue grafts. Infants with atypical cDGA develop rashes and autoimmune phenomena before transplantation, requiring treatment with immunosuppression, which was discontinued successfully subsequent to the observed thymopoiesis. Post-transplantation, diverse TCR-Vβ family expression was also observed in FoxP3(+) CD4(+) T cells. Interestingly, the percentages of each of the TCR-Vβ families expressed on FoxP3(+) and total CD4(+) T cells differed significantly between these T lymphocyte subpopulations before transplantation. By 16 months post-transplantation, however, the percentages of expression of each TCR-Vβ family became significantly similar between FoxP3(+) and total CD4(+) T cells. Sequencing of TCRBV DNA confirmed the presence of clonally amplified pretransplantation FoxP3(+) and FoxP3(-) T cells. After thymus transplantation, increased polyclonality was observed for both FoxP3(+) and FoxP3(-) cells, and pretransplantation FoxP3(+) and FoxP3(-) clonotypes essentially disappeared. Thus, post-transplantation thymic function was associated with the development of a diverse repertoire of FoxP3(+) T cells in cDGA, corresponding with immunological and clinical recovery.

A prospective study of influenza vaccination and a comparison of immunologic parameters in children and adults with chromosome 22q11.2 deletion syndrome (digeorge syndrome/velocardiofacial syndrome)

Prior to the advent of cardiac bypass, most children with congenital cardiac anomalies and chromosome 22q11.2 deletion syndrome died. With improved technology, there is now a wave of young adults with chromosome 22q11.2 deletion syndrome requiring clinical care. Fifteen young children and 20 adults with chromosome 22q11.2 deletion had flow cytometry, functional T cell analyses, and functional B cell analyses to characterize their immune system. Subjects were vaccinated with the annual inactivated influenza vaccine, and responses were evaluated by hemagglutination inhibition titer assessment. The pattern of T cell subset abnormalities was markedly different between pediatric and adult patients. In spite of the cellular deficits observed in adults, titers produced after influenza vaccine administration were largely intact. We conclude that disruption to T cell production appears to have secondary consequences for T cell differentiation and B cell function although the clinical impact remains to be determined.

Chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

Chromosome 22q11.2 deletion syndrome is a common syndrome also known as DiGeorge syndrome and velocardiofacial syndrome. It occurs in approximately 1:4000 births, and the incidence is increasing due to affected parents bearing their own affected children. The manifestations of this syndrome cross all medical specialties, and care of the children and adults can be complex. Many patients have a mild to moderate immune deficiency, and the majority of patients have a cardiac anomaly. Additional features include renal anomalies, eye anomalies, hypoparathyroidism, skeletal defects, and developmental delay. Each child's needs must be tailored to his or her specific medical problems, and as the child transitions to adulthood, additional issues will arise. A holistic approach, addressing medical and behavioral needs, can be very helpful.

First use of thymus transplantation therapy for FOXN1 deficiency (nude/SCID): a report of 2 cases

FOXN1 deficiency is a primary immunodeficiency characterized by athymia, alopecia totalis, and nail dystrophy. Two infants with FOXN1 deficiency were transplanted with cultured postnatal thymus tissue. Subject 1 presented with disseminated Bacillus Calmette-Guérin infection and oligoclonal T cells with no naive markers. Subject 2 had respiratory failure, human herpes virus 6 infection, cytopenias, and no circulating T cells. The subjects were given thymus transplants at 14 and 9 months of life, respectively. Subject 1 received immunosuppression before and for 10 months after transplantation. With follow up of 4.9 and 2.9 years, subjects 1 and 2 are well without infectious complications. The pretransplantation mycobacterial disease in subject 1 and cytopenias in subject 2 resolved. Subject 2 developed autoimmune thyroid disease 1.6 years after transplantation. Both subjects developed functional immunity. Subjects 1 and 2 have 1053/mm(3) and 1232/mm(3) CD3(+) cells, 647/mm(3) and 868/mm(3) CD4(+) T cells, 213/mm(3) and 425/mm(3) naive CD4(+) T cells, and 10 200 and 5700 T-cell receptor rearrangement excision circles per 100 000 CD3(+) cells, respectively. They have normal CD4 T-cell receptor β variable repertoires. Both subjects developed antigen-specific proliferative responses and have discontinued immunoglobulin replacement. In summary, thymus transplantation led to T-cell reconstitution and function in these FOXN1 deficient infants.

Secondary immunologic consequences in chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

Clinical evidence suggests that patients with Chromosome 22q11.2 deletion (Ch22q11.2D) have an increased prevalence of atopic and autoimmune disease and this has been without explanation. We hypothesized that the increase in atopy was due to homeostatic proliferation of T cells leading to a Th2 skew. We performed intracellular cytokine staining to define Th1/Th2 phenotypes in toddlers (early homeostatic proliferation) and adults (post homeostatic proliferation) with this syndrome. To attempt to understand the predisposition to autoimmunity we performed immunophenotyping analyses to define Th17 cells and B cell subsets. Adult Ch22q11.2D patients had a higher percentage of IL-4+CD4+ T cells than controls. Th17 cells were no different in patients and controls. In addition, adult Ch22q11.2D syndrome patients had significantly lower switched memory B cells, suggesting a dysregulated B cell compartment. These studies demonstrate that the decrement in T cell production has secondary consequences in the immune system, which could mold the patients' clinical picture.

Low thymic output in the 22q11.2 deletion syndrome measured by CCR9+CD45RA+ T cell counts and T cell receptor rearrangement excision circles

Thymic hypoplasia is a frequent feature of the 22q11.2 deletion syndrome, but we know little about patients' age-related thymic output and long-term consequences for their immune system. We measured the expression of T cell receptor rearrangement excision circles (TREC) and used flow cytometry for direct subtyping of recent thymic emigrant (RTE)-related T cells in 43 patients (aged 1-54 years; median 9 years) from all over Norway and in age-matched healthy controls. Thymic volumes were estimated by ultrasound in patients. TREC levels correlated well with RTE-related T cells defined by co-expression of CD3, CD45RA and CCR9 (r=0.84) as well as with the CD4+ and CD8+ T cell subtypes. RTE-related T cell counts also paralleled age-related TREC reductions. CD45RA+ T cells correlated well with absolute counts of CD4+ (r=0.87) and CD8+ (r=0.75) RTE-related T cells. Apart from CD45RA- T cells, all T cell subsets were lower in patients than in controls. Thymic volumes correlated better with RTE-related cells (r=0.46) than with TREC levels (r=0.38). RTE-related T cells and TREC levels also correlated well (r=0.88) in patients without an identifiable thymus. Production of RTEs is impaired in patients with a 22q11.2 deletion, and CCR9 appears to be a good marker for RTE-related T cells.

Thymus transplantation

Thymus transplantation is a promising investigational therapy for infants born with no thymus. Because of the athymia, these infants lack T cell development and have a severe primary immunodeficiency. Although thymic hypoplasia or aplasia is characteristic of DiGeorge anomaly, in "complete" DiGeorge anomaly, there is no detectable thymus as determined by the absence of naive (CD45RA(+), CD62L(+)) T cells. Transplantation of postnatal allogeneic cultured thymus tissue was performed in sixty subjects with complete DiGeorge anomaly who were under the age of 2 years. Recipient survival was over 70%. Naive T cells developed 3-5 months after transplantation. The graft recipients were able to discontinue antibiotic prophylaxis, and immunoglobulin replacement. Immunosuppression was used in a subset of subjects but was discontinued when naive T cells developed. The adverse events have been acceptable with thyroid disease being the most common. Research continues on mechanisms underlying immune reconstitution after thymus transplantation.

Thymus transplantation in complete DiGeorge anomaly

Complete DiGeorge anomaly is characterized by athymia, congenital heart disease, and hypoparathyroidism. This congenital disease is fatal by age 2 years unless immune reconstitution is successful. There are multiple underlying syndromes associated with complete DiGeorge anomaly including 22q11 hemizygosity in approximately 50%, CHARGE association in approximately 25%, and diabetic embryopathy in approximately 15%. Approximately one-third of patients present with rash and lymphadenopathy associated with oligoclonal "host" T cells. This condition resembles Omenn syndrome. Immunosuppression is necessary to control the oligoclonal T cells. The results of thymus transplantation are reported for a series of 50 patients, of whom 36 survive. The survivors develop naïve T cells and a diverse T cell repertoire.

Development of specific T-cell responses to Candida and tetanus antigens in partial DiGeorge syndrome

BACKGROUND

Partial DiGeorge syndrome (pDGS) presents with thymic hypoplasia and a variable decrease in T-cell numbers. Although lymphocyte proliferation to mitogens is generally preserved, it is uncertain whether the development of specific cellular immunity in pDGS is similarly preserved.

OBJECTIVE

We sought to study the development of antigen-specific T-cell responses in patients with pDGS with regard to their initial CD3 T-cell counts.

METHODS

A retrospective review of 93 patients with pDGS followed at Texas Children's Hospital Allergy and Immunology Clinic from 1991 to 2006 was performed. Serial lymphocyte proliferation to Candida and tetanus antigens was longitudinally analyzed. Antigen-specific lymphoproliferation was compared with initial patient CD3 T-cell counts of less than the 10th percentile (n = 63), the 10th to 50th percentile (n = 20), and greater than the 50th percentile (n = 10) of age-matched normal control values. Tetanus-specific IgG levels and the number of tetanus immunizations were also studied.

RESULTS

The median CD3 T-cell counts at baseline in all 3 groups were as follows: 10th percentile, 1188 cells/mm(3) (range, 168-3272 cells/mm(3)); 10th to 50th percentile, 2816 cells/mm(3) (range, 1484-4155 cells/mm(3)); greater than 50th percentile, 4246 cells/mm(3) (range, 2573-6481 cells/mm(3)). Thirty-one (46%) of 68 patients with pDGS who received at least 3 tetanus vaccines had persistent Candida and tetanus-specific cellular immunity, and 24 (35%) did not have immunity to either antigen. Most (22/24) of these patients had CD3 T-cell counts at presentation of less than the 10th percentile of normal values. Protective tetanus-specific IgG titers (>0.10 IU/mL) were detected in all patients tested from the age of 2 to 85 months (n = 72).

CONCLUSION

Some patients with pDGS with low CD3 T-cell counts might not have specific Candida and tetanus cellular immunity.

Approach to the patient with recurrent infections

Children with a history of recurrent or unusual infections present a diagnostic challenge. Differentiation between frequent infections caused by common risk factors, versus primary immune dysfunction should be based on a detailed history and physical examination and, if indicated, followed by appropriate laboratory studies. A high index of suspicion could lead to an early diagnosis and treatment of an underlying immune deficiency disease. This article presents to physicians an approach to the evaluation of children with recurrent infections. Important details from the history and physical examination, and an appropriate choice of screening laboratory test to be ordered in a given situation are discussed.

Factors affecting success of thymus transplantation for complete DiGeorge anomaly

Thymus transplantation shows promise for the treatment of athymia in complete DiGeorge anomaly. This report reviews the effects of dose of thymus tissue, ABO compatibility, HLA matching, culture conditions, age of donor and immunosuppression of recipient on immune outcomes at 1 year after transplantation. Forty-nine athymic subjects have been treated with cultured postnatal allogeneic thymus tissue; 36 (73%) survive with only one subject on immunosuppression at 1.5 years. Of 31 surviving subjects more than 1 year after transplantation, 30 (97%) developed naive T cells, T-cell proliferative responses to mitogens and a diverse T-cell receptor beta variable (TCRBV) repertoire. The dose of thymus tissue, HLA matching and use of immunosuppression had nonsignificant effects on these outcome variables. Removal of deoxyguanosine from culture medium and length of culture did not adversely affect outcomes. Use of thymus tissue from donors over 1 month of age, versus under 1 month, resulted in higher total T-cell numbers (p = 0.03). However, this finding must be confirmed in a prospective trial. Although subtle immune effects may yet be associated with some of the factors tested, it is remarkable that consistently good immune outcomes result despite variation in dose, HLA matching and use of immunosuppression.

Immune constitution monitoring after PBMC transplantation in complete DiGeorge syndrome: an eight-year follow-up

A young boy with a confirmed complete DiGeorge Syndrome (cDGS) underwent a peripheral blood mononuclear cell transplantation (PBMCT) from his HLA-identical sister at 4.5 years of age, without a conditioning regimen. Eight years later, he is healthy with good immunological functions in the presence of a stable mixed T-cell chimerism. Absence of recent thymic emigrants is confirmed. We observe an inverted CD4+/CD8+ ratio, related to the CD8 subset expansion, a skewing of the TCR repertoire, especially on the CD8+ subset and a telomere loss on the CD8+ cells compared to the donor. However, these anomalies do not seem to have an impact on functional immunity. PBMCT in cDGS using an HLA-matched sibling donor provides good long-lasting immunity and is an easy alternative to bone marrow transplantation and to thymic transplantation.

Thymus Transplantation

Thymus transplantation was first attempted in the 1960s and 1970s using fetal thymus tissue [1, 2]. The results overall were disappointing [3–6]. In part the poor outcomes related to the lack of reagents needed to characterize and identify the patients into those who were truly athymic (complete DiGeorge anomaly) and those who had bone marrow stem cell problems (severe combined immunodeficiency). It is also possible that the fetal thymus tissue was too small to reconstitute a human infant [7]. The use of fetal thymus carried the risk of fatal graft versus host disease since mature T-cells can be found in the human thymus by the end of the first trimester [3]. By 1986, in a review of 26 infants treated with fetal thymus transplantation, 22 had died; the other 4 patients had achieved a 3-year survival [6].

Primary Immunodeficiencies

Primary immunodeficiencies (PIDs), once considered to be very rare, are now increasingly recognized because of growing knowledge in the immunological field and the availability of more sophisticated diagnostic techniques and therapeutic modalities [161]. However in a database of >120,000 inpatients of a general hospital for conditions suggestive of ID 59 patients were tested, and an undiagnosed PID was found in 17 (29%) of the subjects tested [107]. The publication of the first case of agammaglobulinemia by Bruton in 1952 [60] demonstrated that the PID diagnosis is first done in the laboratory. However, PIDs require specialized immunological centers for diagnosis and management [33]. A large body of epidemiological evidence supports the hypothesis of the existence of a close etiopathogenetic relation between PID and atopy [73]. In particular, an elevated frequency of asthma, food allergy (FA), atopic dermatitis and enteric pathologies can be found in various PIDs. In addition we will discuss another subject that is certainly of interest: the pseudo-immunodepressed child with recurrent respiratory infections (RRIs), an event that often requires medical intervention and that very often leads to the suspicion that it involves antibody deficiencies [149].

Velocardiofacial syndrome, DiGeorge syndrome: the chromosome 22q11.2 deletion syndromes

Velocardiofacial syndrome, DiGeorge syndrome, and some other clinical syndromes have in common a high frequency of hemizygous deletions of chromosome 22q11.2. This deletion syndrome is very common, affecting nearly one in 3000 children. Here, we focus on recent advances in cardiac assessment, speech, immunology, and pathophysiology of velocardiofacial syndrome. The complex medical care of patients needs a multidisciplinary approach, and every patient has his own unique clinical features that need a tailored approach. Patients with chromosome 22q11.2 deletion syndrome might have high level of functioning, but most often need interventions to improve the function of many organ systems.

Review of 54 patients with complete DiGeorge anomaly enrolled in protocols for thymus transplantation: outcome of 44 consecutive transplants

The purpose of this study was to characterize a large group of infants with complete DiGeorge anomaly and to evaluate the ability of thymus transplantation to reconstitute immune function in these infants. DiGeorge anomaly is characterized by varying defects of the heart, thymus, and parathyroid glands. Complete DiGeorge anomaly refers to the subgroup that is athymic (< 1%). The characteristics of 54 subjects at presentation and results from 44 consecutive thymus transplantations are reported. Remarkably, only 52% had 22q11 hemizygosity and only 57% had congenital heart disease requiring surgery. Thirty-one percent developed an atypical phenotype with rash and lymphadenopathy. To date, 33 of 44 subjects who received a transplant survive (75%) with post-transplantation follow-up as long as 13 years. All deaths occurred within 12 months of transplantation. All 25 subjects who were tested 1 year after transplantation had developed polyclonal T-cell repertoires and proliferative responses to mitogens. Adverse events developing after transplantation included hypothyroidism in 5 subjects and enteritis in 1 subject. In summary, diagnosis of complete DiGeorge anomaly is challenging because of the variability of presentation. Thymus transplantation was well tolerated and resulted in stable immunoreconstitution in these infants.

DiGeorge Syndrome/Velocardiofacial Syndrome: The Chromosome 22q11.2 Deletion Syndrome

Chromosome 22q11.2 deletion (CH22qD) syndrome is also known as DiGeorge syndrome or velocardiofacial syndrome. This deletion syndrome is extremely common with nearly one in 4000 children being affected. Recent advances and a holistic approach to patients have improved the care and well-being of these patients. This review will summarize advances in understanding the health needs and immune system of patients with CH22qD syndrome. Patients will most often need interventions directed at maximizing function for many organ systems but can ultimately have a high level of functioning.

Humoral immune responses and CD27+ B cells in children with DiGeorge syndrome (22q11.2 deletion syndrome)

The spectrum of T-cell abnormalities in 22q11.2 syndrome is quite broad, ranging from profound and life threatening to non-existent defects. Humoral abnormalities have been described in some of these patients, although no data are currently available on their phenotypical and functional B cell subsets. The purpose of this study was to investigate humoral immune function in a cohort of 13 children with DiGeorge syndrome by immunophenotyping B and by analysing their functionality in vivo. Humoral immunity was assessed by serum immunoglobulin evaluation, IgG subclasses determination, and testing of specific antibody titers to recall antigens. B cells were analyzed by flow cytometry and the relevant percentage of membrane surface expression of CD27, IgM, IgD was evaluated. In our cohort, one of 13 children (7.7%) had a complete IgA deficiency, four of 13 (30.7%) had minor immunoglobulin abnormalities, and five (38%) had an impaired production of specific antibodies. Five of 13 children (38%) had recurrent infections. Interestingly, peripheral CD27+ B cells were reduced in our patients as compared with age-matched healthy controls, and this decrement was statistically significant for IgM+ IgD+ CD27+ B cells. Immunoglobulin abnormalities were associated with the occurrence of recurrent infections. We conclude that a significant proportion of patients with DiGeorge syndrome have defective humoral immunity, which may represent an additional pathogenic mechanism underlying the increased susceptibility to infections. Whether the decreased CD27+ B-cell subset might be one of the defects that contribute to impaired humoral immunity, and to susceptibility to infection remains to be elucidated.

The clinical, immunological, and molecular spectrum of chromosome 22q11.2 deletion syndrome and DiGeorge syndrome

PURPOSE OF REVIEW

New findings regarding the clinical manifestations and care of patients with DiGeorge syndrome or chromosome 22q11.2 deletion syndrome will be reviewed. Immunologists and primary care providers often are in a position to coordinate the complex care needs of these patients and an awareness of the clinical features is essential.

RECENT FINDINGS

DiGeorge syndrome typically occurs in association with a hemizygous deletion of chromosome 22q11.2. Approximately 5-10% of patients with the clinical entity of DiGeorge syndrome do not have the deletion. Recent evidence indicates that the T cell compartment in both patients with the deletion and patients with clinical DiGeorge syndrome without the deletion is less robust than is often indicated by standard T cell enumeration.

SUMMARY

This past year has seen a dramatic increase in our understanding of the clinical features of patients with the deletion. Advances in our understanding of the immunodeficiency have been particularly exciting and clinicians should be aware of the characteristics of the immunodeficiency and its changes with age.

Maturational alterations of peripheral T cell subsets and cytokine gene expression in 22q11.2 deletion syndrome

Chromosome 22q11.2 deletion syndrome is a common disorder characterized by thymic hypoplasia, conotruncal cardiac defect and hypoparathyroidism. Patients have a risk of infections and autoimmunity associated with T lymphocytopenia. To assess the immunological constitution of patients, the numerical changes and cytokine profile of circulating T cells were analysed by flow cytometry and real-time polymerase chain reaction (PCR). CD3+, CD4+, T cell receptor (TCR)alphabeta+ or CD8alphaalpha+ cell counts were lower, and CD56+ cell counts were higher in patients than in controls during the period from birth to adulthood. The ageing decline of CD3+ or CD4+ cell counts was slower in patients than in controls. The proportion of CD8alphaalpha+ cells increased in controls, and the slope index was larger than in patients. On the other hand, both the number and proportion of Valpha24+ cells increased in patients, and the slope indexes tended to be larger than in controls. The positive correlation of the number of T cells with CD8alphaalpha+ cells was observed only in patients, and that with Valpha24+ cells was seen only in controls. No gene expression levels of interferon (IFN)-gamma, interleukin (IL)-10, transforming growth factor (TGF)-beta, cytotoxic T lymphocyte antigen 4 (CTLA4) or forkhead box p3 (Foxp3) in T cells differed between patients and controls. There was no significant association between the lymphocyte subsets or gene expression levels and clinical phenotype including the types of cardiac disease, hypocalcaemia and frequency of infection. These results indicated that T-lymphocytopenia in 22q11.2 deletion patients became less severe with age under the altered composition of minor subsets. The balanced cytokine profile in the limited T cell pool may represent a T cell homeostasis in thymic deficiency syndrome.

Post-natal ontogenesis of the T-cell receptor CD4 and CD8 Vbeta repertoire and immune function in children with DiGeorge syndrome

DiGeorge syndrome (DGS) is a congenital disorder characterized by typical facial features, hypoparatyroidism, conotruncal cardiac defects and thymic hypoplasia. Although there are some reports addressing lymphocytes counts and function in DGS children over time, few data have been reported on the T-cell receptor V beta (TCRBV) repertoire in relation to disease progression. The aim of this study was to evaluate the degree and nature of immunodeficiency and to investigate a possible correlation to clinical findings. We used third complementary region (CDR3) size spectratyping as a tool for monitoring T-cell repertoire diversity in 7 DGS's children. The rate of thymic output, the phenotype and function of peripheral T-cells and the humoral immunity were also investigated. At baseline a profound alteration of the TCR repertoire was noted, mainly in the CD8+ T-cells, in DGS patients when compared to a control group. Furthermore, analysis of thymic output showed a significant decrease in TCR rearrangement excision circles (TRECs) levels in the patient group. Immunoglobulin abnormalities were also detected. The observed TCR repertoire alterations, although not statistically significant, may suggest an increased susceptibility to infections. A parallel increase in the TCR repertoire diversity and clinical improvement occurred during the follow-up. Our results confirm that the extent of immunodeficiency is highly variable and could improve through childhood, and indicate that TCR repertoire may be a useful marker to clinically monitor thymic function in this primary immunodeficiency.

Complete DiGeorge anomaly in the absence of neonatal hypocalcemia and velofacial and cardiac defects

We report an atypical case of complete DiGeorge (DG) anomaly that presented initially exclusively as severe combined immunodeficiency (SCID). The child had severe infections at diagnosis, in keeping with the SCID phenotype; however, normal lymphocyte counts and immunoglobulin levels were noted at admission, which delayed diagnosis. Importantly, the child presented without neonatal hypocalcemia or velofacial or cardiac abnormalities at the time of diagnosis, which masked underlying DG. This case outlines the difficulties in making the diagnosis of SCID in a timely manner and illustrates the variation in presentation of the 22q11.2 deletion syndrome. There should be a high index of suspicion for primary immunodeficiency among children with severe infections and, because management may vary, DG anomaly should be considered in the differential diagnosis of T- B+ natural killer+ SCID.

Allergies in patients with chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome) and patients with chronic granulomatous disease

Humoral immunodeficiencies have a recognized association with atopy. This study investigated the association of a T-cell disorder (chromosome 22q11.2 deletion) and a neutrophil disorder [chronic granulomatous disease (CGD)] with asthma, eczema, and rhinitis using a standardized survey instrument. Patients were recruited from either a national referral center (chromosome 22q11.2 deletion syndrome) or from a registry (CGD). Controls consisted of siblings of patients. Chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome) was found to be significantly associated with both eczema and asthma but not allergic rhinitis. CGD was not found to be significantly associated with atopic diseases.

Thymic transplantation for complete DiGeorge syndrome: medical and surgical considerations

BACKGROUND/PURPOSE

Complete DiGeorge syndrome results in the absence of functional T cells. Our program supports the transplantation of allogeneic thymic tissue in infants with DiGeorge syndrome to reconstitute immune function. This study reviews the multidisciplinary care of these complex infants.

METHODS

From 1991 to 2001, the authors evaluated 16 infants with complete DiGeorge syndrome. All infants received multidisciplinary medical and surgical support. Clinical records for the group were reviewed.

RESULTS

Four infants died without receiving a thymic transplantation, and 12 children survived to transplantation. The mean age at time of transplantation was 2.7 months (range, 1.1 to 4.4 months). All 16 infants had significant comorbidity including congenital heart disease (16 of 16), hypocalcemia (14 of 16), gastroesophageal reflux disease or aspiration (13 of 16), CHARGE complex (4 of 16), and other organ involvement (14 of 16). Nontransplant surgical procedures included central line placement (15 of 16), fundoplication or gastrostomy (10 of 16), cardiac repair (10 of 16), bronchoscopy or tracheostomy (6 of 16), and other procedures (12 of 16). Complications were substantial, and 5 of the 12 transplanted infants died of nontransplant-related conditions. All surviving infants have immune reconstitution, with follow-up from 2 to 10 years.

CONCLUSIONS

Although the transplantation of thymic tissue can restore immune function in infants with complete DiGeorge syndrome, these children have substantial comorbidity. Care of these children requires coordinated multidisciplinary support.

Postnatal thymus transplantation with immunosuppression as treatment for DiGeorge syndrome

Complete DiGeorge syndrome is a fatal congenital disorder characterized by athymia, hypoparathyroidism, and heart defects. Less than half of patients are 22q11 hemizygous. The goal of this study was to assess if immune suppression followed by postnatal thymus transplantation would lead to T-cell function in 6 infant patients who had host T cells at the time of transplantation. All infants had fewer than 50 recent thymic emigrants (CD3+CD45RA+CD62L+) per cubic millimeter (mm3) and all had some proliferative response to the mitogen phytohemagglutinin. Four infants had rash, lymphadenopathy, and oligoclonal populations of T cells in the periphery. Five of 6 patients are alive at the follow-up interval of 15 months to 30 months. The 5 surviving patients developed a mean of 983 host CD3+ T cells/mm3 (range, 536/mm3-1574/mm3), a mean of 437 recent thymic emigrants/mm3 (range, 196/mm3-785/mm3), and normal proliferative responses to phytohemaglutinin (follow-up from day 376 to day 873). The TCR repertoire became polyclonal in patients who presented with oligoclonal T cells. All patients had thymopoiesis on allograft biopsy. Postnatal thymus transplantation after treatment with Thymoglobulin shows promise as therapy for infants with complete DiGeorge syndrome who have significant proliferative responses to mitogens or who develop rash, lymphadenopathy, and oligoclonal T cells.

Live viral vaccines in patients with partial DiGeorge syndrome: clinical experience and cellular immunity

Partial DiGeorge syndrome (pDGS) is an inherited primary immunodeficiency syndrome (incidence, 1:3000 live births) primarily affecting cellular immune function; partial, infers thymic hypoplasia with detectable circulating T-lymphocytes and adequate function. No guidelines exist regarding the recommendations for use of live viral vaccines (LVVs) in this extensive population of pediatric patients. We reviewed the experience with live viral vaccines in our cohort of patients with pDGS. Of 53 patients, 25 (47%) had received a live viral vaccine. No significant adverse events were recorded in association with administration of live viral vaccines. There was no statistically significant difference between cellular immune function at initial presentation between those patients that received live viral vaccines and those that did not. Adequate cellular immune function was documented for 15 of the 25 LVV recipients at the time of vaccine administration without significant change from baseline. These observations suggest that live viral vaccines appear safe in patients with pDGS and stable immune function.

Complete DiGeorge syndrome: Development of rash, lymphadenopathy, and oligoclonal T cells in 5 cases

BACKGROUND

Five patients with DiGeorge syndrome presented with infections, skin rashes, and lymphadenopathy after the newborn period. T-cell counts and function varied greatly in each patient. Initial laboratory testing did not suggest athymia in these patients.

OBJECTIVE

The purpose of this study was to determine whether the patients had significant immunodeficiency.

METHODS

Research testing of peripheral blood included immunoscope evaluation of T-cell receptor beta variable gene segment repertoire diversity, quantification of T-cell receptor rearrangement excision circles, and detection of naive T cells (expressing CD45RA and CD62L).

RESULTS

The patients were classified as having DiGeorge syndrome on the basis of syndromic associations and heart, parathyroid, and immune abnormalities. Immunoscope evaluation revealed that the T-cell repertoires were strikingly oligoclonal in all patients. There were few recent thymic emigrants, as indicated by the very low numbers of naive T cells (<50/mm(3)) and the absence of T-cell receptor rearrangement excision circles. These studies showed that all 5 patients were athymic. Two patients died, one from infection. No thymus was found during the complete autopsy performed on one patient.

CONCLUSION

Patients with DiGeorge syndrome, skin rash, and lymphadenopathy should undergo analysis of naive T-cell numbers and of T-cell receptor beta variability segment repertoire to determine whether they are athymic, even if they have T cells with mitogen responsiveness. It is important for physicians to realize that patients with complete DiGeorge syndrome remain profoundly immunodeficient after development of these atypical features (rash, lymphadenopathy, and oligoclonal T cells). Prompt diagnosis is necessary for appropriate management.

T-cell homeostasis in humans with thymic hypoplasia due to chromosome 22q11.2 deletion syndrome

Patients with chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome) typically exhibit thymic hypoplasia, conotruncal cardiac defects, and hypoparathyroidism. The immunodeficiency that results from the thymic hypoplasia has been extensively described and consists primarily of T-cell lymphopenia. A curious feature of the T-cell lymphopenia is that the age-related rate of decline of T-cell numbers is slower in patients than controls. This leads to T-cell numbers in adulthood that are minimally decreased compared with controls. This suggests that homeostatic mechanisms might be acting to preserve the peripheral blood T-cell numbers in patients. We characterized changes in CD4/CD45RA and CD4/CD45RO T-cell populations in patients and controls of various ages and determined T-cell recombination excision circles and telomere length within the CD4/CD45RA population. Patients had evidence of accelerated conversion of naive to memory cells and had evidence of more extensive replicative history within the CD4/CD45RA compartment compared with controls. Oligoclonal T-cell receptor (TCR) Vbeta families and missing Vbeta families were seen more often in patients than controls. These data are consistent with homeostatic proliferation of T cells in patients with limited T-cell production due to thymic hypoplasia.

Thymus transplantation in complete DiGeorge syndrome: immunologic and safety evaluations in 12 patients

Complete DiGeorge syndrome is a fatal condition in which infants have no detectable thymus function. The optimal treatment for the immune deficiency of complete DiGeorge syndrome has not been determined. Safety and efficacy of thymus transplantation were evaluated in 12 infants with complete DiGeorge syndrome who had less than 20-fold proliferative responses to phytohemagglutinin. All but one had fewer than 50 T cells/mm3. Allogeneic postnatal cultured thymus tissue was transplanted. T-cell development was followed by flow cytometry, lymphocyte proliferation assays, and T-cell receptor Vbeta (TCRBV) repertoire evaluation. Of the 12 patients, 7 are at home 15 months to 8.5 years after transplantation. All 7 survivors developed T-cell proliferative responses to mitogens of more than 100 000 counts per minute (cpm). By one year after transplantation, 6 of 7 patients developed antigen-specific proliferative responses. The TCRBV repertoire showed initial oligoclonality that progressed to polyclonality within a year. B-cell function developed in all 3 patients tested after 2 years. Deaths were associated with underlying congenital problems. Risk factors for death included tracheostomy, long-term mechanical ventilation, and cytomegalovirus infection. Adverse events in the first 3 months after transplantation included eosinophilia, rash, lymphadenopathy, development of CD4-CD8- peripheral T cells, elevated serum immunoglobulin E (IgE), and possible pulmonary inflammation. Adverse events related to the immune system occurring more than 3 months after transplantation included thrombocytopenia in one patient and hypothyroidism and alopecia in one other patient. Thymic transplantation is efficacious, well tolerated, and should be considered as treatment for infants with complete DiGeorge syndrome.

Biased T-cell receptor repertoires in patients with chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

Chromosome 22q11.2 deletion (del22q11.2) syndrome (DiGeorge syndrome/velocardiofacial syndrome) is a common syndrome typically consisting of congenital heart disease, hypoparathyroidism, developmental delay and immunodeficiency. Although a broad range of immunologic defects have been described in these patients, limited information is currently available on the diversity of the T-cell receptor (TCR) variable beta (BV) chain repertoire. The TCRBV repertoires of nine patients with del22q11.2 syndrome were determined by flow cytometry, fragment size analysis of the third complementarity determining region (CDR3 spectratyping) and sequencing of V(D)J regions. The rate of thymic output and the phenotype and function of peripheral T cells were also studied. Expanded TCRBV families were detected by flow cytometry in both CD4+ and CD8+ T cells. A decreased diversity of TCR repertoires was also demonstrated by CDR3 spectratyping, showing altered CDR3 profiles in the majority of TCRBV families investigated. The oligoclonal nature of abnormal peaks detected by CDR3 spectratyping was confirmed by the sequence analysis of the V(D)J regions. Thymic output, evaluated by measuring TCR rearrangement excision circles (TRECs), was significantly decreased in comparison with age-matched controls. Finally, a significant up-regulation in the percentage, but not in the absolute count, of activated CD4+ T cells (CD95+, CCR5+, HLA-DR+), IFN-gamma - and IL-2-expressing T cells was detected. These findings suggest that the diversity of CD4 and CD8 TCRBV repertoires is decreased in patients with del22q11.2 syndrome, possibly as a result of either impaired thymic function and/or increased T-cell activation.

Long-term assessment of T-cell populations in DiGeorge syndrome

BACKGROUND

Patients with DiGeorge syndrome present with a broad range of T-cell deficiency. Partial DiGeorge syndrome (pDGS) is a preferred designation for patients with detectable T-cell function. Among immunology experts, there is no uniform opinion on the necessity of T-cell precautions for pDGS patients. Few studies have addressed the natural course of their immune function over time.

OBJECTIVE

The objective of this study was to describe the natural history of immune parameters in pDGS.

METHODS

We reviewed the medical records of 45 pDGS patients. Peripheral blood T-cell subsets counts and percentages were recorded at 1, 6, 12, 18, 24, 30, 48, 60, 72, 96, and 120 months of age, and the rates of change of T-cell measurements over the follow-up period (slopes) were calculated for each individual. Humoral immunity was evaluated by quantification of immunoglobulins and by testing antibody titers to recall antigens.

RESULTS

T-cell subsets counts from pDGS patients were generally lower than those of age-matched normal populations but were not severely depressed (ie, CD4+ T-cell percentage less than 15%). The median of the slopes for CD3+, CD4+, and CD8+ T-cell percentages were -0.7%, -0.8%, and -0.1%/month, respectively, in the first year of age and 0.1%/month for each subpopulation from 12 to 120 months of age. Lymphoproliferative responses to phytohemagglutinin were adequate at all ages. Immunoglobulin deficiencies or inadequate production of specific antibodies were not detected.

CONCLUSIONS

In our pDGS patient cohort, a significant deterioration of T-cell number or function did not occur over time. Clinical implications of this finding include the possibility of discontinuing T-cell deficiency precautions and frequency of reevaluations of pDGS patients with stable and adequate immune function.

T-cell immune constitution after peripheral blood mononuclear cell transplantation in complete DiGeorge syndrome

Complete DiGeorge syndrome (cDGS) is a congenital disorder characterized by typical facies, thymic aplasia, susceptibility to infections, hypoparathyroidism and conotruncal cardiac defect. Fetal thymus or post-natal thymus tissue transplantations and human leucocyte antigen (HLA)-genoidentical bone marrow transplantations were followed in a few cases by immune reconstitution. More recently, a peripheral blood mononuclear cell transplantation (PBMCT) was performed with an HLA-genoidentical donor and followed by a partial T-cell engraftment and immune reconstitution. We report a boy with cDGS, without cardiac defect, who suffered recurrent severe infections. At the age of 4 years, he underwent PBMCT from his HLA-genoidentical sister. He received no conditioning regimen, but graft-versus-host disease (GVHD) prophylaxis was with oral cyclosporin A and mycophenolate mofetil. Toxicity was mild, with grade I acute GVHD. The patient is currently 2.5 years post-PBMCT with excellent clinical performances. Mixed chimaerism can only be observed on the T-cell population (50% donor T cells). T-lymphocyte count fluctuated (CD3 more than 400 x 10(6)/l at d 84 and CD4 more than 200 x 10(6)/l at d 46). Exclusive memory phenotype T cells and absence of new thymic emigrants suggest expansion of infused T cells. T-cell mitogen and tetanus antigen responses normalized a few months after transplantation. After immunizations, specific antibodies were produced. PBMCT from an HLA identical sibling could be an efficient treatment of immune deficiency in cDGS.

Immunologic features of chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

OBJECTIVES

To characterize immunologic function and clinical characteristics in patients with chromosome 22q11.2 deletion syndrome and determine whether there was significant change over time.

METHODS

This study characterized the laboratory and clinical features of the immunodeficiency in a cohort of 195 patients with chromosome 22q11.2 deletion syndrome and used cross-sectional and analysis of variance to compare the findings in different age groups with control patients. Changes over time were also characterized by a model effect method in a subset of patients who were studied serially.

RESULTS

Diminished T cell counts in the peripheral blood are common in patients with chromosome 22q11.2 deletion syndrome. The pattern of changes seen with aging in normal control patients was also seen in patients with chromosome 22q11.2 deletion syndrome, although the decline in T cells was blunted. Autoimmune disease was seen in most age groups, although the types of disorders varied according to age. Infections were also common in older patients, though they were seldom life threatening.

CONCLUSIONS

Slow declines in T cell populations are seen in chromosome 22q11.2 deletion syndrome. Clinical manifestations of immunodeficiency, such as recurrent infection and autoimmune disease, were common in this population but had little relationship to specific immunologic laboratory features.

22q11.2 deletion syndrome: DiGeorge, velocardiofacial, and conotruncal anomaly face syndromes

A microdeletion of chromosome 22q11.2 is found in most patients with velocardiofacial syndrome, DiGeorge syndrome, and conotruncal anomaly face syndrome, and in some patients with Cayler cardiofacial and autosomal dominant Opitz-G/BBB syndromes. A wide spectrum of clinical findings accompanies the 22q11.2 deletion, without genotype or phenotype correlation even among affected family members. Classic features are dysmorphic facies, conotruncal cardiac defects, hypocalcemic hypoparathyroidism, T-cell mediated immune deficiency, and palate abnormalities. Less well recognized are learning, speech, feeding, and psychiatric disorders, and renal and musculoskeletal defects. Parathyroid and immune deficiencies in the same individual can progress or resolve with time. The 22q11.2 deletion can be inherited as an autosomal dominant or arise as a de novo deletion or translocation. Fluorescent in situ hybridization using cosmid probes mapping to the DiGeorge chromosomal region is a widely available method to detect the 22q11.2 deletion in metaphase chromosomes from cultured lymphocytes, amniocytes, or chorionic villi. The ubiquitin-fusion-degradation-1-like gene, expressed in embryonic branchial arches and in the conotruncus, appears to play a prominent role in the pathogenesis of the 22q11.2 deletion syndrome.

DiGeorge syndrome/chromosome 22q11.2 deletion syndrome

DiGeorge syndrome is characterized by conotruncal cardiac defects, hypocalcemia, and a hypoplastic thymus. Many, but not all, patients have a heterozygous deletion of chromosome 22q11.2. In its most severe form, it represents a devastating syndrome with high mortality. Patients with severe immunodeficiency are candidates for a thymic transplant or a fully matched bone marrow transplant. Fortunately, the majority of patients with either DiGeorge syndrome or chromosome 22q11.2 deletion syndrome have a mild to moderate immunodeficiency. These patients may develop recurrent infections or autoimmune disease.