Classical Severe Combined Immunodeficiency Research Articles

Shorter birth length and decreased T-cell production and function predict severe infections in children with non–severe combined immunodeficiency cartilage–hair hypoplasia

Cartilage-hair hypoplasia (CHH) is a syndromic inborn error of immunity caused by variants in the RMRP gene. Disease manifestations vary, and their ability to predict outcome is uncertain. The optimal management of infants with CHH who do not fulfill classical severe combined immunodeficiency (SCID) criteria is unknown. We described longitudinal changes in lymphocyte counts during childhood and explored correlations of early childhood clinical and laboratory features with clinical outcomes on long-term follow-up of CHH patients. Immunologic laboratory parameters, birth length, the presence of Hirschsprung disease, and severe anemia correlated to the primary end points of respiratory and severe infections. We implemented traditional statistical methods and machine learning techniques. Thirty-two children with CHH were followed up for 2.7 to 22.1 years (median, 8.2 years, in total 331.3 patient-years). None of the patients had classical SCID. Median lymphocyte subclass counts, apart from CD16+/56+ cells, were subnormal throughout childhood, but did not show age-related decline seen in healthy children. Low immunoglobulin levels were uncommon and often transient. Respiratory and/or severe infections developed in 14 children, 8 of whom had low naive T-cell counts, absent T-cell receptor excision circles, and/or partial "leaky" SCID-level lymphopenia. Shorter birth length correlated with lower lymphocyte counts and the occurrence of infections. Of the laboratory parameters, decreased naive T-cell counts and abnormal lymphocyte proliferation responses contributed most to the development of severe infections. In addition, all participants with absent T-cell receptor excision circles developed severe infections. Opportunistic infections occurred only in children with leaky SCID-level lymphopenia. Shorter birth length and a combination of laboratory abnormalities can predict the development of severe infections in children with CHH.

Clinical and Laboratory Factors Affecting the Prognosis of Severe Combined Immunodeficiency.

Severe combined immunodeficiency (SCID) is one of the most severe forms of inborn errors of immunity characterized by absence or loss of function in T cells. The long-term outcomes of all forms of SCID have been evaluated in a limited number of studies. We aimed to evaluate the pre- and post-transplant manifestations of SCID patients and determine the factors affecting the survival of patients. We included 54 SCID patients (classical SCID, Omenn syndrome, atypical SCID (AS)) in this study. We evaluated the clinical presentation, infections, and outcome of hematopoietic stem cell transplantation (HSCT). Lymphocyte subsets and T-cell receptor (TCR) repertoire were analyzed by flow cytometry. The median age at diagnosis was 5 (range: 3-24) months and follow-up time was 25 (range: 5-61) months. Symptom onset and diagnostic ages were significantly higher in AS compared to others (p = 0.001; p < 0.001). The most common SCID phenotype was T-B-NK + , and mutations in recombination-activating genes (RAG1/2) were the prominent genetic defect among patients. The overall survival (OS) rate was 83.3% after HSCT, higher than in non-transplanted patients (p = 0.001). Peripheral blood stem cell sources and genotypes other than RAG had a significant favorable impact on CD4+ T cells immune reconstitution after transplantation (p = 0.044, p = 0.035; respectively). Gender matching transplantations from human leukocyte antigen (HLA)-identical and non-identical donors and using peripheral blood stem cell source yielded higher B-cell reconstitution (p = 0.002, p = 0.028; respectively). Furthermore, receiving a conditioning regimen provided better B-cell reconstitution and chimerism (p = 0.003, p = 0.001). Post-transplant TCR diversity was sufficient in the patients and showed an equal distribution pattern as healthy controls. The OS rate was lower in patients who underwent transplant with active infection or received stem cells from mismatched donors (p = 0.030, p = 0.015; respectively). This study identifies diagnostic and therapeutic approaches predictive of favorable outcomes for patients with SCID.

Influence of clinical and immunophenotypic variants of severe combined immunodeficiency on severity and outcomes of opportunistic infections

Severe combined immunodeficiency (SCID) is a primary immunodeficiency that presents with life-threating symptoms in early infancy and has poor prognosis if not promptly treated. Here we present an analysis of infectious presentation and its course depending on clinical and immunophenotypic form of SCID. This study is supported by the Independent Ethics Committee and approved by the Academic Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. 54 patients were diagnosed with SCID in our center from 2012 to June 2020 and included to this study. The median age at diagnosis was 5.8 months. All patients were divided into 3 groups: classic SCID ( n = 31); Omenn syndrome ( n = 11); SCID with maternal fetal engraftment ( n = 12). To determine opportunistic infections severity, based on a number of infected organs at disease presentation, 3 groups were formed: with no infections or 1 infected organ, n=15; with 2 infected organs ( n = 15); with 3 and more infected organs ( n = 22). 22 of 46 BCG vaccinated patients (48%) developed BCG-infection: 16 local and 6 disseminated. There was no difference in severity of infections between 3 groups of SCID ( p = 0.22), with more severe infections found in patients older than 6 months of age at diagnosis. T- and NK-cell numbers lower than median level predisposed to severer infections in Omenn syndrome patients ( p = 0.041). There was a higher risk of BCG infections in classic SCID with low levels of NK-cells ( p = 0.009). 45 patients received allogeneic hematopoietic stem cell transplantation (HSCT). 9 patients died before HSCT and 21 after HSCT of infections and infections-related inflammatory syndromes. Though Т- and NKcells might have a role in protecting from severe infections, the early diagnosis is the most important factor of better prognosis of SCID patients.

Second-Tier Next Generation Sequencing Integrated in Nationwide Newborn Screening Provides Rapid Molecular Diagnostics of Severe Combined Immunodeficiency.

Severe combined immunodeficiency (SCID) and other T cell lymphopenias can be detected during newborn screening (NBS) by measuring T cell receptor excision circles (TRECs) in dried blood spot (DBS) DNA. Second tier next generation sequencing (NGS) with an amplicon based targeted gene panel using the same DBS DNA was introduced as part of our prospective pilot research project in 2015. With written parental consent, 21 000 newborns were TREC-tested in the pilot. Three newborns were identified with SCID, and disease-causing variants in IL2RG, RAG2, and RMRP were confirmed by NGS on the initial DBS DNA. The molecular findings directed follow-up and therapy: the IL2RG-SCID underwent early hematopoietic stem cell transplantation (HSCT) without any complications; the leaky RAG2-SCID received prophylactic antibiotics, antifungals, and immunoglobulin infusions, and underwent HSCT at 1 year of age. The child with RMRP-SCID had complete Hirschsprung disease and died at 1 month of age. Since January 2018, all newborns in Norway have been offered NBS for SCID using 1st tier TRECs and 2nd tier gene panel NGS on DBS DNA. During the first 20 months of nationwide SCID screening an additional 88 000 newborns were TREC tested, and four new SCID cases were identified. Disease-causing variants in DCLRE1C, JAK3, NBN, and IL2RG were molecularly confirmed on day 8, 15, 8 and 6, respectively after birth, using the initial NBS blood spot. Targeted gene panel NGS integrated into the NBS algorithm rapidly delineated the specific molecular diagnoses and provided information useful for management, targeted therapy and follow-up i.e., X rays and CT scans were avoided in the radiosensitive SCID. Second tier targeted NGS on the same DBS DNA as the TREC test provided instant confirmation or exclusion of SCID, and made it possible to use a less stringent TREC cut-off value. This allowed for the detection of leaky SCIDs, and simultaneously reduced the number of control samples, recalls and false positives. Mothers were instructed to stop breastfeeding until maternal cytomegalovirus (CMV) status was determined. Our limited data suggest that shorter time-interval from birth to intervention, may prevent breast milk transmitted CMV infection in classical SCID.

Adenylate Kinase 2 Links Energy Metabolism and Cell Fate in Hematopoietic Stem and Progenitor Cells

While hematopoietic stem and progenitor cells (HSPCs) were thought to rely mainly on glycolysis for energy supply, emerging evidence suggests that defects in mitochondrial functions can impact HSPC development with respect to self-renewal, differentiation and aging. The exact mechanisms underlying metabolic reprogramming and cell fate decisions during human hematopoiesis, however, remain elusive. Biallelic mutations in the mitochondrial enzyme adenylate kinase 2 (AK2), cause reticular dysgenesis (RD), one of the most profound forms of severe combined immunodeficiency (SCID). AK2 catalyzes the interconversion between adenine nucleotides and thereby controls the availability of ADP for oxidative phosphorylation. Clinically, RD patients not only present with profound lymphopenia, typical for classic SCID, but also suffer from severe congenital neutropenia. The developmental arrest across the T, NK and granulocytic lineages suggests that AK2 deficiency causes a metabolic defect with global impact on hematopoiesis. Our prior work in induced pluripotent stem cells (iPSCs) from RD patients has shown that maturation-arrested iPSC-derived HSPCs exhibit increased oxidative stress and an energy-depleted adenine nucleotide profile, suggesting that AK2-regulated mitochondrial bioenergetics play an integral role in HSPC differentiation. Therefore, RD serves as an excellent model to study the impact of mitochondrial metabolism during human HSPC development. Methods: Since iPSCs do not recapitulate definitive hematopoiesis, we developed an AK2 biallelic knock-out model in primary human HSPCs using CRISPR/Cas9 gene editing. Employing a homologous recombination-mediated dual color reporter strategy, we were able to select for HSPCs with biallelic AK2 knock-out. HSPCs edited at the safe harbor AAVS1 site were used as a control. FACS purified AK2-/- and AAVS1-/- HSPCs were in vitro differentiated along the granulocytic lineage, and cells at various differentiation stages were sorted for RNA-seq and metabolomics analysis. Results: We analyzed the myeloid differentiation potential of AK2-/- HSPCs in vitro. Compared to AAVS1-/- controls, AK2-/- HSPCs displayed a severely decreased colony forming potential of both myeloid and erythroid lineages. In addition, AK2-/- HSPCs showed a granulocytic maturation arrest at the HLA-DR-, CD117+ promyelocyte stage, consistent with the characteristic phenotype observed in RD patients. We then performed RNA-seq studies on in vitro differentiated promyelocyte and neutrophil subpopulations derived from AK2-/- and control HSPCs. The RNA-seq analysis showed differential gene expression in glutathione metabolism and IL-10 signaling pathways, suggesting an increase in oxidative stress and inflammation, respectively, caused by AK2 deficiency. In addition, genes implicated in antimicrobial function and granule synthesis were downregulated in AK2-/- neutrophils, suggesting a functional defect. Liquid chromatography-mass spectrometry (LC-MS/MS) studies to delineate differences in metabolite profile conferred by AK2 deficiency at different stages of HSPC development are currently in progress. Conclusions: We have established the first cell-traceable biallelic AK2 CRISPR knock-out model in primary human HSPCs that recapitulates the myeloid phenotype of RD patients. This model allows us to profile AK2 knock-out cells at different developmental stages. AK2-/- granulocyte precursors showed a transcriptional signature suggestive of worsening oxidative stress, inflammation and defective effector cell functions during maturation. To understand the mechanistic underpinnings for these observations we are now using a global metabolomics approach to profile the changes in energy metabolites that occur during development in AK2-deficient and control HSPC subpopulations. Understanding how metabolism governs differentiation and self-renewal of human HSPCs has important translational implications to improve hematopoietic stem cell products and transplantation outcomes. Disclosures Morrison: Frequency Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees; OncoMed Pharmaceuticals: Equity Ownership; GI Therapeutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Kolon Gene Therapeutics: Consultancy; Protein Fluidics: Other: Stock Options.

An Engineered Cell-Traceable Model of Reticular Dysgenesis in Human Hematopoietic Stem Cells Linking Metabolism and Differentiation

Hematopoietic stem cell (HSC) differentiation is accompanied by a metabolic shift from glycolysis to oxidative phosphorylation (OXPHOS) to meet the increasing energy demand during proliferation and differentiation. However, the role of mitochondrial metabolism in HSC differentiation goes beyond ATP production. Metabolites generated during mitochondrial metabolism may impact in HSC fate decisions through stable epigenetic modifications. Despite some progress in understanding mitochondrial communication during HSC development, their role in human hematopoiesis remains largely elusive, where the lack of appropriate model systems poses a major obstacle. Reticular Dysgenesis (RD), a rare and particularly severe form of severe combined immunodeficiency (SCID), offers an attractive model for studying the role of mitochondrial metabolism in hematopoiesis. RD is an autosomal recessive disease caused by biallelic mutations of the mitochondrial enzyme Adenylate Kinase 2 (AK2). AK2 catalyzes the reversible phosphorylation of adenosine monophosphate (AMP) to adenosine diphosphate (ADP), which serves as the substrate for the ATP synthase. In addition to defective lymphocyte development typical of classic SCID, RD patients also suffer from impaired myeloid development, suggestive of a global defect in hematopoiesis. In a human induced pluripotent stem cell (iPSC) model for RD, hematopoietic stem and progenitor cells (HSPCs) recapitulate a profound maturation arrest of the myeloid lineage, increased oxidative stress and an energy-depleted metabolite and transcriptional profile. We hypothesize that AK2 defects drive hematopoietic cell fate decisions through changes in metabolites that regulate the activities of DNA/histone modifying enzymes and result in stable epigenetic modifications.Methods: Since iPSCs are not suitable to model the epigenetic characteristics of definitive hematopoiesis, we developed a novel model system in which we deleted AK2 in primary human HSCs using CRISPR/Cas9 gene editing technique. We found a highly effective single-guide RNA (sgRNA) targeting the catalytic LID domain of the AK2 gene to introduce directed DNA double stranded breaks (DSBs), and use a homologous recombination (HR)-mediated dual reporter system to track and isolate cells with biallelic AK2 disruption.Results: Our single-color GFP reporter system consistently produces a >60% GFP+ population of AK2-targeted CD34+ umbilical cord blood (UCB) cells. With dual GFP/BFP reporters, we were able to achieve 6% GFP/BFP double positive cells with confirmed biallelic AK2 knock-out. Since HR events on one allele are biologically linked to CRISPR/Cas9 mediated DSBs on the other, we assessed insertion and/or deletion (INDEL) frequency and protein expression in a single reporter (GFP+) population of AK2-targeted UCBs. We detected an INDEL frequency of over 90% on the non-HR alleles along with nearly absent AK2 protein expression by Western Blot. These results indicated that the highly efficient single-color reporter system with >60% targeting efficiency is sufficient to achieve an AK2 biallelic knock-out population in primary HSCs. in vitro myeloid differentiation of these AK2-targeted HSCs recapitulates the RD phenotype with impaired neutrophil but preserved monocyte development.Conclusion: This novel disease model for RD will now allow us to examine the cellular and molecular impact of perturbations in metabolism on human HSC development. We will investigate the effect on differentiation potential, metabolite profile, transcriptome and epigenome in vitro as well as in a xenograft mouse model. Elucidating how metabolism governs differentiation and self-renewal of human HSCs will not only advance our basic understanding of many blood and immune diseases, but has important translational implications for improving the use of HSCs in hematopoietic stem cell transplantation, gene and cell therapy. DisclosuresPorteus:CRISPR Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Phenotypical heterogeneity in RAG-deficient patients from a highly consanguineous population.

Mutations affecting recombination activation genes RAG1 and RAG2 are associated with variable phenotypes, depending on the residual recombinase activity. The aim of this study is to describe a variety of clinical phenotypes in RAG-deficient patients from the highly consanguineous Egyptian population. Thirty-one patients with RAG mutations (from 28 families) were included from 2013 to 2017. On the basis of clinical, immunological and genetic data, patients were subdivided into three groups; classical T- B- severe combined immunodeficiency (SCID), Omenn syndrome (OS) and atypical SCID. Nineteen patients presented with typical T- B- SCID; among these, five patients carried a homozygous RAG2 mutation G35V and five others carried two homozygous RAG2 mutations (T215I and R229Q) that were detected together. Four novel mutations were reported in the T- B- SCID group; three in RAG1 (A565P, N591Pfs*14 and K621E) and one in RAG2 (F29S). Seven patients presented with OS and a novel RAG2 mutation (C419W) was documented in one patient. The atypical SCID group comprised five patients. Two had normal B cell counts; one had a previously undescribed RAG2 mutation (V327D). The other three patients presented with autoimmune cytopaenias and features of combined immunodeficiency and were diagnosed at a relatively late age and with a substantial diagnostic delay; one patient had a novel RAG1 mutation (C335R). PID disorders are frequent among Egyptian children because of the high consanguinity. RAG mutations stand behind several variable phenotypes, including classical SCID, OS, atypical SCID with autoimmunity and T- B+ CID.

The diverse phenotypes of RAG mutation associated immunodeficiency

RAG mutations cause a spectrum of severe immunodeficiencies ranging from classical severe combined immunodeficiency(SCID) and Omenn syndrome to an increasing number of peculiar phenotypes.Based on the distinct levels of RAG expression in various patients, their immunophenotypes, histopathological findings and clinical manifestations are diverse.The subtypes of RAG-defect diseases have been described as classical SCID, SCID with maternal T cells, classical Omenn syndrome, atypical Omenn syndrome, granulomatous inflammation, predominance/expansion of γδ-T cells and maternal T-cell engraftment.The complete failure or partial blockage of lymphocyte development and differentiation can cause repeated infections with autoimmune reactions frequently, and may be lethal.Thorough assessment and interpretation of various phenotypes will guide accurate diagnosis, definitive treatment and the mechanism research. Key words: Recombination activating genes; Primary immunodeficiency; Severe combined immunodeficiency; Omenn syndrome

O013 Novel RAG-1 mutation identified in a patient with hypomorphic severe combined immunodeficiency (SCID)

TREC newborn screening facilitates early diagnosis of both typical and hypomorphic SCID. Hypomorphic SCID patients often have abnormalities in RAG1/RAG2 enzymes. RAG1/RAG2 mediate the process of VDJ rearrangement in T and B cell progenitors, with defects leading to a T-B-NK+ SCID that can have a highly variable clinical presentation, including classic SCID, Omenn Syndrome and late-onset autoimmunity.

IL2RG: A series of three novel mutations with clinical manifestations

Background: X-linked severe combined immunodeficiency (SCID) is caused by mutations in the IL2RG gene and classically presents with absent T cells and natural killer (NK) cells. Mutational analysis has contributed to the understanding of this gene. Methods: The primary immunodeficiency (PID) registry was reviewed for patients with SCID with novel IL2RG mutations. The clinical phenotype was assessed using a retrospective chart review. Results: We describe 3 novel mutations in the IL2RG. The first was a guanine to adenine substitution at position 215 (c.215 G &gt; A) in exon 2 leading to a cysteine to tyrosine substitution at position 72 (p.Cys72Tyr), with a typical T− B+ NK− phenotype. The second was a deletion of thymine at position 618 and adenine at position 619 (c.618_619TA) in exon 5, leading to a frameshift at the 206 amino acid (p.His206fs). The phenotype was characterized by a classic SCID presentation and immunophenotyping revealed a low number of absolute lymphocytes with mostly B cells, low levels of immunoglobulins, as well as very low NK cells. Finally, the third mutation was a guanine to cytosine substitution at position 341 (c.341 G &gt; C) in exon 3 leading to a glycine to alanine substitution at position 114 (p.Gly114Ala), presenting with a T+ B+ NK+ phenotype. The presence of T and NK cells in IL2RG are discussed in the context of other mutations allowing for T and NK cells in IL2RG mutations, as well as in the setting of maternal engraftment. Conclusion: To the best of our knowledge we describe 3 novel mutations in the IL2RG gene and the associated phenotypes. These mutations illustrate that these patients can have atypical immunological evaluations. Statement of novelty: To the best of our knowledge, this paper describes 3 novel mutations in the IL2RG gene.

Positive Family History, Infection, Low Absolute Lymphocyte Count (ALC), and Absent Thymic Shadow: Diagnostic Clues for All Molecular Forms of Severe Combined Immunodeficiency (SCID)

Severe combined immunodeficiency (SCID) is a syndrome uniformly fatal during infancy unless recognized and treated successfully by bone marrow transplantation or gene therapy. Because infants with SCID have no abnormal physical appearance, diagnosis is usually delayed unless newborn screening is performed. In this study, we sought to evaluate the presenting features of all 172 patients with SCID transplanted at this institution over the past 31 years. We reviewed original charts from 172 consecutive patients with classic SCID who received either T-cell-depleted HLA-haploidentical (N = 154) or HLA-identical (N = 18) nonablative related marrow transplants at Duke University Medical Center from 1982 to 2013. The mean age at presentation was 4.87 months. When there was a family history of early infant death or known SCID (37%), the mean presentation age was much earlier, 2.0 months compared with 6.6 months. Failure to thrive was common, with 84 patients (50%) having a weight less than the 5th percentile. The leading infections included oral moniliasis (43%), viral infections (35.5%), and Pneumocystis jiroveci (26%) pneumonia. The group mean absolute lymphocyte count (ALC) was 1454/cmm; 88% of the infants had an ALC less than 3000/cmm. An absent thymic shadow was seen in 92% of infants with electronic radiographic data available. An absence of T-cell function was found in all patients. Infants with SCID appear normal at birth but later present with failure to thrive and/or recurrent fungal, viral, and bacterial infections. Low ALCs and an absent thymic shadow on chest x-ray are key diagnostic clues. The absence of T-cell function confirms the diagnosis.

Silent brain infarcts in two patients with zeta chain-associated protein 70 kDa (ZAP70) deficiency

Zeta-chain associated protein 70kDa deficiency (ZAP70) is a form of severe combined immunodeficiency (SCID). It is caused by defects in the signaling pathways associated with T-lymphocyte activation. ZAP70 deficiency is characterized by a marked reduction in peripheral CD8+ T-cells. In this report, we described two patients with ZAP70 deficiency who presented with recurrent infections, lung tuberculosis (TBC), congenital nephrotic syndrome (CNS), and silent brain infarcts (SBIs) as a common feature. The first patient initially presented with recurrent infections and TBC as in a classic SCID patient. At the age of 4, he was interned with febrile seizure. Cranial magnetic resonance imaging (MRI) showed SBIs. The second patient, an 8-month-old boy, presented with congenital nephrotic syndrome caused by cytomegalovirus (CMV) and he had also SBIs.

The Genetic and Molecular Basis of Severe Combined Immunodeficiency

Severe combined immunodeficiency (SCID) is a life-threatening disease caused by a heterogeneous group of genetic defects. It is characterized by profound defects of T-cell development, also affecting B and NK cells in some cases. Since the first molecular identification of a causal gene for SCID in 1985, 14 more molecular causes have been identified in patients with a classical SCID phenotype, with no T cells. Some genetic defects specifically block lymphocyte ontogeny, whereas others affect T-cell function and a few cause extra-hematopoietic alterations with a rare complex phenotype. Over the last 15 years, several new causal genes have been identified in patients with low T-cell counts and impaired T-cell function. Patients with a clinical SCID phenotype with normal numbers of dysfunctional T cells have also recently been reported. This last condition is described immunologically as combined immunodeficiency. These discoveries have expanded the complexity and difficulties of molecular characterization in patients with a clinical SCID phenotype. Studies of these disorders have increased our understanding of the role of single-gene products in the development, differentiation, and function of the immune system in humans.

A novel homozygous mutation in recombination activating gene 2 in 2 relatives with different clinical phenotypes: Omenn syndrome and hyper-IgM syndrome

A novel homozygous mutation in recombination activating gene 2 in 2 relatives with different clinical phenotypes: Omenn syndrome and hyper-IgM syndrome

Severe combined immunodeficiency: A national surveillance study

National immunodeficiency registers in several countries have reported prevalence but not incidence rates for severe combined immunodeficiency (SCID). The objective of this study was to document the incidence and type of SCID in Australia, the age and clinical features at presentation and short-term management. The Australian Paediatric Surveillance Unit conducts active, monthly, national surveillance of rare disorders with reporting by child-health specialists. Between May 1995 and December 2001, clinicians provided clinical and laboratory data on children newly diagnosed with SCID. Thirty-three incident cases of SCID were identified [incidence 1.8/10(5) live births per annum; 95% confidence interval (CI) 1.2-2.5]. Twenty-six children had classical SCID (1.45/10(5) live births; 95% CI, 0.9-2.0) and 20 (77%) of these were boys. Classical SCID was X-linked in 13 children, autosomal recessive (AR), not further classified in four, and attributed to adenosine deaminase deficiency (ADA) in four, interleukin-7 receptor alpha chain deficiency in one, Ommen syndrome in two, and Di George syndrome in two. Twenty-one (81%) received bone marrow/stem cell transplantation, three of whom died between 1 and 4 months after transplantation (two ADA deficient, one AR). Seven children had atypical SCID, five of whom died within 1-4 yr of diagnosis. Most children with SCID presented with failure to thrive and recurrent infections and there was no significant delay between presentation and diagnosis. The reported national incidence of classical SCID in Australia (1.45/10(5) or approximately 4 cases per year or 1/69,000 live births) is consistent with the rate (1.4/10(5)) previously reported in Victoria. Diagnosis is rarely delayed, and transplantation is associated with good short-term survival.

Severe combined immunodeficiencies, primary T-cell defects and DiGeorge syndrome in humans: Characterization by monoclonal antibodies and natural killer cell activity

Peripheral blood mononuclear cells from three patients with severe combined immunodeficiency (SCID), three with SCID whether B cell positive or with pure T-cell defect, and two with DiGeorge syndrome were analyzed with a panel of monoclonal antibodies against immature and mature T-cell subsets. Natural killer (NK) cells were enumerated by the use of the HNK-1 monoclonal antibody. NK activity against the K562 and MOLT 4 cell lines was also investigated. According to the monoclonal antibodies profile and the NK activity, patients could be divided into three groups. Patients with classical SCID had no detectable circulating T cells as well as NK cells and activity, probably due to an early block in stem cell differentiation. Patients affected by SCID with B cells or pure T cell defect showed a decrease in lymphocytes with mature phenotypes but prothymocytes or immature thymocytes circulated in peripheral blood. Children with DiGeorge syndrome had a decrease in mature thymocytes and, in this study, NK cells were normal. These data help to clarify both the preeminent immunologic features of SCID and related syndromes and the character of NK cells.