Search

Reticular dysgenesis (RD) is a rare form of severe combined immunodeficiency (SCID) involving agranulocytosis and sensorineural hearing loss (SNHL) due to mutations in adenylate kinase 2 (AK2), a ubiquitously expressed intermembranous mitochondrial protein. RD is fatal unless hematopoietic stem cell transplant (HSCT) is performed.

•Active metabolic checkpoints respond to AK2 deficiency by decreasing anabolic pathways to maintain nutrient homeostasis and proliferation.•When metabolic checkpoints are ineffective, AK2 deficiency leads to ectopic mTOR activation, nucleotide imbalance, and proliferation arrest.

Reticular Dysgenesis (RD) is a particularly grave syndromic form of severe combined immunodeficiency. The hematopoietic phenotype manifests in defective myeloid and lymphoid development with profound neutropenia and lymphopenia. RD is caused by biallelic mutations in the mitochondrial enzyme adenylate kinase 2 (AK2), which catalyzes the phosphorylation of adenosine monophosphate (AMP) to adenosine diphosphate (ADP) in the mitochondrial intermembrane space. ADP is then phosphorylated to adenosine triphosphate (ATP) during the OXPHOS process. While there are abundant other sources of APD, AK2 constitutes the only mitochondrial enzyme that contributes to AMP “recycling” by phosphorylation. Accordingly, AK2-deficient myeloid cells have been shown to exhibit increased AMP levels 1. Beyond this observation, the cellular basis for the combined hematopoietic defect in RD remains elusive.

Reticular dysgenesis (RD) is a rare congenital disorder defined clinically by the combination of severe combined immunodeficiency (SCID), agranulocytosis, and sensorineural deafness. Mutations in the gene encoding adenylate kinase 2 were identified to cause the disorder. Hematopoietic stem cell transplantation (HSCT) is the only option to cure this otherwise fatal disease. Retrospective data on clinical presentation, genetics, and outcome of HSCT were collected from centers in Europe, Asia, and North America for a total of 32 patients born between 1982 and 2011. Age at presentation was <4 weeks in 30 of 32 patients (94%). Grafts originated from mismatched family donors in 17 patients (55%), from matched family donors in 6 patients (19%), and from unrelated marrow or umbilical cord blood donors in 8 patients (26%). Thirteen patients received secondary or tertiary transplants. After transplantation, 21 of 31 patients were reported alive at a mean follow-up of 7.9 years (range: 0.6-23.6 years). All patients who died beyond 6 months after HSCT had persistent or recurrent agranulocytosis due to failure of donor myeloid engraftment. In the absence of conditioning, HSCT was ineffective to overcome agranulocytosis, and inclusion of myeloablative components in the conditioning regimens was required to achieve stable lymphomyeloid engraftment. In comparison with other SCID entities, considerable differences were noted regarding age at presentation, onset, and type of infectious complications, as well as the requirement of conditioning prior to HSCT. Although long-term survival is possible in the presence of mixed chimerism, high-level donor myeloid engraftment should be targeted to avoid posttransplant neutropenia.

Reticular dysgenesis (RD) is a rare congenital disorder defined clinically by the combination of severe combined immunodeficiency (SCID), agranulocytosis, and sensorineural deafness. Mutations in the gene encoding adenylate kinase 2 were identified to cause the disorder. Hematopoietic stem cell transplantation (HSCT) is the only option to cure this otherwise fatal disease. Retrospective data on clinical presentation, genetics, and outcome of HSCT were collected from centers in Europe, Asia, and North America for a total of 32 patients born between 1982 and 2011. Age at presentation was <4 weeks in 30 of 32 patients (94%). Grafts originated from mismatched family donors in 17 patients (55%), from matched family donors in 6 patients (19%), and from unrelated marrow or umbilical cord blood donors in 8 patients (26%). Thirteen patients received secondary or tertiary transplants. After transplantation, 21 of 31 patients were reported alive at a mean follow-up of 7.9 years (range: 0.6-23.6 years). All patients who died beyond 6 months after HSCT had persistent or recurrent agranulocytosis due to failure of donor myeloid engraftment. In the absence of conditioning, HSCT was ineffective to overcome agranulocytosis, and inclusion of myeloablative components in the conditioning regimens was required to achieve stable lymphomyeloid engraftment. In comparison with other SCID entities, considerable differences were noted regarding age at presentation, onset, and type of infectious complications, as well as the requirement of conditioning prior to HSCT. Although long-term survival is possible in the presence of mixed chimerism, high-level donor myeloid engraftment should be targeted to avoid posttransplant neutropenia.

Adenylate kinases (AKs) are phosphotransferases that regulate the cellular adenine nucleotide composition and play a critical role in the energy homeostasis of all tissues. The AK2 isoenzyme is expressed in the mitochondrial intermembrane space and is mutated in reticular dysgenesis (RD), a rare form of severe combined immunodeficiency (SCID) in humans. RD is characterized by a maturation arrest in the myeloid and lymphoid lineages, leading to early onset, recurrent, and overwhelming infections. To gain insight into the pathophysiology of RD, we studied the effects of AK2 deficiency using the zebrafish model and induced pluripotent stem cells (iPSCs) derived from fibroblasts of an RD patient. In zebrafish, Ak2 deficiency affected hematopoietic stem and progenitor cell (HSPC) development with increased oxidative stress and apoptosis. AK2-deficient iPSCs recapitulated the characteristic myeloid maturation arrest at the promyelocyte stage and demonstrated an increased AMP/ADP ratio, indicative of an energy-depleted adenine nucleotide profile. Antioxidant treatment rescued the hematopoietic phenotypes in vivo in ak2 mutant zebrafish and restored differentiation of AK2-deficient iPSCs into mature granulocytes. Our results link hematopoietic cell fate in AK2 deficiency to cellular energy depletion and increased oxidative stress. This points to the potential use of antioxidants as a supportive therapeutic modality for patients with RD.

Reticular dysgenesis is a rare inherited immunodeficiency characterized by the lack of blood monocytes and neutrophils and low lymphocyte counts, contrasting with normal red blood cell counts and normal or decreased platelet counts. Whether dendritic cells or macrophages, both of which derive primarily from blood monocytes, are affected in this condition remains unknown. We studied 7 patients with reticular dysgenesis. Macrophages were present in normal numbers in the dermis and in the atrophic lymphoid tissues of these patients, proving that at least some subsets of macrophages can differentiate despite very low monocyte counts. By contrast, Langerhans cells, which are CD1a-positive epidermal dendritic cells, were absent in all (n = 5) patients before bone marrow transplantation. After bone marrow transplantation, Langerhans cells were present (n = 2), suggesting that the defect is not related to keratinocyte dysfunction. A split chimeric reconstitution, characterized by the presence of autologous blood monocytes able to differentiate in vitro into CD1a-positive dendritic cells, was observed in a patient who underwent successful engraftment. These results suggest that an intrinsic cell defect is unlikely and that a bone marrow-derived factor may be defective in reticular dysgenesis; it may be responsible for the Langerhans cell defect but not involved in macrophage differentiation.

Reticular Dysgenesis (RD) is a particularly grave form of severe combined immunodeficiency (SCID), characterized by maturation arrest of both myeloid and lymphoid lineages paired with sensorineural hearing loss. RD is caused by biallelic mutations in the mitochondrial enzyme adenylate kinase 2 (AK2). AK2 catalyzes the phosphorylation of adenosine monophosphate (AMP) to adenosine diphosphate (ADP) in the mitochondrial intermembrane space. Using a CRISPR/Cas9 AK2 biallelic knock out model in human hematopoietic stem and progenitor cells (HSPCs), we have shown that AK2 -/-HSPCs mimic the neutrophil maturation defect in RD patients. Mitochondrial respiration is compromised in AK2 -/-HSPCs, which leads to a decreased NAD +/NADH ratio resulting in reductive stress. Metabolomics analysis by LC-MS/MS showed a significant accumulation of AMP, along with increased AMP/ADP and AMP/ATP ratios in AK2 -/-HSPCs, suggesting that purine metabolism is compromised by AK2 deficiency. Purine metabolism defects, such as deficiencies in adenosine deaminase (ADA) and purine nucleotide phosphorylase (PNP), have long been recognized as a cause of SCID. Furthermore, pharmacological interference with purine metabolism is a highly effective antiproliferative strategy in cancer therapy. In this study, we sought to investigate whether impaired purine metabolism contributes to the myelopoietic defect caused by AK2 deficiency.

• We report fatal reticular dysgenesis in a premature infant presenting with severely decreased blood and bone marrow granulocytes and lymphocytes, an absent thymic shadow by x-ray film, and generalized lymphoid hypoplasia. Immunologic and electron microscopic evaluation of his white blood cells demonstrated that, despite extremely low cell numbers, cells from all stages of both granulocytic and lymphocytic development were present. Immature bone marrow cells of both myeloid and lymphoid lineages were found in much greater proportions than were mature cells; preB cells outnumbered B cells by more than tenfold. Megakaryocytes and erythroid cells appeared to be present in normal numbers, and tritiated-thymidine incorporation by bone marrow nucleated cells was also normal, although it may have largely occurred in erythroblasts. These data suggest that the primary defect in reticular dysgenesis is not failure in initiation of stem cell differentiation along lymphoid and myelomonocytic lines but rather an, as yet, undefined abnormality that interferes with normal growth and maturation of immune cells committed to these differentiation pathways.(AJDC 1985;139:832-835)

Porteus: CRISPR Therapeutics: Current equity holder in publicly-traded company; Allogene Therapeutics: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Versant Ventures: Consultancy; Ziopharm: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Graphite Bio: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees. Morrison: Garuda Therapeutics: Other: founder and SAB member ; Kojin Therapeutics: Other: SAB member ; Frequency Therapeutics: Other: SAB member ; Ona Terapeutics: Other: SAB member ; Protein Fluidics: Other: SAB member .

Energy deficiency and redox stress are hallmarks of mitochondrial pathology. Reductive stress is marked by an accumulation of reducing species and can arise from defects in the electron transport chain (ETC) that prevent NAD+regeneration from NADH. Reticular Dysgenesis (RD) is a particularly grave form of severe combined immunodeficiency (SCID), characterized by maturation arrest of both myeloid and lymphoid lineages. Unlike other forms of SCID, RD is a mitochondriopathy caused by biallelic mutations in the mitochondrial enzyme adenylate kinase 2 (AK2). AK2 catalyzes the phosphorylation of adenosine monophosphate (AMP) to adenosine diphosphate (ADP), and maintains ADP availability for ATP synthase. We hypothesize that AK2 deficiency leads to decreased ETC activities and defective NAD+regeneration. Emerging evidence suggests that the development of hematopoietic stem and progenitor cells (HSPCs) is intricately intertwined with various aspects of mitochondrial function. Investigating the cellular and molecular consequences of AK2 deficiency during myelopoiesis provides fundamental insight into the pathology of many mitochondrial disorders.

Mutations in the gene AK2 are responsible for reticular dysgenesis (RD), a rare and severe form of primary immunodeficiency in children. RD patients have a severely shortened life expectancy and without treatment die, generally from sepsis soon after birth. The only available therapeutic option for RD is hematopoietic stem cell transplantation (HSCT). To gain insight into the pathophysiology of RD, we previously created zebrafish models for Ak2 deficiencies. One of the clinical features of RD is hearing loss, but its pathophysiology and causes have not been determined. In adult mammals, sensory hair cells of the inner ear do not regenerate; however, their regeneration has been observed in several non-mammalian vertebrates, including zebrafish. Therefore, we used our RD zebrafish models to determine whether Ak2 deficiency affects sensory organ development and/or hair cell regeneration. Our studies indicated that Ak2 is required for the correct development, survival and regeneration of sensory hair cells. Interestingly, Ak2 deficiency induces the expression of several oxidative stress markers and it triggers an increased level of cell death in the hair cells. Finally, we show that glutathione treatment can partially rescue hair cell development in the sensory organs in our RD models, pointing to the potential use of antioxidants as a therapeutic treatment supplementing HSCT to prevent or ameliorate sensorineural hearing deficits in RD patients.

A male infant with reticular dysgenesis received a bone-marrow transplant from his HLA-identical brother. Severe graft-versus-host disease developed but he responded to high-dose methylprednisolone. 3 years after grafting, the child is thriving with full haematological reconstitution and normal cell-mediated and humoral immunity. This is the first report of the survival beyond 17 weeks of a child with reticular dysgenesis.

Reticular dysgenesis is a rare congenital disorder characterized by severe combined immunodeficiency and profound neutropenia, curable to date, only by bone marrow transplantation. This report describes the association of bilateral sensorineural deafness with this disease. (J Pediatr 1999;135:387-9)

t the case of a 2-month-old infant with reticular dysgenesis who was treated with recombinant granulocyte-macrophage colony stimulating factor with the aim of stimulating granulopoiesis while awaiting bone marrow transplant.

Dever: Integral Medicines: Current Employment.

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.

Porteus: CRISPR Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Reticular Dysgenesis (RD) is one of the most serious forms of severe combined immune deficiency (SCID). It is characterized by complete absence of circulating lymphocytes and neutrophils. In addition, patients suffer from sensorineural hearing loss. Before newborn screening for SCID was implemented, the majority of patients succumbed to infection long before hematopoietic cell transplantation (HCT) could be attempted. To this date, the prognosis for RD remains grim. RD is caused by mutations in the mitochondrial ADP-generator Adenylate Kinase 2 (AK2). AK1 is a cytosolic protein that may compensate in various tissues for the lack of AK2. However, AK1 is not expressed in leukocytes and the stria vascularis of the inner ear [1]. While this observation may explain whereAK2 defects manifest, the molecular mechanisms howAK2 defects take effect, remain largely obscure. Significant obstacles to elucidating disease pathology have been the lack of a suitable animal models and the unavailability of patient specimens.

No relevant conflicts of interest to declare.

The adenylate kinase (AK) gene family consists of 7 different members that contribute to energy cell metabolism by converting ATP+AMP to 2ADP. AKs are critical players in ensuring cellular energy homeostasis in all tissues. Mutations in the AK2 gene are responsible for reticular dysgenesis (RD), an autosomal recessive form of severe combined immunodeficiency (SCID). RD is characterized by an early differentiation arrest in the granulocyte lineage and impaired lymphoid maturation and it represents less than 2% of total SCID. Affected children succumb to overwhelming infections early in life unless their immune system is successfully restored with allogeneic hematopoietic stem cells transplant (HSCT). The mechanisms underlying the pathophysiology of RD remain unclear. The phenotype of AK2 deficient animals has never been reported in the literature, but murine lines carrying homozygous inactivating retroviral insertions are embryonically lethal (our personal observations). We used the zebrafish model to perform a comprehensive study of the effects of AK2 deficiency using Morpholino oligomers injections and two different kinds of AK2 mutants (a ENU-induced T371C/L124P missense mutant and two null mutant lines generated using zinc-finger nuclease technology). In situ hybridization analyses of AK2-deficient embryos indicated that only erythroid development was affected during primitive hematopoiesis. Conversely, during definitive hematopoiesis, the loss of function of AK2 resulted in abnormalities distributed along all hematopoietic lineages suggesting an impairment of hematopoietic stem cell (HSC) development. Moreover, we observed that the AK2 deficiency induced oxidative stress and consequent apoptosis in both primitive erythroid cells and definitive HSCs. Importantly, antioxidant treatment of AK2 mutant embryos rescued the hematopoietic phenotypes as indicated by the recovered expression of HSC and lymphoid markers (such as c-myb and rag1). Overall, our data indicate that zebrafish represents a good model for studying the molecular mechanisms involved in RD and testing of new therapeutic interventions. To date, our mutant lines remain the only animal model of this rare and lethal human disease.

No relevant conflicts of interest to declare.

No relevant conflicts of interest to declare.

Abstract 2142

Reticular dysgenesis is a rare syndrome characterized by combined immunodeficiency and neutropenia. We have cared for a child, whose sister died of overwhelming sepsis at 2 months of age, who was referred for neutropenia. Further work-up revealed a severe combined immunodeficiency. The patient had evidence of excessive suppressor cell activity as detected in both mixed lymphocyte cultures and an assay designed to measure in vitro immunoglobulin synthesis. He had circulating T cells that bore the maternal HLA haplotype. He was treated without pre-transplant immunosuppression by allogenic marrow transplantation from his histocompatible 5 yr old nonaffected sister. Within one week the maternal T cell haplotype was no longer detectable. Excessive suppressor cell activity was not detectable by 3 weeks. There was significant improvement in his immune function as early as one month (PHA stimulation index 2.7 → 143; serum IgG 134 mg/dl → 512 mg/dl). However the patient has remained neutropenic with a maximum neutrophil count of 0.3 × 109/1. Cytogenetic analysis revealed an xx karotype in peripheral blood and an xy karotype in marrow chromosomes. Six months post transplant he is developing normally without infection. Marrow transplantation without preparation can restore immune function but additional immunosuppression may be necessary for complete myeloid reconstitution.

Chronic neutropenia (CrN) is defined as neutropenia lasting longer than 3 months and has various underlying etiologies, including congenital neutropenia (CN). We aimed to determine the underlying etiologies of patients with CrN and define the characteristics at diagnosis suggestive for CN as a final diagnosis. The study included 197 pediatric and adolescent patients who were diagnosed with CrN between 2010 and 2022 in a single-center. Patients with transient neutropenia, splenomegaly, alloimmune, secondary autoimmune, myelodysplastic syndrome and hematological malignancies, other bone marrow failure syndromes such as Fanconi anemia, and aplastic anemia due to CrN were excluded from the study. The patients included in the study were sub-classified into 5 groups according to their final diagnosis. Group 1, patients with CN (n=64, %32.5) included all genetically verified CrN patients. Group 2, patients with primary autoimmune neutropenia (pIN) group (n=10, %5.1) with anti-granulocyte antibody (AGA) positivity. Group 3, patients with unclassified chronic idiopathic neutropenia (UCIN) (n=73, %37.1). Group 3 included patients who had a clinical severity resembling immune neutropenia, but whose AGA testing was either negative or not available; but the CrN resolved during follow-up. Group 4, included the patients with unclassified chronic benign neutropenia (UCBN) (n=34, %17.3) and included the patients with ongoing neutropenia, who do not have a history of serious infections, no underlying genetic cause for neutropenia, no AGA positivity. Group 5, unspecified congenital neutropenia (UCN) group (n=16, %8,1), was defined as the group of patients whose genetic tests did not detect a mutation in genes related to CN, but history reveales severe infections and a possible CN as an underlying cause. Genetic testing of patients varies from single gene evaluation with Sanger sequencing analysis to Whole Exome Sequencing (WES). The median age at diagnosis of neutropenia of the patients included in the study was 12 (0-168) months 53.8% of the patients were male (n=106). There was consanguinity between parents in 34.5% and at least 1 family member was diagnosed with neutropenia in the in 18.8%. Among the patients in Group 1, HAX-1mutation was detected in 19 (29.7%) patients and it was found to be the most common genetic defect causing CN. Other common genetic disorders include ELANEmutations (18.8%), Shwachman Diamond Syndrome (10.9%), Hermansky Pudlak Syndrome (7.8%) and glycogen storage type 1 b (6.3%). G6PC3 deficiency, VPS45 deficiency, Barth syndrome and Kabuki syndrome in 2 each (3.1%), ADA2 deficiency, Cohen Syndrome, Poikiloderma with neutropenia, Prolidase deficiency, CLPB deficiency, Majeed syndrome, GINS4 deficiency, reticular dysgenesis, germline RUNX1 mutation were detected in 1 patient. There are 3 patients with acute myeloid leukemia and all of them died before hematopoietic stem cell transplantation (HSCT). Two of these patients were diagnosed with SDS, and one had ELANEmutation. One patient with the HAX-1mutation developed non-Hodgkin lymphoma and was treated with HSCT and is still alive. There were 7 patients (3.6%) who underwent HSCT. 9 patients (4.6%) died. Except for 3 patients who died from AML and 1 who died after HSCT; 1 patient with Barth syndrome deceased related to associated dilated cardiomyopathy, Another patient with G6PC3mutation died after complications of cardiac surgery due to associated cardiac anomaly and 3 patients (2 VPS45, 1 CLPB) died due to infections. Patients in Group1 and Group 2+Group3 were compared, in order to answer the question of “Can we create a model that predicts CN?”. Many parameters were compared and a multivariate model was created with statistically significant risk factors. CN was seen 6,3 times more in those with parental consanguinity, 8,9 times in those with a family history of neutropenia, 4,8 times in those with more than 2 hospitalizations due to infection, and 4,1 times more in those with recurrent oral involvement (p<0.05). Patients diagnosed with CN were estimated based on the results of the multifactor logistic regression model. The rate of correct identification of the patients by the model is 88.9%. In conclusion, our study is one of the largest single-center studies and suggests a novel classification of CrN patients.

Background:Hematopoietic stem-cell transplantation is the treatment of choice for severe primary T-cell immunodeficiencies. When an HLA-identical sibling donor is not available, an alternative donor stem-cell source is needed. In primary T-cell immunodeficiencies, T-cell–depleted HLA-haploidentical bone marrow transplantation has been particularly successful in reconstituting the T-cell immune system in many of the severe combined immunodeficiency syndrome types. However, there are some problems associated with this preparation as a stem donor source, such as increased resistance to engraftment, a long period of time for T-cell engraftment to occur, and failure to engraft B cells and B-cell functions. These problems can be especially troublesome if the patient is infected before the transplantation. Objective:Umbilical cord blood was evaluated as a stem-cell source for immune reconstitution in children with severe primary T-cell immunodeficiency disorders, such as severe combined immunodeficiency syndrome, reticular dysgenesis, thymic dysplasia, and combined immunodeficiency disease, when a matched sibling donor was unavailable. Methods:From January 1996 through July 1997, 6 children received unrelated cord blood stem-cell transplantation after a preparative regimen for the treatment of combined immunodeficiency diseases. The patients ranged in age from 2 weeks to 6 years. The cord blood units were 3 of 6 HLA antigen matches in 2 children, 4 of 6 HLA antigen matches in 3 children, and 5 of 6 HLA antigen matches in 1 child, with molecular HLA-DR mismatch in 3 of the children. Results:The average time for neutrophil engraftment (absolute neutrophil count, 500/mm3) was 12 days (range, 10 to 15 days), and the average time for platelet engraftment (platelet count, 20,000/mm3) was 36 days (range, 24 to 50 days). In a patient with reticular dysgenesis, the first transplant failed to engraft but fully engrafted after a second unrelated donor cord blood transplantation. Five of 6 patients exhibited grade I graft-versus-host disease (GvHD), although 1 child experienced grade IV skin and gut GvHD. Immunologic reconstitution demonstrated that cord blood stem-cell transplantation resulted in consistent and stable T-cell, B-cell, and natural killer–cell development. The kinetics of recovery of phenotypic expression and function of T cells occurred between 60 to 100 days and that of natural killer cells at approximately 180 days. B cells engrafted early, and a study of functional B-cell antibody responses revealed that 2 of 2 patients in whom intravenous immune globulin was discontinued have low detectable antibody responses to tetanus and diphtheria toxoid immunizations more than 1 year after the transplantation. Conclusions:Unrelated umbilical donor cord blood is an excellent source of stem cells for transplantation of children with immune deficiency disorders. Benefits include rapid and reliable recovery of immune function, low risk of GvHD, and low viral transmission rate. (J Allergy Clin Immunol 1999;103:823-32.)

The Primary Immune Deficiency Treatment Consortium (PIDTC) is enrolling children with severe combined immunodeficiency (SCID) to a prospective natural history study. We analyzed patients treated with allogeneic hematopoietic cell transplantation (HCT) from 2010 to 2014, including 68 patients with typical SCID and 32 with leaky SCID, Omenn syndrome, or reticular dysgenesis. Most (59%) patients were diagnosed by newborn screening or family history. The 2-year overall survival was 90%, but was 95% for those who were infection-free at HCT vs 81% for those with active infection (P= .009). Other factors, including the diagnosis of typical vs leaky SCID/Omenn syndrome, diagnosis via family history or newborn screening, use of preparative chemotherapy, or the type of donor used, did not impact survival. Although 1-year post-HCT median CD4 counts and freedom from IV immunoglobulin were improved after the use of preparative chemotherapy, other immunologic reconstitution parameters were not affected, and the potential for late sequelae in extremely young infants requires additional evaluation. After a T-cell–replete graft, landmark analysis at day +100 post-HCT revealed that CD3 < 300 cells/μL, CD8 < 50 cells/μL, CD45RA < 10%, or a restricted Vβ T-cell receptor repertoire (<13 of 24 families) were associated with the need for a second HCT or death. In the modern era, active infection continues to pose the greatest threat to survival for SCID patients. Although newborn screening has been effective in diagnosing SCID patients early in life, there is an urgent need to identify validated approaches through prospective trials to ensure that patients proceed to HCT infection free. The trial was registered at www.clinicaltrials.govas #NCT01186913.

The Primary Immune Deficiency Treatment Consortium (PIDTC) is enrolling children with severe combined immunodeficiency (SCID) to a prospective natural history study. We analyzed patients treated with allogeneic hematopoietic cell transplantation (HCT) from 2010 to 2014, including 68 patients with typical SCID and 32 with leaky SCID, Omenn syndrome, or reticular dysgenesis. Most (59%) patients were diagnosed by newborn screening or family history. The 2-year overall survival was 90%, but was 95% for those who were infection-free at HCT vs 81% for those with active infection (P = .009). Other factors, including the diagnosis of typical vs leaky SCID/Omenn syndrome, diagnosis via family history or newborn screening, use of preparative chemotherapy, or the type of donor used, did not impact survival. Although 1-year post-HCT median CD4 counts and freedom from IV immunoglobulin were improved after the use of preparative chemotherapy, other immunologic reconstitution parameters were not affected, and the potential for late sequelae in extremely young infants requires additional evaluation. After a T-cell–replete graft, landmark analysis at day +100 post-HCT revealed that CD3 < 300 cells/μL, CD8 < 50 cells/μL, CD45RA < 10%, or a restricted Vβ T-cell receptor repertoire (<13 of 24 families) were associated with the need for a second HCT or death. In the modern era, active infection continues to pose the greatest threat to survival for SCID patients. Although newborn screening has been effective in diagnosing SCID patients early in life, there is an urgent need to identify validated approaches through prospective trials to ensure that patients proceed to HCT infection free. The trial was registered at www.clinicaltrials.gov as #NCT01186913.

Thymocytes and thymic epithelial cell (TEC) cross-talk is crucial to preserve thymic architecture and function, including maturation of TECs and dendritic cells, and induction of mechanisms of central tolerance. We have analyzed thymic maturation and organization in 9 infants with various genetic defects leading to complete or partial block in T-cell development. Profound abnormalities of TEC differentiation (with lack of AIRE expression) and severe reduction of thymic dendritic cells were identified in patients with T-negative severe combined immunodeficiency, reticular dysgenesis, and Omenn syndrome. The latter also showed virtual absence of thymic Foxp3+T cells. In contrast, an IL2RG-R222C hypomorphic mutation permissive for T-cell development allowed for TEC maturation, AIRE expression, and Foxp3+T cells. Our data provide evidence that severe defects of thymopoiesis impinge on TEC homeostasis and may affect deletional and nondeletional mechanisms of central tolerance, thus favoring immune dysreactive manifestations, as in Omenn syndrome.

Thymocytes and thymic epithelial cell (TEC) cross-talk is crucial to preserve thymic architecture and function, including maturation of TECs and dendritic cells, and induction of mechanisms of central tolerance. We have analyzed thymic maturation and organization in 9 infants with various genetic defects leading to complete or partial block in T-cell development. Profound abnormalities of TEC differentiation (with lack of AIRE expression) and severe reduction of thymic dendritic cells were identified in patients with T-negative severe combined immunodeficiency, reticular dysgenesis, and Omenn syndrome. The latter also showed virtual absence of thymic Foxp3+ T cells. In contrast, an IL2RG-R222C hypomorphic mutation permissive for T-cell development allowed for TEC maturation, AIRE expression, and Foxp3+ T cells. Our data provide evidence that severe defects of thymopoiesis impinge on TEC homeostasis and may affect deletional and nondeletional mechanisms of central tolerance, thus favoring immune dysreactive manifestations, as in Omenn syndrome.

Hematopoietic stem cell transplantation is the treatment of choice for severe primary T-cell immunodeficiencies. When an HLA-identical sibling as the donor is not available, an alternative donor stem cell source is needed. In primary T-cell immunodeficiencies, T-cell–depleted HLA-haploidentical bone marrow transplantation has been particularly successful in reconstituting the immune system in many but not all of the severe T-cell immune deficiency disorders. This study reports the use of umbilical cord blood (UCB) stem cell transplantation in 16 patients with severe T cell immune deficiency disorders. UCB was evaluated as a stem cell source for immune reconstitution in children with severe primary T-cell immunodeficiency disorders, such as severe combined immunodeficiency syndrome (SCID), reticular dysgenesis, thymic dysplasia, combined immunodeficiency disease (CID), and Wiskott-Aldrich syndrome (WAS) when an HLA-matched sibling donor was unavailable. From 1996 through 2004, 16 children diagnosed with severe T-cell immunodeficiencies received allogeneic, unrelated cord blood stem cell transplantation. Initially, the preparative regimen consisted of ablative doses of busulfan, with either cyclophosphamide or fludarabine and ATG; subsequently a non-myeloablative regimen consisting of fludarabine, cyclophosphamide and ATG was used. All patients with WAS received a myeloablative preparative regimen. Twelve of 16 patients engrafted and are alive with a mean of 6.5 ± 2.6 years (mean ± standard deviation [SD]) posttransplantation. Four patients died, two from veno-occlusive disease, one from sepsis, and one from chronic graft-versus-host disease (GVHD) and sepsis. Acute GVHD was observed in 12 patients; 6 patients with grade I–II and 6 with grade III–IV acute GVHD. Only one patient in our series experienced chronic GVHD. The median time for neutrophil and platelet engraftment was 12 ± 2 was 33 ± 5 days, respectively. Cord blood stem cell transplantation resulted in consistent and stable T, B and NK cell numbers and functions. Measurable T-cell numbers were seen between 60 to 100 days. Initial T-cell engraftment consisted predominantly of memory T cells, and at 12 to 24 months changed to naive T cells, indicating de novomaturation of T cells. Natural killer (NK) cells developed at approximately 6 months. B-cell engraftment was present by 4 months posttransplantation; antibody responses were detected after intravenous immune globulin (IVIG) was discontinued after immunizations with tetanus and diphtheria toxoids and Hemophilus influenzaetype B at 18 to 24 months posttransplantation. Unrelated umbilical donor cord blood is an alternative source of stem cells for transplantation in children with severe T-cell immune deficiency disorders when a suitable HLA-matched donor is not available. Benefits of UCB include rapid and reliable development of T-, NK-, and B-cell immune functions. (Pediatr Asthma Allergy Immunol 2005; 18[4];189–200.)

Severe combined immunodeficiencies (SCIDs) constitute a heterogeneous group of life-threatening genetic disorders that typically present in the first year of life. Reticular dysgenesis (RD) is an autosomal recessive form of human Severe Combined Immunodeficiency (SCIDs) characterized by the absence of blood neutrophils and T lymphocytes. This pathology is due to biallelic mutations in the adenylate kinase 2 (AK2) gene, encoding for a mitochondrial protein which regulates the homeostasis of adenine nucleotides.

Diagnosis of the inherited bone marrow failure syndromes depends on a combination of clinical suspicion and laboratory specificity. The major pancytopenias include Fanconi’s anemia, dyskeratosis congenita, Schwachman-Diamond syndrome, cartilage-hair hypoplasia, Pearson’s syndrome, reticular dysgenesis, amegakaryocytic thrombocytopenia, and familial aplastic anemias. The single cytopenias include Diamond-Blackfan anemia, Kostmann’s syndrome, and thrombocytopenia with absent radii. This chapter discusses the laboratory analyses which may be useful for these diagnoses.

Dendritic cells are the major antigen‐presenting cells, especially for naive T lymphocytes; it is conceivable therefore that their absence or dysfunction may induce an immune deficiency (ID). Few data are available, however, concerning dendritic cells in human primary ID. Langerhans' cells (LC) are intraepidermal dendritic cells which express specific markers and may therefore be studied by immunohistochemistry on paraffin‐embedded skin samples. Skin samples of nine children with primary ID were studied and compared with five age‐matched controls. LC were present within the epidermis of two children with X‐linked severe combined ID, a condition related to the lack of the common γ‐chain of interleukin‐2 (IL‐2), IL‐4, IL‐7, IL‐9, and IL‐15 receptors. LC were also present in skin samples of a child with Omenn syndrome and in three children with combined ID. By contrast, no LC were detected in the skin samples of two children with alymphocytosis and of a child with reticular dysgenesis, a condition characterized by the absence of peripheral blood leukocytes. © 1997 by John Wiley & Sons, Ltd.

The clinical and hematological findings in 4 boys of a family with a chronic constitutional leukocytopenia are described. Possible X-chromosomal sex-linked genetic transmission, the benign clinical course as well as the association with clinical and cytological hints of the involvement of the lymphatic cellular immunological system suggest a disease of its own. It was classified as a mild form of myelolymphatic insufficiency similar to reticular dysgenesis. The significance of Pelger-Huët anomalies of neutrophils demonstrated in the blood of the mother and of Pelger-like forms in the blood of children are discussed.

Objective: To determine the relative frequencies of the different genetic forms of severe combined immunodeficiency (SCID) and whether there are distinctive characteristics of the particular genotypes. Study design: The demographic, genetic, and immunologic features of 108 infants with SCID who were treated consecutively at Duke University Medical Center were analyzed. Results: Eighty-nine subjects were boys and 19 were girls; there were 84 white infants, 16 black infants, and 8 Hispanic infants. Forty-nine had X-linked SCID with mutations of common cytokine receptor gamma chain (@c"c ), 16 had adenosine deaminase (ADA) deficiency, 8 had Janus kinase 3 (Jak3) deficiency, 21 had unknown autosomal recessive mutations, 1 had reticular dysgenesis, 1 had cartilage hair hypoplasia, and 12 (all boys) had SCID of undetermined type. Deficiency of ADA caused the most profound lymphopenia; @c"cor Jak3 deficiency resulted in the most B cells and fewest natural killer (NK) cells; NK cells and function were highest in autosomal recessive and unknown types of SCID. Conclusions: Different SCID genotypes are associated with distinctive lymphocyte characteristics. The presence of NK function in ADA-deficient, autosomal recessive, and unknown type SCIDs, and low NK function in a majority of @c"cand Jak3 SCIDs indicates that some molecular lesions affect T, B, and NK cells (@c"cand Jak3), others primarily T cells (ADA deficiency), and others just T and B cells. (J Pediatr 1997;130:378-87)