Lung infections in immunocompromised children.

Pulmonary infection is the leading cause of infectious morbidity and mortality in children with immune defects. We provide a comprehensive review of lung infections in immunocompromised children, with a focus on imaging findings and imaging-based management. We include an overview of the immune defences of the respiratory tract, the aetiologies of immune defects in children, the features of specific infections and important differential diagnoses and describe diagnostic strategies using imaging and non-imaging-based techniques.

Non-osteopenic Bone Pathology After Allo-hematopoietic Stem Cell Transplantation in Patients with Inborn Errors of Immunity.

PURPOSE: There is a lack of data on post-HSCT non-osteopenic bone pathology specifically for children with inborn errors of immunity (IEI). We collected data on non-osteopenic bone pathology in children with IEI post-HSCT over two decades in a large tertiary pediatric immunology center. METHODS: Descriptive study with data analysis of bone pathology in allo-HSCT for IEI was performed between 1/1/2000 to 31/12/2018 including patients alive at follow-up to July 2022. Records were analyzed for bone pathology and risk factors. Exclusion criteria included isolated reduced bone density, fractures, and skeletal anomalies due to underlying IEI and short stature without other bone pathology. Bone pathologies were divided into 5 categories: bone tumors; skeletal dysplasia; avascular necrosis; evolving bone deformities; slipped upper femoral epiphysis. RESULTS: A total of 429 children received HSCT between 2000 and 2018; 340 are alive at last assessment. Non-osteopenic bone pathology was observed post-HSCT in 9.4% of patients (32/340, mean 7.8 years post-HSCT). Eleven patients (34%) had > 1 category of bone pathology. Seventeen patients (17/32; 53%) presented with bilateral bone pathology. The majority of patients received treosulfan-based conditioning (26/32; 81.2%). Totally, 65.6% (21/32) of patients had a history of prolonged steroid use (> 6 months). Pain was the presenting symptom in 66% of patients, and surgical intervention was required in 43.7%. The highest incidence of bone pathologies was seen in Wiskott-Aldrich syndrome (WAS) (n = 8/34; 23.5%) followed by hemophagocytic lymphohistiocytosis patients (n = 3/16; 18.8%). CONCLUSION: Non-osteopenic bone pathology in long-term survivors of allo-HSCT for IEI is not rare. Most patients did not present with complaints until at least 5 years post-HSCT highlighting the need for ongoing bone health assessment for patients with IEI. Children presenting with stunted growth and bone pathology post-HSCT should undergo skeletal survey to rule out development of post-HSCT skeletal dysplasia. Increased rates and complexity of bone pathology were seen amongst patients with Wiskott-Aldrich syndrome.

Curation and expansion of Human Phenotype Ontology for defined groups of inborn errors of immunity.

BACKGROUND: Accurate, detailed, and standardized phenotypic descriptions are essential to support diagnostic interpretation of genetic variants and to discover new diseases. The Human Phenotype Ontology (HPO), extensively used in rare disease research, provides a rich collection of vocabulary with standardized phenotypic descriptions in a hierarchical structure. However, to date, the use of HPO has not yet been widely implemented in the field of inborn errors of immunity (IEIs), mainly due to a lack of comprehensive IEI-related terms. OBJECTIVES: We sought to systematically review available terms in HPO for the depiction of IEIs, to expand HPO, yielding more comprehensive sets of terms, and to reannotate IEIs with HPO terms to provide accurate, standardized phenotypic descriptions. METHODS: We initiated a collaboration involving expert clinicians, geneticists, researchers working on IEIs, and bioinformaticians. Multiple branches of the HPO tree were restructured and extended on the basis of expert review. Our ontology-guided machine learning coupled with a 2-tier expert review was applied to reannotate defined subgroups of IEIs. RESULTS: We revised and expanded 4 main branches of the HPO tree. Here, we reannotated 73 diseases from 4 International Union of Immunological Societies-defined IEI disease subgroups with HPO terms. We achieved a 4.7-fold increase in the number of phenotypic terms per disease. Given the new HPO annotations, we demonstrated improved ability to computationally match selected IEI cases to their known diagnosis, and improved phenotype-driven disease classification. CONCLUSIONS: Our targeted expansion and reannotation presents enhanced precision of disease annotation, will enable superior HPO-based IEI characterization, and hence benefit both IEI diagnostic and research activities.

Inborn Errors of Adaptive Immunity in Down Syndrome.

Down syndrome fits an immunophenotype of combined immunodeficiency with immunodysregulation, manifesting with increased susceptibility to infections, autoimmunity, autoinflammatory diseases, and hematologic malignancies. Qualitative and quantitative alterations in innate and adaptive immunity are found in most individuals with Down syndrome. However, there is substantial heterogeneity and no correlation between immunophenotype and clinical presentation. Previously, it was thought that the immunological changes in Down syndrome were caused by precocious aging. We emphasize in this review that the immune system in Down syndrome is intrinsically different from the very beginning. The overexpression of specific genes located on chromosome 21 contributes to immunodeficiency and immunodysregulation, but gene expression differs between genes located on chromosome 21 and depends on tissue and cell type. In addition, trisomy 21 results in gene dysregulation of the whole genome, reflecting the complex nature of this syndrome in comparison to well-known inborn errors of immunity that result from monogenic germline mutations. In this review, we provide an updated overview focusing on inborn errors of adaptive immunity in Down syndrome.

Clinical implications of immune-mediated diseases in children with Down syndrome.

Children with Down syndrome have changes in their innate and adaptive immunity, which contribute to increased rates of infections, autoimmune diseases, and haematological malignancies. While improved care for congenital heart disease has decreased mortality and morbidity, complications related to immune-mediated diseases continue to limit the life expectancy in Down syndrome. Infectious diseases are common and have a significant effect on development, behaviour and quality of life. Infection frequency and severity are influenced by various anatomical and physiological alterations in addition to immunological changes in Down syndrome. Thus, prevention of respiratory tract infections requires a multifactorial approach. This could include additional active and/or passive immunizations, prophylactic antibiotics, immunoglobulin replacement and ear, nose and throat surgical interventions. Autoimmune conditions like coeliac disease, type I diabetes mellitus and thyroid disease are classically mentioned in the context of Down syndrome. However, autoinflammatory conditions are more prevalent as well. Screening for autoimmune diseases is required and immunosuppression has to be used with caution. Future studies should address optimal screening programmes for immune-mediated diseases in individuals with Down syndrome, as well as the effect of immune modulation, to further decrease morbidity and mortality, and improve the quality of life of individuals with Down syndrome.

Down syndrome B-lymphocyte subpopulations, intrinsic defect or decreased T-lymphocyte help.

Down syndrome (DS) is known for increased incidence of respiratory infections and autoimmune diseases, indicating impaired immunity. Until now, attention has been mainly focused on T lymphocytes. Therefore, we determined B-lymphocyte subpopulations in 95 children with DS compared with 33 age-matched control (AMC) children. DS serum immunoglobulin levels were compared with 962 non-DS children with recurrent infections. The results were combined with clinical data. Transitional and naive B lymphocytes are profoundly decreased in the children with DS. This could be caused by an intrinsic B-lymphocyte defect resulting in (partial) failure of B-lymphocyte generation, decreased antigen-induced proliferation and/or increased apoptosis, or by decreased proliferation due to deficient T-lymphocyte help, or a combination of these. The decreased CD27, CD21, and CD23 cells are reminiscent of common variable immunodeficiency and suggestive of disturbed peripheral B-lymphocyte maturation. Immunoglobulin levels in DS are abnormal-as has been described before-and different from non-DS children with recurrent infections. We conclude that the humoral immune system is abnormal in DS, but could not find a relation between B-lymphocyte subsets, immunoglobulins and clinical features of the children with DS in our cohort, nor could we answer the question whether DS lymphocytes are truly intrinsically deficient, or could all findings be explained by deficient T-lymphocyte help.

Both normal memory counts and decreased naive cells favor intrinsic defect over early senescence of Down syndrome T lymphocytes.

Because of their increased malignancies, autoimmune diseases, and infections, patients with Down syndrome (DS) show features of immunodeficiency. The DS thymus and T lymphocyte subsets have indeed proven to be different, and this has been interpreted as precocious aging. Our study on T lymphocyte subpopulations in DS shows that the normal expansion of naive helper (CD4CD45RA) and cytotoxic (CD8CD45RACD27) T lymphocytes is lacking in the first years of life; this is more logically explainable with an intrinsic T lymphocyte defect. Furthermore, memory cell numbers are not different from age-matched controls (AMC), which does not support the hypothesis of precocious aging. Although the absolute numbers of T lymphocyte subpopulations approach AMC levels toward adulthood, the persistent clinical problems suggest that these cells may not function optimally. However, the clinical picture does not fit severe T lymphocyte deficiency. The latter concept is also supported by our finding that cytomegalovirus (CMV)-seropositive DS children show similar numbers of terminally differentiated cytotoxic T lymphocytes when compared with healthy children, not increased numbers as are seen in immunocompromised hosts.

Influenza A/H1N1 vaccination response is inadequate in down syndrome children when the latest cut-off values are used.

We determined the response of 48 Down syndrome children to 2 doses of influenza A/H1N1 vaccination. Ninety-two percent of the children reached the previously defined protective level (hemagglutination-inhibition titer ≥1:40), but only 27% of the children reached the level of ≥1:110 which was recently described to predict the conventional 50% clinical protection rate in children. Further studies, and potentially adaptations of the schedule, are needed.

Impaired avidity maturation after tetanus toxoid booster in children with Down syndrome.

Down syndrome children show a decreased avidity of the antibody response after tetanus toxoid booster vaccination at 9 years of age suggesting impaired memory B cell selection in the germinal center. Clinicians need to be aware of this ongoing subtle immunologic deficit in Down syndrome.