Study Design for an Evaluation of Newborn Screening for SCID in the UK

Severe combined immunodeficiency is a rare inherited disorder, which, if untreated, invariably proves fatal in late infancy or early childhood. With treatment, the prognosis is much improved. Early treatment of the siblings of cases, before they become symptomatic, has shown considerable improvements in outcomes. Based on this and the development of a test that can be used on the whole population of neonates (measurement of T-cell receptor excision circles—TRECs), many countries have added it to their routine newborn bloodspot screening programmes. The UK National Screening Committee (UKNSC) has considered whether SCID should be added to the UK screening programme and concluded that it was likely to be cost effective, but that there were a number of uncertainties that should be resolved before a national roll-out could be recommended. These include some aspects of the test, such as: cost; the use of different assays and cut-off levels to reduce false positive rates, while maintaining sensitivity; the overall benefits of screening for disease outcome in patients with SCID and other identified disorders; the need for a separate pathway for premature babies; the acceptability of the screening programme to parents of babies who have normal and abnormal (both true and false positive) screening results. To achieve this, screening of two thirds of babies born in England over a two-year period has been planned, beginning in September 2021. The outcomes and costs of care of babies identified by the screening will be compared with those of babies identified with SCID in the rest of the UK. The effect of the screening programme on parents will form part of a separate research project.

Catalytically active holo Homo sapiens adenosine deaminase I adopts a closed conformation

Homo sapiens adenosine deaminase 1 (HsADA1; UniProt P00813) is an immunologically relevant enzyme with roles in T-cell activation and modulation of adenosine metabolism and signaling. Patients with genetic deficiency in HsADA1 suffer from severe combined immunodeficiency, and HsADA1 is a therapeutic target in hairy cell leukemias. Historically, insights into the catalytic mechanism and the structural attributes of HsADA1 have been derived from studies of its homologs from Bos taurus (BtADA) and Mus musculus (MmADA). Here, the structure of holo HsADA1 is presented, as well as biochemical characterization that confirms its high activity and shows that it is active across a broad pH range. Structurally, holo HsADA1 adopts a closed conformation distinct from the open conformation of holo BtADA. Comparison of holo HsADA1 and MmADA reveals that MmADA also adopts a closed conformation. These findings challenge previous assumptions gleaned from BtADA regarding the conformation of HsADA1 that may be relevant to its immunological interactions, particularly its ability to bind adenosine receptors. From a broader perspective, the structural analysis of HsADA1 presents a cautionary tale for reliance on homologs to make structural inferences relevant to applications such as protein engineering or drug development.

Flow Cytometry Confirmation Post Newborn Screening for SCID in England

An evaluation program for newborn screening for Severe Combined Immunodeficiency began in England in September 2021 based on TREC analysis. Flow cytometry is being used as the follow up diagnostic test for patients with low/absent TRECS. The immunology laboratories have established a protocol and values for diagnosing SCID, other T lymphopenias and identifying healthy babies. This commentary describes the flow cytometry approach used in England to define SCID, T lymphopenia and normal infants after a low TREC result. It provides background to the flow cytometry assays being used and discusses the need to monitor and potentially change these values over time.

Somatic Reversion of a Novel IL2RG Mutation Resulting in Atypical X-Linked Combined Immunodeficiency

Mutations of the IL2RG gene, which encodes for the interleukin-2 receptor common gamma chain (γC, CD132), can lead to X-linked severe combined immunodeficiency (X-SCID) associated with a T−B+NK− phenotype as a result of dysfunctional γC-JAK3-STAT5 signaling. Lately, hypomorphic mutations of the IL2RG gene have been described causing atypical SCID with a milder phenotype. Here, we report three brothers with low-normal lymphocyte counts and susceptibility to recurrent respiratory infections and cutaneous warts. The clinical presentation combined with dysgammaglobulinemia suspected an inherited immunity disorder, which has been proven by Next Generation Sequencing as a novel c.458T > C; p.Ile153Thr IL2RG missense-mutation. Subsequent functional characterization revealed impaired T-cell proliferation, low TREC levels and a skewed TCR Vβ repertoire in all three patients. Interestingly, investigation of various subpopulations showed normal expression of CD132 but with partially impaired STAT5 phosphorylation compared to healthy controls. Additionally, we performed precise genetic analysis of subpopulations revealing spontaneous somatic reversion, predominately in lymphoid derived CD3+, CD4+ and CD8+ T cells. Our data demonstrate that the atypical SCID phenotype noticed in these three brothers is due to the combination of hypomorphic IL-2RG function and somatic reversion.

Unique Sensitivity of Uterine Tissue and the Immune System for Endometriotic Lesion Formation

Endometriosis is a debilitating disease that affects about 10% of reproductive-aged adolescents and women. The etiology of the disease is unknown; however, a prevailing hypothesis is that endometriosis develops from retrograde menstruation, where endometrial tissue and fluids flow back through the oviducts into the peritoneal cavity. There is no cure for endometriosis, and symptoms are treated palliatively. Despite the advances in knowledge, the complexity of endometriosis etiology is still unknown. Recent work by our group suggests that the initiation of endometriosis is immune-dependent. Using a mouse model of endometriosis, we hypothesized the initiation of endometriosis is immune regulated and uterine endometrium specific. In the absence of a functional immune system non-obese diabetic/severe combined immunodeficiency (NOD/SCID mice), endometriotic lesions did not form. Uterine endometrial tissue forms endometriotic lesions, whereas tissues with differing basal expression levels of estrogen receptor alpha (ESR1) and estrogen receptor beta (ESR2), similar cellular composition to uterus (i.e. bladder, mammary gland, and lung), and treated with estradiol did not form lesions. As MMP7 is known to play a major role in the organization/reorganization of the endometrium during the menstrual cycle, blocking metalloproteinase (MMP) activity significantly decreased the invasive properties of these cells. Together, these findings suggest that endometriosis is immune and uterine specific and that MMP7 likely plays a role in the ability of uterine tissue and the innate immune system to establish and maintain endometriotic lesions.

Pulmonary Radiological Manifestations of Humoral and Combined Immunodeficiencies in a Tertiary Pediatric Center

Respiratory diseases are considered as significant causes of morbidity and mortality in primary immunodeficiencies. This study aimed to reveal the radiologic patterns of thoracic involvement in these disorders. A total of 58 patients, including 38 cases with combined cellular-humoral and 20 cases with humoral immunodeficiencies, were enrolled in this study. The “combined” group consisted of 12 cases with severe combined immunodeficiency (SCID) and 26 cases with combined immunodeficiency. The “humoral” group included seven patients with Hyper IgM syndrome (HIGMs), seven cases with common variable immunodeficiency (CVID), three patients with X-linked agammaglobulinemia, and three patients with other types of humoral primary immunodeficiencies (PIDs). The mean age of patients at the time of evaluation was 3.3±3.8 and 5.3±3.9 years in combined and humoral groups, respectively. The findings of chest X-rays and CT scans were interpreted and compared. There was a significant difference for alveolar opacification between combined and humoral immunodeficiencies (58% vs. 30%). The bronchopneumonia-like pattern was detected as a significant finding in patients with SCID (42%) and HIGMs (43%). Atrophy of the thymus was detected significantly often in cases of SCID (67%). Two patients with CVID and lipopolysaccharide-responsive and beige-like anchor protein deficiency showed parenchymal changes of granulomatous lymphocytic interstitial lung disease. No significant difference was detected for bronchiectasis, bronchitis/bronchiolitis patterns, pleural effusion, and thoracic lymphadenopathy. lymphadenopathy. Distinct subtypes of primary immunodeficiency may provoke differing and comparable radiological patterns of thoracic involvement; which can clue the clinician and radiologist to the diagnosis of the disease.

Omenn Syndrome due to RAG1 Mutation Presenting With Nonimmune Hydrops Fetalis in Two Siblings

Omenn syndrome (OS) is a rare variant of severe combined immunodeficiency characterized by susceptibility to severe opportunistic infections and peculiar manifestations, such as protein-losing erythroderma, alopecia, hepatosplenomegaly, lymphadenopathies, and severe diarrhea. The typical form of the disease is caused by hypomorphic mutation of the recombination-activating genes (RAG1 and RAG2), which are critical in initiating the molecular processes leading to lymphocyte and immunoglobulin receptor formation. Affected patients lack B cells, whereas autoreactive oligoclonal T cells infiltrate the skin, gut, spleen, and liver. In the absence of hematopoietic stem cell transplantation, patients with OS usually succumb early in life because of opportunistic infections. The incidence of OS is estimated to be <1 per 1 000 000; however, the actual frequency is difficult to ascertain. We report 2 siblings affected by OS due to a homozygous frameshift mutation (NM_000448.3:c.519delT, p.E174Sfs*26) in the RAG1 gene presenting with nonimmune hydrops fetalis (NIHF). To the best of our knowledge, this is the first reported association between OS and NIHF. NIHF specifically refers to the presence of ≥2 abnormal fluid collections in the fetus, without red blood cell alloimmunization. A broad spectrum of pathologies is associated with NIHF; however, in ∼20% of the cases, the primary cause remains unclear. Understanding the etiology of NIHF is essential for guiding clinical management, determining prognosis, and informing parents regarding recurrence risk. Our case contributes to expanding the spectrum of OS presentation and highlights the importance of a complete immunologic and genetic workup in otherwise unexplained cases of NIHF.