The Primary Immune Deficiency Treatment Consortium performed a retrospective analysis of 133 patients with severe combined immunodeficiency (SCID) receiving matched sibling donor (MSD) hematopoietic cell transplantation (HCT) between 1980 and 2023 at 30 North American institutions. In this largest cohort of MSD outcomes in patients with SCID to date, we examined the impact of conditioning regimen and graft-versus-host disease (GVHD) prophylaxis on survival and immune recovery. Outcomes after MSD HCT for SCID were excellent. Patients without an active infection or failure to thrive (FTT) at the time of HCT had 5-year overall survival superior to those with infection or FTT. Acute and chronic GVHD outcomes were independent of GVHD prophylaxis, conditioning regimen, SCID type, or presence of maternal engraftment. Patients without active infection at the time of HCT had superior chronic GVHD-free event-free survival vs those with infection. T-cell reconstitution at 6 months was less likely achieved with use of GVHD prophylaxis or serotherapy, and in patients with leaky SCID or Omenn syndrome. At 6 months, 1 year, and 2-5 years, T-cell reconstitution was less likely with ADA, DCLRE1C, or RAG genotype. B-cell reconstitution at 1 year and 2-5 years was negatively affected by development of grade 2 to 4 or 3 to 4 acute GVHD. Conditioning did not affect T- or B-cell reconstitution. Our data suggest omitting conditioning and GVHD prophylaxis for patients with typical SCID did not negatively affect 5-year outcomes after MSD HCT, but the data are insufficient to recommend this approach for best long-term outcomes. This trial was registered at www.clinicaltrials.gov as #NCT01186913 and #NCT01346150.

Background and Objectives: Severe combined immunodeficiency (SCID) represents a group of rare and potentially fatal monogenic disorders arising from pathogenic variants in a broad spectrum of genes. Diagnostic delays beyond the first few months of life have been associated with poor overall survival and hematopoietic stem cell transplantation (HSCT) outcomes. Therefore, the aim of our study was to apply an NGS assay enabling the rapid and reliable diagnosis of SCID. Materials and Methods: We developed a targeted NGS panel of 30 genes implicated in the pathogenesis of most SCID cases and we applied it to three Greek infants with suspected SCID. Results: Each patient displayed a distinct immunophenotype-T-B-NK-, T-B-NK+ and T-B+NK-, respectively-and was found to harbor pathogenic or likely pathogenic variants in the analyzed SCID-related genes. In particular, patient 1 carried two heterozygous ADA variants (c.58G>A, p.Gly20Arg and c.956_960del, p.Glu319Glyfs); patient 2 harbored two discrete pathogenic variants in the DCLRE1C gene (a large deletion of exons 1-3 and the nonsense mutation c.241C>T, p.Arg81*), causing Artemis deficiency; and patient 3 carried a hemizygous IL2RG missense variant (c.437T>C, p.Leu146Pro), associated with X-linked SCID. All variants were confirmed by Sanger sequencing. Conclusions: Our method successfully identified the underlying genetic defects in all patients, thereby establishing a molecular diagnosis of SCID. These findings highlight the potential of targeted NGS assays for achieving rapid and accurate molecular diagnosis of SCID, which is crucial for the timely treatment of life-threatening conditions in affected children.

Artemis (DCLRE1C) deficiency causes radiosensitive severe combined immunodeficiency (SCID), although hypomorphic cases can manifest later-onset immunodeficiency, autoimmunity, or lymphoproliferation. We report a 45-year-old man with humoral immunodeficiency, opportunistic infections, and recurrent EBV-positive diffuse large B-cell lymphoma (DLBCL). Genetic analysis was performed to identify mutations in the DCLRE1C gene. Functional studies, including γH2AX assays to assess DNA damage repair and measurement of Type I interferon responses, were conducted to evaluate the impact of the variant. A literature review was performed to contextualize the findings. Biallelic p.Leu70del frameshift mutation in DCLRE1C was identified, leading to significantly decreased mutant protein expression. Functional testing confirmed impaired DNA damage repair, via γH2AX measurement, and elevated Type I interferon responses, indicating cytosolic DNA damage accumulation. A literature review highlighted EBV-positive lymphomas in leaky Artemis deficiency with high mortality rate. Our report adds hypomorphic DCLRE1C deficiency as an inborn error of immunity that predisposes to EBV-associated lymphoproliferative disease. The authors have confirmed clinical trial registration is not needed for this submission.

In recent years, due to the widespread use of advanced molecular diagnostic methods, it has become clear that individuals in particular born from consanguineous marriages may be carriers of different genetic diseases. For this reason, cases where diseases related to inborn errors of immunity (IEI) and metabolism errors are detected in the same patient are encountered more frequently. In patients affected by different genetic defects, the pathophysiology is more complex, and disease management is more difficult. In this article, we aimed to draw attention to this complex genetic carrier state in a male with primary immunodeficiency (PID). In the patient who presented with recurrent lower respiratory tract infections, bronchiectasis, asthma and nasal polyps, and antibody deficiencies as well as cellular immunodeficiency findings were detected in the immunological analyses. In the whole exome sequencing (WES) study, three different variants were detected, two in genes related to PIDs (DCLRE1C and TNFRSF13B) and one in the gene related to phenylalanine metabolism (phenylalanine hydroxylase (PAH)). In the light of the current findings, the patient was evaluated as having leaky severe combined immunodeficiency (SCID) with immune phenotype T-B-natural killer (NK)+ and hyperphenylalaninemia (HPA). This case showed us that metabolic diseases may accompany a delay in the diagnosis of SCID and patients should be evaluated with a multidisciplinary approach.

Genetic defects in one of the DNA double strand break (DSB) repair proteins lead to distinct human syndromes with severe clinical manifestations, including impaired neurological and immunological development, cancer proneness and sensitivity to ionizing radiation. Since diagnostic and therapeutic procedures frequently use DNA damaging agents, identification of radiosensitive individuals is imperative to optimize patient management. However, patients with a (severe) combined immunodeficiency (S)CID are often ineligible for lymphocyte-based radiosensitivity testing. Therefore, this study investigated the suitability of two fibroblast-based assays as alternative methods. DSB repair was evaluated following X-ray irradiation by an optimized cytokinesis-block micronucleus (MN) assay and the γH2AX focus test in fibroblasts from patients with a confirmed or suspected diagnosis of radiosensitive (S)CID. Using both assays, patients with a defect in Artemis were identified as radiosensitive while those with a RAG1/2 deficiency were not considered as radiosensitive. Although MN scoring was not feasible in irradiated fibroblasts deficient in XLF, LIG4 or NBS1, radiosensitivity could be readily demonstrated through impaired DNA DSB repair kinetics with the γH2AX focus assay in fibroblasts deficient in XLF or LIG4, but not in those deficient in NBS1. While both ATM defective fibroblasts clearly showed increased radiation-induced MN yields, one of the two fibroblast cell lines could not be identified as radiosensitive based on residual γH2AX focus levels. This study suggests that combining the fibroblast MN assay and γH2AX focus test can effectively exclude in vitro radiosensitivity in patients with a suspicion of radiosensitive (S)CID, particularly when lymphocyte-based radiosensitivity testing is not feasible.