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Severe combined immunodeficiency (SCID) is characterized by a severe deficiency in T cell numbers. We analyzed data collected (n = 307) for PHA-based T cell proliferation from the PIDTC SCID protocol 6901, using either a radioactive or flow cytometry method. In comparing the two groups, a smaller number of the patients tested by flow cytometry had <10% of the lower limit of normal proliferation as compared to the radioactive method (p = 0.02). Further, in patients with CD3+ T cell counts between 51 and 300 cells/μL, there was a higher proliferative response with the PHA flow assay compared to the 3 H-T assay (p < 0.0001), suggesting that the method of analysis influences the resolution and interpretation of PHA results. Importantly, we observed many SCID patients with profound T cell lymphopenia having normal T cell proliferation when assessed by flow cytometry. We recommend this test be considered only as supportive in the diagnosis of typical SCID., Competing Interests: Declaration of competing interest RSA has been on the advisory board for Horizon Pharma (now Amgen) and Sobi in the past 2 years but is not currently serving in that capacity. RM is an employee of Pharming Healthcare Inc., Warren, NJ. JWL is an employee and shareholder of Bluebird Bio, and has been a speaker/consultant and on the advisory board for Sobi, Inc., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Background: The Primary Immune Deficiency Treatment Consortium (PIDTC) enrolled children in the United States and Canada onto a retrospective multicenter natural history study of hematopoietic cell transplantation (HCT)., Objective: We investigated outcomes of HCT for severe combined immunodeficiency (SCID)., Methods: We evaluated the chronic and late effects (CLE) after HCT for SCID in 399 patients transplanted from 1982 to 2012 at 32 PIDTC centers. Eligibility criteria included survival to at least 2 years after HCT without need for subsequent cellular therapy. CLE were defined as either conditions present at any time before 2 years from HCT that remained unresolved (chronic), or new conditions that developed beyond 2 years after HCT (late)., Results: The cumulative incidence of CLE was 25% in those alive at 2 years, increasing to 41% at 15 years after HCT. CLE were most prevalent in the neurologic (9%), neurodevelopmental (8%), and dental (8%) categories. Chemotherapy-based conditioning was associated with decreased-height z score at 2 to 5 years after HCT (P < .001), and with endocrine (P < .001) and dental (P = .05) CLE. CD4 count of ≤500 cells/μL and/or continued need for immunoglobulin replacement therapy >2 years after transplantation were associated with lower-height z scores. Continued survival from 2 to 15 years after HCT was 90%. The presence of any CLE was associated with increased risk of late death (hazard ratio, 7.21; 95% confidence interval, 2.71-19.18; P < .001)., Conclusion: Late morbidity after HCT for SCID was substantial, with an adverse impact on overall survival. This study provides evidence for development of survivorship guidelines based on disease characteristics and treatment exposure for patients after HCT for SCID., (Copyright © 2023. Published by Elsevier Inc.)

Purpose of Review: Hematopoietic stem cell-based therapies, including allogeneic hematopoietic cell transplantation (HCT) and autologous gene therapy (GT), have been used as curative therapy for many inborn errors of immunity (IEI). As the number of genetically defined IEI and the use of HCT and GT increase, valuable data on outcomes and approaches for specific disorders are available. We review recent progress in HCT and GT for IEI in this article., Recent Findings: Novel approaches to prevention of allogeneic complications and experience in adolescents and young adults have expanded the use of HCT. Universal newborn screening for severe combined immunodeficiency (SCID) has led to improved outcome after HCT. Analysis of outcomes of HCT and GT for SCID, Wiskott-Aldrich syndrome (WAS) and chronic granulomatous disease (CGD) reveal risk factors for survival, the impact of specific conditioning regimens, and vector- or disease-specific impacts on efficacy and safety. Preclinical studies of GT and gene editing show potential for translation to the clinic., Summary: Emerging data on outcome after HCT for specific IEI support early evaluation and treatment, before development of co-morbidities. Data in large cooperative retrospective databases continues to yield valuable insights clinicians can use in patient selection and choice of therapy., (Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Severe combined immunodeficiency (SCID) is fatal unless durable adaptive immunity is established, most commonly through allogeneic haematopoietic cell transplantation (HCT). The Primary Immune Deficiency Treatment Consortium (PIDTC) explored factors affecting the survival of individuals with SCID over almost four decades, focusing on the effects of population-based newborn screening for SCID that was initiated in 2008 and expanded during 2010-18., Methods: We analysed transplantation-related data from children with SCID treated at 34 PIDTC sites in the USA and Canada, using the calendar time intervals 1982-89, 1990-99, 2000-09, and 2010-18. Categorical variables were compared by χ 2 test and continuous outcomes by the Kruskal-Wallis test. Overall survival was estimated by the Kaplan-Meier method. A multivariable analysis using Cox proportional hazards regression models examined risk factors for HCT outcomes, including the variables of time interval of HCT, infection status and age at HCT, trigger for diagnosis, SCID type and genotype, race and ethnicity of the patient, non-HLA-matched sibling donor type, graft type, GVHD prophylaxis, and conditioning intensity., Findings: For 902 children with confirmed SCID, 5-year overall survival remained unchanged at 72%-73% for 28 years until 2010-18, when it increased to 87% (95% CI 82·1-90·6; n=268; p=0·0005). For children identified as having SCID by newborn screening since 2010, 5-year overall survival was 92·5% (95% CI 85·8-96·1), better than that of children identified by clinical illness or family history in the same interval (79·9% [69·5-87·0] and 85·4% [71·8-92·8], respectively [p=0·043]). Multivariable analysis demonstrated that the factors of active infection (hazard ratio [HR] 2·41, 95% CI 1·56-3·72; p<0·0001), age 3·5 months or older at HCT (2·12, 1·38-3·24; p=0·001), Black or African-American race (2·33, 1·56-3·46; p<0·0001), and certain SCID genotypes to be associated with lower overall survival during all time intervals. Moreover, after adjusting for several factors in this multivariable analysis, HCT after 2010 no longer conveyed a survival advantage over earlier time intervals studied (HR 0·73, 95% CI 0·43-1·26; p=0·097). This indicated that younger age and freedom from infections at HCT, both directly driven by newborn screening, were the main drivers for recent improvement in overall survival., Interpretation: Population-based newborn screening has facilitated the identification of infants with SCID early in life, in turn leading to prompt HCT while avoiding infections. Public health programmes worldwide can benefit from this definitive demonstration of the value of newborn screening for SCID., Funding: National Institute of Allergy and Infectious Diseases, Office of Rare Diseases Research, and National Center for Advancing Translational Sciences., Competing Interests: Declaration of interests MST is a member of the Scientific Advisory Board for Proteios Technology. JMP has received royalties from Up-To-Date, and her spouse is employed by and owns stock in Invitae (a DNA sequencing company). MJC has received royalties from Up-to-Date and is on the scientific board of Homology Medicines, a gene therapy company, and is a data and safety monitoring board (DSMB) member for Bluebird Bio, Chiesi USA, and Rocket Pharmaceuticals. LFS is a member of the adjudication committee for Orchard Therapeutics and has received consulting fees from Takeda, CSL Behring, ADMA Biologics, Grifols, and Horizon. JH is on an Investigator-initiated grant at CSL Behring; is a consultant for ADMA, Horizon, and CIRM; and a clinical trial primary investigator (industry sponsored research) for Regeneron. LMB has received clinical trial support through the Fred Hutchinson Cancer Research Center by Medac including supply of treosulfan), is a member of the DSMB for clinical trials with Rocket Pharmaceuticals and Jasper Therapeutics, and has served on an advisory board for Horizon Therapeutics USA. BDS has undertaken ad-hoc consultancies for Sobi and Orchard Therapeutics. ShC is a member on the advisory board for SOBI. JJB is a member of an advisory board for Sobi and Horizon Therapeutics. GDEC has received consultancy fees from Miltenyi Biotech. FDG has received consultancy fees from GLG and Guidepoint Global, and is on the advisory board for Omerus. EBS is on the speaker's bureau for Sobi. EHC is an advisory board member for Pfizer. SP has received funding for the conduct of sponsored trials Atara Biotherapeutics, AlloVir, and Jasper Therapeutics and is on the advisory board for ADMA and Neovii; and is the inventor of IP Licensed to Atara with all rights assigned to Memorial Sloan Kettering Cancer Center. KES has served as a consultant for Enzyvant and the Immune Deficiency Foundation. AP is on the advisory boards for Orchard (MLD GT), Horizon, and Enzyvant, serves on the DSMB for ExCellTheraMK, and is a consultant for Enzyvant (2020). TCQ has been on the speaker's bureau and advisory board for Alexion Pharmaceuticals. SS is on the advisory board and provides consultancy for Graphite, Takeda, Janssen, Bristol Myers Squibb, data and safety monitoring committee for the National Heart, Lung, and Blood Institute (NHLBI), and Aruvant Sciences. HD was an advisor on an Eli Lilly Canada Scientific Advisory Board in April 2020. JWL in the past 12 months has been a speaker and consultant for Sobi; has been a speaker and consultant, and has received research funding from Horizon Therapeutics; has been a speaker, consultant, and on an advisory board for Pharming; has been a speaker and consultant for CSL Behring; is on the advisory board for ADMA Biologics; and is the site primary investigator for Therapure and a GreenCross employee and shareholder at Bluebird Bio. MAP has served on the advisory boards of Novartis, Medexus, Equillium, and Mesoblast; has received clinical study support from Adaptive and Miltenyi Biotech; and has received financial support for educational lectures for Miltenyi Biotech and Novartis. DBK is an inventor for the UC Regents on a lentiviral vector for gene therapy of ADA-SCID and is a member of the DSMB for Revcovi PEG-ADA (Chiesi USA). EH has received consultancy fees from JASPERS, Takeda, CSL-Behring, Octapharma, and Leadiant Biosciences. CCD is a member of the DSMB for Revcovi PEG-ADA and is a consultant for Orchard Therapeutics. All other authors declare no competing interests., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Background: Shearer et al in 2014 articulated well-defined criteria for the diagnosis and classification of severe combined immunodeficiency (SCID) as part of the Primary Immune Deficiency Treatment Consortium's (PIDTC's) prospective and retrospective studies of SCID., Objective: Because of the advent of newborn screening for SCID and expanded availability of genetic sequencing, revision of the PIDTC 2014 Criteria was needed., Methods: We developed and tested updated PIDTC 2022 SCID Definitions by analyzing 379 patients proposed for prospective enrollment into Protocol 6901, focusing on the ability to distinguish patients with various SCID subtypes., Results: According to PIDTC 2022 Definitions, 18 of 353 patients eligible per 2014 Criteria were considered not to have SCID, whereas 11 of 26 patients ineligible per 2014 Criteria were determined to have SCID. Of note, very low numbers of autologous T cells (<0.05 × 10 9 /L) characterized typical SCID under the 2022 Definitions. Pathogenic variant(s) in SCID-associated genes was identified in 93% of patients, with 7 genes (IL2RG, RAG1, ADA, IL7R, DCLRE1C, JAK3, and RAG2) accounting for 89% of typical SCID. Three genotypes (RAG1, ADA, and RMRP) accounted for 57% of cases of leaky/atypical SCID; there were 13 other rare genotypes. Patients with leaky/atypical SCID were more likely to be diagnosed at more than age 1 year than those with typical SCID lacking maternal T cells: 20% versus 1% (P < .001). Although repeat testing proved important, an initial CD3 T-cell count of less than 0.05 × 10 9 /L differentiated cases of typical SCID lacking maternal cells from leaky/atypical SCID: 97% versus 7% (P < .001)., Conclusions: The PIDTC 2022 Definitions describe SCID and its subtypes more precisely than before, facilitating analyses of SCID characteristics and outcomes., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Severe combined immunodeficiency (SCID) results from defects in the differentiation of hematopoietic stem cells into mature T lymphocytes, with additional lymphoid lineages affected in particular genotypes. In 2014, the Primary Immune Deficiency Treatment Consortium published criteria for diagnosing SCID, which are now revised to incorporate contemporary approaches. Patients with typical SCID must have less than 0.05 × 10 9 autologous T cells/L on repetitive testing, with either pathogenic variant(s) in a SCID-associated gene, very low/undetectable T-cell receptor excision circles or less than 20% of CD4 T cells expressing naive markers, and/or transplacental maternally engrafted T cells. Patients with less profoundly impaired autologous T-cell differentiation are designated as having leaky/atypical SCID, with 2 or more of these: low T-cell numbers, oligoclonal T cells, low T-cell receptor excision circles, and less than 20% of CD4 T cells expressing naive markers. These patients must also have either pathogenic variant(s) in a SCID-associated gene or reduced T-cell proliferation to certain mitogens. Omenn syndrome requires a generalized erythematous rash, absent transplacentally acquired maternal engraftment, and 2 or more of these: eosinophilia, elevated IgE, lymphadenopathy, hepatosplenomegaly. Thymic stromal defects and other causes of secondary T-cell deficiency are excluded from the definition of SCID. Application of these revised Primary Immune Deficiency Treatment Consortium 2022 Definitions permits precise categorization of patients with T-cell defects but does not imply a preferred treatment strategy., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Severe combined immunodeficiency (SCID) comprises rare inherited disorders of immunity that require definitive treatment through hematopoietic cell transplantation (HCT) or gene therapy for survival. Despite successes of allogeneic HCT, many SCID patients experience incomplete immune reconstitution, persistent T-cell lymphopenia, and poor long-term outcomes., Objective: We hypothesized that CD4 + T-cell lymphopenia could be associated with a state of T-cell exhaustion in previously transplanted SCID patients., Methods: We analyzed markers of exhaustion in blood samples from 61 SCID patients at a median of 10.4 years after HCT., Results: Compared to post-HCT SCID patients with normal CD4 + T-cell counts, those with poor T-cell reconstitution showed lower frequency of naive CD45RA + /CCR7 + T cells, recent thymic emigrants, and TCR excision circles. They also had a restricted TCR repertoire, increased expression of inhibitory receptors (PD-1, 2B4, CD160, BTLA, CTLA-4), and increased activation markers (HLA-DR, perforin) on their total and naive CD8 + T cells, suggesting T-cell exhaustion and aberrant activation, respectively. The exhaustion score of CD8 + T cells was inversely correlated with CD4 + T-cell count, recent thymic emigrants, TCR excision circles, and TCR diversity. Exhaustion scores were higher among recipients of unconditioned HCT, especially when further in time from HCT. Patients with fewer CD4 + T cells showed a transcriptional signature of exhaustion., Conclusions: Recipients of unconditioned HCT for SCID may develop late post-HCT T-cell exhaustion as a result of diminished production of T-lineage cells. Elevated expression of inhibitory receptors on their T cells may be a biomarker of poor long-term T-cell reconstitution., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Adenosine deaminase (ADA) deficiency causes ∼13% of cases of severe combined immune deficiency (SCID). Treatments include enzyme replacement therapy (ERT), hematopoietic cell transplant (HCT), and gene therapy (GT). We evaluated 131 patients with ADA-SCID diagnosed between 1982 and 2017 who were enrolled in the Primary Immune Deficiency Treatment Consortium SCID studies. Baseline clinical, immunologic, genetic characteristics, and treatment outcomes were analyzed. First definitive cellular therapy (FDCT) included 56 receiving HCT without preceding ERT (HCT); 31 HCT preceded by ERT (ERT-HCT); and 33 GT preceded by ERT (ERT-GT). Five-year event-free survival (EFS, alive, no need for further ERT or cellular therapy) was 49.5% (HCT), 73% (ERT-HCT), and 75.3% (ERT-GT; P < .01). Overall survival (OS) at 5 years after FDCT was 72.5% (HCT), 79.6% (ERT-HCT), and 100% (ERT-GT; P = .01). Five-year OS was superior for patients undergoing HCT at <3.5 months of age (91.6% vs 68% if ≥3.5 months, P = .02). Active infection at the time of HCT (regardless of ERT) decreased 5-year EFS (33.1% vs 68.2%, P < .01) and OS (64.7% vs 82.3%, P = .02). Five-year EFS (90.5%) and OS (100%) were best for matched sibling and matched family donors (MSD/MFD). For patients treated after the year 2000 and without active infection at the time of FDCT, no difference in 5-year EFS or OS was found between HCT using a variety of transplant approaches and ERT-GT. This suggests alternative donor HCT may be considered when MSD/MFD HCT and GT are not available, particularly when newborn screening identifies patients with ADA-SCID soon after birth and before the onset of infections. This trial was registered at www.clinicaltrials.gov as #NCT01186913 and #NCT01346150.

Background: Massachusetts began newborn screening (NBS) for severe combined immunodeficiency (SCID) using measurement of T-cell receptor excision circles (TRECs) from dried blood spots., Objective: We describe developments and outcomes from the first 10 years of this program (February 1, 2009, to January 31, 2019)., Methods: TREC values, diagnostic, and outcome data from all patients screened for SCID were evaluated., Results: NBS of 720,038 infants prompted immunologic evaluation of 237 (0.03%). Of 237, 9 were diagnosed with SCID/leaky SCID (4% of referrals vs 0.001% general population). Another 7 were diagnosed with other combined immunodeficiencies, and 3 with athymia. SCID/leaky SCID incidence was approximately 1 in 80,000, whereas approximately 1 in 51,000 had severe T-cell lymphopenia for which definitive treatment was indicated. All patients with SCID/leaky SCID underwent hematopoietic cell transplant or gene therapy with 100% survival. One patient with athymia underwent successful thymus transplant. No known cases of SCID were missed. Compared with outcomes from the 10 years before SCID NBS, survival trended higher (9 of 9 vs 4 of 7), likely due to a lower rate of infection before treatment., Conclusions: Our data support a single NBS testing-and-referral algorithm for all gestational ages. Despite lower median TREC values in premature infants, the majority for all ages are well above the TREC cutoff and the algorithm, which selects urgent (undetectable TREC) and repeatedly abnormal TREC values, minimizes referral. We also found that low naïve T-cell percentage is associated with a higher risk of SCID/CID, demonstrating the utility of memory/naïve T-cell phenotyping as part of follow-up flow cytometry., (Copyright © 2021 American Academy of Allergy, Asthma & Immunology. All rights reserved.)

Purpose: The Primary Immune Deficiency Treatment Consortium (PIDTC) enrolled children with severe combined immunodeficiency (SCID) in a prospective natural history study of hematopoietic stem cell transplant (HSCT) outcomes over the last decade. Despite newborn screening (NBS) for SCID, infections occurred prior to HSCT. This study's objectives were to define the types and timing of infection prior to HSCT in patients diagnosed via NBS or by family history (FH) and to understand the breadth of strategies employed at PIDTC centers for infection prevention., Methods: We analyzed retrospective data on infections and pre-transplant management in patients with SCID diagnosed by NBS and/or FH and treated with HSCT between 2010 and 2014. PIDTC centers were surveyed in 2018 to understand their practices and protocols for pre-HSCT management., Results: Infections were more common in patients diagnosed via NBS (55%) versus those diagnosed via FH (19%) (p = 0.012). Outpatient versus inpatient management did not impact infections (47% vs 35%, respectively; p = 0.423). There was no consensus among PIDTC survey respondents as to the best setting (inpatient vs outpatient) for pre-HSCT management. While isolation practices varied, immunoglobulin replacement and antimicrobial prophylaxis were more uniformly implemented., Conclusion: Infants with SCID diagnosed due to FH had lower rates of infection and proceeded to HSCT more quickly than did those diagnosed via NBS. Pre-HSCT management practices were highly variable between centers, although uses of prophylaxis and immunoglobulin support were more consistent. This study demonstrates a critical need for development of evidence-based guidelines for the pre-HSCT management of infants with SCID following an abnormal NBS., Trial Registration: NCT01186913.

Vasculitis can be a life-threatening complication associated with high mortality and morbidity among patients with primary immunodeficiencies (PIDs), including variants of severe and combined immunodeficiencies ((S)CID). Our understanding of vasculitis in partial defects in recombination activating gene (RAG) deficiency, a prototype of (S)CIDs, is limited with no published systematic evaluation of diagnostic and therapeutic modalities. In this report, we sought to establish the clinical, laboratory features, and treatment outcome of patients with vasculitis due to partial RAG deficiency. Vasculitis was a major complication in eight (13%) of 62 patients in our cohort with partial RAG deficiency with features of infections and immune dysregulation. Vasculitis occurred early in life, often as first sign of disease (50%) and was complicated by significant end organ damage. Viral infections often preceded the onset of predominately non-granulomatous-small vessel vasculitis. Autoantibodies against cytokines (IFN-α, -ω, and IL-12) were detected in a large fraction of the cases tested (80%), whereas the majority of patients were anti-neutrophil cytoplasmic antibodies (ANCA) negative (>80%). Genetic diagnosis of RAG deficiency was delayed up to 2 years from the onset of vasculitis. Clinical cases with sole skin manifestation responded well to first-line steroid treatment, whereas systemic vasculitis with severe end-organ complications required second-line immunosuppression and/or hematopoietic stem cell transplantation (HSCT) for definitive management. In conclusion, our data suggest that vasculitis in partial RAG deficiency is prevalent among patients with partial RAG deficiency and is associated with high morbidity. Therefore, partial RAG deficiency should be included in the differential diagnosis of patients with early-onset systemic vasculitis. Diagnostic serology may be misleading with ANCA negative findings, and search for conventional autoantibodies should be extended to include those targeting cytokines., (Copyright © 2020 Geier, Farmer, Foldvari, Ujhazi, Steininger, Sleasman, Parikh, Dilley, Pai, Henderson, Hazen, Neven, Moshous, Sharapova, Mihailova, Yankova, Naumova, Özen, Byram, Fernandez, Wolf, Eibl, Notarangelo, Calabrese and Walter.)

The treatment of primary immunodeficiency disorders with allogeneic hematopoietic cell transplantation (HCT) has a history dating back to 1968 with the first successful transplant for a patient with severe combined immunodeficiency (SCID). The omission of conditioning for patients with SCID owing to their inability to reject allogeneic grafts and the increasing use of reduced intensity conditioning regimens often result in a state of mixed or split donor-recipient chimerism. The use of gene therapy (GT) via retroviral or lentiviral transduction of autologous CD34+ hematopoietic stem and progenitor cells is expected to correct only a portion of the hematopoietic stem cell compartment. The consequences of partial correction after either form of cellular therapy differ according to how the genetic deficiency affects immune cell development and function. Moreover, the conditioning regimen or lack thereof impacts the cell lineages at risk of partial correction. Advances in our understanding of immune reconstitution after HCT and GT for SCID, Wiskott-Aldrich syndrome, and chronic granulomatous disease are discussed., Competing Interests: Conflict-of-interest disclosure: S.-Y.P. declares no competing financial interests., (© 2019 by The American Society of Hematology. All rights reserved.)

The Primary Immune Deficiency Treatment Consortium (PIDTC) performed a retrospective analysis of 662 patients with severe combined immunodeficiency (SCID) who received a hematopoietic cell transplantation (HCT) as first-line treatment between 1982 and 2012 in 33 North American institutions. Overall survival was higher after HCT from matched-sibling donors (MSDs). Among recipients of non-MSD HCT, multivariate analysis showed that the SCID genotype strongly influenced survival and immune reconstitution. Overall survival was similar for patients with RAG , IL2RG , or JAK3 defects and was significantly better compared with patients with ADA or DCLRE1C mutations. Patients with RAG or DCLRE1C mutations had poorer immune reconstitution than other genotypes. Although survival did not correlate with the type of conditioning regimen, recipients of reduced-intensity or myeloablative conditioning had a lower incidence of treatment failure and better T- and B-cell reconstitution, but a higher risk for graft-versus-host disease, compared with those receiving no conditioning or immunosuppression only. Infection-free status and younger age at HCT were associated with improved survival. Typical SCID, leaky SCID, and Omenn syndrome had similar outcomes. Landmark analysis identified CD4 + and CD4 + CD45RA + cell counts at 6 and 12 months post-HCT as biomarkers predictive of overall survival and long-term T-cell reconstitution. Our data emphasize the need for patient-tailored treatment strategies depending upon the underlying SCID genotype. The prognostic significance of CD4 + cell counts as early as 6 months after HCT emphasizes the importance of close follow-up of immune reconstitution to identify patients who may need additional intervention to prevent poor long-term outcome., (© 2018 by The American Society of Hematology.)

Allogeneic hematopoietic stem cell transplant (HSCT) typically results in donor T-cell engraftment and function in patients with severe combined immunodeficiency (SCID), but humoral immunity, particularly when using donors other than matched siblings, is variable. B-cell function after HSCT for SCID depends on the genetic cause, the use of pre-HSCT conditioning, and whether donor B-cell chimerism is achieved. Patients with defects in IL2RG or JAK3 undergoing HSCT without conditioning often have poor B-cell function post-HSCT, perhaps as a result of impairment of IL-21 signaling in host-derived B cells. To investigate the effect of pre-HSCT conditioning on B-cell function, and the relationship of in vitro B-cell function to clinical humoral immune status, we analyzed 48 patients with IL2RG/JAK3 SCID who were older than 2 years after HSCT with donors other than matched siblings. T follicular helper cells (T FH ) developed in these patients with kinetics similar to healthy young children; thus, poor B-cell function could not be attributed to a failure of T FH development. In vitro differentiation of B cells into plasmablasts and immunoglobulin secretion in response to IL-21 strongly correlated with the use of conditioning, donor B-cell engraftment, freedom from immunoglobulin replacement, and response to tetanus vaccine. Patients receiving immunoglobulin replacement who had normal serum immunoglobulin M showed poor response to IL-21 in vitro, similar to those with low serum IgM. In vitro response of B cells to IL-21 may predict clinically relevant humoral immune function in patients with IL2RG/JAK3 SCID after HSCT.

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.

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., (© 2017 by The American Society of Hematology.)

Purpose of Review: This review describes recent studies on outcomes after allogeneic hematopoietic cell transplantation for primary immunodeficiency in North America, including severe combined immunodeficiency (SCID), Wiskott-Aldrich syndrome and chronic granulomatous disease., Recent Findings: Using uniform diagnostic criteria, the Primary Immune Deficiency Treatment Consortium described the baseline characteristics of newly diagnosed infants with SCID in North America. Analysis of outcomes of hematopoietic cell transplantation for SCID in North America from 2000 to 2009 showed that young infants, and older infants without active infection, had excellent survival irrespective of type of donor or transplant approach with regard to conditioning. Although pretransplant conditioning with chemotherapy had a clear and strong negative impact on survival in infants with active infection at the time of transplant, among survivors, conditioning was associated with improved immune reconstitution. However, the potential late effects of conditioning in these infants remain to be characterized. Advances in transplant outcomes for Wiskott-Aldrich syndrome and chronic granulomatous disease support the strategy of early transplantation before the onset of severe complications; additional multicenter studies are needed to fully define optimal approaches., Summary: The formation of the Primary Immune Deficiency Treatment Consortium, a multiinstitutional North American consortium, has contributed to our understanding of outcomes after transplant for primary immunodeficiency.

Background: Patients with severe combined immunodeficiency disease who have matched sibling donors (MSDs) can proceed to hematopoietic cell transplantation (HCT) without conditioning chemotherapy., Objective: We sought to determine whether the results of HCT without chemotherapy-based conditioning from matched unrelated donors (URDs), either from volunteer adults or umbilical cord blood, are comparable with those from MSDs., Methods: We performed a multicenter survey of severe combined immunodeficiency transplantation centers in North America, Europe, and Australia to compile retrospective data on patients who have undergone unconditioned HCT from either URDs (n = 37) or MSDs (n = 66)., Results: Most patients undergoing URD HCT (92%) achieved donor T-cell engraftment compared with 97% for those with MSDs; however, estimated 5-year overall and event-free survival were worse for URD recipients (71% and 60%, respectively) compared with MSD recipients (92% and 89%, respectively; P < .01 for both). URD recipients who received pre-HCT serotherapy had similar 5-year overall survival (100%) to MSD recipients. The incidences of grade II to IV acute and chronic graft-versus-host disease were higher in URD (50% and 39%, respectively) compared with MSD (22% and 5%, respectively) recipients (P < .01 for both). In the surviving patients there was no difference in T-cell reconstitution at the last follow-up between the URD and MSD recipients; however, MSD recipients were more likely to achieve B-cell reconstitution (72% vs 17%, P < .001)., Conclusion: Unconditioned URD HCT achieves excellent rates of donor T-cell engraftment similar to that seen in MSD recipients, and reconstitution rates are adequate. However, only a minority will have myeloid and B-cell reconstitution, and attention must be paid to graft-versus-host disease prophylaxis. This approach might be safer in children ineligible for intense regimens to spare the potential complications of chemotherapy., (Copyright © 2014 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)

Importance: Newborn screening for severe combined immunodeficiency (SCID) using assays to detect T-cell receptor excision circles (TRECs) began in Wisconsin in 2008, and SCID was added to the national recommended uniform panel for newborn screened disorders in 2010. Currently 23 states, the District of Columbia, and the Navajo Nation conduct population-wide newborn screening for SCID. The incidence of SCID is estimated at 1 in 100,000 births., Objectives: To present data from a spectrum of SCID newborn screening programs, establish population-based incidence for SCID and other conditions with T-cell lymphopenia, and document early institution of effective treatments., Design: Epidemiological and retrospective observational study., Setting: Representatives in states conducting SCID newborn screening were invited to submit their SCID screening algorithms, test performance data, and deidentified clinical and laboratory information regarding infants screened and cases with nonnormal results. Infants born from the start of each participating program from January 2008 through the most recent evaluable date prior to July 2013 were included. Representatives from 10 states plus the Navajo Area Indian Health Service contributed data from 3,030,083 newborns screened with a TREC test., Main Outcomes and Measures: Infants with SCID and other diagnoses of T-cell lymphopenia were classified. Incidence and, where possible, etiologies were determined. Interventions and survival were tracked., Results: Screening detected 52 cases of typical SCID, leaky SCID, and Omenn syndrome, affecting 1 in 58,000 infants (95% CI, 1/46,000-1/80,000). Survival of SCID-affected infants through their diagnosis and immune reconstitution was 87% (45/52), 92% (45/49) for infants who received transplantation, enzyme replacement, and/or gene therapy. Additional interventions for SCID and non-SCID T-cell lymphopenia included immunoglobulin infusions, preventive antibiotics, and avoidance of live vaccines. Variations in definitions and follow-up practices influenced the rates of detection of non-SCID T-cell lymphopenia., Conclusions and Relevance: Newborn screening in 11 programs in the United States identified SCID in 1 in 58,000 infants, with high survival. The usefulness of detection of non-SCID T-cell lymphopenias by the same screening remains to be determined.

Background: The Primary Immune Deficiency Treatment Consortium was formed to analyze the results of hematopoietic-cell transplantation in children with severe combined immunodeficiency (SCID) and other primary immunodeficiencies. Factors associated with a good transplantation outcome need to be identified in order to design safer and more effective curative therapy, particularly for children with SCID diagnosed at birth., Methods: We collected data retrospectively from 240 infants with SCID who had received transplants at 25 centers during a 10-year period (2000 through 2009)., Results: Survival at 5 years, freedom from immunoglobulin substitution, and CD3+ T-cell and IgA recovery were more likely among recipients of grafts from matched sibling donors than among recipients of grafts from alternative donors. However, the survival rate was high regardless of donor type among infants who received transplants at 3.5 months of age or younger (94%) and among older infants without prior infection (90%) or with infection that had resolved (82%). Among actively infected infants without a matched sibling donor, survival was best among recipients of haploidentical T-cell-depleted transplants in the absence of any pretransplantation conditioning. Among survivors, reduced-intensity or myeloablative pretransplantation conditioning was associated with an increased likelihood of a CD3+ T-cell count of more than 1000 per cubic millimeter, freedom from immunoglobulin substitution, and IgA recovery but did not significantly affect CD4+ T-cell recovery or recovery of phytohemagglutinin-induced T-cell proliferation. The genetic subtype of SCID affected the quality of CD3+ T-cell recovery but not survival., Conclusions: Transplants from donors other than matched siblings were associated with excellent survival among infants with SCID identified before the onset of infection. All available graft sources are expected to lead to excellent survival among asymptomatic infants. (Funded by the National Institute of Allergy and Infectious Diseases and others.).

Background: The approach to the diagnosis of severe combined immunodeficiency disease (SCID) and related disorders varies among institutions and countries., Objectives: The Primary Immune Deficiency Treatment Consortium attempted to develop a uniform set of criteria for diagnosing SCID and related disorders and has evaluated the results as part of a retrospective study of SCID in North America., Methods: Clinical records from 2000 through 2009 at 27 centers in North America were collected on 332 children treated with hematopoietic stem cell transplantation (HCT), enzyme replacement therapy, or gene therapy for SCID and related disorders. Eligibility for inclusion in the study and classification into disease groups were established by using set criteria and applied by an expert review group., Results: Two hundred eighty-five (86%) of the patients were determined to be eligible, and 47 (14%) were not eligible. Of the 285 eligible patients, 84% were classified as having typical SCID; 13% were classified as having leaky SCID, Omenn syndrome, or reticular dysgenesis; and 3% had a history of enzyme replacement or gene therapy. Detection of a genotype predicting an SCID phenotype was accepted for eligibility. Reasons for noneligibility were failure to demonstrate either impaired lymphocyte proliferation or maternal T-cell engraftment. Overall (n = 332) rates of testing were as follows: proliferation to PHA, 77%; maternal engraftment, 35%; and genotype, 79% (mutation identified in 62%)., Conclusion: Lack of complete laboratory evaluation of patients before HCT presents a significant barrier to definitive diagnosis of SCID and related disorders and prevented inclusion of subjects in our observational HCT study. This lesson is critical for patient care, as well as the design of future prospective treatment studies for such children because a well-defined and consistent study population is important for precision in outcomes analysis., (Published by Mosby, Inc.)

Background: The recombination-activating gene (RAG) 1/2 proteins play a critical role in the development of T and B cells by initiating the VDJ recombination process that leads to generation of a broad T-cell receptor (TCR) and B-cell receptor repertoire. Pathogenic mutations in the RAG1/2 genes result in various forms of primary immunodeficiency, ranging from T(-)B(-) severe combined immune deficiency to delayed-onset disease with granuloma formation, autoimmunity, or both. It is not clear what contributes to such heterogeneity of phenotypes., Objective: We sought to investigate the molecular basis for phenotypic diversity presented in patients with various RAG1 mutations., Methods: We have developed a flow cytometry-based assay that allows analysis of RAG recombination activity based on green fluorescent protein expression and have assessed the induction of the Ighc locus rearrangements in mouse Rag1(-/-) pro-B cells reconstituted with wild-type or mutant human RAG1 (hRAG1) using deep sequencing technology., Results: Here we demonstrate correlation between defective recombination activity of hRAG1 mutant proteins and severity of the clinical and immunologic phenotype and provide insights on the molecular mechanisms accounting for such phenotypic diversity., Conclusions: Using a sensitive assay to measure the RAG1 activity level of 79 mutations in a physiologic setting, we demonstrate correlation between recombination activity of RAG1 mutants and the severity of clinical presentation and show that RAG1 mutants can induce specific abnormalities of the VDJ recombination process., (Copyright © 2013 American Academy of Allergy, Asthma & Immunology. Published by Mosby, Inc. All rights reserved.)

The Primary Immune Deficiency Treatment Consortium (PIDTC) consists of 33 centers in North America. We hypothesized that the analysis of uniform data on patients with severe combined immunodeficiency (SCID) enrolled in a prospective protocol will identify variables that contribute to optimal outcomes following treatment. We report baseline clinical, immunologic, and genetic features of the first 50 patients enrolled, and the initial therapies administered, reflecting current practice in the diagnosis and treatment of both typical (n = 37) and atypical forms (n = 13) of SCID. From August 2010 to May 2012, patients with suspected SCID underwent evaluation and therapy per local center practices. Diagnostic information was reviewed by the PIDTC eligibility review panel, and hematopoietic cell transplantation (HCT) details were obtained from the Center for International Blood and Marrow Transplant Research. Most patients (92 %) had mutations in a known SCID gene. Half of the patients were diagnosed by newborn screening or family history, were younger than those diagnosed by clinical signs (median 15 vs. 181 days; P = <0.0001), and went to HCT at a median of 67 days vs. 214 days of life (P = <0.0001). Most patients (92 %) were treated with HCT within 1-2 months of diagnosis. Three patients were treated with gene therapy and 1 with enzyme replacement. The PIDTC plans to enroll over 250 such patients and analyze short and long-term outcomes for factors beneficial or deleterious to survival, clinical outcome, and T- and B-cell reconstitution, and which biomarkers are predictive of these outcomes.

Background: Mutations in Janus kinase 3 (JAK3) are a cause of severe combined immunodeficiency, but hypomorphic JAK3 defects can result in a milder clinical phenotype, with residual development and function of autologous T cells. Maternal T-cell engraftment is a common finding in infants with severe combined immunodeficiency but is not typically observed in patients with residual T-cell development., Objective: We sought to study in detail the molecular, cellular, and humoral immune phenotype and function of 3 patients with hypomorphic JAK3 mutations., Methods: We analyzed the distribution and function of T and B lymphocytes in 3 patients and studied the in vitro and in vivo responses of maternal T lymphocytes in 1 patient with maternal T-cell engraftment and residual production of autologous T lymphocytes., Results: B cells were present in normal numbers but with abnormal distribution of marginal zone-like and memory B cells. B-cell differentiation to plasmablasts in vitro in response to CD40 ligand and IL-21 was abolished. In 2 patients the T-cell repertoire was moderately restricted. Surprisingly, 1 patient showed coexistence of maternal and autologous T lymphocytes. By using an mAb recognizing the maternal noninherited HLA-A2 antigen, we found that autologous cells progressively accumulated in vivo but did not compete with maternal cells in vitro., Conclusion: The study of 3 patients with hypomorphic JAK3 mutations suggests that terminal B-cell maturation/differentiation requires intact JAK3 function, even if partially functioning T lymphocytes are present. Maternal T-cell engraftment can occur in patients with JAK3 mutations despite the presence of autologous T cells., (Copyright © 2013 American Academy of Allergy, Asthma & Immunology. Published by Mosby, Inc. All rights reserved.)

Objective: To evaluate the cost-effectiveness of universal neonatal screening for T cell lymphocytopenia in enhancing quality of life and life expectancy for children with severe combined immunodeficiency (SCID)., Methods: Decision trees were created and analyzed to estimate the cost, life years, and quality adjusted life years (QALYs) across a population when universal screening for lack of T cells is used to detect SCID, as implemented in five states, compared to detection based on recognizing symptoms and signs of disease. Terminal values of each tree limb were derived through Markov models simulating the natural history of three cohorts: unaffected subjects; those diagnosed with SCID as neonates (early diagnosis); and those diagnosed after becoming symptomatic and arousing clinical suspicion (late diagnosis). Models considered the costs of screening and of care including hematopoietic cell transplantation for affected individuals. Key decision variables were derived from the literature and from a survey of families with children affected by SCID, which was used to describe the clinical history and healthcare utilization for affected subjects. Sensitivity analyses were conducted to explore the influence of these decision variables., Results: Over a 70-year time horizon, the average cost per infant was $8.89 without screening and $14.33 with universal screening. The model predicted that universal screening in the U.S. would cost approximately $22.4 million/year with a gain of 880 life years and 802 QALYs. Sensitivity analyses showed that screening test specificity and disease incidence were critical driving forces affecting the incremental cost-effectiveness ratio (ICER). Assuming a SCID incidence of 1/75,000 births and test specificity and sensitivity each at 0.99, screening remained cost-effective up to a maximum cost of $15 per infant screened., Conclusion: At our current estimated screening cost of $4.22/infant, universal screening for SCID would be a cost effective means to improve quality and duration of life for children with SCID., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Severe combined immunodeficiency (SCID) is a Primary Immune Deficiency that is under consideration for population-based newborn screening (NBS) by many NBS programs, and has recently been recommended for inclusion in the US uniform panel of newborn screening conditions. A marker of SCID, the T cell receptor excision circle (TREC), is detectable in the newborn dried blood spot using a unique molecular assay as a primary screen. The New England Newborn Screening Program developed and validated a multiplex TREC assay in which both the TREC analyte and an internal control are acquired from a single punch and run in the same reaction. Massachusetts then implemented a statewide pilot SCID NBS program. The authors describe the rationale for a pilot SCID NBS program, a comprehensive strategy for successful implementation, the screening test algorithm, the screening follow-up algorithm and preliminary experience based on statewide screening in the first year. The Massachusetts experience demonstrates that SCID NBS is a program that can be implemented on a population basis with reasonable rates of false positives.

Background: Real-time quantitative PCR (qPCR) targeting a specific marker of functional T cells, the T-cell-receptor excision circle (TREC), detects the absence of functional T cells and has a demonstrated clinical validity for detecting severe combined immunodeficiency (SCID) in infants. There is need for a qPCR TREC assay with an internal control to monitor DNA quality and the relative cellular content of the particular dried blood spot punch sampled in each reaction. The utility of the qPCR TREC assay would also be far improved if more tests could be performed on the same newborn screening sample., Methods: We approached the multiplexing of qPCR for TREC by attenuating the reaction for the reference gene, with focus on maintaining tight quality assurance for reproducible slopes and for prevention of sample-to-sample cross contamination. Statewide newborn screening for SCID using the multiplexed assay was implemented, and quality-assurance data were recorded., Results: The multiplex qPCR TREC assay showed nearly 100% amplification efficiency for each of the TREC and reference sequences, clinical validity for multiple forms of SCID, and an analytic limit of detection consistent with prevention of contamination. The eluate and residual ghost from a 3.2-mm dried blood spot could be used as source material for multiplexed immunoassays and multiplexed DNA tests (Multiplex Plus), with no disruption to the multiplex TREC qPCR., Conclusions: Population-based SCID newborn screening programs should consider multiplexing for quality assurance purposes. Potential benefits of using Multiplex Plus include the ability to perform multianalyte profiling.