Ten Years of Newborn Screening for Severe Combined Immunodeficiency (SCID) in Massachusetts

Flow Cytometry-based Immune Phenotyping of T and B Lymphocytes in the Evaluation of Immunodeficiency and Immune Dysregulation

There are approximately 500 congenital disorders that impair immune cell development and/or function. Patients with these disorders may present with a wide range of symptoms, including increased susceptibility to infection, autoimmunity, autoinflammation, lymphoproliferation, and/or atopy. Flow cytometry-based immune phenotyping of T and B lymphocytes plays an essential role in the evaluation of patients with these presentations. In this review, we describe the clinical utility of flow cytometry as part of a comprehensive evaluation of immune function and how this testing may be used as a diagnostic tool to identify underlying aberrant immune pathways, monitor disease activity, and assess infection risk.

Incidence and risk factors for CMV and EBV infection in infants with low T-cell receptor excision circles on newborn screen

BACKGROUND

Newborn screening for severe combined immunodeficiency (SCID) using T cell receptor excision circles (TRECs) identifies patients with other causes of lymphopenia. The risk of opportunistic infection in patients with non-SCID lymphopenia is poorly understood. We aim to describe incidence and risk factors associated with cytomegalovirus (CMV) and Epstein-Barr virus (EBV) infection in patients with low TRECs.

METHODS

This retrospective study analyzed 289 patients with ≥1 abnormal TREC result.

RESULTS

Nineteen patients had CMV or EBV detected by PCR. Most had resolution of infection (n = 13). Two have chronic viremia, and four expired due to disseminated CMV. Risk factors included undetectable TRECs, consanguinity, family history, low NK, naïve CD4, naïve CD8 cells, and phytohemagglutinin.

CONCLUSION

Infection with CMV and EBV in patients with low TRECs is rare, however some may benefit from preventative measures. Consideration of risk factors may aid in decision-making and improve outcomes.

Newborn screening for SCID: the very first prospective pilot study from Türkiye

Purpose

The measurement of T-cell receptor excision circle (TREC) is used for newborn screening (NBS) in dried blood spot (DBS) samples from Guthrie card for severe combined immunodeficiency (SCID). Here, we report the results of first newborn screening pilot program for SCID conducted in Türkiye.

Methods

The study was carried out together with Ankara University School of Medicine and The Ministry of Health, Public Health General Directorate, Pediatric and Adolescent Health Department. TREC measurements were performed in randomly selected Guthrie card samples obtained from 20253 babies born between October 2018 and October 2020. The TREC analyses were performed together with beta Actin (β-Actin) via RT-PCR (Real Time Polymerase Chain Reaction).

Results

TRECs found to be normal (≥15 copies/µl) in 98,6% of the newborns (n: 19975) but low (<15 copies/µl) in 1.4% (n:278) at the initial analyses. TRECs were retested in 278 suspected infants and found to be normal in 160 (0.8%) while low in 118 (0.58%). New DBS were obtained from the babies with low TRECs (new sample test). TRECs were normal in 108 (0.53%) of the new sample tests and low in 10 (0.049%). Two among 10 babies who had abnormal (undetectable) TRECs were diagnosed as SCID; ADA (P1) and RAG1 (P2) defects were confirmed respectively. They both received curative treatments [gene therapy (P1) and HSCT (P2)]. The remaining 6 of 8 newborns with abnormal TRECs were found normal after clinical and laboratory immune work-up, while medical records of other two revealed early postnatal death due to extreme prematurity.

Conclusion

In the light of this study the incidence of SCID was detected at least 1/10000 live births in Türkiye. This study shows the feasibility and usefulness of initiating SCID screening in Türkiye.

Flow Cytometry-based Immune Phenotyping of T and B Lymphocytes in the Evaluation of Immunodeficiency and Immune Dysregulation

There are approximately 500 congenital disorders that impair immune cell development and/or function. Patients with these disorders may present with a wide range of symptoms, including increased susceptibility to infection, autoimmunity, autoinflammation, lymphoproliferation, and/or atopy. Flow cytometry-based immune phenotyping of T and B lymphocytes plays an essential role in the evaluation of patients with these presentations. In this review, we describe the clinical utility of flow cytometry as part of a comprehensive evaluation of immune function and how this testing may be used as a diagnostic tool to identify underlying aberrant immune pathways, monitor disease activity, and assess infection risk.

Health-related quality of life in patients with inborn errors of immunity: A systematic review and meta-analysis

BACKGROUND

Inborn Errors of Immunity (IEI) significantly affect patients' health-related quality of life (HRQOL), presenting greater challenges than those faced by the healthy population and other chronic disease sufferers. Current research lacks comprehensive integration of this critical issue.

OBJECTIVE

This study explores HRQOL in IEI patients, identifies impacting factors, and advocates for increased research focus on their quality of life.

METHODS

Following systematic review and meta-analysis guidelines, a search of Scopus and PubMed until November 15, 2023, yielded 1633 publications. We evaluated the literature, assessed study quality, and compared the HRQOL of IEI patients to that of healthy individuals and other chronic disease patients.

RESULTS

Of 90 articles and 10,971 IEI patients analyzed, study quality varied (nine good, 63 moderate, and 18 poor). The Short Form-36 (SF-36) and Pediatric Quality of Life Inventory generic core scales (PedsQL) were the primary generic instruments used among adults and children, respectively, with 12 studies each using the disease-specific instruments. Meta-analysis showed IEI patients have significantly lower scores in general health, physical and mental health, and social and emotional roles compared to healthy populations. We noted significant differences between self and proxy reports, indicating caregiver anxiety and perception disparities.

CONCLUSION

Despite limitations like small sample sizes and reliance on generic instruments, this research underscores the substantially lower HRQOL among IEI patients, emphasizing the need for a patient-centered, multidisciplinary approach to improve their life quality and calling for more focused attention on IEI patients and their caregivers' HRQOL.

Current Status of Newborn Bloodspot Screening Worldwide 2024: A Comprehensive Review of Recent Activities (2020-2023)

Newborn bloodspot screening (NBS) began in the early 1960s based on the work of Dr. Robert "Bob" Guthrie in Buffalo, NY, USA. His development of a screening test for phenylketonuria on blood absorbed onto a special filter paper and transported to a remote testing laboratory began it all. Expansion of NBS to large numbers of asymptomatic congenital conditions flourishes in many settings while it has not yet been realized in others. The need for NBS as an efficient and effective public health prevention strategy that contributes to lowered morbidity and mortality wherever it is sustained is well known in the medical field but not necessarily by political policy makers. Acknowledging the value of national NBS reports published in 2007, the authors collaborated to create a worldwide NBS update in 2015. In a continuing attempt to review the progress of NBS globally, and to move towards a more harmonized and equitable screening system, we have updated our 2015 report with information available at the beginning of 2024. Reports on sub-Saharan Africa and the Caribbean, missing in 2015, have been included. Tables popular in the previous report have been updated with an eye towards harmonized comparisons. To emphasize areas needing attention globally, we have used regional tables containing similar listings of conditions screened, numbers of screening laboratories, and time at which specimen collection is recommended. Discussions are limited to bloodspot screening.

Newborn Screening for Severe T and B Cell Lymphopenia Using TREC/KREC Detection: A Large-Scale Pilot Study of 202,908 Newborns

Newborn screening (NBS) for severe inborn errors of immunity (IEI), affecting T lymphocytes, and implementing measurements of T cell receptor excision circles (TREC) has been shown to be effective in early diagnosis and improved prognosis of patients with these genetic disorders. Few studies conducted on smaller groups of newborns report results of NBS that also include measurement of kappa-deleting recombination excision circles (KREC) for IEI affecting B lymphocytes. A pilot NBS study utilizing TREC/KREC detection was conducted on 202,908 infants born in 8 regions of Russia over a 14-month period. One hundred thirty-four newborns (0.66‰) were NBS positive after the first test and subsequent retest, 41% of whom were born preterm. After lymphocyte subsets were assessed via flow cytometry, samples of 18 infants (0.09‰) were sent for whole exome sequencing. Confirmed genetic defects were consistent with autosomal recessive agammaglobulinemia in 1/18, severe combined immunodeficiency - in 7/18, 22q11.2DS syndrome - in 4/18, combined immunodeficiency - in 1/18 and trisomy 21 syndrome - in 1/18. Two patients in whom no genetic defect was found met criteria of (severe) combined immunodeficiency with syndromic features. Three patients appeared to have transient lymphopenia. Our findings demonstrate the value of implementing combined TREC/KREC NBS screening and inform the development of policies and guidelines for its integration into routine newborn screening programs.

Health-related quality of life in patients with inborn errors of immunity: a bibliometric analysis

Background

Inborn Errors of Immunity (IEI) are characterized by a heightened susceptibility to infections, allergies, and various other health complications. Health-Related Quality of Life (HRQOL) in patients with IEI is a critical area of research that demands attention due to the impact of IEI on patients' lives. This study utilized bibliometric methods, aiming to comprehensively explore the research content and hotspots in the field of HRQOL in patients with IEI.

Methods

This bibliometric analysis utilized data from the Science Citation Index Expanded (SCIE) and Social Sciences Citation Index (SSCI) within the Web of Science core datasets up to January 1, 2024. The study focused on literature that addressed HRQOL in IEI patients, involving a total of 1,807 authors and 309 articles published across 112 journals. The analysis included publication volume and growth trends, country and institutional contributions, authorship, and journal analysis.

Results

The research found that despite the importance of HRQOL in IEI, the volume of publications in this field remains consistently low, with no significant increase in trend. The USA leads in publication and citation volumes, reflecting a geographical imbalance in research contributions. Key journals in this field include the Journal of Clinical Immunology, Frontiers in Immunology, and the Journal of Allergy and Clinical Immunology. The study highlights that while treatments like hematopoietic stem cell transplants and gene therapy have improved patient IEI survival rates, they still often come with significant side effects impacting HRQOL. The analysis underlines the need for comprehensive HRQOL assessments in IEI, considering the physical and psychological impacts of treatments.

Conclusions

This study represents a bibliometric analysis focusing on HRQOL in patients with. It underscores the need for more extensive and systematic research in this area, emphasizing the importance of a multidisciplinary approach. Despite advancements in medical treatments for IEI, there is a crucial need to focus on HRQOL to enhance patient satisfaction and overall well-being. The findings advocate for more personalized treatment plans and a better understanding of the psychosocial needs of patients with IEI to improve their quality of life.

Non-conditioned cord blood transplantation for infection control in athymic CHARGE syndrome

OBJECTIVE

CHARGE syndrome is a congenital malformation syndrome caused by heterozygous mutations in the CHD7 gene. Severe combined immunodeficiency (SCID) arises from congenital athymia called CHARGE/complete DiGeorge syndrome. While cultured thymus tissue implantation (CTTI) provides an immunological cure, hematopoietic cell transplantation (HCT) is an alternative option for immuno-reconstitution of affected infants. We aimed to clarify the clinical outcomes of patients with athymic CHARGE syndrome after HCT.

METHODS

We studied the immunological reconstitution and outcomes of four patients who received non-conditioned unrelated donor cord blood transplantation (CBT) at Kyushu University Hospital from 2007 to 2022. The posttransplant outcomes were compared with the outcomes of eight reported patients.

RESULTS

Four index cases received CBT 70-144 days after birth and had no higher than grade II acute graft-versus-host disease. One infant was the first newborn-screened athymic case in Japan. They achieved more than 500/μL naïve T cells with balanced repertoire 1 month post transplant, and survived more than 12 months with home care. Twelve patients including the index cases received HCT at a median 106 days after birth (range: 70-195 days). One-year overall survival rate was significantly higher in patients who underwent non-conditioned HCT than in those who received conditioned HCT (100% vs. 37.5%, p = .02). Nine patients died, and the major cause of death was cardiopulmonary failure.

CONCLUSIONS

Athymic infants achieved a prompt reconstitution of non-skewing naïve T cells after non-conditioned CBT that led to home care in infancy without significant infections. Non-conditioned CBT is a useful bridging therapy for newborn-screened cases toward an immunological cure by CTTI.

Reducing Mortality and Morbidity in Children with Severe Combined Immunodeficiency in Switzerland: the Role of Newborn Screening

Newborn screening (NBS) for severe combined immunodeficiency (SCID) has been introduced in various countries with the aim of reducing morbidity and mortality. However, studies analyzing outcomes before and after the implementation of NBS programs remain limited. This study sought to compare the outcomes of SCID patients identified through Switzerland's national SCID NBS program, introduced in January 2019, with those of a historical cohort diagnosed between 2007 and 2019. The study included seven patients (32%) identified through NBS, and 15 (68%) born before NBS implementation and diagnosed based on clinical signs. Children in the NBS group were younger at diagnosis (median age 9 days vs 9 months, P = .002) and at hematopoietic stem cell transplantation (HSCT, median age 5 months vs 11 months, P = .003) compared to the clinical group. The NBS group had a lower incidence of infections before HSCT (29% vs 93%, P = .004). Although not statistically significant, the overall survival rate on last follow-up was higher in the NBS group (86% vs 67%, P = .62). Importantly, patients with active infections undergoing HSCT had a significantly lower overall survival probability compared to those without (P = .01). In conclusion, the introduction of NBS in Switzerland has led to earlier and often asymptomatic diagnosis of affected children, enabling timely intervention, infection prevention, and prompt treatment. These factors have contributed to higher survival rates in the NBS group. These findings underscore the critical importance of NBS for SCID, offering potential life-saving benefits through early detection and intervention.

Newborn Screening for Severe Combined Immunodeficiency: Lessons Learned from Screening and Follow-Up of the Preterm Newborn Population

Newborn screening (NBS) for Severe Combined Immunodeficiency (SCID) by measurement of T-cell receptor excision circles (TRECs) successfully identifies newborns with SCID and severe T-cell lymphopenia, as intended. At the same time, NBS programs face the challenge of false positive results, with a disproportionately high number in the premature newborn population. This study evaluates TREC values and SCID screening outcomes in premature newborns and elucidates evidence-based SCID screening practices that reduce unnecessary follow-up activities in this population. De-identified individual SCID newborn screening data and aggregate SCID screening data were obtained from seven states across the US for babies born between 2018 and 2020. Relevant statistics were performed on data pooled from these states to quantify screening performance metrics and clinical impact on various birth and gestational age categories of newborns. The data were normalized using multiples-of-the-median (MoM) values to allow for the aggregation of data across states. The aggregation of NBS data across a range of NBS programs highlighted the trajectory of TREC values over time, both between and within newborns, and provides evidence for improved SCID screening recommendations in the premature and low birth weight population.

Newborn screening for severe combined immunodeficiency and inborn errors of immunity

PURPOSE OF REVIEW

Severe combined immune deficiency (SCID) is the most devastating genetic disease of the immune system with an unfavorable outcome unless diagnosed early in life. Newborn screening (NBS) programs play a crucial role in facilitating early diagnoses and timely interventions for affected infants.

RECENT FINDINGS

SCID marked the pioneering inborn error of immunity (IEI) to undergo NBS, a milestone achieved 15 years ago through the enumeration of T-cell receptor excision circles (TRECs) extracted from Guthrie cards. This breakthrough has revolutionized our approach to SCID, enabling not only presymptomatic identification and prompt treatments (including hematopoietic stem cell transplantation), but also enhancing our comprehension of the global epidemiology of SCID.

SUMMARY

NBS is continuing to evolve with the advent of novel diagnostic technologies and treatments. Following the successful implementation of SCID-NBS programs, a call for the early identification of additional IEIs is the next step, encompassing a broader spectrum of IEIs, facilitating early diagnoses, and preventing morbidity and mortality.

Screening Newborns for Low T Cell Receptor Excision Circles (TRECs) Fails to Detect Immunodeficiency, Centromeric Instability, and Facial Anomalies Syndrome

BACKGROUND

Assessment of T-cell receptor excision circles (TRECs) in dried blood spots of newborns allows the detection of severe combined immunodeficiency (SCID) (T cells <300/μL at birth) with a presumed sensitivity of 100%. TREC screening also identifies patients with selected combined immunodeficiency (CID) (T cells >300/μL, yet <1500/μL at birth). Nevertheless, relevant CIDs that would benefit from early recognition and curative treatment pass undetected.

OBJECTIVE

We hypothesized that TREC screening at birth cannot identify CIDs that develop with age.

METHODS

We analyzed the number of TRECs in dried blood spots in archived Guthrie cards of 22 children who had been born in the Berlin-Brandenburg area between January 2006 and November 2018 and who had undergone hematopoietic stem-cell transplantation (HSCT) for inborn errors of immunity.

RESULTS

All patients with SCID would have been identified by TREC screening, but only 4 of 6 with CID. One of these patients had immunodeficiency, centromeric instability, and facial anomalies syndrome type 2 (ICF2). Two of 3 patients with ICF whom we have been following up at our institution had TREC numbers above the cutoff value suggestive of SCID at birth. Yet all patients with ICF had a severe clinical course that would have justified earlier HSCT.

CONCLUSIONS

In ICF, naïve T cells may be present at birth, yet they decline with age. Therefore, TREC screening cannot identify these patients. Early recognition is nevertheless crucial, as patients with ICF benefit from HSCT early in life.

Retrospective analysis of patients with severe combined immunodeficiency and alternative diagnostic criteria: A 20-year single centre experience

Severe combined immunodeficiency (SCID) is an inborn errors of immunity (IEI) disorder characterized by impairment in the development and function of lymphocytes and could be fatal if not treated with hematopoietic stem cell transplant in the first 2 years of life. There are various diagnostic criteria for SCID among different primary immunodeficiency societies. We retrospectively evaluated clinical and laboratory findings of 59 patients followed up with the diagnosis of SCID at our clinic over the past 20 years in order to develop an algorithm that would help diagnosis of SCID for the countries where a high ratio of consanguineous marriage is present because these countries have not launched TREC assay in their newborn screening programs. The mean age at diagnosis was 5.80 ± 4.90 months, and the delay was 3.29 ± 3.99 months. The most common complaint and physical examination findings were cough (29.05%), eczematous rash (63%) and organomegaly (61%). ADA (17%), Artemis (14%), RAG1/2 (15%), MHC Class II (12%) and IL-2R (12%) deficiencies were the most common genetic defects. Lymphopenia (87.5%) was the most frequent abnormal laboratory finding and below 3000/mm3 in 95% of the patients. The CD3+ T cell count was 300/mm3 and below in 83% of the patients. As a result, a combination of low lymphocyte count and CD3 lymphopenia for SCID diagnosis would be more reliable for countries with high rate of consanguineous marriage. Physicians should consider diagnosis of SCID in a patient presenting with severe infections and lymphocyte counts below 3000/mm3 under 2 years of age.

Human thymus in health and disease: Recent advances in diagnosis and biology

The thymus is the crucial tissue where thymocytes develop from hematopoietic precursors that originate from the bone marrow and differentiate to generate a repertoire of mature T cells able to respond to foreign antigens while remaining tolerant to self-antigens. Until recently, most of the knowledge on thymus biology and its cellular and molecular complexity have been obtained through studies in animal models, because of the difficulty to gain access to thymic tissue in humans and the lack of in vitro models able to faithfully recapitulate the thymic microenvironment. This review focuses on recent advances in the understanding of human thymus biology in health and disease obtained through the use of innovative experimental techniques (eg. single cell RNA sequencing, scRNAseq), diagnostic tools (eg. next generation sequencing), and in vitro models of T-cell differentiation (artificial thymic organoids) and thymus development (eg. thymic epithelial cell differentiation from embryonic stem cells or induced pluripotent stem cells).

Genetic Causes, Clinical Features, and Survival of Underlying Inborn Errors of Immunity in Omani Patients: a Single-Center Study

PURPOSE

Early identification of inborn errors of immunity (IEIs) is crucial due to the significant risk of morbidity and mortality. This study aimed to describe the genetic causes, clinical features, and survival rate of IEIs in Omani patients.

METHODS

A prospective study of all Omani patients evaluated for immunodeficiency was conducted over a 17-year period. Clinical features and diagnostic immunological findings were recorded. Targeted gene testing was performed in cases of obvious immunodeficiency. For cases with less conclusive phenotypes, a gene panel was performed, followed by whole-exome sequencing if necessary.

RESULTS

A total of 185 patients were diagnosed with IEIs during the study period; of these, 60.5% were male. Mean ages at symptom onset and diagnosis were 30.0 and 50.5 months, respectively. Consanguinity and a family history of IEIs were present in 86.9% and 50.8%, respectively. Most patients presented with lower respiratory infections (65.9%), followed by growth and development manifestations (43.2%). Phagocytic defects were the most common cause of IEIs (31.9%), followed by combined immunodeficiency (21.1%). Overall, 109 of 132 patients (82.6%) who underwent genetic testing received a genetic diagnosis, while testing was inconclusive for the remaining 23 patients (17.4%). Among patients with established diagnoses, 37 genes and 44 variants were identified. Autosomal recessive inheritance was present in 81.7% of patients with gene defects. Several variants were novel. Intravenous immunoglobulin therapy was administered to 39.4% of patients and 21.6% received hematopoietic stem cell transplantation. The overall survival rate was 75.1%.

CONCLUSION

This study highlights the genetic causes of IEIs in Omani patients. This information may help in the early identification and management of the disease, thereby improving survival and quality of life.

Advances and Challenges of the Decade: The Ever-Changing Clinical and Genetic Landscape of Immunodeficiency

In the past 10 years, we have witnessed major advances in clinical immunology. Newborn screening for severe combined immunodeficiency has become universal in the United States and screening programs are being extended to severe combined immunodeficiency and other inborn errors of immunity globally. Early genetic testing is becoming the norm for many of our patients and allows for informed selection of targeted therapies including biologics repurposed from other specialties. During the COVID-19 pandemic, our understanding of essential immune responses expanded and the discovery of immune gene defects continued. Immunoglobulin products, the backbone of protection for antibody deficiency syndromes, came into use to minimize side effects. New polyclonal and monoclonal antibody products emerged with increasing options to manage respiratory viral agents such as SARS-CoV-2 and respiratory syncytial virus. Against these advances, we still face major challenges. Atypical is becoming typical as phenotypes of distinct genetic disease overlap whereas the clinical spectrum of the same genetic defect widens. Therefore, clinical judgment needs to be paired with repeated deep immune phenotyping and upfront genetic testing, as technologies rapidly evolve, and clinical disease often progresses with age. Managing patients with organ damage resulting from immune dysregulation poses a special major clinical challenge and management often lacks standardization, from autoimmune cytopenias, granulomatous interstitial lung disease, enteropathy, and liver disease to endocrine, rheumatologic, and neurologic complications. Clinical, translational, and basic science networks will continue to advance the field; however, cross-talk and education with practicing allergists/immunologists are essential to keep up with the ever-changing clinical and genetic landscape of inborn errors of immunity.

Lessons Learned From Five Years of Newborn Screening for Severe Combined Immunodeficiency in Israel

BACKGROUND

Implementation of newborn screening (NBS) programs for severe combined immunodeficiency (SCID) have advanced the diagnosis and management of affected infants and undoubtedly improved their outcomes. Reporting long-term follow-up of such programs is of great importance.

OBJECTIVE

We report a 5-year summary of the NBS program for SCID in Israel.

METHODS

Immunologic and genetic assessments, clinical analyses, and outcome data from all infants who screened positive were evaluated and summarized.

RESULTS

A total of 937,953 Guthrie cards were screened for SCID. A second Guthrie card was requested on 1,169 occasions (0.12%), which resulted in 142 referrals (0.015%) for further validation tests. Flow cytometry immune-phenotyping, T cell receptor excision circle measurement in peripheral blood, and expression of TCRVβ repertoire for the validation of positive cases revealed a specificity and sensitivity of 93.7% and 75.9%, respectively, in detecting true cases of SCID. Altogether, 32 SCID and 110 non-SCID newborns were diagnosed, making the incidence of SCID in Israel as high as 1:29,000 births. The most common genetic defects in this group were associated with mutations in DNA cross-link repair protein 1C and IL-7 receptor α (IL-7Rα) genes. No infant with SCID was missed during the study time. Twenty-two SCID patients underwent hematopoietic stem cell transplantation, which resulted in a 91% survival rate.

CONCLUSIONS

Newborn screening for SCID should ultimately be applied globally, specifically to areas with high rates of consanguineous marriages. Accumulating data from follow-up studies on NBS for SCID will improve diagnosis and treatment and enrich our understanding of immune development in health and disease.

Can we identify WHIM in infancy? Opportunities with the public newborn screening process

Newborn screening (NBS) for severe combined immunodeficiency (SCID) utilizing T-cell receptor excision circles (TRECs) has been implemented in all 50 states as of December 2018 and has been transformative for the clinical care of SCID patients. Though having high sensitivity for SCID, NBS-SCID has low specificity, therefore is able to detect other causes of lymphopenia in newborns including many inborn errors of immunity (IEIs). In a recent study, three of six newborns later diagnosed with Warts, Hypogammaglobulinemia, Infections, and Myelokathexis (WHIM) syndrome were found to have a low TRECs and lymphopenia at birth. This presents an opportunity to increase the detection and diagnosis of WHIM syndrome by NBS-SCID with immunological follow-up along with a combination of flow cytometry for immune cell subsets, absolute neutrophil count, and genetic testing, extending beyond the conventional bone marrow studies. Coupled with emerging technologies such as next-generation sequencing, transcriptomics and proteomics, dried blood spots used in NBS-SCID will promote earlier detection, diagnosis, and therefore treatment of IEIs such as WHIM syndrome.

Spontaneous resolution of severe idiopathic T cell lymphopenia

Potential etiologies of T-B + NK+ SCID include both hematopoietic defects and thymic aplasia. The management of patients with this phenotype, identified by newborn screen, may be unclear in the absence of a genetic diagnosis. We report an infant with lymphocyte flow cytometry consistent with T-B + NK+ SCID and reduced proliferative response to phytohemagglutinin. The patient had no genetic diagnosis after targeted panel and exome sequencing. The decision to trend laboratory values rather than move immediately to hematopoietic cell transplant was made given the absence of a genetic defect and the finding of a normal thymus on ultrasound. During the course of evaluation for transplant, the patient unexpectedly had normalization of T cell number and function. This case demonstrates a role for mediastinal ultrasound and the utility of trending laboratory values in patients with severe T cell lymphopenia but no genetic diagnosis, given the small but important possibility of spontaneous resolution.

Future of Therapy for Inborn Errors of Immunity

Over the past 20 years, the rapid evolution in the diagnosis and treatment of primary immunodeficiencies (PI) and the recognition of immune dysregulation as a feature in some have prompted the use of "inborn errors of immunity" (IEI) as a more encompassing term used to describe these disorders [1, 2] . This article aims to review the future of therapy of PI/IEI (referred to IEI throughout this paper). Historically, immune deficiencies have been characterized as monogenic disorders resulting in immune deficiencies affecting T cells, B cells, combination of T and B cells, or innate immune disorders. More recently, immunologists are also recognizing a variety of phenotypes associated with one genotype or similar phenotypes across genotypes and a role for incomplete penetrance or variable expressivity of some genes causing inborn errors of immunity [3]. The IUIS classification of immune deficiencies (IEIs) has evolved over time to include 10 categories, with disorders of immune dysregulation accounting for a new subset, some treatable with small molecule inhibitors or biologics. [1] Until recently, management options were limited to prompt treatment of infections, gammaglobulin replacement, and possibly bone marrow transplant depending on the defect. Available therapies have expanded to include small molecule inhibitors, biologics, gene therapy, and the use of adoptive transfer of virus-specific T cells to fight viral infections in immunocompromised patients. Several significant contributions to the field of clinical immunology have fueled the rapid advancement of therapies over the past two decades. Among these are educational efforts to recruit young immunologists to the field resulting in the growth of a world-wide community of clinicians and investigators interested in rare diseases, efforts to increase awareness of IEI globally contributing to international collaborations, along with advancements in diagnostic genetic testing, newborn screening, molecular biology techniques, gene correction, use of immune modulators, and ex vivo expansion of engineered T cells for therapeutic use. The development and widespread use of newborn screening have helped to identify severe combined immune deficiency (SCID) earlier resulting in better outcomes [4]. Continual improvements and accessibility of genetic sequencing have helped to identify new IEI diseases at an accelerated pace [5]. Advances in gene therapy and bone marrow transplant have made treatments possible in otherwise fatal diseases. Furthermore, the increased awareness of IEI across the world has driven networks of immunologists working together to improve the diagnosis and treatment of these rare diseases. These improvements in the diagnosis and treatment of IEI noted over the past 20 years bring hope for a better future for the IEI community. This paper will review future directions in a few of the newer therapies emerging for IEI. For easy reference, most of the diseases discussed in this paper are briefly described in a summary table, in the order mentioned within the paper (Appendix).

Second Tier Testing to Reduce the Number of Non-actionable Secondary Findings and False-Positive Referrals in Newborn Screening for Severe Combined Immunodeficiency

PURPOSE

Newborn screening (NBS) for severe combined immunodeficiency (SCID) is based on the detection of T-cell receptor excision circles (TRECs). TRECs are a sensitive biomarker for T-cell lymphopenia, but not specific for SCID. This creates a palette of secondary findings associated with low T-cells that require follow-up and treatment or are non-actionable. The high rate of (non-actionable) secondary findings and false-positive referrals raises questions about the harm-benefit-ratio of SCID screening, as referrals are associated with high emotional impact and anxiety for parents.

METHODS

An alternative quantitative TREC PCR with different primers was performed on NBS cards of referred newborns (N = 56) and epigenetic immune cell counting was used as for relative quantification of CD3 + T-cells (N = 59). Retrospective data was used to determine the reduction in referrals with a lower TREC cutoff value or an adjusted screening algorithm.

RESULTS

When analyzed with a second PCR with different primers, 45% of the referrals (25/56) had TREC levels above cutoff, including four false-positive cases in which two SNPs were identified. With epigenetic qPCR, 41% (24/59) of the referrals were within the range of the relative CD3 + T-cell counts of the healthy controls. Lowering the TREC cutoff value or adjusting the screening algorithm led to lower referral rates but did not prevent all false-positive referrals.

CONCLUSIONS

Second tier tests and adjustments of cutoff values or screening algorithms all have the potential to reduce the number of non-actionable secondary findings in NBS for SCID, although second tier tests are more effective in preventing false-positive referrals.

Immunological Findings and Clinical Outcomes of Infants With Positive Newborn Screening for Severe Combined Immunodeficiency From a Tertiary Care Center in the U.S

The implementation of severe combined immunodeficiency (SCID) newborn screening has played a pivotal role in identifying these patients early in life as well as detecting various milder forms of T cell lymphopenia (TCL). In this study we reviewed the diagnostic and clinical outcomes, and interesting immunology findings of term infants referred to a tertiary care center with abnormal newborn SCID screens over a 6-year period. Key findings included a 33% incidence of non-SCID TCL including infants with novel variants in FOXN1, TBX1, MYSM1, POLD1, and CD3E; 57% positivity rate of newborn SCID screening among infants with DiGeorge syndrome; and earlier diagnosis and improved transplant outcomes for SCID in infants diagnosed after compared to before implementation of routine screening. Our study is unique in terms of the extensive laboratory workup of abnormal SCID screens including lymphocyte subsets, measurement of thymic output (TREC and CD4TE), and lymphocyte proliferation to mitogens in nearly all infants. These data allowed us to observe a stronger positive correlation of the absolute CD3 count with CD4RTE than with TREC copies, and a weak positive correlation between CD4RTE and TREC copies. Finally, we did not observe a correlation between risk of TCL and history of prenatal or perinatal complications or low birth weight. Our study demonstrated SCID newborn screening improves disease outcomes, particularly in typical SCID, and allows early detection and discovery of novel variants of certain TCL-associated genetic conditions.

First Year of TREC-Based National SCID Screening in Sweden

Screening for severe combined immunodeficiency (SCID) was introduced into the Swedish newborn screening program in August 2019 and here we report the results of the first year. T cell receptor excision circles (TRECs), kappa-deleting element excision circles (KRECs), and actin beta (ACTB) levels were quantitated by multiplex qPCR from dried blood spots (DBS) of 115,786 newborns and children up to two years of age, as an approximation of the number of recently formed T and B cells and sample quality, respectively. Based on low TREC levels, 73 children were referred for clinical assessment which led to the diagnosis of T cell lymphopenia in 21 children. Of these, three were diagnosed with SCID. The screening performance for SCID as the outcome was sensitivity 100%, specificity 99.94%, positive predictive value (PPV) 4.11%, and negative predictive value (NPV) 100%. For the outcome T cell lymphopenia, PPV was 28.77%, and specificity was 99.95%. Based on the first year of screening, the incidence of SCID in the Swedish population was estimated to be 1:38,500 newborns.

Newborn Screening for Severe Combined Immunodeficiency: Do Preterm Infants Require Special Consideration?

The Wisconsin Newborn Screening (NBS) Program began screening for severe combined immunodeficiency (SCID) in 2008, using real-time PCR to quantitate T-cell receptor excision circles (TRECs) in DNA isolated from dried blood NBS specimens. Prompted by the observation that there were disproportionately more screening-positive cases in premature infants, we performed a study to assess whether there is a difference in TRECs between full-term and preterm newborns. Based on de-identified SCID data from 1 January to 30 June 2008, we evaluated the TRECs from 2510 preterm newborns (gestational age, 23-36 weeks) whose specimens were collected ≤72 h after birth. The TRECs from 5020 full-term newborns were included as controls. The relationship between TRECs and gestational age in weeks was estimated using linear regression analysis. The estimated increase in TRECs for every additional week of gestation is 9.60%. The 95% confidence interval is 8.95% to 10.25% (p ≤ 0.0001). Our data suggest that TRECs increase at a steady rate as gestational age increases. These results provide rationale for Wisconsin's existing premature infant screening procedure of recommending repeat NBS following an SCID screening positive in a premature infant instead of the flow cytometry confirmatory testing for SCID screening positives in full-term infants.