Nonsevere combined immunodeficiency T-cell lymphopenia identified through newborn screening

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.

Efficient screening strategies for severe combined immunodeficiencies in newborns

INTRODUCTION

Severe combined immunodeficiency (SCID) is one of the most severe forms of inborn errors of immunity (IEI), affecting both cellular and humoral immunity. Without curative treatment such as hematopoietic stem cell transplantation or gene therapy, affected infants die within the first year of life. Due to the severity of the disease, asymptomatic status early in life, and improved survival in the absence of pretransplant infections, SCID was considered a suitable candidate for newborn screening (NBS).

AREAS COVERED

Many countries have introduced SCID screening based on T-cell receptor excision circle (TREC) detection in their NBS programs. Screening an entire population is a radical departure from previous paradigms in the field of immunology. Efficient screening strategies are cost-efficient and balance high sensitivity while preventing high numbers of referrals. NBS for SCID is accompanied by (actionable) secondary findings, but many NBS programs have optimized their screening strategy by adjusting algorithms or including second-tier tests. Harmonization of screening terminology is of great importance for international shared learning.

EXPERT OPINION

The expansion of NBS is driven by the development of new test modalities and treatment options. In the near future, other techniques such as next-generation sequencing will pave the way for NBS of other IEI. Exciting times await for population-based screening programs.

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.

TREC Screening for WHIM Syndrome

PURPOSE

T cell receptor excision circle (TREC) quantification is a recent addition to newborn screening (NBS) programs and is intended to identify infants with severe combined immunodeficiencies (SCID). However, other primary immunodeficiency diseases (PID) have also been identified as the result of TREC screening. We recently reported a newborn with a low TREC level on day 1 of life who was diagnosed with WHIM (warts, hypogammaglobulinemia, infections, myelokathexis) syndrome, a non-SCID primary immunodeficiency caused by mutations in the chemokine receptor CXCR4.

METHODS

We have now retrospectively reviewed the birth and clinical histories of all known WHIM infants born after the implementation of NBS for SCID.

RESULTS

We identified six infants with confirmed WHIM syndrome who also had TREC quantification on NBS. Three of the six WHIM infants had low TREC levels on NBS. All six patients were lymphopenic but only one infant had a T cell count below 1,500 cells/μL. The most common clinical manifestation was viral bronchiolitis requiring hospitalization. One infant died of complications related to Tetralogy of Fallot, a known WHIM phenotype.

CONCLUSION

The results suggest that WHIM syndrome should be considered in the differential diagnosis of newborns with low NBS TREC levels.

TRIAL REGISTRATION

Not applicable.

Characterization of Infants with Idiopathic Transient and Persistent T Cell Lymphopenia Identified by Newborn Screening-a Single-Center Experience in New York State

PURPOSE

Newborn screening (NBS) quantifies T cell receptor excision circles (TREC) and identifies infants with T cell lymphopenia (TCL). This study elucidates the demographics, laboratory characteristics, genetics, and clinical outcomes following live viral vaccine administration of term infants with transient or persistent idiopathic TCL.

METHODS

A single-center retrospective analysis was performed from September 2010 through June 2018. Laboratory variables were compared with Mann-Whitney tests. Correlations between initial TREC levels and T cell counts were determined by Spearman tests.

RESULTS

Twenty-two transient and 21 persistent TCL infants were identified. Males comprised 68% of the transient and 52% of the persistent TCL cohorts. Whites comprised 23% of the transient and 29% of the persistent cohorts. Median initial TREC levels did not differ (66 vs. 60 TRECs/μL of blood, P = 0.58). The transient cohort had higher median initial CD3⁺ (2135 vs. 1169 cells/μL, P < 0.001), CD4⁺ (1460 vs. 866 cells/μL, P < 0.001), and CD8⁺ (538 vs. 277 cells/μL, P < 0.001) counts. The median age of resolution for the transient cohort was 38 days. Genetic testing revealed 2 genes of interest which warrant further study and several variants of uncertain significance in immunology-related genes in the persistent cohort. 19 transient and 14 persistent subjects received the initial rotavirus and/or MMRV immunization. No adverse reactions to live viral vaccines were reported in either cohort.

CONCLUSION

Transient and persistent TCL infants differ by demographic, laboratory, and clinical characteristics. Select transient and persistent TCL patients may safely receive live attenuated viral vaccines, but larger confirmatory studies are needed.

Follow-Up for an Abnormal Newborn Screen for Severe Combined Immunodeficiencies (NBS SCID): A Clinical Immunology Society (CIS) Survey of Current Practices

Severe combined immunodeficiency (SCID) includes a group of monogenic disorders presenting with severe T cell lymphopenia (TCL) and high mortality, if untreated. The newborn screen (NBS) for SCID, included in the recommended universal screening panel (RUSP), has been widely adopted across the US and in many other countries. However, there is a lack of consensus regarding follow-up testing to confirm an abnormal result. The Clinical Immunology Society (CIS) membership was surveyed for confirmatory testing practices for an abnormal NBS SCID result, which included consideration of gestational age and birth weight, as well as flow cytometry panels. Considerable variability was observed in follow-up practices for an abnormal NBS SCID with 49% confirming by flow cytometry, 39% repeating TREC analysis, and the remainder either taking prematurity into consideration for subsequent testing or proceeding directly to genetic analysis. More than 50% of respondents did not take prematurity into consideration when determining follow-up. Confirmation of abnormal NBS SCID in premature infants continues to be challenging and is handled variably across centers, with some choosing to repeat NBS SCID testing until normal or until the infant reaches an adjusted gestational age of 37 weeks. A substantial proportion of respondents included naïve and memory T cell analysis with T, B, and NK lymphocyte subset quantitation in the initial confirmatory panel. These results have the potential to influence the diagnosis and management of an infant with TCL as illustrated by the clinical cases presented herein. Our data indicate that there is clearly a strong need for harmonization of follow-up testing for an abnormal NBS SCID result.