Identification of non-severe combined immune deficiency T-cell lymphopenia at newborn screening for severe combined immune deficiency

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.

Natural history of infants with non-SCID T cell lymphopenia identified on newborn screen

Newborn screening (NBS) for severe combined immunodeficiency (SCID) can identify infants with non-SCID T cell lymphopenia (TCL). The purpose of this study was to characterize the natural history and genetic findings of infants with non-SCID TCL identified on NBS. We analyzed data from 80 infants with non-SCID TCL in the mid-Atlantic region between 2012 and 2019. 66 patients underwent genetic testing and 41 (51%) had identified genetic variant(s). The most common genetic variants were thymic defects (33%), defects with unknown mechanisms (12%) and bone marrow production defects (5%). The genetic cohort had significantly lower median initial CD3+, CD4+, CD8+ and CD4/CD45RA+ T cell counts compared to the non-genetic cohort. Thirty-six (45%) had either viral, bacterial, or fungal infection; only one patient had an opportunistic infection (vaccine strain VZV infection). Twenty-six (31%) of patients had resolution of TCL during the study period.

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.

Recommendations for uniform definitions used in newborn screening for severe combined immunodeficiency

BACKGROUND

Public health newborn screening (NBS) programs continuously evolve, taking advantage of international shared learning. NBS for severe combined immunodeficiency (SCID) has recently been introduced in many countries. However, comparison of screening outcomes has been hampered by use of disparate terminology and imprecise or variable case definitions for non-SCID conditions with T-cell lymphopenia.

OBJECTIVES

This study sought to determine whether standardized screening terminology could overcome a Babylonian confusion and whether improved case definitions would promote international exchange of knowledge.

METHODS

A systematic literature review highlighted the diverse terminology in SCID NBS programs internationally. While, as expected, individual screening strategies and tests were tailored to each program, we found uniform terminology to be lacking in definitions of disease targets, sensitivity, and specificity required for comparisons across programs.

RESULTS

The study's recommendations reflect current evidence from literature and existing guidelines coupled with opinion of experts in public health screening and immunology. Terminologies were aligned. The distinction between actionable and nonactionable T-cell lymphopenia among non-SCID cases was clarified, the former being infants with T-cell lymphopenia who could benefit from interventions such as protection from infections, antibiotic prophylaxis, and live-attenuated vaccine avoidance.

CONCLUSIONS

By bringing together the previously unconnected public health screening community and clinical immunology community, these SCID NBS deliberations bridged the gaps in language and perspective between these disciplines. This study proposes that international specialists in each disorder for which NBS is performed join forces to hone their definitions and recommend uniform registration of outcomes of NBS. Standardization of terminology will promote international exchange of knowledge and optimize each phase of NBS and follow-up care, advancing health outcomes for children worldwide.

When Screening for Severe Combined Immunodeficiency (SCID) with T Cell Receptor Excision Circles Is Not SCID: a Case-Based Review

Newborn screening efforts focusing on the quantification of T cell receptor excision circles (TRECs), as a biomarker for abnormal thymic production of T cells, have allowed for the identification and definitive treatment of severe combined immunodeficiency (SCID) in asymptomatic neonates. With the adoption of TREC quantification in Guthrie cards across the USA and abroad, typical, and atypical SCID constitutes only ~ 10% of cases identified with abnormal TRECs associated with T cell lymphopenia. Several other non-SCID-related conditions may be identified by newborn screening in a term infant. Thus, it is important for physicians to recognize that other factors, such as prematurity, are often associated with low TRECs initially, but often improve with age. This paper focuses on a challenge that immunologists face: the diagnostic evaluation and management of cases in which abnormal TRECs are associated with variants of T cell lymphopenia in the absence of a genetically defined form of typical or atypical SCID. Various syndromes associated with T cell impairment, secondary forms of T cell lymphopenia, and idiopathic T cell lymphopenia are identified using this screening approach. Yet there is no consensus or guidelines to assist in the evaluation and management of these newborns, despite representing 90% of the patients identified, resulting in significant work for the clinical teams until a diagnosis is made. Using a case-based approach, we review pearls relevant to the evaluation of these newborns, as well as the management dilemmas for the families and team related to the resolution of genetic ambiguities.

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.

Asymptomatic Infant With Atypical SCID and Novel Hypomorphic RAG Variant Identified by Newborn Screening: A Diagnostic and Treatment Dilemma

The T-cell receptor excision circle (TREC) assay detects T-cell lymphopenia (TCL) in newborns and is especially important to identify severe combined immunodeficiency (SCID). A spectrum of SCID variants and non-SCID conditions that present with TCL are being discovered with increasing frequency by newborn screening (NBS). Recombination-activating gene (RAG) deficiency is one the most common causes of classical and atypical SCID and other conditions with immune dysregulation. We present the case of an asymptomatic male with undetectable TRECs on NBS at 1 week of age. The asymptomatic newborn was found to have severe TCL, but normal B cell quantities and lymphocyte proliferation upon mitogen stimulation. Next generation sequencing revealed compound heterozygous hypomorphic RAG variants, one of which was novel. The moderately decreased recombinase activity of the RAG variants (16 and 40%) resulted in abnormal T and B-cell receptor repertoires, decreased fraction of CD3+ TCRVα7.2⁺ T cells and an immune phenotype consistent with the RAG hypomorphic variants. The patient underwent successful treatment with hematopoietic stem cell transplantation (HSCT) at 5 months of age. This case illustrates how after identification of a novel RAG variant, in vitro studies are important to confirm the pathogenicity of the variant. This confirmation allows the clinician to expedite definitive treatment with HSCT in an asymptomatic phase, mitigating the risk of serious infectious and non-infectious complications.