NEWBORN SCREENING FOR SEVERE COMBINED

IMMUNE DEFICIENCYNevin W Wilson, MD

Professor and Chair of Pediatrics

Section of Allergy and Immunology

UNLV School of Medicine

WHAT IS SEVERE COMBINED IMMUNE DEFICIENCY

INTRODUCTION• Severe Combined Immune Deficiency (SCID) are genetic disorders in

which both B cells and T cells of the adaptive immune system are impaired.

• SCID is a severe form of inherited immunodeficiency

• Known as the Bubble Boy disease

• Results in an immune system so highly compromised that it is essentially absent.

• At high risk for life-threatening infections early in life: Frequent, severe, persistent and hard to treat.

• Delay in detection common: Infants look normal and carry maternal antibodies.

LEAKY SCID

• Patients with leaky SCID have 300–1500 T cells/µL or more but lack naïve T cells.

• Their T cells are functionally impaired and have limited diversity, and TME is not detected.

• A subset of infants with leaky SCID have expansion of oligoclonal dysregulated T cells, leading to adenopathy, erythroderma with cutaneous and intestinal T-cell infiltration, hepatomegaly, eosinophilia, and highly increased IgE levels, features collectively known as Omenn syndrome.

TREATMENT

• Hematopoietic cell transplant is the definitive treatment for SCID when there is a human leukocyte antigen-matched sibling, the ideal donor.

• The key to successful treatment outcomes is to avoid infection in the infant before transplant

• In 2014, reported that infants who received transplants before 3.5 months of age had a 5-year survival rate of 94% as did infants older than 3.5 months but with no history of infection (90%) or whose infections had fully resolved with treatment by the time of HCT (82%).

• In contrast, children older than 3.5 months with active infection at the time of HCT and no HLA-matched sibling had the lowest survival rate (50%).

• Gene therapy (GT) for correction of autologous hematopoietic stem cells through research protocols has been successful for children with ADA and X-linked (IL2RG) SCID. Similar GT opportunities for Artemis SCID will soon be available.

NEWBORN SCREENING AND TRECS

SEVERE COMBINED IMMUNE DEFICIENCY

• The diverse specificities of T cells develop exclusively in the thymus.

• Formation of TRECs, DNA byproducts of T cell receptor (TCR) gene rearrangement, occurs during the programmed rearrangements of variable, diversity and joining segments of TCR genes that thymocytes undergo, and absence of TRECs correlates with a lack of T-cell production.

• All infants with SCID fail to generate a diverse repertoire of mature T cells, and consequently have undetectable or very low numbers of TRECs

Chase. Curr. Opin. All. Imm. 2010, 10:521–5256

T-CELL RECEPTOR EXCISION CIRCLES (TRECS)

Generation of a unique T-cell receptor (TCR) clone begins by random selection and combination of TCR regions in germ line DNA

The excised DNA sequences form a non-replicating episome

TREC-positive cells are recent thymic emigrants

EPIDEMIOLOGY OF SCID SINCE NEWBORN SCREENING

• Wisconsin was the first state to implement SCID NBS in 2008.

• In 2014, 11 NBS programs had screened over 3,030,083 newborns with a TREC test

• Screening detected 52 cases of typical SCID, leaky SCID, and Omenn syndrome affecting 1 in 58,000 infants.

• Two years of SCID NBS data from California identified birth prevalence rates of non-SCID TCL at approximately 1/20,000.

• 46 screening programs including those in the Navajo nation and Puerto Rico conduct SCID NBS, with the remaining states soon to follow.

• In 2016, NBS captured 90% of cases of SCID in the US. In contrast, in 2010 90% of new SCID cases enrolled in studies of the North American Primary Immune Deficiency Consortium were diagnosed through family history or after infection developed.

NEWBORN SCREENING IN CALIFORNIA

California’s Laboratory Experience Results of Testing

(August 16 – December 31, 2010)

Number Screened: 217,515 (initial NBS specimen)

– Positive*: 12 (.01%)• SCID 4• DiGeorge Syndrome 1• Non-SCID T Cell Lymphopenia 1• Negative Flow Cytometry 3• Expired 3

– Inconclusive Results: 229 (.11%)• Positive* 10• Inconclusive* 3• Negative 127• Expired 23• Lost to Follow-up 7

* Positives and inconclusives on 2nd heelstick go on to Flow Cytometry

217,515 initial specimens157 Second Heelsticks

(Total 217,672)

26 Referred for Flow Cytometry

• SCID 5

• Di George Syndrome 2

• Non-SCID T Cell Lymphopenia 2

• Negative 10

• Expired 4

• Pending 3

California’s Laboratory Experience Evaluation of Screened Positive Infants

(August 16 – December 31, 2010)

California’s Laboratory Experience Results of Testing

(August 16 – December 31, 2010)

From Second Heelstick

- Positive: 10• DiGeorge Syndrome 1• Non-SCID T Cell Lymphopenia 1• Negative Flow Cytometry 4• Expired 1• Pending 3

- Inconclusive 3• SCID * 1• Negative Flow Cytometry 2

Table 1. Frequency of non-SCID conditions identified by SCID NBS in California.

Conditions %

Multisyndromes with variable T-cell deficiency

DiGeorge/chromosome 22q11.2 deletion 57

Trisomy 21 15

Ataxia telangiectasia 3

CHARGE syndrome 2

Secondary T lymphopenia

Congenital cardiac anomalies 25

Other congenital anomalies 38

Vascular leakage, third spacing, hydrops 13

Neonatal leukemia 3

Maternal immunosuppressive medications 3–5

Extreme preterm birth (T cells become normal over time)

Idiopathic T lymphopenia (no gene defect, few naïve cells, impaired T cell function)

OTHER CAUSES OF LYMPHOPENIA IN NEWBORNS

• NBS also identifies infants with low TREC numbers who do not have SCID but nonetheless have few T lymphocytes in the peripheral blood

• Which is termed T-cell lymphopenia

• Most of these infants have recognized conditions, such as DiGeorge syndrome

• Secondary T lymphopenia due to conditions

• preterm birth,

• lymphatic losses due to cardiothoracic surgery.

• Others still have low T-cells with no apparent underlying cause, and are diagnosed with idiopathic T-cell lymphopenia

Previously referred to as “Variant SCID”

TREC ASSAY PITFALLS AND FUTURE DIRECTIONS

Reference ranges have not been established for neonates < 37 weeks corrected gestation

Many abnormal TREC results have lead to diagnosis of undefined T-cell immunodeficiencies; without identifying underlying genetic defect optimal management remains uncertain

Multi-plex quantitative PCR methods are being developed to screen for additional genetic diseases

WHAT DO WE DO WITH A POSITIVE RESULT?

CONCLUSIONS

• Advances in SCID NBS over the last 9 years have profoundly improved outcomes of children born with SCID in the US.

• Each state institutes different methods of TREC assay and follow up and tracking of abnormal results, but detection of typical and leaky SCID by TREC screening has been universally successful.

PublicationsIdentification of an infant with severe combined immunodeficiency by newborn screening.Hale JE, Bonilla FA, Pai SY, Gerstel-Thompson JL, Notarangelo LD, Eaton RB, Comeau AM. J Allergy Clin Immunol. 2010 Nov;126(5):1073-4. Epub 2010 Oct 8.

A multiplex immunoassay using the Guthrie specimen to detect T-cell deficiencies including severe combined immunodeficiency disease.Janik DK, Lindau-Shepard B, Comeau AM, Pass KA. Clin Chem. 2010 Sep;56(9):1460-5. Epub 2010 Jul 21.

High-throughput multiplexed T-cell-receptor excision circle quantitative PCR assay with internal controls for detection of severe combined immunodeficiency in population-based newborn screening.Gerstel-Thompson JL, Wilkey JF, Baptiste JC, Navas JS, Pai SY, Pass KA, Eaton RB, Comeau AM.Clin Chem. 2010 Sep;56(9):1466-74. Epub 2010 Jul 21.

Guidelines for implementation of population-based newborn screening for severe combined immunodeficiency.Comeau AM, Hale JE, Pai SY, Bonilla FA, Notarangelo LD, Pasternack MS, Meissner HC, Cooper ER, DeMaria A, Sahai I, Eaton RB.J Inherit Metab Dis. 2010 Oct;33(Suppl 2):S273-81. Epub 2010 May 20.

Publications

Development of a routine newborn screening protocol for severe combined immunodeficiency.Baker MW, Grossman WJ, Laessig RH, Hoffman GL, Brokopp CD, Kurtycz DF, Cogley MF, Litsheim TJ, Katcher ML, Routes JM.J Allergy Clin Immunol. 2009 Sep;124(3):522-7. Epub 2009 May 31.

Statewide newborn screening for severe T-cell lymphopenia.Routes JM, Grossman WJ, Verbsky J, Laessig RH, Hoffman GL, Brokopp CD, Baker MW.JAMA. 2009 Dec 9;302(22):2465-70.

Implementing routine testing for severe combined immunodeficiency within Wisconsin's newborn screening program.Baker MW, Laessig RH, Katcher ML, Routes JM, Grossman WJ, Verbsky J, Kurtycz DF, Brokopp CD.Public Health Rep. 2010 May-Jun;125 Suppl 2:88-95.

NEVIN W. WILSON, MDIMMUNOLOGY,

DEPARTMENT OF PEDIATRICSUNLV SCHOOL OF MEDICINE1524 PINTO LANE, 2ND FLOORLAS VEGAS, NEVADA 89106

PHONE 702-992-6834FAX 702-671-2233

CELL: 775-815-8269EMAIL: NEVIN.WILSON@UNLV.EDU