Laboratory technology for population-based screening for severe combined immunodeficiency in neonates: the winner is T-cell receptor excision circles

Abstract

The most profound primary immunodeficiency disease, severe combined immunodeficiency (SCID), is fatal in infancy unless affected infants are provided with an adaptive immune system through allogeneic hematopoietic cell transplantation, enzyme replacement, or gene therapy. However, most infants with SCID lack a family history or any clinical clues before the onset of infections, making this serious but treatable disease a candidate for population-based newborn screening. Of several approaches considered for SCID screening, testing for T-cell receptor excision circles (TRECs), a DNA biomarker of normal T-cell development, has proved successful. TREC numbers can be measured in DNA isolated from the dried bloodspots already routinely collected for newborn screening. Infants with low or absent TRECs can thus be identified and referred for confirmatory testing and prompt intervention. TREC testing of newborns is now being performed in several states, indicating that this addition to the newborn screening panel can be successfully integrated into state public health programs.

Figure 1

Generation of the δRec-ΨJα TREC. The germ line configuration of the TCRA locus, with TCRD embedded, is shown at the top of the Figure, which also shows the points (gray dots) at which the DNA is cut to excise the TCRD locus in T lymphocyte progenitors destined to express the α and β TCRs. After excision, lower left, and ligation, lower right, of the δRec-ΨJα fragment to form a T cell receptor excision circle (TREC), PCR primers (horizontal arrows) can amplify a DNA junction fragment containing the joint.

Figure 2

TREC (○) and actin (×) copy number measured in DNA isolated from (A) 300 anonymous dried blood spots (DBS) obtained in newborn nurseries, showing one sample, far right, with failure of DNA amplification; and (B) 20 newborn nursery DBS recovered from storage from infants later found to have SCID.

Figure 2

TREC (○) and actin (×) copy number measured in DNA isolated from (A) 300 anonymous dried blood spots (DBS) obtained in newborn nurseries, showing one sample, far right, with failure of DNA amplification; and (B) 20 newborn nursery DBS recovered from storage from infants later found to have SCID.