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Abstract
The clinical experience gathered throughout the years has raised awareness of primary immunodeficiency diseases (PIDD). T cell receptor excision circles (TREC) and kappa-deleting recombination excision circles (KREC) assays for thymic and bone marrow outputs measurement have been widely implemented in newborn screening (NBS) programs for Severe Combined Immunodeficiency. The potential applications of combined TREC and KREC assay in PIDD diagnosis and immune reconstitution monitoring in non-neonatal patients have been suggested. Given that ethnicity, gender, and age can contribute to variations in immunity, defining the reference intervals of TREC and KREC levels in the local population is crucial for setting up cut-offs for PIDD diagnosis. In this retrospective study, 479 healthy Chinese sibling donors (240 males and 239 females; age range: 1 month−74 years) from Hong Kong were tested for TREC and KREC levels using a simultaneous quantitative real-time PCR assay. Age-specific 5th–95th percentile reference intervals of TREC and KREC levels (expressed in copies per μL blood and copies per 106 cells) were established in both pediatric and adult age groups. Significant inverse correlations between age and both TREC and KREC levels were observed in the pediatric age group. A significant higher KREC level was observed in females than males after 9–12 years of age but not for TREC. Low TREC or KREC levels were detected in patients diagnosed with mild or severe PIDD. This assay with the established local reference intervals would allow accurate diagnosis of PIDD, and potentially monitoring immune reconstitution following haematopoietic stem cell transplantation or highly active anti-retroviral therapy in the future.
Highlights
Tand B cells undergo V(D)J recombination to generate diverse and functional TCR and BCR repertoires, and these are crucial processes in the maturation of T and B cells that allow the recognition of unlimited numbers of antigens [1]
The medians and ranges of T cell receptor excision circles (TREC) and Kappa-deleting recombination excision circles (KREC) levels of male and female in different age groups were provided in the Supplementary Tables 1, 2
We found the TREC levels decreased with age, which is suggested to be related to thymic involution [37], and lower TREC and KREC levels result from dilution during homeostatic replication of T or B memory cells or antigen-induced proliferation [9, 38]
Summary
Tand B cells undergo V(D)J recombination to generate diverse and functional TCR and BCR repertoires, and these are crucial processes in the maturation of T and B cells that allow the recognition of unlimited numbers of antigens [1]. During the TCR rearrangement process, excised DNA fragments create T cell receptor excision circles (TREC) that are exported to the T cell cytoplasm [2, 3]. The δRec-ψJα signal joint TREC (sjTREC) is produced during TCRD deletion and detected in ∼70% of (alpha-beta) αβ T cells. They are considered the most optimal target to measure the evaluation of thymic output [4,5,6]. Kappa-deleting recombination excision circles (KREC) are produced during BCR rearrangement in naïve B cells and are analogous to TREC [7]. SjKREC formed during intronRSS-Kde rearrangements in IGK locus is a robust target for the evaluation of B cell neogenesis from bone marrow [8, 9]
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