T Cell Receptor Excision Circles (TRECs) as a Marker of Thymic Output

Abstract

T-cell receptor excision circles (TRECs) and kappa-deleting recombination excision circles (KRECs) are circular DNA segments generated in T and B cells during their maturation in the thymus and bone marrow. These circularized DNA elements persist in the cells, are unable to replicate, and are diluted as a result of cell division. Thus they are considered markers of new lymphocyte output. The quantification of TRECs and KRECs, which can be reliably performed using real-time quantitative PCR, provides novel information in the screening, diagnosis and management of T- and B-cell immunity-related diseases as severe combined immune deficiency diseases (SCID). The measure of TRECs and KRECs has contributed to an improved characterization of the primary immune deficiency diseases, to the identification of patients' subgroups, and to the monitoring of stem cell transplantation and enzyme replacement therapy. For the same diseases, the TREC and KREC assays, introduced in the newborn screening program, allow early disease identification and may lead to discovery of new genetic defects. In addition, TRECs decline in an aging immune system in normal individuals can be used as a reference for studies on premature or early immunesenescence under particular disease conditions. Summary & Conclusion 152 In the current study, the aim was to establish a protocol for quantification of TRECs and KRECs in Egyptian individuals in our laboratory, and to set a reference range for the pediatric population in addition to evaluating age dependant changes in TRECs and KRECs levels in the healthy study group as a start for implementation of this technique in new born screening protocols for Primary immune deficiency diseases. Also its application as a marker for evaluation of stem cell replacement therapy in those patients in order to achieve best results for those patients with this only available line of treatment nowadays. This will allow early diagnosis of infants with PIDs mainly SCID with early proper medical interventions saving their lives and salvage the expenses lost as a result of their late or misdiagnosis. In this thesis, we assessed 50 apparently healthy individuals recruited from Ain Shams University Hospitals during routine check up with age ranging from 1 day to 16 years. Using combined TRECs and KRECs quantitative detection by real time PCR the study showed a significant decline in TRECs and KRECs with increasing age and a reference range for both TRECs and KRECs in the study group was set. In conclusion, TREC and KREC quantification can be considered a good estimate of recent thymic and bone marrow Summary & Conclusion 153 output as it ensures highly accurate quantitative results because unknown sample quantities are interpolated from standard curves built upon known amounts of starting material. Moreover it appeared that it is technically feasible to introduce the TRECs/KRECs assay into routine laboratory practice and it can be used in the near future both for new born screening and for a more critical monitoring of the rate of T- and B-cell immune reconstitution following HSCT.