Can Quantification of sjTRECs be Used to Distinguish Between SCID and Non-SCID Piglets?

Severe combined immune deficiency (SCID) is a genetic defect that disrupts a major part of the adaptive immune system through the lack of B and T cells. Natural mutations leading to this defect have been found in humans, horses, dogs and recently also in our pigs. Sequencing of the region of interest is ongoing in order to find the causative mutation. In this abstract, we discuss the screening for T cell functional characteristics in non-SCID piglets versus SCID littermates, and this for two different SCID genotypes. To detect T cells with rearranged T cell receptor genes in these pigs the presence/absence of signal joint TCR rearrangement excision circles (sjTRECs) was determined. sjTRECs are byproducts formed during V-D-J rearrangements in developing αβ T lymphocytes. These extra-chromosomal DNA circles are very stable yet do not replicate during mitosis; therefore, the amount of sjTRECs equals the amount of naïve αβ T cells. A quantitative PCR was performed to measure sjTREC sequences present in DNA extracted from primary and secondary lymphoid organs (thymus, bone marrow, spleen, mesenteric lymph nodes) taken at necropsy, and from peripheral blood and PBMCs collected at several post-natal time points. Preliminary results indicate that sjTREC molecules are detected only in non-SCID pigs. If sjTREC quantification differs significantly between SCID and non-SCID pigs, the latter will become even more important when monitoring bone marrow transplanted SCID animals. Screening for sjTRECs at several time points after transplantation would offer a method to validate engraftment.