T-cell receptor excision circles (TREC) used as a marker for recent thymic emigrants. These circles are a by-product of the initial T cell receptor gene rearrangement in naïve T cells. TRECs are stable but do not replicate. Therefore, their concentration is reduced after cell division. TREC concentration can be used to evaluate immune reconstitution after BMT, intensive chemotherapy, or therapy for immunodeficiency.
The generation and maintenance of a diverse repertoire of T cells is an important component of T cell immunity. The T cell receptor (TCR) repertoire of mature T cells is the result of complex rearrangements of the α and β TCR genes followed by selection processes resulting in approximately 25 million different TCR in health adults.
Several factors influence the TCR repertoire of each individual including negative and positive selection in the thymus, HLA type, and infections. After hematopoietic stem cell transplantation, the T cell receptor repertoire must be reconstituted. Reconstitution of the T-cell repertoire is influenced by several factors including pre-HSCT conditioning, the number of T cells in the donor graft, thymic function, infections, GVHD, immunosuppressive medications, and interactions between recipient and donor hematopoietic cells. In general, the repertoire complexity of the marrow correlates with the immune function of the recipient.
TCR diversity is created by rearrangement and fusion between exons encoding the V, D, and J segments of the gene along with insertion and deletion of nucleotides at junctional regions. TCR families can be selectively amplified using primers that are specific for each TCR gene family and diversity within the family can be evaluated by determining the length of amplicons spanning the complementary determining region 3 (CDR3) which plays an important role in defining TCR specificity.
This is a robust method with sufficient sensitivity to detect differences that are correlated with the clinical status of transplant recipients. It is generally accepted that normal, healthy individuals show a Gaussian distribution for the amount of each allowed TCR length for each TCR gene family. The distribution becomes abnormal (i.e., "oligoclonal" with one or a small number of peaks and non-Gaussian distribution, or "skewed" with several peaks but non-Gaussian distribution) under a variety of circumstances (e.g., transplant, infection, GvHD).
MIC Genotyping and MIC Antibody Detection
The human major histocompatibility complex class I chain-related gene A (MICA) is both very polymorphic and the protein products cause allogeneic immune responses similar to those associated with HLA disparity. MICA typing can be used to detect these differences and MIC antibodies are an indicator of an immune response to those differences. MICA antibodies have been associated with rejection of solid organ allografts. Their role in hematopoietic stem cell transplantation is under investigation.
The ITL laboratory has a long-standing record of research in HLA polymorphism and its relevance to clinical transplantation.
Current Projects Include:
Chimerism and Microchimerism
The laboratory researches the role of mixed chimerism in allogeneic transplantation and human disease, specifically:
The ITL laboratory conducts research in the importance of pre/post transplant antibodies in patients peripheral blood. The impact of these antibodies can be assessed by comparing the wide variety of assay results we collect on individual patients with their clinical outcomes.
Continuing work also includes: