Abstract
During early T lymphopoiesis, rearrangement of the V, D and J segments of the TCR genes result in deletion of the intervening chromosomal DNA and formation of circular excision circles, the so-called signal joint T-cell receptor rearrangement excision circles (sjTRECs, TRECs). TRECs are assumed to have a high stability, and can not multiply and consequently are diluted during T cell proliferation. It has been used to evaluate thymic function in T-cell immune reconstruction after treatment in HTLV-I-infected or stem cell transplantation. Defects of cellular immunity, however, may also play a role in hematologic malignancies. On the other hand, examination of T cell receptor (TCR) gene repertoire is important to analysis the immune status of the patients with malignant neoplasms, because clonal expansion of T cells permit the identification of specific antigen response of T cells. Little is known about the feature of T-cell immune state in CML. In order to evaluate the thymic recent output function and the expansion feature of TCR V beta subfamily T cells in patients with chronic myelogenous leukemia (CML in chronic phase), TRECs level and TCR V beta repertoire usage and clonality were analyzed. Quantitative detection of TRECs in DNA of peripheral blood mononuclear cells from 20 cases with CML, purified CD4+ or CD8+ cells from 3 cases with CML were preformed by real-time PCR (TaqMan) analysis. And the TRECs-number was related to the number of T-cells by determination of the number of CD3-positive cells. The expression and cloanlity analysis of TCR V beta repertoire were detected by RT-PCR and genescan technique in PBMC from the 14 out of 20 patients. 9 normal individuals served as controls. A dramatic reduction of TRECs values in patients with CML was showed. The mean value of TRECs was 0.06±0.16 copies /1000 T cells in CML patients and 6.84±4.71 copies /1000 T cells in normal individuals, respectively (p<0.01). In 16 out of 20 CML cases no TRECs copies could be detected in peripheral blood, and lower value of TRECs could be identified in sorted CD4+ or CD8+ cells. The expression of 1–12 V beta subfamilies was found in samples from 14 patients. Clonal expanded T cells from 13 cases could be identified in some V beta subfamilies, which were preferentially used in V beta 3, V beta 10, V beta 19, V beta 21 and V beta 22 subfamilies. In conclusion, this is, to our knowledge, the first description of TRECs level in CML patients. These results showed a prominent reduction of TREC levels in CML. The predominant usage and clonal expansion of TCR Vβ subfamily T cells could be identified in CML patients, indicating the host could have the ability for specific immune response to leukemia associated antigen, in despite of T cell immunodeficiency was showed in patients.
Quantification of T cell receptor rearrangement excision circles to estimate thymic function: an important new tool for endocrine-immune physiology