In patients with CML, cellular immune deficiency is a common feature which may be due to decreased output of recent thymic emigrants, the abnormal expression of T cell receptor repertoire and, may in part, due to altered expression of TCR-CD3 complex. Our previous study showed decreased δRec-ψJα sjTRECs level and skewed TRBV repertoire in peripheral blood mononuclear cells (PBMCs) from CML patients [19, 21]. And TCR ζ chain expression was decreased in T cells from patients with CML [22, 23].
In order to further evaluate the T-cell immune function, the T cell proliferative history in CML patients was analyzed. The sjTRECs-content in PBMCs and CD3+ T cells from 48 CML cases was determined. The results confirmed our previous smaller study . We showed a dramatic reduction of sjTRECs values in CML patients. In some cases no sjTRECs could be detected in 40 000 T cells. This suggests poor thymic output in CML patients, which may be even more pronounced than in ALL patients . To date there are only a few papers describing TRECs level in hematopoietic malignancies [16, 17]. The exact value of sjTRECs level in PBMCs from CML patients are influenced by contaminating normal non-T cells and leukemia blast cells; therefore the sjTRECs numbers were normalized with the percentage of CD3+cells in the analyzed samples. Furthermore, we analyzed sjTRECs in sorted CD4+ and CD8+ T cells. This is the most sensitive and accurate method for quantitation of naïve T-cells. It allows also the comparison of sjTRECs levels in CD4+ and CD8+ subsets. The levels of sjTRECs-expressing CD4+ and CD8+ T cells were significantly decreased in CML patients, as compared with age and sex matched healthy individuals. The decrease of sjTRECs levels was similar in both T cell subsets. These findings suggest that an impaired thymic output function and, as a consequence, an altered ability to maintain T cell homeostasis, which may play an important role in the immunodeficiency in CML patients. However, whether this is due to the clonal expansion of T-cells to antigens, for example leukemia associated antigens, or reflects the impairment of immune function associated with the malignancy, remains an open question [7, 24–27].
Pido-Lopez et al showed that the decline in number of recent thymic emigrants in the blood with increasing age is gender-linked . Peripheral blood from female contained significantly higher levels of sjTRECs per CD3+ T cell than blood from males. Also in children, the number of sjTRECs was higher in healthy girls than in healthy boys, and a similar pattern was evident in T-cell malignancies . In the present study, we observed slightly, but in-significantly higher sjTRECs levels in healthy females, however, the number of sjTRECs was statistically higher in PBMCs and CD8+ T cells from female CML patients.
The majority of studies published previously focused only on the total thymic output, as measured by quantitative analysis of δRec-ψJα sjTRECs . This approach doesn't allow the evaluation of the complexity of thymic output in different TRBV subfamily naïve T cells, which is an important factor in immune competence. In this study, we analyzed the total 23 subfamilies of TRBV-DB1 sjTRECs in PBMCs, CD4+ and CD8+ T-cells from CML patients by a semi-nested PCR. The results indicate that the percentage of cases positive for TRBV-DB1 sjTRECs varies in different BV subfamilies in healthy controls; the highest for TRBV1, 3, 4, 10, 12-14, 17 and V21, which could be detected in all 10 samples (at 2 × 105 PBMCs). The most important observation in this study was the significantly lower frequency of 23 TRBV-BD1 sjTRECs in PBMCs, as well as in CD4+ and CD8+ T cells from CML patients as compared with healthy individuals, indicating poor thymic output in CML patients. The results further support and explain the significant reduction of recent thymic emigrant numbers in peripheral blood of CML patients, as measured by quantitative detection of δRec-ψJα sjTRECs.
In conclusion, this is, to our knowledge, the first characterization of thymic output function in CD4+ and CD8+ T cells from CML patients based on analyses of both δRec-ψJα sjTRECs and TRBV-DB1 subfamily specific sjTRECs. We showed a prominent decrease of sjTRECs levels in CML, indicating the reduction of recent thymic emigrants affects the majority of TRBV subfamilies.