Pattern of Immunocompetent Peripheral Blood Cell Subpopulations in B-Cell Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma

Abstract

Background. In the WHO classification small lymphocytic lymphoma (SLL) and B-cell chronic lymphocytic leukemia (В-CLL) are combined into one nosological entity of lymphoid tumors due to their similar tumor cell immunophenotype. Up to now, there is no consensus on either their similarities or the differences between them. Distinction between В-CLL and SLL is drawn with respect to clinical and hematological manifestations of tumors. The reason for the differences that determine tumor spreading in a patient may lie in specific states of some immune system components. Comparison of immune system parameters within the CLL/SLL model provides a unique opportunity to trace the behavior of immunity indicators in local und disseminated pathogenetically similar neoplastic processes and to identify possible prognostic factors. Aim. To compare quantitative representations of peripheral blood lymphocyte subpopulations in SLL and В-CLL. Materials & Methods. Immunocompetent cells (relative and absolute Т- and NK-cell counts), immunophenotype, and tumor clone volume were assessed using multicolor flow cytometry based on the expression of СD3, CD4, CD8, CD16, CD19, CD20, CD23, CD5, CD79b, FMC7, CD22, CD43, CD38 antigens, and immunoglobulins light chain IgK and IgA. Before chemotherapy onset, the data of 17 SLL and 81 CLL patients (22 of them with B-lymphocyte count of 35-79 % and 59 with 80-99 %) were compared. As a control, peripheral blood lymphocyte subpopulations in 50 relatively healthy individuals (blood donors) were analyzed. Results. The analysis of NK-cells and Т-lymphocyte subpopulations in SLL showed the preserved number of killer/cytotoxic cells of innate and adaptive immunity (CD16+, CD8+), the reduction of CD4+ Т-cell count, and CD4/CD8 ratio. In CLL a considerable increase of main subpopulations of residual normal lymphocytes was detected. However, the extent of their increase proved to be considerably lower than increase in the volume of tumor B-cell clone, which signifies a rising exhaustion of immune system effector components. Conclusion. The present study yielded characteristic features of residual normal lymphocyte subpopulations in SLL and CLL with different leukocytosis grades. SLL patients demonstrated the reduction of relative and absolute Т-cell counts with Т-helper (CD3+, СD4+) phenotype, and the increase of cytotoxic CD8+ Т-cells and NK-cells. Lymphocytosis (35-79 %) in the CLL-I group was due not only to tumor В-cells but also to Т-killer (CD16+, CD8+) and Т-helper (CD4+) absolute counts, which were 1.7-2.5 times higher than in SLL and the control group. Residual lymphocyte subpopulation pattern (80-99 %) in the CLL-II group compared with the control group was characterized by a significantly higher absolute count of CD8+ T-cells and CD16+ NK-cells, as well as higher Т-regulatory index compared with SLL and CLL-I groups. These data point to the necessity for further and more detailed study of residual lymphocyte subpopulation pattern within the CLL/SLL model in order to identify additional predisposing factors.