Immunosuppressive Treg cells acquire the phenotype of effector-T cells in chronic lymphocytic leukemia patients.

Background: In chronic lymphocytic leukemia (CLL) disease onset and progression are influenced by the behavior of specific CD4 T cell subsets, such as T regulatory cells (Tregs). Here, we focused on the phenotypic and functional characterization of Tregs in CLL patients to improve our understanding of the putative mechanism by which these cells combine immunosuppressive and effector-like properties.

Methods: Peripheral blood mononuclear cells were isolated from newly diagnosed CLL patients (n = 25) and healthy volunteers (n = 25). The phenotypic and functional characterization of Tregs and their subsets was assessed by flow cytometry. In vitro analysis of TH1, TH2, TH17 and Tregs cytokines was evaluated by IFN-γ, IL-4, IL-17A and IL-10 secretion assays. The transcriptional profiling of 84 genes panel was evaluated by RT Profiler PCR Array. Statistical analysis was carried out using exact non parametric Mann-Whitney U test.

Results: In all CLL samples, we found a significant increase in the frequency of IL-10-secreting Tregs and Tregs subsets, a significant rise of TH2 IL-4 and TH17 IL-17A cells, and a higher percentage of IFN-γ/IL-10 and IL-4/IL-10 double-releasing CD4 T cells. In addition, we also observed the up-regulation of innate immunity genes and the down-regulation of adaptive immunity ones.

Conclusions: Our data show that Tregs switch towards an effector-like phenotype in CLL patients. This multifaceted behavior is accompanied by an altered cytokine profiling and transcriptional program of immune genes, leading to a dysfunction in immune response in the peripheral blood environment of CLL patients.