Characterization of regulatory T cells in patients with B-cell chronic lymphocytic leukemia

Abstract

Abstract. The status of the immune system of patients with B-cell chronic lymphocytic leukemia (B-CLL) is not yet sufficiently characterized. Clinically, B-CLL patients present immunodeficiency increasing along with disease progression and signs of autoimmunity. In the current study, we evaluated the expression of FOXP3 in CD4 + CD25 hi T regulatory lymphocytes (Treg) and their influence on immune response against tumor and viral antigens in the complex system of peripheral blood mononuclear cells. In 80 B-CLL patients, the frequency of Treg (CD4 + CD25 hi FOXP3 + ) cells was significantly higher in B-CLL patients when compared to healthy volunteers (HV) and increased with the progression of the disease (median: 8.24% in stage A, 11.24% in stage B and 12.57% in stage C according to the Binet classification). The frequency of Treg showed no correlation with prognostic markers such as ZAP-70, CD38 and HLA-G. Notably, Treg frequency correlated with serum levels of TNF (r 2 =0.45, p=0.001). T-cell immune responses against epitopes derived from the tumor-associated antigens survivin, fibromodulin and RHAMM as well as from the influenza matrix protein were evaluated. Functionally, higher frequencies of Treg correlated with decreased T-cell responses against viral and tumor antigens. In conclusion, we detected higher frequencies of Treg in B-CLL patients than in HV. Furthermore, Treg constitute the crucial mechanism of immunosuppression in B-CLL patients. IntroductionThe immune status of patients with B-cell chronic lymphocytic leukemia (B-CLL) is poorly characterized (1,2). Clinically, CLL patients present immunodeficiency, along with signs of autoimmunity (3). Several studies have aimed to characterize the immunity of B-CLL, however, results were ambiguous and difficult to interpret especially towards active immunotherapy for those patients (4). The graft vs. leukemia effect (5) as well as the 'spontaneous' remissions associated with an increased immunity against viral antigens (6) suggest that CLL cells may be targeted by a T cell-mediated immune response. Naturally occurring tumor-reactive T cells were found in some B-CLL patients (7). During disease progression, patients displayed signs of immunosuppression resulting in an impaired immune response against tumor-associated antigens (TAA) as well as against viral and bacterial antigens. Several immunosuppressive mechanisms allow CLL cells to escape from immunosurveillance. Recently, enhanced frequencies of CD4 + CD25 hi T regulatory cells (Treg) in B-CLL were reported by Beyer et al (8). Apart from CD4 + CD25 hi T cells, other immunomodulatory factors such as cytokines IL-10 and TGF-ß may suppress immune responses (9,10). Defects of immune response might be induced by a direct cell-cell contact suggesting the immunosuppressive role of the B-CLL cell itself that might be mediated by the expression of the non-classic human leukocyte antigen (HLA)-G protein (11). HLA-G released in its soluble (sHLA-G) form may also inhibit immune responses against TAA since sHLA-G in...

Regulatory T cells predict the time to initial treatment in early stage chronic lymphocytic leukemia

“…In line with previous reports, 19,20 T regs (the percentage of CD4-positive T cells) were significantly increased in patients with CLL compared with healthy controls, but the clinical implications of this finding have remained unclear. Experimental evidence in mouse models supports the idea of T reg induction by the tumor cell itself, 24 a finding that has been corroborated further in CLL, in which in vitro experiments have demonstrated that CLL cells themselves directly drive T reg induction.…”

“…T regs Are Elevated in High-Risk CLL In line with previous reports, 19,20 we were able to identify a statistically significant elevation in T regs (the percentage of CD4-positive T cells) in peripheral blood samples from patients with CLL compared with samples from 170 healthy controls, although there was considerable overlap between the 2 groups ( Fig. 3A) (P ¼ .001; Mann-Whitney U test).…”

“…For several solid tumors, there is a clear correlation between high T reg numbers (tumor infiltrating or circulating in the peripheral blood) and a poor prognosis. 10,11,21,22 Although previous reports have indicated an increase of T regs in the peripheral blood of patients with CLL compared with healthy controls, 19,20 their role in disease progression has remained unclear. The objective of the present study was to elucidate the possible clinical relevance of T reg numbers in early stage CLL.…”

Peptide vaccination elicits leukemia-associated antigen-specific cytotoxic CD8+ T-cell responses in patients with chronic lymphocytic leukemia

“…The median Treg frequency in our cohort was 4.22% (range: 2.5-8%), which is consistent with recent studies that report increased frequencies of Tregs in CLL. 18,24 There was no significant difference in Treg frequencies between clinical responders and nonresponders (median 6.12 vs 3.7%). Vaccination was associated with increased Treg frequencies in four patients; two were responders and two were nonresponders.…”

“…Throughout vaccination, we also monitored changes in regulatory CD4 þ T cells (Tregs), which were reported to have a crucial role in the modulation of immune responses in CLL patients. 17,18 Materials and methods…”