Clinical heterogeneity reflects biologic diversity in chronic lymphocytic leukemia

CXCR4 and SDF-1 expression in B-cell chronic lymphocytic leukemia and stage of the disease

The pathogenesis of B-cell chronic lymphocytic leukemia (B-CLL) has been linked to an overexpression of the chemokine receptor CXCR4 and increased in vitro functional response to its natural ligand CXCL12 (SDF-1). The CXCR4/SDF-1 system appears to be important for tissue localization and increased survival of B-CLL cells. The aim of our study was to examine if CXCR4 expression and SDF-1 blood levels were correlated to clinical and pathological stage of B-CLL. Flow cytometry and enzyme-linked immunosorbent assay (ELISA) techniques were used to determine CXCR4 expression and SDF-1 plasma levels, respectively, in a cohort of 51 patients diagnosed with B-CLL to correlate these measurements with several parameters that define the clinical stage of the disease. We confirmed that CXCR4 was consistently expressed on circulating B-CLL cells with a fluorescence intensity that was five-fold greater than in cells from healthy volunteers. There was a correlation between CXCR4 expression and leukocyte count ( r: 0.55, p<0.01), and CD19(+)/CD5(+ )cells ( r: 0.63, p<0.01). Interestingly, the group of B-CLL patients showed lower SDF-1 plasma levels compared to the control group. However, there was no correlation between CXCR4 or SDF-1 expression and the clinical stage of disease or the pattern of bone marrow infiltration. The results obtained suggest that other factors, and not only alteration in the SDF-1/CXCR4 chemokine system, must account for marrow infiltration of neoplastic cells observed in B-CLL and that CXCR4 could be involved in other features that exhibit malignant B cells, such as increased survival, rather than in their homing or migration to the bone marrow.

The class II tumor-suppressor gene RARRES3 is expressed in B cell lymphocytic leukemias and down-regulated with disease progression

The molecular pathogenesis of B cell chronic lymphocytic leukemia (B-CLL), the most common form of leukemia, remains unknown. We have used the mRNA differential display technique to analyze genes that may be involved in the development/progression of B-CLL. We have identified the tumor suppressor retinoic acid receptor responder 3 (RARRES3) as a B-CLL-related gene. RARRES3 maps to chromosome band 11q23, a region frequently deleted in lymphoproliferative disorders. To assess the potential involvement of RARRES3 in leukemogenesis, we examined 24 cases of B-CLL, 10 of acute lymphocytic leukemia (ALL) and five related cell lines by RT-PCR and sequence analyses. We report a correlation between RARRES3 down-regulation and B-CLL progression. We also found decreased RARRES3 gene levels in ALL cases and in the five cell lines studied. We did not find mutations in any of the leukemia samples assayed, including those with 11q23 deletion. These results indicate that RARRES3 may play a role in B-CLL progression.

Disruption of the IFN-gamma cytokine network in chronic lymphocytic leukemia contributes to resistance of leukemic B cells to apoptosis

Recent evidence indicates that the slowly expanding population of CD5+ B cells that characterizes chronic lymphocytic leukemia (CLL) results primarily from defects in responses to cytokines that regulate apoptosis (e.g. I1-4, TGF-beta, IFN-alpha, IFN-gamma). We have now demonstrated not only that the enhanced anti-apoptotic effect of IFN-gamma on these neoplastic B cells is apparently mediated through increased levels of IFN-gamma receptors but also that there are increased numbers of IFN-gamma-expressing CD4 and CD8 T cells in these patients. This is the strongest evidence to date that multiple alterations in the IFN-gamma cytokine network contribute to the pathogenesis of CLL.

TGF-beta activity and expression of its receptors in B-cell chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (B-CLL) is the most common leukemia in Western countries and results from the accumulation of B-lymphocytes which are functionally abnormal and predominantly non-cycling in vivo. Consequently, it is important to understand why B-CLL cells accumulate in GO phase. Since TGF-beta is an important negative regulator of the immune system, a loss of responsiveness to this factor might provide a selective advantage to B-CLL cells. Here we review data on the role of TGF-beta in B-CLL. We show that the B-CLL cell response to TGF-beta signals is abnormal in vitro (inhibition of proliferation and induction of apoptosis). This lack of response of B-CLL cells to TGF-beta inhibition appears to be accompanied by a decrease or a loss of TGF-beta receptor expression.

Trisomy 12 in chronic lymphocytic leukemia--geographical variation

Incidence of trisomy 12 was studied in 60 cases of chronic lymphocytic leukemia (CLL) with chromosome 12 specific alpha-satellite DNA probe by fluorescence in situ hybridization (FISH). Trisomy 12 was observed in 37 (61.8%) patients. Cells with trisomy 12 were detected in a varying proportion, ranging from > 2% to 86%. Patients with trisomy 12 were predominantly observed with total white blood cell (WBC) count > 80 x 10(9) l(-1) (P < 0.001). In addition, the percentage of trisomy 12 positive lymphocytes correlated with the high WBC counts. Trisomy 12 was observed equally in typical and atypical CLL. 90% of our patients were in the intermediate and high risk groups. It was seen that there was significantly higher percentage of trisomy 12 positive lymphocytes ( > 10%) in the high risk groups (P < 0.05). A higher incidence of FMC7 positivity in atypical CLL was seen in our study. However, there was no significant relationship found between trisomy 12 positivity and expression of either FMC7 or CD23 in our cases. It appears that the CLL that we see at our centre is at a different phase of evolution and perhaps biologically different compared to the CLL seen in the West.

Aberrant responses of human lymphocytic neoplasms to cytokine regulation

Studies in this laboratory have recently focused on two hemic neoplasms: B cell chronic lymphocytic leukemia (B-CLL) and a T cell disorder, Sézary syndrome. These tumors do not have consistent cytogenetic or molecular genetic alterations, and so we have concentrated on their response to and production of various regulatory cytokines. Although B-CLL cells show variable proliferative responses when exposed to transforming growth factor beta (TGF beta), these cells have consistently shown resistance to the pro-apoptotic effects of this cytokine. Also, interleukin 4 (IL4), IL5, and interferon-gamma (IFN gamma) all show a consistently increased protective effect against apoptosis in B-CLL cells as compared to normal human B cells. Thus, a defect in apoptosis appears to be an important factor in the pathogenesis of CLL. By contrast, the neoplastic T cells of Sézary syndrome show a consistent resistance to the antiproliferative effects of TGF beta, suggesting that aberrant proliferation is more important than apoptosis in this disorder. In both neoplasms, we have shown that the defective responses to cytokines are in some instances related to alterations in receptor expression, but this has not been true in all circumstances, and other stages in the signaling pathways are being investigated. As we define more precisely the specific defects that contribute to the clonal expansion of these neoplasms, the findings may ultimately lead to improved clinical control of these disorders.