Normal and aberrant expression of cytokines in neoplastic cells from chronic lymphocytic leukemias

Modeling the chronic lymphocytic leukemia microenvironment in vitro

Microenvironments within the lymph node and bone marrow promote proliferation and drug resistance in chronic lymphocytic leukemia (CLL). Successful treatment of CLL must therefore target the leukemic cells within these compartments. A better understanding of the interaction between CLL cells and the tumor microenvironment has led to the development of in vitro models that mimic the mechanisms that support leukemic cell survival and proliferation in vivo. Employing these models as part of the pre-clinical evaluation of novel therapeutic agents enables a better approximation of their potential clinical efficacy. In this review we summarize the current literature describing how different aspects of the tumor microenvironment have been modeled in vitro and detail how these models have been employed to study the biology of the disease and potential efficacy of novel therapeutic agents.

Combinatorial approach to identification of tyrphostin inhibitors of cytokine signaling

Aberrant or deregulated activity of certain cellular kinases has been shown to cause certain malignancies and other disorders. The tyrphostin molecule AG490 inhibits the action of the janus kinases JAK2 and JAK3. JAK2 is an indispensable molecule for transducing the signals conveyed by a large number of cytokines including IL-3 while JAK3 is essential for signaling by a smaller number of cytokines including IL-7. A synthetic combinatorial chemical library containing 599 compounds was created and screened for the ability to inhibit proliferation of IL3- and IL7-dependent cell lines to focus on molecules that interrupt those signaling pathways. This screen identified a meta-trifluoromethyl derivative of AG490, 5H4, that is approximately twice as potent as AG490 in cell-based assays. 5H4 blocked the factor-dependent proliferation of both of these cell lines, actively promoted cell death, and diminished the JAK kinase activity. Administration of 5H4 to lymphoma-prone IL-7 transgenic mice reduced their spontaneous lymphadenopathy. The improved characteristics of this novel compound bring this class of molecules closer to therapeutic utility.

Expression and production of interleukin 4 in B-cell chronic lymphocytic leukaemia

Interleukin (IL) 4 is a T-cell derived pleiotropic cytokine whose properties include alterations of B-cell function. In B-cell chronic lymphocytic leukaemia (B-CLL), IL4 is involved in the mechanism of survival of the leukaemic B-cells. The present study examines the expression and production of IL4 by B- and T-lymphocytes derived from patients with B-CLL and provides evidence that IL4 is not an autocrine factor in B-CLL. Freshly isolated B-CLL cells enriched for B- and T-cells did not express mRNA for IL4 but expressed mRNA for IL4 receptor (IL4R). Activation of B-cells with phorbol ester and calcium ionophore and of T-cells with phytohaemaglutinin (PHA) upregulated IL4 mRNA expression. However phorbol ester and calcium ionophore did not affect the mean level of IL4 production by either B-CLL or normal B-cells. Furthermore, in the presence or absence of activation, the amount of IL4 synthesised by B-CLL B-cells was not significantly different than that observed with peripheral blood B-cells isolated from normal individuals (with activation: P=0.239; without activation: P=0.565). Also, there was no significant difference between normal and B-CLL B-cells in the level of cytoplasmic IL4 (P=0.47). PHA-activated enriched B-CLL T-cells produced significantly higher levels of IL4 compared to normal control T-cells (P=0.0136). In addition, in 47% of cases with B-CLL T-cells, a significant higher level of intracellular IL4 was observed (P=0.0027). The levels of production of IL4 by the T-cell-enriched preparations correlated positively with the intensity of cytoplasmic L4 in CD4+ and CD8+ cells in tested samples (r=0.49 and r=0.76, respectively). The significant differences observed in the production of IL4 by B-CLL B- and T-lymphocytes may suggest a paracrine function of IL4 in B-CLL.

Interleukin 4 content in chronic lymphocytic leukaemia (CLL) B cells and blood CD8+ T cells from B-CLL patients: impact on clonal B-cell apoptosis

B-chronic lymphocytic leukaemia (CLL) clonal B cells are characterized by resistance to apoptosis. We evaluated clonal B cells and blood T cells for interleukin 4 (IL-4) content as IL-4 is able to increase CLL cell resistance to apoptosis. The content of IL-4 in CD8+ T cells of CLL patients (n = 9) ranged from 37% to 63% of the total CD8+ T cells (mean level of 49% +/- 3.4) compared with a range of 5-10% for control CD8+ T cells. Clonal B cells positive for cytoplasmic IL-4 ranged from 1% to 97% (mean value 57.8 +/- 6.9%). CD8+ T cells and clonal B cells secreted detectable levels of IL-4, but only clonal CLL B cells (n = 4) secreted IL-4 in association with increasing cell numbers. Fludarabine (F-ara-AMP, 0.1-100 micromol/ml) was able to downregulate the IL-4 content of CD8+ T cells, but not clonal B-cell IL-4. Culture supernatant from CLL CD8+ T cells decreased the spontaneous apoptotic rate of clonal B cells that was reversed with anti-IL-4 and soluble IL-4 receptor. These findings show that IL-4 is present in the microenvironment of B-CLL. In addition, use of agents that can interfere with IL-4 presentation to clonal B cells can be effective in increasing clonal B-cell apoptosis.

Gene expression in chronic lymphocytic leukemia B cells and changes during induction of apoptosis

Our studies in chronic lymphocytic leukemia (CLL) are directed at understanding which signals maintain viability in vivo and become lost upon removal of leukemic cells from the body, such that they immediately begin to undergo apoptosis ex vivo. In this report, we examine changes in gene expression observed between freshly isolated CLL B cells and after maintenance in vitro with and without Fludara. We compare these effects with an Epstein-Barr virus (EBV)-transformed cell line treated similarly. Kinetic effects of drug treatment on apoptosis and cell division were examined with DNA laddering, radioisotopic labeling, and flow cytometry using the fluorescent dye carboxyfluorescein diacetate succinimidyl ester. Reverse transcriptase polymerase chain reaction and hybridization blots of microarray cDNA analyses were performed to examine gene expression. We demonstrate that many genes, especially cyclin D1, were downregulated after culture of CLL cells. Anti-apoptotic genes BAG-1 and Akt2 were upregulated. The greatest positive effect with Fludara was the upregulation of JNK1. The EBV-transformed cell line was resistant to classic DNA laddering induced with Fludara. Although DNA synthesis was blocked, the EBV-transformed cell line had some ability to recover from treatment following drug washout. CLL cells express cell cycle regulatory genes that are specific for activated cells in the G(1)-S phase of the cell cycle. Growth regulatory signals are lost when the leukemic cells are isolated from the body. Fludara enhances kinetics of apoptosis and induces expression of a gene responsive to stress that regulates expression of a kinase involved in initiation of the apoptotic pathway.

Modulation of apoptosis with cytokines in B-cell chronic lymphocytic leukaemia

In B chronic lymphocytic leukaemia (B-CLL) non-proliferating peripheral blood (PB) B cells have a long life span in vivo. In cultures, these cells die spontaneously by apoptosis. Interleukin (IL) 4 inhibits spontaneous apoptosis (SA) and promotes survival of B-CLL B cells in vitro. No such effect is observed in PB B cells from normal healthy donors. The anti-apoptotic effect of IL4 is independent of mitogen-induced cell activation but depends on the concentration of IL4. The protective effect of IL4 is specific and it is significantly reduced or abolished with anti-IL4 antibody. Interferon (IFN)-gamma and alpha- IFN also protect B-CLL B cells from apoptosis in vitro. Sera from B-CLL patients have increased levels of IFN-gamma when compared with sera from healthy donors. In addition, B-cells in B-CLL express detectable levels of IFN-gamma mRNA. Other cytokines, namely ILl, IL2, IL6 and IL7 do not affect SA of B-CLL B cells. By contrast, IL5 and antibody to apolipoprotein-1 (APO- 1) receptor increase SA significantly and in a dose-dependent manner. Interleukin 4 protects B-CLL B cells from IL5-, anti(alpha) APO-1- and steroid-induced apoptosis. The mode of action of the cytokines inducing apoptosis or protecting B-CLL B cells from dying is largely unknown. Recently the bcl-2 proto-oncogene has been associated with prolonged cell survival. However, the involvement of bel-2 in spontaneous, cytokine-induced or steroid-induced apoptosis in B-CLL has been controversial. Some authors have reported down-regulation of bcl-2 protein expression in B-CLL B-cells undergoing SA or in steroid-treated cells with IL4 preventing this down-regulation. By contrast, others observed no significant loss of bcl-2 protein expression in steroid-, alpha-APO-1 - and IL5-treated cells when compared with untreated or fresh cells. Also, no correlation between bcl-2 protein expression and protection with IL4 has been reported. In conclusion, in B-CLL IL4, IFN-gamma and alpha-IFN promote the survival of the leukaemic cells. These cytokines may therefore be involved in the pathogenesis of the B-CLL.

Apoptosis and interleukin 7 gene expression in chronic B-lymphocytic leukemia cells

mRNA for interleukin 7 (IL-7) was readily detected in leukemic cells immediately upon their removal from patients with chronic B-lymphocytic leukemia (B-CLL). IL-7 mRNA expression and IL-7 gene transcription were down regulated, however, when B-CLL cells were placed in culture at 37 degrees C for 4 hr. Down regulation of the IL-7 gene was prevented in cells maintained at 4 degrees C. Continued culture of B-CLL cells at 37 degrees C resulted in programmed cell death, or apoptosis, as evidenced by DNA fragmentation. The coincident kinetics of IL-7 gene down regulation and apoptosis suggested that IL-7 gene expression may be required for maintenance of CLL viability in vivo. Signals for IL-7 gene regulation and apoptosis induction were thus examined. Activation of normal B cells through their immunoglobulin receptors did not result in upregulation of IL-7 gene expression. Reagents required for CLL cell purification and culture also did not contribute to IL-7 gene regulation and apoptosis induction. IL-7 gene expression was retained and apoptosis was prevented, however, in CLL cells cultured on a monolayer of EA.hy926 human umbilical cord endothelial hybrid cells. Signals specifically presented by EA.hy926 cells supported both CLL cell viability and IL-7 gene expression, whereas culture of CLL cells on A549/8 carcinoma cells, the fusion partner used to generate the EA.hy926 cells, did not. Cell-cell contact was required, as culture supernatants did not prevent apoptosis. Specifically, IL-7 mRNA expression was retained and apoptosis was prevented only by contact with the endothelial cell hybrids. Preliminary data indicated that integrins expressed on CLL cells affected modulation of apoptosis and IL-7 gene regulation, suggesting that integrins may play significant roles in regulating viability of CLL cells.