Non-malignant leukocytes delay spontaneous B-CLL cell apoptosis

Role of Chronic Lymphocytic Leukemia (CLL)-Derived Exosomes in Tumor Progression and Survival

Chronic lymphocytic leukemia (CLL) is a B-lymphoproliferative disease, which consists of the abnormal proliferation of CD19/CD5/CD20/CD23 positive lymphocytes in blood and lymphoid organs, such as bone marrow, lymph nodes and spleen. The neoplastic transformation and expansion of tumor B cells are commonly recognized as antigen-driven processes, mediated by the interaction of antigens with the B cell receptor (BCR) expressed on the surface of B-lymphocytes. The survival and progression of CLL cells largely depend on the direct interaction of CLL cells with receptors of accessory cells of tumor microenvironment. Recently, much interest has been focused on the role of tumor release of small extracellular vesicles (EVs), named exosomes, which incorporate a wide range of biologically active molecules, particularly microRNAs and proteins, which sustain the tumor growth. Here, we will review the role of CLL-derived exosomes as diagnostic and prognostic biomarkers of the disease.

ZO-1 expression shows prognostic value in chronic B cell leukemia

Connexin-mediated gap junctions are vital for tumor cell function. Intracellular pathways of connexin signaling use Zonula Occludens protein-1 (ZO-1) as an intermediate. This report describes the ZO-1 and connexin 43 (Cx43) expression pattern in lymphocytes from chronic B-cell leukemia (B-CLL) patients. The ZO-1 and Cx43 expression in the B cells of 113 B-CLL patients was identified. Western blot and flow cytometry were used to determine protein expression. Results indicated that ZO-1 and Cx43 expression was reduced and correlated negatively with CD38 and Zap-70 expression. Inhibition of intercellular communication with anti-Cx43 antibodies, 1-octanol, or carbenoxolone resulted in induced cell apoptosis. These data suggest that ZO-1, along with CD38 and Zap-70, plays a role in cell cycle regulation in B-CLL and may be used as a prognostic marker in B-CLL monitoring.

The arachidonic acid-LTB4-BLT2 pathway enhances human B-CLL aggressiveness

Deregulation of the oxidative cascade of poly-unsaturated fatty acids (PUFAs) has been associated with several cancers, including chronic lymphocytic leukemia (B-CLL). Leukotriene B4 (LTB4), a metabolite of arachidonic acid (AA), is produced by B-CLL and contributes to their survival. The aim of the present study was to analyze the activity of the oxidative cascade of PUFAs in B-CLL. Purified B cells from patients and normal B CD5 positive cells were subjected to flow cytometry, Western-blot and RT-qPCR analyses. LTB4 plasma and intracellular concentrations were determined by ELISA. Our results showed that aggressive B-CLL tumor cells, i.e. cells with an annual proliferation index above 2, over-expressed calcium-dependent and calcium-independent phospholipases A2 (cPLA2-alpha and iPLA2-beta, respectively), 5-lipoxygenase (5LOX) and leukotriene A4 hydroxylase (LTA4H). Intracellular LTB4 levels were lower in the most aggressive cells than in cells with a smaller proliferation index, despite equivalent plasma levels, and lower expression of cytochrome P450 4F3A (CYP4F3A), one major enzyme involved in LTB4 inactivation. Since BLT2, a LTB4 membrane receptor was also more often expressed on aggressive tumor cells, and since a BLT2 inhibitor significantly impaired B-CLL viability in vitro, we propose that LTB4 was efficiently trapped onto BLT2 present on aggressive tumors, thereby eliciting an autocrine response. Taken together our results demonstrate a major deregulation of the pathway leading to LTB4 synthesis and degradation in B-CLL cells, and provide a framework for understanding how these modifications promote cell survival and proliferation, especially in the most aggressive BCLL.

Chaetoglobosin A preferentially induces apoptosis in chronic lymphocytic leukemia cells by targeting the cytoskeleton

Chronic lymphocytic leukemia (CLL) is an incurable malignancy of mature B cells. One of the major challenges in treatment of CLL is the achievement of a complete remission to prevent relapse of disease originating from cells within lymphoid tissues and subsequent chemoresistance. In search for novel drugs that target CLL cells in protective microenvironments, we performed a fungal extract screen using cocultures of primary CLL cells with bone marrow-derived stromal cells. A secondary metabolite produced by Penicillium aquamarinium was identified as Chaetoglobosin A (ChA), a member of the cytochalasan family that showed preferential induction of apoptosis in CLL cells, even under culture conditions that mimic lymphoid tissues. In vitro testing of 89 CLL cases revealed effective targeting of CLL cells by ChA, independent of bad prognosis characteristics, like 17p deletion or TP53 mutation. To provide insight into its mechanism of action, we showed that ChA targets filamentous actin in CLL cells and thereby induces cell-cycle arrest and inhibits membrane ruffling and cell migration. Our data further revealed that ChA prevents CLL cell activation and sensitizes them for treatment with PI3K and BTK inhibitors, suggesting this compound as a novel potential drug for CLL.

Identification of a STAT5 target gene, Dpf3, provides novel insights in chronic lymphocytic leukemia

STAT5 controls essential cellular functions and is encoded by two genes, Stat5a and Stat5b. To provide insight to the mechanisms linking hematologic malignancy to STAT5 activation/regulation of target genes, we identified STAT5 target genes and focused on Dpf3 gene, which encodes for an epigenetic factor. Dpf3 expression was induced upon IL-3 stimulation in Ba/F3 cells, while strong binding of both STAT5a and STAT5b was detected in its promoter. Reduced expression of Dpf3 was detected in Ba/F3 cells with Stat5a and Stat5b knock-down, suggesting that this gene is positively regulated by STAT5, upon IL-3 stimulation. Furthermore, this gene was significantly up-regulated in CLL patients, where DPF3 gene/protein up-regulation and strong STAT5 binding to the DPF3 promoter, correlated with increased STAT5 activation, mainly in non-malignant myeloid cells (granulocytes). Our findings provide insights in the STAT5 dependent transcriptional regulation of Dpf3, and demonstrate for the first time increased STAT5 activation in granulocytes of CLL patients. Novel routes of investigation are opened to facilitate the understanding of the role of STAT5 activation in the communication between non-malignant myeloid and malignant B-cells, and the functions of STAT5 target genes networks in CLL biology.

A combination of cytokines rescues highly purified leukemic CLL B-cells from spontaneous apoptosis in vitro

B-chronic lymphocytic leukemia (B-CLL), the most common human leukemia, is characterized by predominantly non-dividing malignant mature CD5+ B lymphocytes with an apoptosis defect. Various microenvironmental stimuli confer a growth advantage on these leukemic cells and extend their survival in vivo. Nevertheless, when cultured in vitro, CLL B-cells rapidly die from apoptosis. Certain cytokines may extend the survival capacity of CLL B-cells in vitro and individual anti-apoptotic effects of several cytokines have been reported. The potential cumulative effect of such cytokines has not been studied. We therefore investigated the effects on CLL B-cells survival in vitro of humoral factors, polyclonal lymphocyte activators and a combination of cytokines known for their anti-apoptotic effects. Purified CLL B-cells were cultured in the presence or absence of various soluble molecules and the leukemic cell response was assessed in terms of viability. Apoptotic cell death was detected by flow cytometry using annexinV and 7-amino-actinomycin. The survival of CLL B-cells in vitro was highly variable. When tested separately, cytokines (IL-2, -6, -10, -12, -15, -21, BAFF and APRIL) improved CLL B cell survival moderately; in combination, they significantly enhanced survival of these cells, even up to 7 days of culture. We also report that humoral factors from autologous serum are important for survival of these malignant cells. Our findings support the concept that the CLL microenvironment is critical and suggest that soluble factors may contribute directly to the prolonged survival of CLL B-cells. Therefore, the combination of cytokines we describe as providing strong resistance to apoptosis in vitro might be used to improve the treatment of CLL.

CXCL12 is a costimulator for CD4+ T cell activation and proliferation in chronic lymphocytic leukemia patients

Activated T cells from patients with chronic lymphocytic leukemia (CLL) provide survival and proliferative signals to the leukemic clone within lymphoid tissues. Recruitment of both, CLL cells and T lymphocytes, to this supportive microenvironment greatly depends on CXCL12 production by stromal and myeloid cells. CXCL12 also supplies survival stimuli to leukemic B cells, but whether it exerts stimulatory effects on T lymphocytes from CLL patients is unknown. In order to evaluate the capacity of CXCL12 to increase CD4(+) T cell activation and proliferation in CLL patients, peripheral blood mononuclear cells were cultured with or without recombinant human CXCL12 or autologous nurse-like cells, and then T cell activation was induced by anti-CD3 mAb. CXCL12 increases the proliferation and the expression of CD25, CD69, CD154, and IFNγ on CD3-stimulated CD4(+) T cells from CLL patients, similarly in T cells from ZAP-70(+) to ZAP-70(-) patients. Autologous nurse-like cells establish a close contact with CD4(+) T cells and increase their activation and proliferation partially through a CXCR4-dependent mechanism. In addition, we found that activated T cells in the presence of CXCL12 enhance the activation and proliferation of the leukemic clone. In conclusion, CXCL12 production by lymphoid tissue microenvironment in CLL patients might play a key dual role on T cell physiology, functioning not only as a chemoattractant but also as a costimulatory factor for activated T cells.

T cells from indolent CLL patients prevent apoptosis of leukemic B cells in vitro and have altered gene expression profile

T cells may have a role in sustaining the leukemic clone in chronic lymphocytic leukemia (CLL). In this study, we have examined the ability of T cells from CLL patients to support the survival of the leukemic B cells in vitro. Additionally, we compared global gene expression of T cells from indolent CLL patients with healthy individuals and multiple myeloma (MM) patients. Apoptosis of purified leukemic B cells was inhibited in vitro when co-cultured with increasing numbers of autologous T cells (p < 0.01) but not autologous B and T cells of normal donors. The anti-apoptotic effect exceeded that of the anti-apoptotic cytokine IL-4 (p = 0.002) and was greater with CD8+ cells (p = 0.02) than with CD4+ cells (p = 0.05). The effect was depended mainly on cell-cell contact although a significant effect was also observed in transwell experiments (p = 0.05). About 356 genes involved in different cellular pathways were deregulated in T cells of CLL patients compared to healthy individuals and MM patients. The results of gene expression profiling were verified for 6 genes (CCL4, CCL5 (RANTES), XCL1, XCL2, KLF6, and TRAF1) using qRT-PCR and immunoblotting. Our results demonstrate that CLL-derived T cells can prevent apoptosis of leukemic B cells and have altered expression of genes that may facilitate the survival of the leukemic clone.

CCL2 and CXCL2 enhance survival of primary chronic lymphocytic leukemia cells in vitro

Chronic lymphocytic leukemia (CLL) is predominantly a disease of accumulation rather than rapid proliferation. To date, no cell lines exist, as CLL cells undergo rapid apoptosis when cultured in vitro, suggesting that a favorable in vivo microenvironment is required. To identify survival signals we cultured primary CLL peripheral blood mononuclear cells (PBMCs) at high density, which has previously been shown to dramatically improve survival. Using antibody arrays we measured the level of 42 cytokines in culture supernatants and showed that inerleukin-6 (IL-6), IL-8, CXCL2 and CCL2 were highly up-regulated in culture. This is the first report to describe a role for CCL2 and CXCL2 in CLL cell survival. Importantly, CXCL2, IL-6 and IL-8 were significantly up-regulated in primary patient plasma. The addition of either CXCL2 or CCL2 enhanced CLL cell survival, while antibodies blocking these chemokines reduced survival. Co-culture of CLL cells and PBMC accessory cells separated by transwells provided a similar degree of survival protection compared to normal culture, whereas CLL cells cultured alone died rapidly. Interestingly, CCL2 and CXCL2 appeared to be produced by CLL cells but only when co-cultured with accessory cells. Thus, we speculate that accessory cells release soluble factors that promote the production of these pro-survival chemokines from CLL cells and physical interactions are not required. Our data support the concept that the CLL microenvironment is critical, and suggests that soluble factors are more important than physical interactions.

The cytotoxic activity of Aplidin in chronic lymphocytic leukemia (CLL) is mediated by a direct effect on leukemic cells and an indirect effect on monocyte-derived cells

Aplidin is a novel cyclic depsipeptide, currently in Phase II/III clinical trials for solid and hematologic malignancies. The aim of this study was to evaluate the effect of Aplidin in chronic lymphocytic leukemia (CLL), the most common leukemia in the adult. Although there have been considerable advances in the treatment of CLL over the last decade, drug resistance and immunosuppression limit the use of current therapy and warrant the development of novel agents. Here we report that Aplidin induced a dose- and time-dependent cytotoxicity on peripheral blood mononuclear cells (PBMC) from CLL patients. Interestingly, Aplidin effect was markedly higher on monocytes compared to T lymphocytes, NK cells or the malignant B-cell clone. Hence, we next evaluated Aplidin activity on nurse-like cells (NLC) which represent a cell subset differentiated from monocytes that favors leukemic cell progression through pro-survival signals. NLC were highly sensitive to Aplidin and, more importantly, their death indirectly decreased neoplasic clone viability. The mechanisms of Aplidin-induced cell death in monocytic cells involved activation of caspase-3 and subsequent PARP fragmentation, indicative of death via apoptosis. Aplidin also showed synergistic activity when combined with fludarabine or cyclophosphamide. Taken together, our results show that Aplidin affects the viability of leukemic cells in two different ways: inducing a direct effect on the malignant B-CLL clone; and indirectly, by modifying the microenvironment that allows tumor growth.

Soluble CD14 is a novel monocyte-derived survival factor for chronic lymphocytic leukemia cells, which is induced by CLL cells in vitro and present at abnormally high levels in vivo

Accumulation of leukemic cells in patients with chronic lymphocytic leukemia (CLL) is due to prolonged cell survival rather than increased proliferation. Survival of CLL cells depends on microenvironmental factors. Even though long-lived in vivo, CLL cells rapidly die by spontaneous apoptosis in vitro unless cocultured with stromal cells or their conditioned medium. In the present study, we show that survival of CLL cells is maintained in high cell density cultures, where the main prosurvival activity is delivered by monocytes. Cytokine array and enzyme-linked immunosorbent assay studies revealed increased expression of soluble CD14 by monocytes in the presence of CLL cells. The addition of recombinant soluble CD14 to primary CLL cells resulted in significantly increased cell survival rates, which were associated with higher activity nuclear factor κB. Quantification of serum levels of soluble CD14 revealed abnormally high levels of this protein in CLL patients, indicating a potential role of soluble CD14 in vivo. In summary, the presented data show that monocytes help in the survival of CLL cells by secreting soluble CD14, which induces nuclear factor κB activation in these cells, and that CLL cells actively shape their microenvironment by inducing CD14 secretion in accessory monocytes.

The histone deacetylase inhibitor MGCD0103 induces apoptosis in B-cell chronic lymphocytic leukemia cells through a mitochondria-mediated caspase activation cascade

Clinical trials have shown activity of the isotype-selective histone deacetylase (HDAC) inhibitor MGCD0103 in different hematologic malignancies. There are data to support the use of HDAC inhibitors in association with other cancer therapies. To propose a rational combination therapy, it is necessary to depict the molecular basis behind the cytotoxic effect of MGCD0103. In this study, we found that MGCD0103 was substantially more toxic in neoplastic B cells relative to normal cells, and we described the death pathways activated by MGCD0103 in B-cell chronic lymphocytic leukemia (CLL) cells from 32 patients. MGCD0103 decreased the expression of Mcl-1 and induced translocation of Bax to the mitochondria, mitochondrial depolarization, and release of cytochrome c in the cytosol. Caspase processing in the presence of the caspase inhibitor Q-VD-OPh and time course experiments showed that caspase-9 was the apical caspase. Thus, MGCD0103 induced the intrinsic pathway of apoptosis in CLL cells. Moreover, MGCD0103 treatment resulted in the activation of a caspase cascade downstream of caspase-9, caspase-dependent amplification of mitochondrial depolarization, activation of calpain, and Bax cleavage. We propose a model whereby the intrinsic pathway of apoptosis triggered by MGCD0103 in CLL is associated with a mitochondrial death amplification loop.

All-trans-retinoic acid promotes trafficking of human concentrative nucleoside transporter-3 (hCNT3) to the plasma membrane by a TGF-beta1-mediated mechanism

Human concentrative nucleoside transporter-3 (hCNT3) is a sodium-coupled nucleoside transporter that exhibits high affinity and broad substrate selectivity, making it the most suitable candidate for mediating the uptake and cytotoxic action of most nucleoside-derived drugs. The drug of this class most commonly used in the treatment of chronic lymphocytic leukemia (CLL) is the pro-apoptotic nucleoside analog fludarabine (Flu), which enters CLL cells primarily through human equilibrative nucleoside transporters (hENTs). Although CLL cells lack hCNT3 activity, they do express this transporter protein, which is located mostly in the cytosol. The aim of our study was to identify agents and mechanisms capable of promoting hCNT3 trafficking to the plasma membrane. Here, we report that all-trans-retinoic acid (ATRA), currently used in the treatment of acute promyelocytic leukemia (APL), increases hCNT3-related activity through a mechanism that involves trafficking of pre-existing hCNT3 proteins to the plasma membrane. This effect is mediated by the autocrine action of transforming growth factor (TGF)-beta1, which is transcriptionally activated by ATRA in a p38-dependent manner. TGF-beta1 acts through activation of ERK1/2 and the small GTPase RhoA to promote plasma membrane trafficking of the hCNT3 protein.

Modulation of the human equilibrative nucleoside transporter1 (hENT1) activity by IL-4 and PMA in B cells from chronic lymphocytic leukemia

Nucleoside transporters (NTs) are essential for the uptake of therapeutic nucleoside analogs, broadly used in cancer treatment. The mechanisms responsible for NT regulation are largely unknown. IL-4 is a pro-survival signal for chronic lymphocytic leukemia (CLL) cells and has been shown to confer resistance to nucleoside analogs. The aim of this study was to investigate whether IL-4 is able to modulate the expression and function of the human equilibrative NT1 (hENT1) in primary cultures of CLL cells and, consequently, to affect cytotoxicity induced by therapeutic nucleosides analogs. We found that treatment with IL-4 (20 ng/ml for 24 h) increased mRNA hENT1 expression in CLL cells without affecting that of normal B cells. Given that the enhanced mRNA levels of hENT1 in CLL cells did not result in increased transport activity, we examined the possibility that hENT1 induced by IL-4 may require post-translational modifications to become active. We found that the acute stimulation of PKC in IL-4-treated CLL cells by short-term incubation with PMA significantly increased hENT1 transport activity and favoured fludarabine-induced apoptosis. By contrast, and in line with previous reports, IL-4 plus PMA protected CLL cells from a variety of cytotoxic agents. Our findings indicate that the combined treatment with IL-4 and PMA enhances hENT1 activity and specifically sensitizes CLL cells to undergo apoptosis induced by fludarabine.

17p Deletion is associated with resistance of B-cell chronic lymphocytic leukemia cells to in vitro fludarabine-induced apoptosis

We explored the relationship between the cytogenetic/biologic characteristics of B-chronic lymphocytic leukemia (B-CLL) cells and their tendency to undergo spontaneous or fludarabine-induced apoptosis in vitro. B cells from 36 B-CLL patients were incubated with or without fludarabine for 48 h. Apoptosis was determined by two assays: annexin V staining and DNA staining. Fluorescence in situ hybridization was used for detection of trisomy 12, 11q deletion, and 17p deletion. Bcl-2 and CD38 expressions were determined by flow cytometry. Five patients had 17p deletion, 6 had trisomy 12, and another 6 had 11q deletion. B-CLL cells with 17p deletion had significant resistance to apoptosis induced by fludarabine and a slight spontaneous resistance to apoptosis. Bcl-2 and CD38 were not associated with in vitro spontaneous and fludarabine-induced apoptosis. In conclusion, 17p deletion, which causes loss of p53 gene, is associated with resistance to fludarabine-induced apoptosis in vitro. New treatment modalities should be tried in B-CLL patients with 17p deletion.

Signaling capacity of FcγRII isoforms in B-CLL cells

Two main isoforms of Fcgamma receptor II (CD 32) have been described in humans: activatory FcgammaRIIA and inhibitory FcgammaRIIB. We have previously reported that B cells from a subset of chronic lymphocytic leukemia (B-CLL) patients express not only FcgammaRIIB, as normal B lymphocytes, but also the myeloid FcgammaRIIA. The aim of this study was to evaluate the signaling capacity of both FcgammaRII isoforms in B-CLL cells. We found that FcgammaRIIA expressed by leukemic cells failed to induce Ca(2+) mobilization or protein tyrosine phosphorylation, suggesting that the receptor is not functional. By contrast, FcgammaRIIB effectively diminished BCR-triggered ERK 1 phosphorylation, which indicates that it is able to transduce inhibitory signals in B-CLL cells. Moreover, we found that FcgammaRIIB homoaggregation in either B-CLL or non-malignant tonsillar B cells did not result in apoptosis as was reported for murine B splenocytes. Together, these results show that FcgammaRIIB, but not FcgammaRIIA is biologically active in B-CLL cells and might influence leukemic cell physiology in vivo.

Good prognosis cytogenetics in B-cell chronic lymphocytic leukemia is associated in vitro with low susceptibility to apoptosis and enhanced immunogenicity

Chromosomal abnormalities in B-cell chronic lymphocytic leukemia (B-CLL) have been shown to correlate with prognosis. Little is known about the relationship between chromosomal abnormalities and biological behavior of B-CLL cells in vitro. The present study was designed to explore the impact of chromosomal abnormalities determined by interphase fluorescence in situ hybridization (FISH) on the in vitro survival and immunogenicity of B-CLL. Considerable heterogeneity was noted in the in vitro survival and expression of costimulatory, adhesion, and antigen-presenting molecules by B-CLL cells. Spontaneous apoptosis of B-CLL cells in vitro was significantly lower in samples with good prognosis cytogenetics when compared to samples with poor prognosis cytogenetics. In contrast, B-CLL cells from samples with good prognosis cytogenetics exhibited higher basal expression of molecules involved in costimulation, cellular adhesion, and antigen presentation, and induced significantly more T-cell proliferation in mixed lymphocyte cultures. We conclude that chromosomal aberrations of B-CLL cells correlate with the in vitro biological behavior of B-CLL. Our data indicate that good prognosis cytogenetics correlates with less spontaneous apoptosis but greater in vitro immunogenicity. These findings could have significant implications on the design of future therapeutic approaches in patients with CLL, and the likelihood of response based on cytogenetics.

High expression of bfl-1 contributes to the apoptosis resistant phenotype in B-cell chronic lymphocytic leukemia

In order to identify regulatory genes involved in the development of an apoptosis-resistant phenotype in patients with chemotherapy refractory B-cell chronic lymphocytic leukemia (B-CLL) expression of apoptosis-regulating genes in B-CLL cells was quantified using cDNA arrays and RT-PCR. Data were obtained from and compared between 2 groups of B-CLL patients with either nonprogressive, indolent, previously untreated disease and with leukemic cells sensitive to in vitro fludarabine-induced apoptosis, referred to as sensitive B-CLL (sB-CLL) or with progressive, chemotherapy refractory disease and with leukemic cells resistant to in vitro fludarabine-induced apoptosis, referred to as resistant B-CLL (rB-CLL). By performing a supervised clustering of genes that most strongly discriminated between rB-CLL vs. sB-CLL a small group of genes was identified, where bfl-1 was the strongest discriminating gene (p < 0.05), with higher expression in rB-CLL. A group of apoptosis-regulating genes were modulated during induction of apoptosis by serum deprivation in vitro in a similar manner in all cases studied. However, bfl-1 was preferentially downregulated in sB-CLL as compared to rB-CLL (p < 0.05). We conclude that bfl-1 may be an important regulator of B-CLL apoptosis, which could contribute to disease progression and resistance to chemotherapy, and as such represent a future potential therapeutic target.

In vitro susceptibility of CD4+ and CD8+ T cell subsets to fludarabine

Administration of the adenosine analogue fludarabine (FLU) in vivo induces a profound and prolonged T lymphopenia which mainly affects CD4(+) cells. To better understand the mechanistic basis underlying this preferential depletion, we analyzed the in vitro susceptibility of T cell subsets to FLU-induced apoptosis. Contrasting with observations in vivo, our results showed that treatment of peripheral blood mononuclear cells with FLU induced a higher level of apoptosis in CD8(+) than in CD4(+) T lymphocytes. This increased sensitivity of CD8(+) T cells to FLU was observed in samples from both, healthy donors and B cell chronic lymphocytic leukemia patients, and resulted in higher CD4:CD8 ratios in FLU-treated than in untreated cultures (P<0.01). Expression of factors involved in FLU transport and metabolism was then evaluated by quantitative real time-PCR in normal T cell subsets. It was found that mRNA levels of human equilibrative nucleoside transporter-1 nucleoside transporter were higher whereas deoxycytidine kinase and IMP/GMP selective 5'-nucleotidase mRNA levels were lower in CD4(+) cells. However the dCK/cN-II ratio was 2-fold greater in CD8(+) than in CD4(+) T lymphocytes, which could account for the higher apoptosis levels observed in the CD8(+) subset. These results favor the view that decreased CD4:CD8 ratios in FLU-treated patients should be attributed to differences in cell recovery and/or homing between T cell subsets.

Expansion of natural killer (NK) and natural killer-like T (NKT)-cell populations derived from patients with B-chronic lymphocytic leukemia (B-CLL): a potential source for cellular immunotherapy

B-cell chronic lymphocytic leukemia (B-CLL) is the most common leukemia in the Western world. It is currently an incurable disease, making new treatment options such as immunotherapy desirable. Monoclonal antibodies (Mabs) to surface antigens of the tumor cell is one option. Administration of cytotoxic cells such as natural killer (NK) and natural killer-like T (NKT) cells expanded in vitro might be a useful treatment modality alone or in combination with MAbs. A limiting step in the development of successful cellular immunotherapy has been the availability of appropriate cytotoxic cells. Here, we report the feasibility of expanding populations of the human killer cells, CD3-CD56+ NK and CD3+CD56+ NKT cells, from peripheral blood mononuclear cells (PBMCs) of B-CLL patients. The influence of tumor B cells on the in vitro expansion of killer cells was assessed by depleting B cells from PBMCs by microbead separation before culture. The 21-day cultures from both B-cell- and non-B-cell-depleted PBMC showed a marked expansion of NK cells, and also of T cells, among which almost half had the NKT phenotype. Depletion of B cells before culture did not change the expansion rates of NK and NKT cells significantly. In patients with progressive B-CLL, NK cell expansion capacity was improved after fludarabine treatment when compared to samples obtained before treatment. Repeated samples of PBMCs from individual untreated patients with both indolent and progressive disease cultured under identical conditions gave similar NK cell expansion rates. Expanded killer cell populations had cytotoxic function against the NK-sensitive target K562 cell line and expressed high levels of Granzyme B. From our studies, we conclude that NK cells as well as NKT cells from the peripheral blood of B-CLL patients can be expanded, and that these cells have cytotoxic capacity.