Blood-derived nurse-like cells protect chronic lymphocytic leukemia B cells from spontaneous apoptosis through stromal cell–derived factor-1

CXCR4: a key receptor in the crosstalk between tumor cells and their microenvironment

Signals from the microenvironment have a profound influence on the maintenance and/or progression of hematopoietic and epithelial cancers. Mesenchymal or marrow-derived stromal cells, which constitute a large proportion of the non-neoplastic cells within the tumor microenvironment, constitutively secrete the chemokine stromal cell-derived factor-1 (SDF-1/CXCL12). CXCL12 secretion by stromal cells attracts cancer cells, acting through its cognate receptor, CXCR4, which is expressed by both hematopoietic and nonhematopoietic tumor cells. CXCR4 promotes tumor progression by direct and indirect mechanisms. First, CXCR4 is essential for metastatic spread to organs where CXCL12 is expressed, and thereby allows tumor cells to access cellular niches, such as the marrow, that favor tumor-cell survival and growth. Second, stromal-derived CXCL12 itself can stimulate survival and growth of neoplastic cells in a paracrine fashion. Third, CXCL12 can promote tumor angiogenesis by attracting endothelial cells to the tumor microenvironment. CXCR4 expression is a prognostic marker in various types of cancer, such as acute myelogenous leukemia or breast carcinoma. Promising results in preclinical tumor models indicate that CXCR4 antagonists may have antitumor activity in patients with various malignancies. Collectively, these observations reveal that CXCR4 is an important molecule involved in the spread and progression of a variety of different tumors. As such, CXCR4 antagonists, although initially developed for treatment of AIDS, actually may become effective agents for the treatment of neoplastic disease.

Small peptide inhibitors of the CXCR4 chemokine receptor (CD184) antagonize the activation, migration, and antiapoptotic responses of CXCL12 in chronic lymphocytic leukemia B cells

Growth and survival of chronic lymphocytic leukemia (CLL) B cells are favored by interactions between CLL and nontumoral accessory cells. CLL cells express CXCR4 chemokine receptors that direct leukemia cell chemotaxis. Marrow stromal cells or nurselike cells constitutively secrete CXCL12, the ligand for CXCR4, thereby attracting and rescuing CLL B cells from apoptosis in a contact-dependent fashion. Therefore, the CXCR4-CXCL12 axis represents a potential therapeutic target in CLL. We evaluated the most active CXCR4-specific antagonists (T140, TC14012, TN14003) for their capacity to inhibit CXCL12 responses in CLL cells. T140, or its analogs, inhibited actin polymerization, chemotaxis, and migration of CLL cells beneath stromal cells. CXCL12-induced phosphorylation of p44/42 mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 3 (STAT3) was abolished by CXCR4 antagonists. TC14012 and TN14003 antagonized the antiapoptotic effect of synthetic CXCL12 and stromal cell-mediated protection of CLL cells from spontaneous apoptosis. Furthermore, we found that stromal cells protected CLL cells from chemotherapy-induced apoptosis. Treatment with CXCR4 antagonists resensitized CLL cells cultured with stromal cells to fludarabine-induced apoptosis. These findings demonstrate that CXCR4 blocking agents effectively antagonize CXCL12-induced migratory and signaling responses and stromal protection of CLL cells from spontaneous or fludarabine-induced apoptosis. As such, small molecular CXCR4 antagonists may have activity in the treatment of patients with this disease. (Blood. 2005;106:1824-1830)

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.

Mammalian target of rapamycin (mTOR) inhibition in chronic lymphocytic B-cell leukemia: a new therapeutic option

Chronic lymphocytic B-cell leukemia (B-CLL) is an incurable disease characterized by the accumulation of monoclonal mature B cells, although disease progression relies upon cycling B-CLL cells in proliferation centers in central lymph organs. Rapamycin and its analogs are immunosuppressant drugs that exert their activity by specific inhibition of the mammalian target of rapamycin (mTOR). mTOR inhibition induces cell cycle arrest not only in normal lymphocytes but also in malignant cells. Therefore, rapamycins have recently entered the field of cancer treatment. In the present review we discuss how progression through the cell cycle is regulated in B-CLL cells and how rapamycin and its analogs can be used as target therapies against proliferating B-CLL cells. We also focus on additional effects of rapamycin, such as targeting the interaction between malignant B cells and the microenvironment.

Efficient species C HAdV infectivity in plasmocytic cell lines using a clathrin-independent lipid raft/caveola endocytic route

Hematopoietic cells are known to be refractory to species C human adenovirus (HAdV) infection; however, the reason for this has not been clearly established. We have previously demonstrated that this nonpermissivity is the consequence of inefficient HAdV particle uptake, notably in B lymphocytes. We noted that while the protein clathrin is observed in association with membranes in epithelial cells, it is found predominantly in the cytoplasm of hematopoietic cell lines. So it appears that altered clathrin-coated pit endocytosis could explain the weak HAdV uptake in B cells. In contrast, mature B cell plasmocytes are permissive to HAdV. However, this is not the result of clathrin-coated pit endocytosis since this process is also inefficient in these cells. Confocal microscopy showed colocalization between HAdV particles and caveolae/lipid rafts in plasmocytes. Moreover, inhibiting caveola endocytosis by depletion of cholesterol or expression of dominant negative caveolin-1 in these cells results in a 50-70% reduction in HAdV infectivity. It appears that caveola endocytosis and nonclathrin noncaveola endocytosis are used by HAdV to enter plasmocytes in response to a loss of the clathrin-dependent pathway. Thus targeting of caveolae by modifying the capsid of HAdV may represent an alternative approach to enhancing uptake in most hematopoietic cells for future gene therapy.

Bcl-2 regulatory pathway is functional in chronic lymphocytic leukemia

BACKGROUND

Chronic lymphocytic leukemia (CLL) is characterized by accumulation of clonal, malignant CD5(+), CD23(+) B cells. In vivo, these cells have an antiapoptotic phenotype (high levels of Bcl-2 and low levels of proapoptotic Bcl-2 family proteins, such as Bax). Abnormal B cells accumulate due to altered apoptosis regulation rather than to increased proliferation. However, it is unclear whether there are inherent Bcl-2 apoptotic pathway defects. With in vitro culture, these B cells rapidly apoptosis.

METHODS

To investigate apoptosis regulation, Bcl-2, Bax, mitochondrial membrane potential, annexin V, and caspase activation were simultaneous monitored in individual cells during in vitro apoptosis.

RESULTS

With in vitro culture, 30% to 50% of B cells were apoptotic at 24 h compared with fewer than 10% of T cells. Apoptotic B cells showed dramatic Bax upregulation and slight Bcl-2 decreases accompanied by decreased mitochondrial membrane potential and increased activated caspase-3 protein levels. Caspase-3 and caspase-9 activities were increased 18- to 51-fold and 6- to 11-fold, respectively, after 24 h of culture. Caspase-8 showed limited or no activation (less than fourfold).

CONCLUSIONS

These data show that in vitro apoptosis of CLL B cells occurs through a well-characterized Bcl-2 regulatory pathway consistent with that pathway being functional. Further, these cells' antiapoptotic phenotype is dependent on the in vivo environment, potentially involving paracrine/autocrine interactions.

Microenvironmental interactions and survival of CLL B-cells

Chronic Lymphocytic Leukemia (CLL) B cells display characteristics consistent with a defect in programmed cell death (apoptosis) and exhibit prolonged survival in vivo. When recovered from peripheral blood or lymphoid tissues from the patient and cultured in vitro, these malignant cells rapidly undergo spontaneous apoptosis. This observation suggests that the selective survival advantage enjoyed by CLL B-cells is not entirely autonomous, raising the possibility of manipulating CLL B-cell survival by iatrogenic means. The extended survival of the neoplastic B-cells creates a permissive soil on which oncogene activation, genetic instability and accumulation of gene mutations favoring disease progression can occur. In addition, such survival-promoting microenvironments can rescue leukemia cells from cytotoxic therapy, giving way to disease relapse. Survival of CLL B-cells is influenced by interactions with non-leukemia cells in the microenvironment of lymph nodes, marrow and other tissues. CLL B-cells have developed many different ways to escape undergoing apoptosis. These include: (a) expression of survival receptor as well as their ligands, giving rise to autocrine survival pathways which are leukemia cell specific; (b) defects in plasma membrane receptor cell signaling, triggered by death receptors such as Fas- and TRAIL; and (c) constitutively active survival signaling pathways such as NFkappaB and PI3K/Akt. Here we discuss some of the molecular mechanisms by which interaction with other cells and factors in the microenvironment provides survival advantages to CLL B-cells in specific in vivo niches, and we suggest some strategies for overcoming these anti-apoptotic mechanisms for improving treatment of CLL.

Nurselike cells express BAFF and APRIL, which can promote survival of chronic lymphocytic leukemia cells via a paracrine pathway distinct from that of SDF-1alpha

We examined expression of B cell-activating factor of the tumor necrosis factor (TNF) family (BAFF) and a proliferation-inducing ligand (APRIL) on chronic lymphocytic leukemia (CLL) B cells and nurselike cells (NLCs), which differentiate from CD14+ cells when cultured with CLL B cells. NLCs expressed significantly higher levels of APRIL than monocytes and significantly higher levels of BAFF and APRIL than CLL B cells. Also, the viability of CLL B cells cultured with NLCs was significantly reduced when CLL B cells were cultured with decoy receptor of B-cell maturation antigen (BCMA), which can bind both BAFF and APRIL, but not with BAFF receptor:Fc (BAFF-R:Fc), which binds only to BAFF. The effect(s) of BAFF or APRIL on leukemia cell survival appeared additive and distinct from that of stromal cell-derived factor-1alpha (SDF-1alpha), which in contrast to BAFF or APRIL induced leukemia cell phosphorylation of p44/42 mitogen-activated protein kinase (extracellular signal-regulated kinase-1/2 [ERK1/2]) and AKT. Conversely, BAFF and APRIL, but not SDF-1alpha, induced CLL-cell activation of the nuclear factor-kappaB1 (NF-kappaB1) and enhanced CLL-cell expression of the antiapoptotic protein Mcl-1. However, BAFF, but not APRIL, also induced CLL-cell activation of NF-kappaB2. We conclude that BAFF and APRIL from NLCs can function in a paracrine manner to support leukemia cell survival via mechanisms that are distinct from those of SDF-1alpha, indicating that NLCs use multiple distinct pathways to support CLL-cell survival.

Bodyguards and assassins: Bcl-2 family proteins and apoptosis control in chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is the most common B-cell malignancy in the Western world and exists as subtypes with very different clinical courses. CLL is generally described as a disease of failed apoptosis. Apoptosis resistance may stem from a combination of microenvironmental survival signals as well as from intrinsic alterations in the apoptotic machinery within the CLL cell. The molecular mechanism involved in controlling apoptosis in CLL is complex and is influenced by many factors, including Bcl-2 family proteins, which are critical regulators of cell death. Here we review the significance of apoptosis dysregulation in CLL, focusing on the role of Bcl-2 and related Bcl-2 family proteins, such as Bax and Mcl-1. The differential properties of the newly described subsets of CLL are also highlighted.

Fludarabine-induced apoptosis in CD19+/CD5+B-CLL cells is a direct and nurse-like-cell independent effect

B-cell chronic lymphocytic leukemia (B-CLL) is a hematological malignancy characterized by the accumulation of mature CD5+ B lymphocytes with a defective apoptosis. A subset of blood monocyte-derived adherent cells generated in vitro protects B-CLL cells from apoptosis playing a role as nurse-like cells (NLCs). Fludarabine (9-beta-D-arabinofuranosyl-2-fluoroadenine; F-ara-A) is an adenine nucleoside analog used to treat B-CLL. To gain insight into the mechanisms implicated in the antitumoral effect of fludarabine in B-CLL cells, we performed cross-cultures with B-CLL cells and NLCs treated and untreated with fludarabine. Our results showed that fludarabine blocked the development of NLCs and induced apoptosis in these cells when they were present in culture. Moreover, CD19+/CD5+B-CLL cells treated with fludarabine underwent apoptosis and this event was not related with the presence of NLCs whether treated or not with fludarabine. In conclusion, apoptosis induced by fludarabine in CD19+/CD5+B-CLL cells was due to a direct effect on these cells and not due to its effect in the NLCs.

CD38 and CD100 lead a network of surface receptors relaying positive signals for B-CLL growth and survival

This work addresses the question whether CD38, a negative prognostic marker in B-cell chronic lymphocytic leukemia (B-CLL), plays a role in neoplastic B-cell growth and survival. We show that CD38+ B-CLL cells bind to murine fibroblasts transfected with the CD31 ligand. The interaction triggers an extensive remodeling of the B-CLL membrane, with relocalization of BCR/CD19 to the CD38/CD31 contact areas, and it also increases cell survival and proliferation. A second event is the up-modulation of the survival receptor CD100, restricted to proliferating cells, and a concomitant decrease of CD72 (low-affinity CD100 ligand and negative regulator of immune responses). The most efficient signals are delivered through sequential interactions between CD38/CD31 and CD100/plexin-B1 (high-affinity CD100 ligand), as inferred by coculture experiments using specific transfectants and blocking monoclonal antibodies (mAbs). The finding that nurselike cells from B-CLL patients express CD31 and plexin-B1, which deliver growth and survival signals to CD38+/CD100+ B-CLL cells, further confirms the model proposed. These findings show that a set of normal receptors and ligands ruling physiologic signaling pathways in B lymphocytes becomes detrimental when expressed in the context of B-CLL cells, ultimately leading to the generation of a tumor reservoir.

Inhibition of PI3K, mTOR and MEK signaling pathways promotes rapid apoptosis in B-lineage ALL in the presence of stromal cell support

Bone marrow stromal cells are essential for the differentiation, survival and proliferation of normal and leukemic human B-lineage cells. Leukemic cells require stromal cell support for optimal proliferation and apoptotic resistance. Stromal cell contact can promote resistance to chemotherapeutic agents. In this study, we have made use of small molecular weight inhibitors and an established stromal cell-dependent pre-B-ALL cell line, BLIN-2, to investigate the role of the MAP kinase, PI3K/Akt, JAK/STAT and mTOR pathways in the promotion of leukemic cell growth in the presence of stromal cell support. Treatment with PI3K+JAK, PI3K+MEK, or MEK+JAK inhibitor combinations resulted in an inhibition of proliferation as measured by DNA synthesis. However, only inhibition of both PI3K and MEK or both mTOR and MEK resulted in a dramatic increase in the number of annexinV(+)/PI(+) apoptotic events within a 24 h period. Our data suggest that stromal cell-mediated apoptotic protection in B-lineage ALL is mediated by PI3K/mTOR and MEK via a synergistic mechanism(s).

Williams-Beuren syndrome critical region-5/non-T-cell activation linker: a novel target gene of AML1/ETO

The chromosomal translocation t(8;21) fuses the AML1 (RUNX1) gene on chromosome 21 and the ETO gene on chromosome 8 in human acute myeloid leukemias (AMLs), resulting in expression of the chimeric transcription factor AML1/ETO. AML1/ETO-mediated dysregulation of target genes critical for hematopoietic differentiation and proliferation is thought to contribute to the leukemic phenotype. Several mechanisms, including recruitment of histone deacetylases (HDACs) to AML1 target genes, may be responsible for altered gene expression. We used an ecdysone-inducible expression system in the human monoblastic U-937 cell line to isolate genes that were differentially expressed upon induction of AML1/ETO expression. By representational difference analysis (cDNA-RDA), we identified 26 genes whose expression levels were significantly modulated following AML1/ETO induction for 48 h. None of these genes has previously been described as a target of AML1, ETO or AML1/ETO. One gene downregulated by AML1/ETO in vitro, Williams Beuren syndrome critical region 5 (WBSCR5), was expressed in primary t(8;21)-negative AML blasts but not in primary t(8;21)-positive AML blasts, strongly implying a role of this gene in the phenotype of t(8;21)-positive AML. Four upregulated and four downregulated genes were further studied with all-trans-retinoic acid (ATRA), an inducer of differentiation of U-937 cells, and Trichostatin A (TSA), an HDAC inhibitor. Three out of eight genes including WBSCR5 were regulated during ATRA-induced monocytic differentiation of U-937 cells, however, none of them antagonistically, upon both ATRA treatment and AML1/ETO induction. AML1/ETO-associated dysregulation of gene expression was not mediated by a TSA-sensitive mechanism. The identified genes provide a useful model to study the mechanism by which the AML1/ETO fusion protein exerts its function in transcriptional dysregulation in AML. The possible role of WBSCR5 in normal and malignant hematopoiesis warrants further study.

A novel celecoxib derivative, OSU03012, induces cytotoxicity in primary CLL cells and transformed B-cell lymphoma cell line via a caspase- and Bcl-2–independent mechanism

Chronic lymphocytic leukemia (CLL) is an incurable adult leukemia characterized by disrupted apoptosis. OSU03012 is a bioavailable third-generation celecoxib derivative devoid of cyclooxygenase-2 inhibitory activity that potently induces apoptosis in prostate cancer cell lines and is being developed as an anticancer therapy in the National Cancer Institute (NCI) Rapid Access to Intervention Development (RAID) program. We assessed the ability of OSU03012 to induce apoptosis in primary CLL cells and the mechanism by which this occurs. The LC50 (lethal concentration 50%) of OSU03012 at 24 hours was 7.1 μM, and this decreased to 5.5 μM at 72 hours. Additionally, we have demonstrated that OSU03012 mediates apoptosis by activation of the intrinsic, mitochondrial pathway of apoptosis but also activates alternative cell death pathways that are caspase independent. The early activation of both caspase-dependent and -independent pathways of apoptosis is novel to OSU03012 and suggests it has great potential promise for the treatment of CLL. Moreover, unlike the great majority of therapeutic agents used to treat leukemia or other forms of cancer, OSU03012 induces cell death entirely independent of bcl-2 expression. Overall, these data provide justification for further preclinical development of OSU03012 as a potential therapeutic agent for CLL.

Sustained signaling through the B-cell receptor induces Mcl-1 and promotes survival of chronic lymphocytic leukemia B cells

The clinical course of chronic lymphocytic leukemia (CLL) differs significantly between patients with mutated (M-CLL) and unmutated (U-CLL) immunoglobulin (Ig) variable heavy-chain (V(H)) genes, implying a role for B-cell receptor (BCR) signaling in the pathogenesis of this disease. We have now investigated activation of downstream BCR signaling pathways in U-CLL and M-CLL B cells using soluble anti-IgM (sol-IgM) and immobilized anti-IgM (imm-IgM) antibodies as models for antigenic stimulation. Ligation of the BCR with sol-IgM induced incomplete responses in both CLL subsets, resembling the pattern described for tolerant B cells. This response was characterized by transient phosphorylation of extracellular signal-related kinase (ERK) and Akt (protein kinase B [PKB]), lack of activation of c-JUN NH2-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK), and variable activation of phospholipase Cgamma2 (PLCgamma2) and nuclear factor-kappaB (NF-kappaB). Stimulation with imm-IgM elicited a more complete BCR signal and significantly prolonged phosphorylation of ERK and Akt, indicating persistent or repetitive BCR signaling. Moreover, this type of stimulation increased the levels of the antiapoptotic protein myeloid cell leukemia-1 (Mcl-1) and protected from chemotherapy-induced apoptosis, whereas induction of apoptosis and down-regulation of Mcl-1 was observed following stimulation with sol-IgM. These data demonstrate that only sustained BCR signaling can promote survival of CLL B cells and indicate that the main difference between CLL with mutated and unmutated V(H) genes may reside in the availability of such stimulation.

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.

Chronic lymphocytic leukemia: A review of some new aspects of the biology, factors influencing prognosis and therapeutic options

This review provides some basic information on chronic lymphocytic leukemia (CLL) and attempts to present some of the newer data which have accumulated in recent years including those relating to familial aggregation of CLL and the detection of monoclonal CD5+ lymphocytosis in the general population and families of CLL patients. Novel data on the pathogenesis and concepts of cell origin in CLL are also reviewed stressing the fact that there is biased IgVH gene usage, and the importance of mutational status of the CLL cell, as reported in recent years by different authors. A brief review of the significance of the microenvironmental interactions between stromal cells and other accessory cells, and the leukemic CLL cells is also provided. Other clinical aspects are discussed including diagnostic criteria, clinical staging, and the newer prognostic factors which influence survival and timing of therapy for CLL patients. We also attempt to outline the therapeutic options available and the principles of planning risk and age-adapted treatment, stressing the importance and the necessity for participating in ongoing and future international clinical trials.

Clonal lymphocytes in persons without known chronic lymphocytic leukemia (CLL): implications of recent findings in family members of CLL patients

Several genetic abnormalities have been characterized in chronic lymphocytic leukemia (CLL) but these are predominantly secondary events and the initiating phenomena in the etiology of the disease are yet to be established. Studies of inherited susceptibility have identified the early oncogenic events in both familial and "sporadic" forms of several malignant disorders, and this may also be possible in CLL. However, the utility of linkage analysis in identifying a predisposition locus for the disease is limited because large multigenerational families segregating CLL are rare, while the more frequent small nuclear CLL families contain insufficient numbers of affected individuals. The power to detect predisposition gene(s) could be greatly increased by extending the number of affected individuals within a particular family, for example, by identifying family members with subclinical levels of disease. High-sensitivity flow cytometry techniques, developed to monitor disease in CLL patients undergoing treatment, have allowed accurate enumeration of subclinical levels of CLL cells in healthy individuals from the general population and CLL families. Emerging evidence confirms the phenotypic, genotypic, and clinical associations between the aberrant cells in healthy individuals and those in CLL patients. The data suggest that inherited factors increase the susceptibility to both indolent and aggressive CLL, and they provide unbiased demonstration that the age of onset in CLL families is younger than in the general population.

Functional gene expression analysis of clonal plasma cells identifies a unique molecular profile for light chain amyloidosis

Immunoglobulin light chain amyloidosis (AL) is characterized by a clonal expansion of plasma cells within the bone marrow. Gene expression analysis was used to identify a unique molecular profile for AL using enriched plasma cells (CD138+) from the bone marrow of 24 patients with AL and 28 patients with multiple myeloma (MM) and 6 healthy controls. Class prediction analysis (PAM) revealed a subset of 12 genes, which included TNFRSF7 (CD27), SDF-1, and PSMA2, that distinguished between these 2 groups with an estimated and observed accuracy of classification of 92%. This model was validated with an independent dataset of 11 patients with AL and 12 patients with MM with 87% accuracy. Differential expression for the most discriminant genes in the 12-gene subset was validated using quantitative real-time polymerase chain reaction and protein expression analysis, which upheld the observations from the micro-array expression data. Functional analyses using a novel network mapping software revealed a number of potentially significant pathways that were dysregulated in patients with AL, with those regulating proliferation, apoptosis, cell signaling, chemotaxis, and migration being substantially represented. This study provides new insight into the molecular profile of clonal plasma cells and its functional relevance in the pathogenesis of light chain amyloidosis.

Differential effects on CLL cell survival exerted by different microenvironmental elements

Selected microenvironmental stimuli confer to leukemic cells a growth advantage and an extended survival. We aimed at dissecting the differential support provided by the different cellular components of the microenvironment where CLL cells accumulate. To this end we cultured purified CLL cells in vitro in the presence or absence of different accessory cells (stromal cells, autologous T lymphocytes) and/or soluble molecules (IL-4, sCD40L) and assessed the leukemic cell response in terms of cell viability and chemoattracting capacity. The results indicate that both T lymphocytes and stromal cells are involved in sustaining the survival of leukemic B cells, but indicate that their support is different in terms of time of onset and duration. T cells have a short-term support activity while stromal cells provide long-term support.

Lysophosphatidic acid (LPA) protects primary chronic lymphocytic leukemia cells from apoptosis through LPA receptor activation of the anti-apoptotic protein AKT/PKB

Lysophosphatidic acid (LPA) protects epithelial and fibroblast cell lines from apoptosis. In B-cells, LPA acts as a growth factor promoting cell proliferation. Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of CD19+/CD5+ B-lymphocytes primarily through a block in apoptosis. The mechanisms underlying this defect are not fully understood. We investigated whether LPA could be a survival factor in CLL cells. Herein, we demonstrate that LPA protects B-cell lines BJAB and I-83 and primary CLL cells but not normal B-cells from fludarabine- and etoposide-induced apoptosis. Furthermore, LPA prevented spontaneous apoptosis in primary CLL cells. The LPA1 expression was found to be increased in primary CLL cells compared with normal B-cells correlating with LPA prevention of apoptosis. Treatment of primary CLL cells with the LPA receptor antagonist, diacylglycerol pyrophosphate, reverses the protective effect of LPA against apoptosis, and down-regulation of the LPA1 by siRNA blocked LPA-mediated protection against spontaneous apoptosis in primary CLL cells. The protective effect of LPA was inhibited by blocking activation of the phosphatidylinositol 3-kinase/AKT signaling pathway. These results indicate that LPA is a survival factor in B-cell lines and primary CLL cells but not normal B-cells. Thus, drugs targeting the LPA receptors might be an effective therapy against B-cell-derived malignancies such as CLL.

Selective cytotoxicity and telomere damage in leukemia cells using the telomerase inhibitor BIBR1532

Telomerase represents an attractive target for a mechanism-based therapeutic approach because its activation has been associated with unlimited proliferation in most cancer cells. Recently, a nonnucleosidic small molecule inhibitor, BIBR1532 (2-[(E)-3-naphtalen-2-yl-but-2-enoylamino]-benzoic acid), has been identified that is highly selective for inhibition of telomerase, resulting in delayed growth arrest of tumor cells. Here we examined the effects of BIBR1532 in different leukemia cell lines as well as in primary cells from patients with acute myeloid leukemia (AML) and chronic lymphocytic leukemia (CLL) in short-term culture assays. We observed a dose-dependent direct cytotoxicity in concentrations ranging from 30 to 80 microM. Interestingly, cell death was not dependent on the catalytic activity of telomerase but was delayed in cells with very long telomeres. We observed time-dependent individual telomere erosion, which was associated with loss of telomeric repeat binding factor 2 (TRF2) and increased phosphorylation of p53. Importantly, the proliferative capacity of normal CD34(+) cells from cord blood and leukapheresis samples was not affected by treatment with BIBR1532. We conclude that using this class of telomerase inhibitor at higher concentrations exerts a direct cytotoxic effect on malignant cells of the hematopoietic system, which appears to derive from direct damage of the structure of individual telomeres and must be dissected from telomerase-suppressed overall telomere shortening.

Grb7 expression and cellular migration in chronic lymphocytic leukemia: a comparative study of early and advanced stage disease

Grb7, a noncatalytic intracellular adaptor protein involved in cell migration, is overexpressed in certain invasive and metastatic solid tumors. We found a highly significant difference in the level of expression of Grb7 between chronic lymphocytic leukemia (CLL) cells obtained from stage I and stage IV patients (P<0.001). Using semiquantitative RT-PCR, we detected high levels of Grb7 in 88% of stage IV patients vs only 18% in stage I patients. A corresponding increase was found in the in vitro migration of stage IV CLL cells in comparison to stage I cells. The statistically significant difference in the expression of Grb7 between stage IV and stage I patients was preserved even when tested specifically in the ZAP70-positive group (P<0.01). These findings show that Grb7 levels reflect the severity of the disease, and may be used, in conjunction with ZAP70, to predict disease progression.

A sustained activation of PI3K/NF-kappaB pathway is critical for the survival of chronic lymphocytic leukemia B cells

The progressive rise of mature CD5+ B lymphocytes, despite the low proportion of proliferating cells, has led to the notion that B cell chronic lymphocytic leukemia (B-CLL) is primarily related to defective apoptosis. The microenvironment likely plays a prominent role because the malignant cells progressively accumulate in vivo, whereas they rapidly undergo spontaneous apoptosis when cultured in vitro. To assess microenvironment-mediated survival signals, B-CLL cells were cultured with a murine fibroblast cell line, Ltk-, with and without an agonistic antibody to CD40. Spontaneous apoptosis was associated with the loss of Akt and NF-kappaB activities. Interactions with fibroblasts sustained a basal level of Akt and NF-kappaB activities, which was dependent on phosphatidylinositol-3 kinase (PI3K). Constitutive activity of the PI3K pathway in B-CLL cells when cultured with fibroblasts prevented the downregulation of the prosurvival Bcl-2 family protein Bcl-xL and the caspase inhibitor proteins FLIPL and XIAP, and consequently caspase-3 activation and apoptosis. CD40 crosslinking in B-CLL cells did not further prevent murine fibroblasts-mediated apoptosis but induced cell proliferation, which was associated with an increase of Akt and NF-kappaB activation compared with cells cultured with fibroblasts alone. The PI3K pathway seems to play a pivotal role in B-CLL cell survival and growth.

Antibody therapy for chronic lymphocytic leukemia: a promising new modality

Therapeutic options for chronic lymphocytic leukemia (CLL) have been limited, with low complete response rates (CR) and no treatments demonstrating a survival advantage. The recent introduction of the monoclonal antibodies rituximab and alemtuzumab into clinical trials for patients with CLL has generated promising results. Rituximab targets the CD20 antigen and demonstrates varied single-agent activity that is highly dependent upon the dosing schedule and treatment status of the patient. More importantly, when rituximab is combined with fludarabine or fludarabine and cyclophosphamide, a high frequency of CR and prolonged progression-free survival are observed without an appreciable increase in significant toxicity. Alemtuzumab targets the more ubiquitously expressed CD52 antigen and is therefore associated with a higher frequency of toxicity, particularly immunosuppression, but has appreciable activity in fludarabine refractory CLL. Additionally, alemtuzumab is effective against CLL clones that have p53 mutations or deletions. Future efforts in developing combination strategies with rituximab, alemtuzumab, and potentially other new antibodies offer great promise for the future treatment of CLL.

Engagement of the B-cell antigen receptor (BCR) allows efficient transduction of ZAP-70-positive primary B-CLL cells by recombinant adeno-associated virus (rAAV) vectors

Engagement of the B-cell antigen receptor (BCR) by crosslinking of the surface immunoglobulin (sIg) homodimer was studied for recombinant adeno-associated virus (rAAV)-mediated gene transfer into B-cell chronic lymphocytic leukaemia (B-CLL) cells. Leukemic cells obtained from 20 patients were stimulated with anti-sIg-directed antibodies and transduced with rAAV vectors coding for enhanced green fluorescent protein (EGFP) (AAV/EGFP) or CD40L (AAV/CD40L). Transduction of B-CLL cells was enhanced after BCR engagement compared to unstimulated controls (P=0.0356). BCR crosslinking induced a significant, dose- and time-dependent upregulation of heparan sulfate proteoglycan (HSPG), the primary receptor for AAV, on B-CLL cells (mean: 38.2 versus 1.7%; P=0.0006). A correlation of HSPG expression after BCR crosslinking with transduction efficiency by AAV/EGFP (P=0.0153) and AAV/CD40L (P=0.0347) was observed. High expression of zeta-associated protein 70 (ZAP-70) in B-CLL cells correlated with a better transduction efficiency by AAV/EGFP (P<0.0001) and AAV/CD40L (P=0.002), respectively: 48 h after transduction of ZAP-70-positive samples, transgene expression was seen in a mean of 33.8% (s.e.m. 3.7%) and 28.9% (s.e.m. 6.7%) of cells, respectively, and could be specifically blocked by heparin, a soluble competitor of HSPG (P<0.0001). In summary, engagement of the BCR on ZAP-70 positive B-CLL cells allows efficient rAAV-mediated gene delivery.

Recent advances in the molecular biology and immunobiology of chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (B-CLL) has long been viewed as a relatively homogeneous disease caused by the accumulation of monoclonal immature, immunoincompetent B cells with faulty apoptotic capacities. However, recent evidence, reviewed here, demonstrates that at least two different B-CLL subgroups exist with different clinical courses and outcomes. The malignant cells from both B-CLL subgroups are antigen-experienced cells that have a normal apoptotic apparatus and turnover continually. The leukemic cells of the two B-CLL subgroups have engaged antigen before transformation, although primarily the cells of patients in the poor outcome subgroup can respond to antigens following transformation. The difference in the ability to respond to antigen as a full-fledged B-CLL probably accounts for the different biological features and clinical outcomes of the patients in these subgroups.

Protein kinases in the regulation of apoptosis in B-cell chronic lymphocytic leukemia

The involvement of several protein kinase pathways in the regulation of apoptosis and cell survival has been analyzed in a wide range of models. This article reviews current understanding of the protein kinases involved in the control of apoptosis in B-cell chronic lymphocytic leukemia (B-CLL) cells. Protein kinase C (PKC), phosphatidylinositol 3-kinase (P13K) and nuclear factor-kappa B (NF-kappaB) play important roles in the survival of these leukemic cells. These survival pathways affect proteins involved in the control of apoptosis by altering their expression or function. The elucidation of the signal transduction network involved in the survival of B-CLL cells could provide novel pharmacological targets for the therapy of B-CLL.

Engraftment of Acute Myeloid Leukemia in NOD/SCID Mice Is Independent of CXCR4 and Predicts Poor Patient Survival

The aim of this study was to investigate factors influencing the engraftment potential of acute myeloid leukemia (AML) CD34+ cells in nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. We examined the relationship between engraftment, CXCR4 expression on CD34+ and CD34+CD38- cells, and patient (Pt) clinical/laboratory characteristics in 44 samples from 11 Pts. Engraftment, evaluated by Southern blot and CD45 flow cytometric analyses, was observed in murine bone marrow of 6 of 11 Pt samples, ranging from 0.1% to 73.9% by Southern blot and from 0.1%-36.8% by flow cytometry. Poor Pt prognosis was inversely correlated with engraftment; the median overall survival was 95.9 weeks for Pts whose cells did not engraft and 26.1 weeks for those whose cells did engraft (p = 0.012, log-rank test). No other clinical/laboratory variable predicted engraftment. No correlation between the level of CXCR4 expression on AML cells and engraftment was observed. Cells with virtually absent CXCR4 expression were able to engraft, and cells from two Pts with high expression levels of CXCR4 did not engraft. Furthermore, anti-CXCR4 antibody failed to block the engraftment of AML cells into NOD/SCID mice. In conclusion, we demonstrated that CXCR4 is not critical for the engraftment of AML CD34+ cells in NOD/SCID mice. The model may, however, reflect the clinical course of the disease.

Expression of the chemokine receptors CXCR4 and CCR7 and disease progression in B-cell chronic lymphocytic leukemia/ small lymphocytic lymphoma

OBJECTIVE

To assess the clinical relevance of chemokine receptor expression on the progression of B-cell chronic lymphocytic leukemia (B-CLL).

PATIENTS AND METHODS

Peripheral blood mononuclear cells from 45 patients with B-CLL were purified and compared with lymph node samples collected from 17 of these patients. Also compared were B cells obtained from peripheral blood samples from 5 healthy controls and B cells from reactive lymph nodes from 3 otherwise healthy persons. The patients were treated at the Mayo Clinic in Rochester, Minn, between January 15,1991, and February 7, 2003. Mononuclear cells were stained by a 2-color (fluorescein isothiocyanate/phycoerythrin) flow cytometric assay using antibodies to the chemokine receptors (CXCR1, CXCR2, CXCR3, CXCR4, CXCR5, CCR2, CCR4, CCR5, CCR6, and CCR7) and also to CD19.

RESULTS

Of the 45 patients in this study, 20 had Rai stage 0 disease, 12 had stage I disease, 3 had stage II disease, 2 had stage III disease, and 8 had stage IV disease. The mean fluorescent intensity (MFI) of the chemokine receptor expression on B-CLL cells was compared with normal controls and was not significantly different, except for an increase in the median expression of CXCR3 (P = .003) and CCR7 (P = .001) on B-CLL cells. We also found a significant increase in the expression of CXCR4 and CCR7 in B-CLL cells from patients with stage IV compared with stage 0 disease (P = .001 and P = .02, respectively). Furthermore, circulating B-CLL cells showed significantly higher expression of CXCR4 and CCR7 when compared with B lymphocytes in lymph nodes (P = .003 and P < .001, respectively).

CONCLUSION

The expression of CXCR4 and CCR7 on B-CLL cells correlates with Rai stage. Also, these chemokine receptors may be down-regulated once malignant B cells enter the lymph nodes. To our knowledge, this is the first published report that shows the strong association of Rai stage with CXCR4 and CCR7 expression levels in B-CLL cells.

Activation-induced cytidine deaminase in chronic lymphocytic leukemia B cells: expression as multiple forms in a dynamic, variably sized fraction of the clone

The degree of somatic mutation of immunoglobulin variable (Ig V) region genes is an important prognostic indicator of clinical course and outcome in B-cell chronic lymphocytic leukemia (B-CLL), although the reason for this association remains unclear. Furthermore, some B-CLL cells continue to acquire Ig V gene mutations after the transforming event. Because activation-induced cytidine deaminase (AID) is an essential component of the canonical somatic hypermutation process in healthy B cells, its expression in B-CLL is potentially relevant to the disease. We detected full-length AID transcripts and 3 splice variants by conventional reverse transcription polymerase chain reaction (RT-PCR) in approximately 40% of the cases examined. More sensitive real-time quantitative PCR detected AID transcripts in virtually all B-CLL samples tested, although the range of transcript levels was very large between different cases and varied within individual cases over time. Limiting dilution assays revealed that AID expression was restricted to a small fraction of the leukemic cells in the blood. However, this small fraction is not unique in its ability to express AID, because in vitro stimulation of B-CLL cells with appropriate stimuli significantly increased the fraction of AID-expressing cells. These data suggest that AID-mediated DNA alterations may occur in a variably sized, minor subset of B-CLL cells at any given time.

Rheumatoid fibroblast-like synoviocytes overexpress the chemokine stromal cell-derived factor 1 (CXCL12), which supports distinct patterns and rates of CD4+ and CD8+ T cell migration within synovial tissue

OBJECTIVE

A characteristic feature of the inflammatory infiltrate in rheumatoid arthritis is the segregation of CD4 and CD8 T lymphocyte subsets into distinct microdomains within the inflamed synovium. The aim of this study was to test the hypothesis that chemokines in general and stromal cell-derived factor 1 (SDF-1; CXCL12) in particular are responsible for generating this distinctive microcompartmentalization.

METHODS

We examined how synovial CD4/CD8 T cell subsets interacted in coculture assays with fibroblasts derived from chronic inflammatory synovial lesions and normal synovial tissue as well as from fetal lung and adult skin. We used the ability of T cells to migrate beneath fibroblasts (a process called pseudoemperipolesis) as an in vitro marker of T cell accumulation within synovial tissue.

RESULTS

Rheumatoid fibroblast-like synoviocytes (FLS) displayed a unique ability to support high levels of CD4 and CD8 T cell pseudoemperipolesis. Nonrheumatoid FLS as well as fetal lung fibroblasts supported low levels of pseudoemperipolesis, while skin-derived fibroblasts were unable to do so. CD8 T cells migrated under fibroblasts more efficiently and at a higher velocity than CD4 T cells, a feature that was intrinsic to CD8 T cells. Rheumatoid fibroblasts constitutively produced high levels of SDF-1 (CXCL12), which was functionally important, since blocking studies showed reductions in T cell pseudoemperipolesis to levels seen in nonrheumatoid FLS. Rheumatoid fibroblasts also constitutively produced high levels of vascular cell adhesion molecule 1 (VCAM-1; CD106), but this did not contribute to T cell pseudoemperipolesis, unlike the case for B cells, which require SDF-1 (CXCL12)-CXCR4 and CD49d-VCAM-1 (CD106) interactions. Importantly, only combinations of rheumatoid FLS and rheumatoid-derived synovial fluid T cells supported pseudoemperipolesis when examined ex vivo, confirming the in vivo relevance of these findings.

CONCLUSION

These studies demonstrate that features intrinsic to both fibroblasts (the production of SDF-1) and CD8/CD4 T cells (the expression of CXCR4) are responsible for the characteristic pattern of T lymphocyte accumulation seen in the rheumatoid synovium. These findings suggest that the SDF-1/CXCR4 ligand/receptor pair is likely to play an important functional role in T lymphocyte accumulation and positioning within the rheumatoid synovium.

Alemtuzumab therapy in B-cell lymphoproliferative disorders

Alemtuzumab (Campath-1H, Ilex Pharmaceuticals, San Antonio, TX) is a humanized monoclonal antibody that recognizes the CD52 antigen expressed on malignant and normal B lymphocytes. It has come to be used therapeutically in B-cell malignancies. Responses are seen in non-Hodgkin's lymphoma (NHL), and alemtuzumab can induce molecular remissions in relapsed chronic lymphocytic leukaemia (CLL), even when refractory to purine analogues. Most studies reveal the responses to be superior in the absence of bulky disease. Infusion-related side effects such as rigors, hypotension, and nausea are reduced by using the subcutaneous route of administration. Infectious complications are the most important toxicity seen and are related to the depletion of normal lymphocytes. The clinical efficacy in combination with both fludarabine and rituximab is under investigation.

Homing of antibody secreting cells

As activated B cells differentiate into plasma cells they complete a final series of migration steps that take them to locations where they can efficiently carry out their effector function, secreting immunoglobulin (Ig) M or IgG into circulation or releasing dimeric IgA adjacent to the epithelium for transcytosis. Recent experiments have established a key role for chemokines in directing antibody secreting cell (ASC) movement within the secondary lymphoid organs where they are generated, as well as in guiding the cells to the bone marrow or mucosal surfaces. This review discusses the chemokines involved in directing ASC movements, particularly focusing on the role of CXCR4 and CXCL12/SDF1. The function of CCR9 and CCR10 in IgA ASC homing and contributions made by integrins and lectins are also discussed.

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.

Effects of inhibitors of the chemokine receptor CXCR4 on acute lymphoblastic leukemia cells in vitro

Stromal cell-derived factor-1 (SDF-1) is a key regulator of the behavior of normal and leukemic precursor-B (pre-B) cells. It is possible that inhibiting SDF-1-driven processes in pre-B acute lymphoblastic leukemia (ALL) may have therapeutic implications. In this study, we examined the ability of SDF-1 inhibitors to modulate pre-B ALL cell responses to SDF-1, including chemotaxis, migration into bone marrow stroma, and stroma-supported survival and proliferation on human bone marrow stromal layers. The polyphemusin II-derived inhibitors, T140, TC140012, and T134, and the bicyclam AMD3100, effectively inhibited binding of the anti-CXCR4 monoclonal antibody 12G5 on the pre-B ALL cell line NALM6, with IC(50) values of 0.9, 0.9, 0.9, and 1.9 nM, respectively. Similar results were obtained with ALL samples. T140 (0.1 micro M) and AMD3100 (1 micro M) completely blocked SDF-1-induced chemotaxis and attenuated the migration of pre-B ALL cells into bone marrow stromal layers. AMD3100 and TC140012 at a concentration of 50 micro M significantly inhibited stroma-dependent proliferation of six and four of the eight cases tested, respectively, without reducing the cell viability. In addition, AMD3100 and TC140012 enhanced the cytotoxic and antiproliferative effects of the cytotoxic agents vincristine and dexamethasone. The ability of SDF-1 inhibitors to modulate these biologically important functions of leukemic cells warrants further investigation.

Immunobiology of chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia increasingly is being recognized as a useful model disease with which to study more general processes involved in the evolution of neoplastic disease. The accessibility of the tumor cells and the capacity to confirm their clonal relatedness allow for evaluation of the processes associated with neoplastic transformation and/or disease progression. Recent studies have provided fascinating insight into the potential pathogenesis and pathophysiology of this disease. In addition, features of leukemia cells have been identified that can distinguish subsets of patients that have different tendencies for disease progression. Gene expression studies have identified a relatively small number of genes that are differentially expressed between these subsets, allowing for focused attention on proteins that might contribute to the noted differences in clinical behavior. Finally, recognition that chronic lymphocytic leukemia cells depend upon specific microenvironmental growth and survival factors identifies novel targets for disease intervention. This article focuses on the reports of the past year that have contributed to these areas of active research on chronic lymphocytic leukemia, the most common adult leukemia in Western societies.

The SDF1-G801A polymorphism is not associated with SDF1 gene expression in Epstein-Barr virus-transformed lymphoblastoid cells

The effects of the SDF1-3'A on AIDS progression have been attributed to the altered amount of stromal cell-derived factor 1 (SDF-1). However, the contribution of the SDF1-G801A polymorphism to SDF-1 expression is still unclear. In contrast to fresh peripheral blood mononuclear cells (PBMCs), Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCLs) express the SDF-1 mRNA. Using EBV-transformed LCLs from 42 individuals with different genotypes, we investigated the SDF-1 mRNA levels and methylation status in the SDF1 gene. Both in PBMCs and in EBV-transformed LCLs, CpG dinucleotides in the 5' region of the SDF1 gene were unmethylated. As for the 3' untranslated region (3'UTR), by contrast, CpG dinucleotides were methylated in PBMCs, whereas site-specific demethylation around the polymorphic site was detected in EBV-transformed LCLs. The levels of the demethylation were correlated with the SDF-1 mRNA levels. However, the genotype for the SDF1-G801A polymorphism did not significantly alter the SDF-1 mRNA levels. The allele preferences in transcription and methylation were also absent in the heterozygous cells. In conclusion, this study suggested a contribution of site-specific demethylation in the 3'UTR to the SDF1 gene expression, but did not show any evidence for the contribution of the SDF1-G801A polymorphism to the amount of the SDF-1 mRNA.

SDF-1alpha production is negatively regulated by mouse estrogen enhanced transcript in a mouse thymus epithelial cell line

SDF-1/CXCR4 plays an important role in promoting survival, expansion, and differentiation of T cell progenitors. The present study investigates the mechanism by which estrogen inhibits SDF-1alpha expression in mouse thymus. Mouse estrogen enhanced transcript (mEET) is endogenously expressed in a mouse thymus epithelial cell line 1 (MTEC1). In MTEC1 cells that express the transfected sense mEET, the SDF-1alpha transcription and its chemotactic activity were profoundly inhibited. Conversely, in MTEC1 that express the transfected anti-sense mEET, the SDF-1alpha transcription and its chemotactic activity were substantially augmented. Moreover, we disclosed that mEET inhibited the production of SDF-1alpha by its suppression of NF-kappaB translocation into nucleus. Using a combinatorial induction of doxycycline (Dox) and 17beta-estradiol (E2) on the sense and anti-sense mEET transfectants, it was demonstrated that an increase of mEET expression enhanced E2-induced inhibition of SDF-1alpha production, while a blockade of mEET expression alleviated E2-induced inhibition of SDF-1alpha production. In conclusion, the E2-imposed suppression of SDF-1alpha production is partly mediated by mEET involved signaling pathway.

The antiapoptotic effects of blood constituents in patients with chronic lymphocytic leukemia

OBJECTIVE

Clonal B-lymphocytes of chronic lymphocytic leukemia (B-CLL) are characterized by decreased sensitivity to programmed cell death and, therefore, they accumulate in vivo. However, these malignant cells die rapidly in vitro. In the current study we concentrated on the contribution of autologous serum (AS) and lymphocyte subsets to the survival of the malignant cells in vitro.

METHODS

Mononuclear cells from the peripheral blood of 26 CLL patients and 24 controls were incubated overnight in the presence or absence of AS and heat-inactivated AS (HI-AS) or fetal calf serum (FCS). Also, isolated B cells were incubated at different concentrations in the presence of AS and/or isolated T cells. The level of apoptosis of CD19+ cells was measured by flow cytometry.

RESULTS

Spontaneous apoptosis of unfractionated B-CLL cells incubated with AS, FCS or without serum was significantly lower than the rate of B-cell death in the control group, in similar culture conditions. AS had an antiapoptotic effect on unfractionated B-CLL cells when compared with FCS. The rate of apoptosis of B-CLL cells was directly associated with stage. HI of AS had a variable effect, which was related to the stage of the disease. High concentrations of B cells and the addition of autologous T cells reduced the rate of apoptosis when incubated without serum. The antiapoptotic effect of T cells was most prominent in progressive stages.

CONCLUSIONS

B-CLL cells exhibit decreased spontaneous apoptosis, which is partially prevented by humoral (AS) and cellular (T cells and B-CLL cells) factors. The equilibrium between apoptotic and antiapoptotic factors changes with disease progression.

Mutations in the chemokine receptor gene CXCR4 are associated with WHIM syndrome, a combined immunodeficiency disease

WHIM syndrome is an immunodeficiency disease characterized by neutropenia, hypogammaglobulinemia and extensive human papillomavirus (HPV) infection. Despite the peripheral neutropenia, bone marrow aspirates from affected individuals contain abundant mature myeloid cells, a condition termed myelokathexis. The susceptibility to HPV is disproportionate compared with other immunodeficiency conditions, suggesting that the product of the affected gene may be important in the natural control of this infection. We describe here the localization of the gene associated with WHIM syndrome to a region of roughly 12 cM on chromosome 2q21 and the identification of truncating mutations in the cytoplasmic tail domain of the gene encoding chemokine receptor 4 (CXCR4). Haplotype and mutation analyses in a pedigree transmitting myelokathexis as an apparently autosomal recessive trait support genetic heterogeneity for this aspect of the WHIM syndrome phenotype. Lymphoblastoid cell lines carrying a 19-residue truncation mutation show significantly greater calcium flux relative to control cell lines in response to the CXCR4 ligand, SDF-1, consistent with dysregulated signaling by the mutant receptor. The identification of mutations in CXCR4 in individuals with WHIM syndrome represents the first example of aberrant chemokine receptor function causing human disease and suggests that the receptor may be important in cell-mediated immunity to HPV infection.

Albumin activates the AKT signaling pathway and protects B-chronic lymphocytic leukemia cells from chlorambucil- and radiation-induced apoptosis

Activation of the phosphatidylinositol 3- kinase/AKT pathway antagonizes apoptosis in diverse cellular systems. We previously showed that human plasma activated AKT and potently blocked the ability of chlorambucil or gamma radiation to induce apoptosis of B-chronic lymphocytic leukemia (CLL) cells. Here we report experiments that identify albumin as the major component of plasma that blocks CLL cell killing by chlorambucil or radiation. Intact plasma depleted of albumin by chromatography on Cibacron blue-Sepharose or plasma from a subject with analbuminemia failed either to activate AKT or to protect CLL cells from chlorambucil-induced apoptosis. Both functions were restored by re-addition of albumin. The protective action of albumin as well as AKT activation was compromised by the binding of lipids. Fluorescence-activated cell sorter (FACScan) analysis demonstrated the uptake of fluoresceinated albumin by CLL cells. Accumulation of albumin in intracellular vesicles was also shown by confocal microscopy. Indirect inhibition of AKT activation by the phosphatidylinositol 3-kinase inhibitor LY294002 reversed the blockade of chlorambucil-induced killing by plasma albumin. The data suggest that activation of AKT consequent to binding of albumin by CLL cells blocks chlorambucil- and radiation-induced apoptosis. Strategies designed to block albumin-induced antiapoptotic signaling may, therefore, be of value in enhancing cytotoxic drug action on CLL cells.

CD100/Plexin-B1 interactions sustain proliferation and survival of normal and leukemic CD5+ B lymphocytes

Growth and survival of chronic B-cell tumors are favored by the malignant cell's capacity to respond to selected microenvironmental stimuli provided by nontumoral bystander cells. To investigate which mechanisms operate in these crosstalks and whether they are malignancy-related or reproduce the mechanisms used by normal B cells we have studied the expression and functional role of semaphorin CD100 (now called Sema4D) in chronic lymphocytic leukemia (CLL) cells and normal CD5+ B cells. We demonstrate here that (1) leukemic and normal CD5+ B lymphocytes uniformly express CD100; (2) the CD100 high-affinity receptor Plexin-B1 is expressed by bone marrow stromal cells, follicular dendritic cells, and activated T lymphocytes, and is thus available to CD100+ lymphocytes in different specific microenvironments; and (3) upon interaction between CD100 and Plexin-B1 both CLL and normal CD5+ B cells increase their proliferative activity and extend their life span. These findings establish that Plexin-B1 is an easily accessible receptor for CD100 within the immune system. The encounter of CD100+ leukemic cells with Plexin-B1 may promote the proliferation and survival of malignant cells. The crosstalk operated by the CD100/Plexin-B1 interaction is not malignancy related but reproduces a mechanism used by normal CD5+ B cells.

Sildenafil and vardenafil, types 5 and 6 phosphodiesterase inhibitors, induce caspase-dependent apoptosis of B-chronic lymphocytic leukemia cells

Type 4 phosphodiesterase (PDE4) inhibitors reportedly induce apoptosis in chronic lymphocytic leukemia (CLL) cells. Following clinical improvement of one previously untreated CLL patient with sildenafil therapy, we evaluated the in vitro induction of apoptosis in CLL cells by 4 PDE5/6 inhibitors, including sildenafil, vardenafil, zaprinast, and methoxyquinazoline (MQZ). After 24 hours of culture, the various PDE inhibitors differed in their ability to induce apoptosis, with zaprinast displaying no killing effect. Normal B cells isolated from control donors were totally resistant to PDE-induced apoptosis. Vardenafil was 3 and 30 times more potent an inducer of apoptosis than sildenafil and MQZ, respectively. Both vardenafil and sildenafil failed to elevate adenosine 3'5' cyclic monophosphate (cAMP) levels, largely excluding an inhibitory effect on cAMP-PDE3, -PDE4, and -PDE7. Vardenafil- or sildenafil-treated B-CLL cells displayed up to 30% intracellular active caspase 3. Drug-induced apoptosis was inhibited by the caspase inhibitor z-VAD.fmk, prevented by interleukin-4 (IL-4), and significantly reduced by stromal-derived factor1-alpha (SDF-1alpha). We conclude that vardenafil and sildenafil induce caspase-dependent apoptosis of B-CLL cells in vitro and thus might be considered in the treatment of CLL patients. However, further in vivo investigations should be warranted.

Biology and treatment of chronic lymphocytic leukemia

Major advances have occurred in our understanding of the biology, immunology, and opportunities for treatment of chronic lymphocytic leukemia (CLL) in recent times. Surface antigen analysis has helped us define classical CLL and differentiate it from variants such as marginal zone leukemia, mantle cell leukemia, and prolymphocytic leukemia. An important observation has been that the B-cells in indolent types of CLL, which do not require therapy, have undergone somatic hypermutation and function as memory B-lymphocytes whereas those more likely to progress have not undergone this process. Section I by Dr. Nicholas Chiorazzi encompasses emerging elements of the new biology of CLL and will address the types of somatic hypermutation that occur in CLL cells and their correlation with other parameters such as telomere length and ZAP70 status. In addition he addresses the concept of which cells are proliferating in CLL and how we can quantitate the proliferative thrust using novel methods. The interaction between these parameters is also explored. Section II by Dr. Thomas Kipps focuses on immune biology and immunotherapy of CLL and discusses new animal models in CLL, which can be exploited to increase understanding of the disease and create new opportunities for testing the interaction of the CLL cells with a variety of elements of the immune system. It is obvious that immunotherapy is emerging as a major therapeutic modality in chronic lymphocytic leukemia. Dr. Kipps addresses the present understanding of the immune status of CLL and the role of passive immunotherapy with monoclonal antibodies such as rituximab, alemtuzumab, and emerging new antibodies. In addition the interaction between the CLL cells and the immune system, which has been exploited in gene therapy with transfection of CLL cells by CD40 ligand, is discussed. In Section III, Dr. Michael Keating examines the question "Do we have the tools to cure CLL?" and focuses on the fact that we now have three distinct modalities, which are able to achieve high quality remissions with polymerase chain reaction (PCR) negativity for the immunoglobulin heavy chain in CLL. These modalities include initial chemoimmunotherapy with fludarabine, cyclophosphamide, and rituximab, the use of alemtuzumab for marrow cytoreduction in minimal residual disease and allogeneic bone marrow transplants. The emergence of non-ablative marrow transplants in CLL has led to the broadening of the range of opportunities to treat older patients. The addition of rituximab to the chemotherapy preparative regimens appears to be a significant advance. The combination of our increased understanding of the biology, immune status, and therapy of CLL provides for the first time the opportunity for curative strategies.

Crosstalk between BCR/ABL oncoprotein and CXCR4 signaling through a Src family kinase in human leukemia cells

Stromal-derived factor (SDF)-1 and its G protein-coupled receptor, CXCR4, regulate stem/progenitor cell migration and retention in the marrow and are required for hematopoiesis. We show here an interaction between CXCR4 and the Src-related kinase, Lyn, in normal progenitors. We demonstrate that CXCR4-dependent stimulation of Lyn is associated with the activation of phosphatidylinositol 3-kinase (PI3-kinase). This chemokine signaling, which involves a Src-related kinase and PI3-kinase, appears to be a target for BCR/ABL, a fusion oncoprotein expressed only in leukemia cells. We show that the binding of phosphorylated BCR/ABL to Lyn results in the constitutive activation of Lyn and PI3-kinase, along with a total loss of responsiveness of these kinases to SDF-1 stimulation. Inhibition of BCR/ABL tyrosine kinase with STI571 restores Lyn responsiveness to SDF-1 signaling. Thus, BCR/ABL perturbs Lyn function through a tyrosine kinase-dependent mechanism. Accordingly, the blockade of Lyn tyrosine kinase inhibits both BCR/ABL-dependent and CXCR4-dependent cell movements. Our results demonstrate, for the first time, that Lyn-mediated pathological crosstalk exists between BCR/ABL and the CXCR4 pathway in leukemia cells, which disrupts chemokine signaling and chemotaxis, and increases the ability of immature cells to escape from the marrow. These results define a Src tyrosine kinases-dependent mechanism whereby BCR/ABL (and potentially other oncoproteins) dysregulates G protein-coupled receptor signaling and function of mammalian precursors.

Chronic lymphocytic leukaemia: a model for investigating potential new targets for the therapy of indolent lymphomas

We address two key issues whose investigation may help to define new prognostic parameters and new potential targets for therapeutic intervention. First, which are the conceptual implications of the cellular origin of indolent lymphomas? Second, how may deciphering the biology of chronic lymphocytic leukaemia (CLL) lead to the development of new modalities of treatment? The latter issue is articulated in the following three key questions. (1) Which are the molecular pathways through which the microenvironment exerts its influence on the malignant clone? (2) What are the relationships between proliferation and defective apoptosis? (3)Is there any evidence of a role for antigenic stimulation?

Protection of CLL B cells by a follicular dendritic cell line is dependent on induction of Mcl-1

Chronic lymphocytic leukemia (CLL) B cells have defects in apoptosis pathways and therefore accumulate in vivo. However, when removed from the patient and cultured in vitro, these malignant cells rapidly undergo apoptosis. Recent studies suggest that leukemia cell survival is influenced by interactions with nonleukemia cells in the microenvironment of lymph nodes, marrow, and other tissues. To model such cell-cell interactions in vitro, we cultured freshly isolated CLL B cells with a follicular dendritic cell line, HK. CLL B cells cocultured with HK cells were protected from apoptosis, either spontaneous or induced by treatment with anticancer drugs. Protection against spontaneous apoptosis could also be induced by coculturing the CLL B cells with normal dendritic cells (DCs) or with a CD40-ligand (CD154)–expressing fibroblast cell line. Examination of the expression of several apoptosis-regulatory proteins revealed that coculture with HK cells or DCs induced up-regulation of the antiapoptotic Bcl-2 family protein Mcl-1 in CLL B cells, whereas CD40 ligation increased expression of Bcl-XL. Cell-cell contact was required for HK-induced protection, and introducing neutralizing antibodies against various adhesion molecules showed that CD44 was involved in HK-mediated survival, whereas CD40, intercellular adhesion molecule–1 (ICAM-1) and vascular cell adhesion molecule–1 (VCAM-1) were not. Anti-CD44 antibodies also blocked Mcl-1 induction by HK cells. Mcl-1 antisense oligonucleotides reduced leukemia cell expression of Mcl-1, and significantly suppressed HK-induced protection against apoptosis, whereas control oligonucleotides had no effect. Thus, HK cells protect CLL B cells against apoptosis, at least in part through a CD44-dependent mechanism involving up-regulation of Mcl-1, and this mechanism is distinct from that achieved by CD40 ligation. Consequently, the particular antiapoptotic proteins important for CLL survival may vary depending on the microenvironment.