Expression of Vascular Endothelial-Cadherin on Leukemic Cells Mediates Their Interaction with Vascular Endothelium.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 2761-2761
Author(s):  
Leslie R. Ellis ◽  
Loic Vincent ◽  
Sergey Shmelkov ◽  
Andrea Hooper ◽  
Scott Avecilla ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Minimal Residual Disease ◽  
Cell Lines ◽  
Residual Disease ◽  
Leukemic Cell ◽  
Angiogenic Factors ◽  
Leukemic Cells ◽  
Vascular Endothelial ◽  
Leukemic Cell Lines ◽  
Minimal Residual

Abstract It has already been established that subsets of leukemic cells express receptors for pro-angiogenic factors, such as vascular endothelial growth factor receptor-2 (VEGFR-2). Further studies have shown that these same leukemic cells also produce the ligand for these VEGF receptors, VEGF-A. This autocrine loop supports the invasion and proliferation of these particular leukemic cells. The VEGFR-2 signaling pathway is further dependent upon the co-activation of other pro-angiogenic factors, such as vascular endothelial (VE)-cadherin. VE-cadherin is an endothelial cell-specific transmembrane cellular adhesion protein that when bound results in the dephosphorylation of VEGFR-2 and contributes to neo-vessel formation. Recent studies have suggested that VE-cadherin may be expressed by a unique subset of hematopoietic cells, raising the possibility that leukemic cells may express VE-cadherin as well. We therefore sought to identify the expression of VE-cadherin on leukemic cell lines and primary samples, and further determine its role in the interaction with VE-cadherin-positive endothelial cells. Leukemic cell lines and primary leukemias were screened for the presence of VE-cadherin by both RT-PCR and Western blot analysis. Primary leukemic samples, as well as established cell lines for human erythroblastic leukemia (HEL) and acute myelogenous leukemia (KG-1a) were found to express VE-cadherin. VE-cadherin expression was further confirmed by flow cytometry and immunocytochemistry, which demonstrated that approximately 15% of the total population was VE-cadherin-positive. Proliferation and migration assays utilizing neutralizing monoclonal antibodies to VE-cadherin were performed with no obvious effects. However, immunofluorescent staining of a co-culture performed with the above leukemic cells grown on a layer of human umbilical vein endothelial cells (HUVECs) demonstrated that the leukemic cells and HUVECs interact via VE-cadherin. Furthermore, when these leukemic cells were injected into NOD-SCID mice subcutaneously, the VE-cadherin-positive cells localized around the vessels present within the leukemic chloroma. These data set forth the concept that a subset of leukemic cells expresses the protein VE-cadherin and that VE-cadherin is involved in the cell-to-cell interaction between a subset of leukemic cells and vascular endothelial cells. Heterotypic VE-cadherin interaction between leukemic cells and neo-vessels may increase the survival of leukemic cells and contribute to the generation of minimal residual disease. Therefore, inhibition of VEGFR-2 in conjunction with VE-cadherin may provide a novel strategy to eradicate minimal residual disease.

scholarly journals Nonhomogeneous distribution of leukemia in the bone marrow during minimal residual disease

Blood ◽  
1987 ◽  
Vol 70 (4) ◽  
pp. 1073-1078 ◽  
Author(s):  
AC Martens ◽  
FW Schultz ◽  
A Hagenbeek
Keyword(s):  
Bone Marrow ◽  
Minimal Residual Disease ◽  
Extreme Values ◽  
Residual Disease ◽  
Leukemic Cell ◽  
Leukemic Cells ◽  
Accurate Estimation ◽  
Acute Myelocytic Leukemia ◽  
Single Bone ◽  
Minimal Residual

Abstract In a rat model (BNML) for human acute myelocytic leukemia the distribution of leukemic cells in bone marrow samples from various sites was investigated, using monoclonal antibodies (MoAbs) and flow cytometry. Rats were studied before chemotherapy as well as thereafter, ie, in the “minimal residual disease” (MRD) phase. Bone marrow from different types of bones was analyzed from each animal. Before treatment, the ratio of the measured extreme values (ie, highest/lowest value) for leukemic cell frequencies in bones from individual rats ranged from 3.7 to 11.7. During the MRD phase the ratios of the extremes ranged from a factor of 36 to more than 13,000 from one rat to another. The variability between bones of comparable size was estimated by studying the ribs from each individual animal. Within individuals the extremes differed by a factor of 1.2 to 4.0 before chemotherapy and from 2.4 to greater than 320 after chemotherapy. The variability within the marrow cavity of a single bone was determined by analyzing multiple samples from femoral bones cut into slices. The leukemic cell frequency appeared to vary considerably, ie, before treatment from 1.7 to 7.3 and during MRD from 4 to 28,000. The presented data may contribute to understanding the sometimes conflicting observations in leukemic patients. Improvement of methods for detecting MRD will not automatically lead to a more accurate estimation of the total tumor burden. The reliability of diagnoses based on the analysis of single bone marrow aspirates appears to be highly questionable.

scholarly journals Nonhomogeneous distribution of leukemia in the bone marrow during minimal residual disease

Blood ◽  
1987 ◽  
Vol 70 (4) ◽  
pp. 1073-1078 ◽  
Author(s):  
AC Martens ◽  
FW Schultz ◽  
A Hagenbeek
Keyword(s):  
Bone Marrow ◽  
Minimal Residual Disease ◽  
Extreme Values ◽  
Residual Disease ◽  
Leukemic Cell ◽  
Leukemic Cells ◽  
Accurate Estimation ◽  
Acute Myelocytic Leukemia ◽  
Single Bone ◽  
Minimal Residual

In a rat model (BNML) for human acute myelocytic leukemia the distribution of leukemic cells in bone marrow samples from various sites was investigated, using monoclonal antibodies (MoAbs) and flow cytometry. Rats were studied before chemotherapy as well as thereafter, ie, in the “minimal residual disease” (MRD) phase. Bone marrow from different types of bones was analyzed from each animal. Before treatment, the ratio of the measured extreme values (ie, highest/lowest value) for leukemic cell frequencies in bones from individual rats ranged from 3.7 to 11.7. During the MRD phase the ratios of the extremes ranged from a factor of 36 to more than 13,000 from one rat to another. The variability between bones of comparable size was estimated by studying the ribs from each individual animal. Within individuals the extremes differed by a factor of 1.2 to 4.0 before chemotherapy and from 2.4 to greater than 320 after chemotherapy. The variability within the marrow cavity of a single bone was determined by analyzing multiple samples from femoral bones cut into slices. The leukemic cell frequency appeared to vary considerably, ie, before treatment from 1.7 to 7.3 and during MRD from 4 to 28,000. The presented data may contribute to understanding the sometimes conflicting observations in leukemic patients. Improvement of methods for detecting MRD will not automatically lead to a more accurate estimation of the total tumor burden. The reliability of diagnoses based on the analysis of single bone marrow aspirates appears to be highly questionable.

Differential expression of a novel proline-rich homeobox gene (Prh) in human hematolymphopoietic cells

Blood ◽  
1995 ◽  
Vol 85 (5) ◽  
pp. 1237-1245 ◽  
Author(s):  
G Manfioletti ◽  
V Gattei ◽  
E Buratti ◽  
A Rustighi ◽  
A De Iuliis ◽  
...  
Keyword(s):  
Cell Lines ◽  
Constitutive Expression ◽  
Leukemic Cell ◽  
Leukemic Cells ◽  
Maturation Stage ◽  
Lymphoid Tissues ◽  
Specific Cell ◽  
B Cell Differentiation ◽  
Leukemic Cell Lines

Proline-rich homeobox (Prh) is a novel human homeobox-containing gene recently isolated from the CD34+ cell line KG-1A, and whose expression appears mainly restricted to hematopoietic tissues. To define the pattern of Prh expression within the human hematopoietic system, we have analyzed its constitutive expression in purified cells obtained from normal hematopoietic tissues, its levels of transcription in a number of leukemia/lymphoma cell lines representing different lineages and stages of hematolymphopoietic differentiation, and its regulation during in vitro maturation of human leukemic cell lines. Prh transcripts were not detected in leukemic cells of T-lymphoid lineage, irrespective of their maturation stage, and in resting or activated normal T cells from peripheral blood and lymphoid tissues. In contrast, high levels of Prh expression were shown in cells representing early stages of B lymphoid maturation, being maintained up to the level of circulating and tissue mature B cells. Terminal B-cell differentiation appeared to be conversely associated with the deactivation of the gene, since preplasmacytic and plasmocytoma cell lines were found not to express Prh mRNA. Prh transcripts were also shown in human cell lines of early myelomonocytic, erythromegakaryocytic, and preosteoclast phenotypes. Prh expression was lost upon in vitro differentiation of leukemic cell lines into mature monocyte-macrophages and megakaryocytes, whereas it was maintained or upregulated after induction of maturation to granulocytes and osteoclasts. Accordingly, circulating normal monocytes did not display Prh mRNA, which was conversely detected at high levels in purified normal granulocytes. Our data, which show that the acquisition of the differentiated phenotype is associated to Prh downregulation in certain hematopoietic cells but not in others, also suggest that a dysregulated expression of this gene might contribute to the process of leukemogenesis within specific cell lineages.

scholarly journals Immunophenotyping Investigation of Minimal Residual Disease Is a Useful Approach for Predicting Relapse in Acute Myeloid Leukemia Patients

Blood ◽  
1997 ◽  
Vol 90 (6) ◽  
pp. 2465-2470 ◽  
Author(s):  
J.F. San Miguel ◽  
A. Martı́nez ◽  
A. Macedo ◽  
M.B. Vidriales ◽  
C. López-Berges ◽  
...  
Keyword(s):  
Acute Myeloid Leukemia ◽  
Multidrug Resistance ◽  
Minimal Residual Disease ◽  
Myeloid Leukemia ◽  
Residual Disease ◽  
Leukemic Cells ◽  
Rhodamine 123 ◽  
Minimal Residual ◽  
Acute Myeloid

Abstract A high complete remission rate is currently achieved in patients with acute myeloid leukemia (AML). However, many patients eventually relapse due to the persistence of low numbers of residual leukemic cells that are undetectable by conventional cytomorphologic criteria (minimal residual disease [MRD]). Using immunophenotypic multiparametric flow cytometry, we have investigated in sequential studies (diagnosis and follow-up) the impact of MRD detection on the outcome of 53 AML patients that had achieved morphologic remission with standard AML protocols and displayed at diagnosis an aberrant phenotype. Patients were studied at diagnosis with a panel of 35 monoclonal antibodies in triple staining combinations for detection of aberrant or uncommon phenotypic features. According to these features, a patient's probe was custom-built at diagnosis for the identification of possible residual leukemic cells during follow-up. The level of MRD at the end of induction and intensification therapy correlated with the number of relapses and relapse-free survival (RFS). Thus, patients with more than 5 × 10−3 residual cells (5 residual cells among 1,000 normal bone marrow [BM] cells) identified as leukemic by immunophenotyping in the first remission BM showed a significant higher rate of relapse (67% v 20% for patients with less than 5 × 10−3 residual cells; P = .002) and a lower median RFS (17 months v not reached; P = .01). At the end of intensification, with a cut-off value of 2 × 10−3 leukemic cells, AML patients also separated into two distinct groups with relapse rates of 69% versus 32% (P = .02), respectively, and median RFS of 16 months versus not reached (P = .04). In addition, overall survival was also significantly related to the level of residual cells in the marrow obtained at the end of induction and particularly after intensification therapy (P = .008). Furthermore, we have explored whether residual disease was related with the functional expression of multidrug resistance (MDR-1) at diagnosis as assessed by the rhodamine-123 assay. Patients with ≥5 × 10−3 residual leukemic cells at the end of induction therapy had a significantly higher rhodamine-123 efflux (mean, 56% ± 24%) than those with less than 5 × 10−3 residual cells (mean, 32% ± 31%; P = .04). Finally, multivariate analysis showed that the number of residual cells at the end of induction or intensification therapy was the most important prognostic factor for prediction of RFS. Overall, our results show that immunophenotypical investigation of MRD strongly predicts outcome in patients with AML and that the number of residual leukemic cells correlates with multidrug resistance.

scholarly journals Signal transduction and glycophosphatidylinositol-linked proteins (lyn, lck, CD4, CD45, G proteins, and CD55) selectively localize in Triton- insoluble plasma membrane domains of human leukemic cell lines and normal granulocytes

Blood ◽  
1996 ◽  
Vol 87 (9) ◽  
pp. 3783-3794 ◽  
Author(s):  
I Parolini ◽  
M Sargiacomo ◽  
MP Lisanti ◽  
C Peschle
Keyword(s):  
Signal Transduction ◽  
G Proteins ◽  
Cell Lines ◽  
Tyrosine Kinases ◽  
Leukemic Cell ◽  
Receptor Activation ◽  
Leukemic Cells ◽  
Human Leukemic Cell ◽  
Leukemic Cell Lines ◽  
B Lymphoid

Src-family nonreceptor protein tyrosine kinases (NRPTK) are associated with cell surface receptors in large detergent-resistant complexes: in epithelial cells, yes is selectively located in vesicle structures containing caveolin (“caveolae”). These formations are typically also endowed with glycophosphatidylinositol (GPI)-anchored proteins. In the present study, we observed lck, lyn, src, hck, CD4, CD45, G proteins, and CD55 (decay-accelerating factor) expression in the buoyant low- density Triton-insoluble (LDTI) fraction of selected leukemic cell lines and granulocytes. We provide a detailed analysis of the two most highly expressed NRPTK, p53/p56lyn and p56lck, which are involved in the transduction of signals for proliferation and differentiation of monocytes/B lymphocytes and T lymphocytes, respectively. We show that lyn is selectively recovered in LDTI complexes isolated from human leukemic cell lines (promyelocytic [HL-60], erythroid [K562] and B- lymphoid [697]) and from normal human granulocytes, and that lck is recovered from LDTI fractions of leukemic T- and B-lymphoid cell lines (CEM, 697). In LDTI fractions of leukemic cells, lck and lyn are enriched 100-fold as compared with the total cell lysates. Analysis of these fractions by electron microscopy shows the presence of 70- to 200- nm vesicles: lyn and lck are homogenously distributed in the vesicles, as revealed by an immunogold labeling procedure. These novel results propose a role for these vesicles in signal transduction mechanisms of normal and neoplastic hematopoietic cells. In support of this hypothesis, we further observed that molecules participating in B- and T-cell receptor activation cofractionate in the LDTI fractions, CD45/lyn (B cells) and CD45/lck/CD4 (T cells).

scholarly journals Loss of suppression of normal bone marrow colony formation by leukemic cell lines after differentiation is induced by chemical agents

Blood ◽  
1985 ◽  
Vol 65 (1) ◽  
pp. 100-106 ◽  
Author(s):  
HN Steinberg ◽  
AS Tsiftsoglou ◽  
SH Robinson
Keyword(s):  
Bone Marrow ◽  
Cell Lines ◽  
Colony Formation ◽  
Leukemic Cell ◽  
K562 Cells ◽  
Leukemic Cells ◽  
Cell Phenotype ◽  
Normal Bone Marrow ◽  
Normal Bone ◽  
Leukemic Cell Lines

Abstract The human leukemic cell lines K562 and HL-60 were cocultured with normal bone marrow (BM) cells. Coculture with 10(4) K562 or HL-60 cells results in 50% inhibition of normal CFU-E and BFU-E colony formation. However, when the same number of K562 and HL-60 cells is first treated for two to five days with agents that induce their differentiation, a gradual loss in their capacity to inhibit CFU-E and BFU-E colony formation is observed. The inhibitory material in K562 cells is soluble and present in conditioned medium from cultures of these cells. The degree to which leukemic cell suppression of CFU-E and BFU-E growth is reversed is correlated with the time of exposure to the inducing agent. Suppression is no longer evident after five days of prior treatment with inducers. In fact, up to a 90% stimulation of CFU-E growth is observed in cocultures with K562 cells that have been pretreated with 30 to 70 mumol/L hemin for five days. K562 cells treated with concentrations of hemin as low as 30 mumol/L demonstrate increased hemoglobin synthesis and grow normally, but no longer have an inhibitory effect on CFU-E growth. Hence, reversal of normal BM growth inhibition must be caused by the more differentiated state of the K562 cells and not by a decrease in the number of these cells with treatment. Thus, induction of differentiation in cultured leukemic cells not only alters the malignant cell phenotype but also permits improved growth of accompanying normal marrow progenitor cells. Both are desired effects of chemotherapy.

Pioglitazone Inhibits the Growth of Human Leukemic Cell Lines and Primary Leukemic Cells in Vitro.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 4493-4493 ◽  
Author(s):  
Yoshihiro Hatta ◽  
Minoru Saiki ◽  
Yuko Enomoto ◽  
Shin Aizawa ◽  
Umihiko Sawada ◽  
...  
Keyword(s):  
Cell Lines ◽  
Colony Formation ◽  
Mononuclear Cells ◽  
Hematopoietic Cells ◽  
Leukemic Cell ◽  
Leukemic Cells ◽  
Peroxisome Proliferator ◽  
Leukemic Cell Lines ◽  
Ppar Γ

Abstract Troglitazone and pioglitazone are one of thiazolidinediones that are high affinity ligand for the nuclear receptor called peroxisome proliferator-activated receptor gamma (PPAR-γ). Troglitazone is a potent inhibitor of clonogenic growth of acute myeloid leukemia cells when combined with a retinoid. However, the effect of pioglitazone to neoplastic cells and normal hematopoietic cells has not been studied yet. Adult T-cell leukemia (ATL), prevalent in western Japan, is a highly aggressive malignancy of mature T lymphocyte. Therefore, we studied antitumor effect of pioglitazone against leukemic cells including ATL as well as normal hematopoietic cells. With 300 μM of pioglitazone, colony formation of ATL cell lines (MT1, MT2, F6T, OKM3T, and Su9T01) was completely inhibited. Colony formation of HUT102, another ATL cell line, was 12 % compared to untreated control. Clonogenic cells of other leukemic cell lines (K562, HL60, U937, HEL, CEM, and NALM1) was also inhibited to 0–30% of control. Colony formation of primary leukemic cells from 5 AML patients was decreased to 15 %. However, normal hematopoietic cells were weakly inhibited with 300 μM pioglitazone; 77 % of CFU-GM, 70 % of CFU-E, and 33 % of BFU-E survived. Cell cycle analysis showed that pioglitazone decreased the ratio of G2/M phase in HL60 cells, suggesting the inhibition of cell division. By Western blotting, PPAR-γ protein level was similar in all leukemic cells and normal bone marrow mononuclear cells. Taken together, pioglitazone effectively eliminate leukemic cells and could be used as an antitumor agent in vivo.

Precursor T Cell Acute Lymphoblastic Leukemia (T-ALL) Blasts Lose Expression of Markers of Immaturity during Chemotherapy: Implications for the Detection of Minimal Residual Disease.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1521-1521 ◽  
Author(s):  
Mikhail Roshal ◽  
Jonathan Fromm ◽  
Stuart Winter ◽  
Kimberly Dunsmore ◽  
Brent Wood
Keyword(s):  
T Cells ◽  
Minimal Residual Disease ◽  
Residual Disease ◽  
Lymphoblastic Leukemia ◽  
Positive Sample ◽  
High Expression ◽  
Leukemic Cells ◽  
Rank Test ◽  
Multiparameter Flow Cytometry ◽  
Minimal Residual

Abstract Immunophenotyping has become a primary modality in detection of minimal residual disease (MRD) in acute leukemia. Detection and enumeration of leukemic blasts relies on the recognition of the aberrancies in the immunophenotype of the abnormal population. Antigens associated with immature phenotype are thought to represent particularly good markers for identification of leukemic cells. In particular the expression of terminal deoxynucleotide transferase (TdT) on the T-lineage blasts outside the thymus and aberrantly high expression CD99 have been shown to be present in virtually all cases of T-ALL at diagnosis. CD34 and CD10 have also been used as markers of immaturity and aberrancy in MRD. Upon therapy precursor B cell ALL blasts have been shown to lose markers associated with immaturity complicating the detection of MRD. Immunophenotypic changes in T-ALL have not been well characterized. We studied the utility of these markers in the detection of MRD in pediatric patients undergoing chemotherapy under the Children’s Oncology Group (COG) research protocol for treatment of T-ALL. Per protocol (COG-AALL0434) patients received cytarabine intrathecally (IT) on day 1; vincristine IV and daunorubicin hydrochloride IV on days 1, 8, 15, and 22; prednisone IV or orally twice daily on days 1–28; pegaspargase intramuscularly (IM) on day 4, 5, or 6; and methotrexate (MTX) IT on days 8 and 29. Blood and bone marrow samples from 74 consecutive patients enrolled in the protocol between 05/2007 and 04/2008 and who had at least one positive sample (>0.1% blasts of total white cells) at days 8, 15 or 29 post first day of induction were analyzed at diagnosis and in the setting of MRD detection for abnormal expression of TdT, CD99, CD34 and CD10 by multiparameter flow cytometry. Expression of individual antigens was assessed both by percentage of the leukemic blasts with levels of expression above those of normal mature T cells in the samples and by mean fluorescence quotient relative to normal T cells. Consistent with prior reports, nearly all patient samples demonstrated expression of TdT (96%, MFQ=1.35(central 95%=1.01–1.74)) and high expression of CD99 (96%, MFQ=1.34(1.01–1.59)) on at least 20% of abnormal cells at diagnosis. Moreover, TdT and CD99 could be used for blast enumeration with 88% of cases showing greater than 50% positivity for each marker. Expression of these markers began to decline by day 8 and continued to decrease through day 29. Thus only a minority of positive cases showed expression of TdT (24%, MFQ=1.08(0.9–1.62), p<0.001, by Wilcoxon signed-rank test) or CD99 (44%, MFQ=1.14 (0.88–1.51) p<0.001) and in yet smaller proportion of cases could these markers be used for blast enumeration (11% and 26% respectively) by day 29. Median decline for CD99 positivity on the abnormal blasts was 24%, 26% and 62% at day 8, 15 and 29 respectively. Similarly, the differences for TdT were 30%, 44% and 60% respectively. CD34 and CD10 were expressed on a minority of pre-treatment cases (41% and 28% respectively) and expressed similar but less dramatic decline. At day 29, 25.9% of cases expressed CD34 and 16.2% of cases expressed CD10. Median change was 16% for CD34 and 17% for CD10 for cases that expressed those antigens before treatment. Figure 1 demonstrates the declines in both “high positive” with abnormal blasts showing greater than 50% positivity for a marker and of “low positive” cases showing between 20–50% positivity. We conclude that expression of common T-ALL markers of immaturity dramatically declines in the setting of chemotherapy, reducing their value for immunophenotypic detection of MRD. We speculate that this change is due to either chemotherapy induced partial maturation or selective survival of more mature aberrant cells. These results suggest the need for expansion of immunophenotyping panels to decrease reliance on individual markers of immaturity for T-ALL detection in order to achieve a more accurate evaluation of MRD. Figure 1: Loss of markers of immaturity in T-ALL Figure 1:. Loss of markers of immaturity in T-ALL

Expression and Function of the CXCR7 Chemokine Receptor in Leukemias

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2423-2423
Author(s):  
Sergej Konoplev ◽  
Hongbo Lu ◽  
Michael A Fiegl ◽  
Zhihong Zeng ◽  
Wenjing Chen ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
Cell Lines ◽  
Lymphoblastic Leukemia ◽  
Leukemic Cell ◽  
Leukemic Cells ◽  
Human Leukemia ◽  
Rt Pcr ◽  
Hematopoietic Stem ◽  
Leukemic Cell Lines ◽  
And Function

Abstract Background: Bone marrow produced stromal-derived factor-1a (SDF-1a) is a key chemokine involved in chemotaxis, homing, mobilization, and expansion of hematopoietic stem and progenitor cells. While the majority of well-defined functions of SDF-1a are mediated via its receptor CXCR4, recent studies have characterized CXCR7 as an alternative receptor capable of binding SDF-1a. Although the functions of CXCR7 are still incompletely understood, the receptor was reported to promote migration and adhesion in certain cell types and function as a pro-survival factor in breast cancer cells. CXCR7 expression and function in human leukemia cells has not been characterized. In this study, we examined CXCR7 expression in leukemia cell lines and primary samples from patients with acute lymphoblastic leukemia (ALL) and utilized a small molecule inhibitor of CXCR7 to probe CXCR7’s function. Materials and methods: CXCR4 and CXCR7 expression was determined by flow cytometry, real-time PCR (RT-PCR) and immunocytochemistry (ICC) in leukemic cell lines including AML (OCI-AML2, OCI-AML3, HL60, U937 NB4, Molm13), ALL (REH, Raji, RS4; 11, Nalm6, Molt4) and CML (KBM5, K562) cells. In primary ALL patient samples, CD34+CD19+ gating was applied to detect CXCR7 expression on pre-B leukemic cells by flow cytometry. The migration of leukemic cells towards SDF-1a was studied using a transwell system. CXCR4 inhibitor AMD3100 was purchased from Sigma, and CXCR7 inhibitor CCX-733 was provided by ChemoCentryx Inc., Mountain View, CA. Results: CXCR4 was found to be ubiquitously expressed on the cell surface of all leukemic cell lines tested. CXCR7 mRNA and protein expression was detectable only in Burkitt lymphoma Raji cells, as analyzed by flow cytometry (clone 11G8, R&D systems), RT-PCR and ICC. Curiously, CXCR7 expression was significantly induced in MOLM13 cells under hypoxic (6% O2) conditions (p=0.01). Low levels of surface CXCR7 were found in 8 of the 9 primary ALL samples by flow cytometry. To determine the respective roles of CXCR4 and CXCR7 in migration of leukemic cells, we utilized CXCR4 inhibitor AMD3100 and CXCR7 inhibitor CCR733 in Raji (CXCR7 positive) and RS4;11 (CXCR7 negative) cells. AMD3100 at 25μM significantly inhibited SDF-1a induced migration (from 38.5% to 12%); CCR733 at 10μM also inhibited SDF-1a induced migration (from 38.5% to 24%) and the combination of AMD3100 and CCR733 resulted in 81% inhibition of migration (from 38.5% to 7.2%). AMD3100 blocked SDF-1a induced migration of CXCR4+CXCR7− RS4;11 cells (from 36.5% to 15.8%), while CCR733 had no effect (36.5% and 39.2%). In conclusion, these studies demonstrate functional expression of the SDF-1 receptor CXCR-7 on Raji and primary ALL cells and suggest that CXCR7 plays an active role in the migration of leukemic cells. CXCR-7 may serve as an alternative receptor to CXCR4. Studies addressing the role of CXCR7 in adhesion, SDF-1a-mediated signaling and survival of leukemic cells are in progress.

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