Expression and release of CD27 in human B-cell malignancies

Abstract CD27, a transmembrane disulfide-linked 55-kD homodimer, belongs to the nerve growth factor-receptor family, a group of homologous molecules involved in lymphocyte differentiation and selection. It is expressed on mature thymocytes, peripheral blood T cells, and a subpopulation of B cells. We investigated the expression of CD27 on malignant B cells representative for a broad range of stages in physiologic antigen- independent and -dependent B-cell development. In normal lymphoid tissue CD27+ B cells were only found in the peripheral blood (29.8% +/- 10.8%, n = 13) and in germinal centers. With the exception of pro-B and the majority of pre-pre-B acute lymphocytic leukemias and of myelomas, CD27 expression of variable intensity was detected on almost all immature and mature malignant B cells tested. Moreover, using a sandwich enzyme-linked immunosorbent assay we could show the presence of sometimes very high (up to 6,000 U/mL; normal values < 190 U/mL) amounts of the soluble 28- to 32-kD form of CD27 (sCD27) in the sera of patients with B-cell malignancies. The highest levels of sCD27 were observed in patients with chronic lymphocytic leukemia and low-grade non-Hodgkin's lymphomas. Most importantly, both in transversal and longitudinal studies, we found a strong correlation between sCD27 levels in the serum and tumor load, indicating that sCD27 can be used as a disease-marker in patients with acute and chronic B-cell malignancies.

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Expression and release of CD27 in human B-cell malignancies

Blood ◽

10.1182/blood.v82.11.3430.bloodjournal82113430 ◽

1993 ◽

Vol 82 (11) ◽

pp. 3430-3436 ◽

Cited By ~ 1

Author(s):

MH van Oers ◽

ST Pals ◽

LM Evers ◽

CE van der Schoot ◽

G Koopman ◽

...

Keyword(s):

B Cells ◽

B Cell ◽

Peripheral Blood ◽

Growth Factor Receptor ◽

Lymphocytic Leukemia ◽

Enzyme Linked Immunosorbent Assay ◽

Low Grade ◽

B Cell Malignancies ◽

Variable Intensity ◽

Hodgkin's Lymphomas

CD27, a transmembrane disulfide-linked 55-kD homodimer, belongs to the nerve growth factor-receptor family, a group of homologous molecules involved in lymphocyte differentiation and selection. It is expressed on mature thymocytes, peripheral blood T cells, and a subpopulation of B cells. We investigated the expression of CD27 on malignant B cells representative for a broad range of stages in physiologic antigen- independent and -dependent B-cell development. In normal lymphoid tissue CD27+ B cells were only found in the peripheral blood (29.8% +/- 10.8%, n = 13) and in germinal centers. With the exception of pro-B and the majority of pre-pre-B acute lymphocytic leukemias and of myelomas, CD27 expression of variable intensity was detected on almost all immature and mature malignant B cells tested. Moreover, using a sandwich enzyme-linked immunosorbent assay we could show the presence of sometimes very high (up to 6,000 U/mL; normal values < 190 U/mL) amounts of the soluble 28- to 32-kD form of CD27 (sCD27) in the sera of patients with B-cell malignancies. The highest levels of sCD27 were observed in patients with chronic lymphocytic leukemia and low-grade non-Hodgkin's lymphomas. Most importantly, both in transversal and longitudinal studies, we found a strong correlation between sCD27 levels in the serum and tumor load, indicating that sCD27 can be used as a disease-marker in patients with acute and chronic B-cell malignancies.

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The basic study on kappa-lambda imaging by delta-curve for the detection of a monoclonal B-cell population in the peripheral blood

Blood ◽

10.1182/blood.v72.5.1461.1461 ◽

1988 ◽

Vol 72 (5) ◽

pp. 1461-1466 ◽

Cited By ~ 10

Author(s):

M Nakano ◽

S Kuge ◽

S Kuwabara ◽

M Yaguchi ◽

Y Kawanishi ◽

...

Keyword(s):

B Cells ◽

B Cell ◽

Peripheral Blood ◽

B Cell Lymphoma ◽

Lymphocytic Leukemia ◽

Basic Study ◽

Minor Population ◽

D Values ◽

A Minor ◽

D Value

Abstract Recently, kappa-lambda analysis with the “D” value was developed by Ault to detect a minor population of malignant B cells in peripheral blood. This analysis is based on the Kolmogorov-Smirnov test, and the D value is calculated by a flowcytometer and a computer. We have recently devised a more sensitive parameter for the kappa-lambda analysis than the D value called the delta-curve (delta c); the delta c applies the same principle as that of the D value. Mixing experiments with kappa- type and lambda-type chronic lymphocytic leukemia cells revealed that the delta c could not only detect a minor population of malignant kappa- B cells, but also that of malignant lambda-B cells using more sensitivity than the D value. A total of 49 blood samples obtained from 27 patients with various B-cell malignancies were investigated. D values were abnormal in 37% of all samples, while abnormal patterns of the delta c were recognized in 71%. On the other hand, 59% of samples obtained from the patients with B-cell lymphoma in aleukemic phase showed abnormal delta c, whereas D values exceeded the upper limit of the normal value in only 15% of the samples. It was suggested that the delta c could detect 3% to 7% of malignant B cells that were mixed with a population of normal lymphocytes.

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Lack of Hcv Infection in Malignant, Cells Refutes the Hypothesis of a Direct Transforming Action of the Virus in the Pathogenesis of Hcv-Associated B-Cell Nhls

Tumori Journal ◽

10.1177/030089160208800510 ◽

2002 ◽

Vol 88 (5) ◽

pp. 400-406 ◽

Cited By ~ 17

Author(s):

Salvatore De Vita ◽

Valli De Re ◽

Domenico Sansonno ◽

Annunziata Gloghini ◽

Daniela Gasparotto ◽

...

Keyword(s):

B Cells ◽

B Cell ◽

Hcv Infection ◽

Low Grade ◽

Immunoglobulin Gene ◽

Pathogenetic Role ◽

Exogenous Trigger ◽

Grade One ◽

Hodgkin's Lymphomas

Aims and background Preliminary evidence suggests that hepatitis C virus (HCV) might play a pathogenetic role in autoimmune-related, non-malignant B-cell lymphoproliferation, as well as in a subset of B-cell non-Hodgkin's lymphomas (NHLs). With regard to the mechanism(s) by which HCV might favor B-cell expansion and malignant transformation, most data support an indirect pathogenetic role of the virus as an exogenous trigger. A direct oncogenetic role of HCV by direct cell infection and deregulation has only been hypothesized on the basis of the lymphotropism of the virus. Methods In this study we investigated the possible HCV infection of NHL B cells by means of sensitive and quantitative polymerase chain reaction (PCR) on affinity-purified neoplastic cells, and by HCV-specific immunohistochemistry and in situ hybridization. Results HCV infection of neoplastic B cells was documented in only three cases, namely the low-grade B-cell NHLs that arose in the course of mixed cryoglobulinemia syndrome (MC). HCV infection, below one viral genome per cell, was detectable only by PCR. All the remaining low-grade (one case) and high-grade B-cell NHLs (two cases) were HCV uninfected. Previous immunoglobulin gene analyses were consistent with an antigen-driven B-cell lymphoproliferation in the studied cases. Conclusions Overall, our data are consistent with an indirect oncogenetic role of HCV in B-cell lymphomagenesis as an exogenous trigger. Infection of B cells by HCV appears possible in some NHL subsets, but the implications remain unknown.

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Telomerase activation in normal B lymphocytes and non-Hodgkin's lymphomas

Blood ◽

10.1182/blood.v88.1.222.222 ◽

1996 ◽

Vol 88 (1) ◽

pp. 222-229 ◽

Cited By ~ 111

Author(s):

KF Norrback ◽

K Dahlenborg ◽

R Carlsson ◽

G Roos

Keyword(s):

B Cells ◽

B Cell ◽

Germinal Center ◽

Telomerase Activity ◽

Lymphoid Tissues ◽

Low Grade ◽

Malignant Lymphomas ◽

Hodgkin's Lymphomas ◽

Germinal Center B Cells

Abstract Activation of telomerase seems to be a prerequisite for immortalization and is found in permanent cell lines and most malignant tumors. Normal somatic cells are generally telomerase negative, except for bone marrow stem cells. Weak activity is also present in peripheral blood cells. In the present study strong telomerase activity was demonstrated in vivo in normal mature cells of the immune system, as well as in malignant lymphomas. Benign lymph nodes had lower telomerase activity than benign tonsils, which exhibited intermediate to high activity comparable with findings in malignant lymphomas. In benign tonsils the activity seemed to be restricted to germinal center B cells. In benign lymphoid tissues telomerase activity correlated with B-cell numbers and cell proliferation, but this was not observed in the lymphoma group. High- grade lymphomas exhibited higher levels of telomerase compared with low- grade cases. The data showed that in vivo activation of telomerase is a characteristic feature of germinal center B cells. Different signals for activation of telomerase are likely to exist, one of them being immune stimulation. The data suggest that telomerase activity in malignant lymphomas can be explained by an “induction and retention” model, ie, transformation occurs in a normal, mature B cell with reactivated telomerase, which is retained in the neoplastic clone.

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Upregulation of Human Pim-2 in B-CLL, Involves Interactions between Oct-1, Oct-2, Bob-1 and NF-kB.

Blood ◽

10.1182/blood.v104.11.1916.1916 ◽

2004 ◽

Vol 104 (11) ◽

pp. 1916-1916

Author(s):

Yosef Dicken ◽

Amos M. Cohen ◽

Hanna Bessler ◽

Daphna Levi-Hirsh ◽

Ariela Arad ◽

...

Keyword(s):

Transcription Factor ◽

B Cells ◽

B Cell ◽

Promoter Region ◽

Lymphocytic Leukemia ◽

Proximal Promoter ◽

Luciferase Reporter ◽

Luciferase Expression ◽

Cell Extracts ◽

Hodgkin's Lymphomas

Abstract hPim-2 is a proto-oncogene that encodes a serine/threonine kinase and inhibits apoptosis by phosphorylation of BAD. We have shown that hPim is upregulated in human non-Hodgkin’s lymphomas (NHL) and in chronic lymphocytic leukemia (B-CLL) and its cellular transcript levels in B-CLL correlates with lymphocyte doubling time. We found no mutations in the promoter region of hPim-2 in B-cells of 30 patients with CLL (~2000 bp upstream). The proximal promoter region of hPim-2 (600 bp) contains two adjacent NF-kB-binding elements, two adjacent Oct-binding elements and an SP1 element by bioinformatic analysis. Studies have recently shown that the transcription factor Oct-2 and the B-cell specific Oct cofactor Bob-1 are overexpressed in certain large B-cell lymphomas, whereas increased expression of Bob-1 has also been observed in T-cell neoplasms. Shift assays (EMSA) analysis, using nuclear extracts from B-CLL cells and various fragments of hPim-2 promoter region used as probes, revealed that complexes containing an Oct elements were consistently heavier in B-CLL extracts compared with control B-cells. Accordingly, Oct-1, Oct-2 and Bob-1 protein levels were significantly higher in B-CLL compared to healthy extracts. Moreover, chromatin immunoprecipitation (Chip) assays confirmed that in-vivo Oct-1+2 and Bob-1 are indeed physically attached to the hPim-2 promoter, and that this interaction is significantly more intensive in B-CLL cells than in control B-cells. Furthermore, we have found in addition that the p52 isoform subunit of NF-kB predominates the interaction with the kB element in the hPim-2 promoter in B-CLL cells, as compared to the p50 isoform observed in control B-cells. To determine whether these interactions are transcriptionaly significant, we fused the luciferase reporter gene to various promoter fragments, and monitored luciferase expression in-vitro after incubation with either B-CLL or normal B-cell extracts. Luciferase expression was consistently higher when Oct element-containing fragment was incubated with B-CLL cell extracts. Together, these results suggest that the upregulation of hPim-2 in B-CLL is due to enhanced expression and transcriptional activity of the Oct-1+2 and Bob-1 complex and that it might synergistically act with the p52 containing NF-kB transcription factor.

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B Cell Activating Factor and c-Myc Regulate the Progression of Chronic Lymphocytic Leukemia.

Blood ◽

10.1182/blood.v114.22.359.359 ◽

2009 ◽

Vol 114 (22) ◽

pp. 359-359

Author(s):

Weizhou Zhang ◽

Arnon P. Kater ◽

Han-Yu Chuang ◽

Thomas Enzler ◽

George F. Widhopf ◽

...

Keyword(s):

Bone Marrow ◽

B Cells ◽

Chronic Lymphocytic Leukemia ◽

B Cell ◽

Disease Progression ◽

Cell Population ◽

Lymphocytic Leukemia ◽

Leukemia Cells ◽

Low Grade ◽

B Cell Activating Factor

Abstract Abstract 359 Chromosomal translocations involving c-Myc are frequently found in high grade lymphoma and multiple myeloma. In contrast, c-Myc translocations rarely occur in low-grade lymphomas/leukemias like chronic lymphocytic leukemia (CLL), but when present they are associated with rapid disease progression and bad prognosis. Overexpression of c-myc may also be the result of increased transcription by several proto-oncogene transcription factors, including NF-kB. Mice with c-Myc de-regulation at different stages of B cell development develop either aggressive B cells lymphomas or plasma cell neoplasm. So far, no c-Myc mouse model developed low-grade lymphoma/leukemia. iMycCa mice develop an expansion of CD5+ peritoneal B1 cells, as compared with WT littermates mice. These mice have a normal life-span and very rarely develop B cell lymphoma at older age. Interestingly, in iMycCa mice mature B cells, but not plasma cells,could be rescued from apoptosis by administration of B cell-activating factor belonging to the TNF family (BAFF). To our surprise, double transgenic iMycCa/Baff-Tg (Myc/Baff) mice developed a disease resembling human CLL, with dramatically shorter mean survival than parental strains, due to early onset and rapid clonal expansion of a mature CD5+B220low B cell population. Those cells transferred the disease into Baff-Tg (Baff) mice with marked infiltration in lymphoid organs and bone marrow. Gene-expression analyses revealed that among the genes altered in Myc/Baff CD5+B220lowleukemia cells were those with known relevance to human CLL disease, including elevated anti-apoptotic Bcl2 family members. Apart from studies on individual genes, sub-network analysis was performed which showed enrichment of apoptosis-related and stress-induced gene sets in Myc/Baff CD5+CD3- leukemia cells. The NF-kB gene set, a major target downstream of BAFF signaling, was also enriched in Myc/Baff CD5+CD3- leukemia cells. We observed a continuum in levels of c-MYC mRNA in 166 samples using Affymetrix array analyses. Changes in c-Myc protein expression were confirmed by immunoblot analyses and correlated with disease progression. In accordance with the functions of c-Myc as a promoter of cell cycle progression, as well as apoptosis, we found enhanced spontaneous cell death in vitro in CLL cells expressing high levels of c-Myc, which could be abrogated by co culture with BAFF expressing nurse-like cells (NLC) or recombinant BAFF. In addition to its anti-apoptotic role, BAFF treatment of primary human CLL cells led to dramatically enhanced expression of c-Myc through the IKK/NF-kB pathway. Inhibition of the NF-kB pathway significantly reduced viability of both Myc/Baff CD5+CD3- leukemia cells and human CLL cells co-cultured with NLC. Also it significantly lowered CD5+B220low leukemia cell population in blood and spleen, and prevented the infiltration of leukemia cells into lymph nodes and bone marrow of transplanted mice. This study demonstrates a potential pathologic role for c-Myc, in the pathogenesis and progression of CLL. Disclosures: No relevant conflicts of interest to declare.

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VLA-4 Expression and Activation in B Cell Malignancies: Functional and Clinical Aspects

International Journal of Molecular Sciences ◽

10.3390/ijms21062206 ◽

2020 ◽

Vol 21 (6) ◽

pp. 2206 ◽

Cited By ~ 2

Author(s):

Andrea Härzschel ◽

Antonella Zucchetto ◽

Valter Gattei ◽

Tanja Nicole Hartmann

Keyword(s):

B Cells ◽

B Cell ◽

Cell Types ◽

Cell Receptor ◽

Lymphocytic Leukemia ◽

Clinical Aspects ◽

Neoplastic Disease ◽

B Cell Differentiation ◽

B Cell Malignancies ◽

Bcr Signaling

Lineage commitment and differentiation of hematopoietic cells takes place in well-defined microenvironmental surroundings. Communication with other cell types is a vital prerequisite for the normal functions of the immune system, while disturbances in this communication support the development and progression of neoplastic disease. Integrins such as the integrin very late antigen-4 (VLA-4; CD49d/CD29) control the localization of healthy as well as malignant B cells within the tissue, and thus determine the patterns of organ infiltration. Malignant B cells retain some key characteristics of their normal counterparts, with B cell receptor (BCR) signaling and integrin-mediated adhesion being essential mediators of tumor cell homing, survival and proliferation. It is thus not surprising that targeting the BCR pathway using small molecule inhibitors has proved highly effective in the treatment of B cell malignancies. Attenuation of BCR-dependent lymphoma–microenvironment interactions was, in this regard, described as a main mechanism critically contributing to the efficacy of these agents. Here, we review the contribution of VLA-4 to normal B cell differentiation on the one hand, and to the pathophysiology of B cell malignancies on the other hand. We describe its impact as a prognostic marker, its interplay with BCR signaling and its predictive role for novel BCR-targeting therapies, in chronic lymphocytic leukemia and beyond.

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Immunoglobulin secretory function of B cells from untreated patients with chronic lymphocytic leukemia and hypogammaglobulinemia: role of T cells

Blood ◽

10.1182/blood.v62.4.767.767 ◽

1983 ◽

Vol 62 (4) ◽

pp. 767-774 ◽

Cited By ~ 21

Author(s):

LA Fernandez ◽

JM MacSween ◽

GR Langley

Keyword(s):

T Cells ◽

B Cells ◽

Chronic Lymphocytic Leukemia ◽

B Cell ◽

B Lymphocytes ◽

Peripheral Blood ◽

Cell Function ◽

Lymphocytic Leukemia ◽

Suppressor Activity ◽

Normal Peripheral Blood

Abstract The mechanism of the hypogammaglobulinemia in patients with chronic lymphocytic leukemia (CLL) was studied by determining the generation of specific immunoglobulin-secreting cells in response to mitogen and antigen stimulation in culture. Normal peripheral blood B lymphocytes from 18 normal subjects cocultured with equal numbers of autologous T cells generated cells secreting 2,542 +/- 695 IgG, 2,153 +/- 615 IgA, and 2,918 +/- 945 IgM. Normal B lymphocytes cocultured with normal allogeneic T cells generated similar numbers. However, B lymphocytes from patients with chronic lymphocytic leukemia cocultured with T cells from the same patient generated only 0.5% as many cells secreting IgG and 11% and 23% as many secreting IgA and IgM, respectively. The reason for this markedly defective generation of immunoglobulin-secreting cells was investigated by evaluating T-helper, T-suppressor, and B-cell function using B cells from tonsil and T and B cells from peripheral blood of normal and leukemic individuals. T cells from patients with chronic lymphocytic leukemia provided somewhat greater help than did normal T cells to normal peripheral blood B cells and normal help to tonsil B cells, whether stimulated with mitogen or antigen. T cells from patients with chronic lymphocytic leukemia did not demonstrate increased suppressor function compared to normals with B cells from normal peripheral blood. The hypogammaglobulinemia in these patients therefore was associated with a markedly defective generation of immunoglobulin secreting cells, and as there was normal or increased T- cell helper activity without excessive suppressor activity, it seems likely that this was due to an intrinsic B-cell defect.

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The BLyS Survival Pathway in NHL-B Cells: Constitutive NF-kB and NFAT Lead to Activation.

Blood ◽

10.1182/blood.v104.11.2279.2279 ◽

2004 ◽

Vol 104 (11) ◽

pp. 2279-2279

Author(s):

Lingchen Fu ◽

Tamayo Archito ◽

Yen-Chiu Lin-Lee ◽

Lan Pham ◽

Linda Yoshimura ◽

...

Keyword(s):

Flow Cytometry ◽

B Cells ◽

B Cell ◽

Cell Lines ◽

Low Grade ◽

Rt Pcr ◽

Protein Levels ◽

Realtime Pcr ◽

Survival Pathway ◽

Hodgkin's Lymphomas

Abstract B-cell non-Hodgkin’s Lymphomas (NHL-B), neoplasms of the immune system have shown a significant increase in incidence in the USA over the last three decades. While the pathophysiology of the NHL-B is still unclear, the need to identify the relevant genes and critical signaling pathways, and their involvement in the disease processes in NHL-B have begun to be elucidated. Recently, B Lymphocyte Stimulator (BLyS) has been described as a relatively new member of the TNF ligand family, as a potent cell survival factor that is expressed in many hematopoietic cells, including neoplastic B cells. BLyS can bind to three receptors: TACI, BCMA, BAFF-R, and plays a critical role in B cell maturation, differentiation and proliferation. Relatively high levels of BLyS has been found in the serum of NHL-B patients as well as of the patients with autoimmune disease. The mechanisms of BLyS gene expression and regulation is still unclear, but we have recently found that BLyS is constitutively expressed in several NHL-B cell lines and patient tumor samples by RT-PCR, confocal microscopy, realtime PCR and flow cytometry (FCM). We detected high levels and differential expression of BLyS receptors (TACI, BCMA, BAFF-R) in several NHL-B cell lines by flow cytometry, RT-PCR and realtime PCR in both NHL-B cell lines and patient tumor samples. We have identified a single binding site for NF-kB and two binding sites for NFAT in the BLyS promoter. We also show in aggressive lymphoma B cells that constitutive NF-kB and NFAT binds to the BLyS promoter constitutively. Inhibiting NF-kB/NFAT activity levels, using the NF-kB inhibitors, BAY-11 or Velcade (PS-341), can decrease NF-kB binding activity in the BLyS promotor by EMSA. These inhibitors also decrease BLyS and BAFF-R mRNA and protein levels by realtime PCR and flow cytometry. Similarly, when NHL-B cells were transfected with dominant negative NFAT or NF-kB constructs, there is a 50% decrease in BLyS and BAFF-R expressions, demonstrating that both the ligand (BLyS) and the receptor (BAFF-R) expression are regulated by NFAT and NF-kB. Interestingly, follicular (low grade) lymphoma cells do not express constitutive NF-kB/NFAT activation, and barely detectable mRNA and protein levels of BlyS, but can be activated with exogenous CD154/anti IgM in vitro, activating NF-kB/NFAT and promoting binding to the BLyS promoter by EMSA. This results in a significant increase of BLyS protein level by flow cytometry. Our studies indicate that constitutive NF-kB and NFAT are critical transcriptional regulators of the BLyS survival pathway in malignant B cells that may provide a future therapeutic target in the aggressive NHL-B.

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In Vivo Depletion of Cynomolgus Monkey B Cells Targeted by a Novel Monoclonal Antibody (Xi-20H5) Specific for a Shared Portion of the Human Immunoglobulin Variable Light Chain Lambda 1.

Blood ◽

10.1182/blood.v110.11.2354.2354 ◽

2007 ◽

Vol 110 (11) ◽

pp. 2354-2354

Author(s):

Thierry Sornasse ◽

Keri Tate ◽

Kimberly Milner ◽

Thomas Theriault ◽

Dan W. Denney ◽

...

Keyword(s):

B Cells ◽

B Cell ◽

Light Chain ◽

Peripheral Blood ◽

Cynomolgus Monkey ◽

Patient Specific ◽

B Cell Malignancies ◽

Variable Regions ◽

Variable Light

Abstract Genitope is developing a novel, personalized treatment for surface immunoglobulin (Ig) positive B cell malignancies. This treatment is based on a panel of monoclonal antibodies (Mabs) directed against shared epitopes expressed on different subsets of the variable regions of human Ig. The concept of targeting surface tumor Ig was explored in a series of clinical trials performed by Dr. Ronald Levy and his colleagues at Stanford. In these studies, Mabs directed against patient specific (idiotypic) determinants of the surface tumor Ig produced significant clinical benefit in relapsed follicular non-Hodgkin’s lymphoma patients. A number of these patients have had long term remissions. In Genitope’s planned clinical use, each patient will receive a single Mab from the panel selected based on its reactivity with the patient’s tumor. The selected Mab will react with the patient’s tumor and a minority of normal B cells, leaving the majority of the normal B cell repertoire intact. The ability of the panel members to provide therapeutic effect requires binding to tumor surface Ig in the presence of serum containing soluble Ig molecules. Mab Xi-20H5, a member of this panel of antibodies, is specific for a shared determinant on the human Ig variable light chain lambda 1. It binds to 25 to 35% of normal human B cells from peripheral blood and to 20 to 30% of normal cynomolgus monkey B cells from peripheral blood. In this study, we sought to demonstrate that, despite the presence of serum Ig, Mab Xi-20H5 would bind to surface Ig expressed on monkey B cells in vivo, resulting in specific depletion of target B cells. Six naïve cynomolgus monkeys received 8 intravenous infusions of the Mab Xi-20H5 at a dose of 40 mg/kg on days 1, 2, 3, 4, 7, 10, 14 & 17. Two naïve control animals received 8 infusions of vehicle only following the same schedule. The frequencies of lymphocyte sub-populations and of target B cells were monitored by flow cytometry on plasma-depleted whole blood samples. Samples were collected 23 hours after each infusion. In addition, two baseline samples were collected prior to treatment. The frequencies of lymphocyte sub-populations and of target B cells were compared to the average of the two baseline measurements. Frequencies of target B cells bound by Mab Xi-20H5 decreased in all treated animals while no significant change was detectable in the control animals. The bulk of the reduction in target B cell frequencies was observed 23 hours after the first infusion (range: 22% – 62%, average 41%). Frequencies of target B cells continued to decrease moderately with additional daily infusions (days 2 – 4), resulting in maximum reduction in target B cell frequency at 23 h post infusion 4 (range: 39% – 78%, average 54%). The frequencies of total B and T lymphocytes did not significantly change during the treatment. In vivo administration of Mab Xi-20H5 results in depletion of target B cells in a manner consistent with the expectation of an immunotherapeutic Mab aimed at treating surface Ig expressing B cell malignancies.

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