VCAM-1 Expression in B-Lymphopoiesis and Leukemia.

Abstract Vascular Cell Adhesion Molecule-1 (VCAM; CD106), a member of the Ig Superfamily of molecules, binds to the β-1 integrin, Very Late Antigen-4 (VLA-4; CD49d); this interaction plays an integral role in leukocyte trafficking as well as lymphocyte-stromal cell interactions. VCAM can be shed from the surface of cells, and, in humans, serum levels of soluble VCAM (sVCAM) parallel activity and remission states in acute lymphocytic leukemia (ALL) and inflammation. Although widely investigated as a stromal-cell associated molecule, our lab and others have recently identified VCAM expression on normal bone-marrow derived B-lymphoid cells. Using FACS technology, we found that surface expression of VCAM is closely modulated at specific stages of B cell development, with relatively high levels on the pro-B cell population, down-modulation in pre-B cells at the onset of immunoglobulin (Ig) gene rearrangement, and subsequent re-expression at variable levels in immature and mature peripheral B cell subsets. We have verified VCAM transcripts by cDNA PCR in highly purified populations of murine precursor B cells. Normal human bone marrow precursor B-lymphoid populations (hematogones) also demonstrate VCAM surface protein expression. Finally, in an animal model of BCR/ABL+ ALL, we found that VCAM expression is dramatically increased on lymphoblasts when compared to normal reference populations in bone marrow and spleen. VCAM expression in human lymphoid malignancies is currently under investigation. Antibody-mediated VCAM cross-linking on primary B-cell precursors ex-vivo generates intracellular reactive oxygen species, demonstrating that signaling through this molecule has functional consequences. Intriguingly, in-vivo, VCAM expression is limited to B-lymphoid cells harvested from tissues such as bone marrow, spleen and lymph node; since, in the same animal, peripheral blood lymphocytes and peritoneal cells do not express readily detectable levels of the surface antigen. VCAM-expressing B-lymphoid cells cultured ex-vivo gradually lose surface expression over 24 hours. The tissue-associated modulation of VCAM expression is preserved in the murine Ph+ lymphoblasts; leukemia cells isolated from the peripheral blood express very low levels of surface VCAM compared to those harvested from bone marrow or spleen. Our data suggests that VCAM expression is dependent on tissue-specific microenvironmental signals in-vivo. B-lymphoid expression of both VCAM and its ligand VLA-4 is a surprising finding that has broad implications regarding leukemic cell interaction with endothelial cells, the bone marrow retention and trafficking of precursor- and leukemic-B cell populations, and the interpretation of an extensive experimental database predicated on the stromal-cell specificity of VCAM expression and function.

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Increased Apoptosis of Peripheral Blood and Bone Marrow B and T Cells Correlates with Advanced Stages and Poor Risk Factors in Patients with B-CLL

Blood ◽

10.1182/blood.v112.11.4162.4162 ◽

2008 ◽

Vol 112 (11) ◽

pp. 4162-4162

Author(s):

Malgorzata Sieklucka ◽

Agnieszka Bojarska-Junak ◽

Agata Surdacka ◽

Iwona Hus ◽

Ewa Wasik-Szczepanek ◽

...

Keyword(s):

Bone Marrow ◽

T Cells ◽

B Cells ◽

B Cell ◽

Disease Progression ◽

Peripheral Blood ◽

Ex Vivo ◽

Lymphocytic Leukemia ◽

High Rate ◽

Advanced Stage

Abstract B-cell chronic lymphocytic leukemia (B-CLL), is characterized by the accumulation of long-lived, neoplastic B-lymphocytes in peripheral blood, bone marrow and secondary lymphoid organs. Apoptotic processes have been shown to be altered in leukemic B cells, however, the role of apoptosis in the mechanisms of disease progression remains unclear. Recent studies suggest that the clonal excess of B-cells is caused not only by a decrease in cell death but also by increased cell proliferation. We have recently reported on a high rate of apoptosis leukemic B cells in peripheral blood (PB) of advanced stage patients and that apoptosis of PB lymphocytes from advanced-stage (III–IV acc. Rai) patients is higher than that in early-stage (0–II acc. Rai) patients. However the spontaneous apoptosis in B-CLL patients was significantly lower compared to the healthy controls that confirmed the defective apoptosis as one of the mechanisms of leukemic lymphocytes accumulation in B-CLL. Continuing our research, in the presented study we measured apoptosis of B and T cells in peripheral blood and bone marrow in correlation with the stage of B-CLL and prognostic factors. Materials and methods: Peripheral blood and bone marrow (BM) samples were obtained from 120 previously untreated B-CLL patients. An analysis of apoptosis within the B and T cells population was performed using flow cytometer and chloromethyl-X-rosamine staining (Mito Tracker Red CMXRos). CMXRos was used to detect disruptions in the mitochondrial membrane potential (ΔΨm), which is one of the earliest events in the apoptotic pathway and allow finding apoptotic cells when there are still in PB and BM. We found that ex vivo lymphocyte apoptosis was higher in BM compared to PB (p<0.05). Moreover, both B-cell and T-cell apoptosis in BM was higher than in PB (p<0.0001 and p<0.001, respectively). When compared, ex vivo apoptosis of T cells was found higher than that of B cells, both in BM (p<0.0001) and PB (p<0.0001). The percentage of apoptotic leukemic B cells correlated negatively with Bcl-2/Bax ratio in CD19+ B cells (p<0.05). Similarly, the percentage of apoptotic CD3+ cells correlated negatively with Bcl-2/Bax ratio in CD3+ cells (p<0.01). We also found that the percentage of apoptotic leukemic B cells correlated positively with the expression of proapoptotic protein Par-4 (prostate apoptosis response-4) in CD19+ B cells (p<0.01). The expression of Par-4 protein in CD19+ B cells correlated positively with the percentage of CD38+ cells (p<0.05), and it was higher in patients with CD38+ and ZAP-70+/CD38+ phenotypes (p<0.05 and p<0.01, respectively). There was a positive correlation between the expression of Par-4 protein and the lactate dehydrogenase (LDH) and β2-microglobulin serum concentrations (p<0.01 and p<0.05, respectively). Furthermore, the percentage of apoptotic CD19+ cells correlated positively with the LDH serum level (p<0.05). These data indicate that high amount of apoptotic leukemic cells in PB and BM might be considered as poor prognosis factor. Higher rate of B and T cells apoptosis in BM than in PB suggest the influence of bone marrow microenviroment on this process. Our results indicate also that high rate of T cells apoptosis might be responsible for immune dysfunction including both impaired anti-infection immunity as well as impaired anti-cancer response resulting in disease progression.

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Hspa9 Haploinsufficiency Induces a Cell-Intrinsic Defect in Mouse B-Cell Progenitors

Blood ◽

10.1182/blood.v120.21.1714.1714 ◽

2012 ◽

Vol 120 (21) ◽

pp. 1714-1714

Author(s):

Kilannin Krysiak ◽

Justin Tibbitts ◽

Tim H Chen ◽

Matthew J. Walter

Keyword(s):

Bone Marrow ◽

B Cells ◽

B Cell ◽

Peripheral Blood ◽

Colony Formation ◽

Bone Marrow Cells ◽

Cell Maturation ◽

Chromosome 5 ◽

B Cell Maturation

Abstract Abstract 1714 Patients with myelodysplastic syndromes (MDS) have a clonal hematopoietic stem cell disorder that results in dysplastic hematopoietic cells in their bone marrow as well as peripheral blood cytopenias. In addition to the commonly described erythroid and myeloid differentiation defects associated with MDS, a reduction in bone marrow B-cell progenitors exists in patients. The genetic events contributing to the reduction in B-cell progenitors remain poorly understood. The most common cytogentic abnormality identified in patients with MDS, occurring in approximately 35% of patients, is heterozygous interstitial deletion or loss of the long arm of chromosome 5 (5q). The interstitial deletions on chromosome 5 are single copy losses, and no biallelic disruptions of genes in deleted regions have been identified, implicating haploinsufficiency as the underlying genetic mechanism. We, and others, have shown that the levels of HSPA9 mRNA expression are reduced ∼50% in patients with del(5q) when compared to MDS patients without del(5q), consistent with a haploinsufficient phenotype. To model haploinsufficiency, we used shRNA to achieve ∼50% knockdown of Hspa9 in a murine bone marrow transplant model. This model showed a significant reduction in mature B-cells in the bone marrow, spleen, and peripheral blood of recipient mice, implicating HSPA9 haploinsufficiency may contribute to the B-cell alterations observed in MDS patients with del(5q). To further evaluate HSPA9 haploinsufficiency in vivo, we created a mouse model with a heterozygous deletion of Hspa9 (Hspa9+/−) and confirmed a 50% reduction in Hspa9 protein levels in bone marrow and spleen of these mice by Western blot. Hspa9+/− mice are born at normal Mendelian frequencies (N>100), however, breeding heterozygous mice suggests Hspa9−/− mice are embryonic lethal (24 Hspa9+/+:38 Hspa9+/−:0 Hspa9−/−). No significant differences in mature lineage markers, complete blood counts, and hematopoietic organ cellularity, have been identified up to 12 months of age. However, as early as 2 months of age, the numbers of bone marrow CFU-preB colonies as assessed by methylcellulose assay, are significantly reduced in Hspa9+/− mice compared to Hspa9+/+ littermates (14 vs 48 colonies/100,000 bone marrow cells plated, respectively, N=10 mice/genotype, p<0.0001). We performed noncompetitive bone marrow transplants of Hspa9+/− or Hspa9+/+ donor cells into Hspa9+/+ recipient mice and confirmed that the reduction of B-cell progenitors is a hematopoietic cell intrinsic phenotype (N=7–9 mice/genotype, p=0.002). We also confirmed that the Hspa9+/− bone marrow microenvironment did not contribute to the phenotype as transplantation of Hspa9+/+ donor bone marrow cells into Hspa9+/− recipients did not alter the number of CFU-preB colonies (N=5). Total frequencies of common lymphoid progenitors and B-cell precursors (Hardy fractions A, B/C, D, E and F) as assessed by flow cytometry are no different in Hspa9+/− and Hspa9+/+ mice. Therefore, we hypothesize that early Hspa9+/− B-cells may have an intrinsic signaling defect which can be compensated for in vivo. Early B-cell maturation is dependent on intracellular signaling mediated through cell surface receptors in response to environmental cytokines. Consistent with our hypothesis, we showed that Hspa9+/− CFU-preB in vitro colony formation is partially rescued by increasing concentrations of IL7 while Hspa9+/+ colony numbers remain unchanged (fold change in colony formation from 10ng/mL to 50ng/mL IL7 was 1.80 for Hspa9+/− vs. 0.80 for Hspa9+/+, p=0.03, N=6 mice/genotype). Supplementation of the media with another cytokine that contributes to early B-cell maturation, Flt3 ligand, does not alter Hspa9+/− or Hspa9+/+ CFU-preB colony formation, further implicating altered IL7 signaling. We are currently investigating the downstream responses to IL7 stimulation in B-cell progenitors from Hspa9+/− mice. Collectively, these data implicate loss of HSPA9 as a contributing factor in the reduction of B-cell progenitors observed in patients with del(5q) associated MDS. Disclosures: No relevant conflicts of interest to declare.

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Transformation-associated alterations in interactions between pre-B cells and fibronectin

Blood ◽

10.1182/blood.v76.11.2311.2311 ◽

1990 ◽

Vol 76 (11) ◽

pp. 2311-2320 ◽

Cited By ~ 22

Author(s):

FM Lemoine ◽

S Dedhar ◽

GM Lima ◽

CJ Eaves

Keyword(s):

B Cells ◽

B Cell ◽

Cell Line ◽

Cell Lines ◽

Stromal Cells ◽

Stromal Cell ◽

Cell Attachment ◽

Attachment Site ◽

Receptor Antibodies

Abstract Marrow stromal elements produce as yet uncharacterized soluble growth factors that can stimulate the proliferation of murine pre-B cells, although close contact between these two cell types appears to ensure a better pre-B cell response. We have now shown that freshly isolated normal pre-B cells (ie, the B220+, surface mu- fraction of adult mouse bone marrow) adhere to fibronectin (FN) via an RGD cell-attachment site, as shown in a serum-free adherence assay, and they lose this functional ability on differentiation in vivo into B cells (ie, the B220+, surface mu+ fraction). Similarly, cells from an immortalized but stromal cell-dependent and nontumorigenic murine pre-B cell line originally derived from a Whitlock-Witte culture were also found to adhere to fibronectin (FN) via an RGD cell-attachment site. Moreover, in the presence of anti-FN receptor antibodies, the ability of this immortalized pre-B cell line to proliferate when co-cultured with a supportive stromal cell line (M2–10B4 cells) was markedly reduced (down to 30% of control). This suggests that pre-B cell attachment to FN on stromal cells may be an important component of the mechanism by which stromal cells stimulate normal pre-B cell proliferation and one that is no longer operative to control their more differentiated progeny. Two differently transformed pre-B cell lines, both of which are autocrine, stromal-independent, tumorigenic in vivo, and partially or completely differentiation-arrested at a very early stage of pre-B cell development, did not bind to FN. In addition, anti-FN receptor antibodies were much less effective in diminishing the ability of these tumorigenic pre-B cells to respond to M2–10B4 cell stimulation, which could still be demonstrated when the tumorigenic pre-B cells were co- cultured with M2–10B4 cells at a sufficiently low cell density. Analysis of cell surface molecules immunoprecipitated from both the nontumorigenic and tumorigenic pre-B cell lines by an anti-FN receptor antibody showed an increase in very late antigen (VLA) alpha chain(s) in both tumorigenic pre-B cell lines and a decrease in the beta 1 chain in one. Interestingly, all of the pre-B cell lines expressed similar amounts of messenger RNA for the beta 1 chain of the FN receptor. These results suggest that alteration of FN receptor expression on pre-B cells may represent a mechanism contributing to the outgrowth of leukemic pre-B cells with an autocrine phenotype and capable of stromal cell-independent, autonomous growth.

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IMMU-29. B-CELL-BASED VACCINE PRODUCES GLIOBLASTOMA-REACTIVE ANTIBODIES THAT CONTRIBUTE TO TUMOR CLEARANCE

Neuro-Oncology ◽

10.1093/neuonc/noab196.388 ◽

2021 ◽

Vol 23 (Supplement_6) ◽

pp. vi98-vi98

Author(s):

Brandyn Castro ◽

Mark Dapash ◽

David Hou ◽

Aida Rashidi ◽

Deepak Kanojia ◽

...

Keyword(s):

B Cells ◽

B Cell ◽

Humoral Immunity ◽

Ex Vivo ◽

Murine Models ◽

Effector Functions ◽

Tumor Bearing ◽

Tumor Clearance ◽

Cellular And Humoral Immunity

Abstract Glioblastomas (GBM) are characterized by a strong immunosuppressive environment, contributing to their poor prognosis and limited therapeutic response to immunotherapies. B-cells represent a unique opportunity to promote immunotherapy due to their potential to kill tumors by both cellular and humoral immunity. To generate our B-cell-based vaccine (BVax) platform, we activated 41BBL+ B cells from tumor bearing mice or GBM patient blood with BAFF, CD40, and IFNg. We have previously demonstrated that BVax potentiates radiation therapy, temozolomide and checkpoint blockade in murine models of GBM via enhancement of CD8+ T-cell based immunity. The aim of this current study is to evaluate the humoral effector functions of BVax. We examined the antibody (Ab) repertoire in vivo from serum of tumor-bearing B-cell knockout mice treated with BVax or by ex vivo stimulation of patient-derived BVax. Upon systemic administration, BVax infiltrates the tumor where it differentiates into plasmablasts. Murine BVax- and BNaive-derived serum immunoglobulin generated in vivo showed that the majority of murine BVax-derived Ab were IgG isotype, while BNaive mainly produced IgM isotype. Transfer of IgG from BVax treated mice directly into tumors of recipient animals significantly prolonged their survival, demonstrating anti-tumor cytotoxicity directly through humoral immunity. Patient-derived BVax activated ex vivo showed a plasmablast phenotype and the Ab repertoire supports the previous findings seen in our murine model. Our work suggests BVax-derived IgGs role in antibody-dependent cellular cytotoxicity and improved survival in murine models. This function, in addition to its role in cellular immunity against GBM, renders BVax a potentially effective alternative immunotherapeutic option for GBM patients.

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Monoclonal antibodies to the 140,000 mol wt glycoprotein of B lymphocyte membranes (CR2 receptor) initiates proliferation of B cells in vitro

Blood ◽

10.1182/blood.v66.4.824.bloodjournal664824 ◽

1985 ◽

Vol 66 (4) ◽

pp. 824-829

Author(s):

BS Wilson ◽

JL Platt ◽

NE Kay

Keyword(s):

Monoclonal Antibodies ◽

B Cells ◽

B Cell ◽

Peripheral Blood ◽

B Lymphocyte ◽

Human Peripheral Blood ◽

Raji Cell ◽

Lymphoid Cells ◽

Humoral Immune

Several mouse monoclonal IgG antibodies (AB1, AB2, AB3, and AB5) were developed that reacted with a 140,000 mol wt glycoprotein on the surface of cultured RAJI B lymphoid cells. The antibodies reacted with purified normal human peripheral blood B cells and CLL Ig+ B cells and showed specific germinal center and mantle zone staining in tissue sections of secondary lymphoid organs. Immunodepletion studies using 125I surface-labeled Raji cell membrane antigens demonstrated that the antigen identified by AB5 is the same 140,000 mol wt glycoprotein detected by anti-B2 that has recently been shown to react with the C3d fragment or CR2 receptor. (Iida et al: J Exp Med 158:1021, 1983). Addition of the AB series and anti-B2 monoclonal antibodies to cultures of purified human peripheral blood B cells resulted in the uptake of 3H- thymidine at two to six times background control levels provided that irradiated autologous T cells were added to the culture. Stimulation was not evoked by other monoclonal antibodies to B cell surface molecules (ie, B1, BA-1, BA-2, and HLA-DR). Pepsin-generated F(ab')2 fragments of anti-CR2 antibodies were essentially as effective as the intact IgG molecule in stimulating B cells. Induction of B cell proliferation by antibody binding to CR2 suggests that the C3d receptor may have an integral role in regulation of humoral immune response.

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Antigen-Specific B Cell Memory

Journal of Experimental Medicine ◽

10.1084/jem.191.7.1149 ◽

2000 ◽

Vol 191 (7) ◽

pp. 1149-1166 ◽

Cited By ~ 135

Author(s):

Louise J. McHeyzer-Williams ◽

Melinda Cool ◽

Michael G. McHeyzer-Williams

Keyword(s):

Bone Marrow ◽

B Cells ◽

B Cell ◽

Memory B Cells ◽

Cell Memory ◽

Specific Memory ◽

B Cell Memory ◽

Cellular Components

The mechanisms that regulate B cell memory and the rapid recall response to antigen remain poorly defined. This study focuses on the rapid expression of B cell memory upon antigen recall in vivo, and the replenishment of quiescent B cell memory that follows. Based on expression of CD138 and B220, we reveal a unique and major subtype of antigen-specific memory B cells (B220−CD138−) that are distinct from antibody-secreting B cells (B220+/−CD138+) and B220+CD138− memory B cells. These nonsecreting somatically mutated B220− memory responders rapidly dominate the splenic response and comprise >95% of antigen-specific memory B cells that migrate to the bone marrow. By day 42 after recall, the predominant quiescent memory B cell population in the spleen (75–85%) and the bone marrow (>95%) expresses the B220− phenotype. Upon adoptive transfer, B220− memory B cells proliferate to a lesser degree but produce greater amounts of antibody than their B220+ counterparts. The pattern of cellular differentiation after transfer indicates that B220− memory B cells act as stable self-replenishing intermediates that arise from B220+ memory B cells and produce antibody-secreting cells on rechallenge with antigen. Cell surface phenotype and Ig isotype expression divide the B220− compartment into two main subsets with distinct patterns of integrin and coreceptor expression. Thus, we identify new cellular components of B cell memory and propose a model for long-term protective immunity that is regulated by a complex balance of committed memory B cells with subspecialized immune function.

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Expression of CD10 by Human T Cells That Undergo Apoptosis Both In Vitro and In Vivo

Blood ◽

10.1182/blood.v94.9.3067 ◽

1999 ◽

Vol 94 (9) ◽

pp. 3067-3076 ◽

Cited By ~ 48

Author(s):

Giovanna Cutrona ◽

Nicolò Leanza ◽

Massimo Ulivi ◽

Giovanni Melioli ◽

Vito L. Burgio ◽

...

Keyword(s):

T Cells ◽

Peripheral Blood ◽

Ex Vivo ◽

Lymphoid Cells ◽

Normal Peripheral Blood ◽

Apoptotic Process ◽

Cd10 Expression ◽

T Cell Lines

Abstract This study shows that human postthymic T cells express CD10 when undergoing apoptosis, irrespective of the signal responsible for initiating the apoptotic process. Cells from continuous T-cell lines did not normally express CD10, but became CD10+ when induced into apoptosis by human immunodeficiency virus (HIV) infection and exposure to CD95 monoclonal antibody, etoposide, or staurosporin. Inhibitors of caspases blocked apoptosis and CD10 expression. Both CD4+ and CD8+ T cells purified from normal peripheral blood expressed CD10 on apoptotic induction. CD10 was newly synthesized by the apoptosing cells because its expression was inhibited by exposure to cycloheximide and CD10 mRNA became detectable by reverse transcription-polymerase chain reaction in T cells cultured under conditions favoring apoptosis. To show CD10 on T cells apoptosing in vivo, lymph node and peripheral blood T cells from HIV+ subjects were used. These suspensions were composed of a substantial, although variable, proportion of apoptosing T cells that consistently expressed CD10. In contrast, CD10+ as well as spontaneously apoptosing T cells were virtually absent in peripheral blood from normal individuals. Collectively, these observations indicate that CD10 may represent a reliable marker for identifying and isolating apoptosing T cells in vitro and ex vivo and possibly suggest novel functions for surface CD10 in the apoptotic process of lymphoid cells.

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B lymphocytes express and lose syndecan at specific stages of differentiation.

Cell Regulation ◽

10.1091/mbc.1.1.27 ◽

1989 ◽

Vol 1 (1) ◽

pp. 27-35 ◽

Cited By ~ 272

Author(s):

R D Sanderson ◽

P Lalor ◽

M Bernfield

Keyword(s):

Bone Marrow ◽

B Cells ◽

B Cell ◽

B Lymphocytes ◽

B Lymphocyte ◽

Plasma Cells ◽

Receptor Expression ◽

Cell Stage ◽

Precursor B Cells

Lymphopoietic cells require interactions with bone marrow stroma for normal maturation and show changes in adhesion to matrix during their differentiation. Syndecan, a heparan sulfate-rich integral membrane proteoglycan, functions as a matrix receptor by binding cells to interstitial collagens, fibronectin, and thrombospondin. Therefore, we asked whether syndecan was present on the surface of lymphopoietic cells. In bone marrow, we find syndecan only on precursor B cells. Expression changes with pre-B cell maturation in the marrow and with B-lymphocyte differentiation to plasma cells in interstitial matrices. Syndecan on B cell precursors is more heterogeneous and slightly larger than on plasma cells. Syndecan 1) is lost immediately before maturation and release of B lymphocytes into the circulation, 2) is absent on circulating and peripheral B lymphocytes, and 3) is reexpressed upon their differentiation into immobilized plasma cells. Thus, syndecan is expressed only when and where B lymphocytes associate with extracellular matrix. These results indicate that B cells differentiating in vivo alter their matrix receptor expression and suggest a role for syndecan in B cell stage-specific adhesion.

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Most of the Short Term Repopulating Cells in Human Mobilized Peripheral Blood Do Not Have a Side Population (SP) Phenotype.

Blood ◽

10.1182/blood.v104.11.2867.2867 ◽

2004 ◽

Vol 104 (11) ◽

pp. 2867-2867

Author(s):

M. Fischer ◽

M. Schmidt ◽

S. Klingenberg ◽

C. Eaves ◽

C. von Kalle4 ◽

...

Keyword(s):

Bone Marrow ◽

Peripheral Blood ◽

Side Population ◽

Isolation Procedure ◽

Lymphoid Cells ◽

Short Term ◽

Hoechst 33342 ◽

Hoechst Staining ◽

Mobilized Peripheral Blood

Abstract The multidrug resistance transporter, ABCG2, is expressed in primitive hematopoietic stem cells from a variety of sources. These cells are detected in dual wave-length fluorescent FACS profiles as a “side population” (SP cells) on the basis of their ability to efflux the fluorescent dye, Hoechst 33342. We have previously shown that 2 types of human short term repopulating cells (STRC) can be enumerated by limiting dilution analysis of their efficient ability to regenerate exclusively myeloid cells after 3 weeks (STRC-Ms), or both myeloid and lymphoid cells after 6–12 weeks (STRC-MLs) in NOD/SCID-b2microglobulin-/- (b2m-/-) mice. Previous findings also implicated these STRCs as determinants of the rapidity of early hematologic recovery in patients transplanted with cultured mobilized peripheral blood (mPB) cells. Here we asked whether any human STRCs have an SP phenotype and hence whether the isolation of SP cells would retain the rapid repopulating activity of a clinical transplant. CD3- SP and non-SP cells were isolated by FACS from low-density (LD) mPB cells after Hoechst staining and transplanted at limiting dilutions into 117 sublethally irradiated b2m-/- mice. The numbers and types of human hematopoietic cells present in the bone marrow of these mice were subsequently monitored by FACS analysis of bone marrow cells aspirated serially, 3, 8 and 12 wks post-transplant. A verapamil-sensitive SP population was reproducibly detected in all 5 patients’ samples studied (0.039 ± 0.012% of the CD3- LD cells). The in vivo assays failed to detect either STRC-Ms or STRC-MLs in the SP fraction and all these activities were obtained from the non-SP cells. If even a single recipient of the largest dose of SP cells transplanted had been positive, this would have detected 10% of the STRCs present. Thus, >90% of all STRC-M and STRC-ML in mPB are non-SP cells. However, 4 of 40 mice transplanted with SP mPB cells produced some B-lymphoid cells only starting 12 wks post-transplant. However, this result is difficult to interpret since subjecting the STRC-Ms to the Hoechst 33342 staining and FACS isolation procedure alone eliminated their ability to generate megakaryocytic progeny in vivo, although this did not occur when these cells were just stained for CD34 and then isolated by FACS. In addition, the differentiation behaviour of STRC-MLs was not affected by the Hoechst staining and subsequent FACS isolation procedure. In summary, we demonstrate that purification of SP cells depletes human mPB transplants of STRCs, thereby raising serious concerns about the safety of any clinical use of SP cell-enriched transplants as stem cell support after myeloablation. Our results also suggest that the staining and enrichment procedure for isolating SP human cells may differentially affect the lineage potential of some types of STRCs, including those whose activity may be indispensable for rapid and multi-lineage hematologic recovery.

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Trisomy of the Down Syndrome Critical Region Suppresses Precursor B-Cell Differentiation and Promotes B-Cell Transformation Associated with Altered Expression of Polycomb Repressor Complex 2 Targets

Blood ◽

10.1182/blood.v120.21.115.115 ◽

2012 ◽

Vol 120 (21) ◽

pp. 115-115

Author(s):

Andrew A. Lane ◽

Diederik van Bodegom ◽

Bjoern Chapuy ◽

Gabriela Alexe ◽

Timothy J Sullivan ◽

...

Keyword(s):

Bone Marrow ◽

Cell Differentiation ◽

B Cells ◽

B Cell ◽

Cell Transformation ◽

B Cell Differentiation ◽

Wild Type ◽

Repressor Complex

Abstract Abstract 115 Extra copies of chromosome 21 (polysomy 21) is the most common somatic aneuploidy in B-cell acute lymphoblastic leukemia (B-ALL), including >90% of cases with high hyperdiploidy. In addition, children with Down syndrome (DS) have a 20-fold increased risk of developing B-ALL, of which ∼60% harbor CRLF2 rearrangements. To examine these associations within genetically defined models, we investigated B-lineage phenotypes in Ts1Rhr mice, which harbor triplication of 31 genes syntenic with the DS critical region (DSCR) on human chr.21. Murine pro-B cell (B220+CD43+) development proceeds sequentially through “Hardy fractions” defined by cell surface phenotype: A (CD24−BP-1−), B (CD24+BP-1−) and then C (CD24+BP-1+). Compared with otherwise isogenic wild-type littermates, Ts1Rhr bone marrow harbored decreased percentages of Hardy fraction B and C cells, indicating that DSCR triplication is sufficient to disrupt the Hardy A-to-B transition. Of note, the same phenotype was reported in human DS fetal liver B-cells, which have a block between the pre-pro- and pro-B cell stages (analogous to Hardy A-to-B). To determine whether DSCR triplication affects B-cell proliferation in vitro, we analyzed colony formation and serial replating in methylcellulose cultures. Ts1Rhr bone marrow (B6/FVB background) formed 2–3-fold more B-cell colonies in early passages compared to bone marrow from wild-type littermates. While wild-type B-cells could not serially replate beyond 4 passages, Ts1Rhr B-cells displayed indefinite serial replating (>10 passages). Ts1Rhr mice do not spontaneously develop leukemia, so we utilized two mouse models to determine whether DSCR triplication cooperates with leukemogenic oncogenes in vivo. First, we generated Eμ-CRLF2 F232C mice, which express the constitutively active CRLF2 mutant solely within B-cells. Like Ts1Rhr B-cells, (but not CRLF2 F232C B-cells) Ts1Rhr/CRLF2 F232C cells had indefinite serial replating potential. In contrast with Ts1Rhr B-cells, Ts1Rhr/CRLF2 F232C B-cells also engrafted into NOD.Scid.IL2Rγ−/− mice and caused fatal and serially transplantable B-ALL. Second, we retrovirally transduced BCR-ABL1 into unselected bone marrow from wild-type and Ts1Rhr mice and transplanted into irradiated wild-type recipients. Transplantation of transduced Ts1Rhr cells (106, 105, or 104) caused fatal B-ALL in recipient mice with shorter latency and increased penetrance compared to recipients of the same number of transduced wild-type cells. By Poisson calculation, the number of B-ALL initiating cells in transduced Ts1Rhr bone marrow was ∼4-fold higher than in wild-type animals (1:60 vs 1:244, P=0.0107). Strikingly, transplantation of individual Hardy A, B, and C fractions after sorting and BCR-ABL1 transduction demonstrated that the increased leukemia-initiating capacity almost completely resides in the Ts1Rhr Hardy B fraction; i.e., the same subset suppressed during Ts1Rhr B-cell differentiation. To define transcriptional determinants of these phenotypes, we performed RNAseq of Ts1Rhr and wild-type B cells in methylcellulose culture (n=3 biologic replicates per genotype). As expected, Ts1Rhr colonies had ∼1.5-fold higher RNA abundance of expressed DSCR genes. We defined a Ts1Rhr signature of the top 200 genes (false discovery rate (FDR) <0.25) differentially expressed compared with wild-type cells. Importantly, this Ts1Rhr signature was significantly enriched (P=0.02) in a published gene expression dataset of DS-ALL compared with non-DS-ALL (Hertzberg et al., Blood 2009). Query of >2,300 signatures in the Molecular Signatures Database (MSigDB) C2 Chemical and Genetic Perturbations with the Ts1Rhr signature identified enrichment in multiple gene sets of polycomb repressor complex (PRC2) targets and H3K27 trimethylation. Most notably, SUZ12 targets within human embryonic stem cells were more highly expressed in Ts1Rhr cells (P=1.2×10−6, FDR=0.003) and the same SUZ12 signature was enriched in patients with DS-ALL compared to non-DS-ALL (P=0.007). In summary, DSCR triplication directly suppresses precursor B-cell differentiation and promotes B-cell transformation both in vitro and by cooperating with proliferative alterations such as CRLF2 activation and BCR-ABL1 in vivo. Pharmacologic modulation of H3K27me3 effectors may overcome the pro-leukemogenic effects of polysomy 21. Disclosures: No relevant conflicts of interest to declare.

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