Immunomagnetic isolation of cells for serological BoLA typing

This paper describes a totally new immunomagnetic (IM) technique adapted to serological BoLA typing. The basic technique has recently been developed by Vartdal et al. (1986) for serological HLA typing. The main advantage is that bovine mononuclear cells (e.g. T-cells and possibly their subsets, B-cells and monocytes) can be quickly and specifically isolated with high yield and viability from whole blood in a one-step procedure. This is achieved by magnetic separation of rosettes formed between the cells and superparamagnetic monosized polystyrene microspheres (Dynabeads TM) coated with cross-species reactive monoclonal antibodies (MAbs) specific for various human T-cell antigens or for HLA class II monomorphic epitopes. The cells are isolated within 5 min after a 5-min incubation at 4 degrees C. Magnetic separation of rosettes with a strong cobalt-samarium magnet eliminates all the laborious centrifugation steps necessary with conventional procedures. The isolated cells, still attached to the particles, are available for microcytotoxic assay. This is carried out within 55 min, including a two-step application of alloantiserum and complement and addition of acridine orange/ethidium bromide for the staining of viable (green) and dead (red) cells. The high viability of isolated cells gives a very low background kill compared with the conventional cytotoxic assay. The IM typing technique is also superior in sensitivity to the conventional technique as standardized for the international BoLA comparison test. The IM technique is likely to have its greatest impact on class II typing; class II positive cells being separated very efficiently. Polymorphic HLA class II MAbs detected likely polymorphic BoLA class II epitopes.

Wnt3A activates canonical Wnt signalling in acute lymphoblastic leukaemia (ALL) cells and inhibits the proliferation of B-ALL cell lines

Acute lymphoblastic leukaemia (ALL) is the most common malignancy in children. Recently, there has been a growing interest in Wnt signalling in several aspects of cellular development, including cancer formation. Little is known about Wnt signalling in B-ALL. We investigated whether activation of canonical Wnt signalling could occur in B-ALL cells and thereby play a potential role in cellular growth and/or survival. This study found that Wnt3A induced beta-catenin accumulation in both primary B-ALL cells and B-ALL leukaemia cell lines. Further, Wnt3A was shown to induce nuclear translocation of beta-catenin and TCF/Lef-1 dependent transcriptions in the B-ALL cell line Nalm-6. Examination of the mRNA expression pattern of WNT ligands, FZD receptors and WNT antagonists in Nalm-6 cells identified a set of ligands and receptors available for signalling, as well as antagonists potentially available for modulating the response. Functional analyses showed that Wnt3A inhibited the proliferation of several, but not all, B-ALL cell lines studied. Finally, microarray analysis was used to identify several Wnt3A target genes involved in a diverse range of cellular activities, which are potential mediators of the Wnt3A-restrained proliferation.

Wnt expression and canonical Wnt signaling in human bone marrow B lymphopoiesis

BACKGROUND

The early B lymphopoiesis in mammals is regulated through close interactions with stromal cells and components of the intracellular matrix in the bone marrow (BM) microenvironment. Although B lymphopoiesis has been studied for decades, the factors that are implicated in this process, both autocrine and paracrine, are inadequately explored. Wnt signaling is known to be involved in embryonic development and growth regulation of tissues and cancer. Wnt molecules are produced in the BM, and we here ask whether canonical Wnt signaling has a role in regulating human BM B lymphopoiesis.

RESULTS

Examination of the mRNA expression pattern of Wnt ligands, Fzd receptors and Wnt antagonists revealed that BM B progenitor cells and stromal cells express a set of ligands and receptors available for induction of Wnt signaling as well as antagonists for fine tuning of this signaling. Furthermore, different B progenitor maturation stages showed differential expression of Wnt receptors and co-receptors, beta-catenin, plakoglobin, LEF-1 and TCF-4 mRNAs, suggesting canonical Wnt signaling as a regulator of early B lymphopoiesis. Exogenous Wnt3A induced stabilization and nuclear accumulation of beta-catenin in primary lineage restricted B progenitor cells. Also, Wnt3A inhibited B lymphopoiesis of CD133+CD10- hematopoietic progenitor cells and CD10+ B progenitor cells in coculture assays using a supportive layer of stromal cells. This effect was blocked by the Wnt antagonists sFRP1 or Dkk1. Examination of early events in the coculture showed that Wnt3A inhibits cell division of B progenitor cells.

CONCLUSION

These results indicate that canonical Wnt signaling is involved in human BM B lymphopoiesis where it acts as a negative regulator of cell proliferation in a direct or stroma dependent manner.

CD10+ stromal cells form B-lymphocyte maturation niches in the human bone marrow

In adult mammals, early B-lymphopoiesis takes place in the bone marrow in close association with stromal cells. Both the phenotype of the stromal cells and the molecules involved in this essential interaction are as yet inadequately described. In this study, all benign, differentiating B-cells (Pax-5+ lymphoid cells) are shown, by using two-colour immunohistochemistry on biopsies from human bone marrow, to be in close contact with scant dendritic CD10+ stromal cells until they leave via the sinusoids. This CD10+ stromal cell population does not fully overlap with the VCAM-1+ stromal cell population. Furthermore, using a set of B-cell differentiation markers (TdT, Pax-5, and CD20), B-cell development is shown to be spatially oriented, with maturation progressing towards bone marrow sinusoids. In conclusion, CD10+ stromal cells form distinct B-lymphocyte maturation niches in the human bone marrow.

[Clinical use of haematopoietic stem cells from cord blood]

A group of experts appointed by the Norwegian Centre for Health Technology Assessment (SMM) has undertaken a systematic review of available literature on the clinical effectiveness of transplanting haematopoietic stem cells from cord blood. A total of 17 studies form the documentary basis of the review. Autologous transplants of stem cells from cord blood have not been published. Retrospective studies suggest that the clinical effect of allogeneic cord blood transplants, at least in children, is comparable to transplants with allogeneic stem cells from bone marrow or peripheral blood cells. This review demonstrates the need for prospective studies comparing transplantations of cord blood with bone marrow or peripheral blood stem cells.

Serological cloning of cancer/testis antigens expressed in prostate cancer using cDNA phage surface display

Serological cloning of tumor-associated antigens (TAAs) using patient autoantibodies and tumor cDNA expression libraries (SEREX) has identified a wide array of tumor proteins eliciting B-cell responses in patients. However, alternative cloning strategies with the possibility of high throughput analysis of patient sera and tumor libraries may be of interest. We explored the pJuFo phage surface display system, allowing display of recombinant tumor proteins on the surface of M13 filamentous phage, for cloning of TAAs in prostate cancer (PC). Control experiments established that after a few rounds of selection on immobilized specific IgG, a high degree of enrichment of seroreactive clones was achieved. With an increasing number of selection rounds, a higher yield of positive clones was offset by an apparent loss of diversity in the repertoire of selected clones. Using autologous patient serum IgG in a combined biopanning and immunoscreening approach, we identified 13 different TAAs. Three of these (NY-ESO-1, Lage-1, and Xage-1) were known members of the cancer/testis family of TAAs, and one other protein had previously been isolated by SEREX in cancer types other than PC. Specific IgG responses against NY-ESO-1 were found in sera from 4/20 patients with hormone refractory PC, against Lage-1 in 3/20, and Xage-1 in 1/20. No reactivity against the remaining proteins was detected in other PC patients, and none of the TAAs reacted with serum from healthy subjects. The results demonstrate that phage surface display combined with postselection immunoscreening is suitable for cloning a diverse repertoire of TAAs from tumor tissue cDNA libraries. Furthermore, candidate TAAs for vaccine development of PC were identified.

Characterization of the novel human transmembrane protein 9 (TMEM9) that localizes to lysosomes and late endosomes

We have identified and characterized the novel human transmembrane protein 9 (TMEM9). TMEM9 encodes a 183 amino-acid protein that contains an N-terminal signal peptide, a single transmembrane region, three potential N-glycosylation sites, and three conserved cys-rich domains in the N-terminus, but no hitherto known functional domains. The protein is highly conserved between species from Caenorhabditis elegans to man and belongs to a novel family of transmembrane proteins. The TMEM9 gene consists of at least 6 exons and is localized to chromosome 1q41. TMEM9 mRNA is expressed in a wide range of tissues and cells. COS-1 cells transfected with a TMEM9 expression plasmid gave three bands of about 28, 31, and 33kDa representing glycosylated forms of TMEM9 with a protein backbone of about 26kDa. In COS-1 cells transfected with a TMEM9-GFP expression construct,TMEM9-GFP is co-expressed with LAMP1 on late endosomes and lysosomes as well as on ER. Thus, TMEM9 is a phylogenetically conserved, widely expressed transmembrane protein with a potential, but unknown function in intracellular transport.

Characterization, expression and functional aspects of a novel protein tyrosine phosphatase epsilon isoform

This report describes the identification and characterization of a novel cytoplasmic isoform of human protein tyrosine phosphatase epsilon (PTPepsilon). The novel isoform, denoted cyt-PTPepsilonPD1, displays only the N-terminal catalytic, active phosphatase domain 1 (PD1) which is common in all known PTPepsilon isoforms. In addition, it contains a unique 132-residue long C-terminal end with no known motifs or homology to other characterized proteins. RNAse protection assay on isolated leucocyte subpopulations and selected cell lines demonstrated highest expression of cyt-PTPepsilonPD1 in monocytes. The mRNA-encoding cyt-PTPepsilonPD1 is detected as distinct transcript(s) by Northern blot analysis and is a result of alternative splicing. cyt-PTPepsilonPD1 shows similar cellular localization in transfected cells, both in the cytoplasm and nucleus, as has been previously described for cytoplasmic PTPepsilon isoform. Our previous data suggest that the expression of cytoplasmic PTPepsilon inhibits the mitogen-activated protein kinase cascade through the extracellular signal-regulated kinase 1 and 2 pathway. A similar functional role is also presented here for cyt-PTPepsilonPD1, supporting our previous data suggesting that the catalytic first PD of PTPepsilon is responsible for this inhibition.

[Stem cells in adults]

BACKGROUND

We present a literature review of the plasticity observed by adult stem cells.

MATERIALS AND METHODS

We have reviewed the literature regarding stem cells from adults in order to summarise their ability to generate cells of other types than those of the tissue/organ from which they were isolated.

RESULTS

Adult stem cells have recently been demonstrated to terminally differentiate into cells of other tissues than those from which they were originally isolated. For example, bone marrow cells have been shown to generate liver, nerve, heart and skeletal muscle cells in addition to their well-known ability to produce blood and mesenchymal cells.

INTERPRETATION

Most studies demonstrate a proof-of-principle in animal models; much more research is needed before adult stem cells can be utilised in human medicine. However, the published reports are encouraging and give reasons for a cautious optimism with regard to future clinical use.

A splice variant of human ephrin-A4 encodes a soluble molecule that is secreted by activated human B lymphocytes

Ephrin-A4 is a ligand for the erythropoietin-producing hepatocellular (Eph) receptor family of tyrosine kinases. We have identified a secreted form of ephrin-A4, denoted ephrin-A4 (s), which is encoded by an alternatively spliced mRNA and is produced by in vivo activated B cells in tonsils. Blood B cells secrete ephrin-A4 (s) upon stimulation via the B-cell antigen receptor. A subpopulation of tonsil cells in the crypts with a dendritic cell phenotype was shown to express EphA2, an Eph receptor tyrosine kinase that was found to be capable of binding an ephrin-A4 immunoglobulin chimeric protein. We conclude that ephrin-A4 (s) may play a role in the interaction between activated B lymphocytes and dendritic cells in human tonsils. (Blood. 2000;95:221-230)

The nature of the subset of MHC class II molecules carrying the CDw78 epitopes

A CDw78 mAb FN1 was shown to recognize DP and/or DR molecules under the conditions of Western blotting. DP molecules were specifically retarded on a column of the FN1 immunosorbent; binding of FITC-labeled FN1 to B cell lines was completely blocked by excess of mAb to DR/DP beta chains, partially by several mAb to DP and weakly by some mAb to DR. The binding of two other CDw78 mAb, FN4 and MR11, to the B cell surface was most strongly inhibited by excess of different mAb to DR. Kinetics of stable binding of the CDw78 mAb indicated that their monovalent binding is of low affinity and that the stable binding to the surface is due to bivalent binding to two spatially close MHC class II molecules. FN1-based immunosorbent effectively immunoisolated complexes of MHC class II proteins with several tetraspanin molecules from a mild detergent lysate of a B cell line. It is concluded that FN1 and most likely also the other two CDw78 mAb recognize with low affinity determinants on MHC class II molecules (DP or DR) and preferentially bind in a stable fashion to dimerized or aggregated MHC class II molecules. Such dimers or aggregates may either exist as preformed on the cell surface or may be gradually formed and stabilized by bivalent interaction with mAb. These structures may be related to the previously described 'superdimers' of MHC class II and/or 'MHC-tetraspanin complexes'. CDw78 mAb may be valuable tools targeting such aggregated fraction of MHC class II molecules which can exhibit important signaling and antigen-presenting properties.

CDw78--a determinant on a major histocompatibility complex class II subpopulation that can be induced to associate with the cytoskeleton

In the present study we demonstrate that CDw78 monoclonal antibody (mAb) recognizes a distinct subpopulation of major histocompatibility complex (MHC) class II molecules. We show that the CDw78 epitope is present on less than 10% of the total number of MHC class II molecules expressed on different cells, is not linked to a single isotype, and exhibits a characteristic expression pattern in tonsils. While mAb against MHC class II (DR, DP and DQ) stained the majority of cells both in the mantle zone and in germinal centers, the CDw78 staining was more heterogeneous with the strongest reactivity and the highest number of positive cells in the mantle zone and in the light centrocyte-rich part of the germinal centers. Antibodies to this MHC class II subpopulation (e.g. FN1) induced association with the cytoskeleton and a subsequent capping in more than 90% of peripheral blood B cells. In contrast, mAb against MHC class II (DR, DP and DQ) did not induce association with the cytoskeleton and only 10-20% of B cells were induced to cap, suggesting that CDw78 defines a population of MHC class II molecules functionally different from the majority of these antigens. Scatchard plot analysis indicates that FN1 mAb is of relatively low affinity (Ka = 1.5 x 10(8) M(-1)) and monovalent Fab fragments fail to bind to the cell surface with measurable affinity. Our data seen in the context of the ability of FN1 to co-stimulate B cells with a suboptimal dose of anti-mu suggest that CDw78 mAb might recognize a functional important subpopulation of MHC class II molecules so far not described. It seems likely that this subpopulation represents dimerized or aggregated MHC class II molecules that can selectively bind this low-affinity mAb.

Immunomagnetic techniques for the enrichment and detection of isolated breast carcinoma cells in bone marrow and peripheral blood

Detection of isolated tumor cells (TC) in bone marrow (BM) from patients with breast cancer is usually accomplished by immunocytochemical (ICC) analysis of up to 2 X 10(6) mononuclear cells (MNC). However, this method is cumbersome if large numbers of BM cells (i.e. > 1 X 10(7) cells) are to be analyzed. This emphasizes the need for TC enrichment strategies. This report describes immunomagnetic separation (IMS) techniques for enrichment and detection of viable breast carcinoma cells in BM and peripheral blood (PB). The positive IMS technique was performed by incubation of MNC with 2.8 microns magnetic particles (rat antimouse IgG1 M280-Dynabeads) coated with monoclonal antibody (mAb) against epithelial surface antigens. The rosetted tumor cells were then visualized by ICC staining using alkaline phosphatase-conjugated A45-B/B3 anticytokeratin mAb (Fab). The negative IMS technique was performed by incubation of MNC with anti-CD45-coated M450-Dynabeads (4.5 microns), followed by ICC staining of the nonrosetted cells. When 1000, 100, and 10 breast carcinoma cells were mixed with 1 X 10(7) MNC, an average of 748 (n = 9), 70 (n = 10), and 7.8 TC (n = 8), respectively, were detected with the positive IMS technique. With the negative IMS technique, 648 (n = 8), 57.8 (n = 6), and 7.3 TC (n = 6), respectively, were detected. The analysis of 1 X 10(7) MNC with the IMS techniques was compared with the ICC analysis of 2 X 10(6) unseparated MNC. A mean 3.7-fold (range 1.5-6.4) to 4.2-fold (2.5-8.2) (positive IMS) and 3.1-fold (range 2.0-5.0) to 3.8-fold (2.0-6.0) (negative IMS) higher TC detection frequency was achieved after enrichment by IMS in experiments with 100 and 1000 TC/10(7) MNC. The IMS techniques were used for examination of BM samples from locally advanced breast cancer patients. A 5.3-fold mean increase (range 2.1-13.3) in the number of TC detected was obtained when the use of positive and negative IMS together was compared with the direct ICC analysis of unseparated MNC (n = 11). Enrichment of TC by IMS techniques enables us to examine large numbers of MNC from BM or PB, which can result in the detection and characterization of minimal residual disease with increased sensitivity and specificity.

Purging of tumor cells from leukapheresis products: experimental and clinical aspects

Peripheral blood progenitor cell autografts are being used increasingly in conjunction with high-dose therapy of cancer patients, in the belief that these products have a low probability of containing tumor cells. However, recent findings demonstrate that tumor cell involvement is frequent in leukapheresis products. Although the clinical value of purging has not been clinically established by prospective randomized trials, several studies indicate that contaminating tumor cells in autografts contribute to relapse of the disease in the recipients. We describe our experimental and clinical experience in purging tumor cells from leukapheresis products. Based on our work with purging of lymphoma cells from bone marrow by the use of anti-B cell and anti-T cell antibodies and immunobeads, a purging procedure to deplete leukapheresis products of lymphoma cells has been developed. Moreover, we present data showing that breast cancer cells can be efficiently removed from leukapheresis products using antibreast cancer antibodies, either in combination with immunobeads or as immunotoxins. Our experience with enrichment of CD34 cells employing immunobeads in leukaphresis products from patients with breast cancer and lymphomas shows high purity and yield of CD34 cells. In spite of this, contaminating tumor cells can be observed, strongly suggesting that a combination of CD34 cell enrichment and a purging procedure might be warranted.

Solid-phase method for differential display of genes expressed in hematopoietic stem cells

A solid-phase differential display method was designed to analyze differential gene expression in samples with low amounts of mRNA. The principle was based on using a biotinylated probe to capture the mRNA and priming both the first-strand synthesis and the subsequent polymerase chain reaction step. Coupling the mRNA to a solid phase during the procedure simplified the purification steps, limited sample loss and enabled rapid handling of mRNA. DNA contamination was also minimized when the mRNA was bound to a solid phase. Optimization of the differential display method was achieved by analyzing both the enzymatic conditions and the required cell amounts. The approach was used for the characterization of genes expressed in the most immature hematopoietic progenitor cells (CD34+CD38-). The majority of the differentially expressed fragments represented previously uncharacterized sequences.

Cyclic AMP-dependent protein kinase (cAK) in human B cells: co-localization of type I cAK (RI alpha 2 C2) with the antigen receptor during anti-immunoglobulin-induced B cell activation

Cyclic AMP (cAMP) inhibits antigen-stimulated B cell proliferation through activation of cAMP-dependent protein kinases (cAK). We have examined the molecular composition and cellular localization of cAK in human B cells. We find that human B cells contain substantial amounts of mRNA for RI alpha, RII alpha, C alpha and C beta, barely detectable levels of RI beta mRNA, and no detectable RII beta or C gamma mRNA. At the protein level, using Western blotting and subunit-specific antibodies against the different R subunits, we find RI alpha and RII alpha, but no RI beta or RII beta. The presence of catalytic subunits was demonstrated using a nonselective anti-C antiserum. By photoaffinity labeling of R subunits with 8-azido-[32P]cAMP, followed by immunoprecipitation with subunit-specific antibodies, we were also able to demonstrate low levels of RI beta. Immunofluorescence staining of RI alpha and RII alpha demonstrates a rather homogeneous intracellular (but extranuclear) distribution of RI alpha, whereas the RII alpha subunits of cAK are localized to distinct perinuclear structures, previously identified as centrosomes in other cell types. Upon anti-Ig-mediated capping of B cells, RI alpha subunits redistribute to the cap, co-localizing with the antigen-receptors, whereas the intracellular localization of RII alpha subunits remains unchanged.

All-trans- and 9-cis-retinoic acid inhibit growth of normal human and murine B cell precursors

In the present paper we demonstrate that physiologic levels (10 nM) of both all-trans- and 9-cis-retinoic acid (RA) are potent inhibitors of the growth of human as well as murine B cell precursors in vitro. Ten nanomolar concentrations of all-trans- and 9-cis-RA reduced the DNA synthesis ([3H]thymidine uptake) of human B cell precursors (CD19+ IgM-) stimulated with O-tetradecanoylphorbol-13-acetate and ionomycin by approximately 55% and 70%, respectively. Human B cell precursors stimulated with low m.w. B cell growth factor were also inhibited by RA. Ten nanomolar concentrations of either isoform of RA reduced DNA synthesis by approximately 50%. No effect of RA on differentiation to sIgM positive cells was noted. The potent growth-inhibiting effect of RA on human B cell precursors was confirmed in the murine cell system. B lymphopoiesis from murine hematopoietic precursors (Lin-B220(+)-containing cells) was induced by stimulation with IL-7. Concentrations of all-trans- and 9-cis-RA as low as 10 pM reduced the colony-forming ability of the IL-7-stimulated Lin-B220(+)-containing cells. Ten nanomolar concentrations of either isoform reduced colony formation by approximately 60%. RA was not toxic to the cells, as the inhibition of colony formation after 24 h was reversible at concentrations as high as 1 microM. The growth-inhibiting effect of RA was directly mediated, as revealed by single cell analysis of the Lin-B220(+)-containing cells. Thus, vitamin A appears to have an important role in regulation of B lymphopoiesis.

All-trans- and 9-cis-retinoic acid inhibit growth of normal human and murine B cell precursors

In the present paper we demonstrate that physiologic levels (10 nM) of both all-trans- and 9-cis-retinoic acid (RA) are potent inhibitors of the growth of human as well as murine B cell precursors in vitro. Ten nanomolar concentrations of all-trans- and 9-cis-RA reduced the DNA synthesis ([3H]thymidine uptake) of human B cell precursors (CD19+ IgM-) stimulated with O-tetradecanoylphorbol-13-acetate and ionomycin by approximately 55% and 70%, respectively. Human B cell precursors stimulated with low m.w. B cell growth factor were also inhibited by RA. Ten nanomolar concentrations of either isoform of RA reduced DNA synthesis by approximately 50%. No effect of RA on differentiation to sIgM positive cells was noted. The potent growth-inhibiting effect of RA on human B cell precursors was confirmed in the murine cell system. B lymphopoiesis from murine hematopoietic precursors (Lin-B220(+)-containing cells) was induced by stimulation with IL-7. Concentrations of all-trans- and 9-cis-RA as low as 10 pM reduced the colony-forming ability of the IL-7-stimulated Lin-B220(+)-containing cells. Ten nanomolar concentrations of either isoform reduced colony formation by approximately 60%. RA was not toxic to the cells, as the inhibition of colony formation after 24 h was reversible at concentrations as high as 1 microM. The growth-inhibiting effect of RA was directly mediated, as revealed by single cell analysis of the Lin-B220(+)-containing cells. Thus, vitamin A appears to have an important role in regulation of B lymphopoiesis.

Characterization of a promoter region supporting transcription of a novel human beta-galactoside alpha-2,6-sialyltransferase transcript in HepG2 cells

In humans, two transcripts encoding beta-galactoside alpha-2,6-sialytransferase (EC 2.4.99.1.) have previously been described. One of the transcripts is widely expressed, whereas the other is restricted to mature B-cells. In this study we demonstrate the existence of a third transcript in the hepatoma cell-line HepG2. The expression of this transcript is controlled by a promoter region which efficiently supports transcription in HepG2 cells, and which harbours putative binding sites for liver-enriched and acute phase inducible transcription factors.

All-trans retinoic acid directly inhibits granulocyte colony-stimulating factor-induced proliferation of CD34+ human hematopoietic progenitor cells

In this study we examine the effects of retinoids on purified CD34+ human hematopoietic progenitor cells. All-trans retinoic acid inhibited granulocyte colony-stimulating factor (G-CSF)-induced proliferation of CD34+ cells in short-term liquid cultures in a dose-dependent fashion with maximal inhibition of 72% at a concentration of retinoic acid of 1 mumol/L. Although no significant effects were observed on granulocyte-macrophage CSF (GM-CSF)--interleukin-3--or stem cell factor (SCF)-induced proliferation, the combinations of G-CSF and each of these cytokines were all inhibited. Moreover, retinol (3 mumol/L) and chylomicron remnant retinyl esters (0.1 mumol/L) in concentrations normally found in human plasma also had inhibitory effects. Single-cell experiments showed that the effects of retinoic acid were directly mediated. Retinoids also significantly inhibited G-CSF-induced colony formation in semisolid medium, with 88% inhibition observed at a concentration of retinoic acid of 1 mumol/L. However, we did not observe any effects of retinoic acid on G-CSF-induced differentiation as assessed by morphology and flowcytometry. Similar to previous findings using total bone marrow mononuclear cells, we observed a stimulation of GM-CSF-induced colony formation after 14 days. We also observed a stimulatory effect of low doses of retinoic acid (30 nmol/L) on blast-cell colony formation on stromal cell layers. Taken together, the data indicate that vitamin A present in human plasma has inhibitory as well as stimulatory effects on myelopoiesis.

Functional differences between CD38- and DR- subfractions of CD34+ bone marrow cells

Several studies have previously demonstrated enrichment in primitive progenitor cells in subfractions of CD34+ bone marrow (BM) cells not expressing CD38 or HLA-DR (DR) antigens. However, no studies have directly compared these two cell populations with regard to their content of primitive and more committed progenitor cells. Flow cytometric analysis of immunomagnetic isolated CD34+ cells demonstrated little overlap between CD34+CD38- and CD34+DR- progenitor subpopulations in that only 12% to 14% of total CD34+DR- and CD34+CD38- cells were double negative (CD34+CD38-DR-). Although the number of committed myeloid progenitor cells (colony-forming units granulocyte-macrophage) was reduced in both subpopulations, only CD34+CD38- cells were significantly depleted in committed erythroid progenitor cells (burst-forming units-erythroid). In single-cell assay, CD34+CD38- cells showed consistently poorer response to single as opposed to multiple hematopoietic growth factors as compared with unfractionated CD34+ cells, indicating that the CD34+CD38- subset is relatively enriched in primitive hematopoietic progenitor cells. Furthermore, CD34+CD38- and CD34+DR- cells, respectively, formed 3.2-fold and 1.6-fold more high proliferative potential colony-forming cell (HPP-CFC) colonies than did unfractionated CD34+ cells. Finally, CD34+CD38-DR- cells were depleted in HPP-CFCs as compared with CD34+CD38+DR+ cells. The results of the present study suggest that both the CD38- and DR- subfractions of CD34+ bone marrow cells are enriched in primitive hematopoietic progenitor cells, with the CD34+CD38- subpopulation being more highly enriched than CD34+DR- cells.

Complement-mediated permeabilization of platelets by monoclonal antibodies to CD9: inhibition by leupeptin, and effects on the GP Ib-actin-binding protein system

Two monoclonal antibodies to CD9 of the IgM and IgG2a categories (FN 52 and FN 99), reproducibly induced platelet alterations in platelet-rich plasma by activation of the complement system with membrane incorporation of the pore-forming C5b-9 complex. The permeabilization could be monitored by measurements of extracellular ATP and observed as a shape change followed by an increase in light transmission in the aggregometer, and was associated with formation of tiny platelet aggregates. This could be accomplished by only minor lysis observed as extracellular lactate dehydrogenase (LDH). When leupeptin was added prior to, or immediately after the antibody, a total inhibition of the platelet alterations could be obtained. When added soon after the shape change, leupeptin had little effect on the liberation of ATP. However, whereas the ability of the platelets to become agglutinated by ristocetin was lost during the complement-mediated platelet alterations, addition of leupeptin immediately after the shape change, prevented this loss. The lost ability of the permeabilized platelets to undergo ristocetin-induced agglutination is not ascribed to degradation of GP Ib as this was relatively little affected in these studies as compared to the actin-binding protein (ABP) which was profoundly degraded. This protein represents a link between GP Ib and the submembraneous cytoskeleton, and the inhibition of its degradation by leupeptin, was clearly demonstrated. Experiments with digitonin-induced permeabilization showed that leupeptin did not inhibit permeabilization as such, but it did prevent the loss of ristocetin-induced agglutination even with this inducer.

CDw75 antigen expression in human gastric carcinoma and adjacent mucosa

BACKGROUND

The amount of sialic acid correlates with the invasiveness and metastasizing potential of several human tumors. The CDw75 epitope is a sialylated carbohydrate determinant generated by the beta-galactosyl alpha 2,6-sialyltransferase, which can be viewed as a target for identifying biologically aggressive tumors.

METHODS

The authors performed an immunohistochemical study of CDw75 epitope expression in 87 cases of gastric carcinoma and adjacent mucosa and 331 metastases (329 lymph node metastases and 2 liver metastases) with the monoclonal antibody HH2.

RESULTS

Normal-appearing mucosa, foci of intestinal metaplasia, and foveolar hyperplasia, adjacent to the carcinomas, were mainly nonimmunoreactive. Only a few parietal cells of the body mucosa were stained with HH2. Two of 12 cases with dysplasia showed CDw75 antigen expression in dysplastic glands. Forty-one cases (47.1%) were immunoreactive for CDw75 antigen in the primary tumors or metastases. A very close relationship was found between the expression of the antigen in primary tumors and their respective metastases. The expression of the antigen was correlated with an infiltrative growth pattern, lymphatic invasiveness, and aneuploidy. All but two immunoreactive cases had lymph node metastases or lymphatic permeation. No relationship was found between CDw75 antigen expression and the morphologic types of gastric carcinoma, amount of lymphoid infiltrate, vascular invasion, and penetration of the gastric wall.

CONCLUSIONS

The authors conclude that CDw75 antigen expression can be used as a marker of malignant transformation of gastric epithelium and is a good indicator of the biologic aggressiveness of gastric carcinoma.

CDw75 antigen expression in breast lesions

Alterations on the cell surface of the oligosaccharide portion of glycoproteins and glycolipids are thought to play a role in tumorigenesis. Sialyltransferase catalyzes the incorporation of sialic acid to the carbohydrate group of glycoconjugates. Sialyltransferase has been found elevated in different tumour tissues and in the serum of cancer patients. In the present study we have examined the expression of the beta-galactosyl alpha 2,6-sialyltransferase requiring epitope CDw75, with the monoclonal antibody HH2. 142 breast lesions were included. 21% of the carcinomas in situ and 35% of the invasive carcinomas showed a diffuse cytoplasmic staining. Seven cases of invasive carcinomas also showed a distinct membrane immunoreactivity. We found no correlation between reactivity for CDw75 in malignant lesions and their metastatic potential. Only five out of 11 primary tumours with metastases expressed CDw75 in the primary tumour. In the benign lesions, there was a positive reaction in proliferating lesions, e.g. intraductal papillomas (2 out of 3 cases) and in epithelial proliferations in fibrocystic disease (10 out of 14 cases). None of the four fibroadenomas and phyllodes tumours and only one out of 22 cases of normal breast tissues showed immunoreactivity for HH2. In the malignant lesions, CDw75 was more frequently expressed in the carcinomas of high malignancy grade. The high frequency of immunoreactivity among the benign breast lesions can be indicative of activation of the epithelial cells.

Cell-specific expression of human beta-galactoside alpha 2,6-sialyltransferase transcripts differing in the 5' untranslated region

In humans, two cDNAs have been isolated encoding beta-galactoside alpha 2,6-sialyltransferase, differing only in part of the 5' untranslated region. Primer extension data show that the two cDNAs are near full-length clones. RNase protection analysis of different cell types showed that the transcript corresponding to the alpha 2,6-sialyltransferase cDNA isolated from a B-cell library resided only in mature B cells. In contrast, the transcript corresponding to the alpha 2,6-sialyltransferase cDNA isolated from a placenta library was found in all cells tested. Our results also indicate the existence of a third alpha 2,6-sialyltransferase transcript in the hepatoma cell line HepG2. Mature B cells were found to express high amounts of alpha 2,6-sialyltransferase mRNA, compared to other cell types tested, as shown by Northern blot analysis. Moreover there was an increased expression of beta-galactoside alpha 2,6-sialyltransferase mRNA in activated B cells compared to resting B cells. In vitro transcription and translation of the cDNAs resulted in a protein of 45 kDa, but the transcripts were translated with different efficiency, suggesting a role for the 5' untranslated region in regulation of translation. We have also made an alpha 2,6-sialyltransferase construct lacking the specific 5' regions of the two cDNAs. A transcript generated from this construct was translated more efficiently in vitro than the two alpha 2,6-sialyltransferase cDNAs.

Human Golgi beta-galactoside alpha-2,6-sialyltransferase generates a group of sialylated B lymphocyte differentiation antigens

The role of the human beta-galactoside alpha-2,6-sialyltransferase (hu alpha-2,6-ST) in the generation of B cell surface antigens was investigated by selecting subclones of COS cells (monkey kidney epithelial cells) constitutively expressing a transfected cDNA which encodes the hu alpha-2,6-ST (COS alpha-2,6-ST cells). Expression of hu alpha-2,6-ST in COS cells was sufficient to generate sialylated cell surface epitopes on different glycosylated antigens recognized by monoclonal antibodies to CDw75, CD76, and the unclustered monoclonal antibodies HB-4 and EBU-65. These epitopes were sensitive to sialidase treatment and are likely to contain terminal alpha-2,6-linked sialic acid residues. A novel antiserum raised against bacterially expressed hu alpha-2,6-ST fusion protein was used to localize the sialyltransferase in two cell lines with high expression of either endogenous (B cell line JOK-1) or recombinant (COS alpha-2,6-ST cells) hu alpha-2,6-ST. In both cell lines, the enzyme was detected only intracellularly in the juxtanuclear region and not on the cell surface. In contrast, CDw75, formerly proposed to be identical with an alpha-2,6-ectosialyltransferase, was strongly expressed on the cell surface. The different expression patterns show that neither the CDw75 antigen nor any of the other sialylated antigens analyzed is identical with the hu alpha-2,6-ST. Furthermore, the presence of a surface-expressed alpha-2,6-ST appears unlikely in these cell lines. We propose that CDw75, CD76, HB-4, and EBU-65 represent a unique group of B cell differentiation antigens the production of which requires the enzymatic activity of alpha-2,6-ST.

Isolation and characterization of human hematopoietic progenitor cells: an effective method for positive selection of CD34+ cells

Immunomagnetic beads are well suited for positive selection of CD34+ cells. However, both unspecific binding of beads to cells as well as the effectiveness of detachment of beads from cells may represent significant problems. We used an anti-Fab antiserum (DETACHaBEAD, Dynal) for rapid and effective detachment of immunomagnetic beads from the positively selected cells. By this detachment technique, the cells remained phenotypically unaltered. To reduce unspecific binding, we have coated various anti-CD34 monoclonal antibodies directly to paramagnetic beads M450 (Dynal). Use of beads coated with BI-3C5 was found to be optimal with regard to yield and purity of the isolated cells. The yield was on average 1.5% (range 0.5-2.5%) of bone marrow mononuclear cells and the purity was usually greater than 95% CD34+ cells of the isolated cells. Subpopulations of the cells expressed myeloid markers (CD13, CD33, and to a lesser extent CD15 and CD14) or early B-lineage markers (CD19 and CD10). Most of the cells expressed CD38, and a majority of the cells also expressed CD41. In general, most of the CD34+ cells with low forward scatter expressed B-lineage markers, as was also the case for the few contaminating CD34- cells which were found to be predominantly CD37+ mature B cells. Reactivity with antibodies against T-lineage markers (CD2, CD3, CD4, CD7, and CD8) was generally detected only on 1-2% of the cells or less. Isolated cells responded to interleukin 3, granulocyte-macrophage colony-stimulating factor, mast cell growth factor, and/or granulocyte colony-stimulating factor alone or in combinations in short-term liquid cultures. The cells were also markedly enriched for granulocyte-macrophage colony-forming units as well as for early progenitor cells capable of forming blast colonies on preformed stromal feeder layers. Moreover, the CD34- population was depleted of 70-80% of CFU-GM and cells capable of blast colony formation. Thus, we conclude that the isolated cells are phenotypically unaltered after isolation, and show a normal response in various in vitro assays.

Cell cycle-dependent regulation of CDw75 (beta-galactoside alpha-2,6-sialyltransferase) on human B lymphocytes

Within the hematopoietic system, CDw75 is primarily expressed on cells of the B cell lineage. Cloning and sequencing of the gene has shown CDw75 to be a beta-galactoside alpha-2,6-sialyltransferase. This enzyme plays an important role in the intracellular terminal glycosylation pathways in various cell types. In this article, we demonstrate that COS cells transfected with the CDw75 cDNA clone displayed sialyltransferase activity, in contrast to mock-transfected cells. We also found that activated B cells displayed an increased enzyme activity compared to resting cells, in accordance with the staining data. Moreover, CDw75 expression was found to be up-regulated approximately 7-9-fold from early G1 to the G2/M phases of the cell cycle in peripheral blood leukocyte B cells. This was shown by staining of in vitro activated B cells with the anti-CDw75 monoclonal antibody HH2, using cell fractions corresponding to different stages of the cell cycle. Using a combination of Hoechst 33258 and propidium iodide after bromodeoxyuridine incorporation, it is possible to distinguish between different phases of the first and second cell cycle. By combining this with HH2 immunofluorescence staining, using a multistation multiparameter flow cytometry program, we confirmed the cell cycle-dependent expression of CDw75. Immunocytochemical stainings of cytospin specimens of elutriated B cells showed that the antigen was up-regulated in late G1 before the appearance of the nuclear activation antigen Ki67. Finally, we showed that activated B cells secreted soluble CDw75 into the medium, as demonstrated by a specific blocking of HH2 staining of B cells using suboptimal concentrations of HH2. In accordance with this, we observed small, but detectable levels of soluble sialyltransferase activity in supernatants of activated B cells.

A new method for detachment of Dynabeads from positively selected B lymphocytes

This paper describes a method for the detachment of immunomagnetic beads from positively selected human B lymphocytes. After rosetting of B cells using anti-CD19 coated magnetic beads (Dynabeads M-450 Pan B, Dynal), the Dynabeads were rapidly detached (efficiency 80%) from the cells using goat anti-mouse-Fab antiserum (DETACHaBEAD, Dynal) at ambient temperature. Isolated B cells did not show significant differences in the expression of a number of B cell antigens when compared to B cells stained in fresh whole blood. In contrast, positively selected B cells that had detached from the beads following overnight incubation, demonstrated a significantly reduced expression of certain of the antigens examined (CD19, CD20 and CD23). It was further demonstrated that neither anti-CD19 nor anti-Fab resided on the surface of the cells after detachment. The cells were still in G0 phase (greater than 90%) at the end of the isolation procedure. Moreover, anti-IgM antibodies stimulated the vast majority of the cells to leave the G0 phase, and to progress through S phase in the presence of growth factors. The cells could also be stimulated to differentiate, further confirming the normal functional capacity of the isolated cells. The method described in this paper can also be used for the detachment of other positively selected cells, such as CD4+ T cells, CD8+ T cells and CD34+ stem cells.

Interleukin-7 differentiates a subgroup of acute lymphoblastic leukemias

The bone marrow stromal cell-derived growth factor interleukin-7 (IL-7) is known to stimulate growth of normal human B-cell precursors. In the present report, we have examined the effect of IL-7 on neoplastic B-cell precursors. Leukemic cells from 20 patients with common acute lymphoblastic leukemia (ALL) were highly purified by removing contaminating T cells and monocytes by rosetting with immunomagnetic beads. IL-7 markedly reduced the DNA synthesis in leukemic cells from three patients. This inhibition of DNA synthesis was accompanied by maturation of the cells, as demonstrated by the induced expression of the differentiation antigens CD19, CD20, CDw75, and surface mu-chain, and a decreased expression of terminal deoxynucleotidyl transferase. By examining G1 parameters, such as MYC, 4F2, and transferrin-receptor levels analyzed by flow cytometry as well as RNA and the cell cycle regulated antigen Ki67, it appeared that the cells were inhibited late in G1. Leukemic cells from the majority of the cases (12 of the 20 patients) responded to IL-7 with enhanced DNA synthesis without detectable maturation, as has been reported for their normal counterparts. Low molecular weight B-cell growth factor greatly potentiated the IL-7-induced growth stimulation of these cells. Thus, we have shown that IL-7 is capable of inhibiting proliferation of leukemic cells isolated from a subgroup of ALLs, and that this growth inhibition is accompanied by maturation of the cells.

Cell cycle-specific expression and nuclear binding of DNA polymerase alpha

The expression and distribution of DNA polymerase alpha was measured by cytometry and confocal laser scanning microscopy. Expression was proportional to DNA content in proliferating cells, while only S-phase cells retained DNA polymerase alpha after detergent extraction. Nuclear DNA polymerase alpha binding may be one of the key events of S-phase entry.

Differential effects of interferon-gamma and low molecular weight BCGF on growth of human B lymphocytes; interferon-gamma prolongs the increased c-MYC mRNA levels after activation

We have characterized the growth-stimulating effect of Interferon-gamma (IFN-gamma) on various parameters of B cell growth, and compared the effects with those of low molecular weight B cell growth factor (lmw BCGF). We have found that IFN-gamma did not affect early changes induced by anti-mu, like initial calcium-flux and rise in mRNA-and protein levels of the proto-oncogene c-myc measured at 3 h. On the other hand, IFN-gamma enhanced the effect of anti-mu on parameters measured later in the G1 phase of the cell cycle, such as expression of the transferrin receptor and general transcriptional activity, measured as an increase in 7-aminoactinomycin D binding. In particular, whereas the c-myc levels in anti-mu-treated cells peaked at 3 h and then gradually declined, IFN-gamma together with anti-mu maintained the c-myc levels at 24 h at approximately the same levels as seen at 3 h. Overall, lmw BCGF had a more potent effect on the parameters affected by IFN-gamma, correlating with stronger enhancement of DNA synthesis. However, in contrast to IFN-gamma lmw BCGF did not affect anti-mu-induced c-myc mRNA levels. Thus this study has revealed differences between two B cell growth factors in effects on B cell cycle parameters.

Independent regulation of 55-kDa and 75-kDa tumor necrosis factor receptors during activation of human peripheral blood B lymphocytes

We have studied the expression of two different tumor necrosis factor receptors (TNFR; 55 kDa and 75 kDa) on resting and activated human peripheral blood B lymphocytes using specific monoclonal antibodies (mAb). Flow cytometric analysis revealed that most resting B cells expressed small amounts of the 75-kDa TNFR, and that the 75-kDa TNFR was markedly up-regulated upon stimulation with anti-mu or Staphylococcus aureus Cowan strain I (SAC). In contrast, the expression of the 55-kDa TNFR was low on resting as well as on activated cells. B cell activation was accompanied by an increased binding of biotinylated TNF-alpha, and this binding could be blocked by preincubation by utr-1 (anti-75-kDa TNRF), but not the htr (anti-55-kDa TNFR) antibodies. Notably, a number of cytokines tested (interleukin 1 to 8, interferon-gamma, TNF-alpha and -beta) did not influence the expression of either the 75-kDa or the 55-kDa TNFR when given to resting B cells. Moreover, phorbol 12-myristate 13-acetate led to an early, marked down-regulation of the 75-kDa TNFR expression, followed by a later modest increase after greater than 24 h. In contrast to other cell systems where htr mAb have been found either to mimic or to inhibit TNF action, htr mAb had insignificant effects in assays for restimulation of preactivated B cells. However, utr-1 markedly inhibited the TNF-beta but only partly inhibited the TNF-alpha-induced proliferation. Taken together, our data suggest that changes in 75-kDa protein expression is responsible for the increased TNFR expression on activated vs. resting peripheral blood B cells and that this protein also may play an important functional role.

Autologous transplantation of an immunomagnetic bead purged marrow in patients with relapsed acute lymphoblastic leukemia

In acute lymphoblastic leukemia (ALL) the expected duration of a second complete remission (CR) following conventional aggressive multi-drug treatment is rather short, and long-term survival is rarely seen. Myeloablative consolidation treatment with ABMT in second CR is thought to benefit "high risk" patients thus allowing the escalation of cytoreductive treatment into a lethal range. In three patients with relapsed ALL bone marrow was collected in the very early second remission phase. The autografts were incubated with a panel of monoclonal antibodies bound to magnetobeads (DYNABEADS M450). The pretransplant regimen consisted of total body irradiation (TBI) (14.4 Gy) and cyclophosphamide (CY) (50 mg/kg b.w. x4). Following autologous transplantation of those immunomagnetobead purged marrow grafts, complete hematologic reconstitution was seen in all three patients. They are alive and disease-free for +26, +24 and +17 months post transplant, which is also proven by the absence of detectable gene rearrangements after transplantation. In two of them disease-free survival exceeds the duration of the preceding remission y 20 and 12 months respectively, which is a definitive parameter for therapy effectiveness. Therefore, "high dose" consolidation treatment in very early second CR followed by autologous transplantation of purged bone marrow seems to allow long-term disease-free survival. The technique of ex vivo immunomagnetic bead purging, i.e. the "direct" and "indirect" method of binding monoclonal antibodies to magnetobeads is described.

Immunomagnetic isolation of NK and LAK cells

The present study describes the immunomagnetic isolation of human natural killer (NK) and lymphokine activated killer (LAK) cells. Antibodies against CD56 and sheep anti-mouse IgG-coated magnetic monodisperse particles (Dynabeads M-450) were used for the positive isolation of CD56+ cells from unstimulated mononuclear cells (PBMC). A highly enriched population of CD56+ cells (less than or equal to 3% contaminating cells) was obtained with this method. The cellular yield of CD56+ cells was high (5.3% of the unseparated PBMC). The CD56+ cells remained unactivated after separation and preserved their functional characteristics, as measured by cytotoxic activity against the NK sensitive K562 cells. Incubating the CD56+ cells with IL-2 resulted in high LAK activity, as measured by cytotoxic activity against Daudi cells. Large numbers of functionally active CD56+ cells were obtained from IL-2 stimulated lymphocytes using anti-CD56 coated Dynabeads 450. A further enrichment of effector cells with LAK activity was accomplished by depleting the CD56+ cells for T-cells by anti-CD3 coated Dynabeads M450. The immunomagnetic isolation technique described was easy to perform, did not require expensive equipment and yielded NK and LAK cells of satisfactory purity.

Simultaneous assessment of chromatin structure, DNA content, and antigen expression by dual wavelength excitation flow cytometry

7-aminoactinomycin D (7-AMD) efficiently discriminates between cells in the G0 and G1 phases of the cell cycle (Stokke et al., Cancer Res. 48:6708, 1988). The fluorescence and light scatter of cells stained with 7-AMD, Hoechst 33258 (H33258), and fluorescein isothiocyanate (FITC)-labeled antibodies were measured by dual wavelength excitation flow cytometry (488 nm, ultraviolet). The H33258 fluorescence was found to reflect DNA content in the presence of 7-AMD, although energy transfer caused an approximately 50% reduction in H33258 fluorescence intensity. However, energy transfer was more pronounced in dead cells, permitting exclusion of such cells during analysis. The G0, G1, S, and G2 phases of the cell cycle could be identified in the 7-AMD versus H33258 fluorescence histograms, as was demonstrated with mitogen-stimulated B lymphocytes and a mixture of unstimulated B lymphocytes and a proliferating B-cell line. One hour fixation with paraformaldehyde was compatible with prefixation labeling of surface antigens with indirectly FITC-labeled antibodies as well as postfixation labeling of intracellular antigens. Studies of expression of some surface and nuclear activation-associated antigens confirmed that cell cycle-resolved antigen expression and the time course of appearance of such antigens could be assessed accurately. Phycoerythrin could be used to label a second antigen.

Use of size fractionation of in vitro-activated human B lymphocytes for studies of cell cycle-dependent growth regulation

Cell cycle progression of in vitro-stimulated human B lymphocytes occurs asynchronously. In order to allow detailed studies of growth control in G1, B cells were stimulated with anti-mu and low molecular weight B-cell growth factor (LMW BCGF) for 50 h and subsequently separated into nine fractions of cells by means of centrifugal elutriation. As judged by volume profiles, activation antigen expression and DNA content, the cells in fractions 1-4 were in early to mid-G1, while fractions 5-7 mainly contained cells in late G1, and fractions 8-9 contained cells mainly in S and G2. Cells in fractions 5-7 had passed the commitment point, as demonstrated by a high spontaneous incorporation of [3H]thymidine when recultured in medium alone. Moreover, S-phase entry of these cells was largely unaffected by exogenous growth-promoting or growth-inhibitory signals. Cells in early (fractions 1-2) and intermediate fractions (fractions 3-4) showed a negligible spontaneous [3H]thymidine incorporation, but a significant proportion of these cells progressed to S phase upon restimulation. Moreover, while IL-4 or the anti-CD40 MoAb G28-5 potently stimulated cells in early and intermediate fractions, the responsiveness of LMW BCGF alone was obtained just prior to the commitment point.

The B cell antigen CD75 is a cell surface sialytransferase

In this work we have isolated a cDNA clone encoding the B cell antigen CD75. The amino acid sequence of CD75 is shown to be identical to that of human alpha 2,6 sialyltransferase, believed to be primarily associated with the Golgi complex. This is the first demonstration of cell surface expression of sialytransferase which, in B cells, may play an important role in intercellular adhesion and antigen presentation events.

Inhibition of polyphosphoinositide breakdown and c-myc induction accompanying inhibition of human B-cell activation by two monoclonal antibodies against the leucocyte common antigen (CD45)

In this report we show that the two monoclonal anti-CD45 antibodies, EO-1 and FN-126, potently inhibit G0 to G1 transition and S phase entry in human B cells stimulated with anti-mu and low molecular weight B-cell growth factor. Both antibodies were found to inhibit anti-mu-induced inositol phospholipid breakdown and c-myc mRNA induction. In contrast, EO-1 and FN-126 only partially inhibited the early anti-mu-induced increase in cytoplasmic Ca2+ levels, both in normal and in Ca2(+)-depleted medium. B-cell activation provoked by 12-O-tetradecanoylphorbol 13-acetate (TPA) was not inhibited by these antibodies, except when using high concentrations of EO-1. In addition, both antibodies were found to inhibit G1 entry induced by the anti-CD20 antibody 1F5, which confers an activation of B cells without any detectable increase in [Ca2+]i or in phospholipid metabolism. This indicates that alternative mechanisms in addition to the inhibition of polyphosphoinositide (PI) breakdown are involved in the inhibitory action of these antibodies.

Immunological typing of acute leukaemias by rosetting with immunomagnetic beads: comparison with immunofluorescence staining

Immunological phenotyping of acute leukaemias is important for a more precise diagnosis with respect to both cell lineage and maturation level. We have developed a rapid and reliable method for immunophenotyping, based on the use of magnetic monodisperse beads coated with monoclonal antibodies. After only a 10-min incubation of immunomagnetic beads (IMB) with mononuclear cells isolated from bone marrow or peripheral blood, the percentage of rosetting cells can be counted in the microscope. A panel of 16 monoclonal antibodies against haematopoietic cell-surface antigens was applied on 29 cases of acute myelogenic (AML) or lymphocytic (ALL) leukaemias, in order to compare immunological typing by immunomagnetic beads with immunofluorescence staining (IF). In all the cases tested, the two methods showed a virtually identical antigen distribution. The procedure described offers the advantages of being fast and simple to perform. Moreover, it has a high specificity and is easy to interpret in cases with low antigen expression.

Functional properties of CD19+ B lymphocytes positively selected from buffy coats by immunomagnetic separation

Here we report that human B lymphocytes can be positively selected directly from buffy coats applying the anti-CD19 antibody AB1 coupled to magnetic beads. This isolation protocol is highly efficient and the isolated cell population is of very high purity and viability. As judged by cell cycle analysis and various parameters for cell activation, the cells are still in a resting state after isolation. Furthermore, different functional assays have shown that the isolation procedure does not interfere with either activation or proliferation/differentiation of CD19 selected cells as compared to negatively isolated cells. As a consequence of cross-linking during the isolation process, the CD19 antigen is temporarily down-regulated as measured by AB1 binding. Despite this decreased expression, monoclonal antibodies to the CD19 antigen nevertheless inhibited anti-mu plus B cell growth factor induced B cell activation as reported also for negatively isolated cells. Taken together, the presented data strongly suggest that B cells isolated through the CD19 antigen can be used in critical functional assays.

Interleukin 4 induces selective production of interleukin 6 from normal human B lymphocytes

In this paper we have shown that extensively purified human B lymphocytes respond to IL-4 treatment with a marked production of IL-6. Addition of anti-mu potentiated the effect of IL-4 on IL-6 production. Other cytokines tested like TNF-alpha and-beta, IFN-gamma, IL-1, IL-2, and IL-5 did not induce IL-6 secretion when given to resting B cells. Although B cells generally also produced TNF-alpha and TNF-beta upon stimulation, IL-4 did not induce TNF secretion and seemingly had a specific effect on IL-6 production.

Immunomagnetic removal of B-lymphoma cells using a novel mono-sized magnetizable polymer bead, M-280, in conjunction with primary IgM and IgG antibodies

The efficacy of a novel monosized and magnetizable polymer bead, denoted M-280, in immunomagnetic removal of Rael B-lymphoma cells was compared with that of M-450 beads, previously used in bone marrow purging. The M-280 beads which are smaller (diameter 2.8 microns) and contain less iron than the M-450 beads were coated with polyclonal IgG sheep antimouse (SAM) antibody. The two types of immunobeads were equally efficacious when used together with the mouse monoclonal IgG antibodies HH1 or FN1, giving tumor cell depletions of about 3 logs in one cycle of operation. However, when used together with the primary IgM monoclonal antibodies (MoAbs) AB1 or HH2, the new immunobeads were significantly more efficacious than the M-450 immunobeads. To elucidate the underlying mechanism flow cytometric studies and measurements of the binding of the labeled primary MoAbs to the cellular antigens as well as to the immunobeads were carried out. Competition experiments showed that in the case of IgG MoAbs, the SAM beads bind predominantly to the Fc portion, whereas in the case of the IgM MoAbs, the Fab part plays a relatively greater role in the binding. The results indicate that if M-280 immunobeads are used, IgM MoAbs may profitably be included in antibody cocktails together with IgG antibodies in immunomagnetic purging of B-lymphoma cells. They suggest that in the case of cell bound MoAbs, the epitopes on IgG are more accessible to SAM beads than those of surface bound IgM molecules.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular events associated with inhibition of B cell activation by monoclonal antibodies to HLA class II antigens

We have investigated several aspects of the inhibitory effects of monoclonal antibodies (mAb) directed against MHC class II antigens in B cell activation/proliferation, using a panel of mAb specifically reactive with antigens encoded by HLA class II loci (DP, DQ, DR). All mAb except the anti-DP mAb inhibited significantly anti-mu plus B cell growth factor-induced DNA synthesis. Only one mAb, however, which was reactive with gene products of all three class II loci (DP, DQ, DR) inhibited anti-mu-induced DNA synthesis as well as c-myc mRNA expression. In addition, the same mAb inhibited the early events induced by anti-mu stimulation alone, including phosphatidylinositol turnover and elevation of [Ca2+]i. In contrast to previous findings in the murine system, none of the anti-MHC class II mAb used in this study increased the cAMP levels.

Heterogeneity of degradation of B-cell endocytosed monoclonal antibodies reacting with different sIgM epitopes

The degradation of a panel of monoclonal antibodies (MoAb) bound to surface IgM (sIgM) was studied in three human Burkitt's lymphoma cell lines. The panel included MoAb that recognize several distinct epitopes associated with the F(c mu)5 domain, the c mu 2 domain and kappa or lambda light chains. The amount of degraded MoAb and the rate of their degradation varied considerably between the various antibodies. Properties of MoAb such as avidity or ability to cross-link sIgM did not significantly influence their degradation. The most consistent correlation between rate of degradation and MoAb used was the location of the epitope recognized by the individual MoAb. Thus, 7 out of 8 anti-light chain MoAb were degraded at a higher rate than 5 out of 5 anti-F(c mu)5 MoAb. One anti-c mu 2 MoAb was degraded at a rate similar to the majority of anti-light chain MoAb. The intracellular transport of an anti-kappa light chain MoAb and an anti-F(c mu)5 MoAb was studied in detail by subcellular fractionation in sucrose gradients. We found that the anti-kappa light chain MoAb was transported more rapidly to lysosomes than the anti-F(c mu)5 MoAb, showing that they were sorted differently intracellularly.

cAMP-mediated growth inhibition of a B-lymphoid precursor cell line Reh is associated with an early transient delay in G2/M, followed by an accumulation of cells in G1

This study was undertaken to gain more insight into the effects of cyclic adenosine monophosphate (cAMP) on cell-cycle progression in the B-lymphoid precursor cell line Reh. The adenylate cyclase activator forskolin reduced the proliferation of asynchronously growing Reh cells by 50% after 72 hr culture. Growth inhibition was associated with an accumulation of cells in G1. Furthermore, we demonstrated that forskolin provoked a delay of cells for approximately 10 hr in G2/M prior to the G1 arrest. Two different methods were applied to elucidate how cells in different phases of the cell cycle were affected by an elevated cAMP level. One method was based on centrifugal elutriation, whereby synchronous cell populations from the different phases of the cell cycle were isolated. By the other method, S-phase cells were selectively stained by pulsing asynchronously growing cells with bromo-deoxyuridine (BrdU). The data demonstrate that the position of a cell in the cell cycle is critical in determining how the cell will respond to an elevated cAMP level. Thus cells in G1 at the time forskolin is added are not delayed in G2/M, but they will subsequently accumulate in G1 after 48 hr. Cells given forskolin in G2/m, however, are delayed for 10 hr in G2/M, but they do not accumulate in G1. Cells given forskolin in the S phase are delayed in G2/M as well as arrested in G1. The results suggest that cAMP inhibits growth of the Reh cells by preventing the cells from passing important restriction points located in the G1 and G2 phases of the cell cycle.