Immunosuppression induced by immature dendritic cells is mediated by TGF-beta/IL-10 double-positive CD4+ regulatory T cells

Dendritic cells (DC) have important functions in T cell immunity and T cell tolerance. Previously, it was believed that T cell unresponsiveness induced by immature DC (iDC) is caused by the absence of inflammatory signals in steady-state in vivo conditions and by the low expression levels of costimulatory molecules on iDC. However, a growing body of evidence now indicates that iDC can also actively maintain peripheral T cell tolerance by the induction and/or stimulation of regulatory T cell populations. In this study, we investigated the in vitro T cell stimulatory capacity of iDC and mature DC (mDC) and found that both DC types induced a significant increase in the number of transforming growth factor (TGF)-beta and interleukin (IL)-10 double-positive CD4(+) T cells within 1 week of autologous DC/T cell co-cultures. In iDC/T cell cultures, where antigen-specific T cell priming was significantly reduced as compared to mDC/T cell cultures, we demonstrated that the tolerogenic effect of iDC was mediated by soluble TGF-beta and IL-10 secreted by CD4(+)CD25(-)FOXP3(-) T cells. In addition, the suppressive capacity of CD4(+) T cells conditioned by iDC was transferable to already primed antigen-specific CD8(+) T cell cultures. In contrast, addition of CD4(+) T cells conditioned by mDC to primed antigen-specific CD8(+) T cells resulted in enhanced CD8(+) T cell responses, notwithstanding the presence of TGF-beta(+)/IL-10(+) T cells in the transferred fraction. In summary, we hypothesize that DC have an active role in inducing immunosuppressive cytokine-secreting regulatory T cells. We show that iDC-conditioned CD4(+) T cells are globally immunosuppressive, while mDC induce globally immunostimulatory CD4(+) T cells. Furthermore, TGF-beta(+)/IL-10(+) T cells are expanded by DC independent of their maturation status, but their suppressive function is dependent on immaturity of DC.

Proinflammatory response of human leukemic cells to dsRNA transfection linked to activation of dendritic cells

Leukemic cells exert immunosuppressive effects that interfere with dendritic cell (DC) function and hamper effective antileukemic immune responses. Here, we sought to enhance the immunogenicity of leukemic cells by loading them with the double-stranded (ds) RNA Toll-like receptor 3 (TLR3) ligand polyriboinosinic polyribocytidylic acid (poly(I:C)), mimicking viral infection of the tumor cells. Given the responsiveness of DC to TLR ligands, we hypothesized that the uptake of poly(I:C)-loaded leukemic cells by immature DC (iDC) would lead to DC activation. Primary acute myeloid leukemia (AML) cells and AML cell lines markedly responded to poly(I:C) electroporation by apoptosis, upregulation of TLR3 expression, enhanced expression of major histocompatibility complex (MHC) and costimulatory molecules and by production of type I interferons (IFN). Upon phagocytosis of poly(I:C)-electroporated AML cells, DC maturation and activation were induced as judged by an increased expression of MHC and costimulatory molecules, production of proinflammatory cytokines and an increase of T helper 1 (T(H)1)-polarizing capacity. These immune effects were suboptimal when AML cells were passively pulsed with poly(I:C), indicating the superiority of poly(I:C) transfection over pulsing. Our results demonstrate that poly(I:C) electroporation is a promising strategy to increase the immunogenicity of AML cells and to convert iDC into activated mature DC following the phagocytosis of AML cells.

Antigen-specific cellular immunotherapy of leukemia

Advances in cellular and molecular immunology have led to the characterization of leukemia-specific T-cell antigens and to the development of strategies for effective augmentation of T-cell immunity in leukemia patients. While several leukemia-related antigens have been identified, this review focuses on the Wilms' tumor 1 (WT1) antigen and the proteinase 3 (Pr3) antigen that are overexpressed in leukemic cells and are already being used in the clinical setting. Moreover, WT1 is also overexpressed in a vast number of nonhematological solid tumors, thereby expanding its use as a promising target for cancer vaccines. Examples of spontaneous immune responses against WT1 and Pr3 in leukemia patients are presented and the potential of WT1 and Pr3 for adoptive T-cell immunotherapy of leukemia is discussed. We also elaborate on the use of professional antigen-presenting cells loaded with mRNA encoding WT1 exploiting the advantage of broad HLA coverage for therapeutic vaccination purposes. Finally, the summarized data underscore the potential of WT1 for the manipulation of T-cell immunity in leukemia and in cancer in general, that will likely pave the way for the development of more effective and generic cancer vaccines.

Ex vivo induction of viral antigen-specific CD8 T cell responses using mRNA-electroporated CD40-activated B cells

Cell-based immunotherapy, in which antigen-loaded antigen-presenting cells (APC) are used to elicit T cell responses, has become part of the search for alternative cancer and infectious disease treatments. Here, we report on the feasibility of using mRNA-electroporated CD40-activated B cells (CD40-B cells) as alternative APC for the ex vivo induction of antigen-specific CD8(+) T cell responses. The potential of CD40-B cells as APC is reflected in their phenotypic analysis, showing a polyclonal, strongly activated B cell population with high expression of MHC and co-stimulatory molecules. Flow cytometric analysis of EGFP expression 24 h after EGFP mRNA-electroporation showed that CD40-B cells can be RNA transfected with high gene transfer efficiency. No difference in transfection efficiency or postelectroporation viability was observed between CD40-B cells and monocyte-derived dendritic cells (DC). Our first series of experiments show clearly that peptide-pulsed CD40-B cells are able to (re)activate both CD8+ and CD4(+) T cells against influenza and cytomegalovirus (CMV) antigens. To demonstrate the ability of viral antigen mRNA-electroporated CD40-B cells to induce virus-specific CD8+ T cell responses, these antigen-loaded cells were co-cultured in vitro with autologous peripheral blood mononuclear cells (PBMC) for 7 days followed by analysis of T cell antigen-specificity. These experiments show that CD40-B cells electroporated with influenza M1 mRNA or with CMV pp65 mRNA are able to activate antigen-specific interferon (IFN)-gamma-producing CD8(+) T cells. These findings demonstrate that mRNA-electroporated CD40-B cells can be used as alternative APC for the induction of antigen-specific (memory) CD8(+) T cell responses, which might overcome some of the drawbacks inherent to DC immunotherapy protocols.

Messenger RNA electroporation is highly efficient in mouse embryonic stem cells: successful FLPe- and Cre-mediated recombination

Development of efficient short-term gene transfer technologies for embryonic stem (ES) cells is urgently needed for various existing and new ES cell-based research strategies. In this study, we present a highly efficient, nonviral non-DNA technology for genetic loading of mouse ES cells based on electroporation of defined mRNA. Here, we show that mouse ES cells can be efficiently loaded with mRNA encoding a green fluorescent reporter protein, resulting in a level of at least 90% of transgene expression without loss of cell viability and phenotype. To show that transgenes, introduced by mRNA electroporation, exert a specific cellular function in transfected cells, we electroporated stably transfected ES cell lines with mRNA encoding FLPe or Cre recombinase proteins in order to excise an FRT- or LoxP-flanked reporter gene. The results, as determined by the disappearance and/or appearance of a fluorescent reporter gene expression, show that FLPe and Cre recombinase proteins, introduced by mRNA electroporation, efficiently exert their function without influence on further culture of undifferentiated ES cell populations and their ability to differentiate towards a specific lineage.

Messenger RNA electroporation: an efficient tool in immunotherapy and stem cell research

Over the last decades medicine has developed tremendously, but still many diseases are incurable. The last years, cellular (gene) therapy has become a hot topic in biomedical research for the potential treatment of cancer, AIDS and diseases involving cell loss or degeneration. Here, we will focus on two major areas within cellular therapy, cellular immunotherapy and stem cell therapy, that could benefit from the introduction of neo-expressed genes through mRNA electroporation for basic research as well as for clinical applications. For cellular immunotherapy, we will provide a state-of-the-art on loading antigen-presenting cells with antigens in the mRNA format for manipulation of T cell immunity. In the area of stem cell research, we will highlight current gene transfer methods into adult and embryonic stem cells and discuss the use of mRNA electroporation for controlling guided differentiation of stem cells into specialized cell lineages.

DFNA5: hearing impairment exon instead of hearing impairment gene?

BACKGROUND

Three mutations in the DFNA5 gene have been described in three families with autosomal dominant non-syndromic hearing impairment. Although these mutations are different at the genomic DNA level, they all lead to skipping of exon 8 at the mRNA level. We hypothesise that hearing impairment associated with DFNA5 is caused by a highly unusual mechanism, in which skipping of one specific exon leads to disease that is not caused by other mutations in this gene. We hypothesise that this represents a very specific "gain of function" mutation, with the truncated protein exerting a deleterious new function.

METHODS

We performed transfection experiments in mammalian cell lines (HEK293T and COS-1) with green fluorescent protein (GFP) tagged wildtype and mutant DFNA5 and analysed cell death with flow cytometry and fluorescence microscopy.

RESULTS

Post-transfection death of HEK293T cells approximately doubled when cells were transfected with mutant DFNA5-GFP compared with wildtype DFNA5-GFP. Cell death was attributed to necrotic events and not to apoptotic events.

CONCLUSION

The transfection experiments in mammalian cell lines support our hypothesis that the hearing impairment associated with DFNA5 is caused by a "gain of function" mutation and that mutant DFNA5 has a deleterious new function.

RNA-based gene transfer for adult stem cells and T cells

Electroporation of mRNA has become an established method for gene transfer into dendritic cells for immunotherapeutic purposes. However, many more cell types and applications might benefit from an efficient mRNA-based gene transfer method. In this study, we investigated the potential of mRNA-based gene transfer to induce short-term transgene expression in adult stem cells and activated T cells, based on electroporation with mRNA encoding the enhanced green fluorescent protein. The results show efficient transgene expression in CD34-positive hematopoietic progenitor cells (35%), in in vitro cultured mesenchymal cells (90%) and in PHA-stimulated T cells (50%). Next to presentation of gene transfer results, potential applications of mRNA-based gene transfer in stem cells and T cells are discussed.

mRNA-electroporated mature dendritic cells retain transgene expression, phenotypical properties and stimulatory capacity after cryopreservation

Genetically modified dendritic cells (DC) are increasingly used in vitro to activate cytotoxic T lymphocyte (CTL) immune responses. Because T cell activation protocols consist of multiple restimulation cycles of peripheral blood lymphocytes with antigen-loaded mature DC, continuous generation of DC is needed throughout the experiment. Therefore, cryopreservation of DC loaded with antigen is a valuable alternative for weekly generation and modification of DC. Recently, we described an antigen loading method for DC based on electroporation of defined tumor antigen mRNA. In this study, we demonstrate that mRNA-electroporated DC can efficiently be prepared for cryopreservation. Using an optimized maturation and freezing protocol after mRNA electroporation, we obtained high transgene-expressing viable mature DC. In addition, we showed that these modified cryopreserved DC retain stimulatory capacity in an influenza model system. Therefore, cryopreservation of mature mRNA-electroporated DC is a useful method for continuous availability of antigen-loaded DC throughout T cell activation experiments.

Antiproliferative effect of plant cytokinin analogues with an inhibitory activity on cyclin-dependent kinases

In this study, analogues of olomoucine, a previously described plant cytokinin analogue with cyclin-dependent kinase (CDK) inhibitory activity, were investigated for effect on CDK1 and CDK2 and for effect on cell proliferation. Eight new compounds exhibit stronger inhibitory activity on CDK1 and CDK2 and on cell proliferation than olomoucine. Some active compounds showed low inhibition of proliferation of normal myeloid growth. Improvement of inhibitory activity of known compounds with a C6-benzylamino group was brought about by substitution with one hydroxyl. Also, new C2 substituents associated with inhibitory activity on CDK and on cell proliferation are described. There was a significant correlation between effect on CDK and antiproliferative effect on the KG1 and Molt3 cell lines and on primary human lymphocytes, strongly suggesting that at least part of the antiproliferative effect of cytokinin analogues was due to inhibition of CDK activity. Cytokinin analogues induced apoptosis in a time- and concentration-dependent manner and changes in cell cycle distribution. The antiproliferative and pro-apoptotic effects of plant cytokinin analogues suggest that they are a new class of cytostatic agents and that they may find an application in the chemotherapy of cancer.

Highly efficient gene delivery by mRNA electroporation in human hematopoietic cells: superiority to lipofection and passive pulsing of mRNA and to electroporation of plasmid cDNA for tumor antigen loading of dendritic cells

Designing effective strategies to load human dendritic cells (DCs) with tumor antigens is a challenging approach for DC-based tumor vaccines. Here, a cytoplasmic expression system based on mRNA electroporation to efficiently introduce tumor antigens into DCs is described. Preliminary experiments in K562 cells using an enhanced green fluorescent protein (EGFP) reporter gene revealed that mRNA electroporation as compared with plasmid DNA electroporation showed a markedly improved transfection efficiency (89% versus 40% EGFP(+) cells, respectively) and induced a strikingly lower cell toxicity (15% death rate with mRNA versus 51% with plasmid DNA). Next, mRNA electroporation was applied for nonviral transfection of different types of human DCs, including monocyte-derived DCs (Mo-DCs), CD34(+) progenitor-derived DCs (34-DCs) and Langerhans cells (34-LCs). High-level transgene expression by mRNA electroporation was obtained in more than 50% of all DC types. mRNA-electroporated DCs retained their phenotype and maturational potential. Importantly, DCs electroporated with mRNA-encoding Melan-A strongly activated a Melan-A-specific cytotoxic T lymphocyte (CTL) clone in an HLA-restricted manner and were superior to mRNA-lipofected or -pulsed DCs. Optimal stimulation of the CTL occurred when Mo-DCs underwent maturation following mRNA transfection. Strikingly, a nonspecific stimulation of CTL was observed when DCs were transfected with plasmid DNA. The data clearly demonstrate that Mo-DCs electroporated with mRNA efficiently present functional antigenic peptides to cytotoxic T cells. Therefore, electroporation of mRNA-encoding tumor antigens is a powerful technique to charge human dendritic cells with tumor antigens and could serve applications in future DC-based tumor vaccines.

Establishment of serum-free pre-colony forming unit assays for differentiation of primitive hematopoietic progenitors: serum induces early macrophage differentiation and inhibits early erythroid differentiation of CD34++CD38- cells

In this report we show that serum has differentiation-inducing effects on primitive hematopoietic progenitor cells with the CD34++CD38- immunophenotype. Using the pre-colony forming unit (pre-CFU) assay as a model for early myelopoiesis, we compared the effects of serum-containing and serum-free media and evaluated different cytokine cocktails [interleukin (IL)-1, IL-3, IL-6, kit ligand with and without the Flt3/Flk2 ligand (FL)]. In this assay, pre-CFUs are defined as cells unable to form colonies when plated directly in semi-solid assays, but which can differentiate into CFUs when cultured in liquid medium containing early-acting cytokines. In one of the investigated serum-free media, the average myeloid expansion in liquid medium reached up to more than 50% of that obtained in serum-containing medium. In addition, our experiments revealed differences in the clonogenic output between cells cultured in serum-free medium and those cultured in serum-containing medium, demonstrating that serum has a monocyte differentiation-inducing effect on primitive hematopoietic progenitors. Also in serum-free medium, higher proportions of erythroid progenitors were generated. These differentiation-inducing effects of serum further emphasize the need for serum-free culture protocols for hematopoietic graft engineering. Addition of FL to the culture media ameliorated cellular expansion and resulted in a decrease in the proportion of erythroid and granulocyte progenitors and an increase in the proportion of monocyte progenitors. In conclusion, this study shows that good serum-free conditions are available for differentiation assays with primitive hematopoietic progenitors and demonstrates that serum and FL have biasing effects on the initial phase of hematopoietic differentiation, favoring the monocyte lineage.

GP130 and c-kit signalling, initiated by the sIL-6R/IL-6 complex, is insufficient to expand the primitive adult bone marrow CD34+CD38- pre-CFU cell

It has previously been shown that gp130 and c-kit signalling synergize for the ex vivo expansion of human cord blood (CB) CD34+ haematopoietic progenitor cells. We were interested in evaluating this synergy within an ontogenetically different haematopoietic tissue [i.e. adult bone marrow (BM)] and on a more primitive progenitor subset (i.e. CD34+ CD38-cells), which are highly enriched for pre-colony forming unit (CFU) cells. These cells were plated out in a primary liquid culture supplemented with either interleukin (IL)-6+stem cell factor (SCF), IL-6+ SCF+soluble IL-6 receptor (sIL-6R), IL-6+SCF+sIL-6R+IL3+IL-1 or SCF+IL-3+IL-6+IL-1. Cell counting after liquid culture revealed an absolute expansion of 2.2-, 4.1-, 89.5- and 65.7-fold compared with initial cell input for the four-cytokine combinations, respectively. The secondary read-out assay revealed that this cell expansion in the liquid culture also resulted in CFU generation, with absolute cloning efficiencies of 0.002, 0.024, 12.13 and 7.73 (per cell initially present) for the respective cytokine combinations. These results indicate that gp130 and c-kit signalling alone (i.e. using IL6+SCF+sIL-6R), in terms of both cell number and CFU generation, insufficiently stimulate primitive adult BM CD34+CD38- haematopoietic cells in order to reach a CFU generation comparable with that obtained after multifactor stimulation. Adding sIL-6R to the multifactor stimulation and compared with this multifactor stimulation, a 1.7-fold synergy in terms of cell expansion and a 3.0-fold synergy in terms of CFU generation are obtained. The sIL-6R/IL-6 complex thus has a narrower spectrum of action on primitive adult BM CD34+CD38- cells than on CB CD34+ cells.

Efficient generation of stably electrotransfected human hematopoietic cell lines without drug selection by consecutive FACsorting

BACKGROUND

Current methods to establish stably transfected cell lines by nonviral techniques involve coselection for a drug selection marker. However, this approach suffers from several drawbacks. We developed a fluorescence-activated cell sorting (FACS)-based protocol for the selection and isolation of stable hematopoietic electrotransfectants without the need for selective growth conditions.

METHODS

Leukemic K562 cells were electroporated with the enhanced green fluorescent protein (EGFP) reporter gene and FACsorted to obtain stably EGFP-expressing cells. Stable EGFP(+) clones were established by single-cell sorting.

RESULTS

Efficiency of stable EGFP gene expression increased steadily in function of number of consecutive FACsorts. Stable transfectants (>99% EGFP(+)) were obtained after four FACsorts. Furthermore, several single-cell derived clones with variable levels of stable EGFP expression were isolated and cultured without the use of selective growth media.

CONCLUSIONS

EGFP is an effective selection marker for the generation and isolation of stably transfected hematopoietic cell clones without the need for selection in toxic media that could create a potentially undesirable stress environment for stably transfected cells.

The effects of psychological stress on leukocyte subset distribution in humans: evidence of immune activation

The aim of the present study was to examine the effects of academic examination stress on leukocyte subset distribution in university students. Thirty-eight university students had repeated blood collections for white blood cell differentiation and flow cytometric assay of lymphocytic subsets a few weeks before and after (i.e. two baseline conditions) as well as the day before a difficult academic examination (i.e. stress condition). Flow cytometry was used to determine the number of peripheral blood mononuclear cells (PBMC). In students, who were reactors to psychological stress (criterion based on changes in the Perceived Stress Scale, PSS), but not in stress non-reactors, a significant increase in the number of neutrophils, monocytes, CD8(+), CD2(+)CD26(+), and CD2(+)HLA-DR+ T cells and CD19(+) B cells, and significant reductions in the CD4(+)/CD8(+) T cell ratio were observed in the stress condition. There were significant and positive relationships between the stress-induced changes in perceived stress (PSS scale) and number of leukocytes, neutrophils, CD2(+), CD2(+)CD26(+) and CD2(+)HLADR+ T cells, and CD19(+) B cells. There were significant and negative relationships between the stress-induced changes in the CD4(+)/CD8(+) ratio and the stress-induced changes in the PSS scale. Female students taking oral contraceptives showed significantly higher stress-induced responses in number of leukocytes, neutrophils and CD19(+) B cells than male and female students without use of oral contraceptives. The results suggest that academic examination stress induces changes in the distribution of PBMC, which indicate immune activation and which are probably orchestrated by a stress-induced production of cytokines.

High-level transgene expression in primary human T lymphocytes and adult bone marrow CD34+ cells via electroporation-mediated gene delivery

The design of effective gene delivery systems for gene transfer in primary human blood cells is important both for fundamental hematopoiesis research and for cancer gene therapy strategies. Here, we evaluated electroporation as a nonviral means for transfection of activated human T lymphocytes and adult bone marrow (BM) CD34+ cells. We describe optimal culture and electroporation parameters for efficient gene delivery in prestimulated T lymphocytes (16.3 +/-1.3%), as well as 2-day cultured adult BM CD34+ cells (29.6+/-4.6%). PHA-stimulated T cells were most receptive for transfection after 48h of in vitro culture, while T cells stimulated by CD3 cross-linking and interleukin (IL)-2 achieved maximum transfection levels after 72 h of prestimulation. Kinetic analysis of EGFP expression revealed that activated T lymphocytes maintained transgene expression at high levels for a prolonged period. In addition, fresh unstimulated BM CD34+ cells were consistently transfected (5.2+/-0.4%) with minimal cytotoxicity (<5%), even without preliminary CD34+ cell purification. Both T cells and CD34+ cells retained their phenotype and functional capacity after electroporation. These results demonstrate that electroporation is a suitable nonviral transfection technique that may serve applications in gene therapy protocols using T lymphocytes or CD34+ cells.

Generation of T cells from adult human hematopoietic stem cells and progenitors in a fetal thymic organ culture system: stimulation by tumor necrosis factor-alpha

To investigate the T-lymphopoietic capacity of human adult bone marrow (ABM) hematopoietic progenitor cells, CD34+Lin-, CD34+CD38+, and CD34++CD38- cells were cultured in a severe combined immunodeficient (SCID) mouse fetal thymic organ culture (FTOC). Direct seeding of these progenitors resulted in a moderate to severe cell loss, particularly for the CD34++CD38- cell fraction, and T cells could only be generated from the CD34+Lin- fraction. Preincubation for 36 hours with interleukin-3 (IL-3) and stem cell factor (SCF) led to an improved cell survival and proliferation, although T-cell development was seen only in the CD34+Lin- fraction. Addition of tumor necrosis factor (TNF)-alpha to IL-3 + SCF-supplemented preincubation medium resulted in optimal cell survival, cell proliferation. and T-cell generation of all 3 cell fractions. The TNF-alpha effect resulted in an up-regulation of CD127 (ie, the IL-7 receptor alpha-chain) in a small subset of the CD34+ cells. No evidence could be generated to support the possibility that TNF-alpha inhibits a cell population that suppresses T-cell differentiation. A quantitatively different T-cell generation potency was still seen between the 3 subpopulations: CD34+Lin- (100% success rate) > CD34+CD38+ (66%) > CD34++CD38- (25%). These data contrast with our previous findings using fetal liver and cord blood progenitors, which readily differentiate into T-lymphocytes in FTOC, even without prestimulation with cytokines. Our results demonstrate that adult CD34++CD38- cells, known to contain hematopoietic stem cells, can differentiate into T-lymphocytes and that a significant difference exists in T-lymphopoietic activity of stem cells derived from ontogenetically different sources. (Blood. 2000;95:2806-2812)

Developmentally regulated responsiveness to transforming growth factor-beta is correlated with functional differences between human adult and fetal primitive hematopoietic progenitor cells

Important functional differences exist between primitive CD34++ CD38- hematopoietic progenitor cells derived from human fetal liver (FL) and adult bone marrow (ABM). FL progenitors are known to have higher proliferative capacities and lower cytokine requirements than their ABM counterparts. In this study, we isolated FL and ABM CD34++ CD38- cells and used a two-stage culture system to investigate the effects of transforming growth factor-beta (TGF-beta) and blocking anti-TGF-beta antibodies (anti-TGF-beta) on these cells. First, we demonstrate that FL progenitors are significantly less sensitive to the inhibitory effects of TGF-beta than ABM cells. Second, whereas ABM cells are significantly stimulated by anti-TGF-beta, only very limited effects are seen on FL cells. Third, we show that the effect of anti-TGF-beta is mainly situated at the level of the initial cell cycles of very primitive progenitor cells with a high proliferation potential. Fourth, we demonstrate that blocking the effects of endogenous TGF-beta reduces the growth factor requirements of ABM cells in order to proliferate and differentiate. Based on these data, we hypothesize that at least part of the functional differences that exist between adult and fetal stem cells can be accounted for by a developmental different responsiveness to TGF-beta.

In vitro evaluation of the haemopoietic defect of CD34+ cells from patients with acute myeloid leukaemia in first remission

Haemopoietic cells from patients with acute myeloid leukaemia (AML) in first complete remission (CR1) show in vitro a haemopoietic defect and a decreased expansion potential. To better characterize this haemopoietic defect, CR1 AML and normal CD34+ cells were analysed for immunophenotype, viability, cell cycle and progenitor content before and during expansion culture in stroma-conditioned medium supplemented with cytokines. The production of haemopoiesis inhibitor by patient cells and the influence of high concentrations of stem cell factor (SCF) and Flt3-ligand (FL) on cell survival and ex vivo expansion potential were also studied. Before expansion, patient CD34+ cells showed viability and cell-cycle phase distribution similar to normal but lower percentages of CD34+DR- or CD34+CD38- cells and lower progenitor content. After 48 h of culture +/-30% of patient cells had died regardless of the cytokine combination used, whereas only 15% of normal cells died. After 7 d of culture, viability and cell cycle analyses showed comparable data for normal and patient samples. Co-culture of patient and normal cells did not show any evidence for haemopoiesis inhibitor production by patient cells. Even at high cytokine concentrations, a low progenitor expansion and a decrease in CD34+ cell numbers was observed for patient samples in contrast to normal samples. In conclusion, CR1 AML CD34+ cells showed excessive early cell mortality. No evidence for cell-cycle arrest or haemopoiesis inhibitor production was shown. SCF and FL used at high concentrations did not correct the patient cell expansion defect.

Belgian consensus recommendations for flow cytometric immunophenotyping. The Belgian Association for Cytometry/Belgische Vereniging voor Cytometrie/Association Belge de Cytométrie

This paper summarises the guidelines and recommendations that were generated during a number of discussion forums attended by the majority of Belgian cytometry laboratory professionals. These forums focused on the rational and optimal use of flow cytometric evaluations in the clinical laboratory setting. The aim was to improve the coherence of the testing panels and the quality of the results and--as such--the clinical diagnostic information. It was also the aim to provide the Belgian prescribing physician and interested laymen with an updated overview of the flow cytometric possibilities. Emphasis is placed on immunophenotyping of haematological malignancies, hematopoietic progenitor cell counting and follow-up of the viral infection caused by the human immunodeficiency virus.

CD34++ CD38- and CD34+ CD38+ human hematopoietic progenitors from fetal liver, cord blood, and adult bone marrow respond differently to hematopoietic cytokines depending on the ontogenic source

CD34++ CD38- and CD34+ CD38+ hematopoietic progenitor cells (HPCs) from human fetal liver (FL), cord blood (CB), and adult bone marrow (ABM) were isolated and investigated for their growth characteristics, cytokine requirements and response to two modulators of early hematopoiesis, interferon (IFN)-gamma and macrophage inflammatory protein (MIP)-1alpha. We observed first that a significantly lower percentage of CD34++ cells were CD38- in ABM than in FL and CB. Second, the functional differences between CD34++ CD38- and CD34+ CD38+ cells were less pronounced in FL and CB than in their ABM counterparts. Third, an inverse correlation was found between growth factor response and the ontogenic age of HPCs, and a direct correlation was noted between cytokine requirements and the ontogenic age of HPCs. Fourth, spontaneous colony formation in a classic semisolid culture system was reproducibly obtained only in the ontogenically earliest cells, that is, in FL but not in CB and ABM, in which no such spontaneous colony formation was observed. Fifth, the modulatory effects of IFN-gamma and MIP-1alpha were qualitatively different depending on the ontogenic age of the progenitor source: whereas IFN-gamma was only a selective inhibitor of primitive CD34++ CD38- ABM progenitor cells, it inhibited both CD34++ CD38- and CD34+ CD38+ FL and CB cells to the same extent. In contrast to the effects of MIP-1alpha on ABM, we could not find any consistently stimulatory or inhibitory effects on FL and CB progenitors. In conclusion, important functional and biologic differences exist between FL, CB, and ABM progenitor cells, and these differences could have major implications for the use of these cell populations in preparative protocols of ex vivo expansion, transplantation strategies, or gene transfer experiments.

Haemopoietic defect and decreased expansion potential of bone marrow autografts from patients with acute myeloid leukaemia in first remission

Autologous bone marrow (BM) transplantation for acute myeloid leukaemia (AML) in complete remission (CR) is frequently followed by a slow haemopoietic recovery. We assessed the haemopoietic capacity of purified BM stem cell (CD34+ DR-) and progenitor cell (CD34+ DR+) populations from patients with AML in CR, and compared these data with those of normal BM. The feasibility of ex vivo expansion in stroma-conditioned medium supplemented with cytokines was also investigated. The number of CFU-GM produced by initial patient CD34+ DR- cells was decreased compared to normal, whereas these values were similar to normal for CD34+ DR+ cells. BFU-E, HPP-CFC and LTC-IC were reduced for both patient CD34+ DR- and CD34+ DR+ subpopulations. In contrast to normal, the patient CD34+ DR- fraction was not enriched in LTC-IC. CFU-GM expansion from patient CD34+ DR- cells was poor and decreased after 14 d of culture. No HPP-CFC expansion could be observed for patient cells. LTC-IC were below the level of detection after 14-21 d of expansion culture of CD34+ DR- patient cells, whereas they were variably maintained or expanded for normal cells. After expansion culture, cytogenetic and/or FISH analyses did not reveal the anomalies present at diagnosis, regardless of the cell subpopulation analysed. In conclusion, BM cells of patients with AML in CR show a profound defect at the level of a stem cell enriched population. No meaningful ex vivo expansion could be obtained in culture conditions allowing for a significant expansion from a normal stem cell population.

Decrease in nucleoside diphosphate kinase (NDPK/nm23) expression during hematopoietic maturation

The nucleoside diphosphate kinase (NDPK/nm23) isoforms H1 and H2 were localized in hematopoietic tissues. Flow cytometric analysis and enzymatic assays were used to quantify the intracellular and extracellular concentrations of NDPK. Bone marrow CD34(+) progenitors contained the highest intracellular levels of both nm23-H1 and nm23-H2. Lower levels were measured in more mature bone marrow cells, whereas peripheral blood leukocytes had the lowest expression of nm23. These data suggest a function of NDPK in early hematopoiesis and a down-regulation of NDPK upon differentiation. In addition, an up-regulation of nm23 expression was observed in lymphocytes after induction of proliferation with phytohemagglutinin. Multiparameter flow cytometry demonstrated that this up-regulation occurred during the G0/G1-transition. Flow cytometric analysis also revealed a weak surface expression of nm23 on a number of hematopoietic cell lines, which was not detected on normal hematopoietic cells. Our data also demonstrated the presence of NDPK in human plasma, probably due to a limited in vivo lysis of red blood cells.

Nonviral transfection of distinct types of human dendritic cells: high-efficiency gene transfer by electroporation into hematopoietic progenitor- but not monocyte-derived dendritic cells

Human dendritic cells (DC) are highly professional antigen presenting cells for the priming of naive cytotoxic T cells. Gene transfer in DC would be a useful strategy to load DC with relevant de novo synthesized antigens for immunotherapeutical purposes. As a first step towards a DC-based gene therapy, we examined the efficiency of nonviral transfection in different types of cultured human dendritic cells with a humanized red-shifted green fluorescent protein reporter gene. Plasmid DNA transfection by electroporation or lipofection was used to transfect CD34+ progenitor cell-derived DC (PC-DC) and Langerhans' cells (PC-LC), as well as monocyte-derived DC (Mo-DC). While lipofection was unsuccessful in all types of DC, we obtained high-efficiency gene transfer by electroporation in PC-LC (16%) and PC-DC (12%). In contrast, electroporation was strikingly less efficient in Mo-DC (< or = 2%). The potent allostimulatory capacity of DC was still retained in electroporated PC-DC and PC-LC. In conclusion, electroporation of antigen expressing plasmid DNA is an efficient tool for nonviral gene transfer in PC-DC and PC-LC, but not in Mo-DC and could be useful for the development of DC-based tumor immunotherapy.

Analysis of variation in results of flow cytometric lymphocyte immunophenotyping in a multicenter study

Fifty-five laboratories participated in a send-out study of four peripheral blood samples comparing a standard protocol vs. local protocols for flow cytometric lymphocyte immunophenotyping. The standard protocol included centrally provided reagents, instrument setup using triple-fluorescent microbeads and a three-color, whole-blood immunostaining technique based on fluorescein isothiocyanate and phycoerythrin-labeled monoclonal antibodies, erythrocyte lysis, washing, fixation, and identification of nucleated cells by the DNA/RNA stain LDS-751. Data analysis guidelines included lymphocyte selection using CD45,CD14-assisted "backgating" on forward (FSC) and sideward (SSC) light scatter and placement of fluorescence (FL) markers on the basis of the isotype control staining. Most (i.e., 77%) of the variation in results of percentage lymphocyte subset assessments using the standard protocol was explained by laboratory, sample, background FL, and the interaction between laboratory and sample. Purity and completeness of the FSC,SSC lymphogate, background FL, flow cytometer type, and flow cytometer setup (which were either partly or entirely determined by laboratory) contributed significantly to the variation. The effect of the leukocyte differential count on the variation in absolute numbers of lymphocyte subsets was particularly large in lymphopenic samples. The use of this standard protocol vs. local protocols did not reduce the interlaboratory variation. Instrument incompatibility with the standard protocol (e.g., incompatible filter combinations for LDS-751 detection) and lack of experience of many participants with three-color flow cytometry (in particular with the use of LDS-751) may have contributed to that result. We suggest that training and experience in a universally applicable standard protocol are critical for minimization of interlaboratory variation in flow cytometric immunophenotyping.

Generation of dendritic cells from bone marrow progenitors using GM-CSF, TNF-alpha, and additional cytokines: antagonistic effects of IL-4 and IFN-gamma and selective involvement of TNF-alpha receptor-1

We report the generation of dendritic cells (DC) starting from CD34+ bone marrow (BM) progenitor cells, using a two-stage culture system in which, besides granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumour necrosis factor-alpha (TNF-alpha), stem-cell factor (SCF) was added during the first 5 days, while interleukin-4 (IL-4) and/or interferon-gamma (IFN-gamma) were added during the secondary culture period of 9 days. Addition of IL-4 favoured the outgrowth of CD1a+, HLA-DR+, CD4+, CD40+, CD80+ but CD14- cells with dendritic morphology and strong antigen-presenting capacity. Addition of IFN-gamma selectively induced HLA-DR and CD86 but did not up-regulate CD1a expression or antigen-presenting capacity of the differentiated cells. An antagonism between IL-4 and IFN-gamma could further be confirmed in that, as compared with IL-4 alone, the simultaneous addition of IL-4 and IFN-gamma to GM-CSF plus TNF-alpha during maturation reduced both the phenotypical (CD1a, CD4, CD40) and functional characteristics of DC. Using receptor-specific TNF-alpha mutants, we investigated the relative involvement of TNF-alpha receptors R1 and R2 in the generation of DC. The induction of CD1a and HLA-DR, as well as the increase in allostimulatory capacity were dependent on TNF-R1 triggering, whereas triggering through TNF-R2 had no measurable effect. We conclude first, that the expansion of DC from BM progenitors could most effectively be enhanced in a two-stage culture assay using SCF, GM-CSF, TNF-alpha and IL-4; second, that the effect of TNF-alpha in DC generation involves signalling via the TNF-R1 receptor; and third, that IFN-gamma counteracts some of the effects of IL-4 in DC generation.

Analysis of variation in results of CD34+ hematopoietic progenitor cell enumeration in a multicenter study

A workshop was held in The Netherlands and Belgium with the aim of investigating whether or not the use of a standard protocol vs. local protocols for flow cytometric enumeration of CD34+ hematopoietic progenitor cells would reduce interlaboratory variation. The standard protocol consisted of a three-color, whole-blood staining technique based on fluorescein isothiocyanate (FITC)-labeled CD34, and phycoerythrin (PE)-labeled CD14 and CD66e monoclonal antibodies (reactive with monocytic and myeloid cells, respectively), followed by erythrocyte lysis, washing, fixation, and selection of nucleated cells during data acquisition on the basis of their positivity for LDS-751 (staining DNA and RNA). Data analysis guidelines included the elimination of nonspecific antibody binding by monocytes and myeloid cells by gating on the CD14-, 66e- cells, followed by setting a window on a CD34 vs. sideward light scatter (SSC) plot around the CD34+, SSClow cells. The FITC-labeled isotype control was analyzed with the same gate and window settings, and the false-positive events were subtracted from CD34 result. Four samples (i.e., peripheral blood and apheresis product from two patients) were sent out. Results were received on patient 1 (2) from 36 (38) laboratories. Data obtained by 24 (26) laboratories after correct application of the standard protocol revealed that the median percentage of CD34+ cells of the four samples ranged between 1.1% and 3.7% and the CVs between 18% and 30%. Incorrect performance of the standard protocol by 12 laboratories, mainly resulting from gating errors, yielded a larger variation (CVs ranging between 50% and 82%). CD34 enumeration using local protocols by 29 (34) laboratories yielded median percentage of CD34+ cells ranging between 1.2% and 3.9% and CVs ranging between 34% and 106%. We conclude that correct application of this standard protocol was effective in reducing the interlaboratory variation in percentage of CD34+ cells assessments.

The combined effects of all-trans retinoic acid and TGF-beta on the initial proliferation of normal human bone marrow progenitor cells

We investigated the cell kinetic effects of retinoic acid (RA) and the functional interaction between RA and TGF-beta on normal human bone marrow progenitor cells (CD34+). Cell cycle progression throughout the first three consecutive cell cycles and alterations in cell kinetic responses were measured using the BrdU-Hoechst quenching technique. RA stimulates the IL-3-induced growth by additionally recruiting quiescent stem and progenitor cells out of the G0/G1-phase and by increasing the cell cycle traverse rate. In contrast, TGF-beta addition resulted in a significant decrease in the number of proliferating cells. Simultaneous addition of RA and TGF-beta resulted in a stronger inhibition compared to addition of TGF-beta alone. Preincubation experiments further showed that RA is capable of sensitizing the progenitors to the inhibitory action of TGF-beta: the inhibitory effect of TGF-beta was significantly increased when cells were pretreated with RA. These data show that, in combination with IL-3, RA additionally stimulates quiescent bone marrow progenitors in a simultaneous way, and that it increases sensitivity of the progenitors to the inhibitory action of TGF-beta. The combination of RA and TGF-beta on normal and leukemic hematopoiesis has to be further investigated, since this combination may possibly provide additional therapeutic benefit.

TGF-beta and MIP-1 alpha exert their main inhibitory activity on very primitive CD34+2CD38- cells but show opposite effects on more mature CD34+CD38+ human hematopoietic progenitors

We investigated the effects of transforming growth factor-beta (TGF-beta) and macrophage inflammatory protein-1 alpha (MIP-1 alpha) on very primitive CD34++CD38- and on more mature CD34++CD38+ human hematopoietic progenitor cells by means of a two stage pre-colony-forming cell (pre-CFC) assay. The first (liquid) stage of this assay allows evaluation of the effects of TGF-beta and MIP-1 alpha on the "primary" proliferation of the progenitors under study and on the generation of "secondary" colony-forming cells (CFC, cells for which a second stage semisolid clonogenic assay was used as a read-out). TGF-beta inhibited the proliferation and CFC generation of CD34++CD38- and CD34+CD38+ cells, showing the strongest inhibitory activity on CD34++CD38- cells. MIP-1 alpha exerted a weaker inhibitory activity on CD34+2CD38- cells, whereas it enhanced the primary proliferation of CD34+CD38+ cells and generation of secondary CFC in this subpopulation. Thus, TGF-beta, and MIP-1 alpha both inhibit very primitive CD34+2)CD38- cells, but they are not equally potent. The effects of TGF-beta and MIP-1 alpha on more mature progenitor cells are more complex. Our results and data from the literature indicate that, as progenitor cells mature, they reach a "pivotal point" at a certain stage in their differentiation pathway, depending on the inhibitor, where they are no longer inhibited or where they may even be stimulated by the former inhibitor to proliferate.

Tumor necrosis factor alpha is a potent synergistic factor for the proliferation of primitive human hematopoietic progenitor cells and induces resistance to transforming growth factor beta but not to interferon gamma

Since tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, and transforming growth factor (TGF)-beta have all been shown to be specific inhibitors of early human hematopoiesis, we wanted to investigate the interactions of these three cytokines on very primitive human adult bone marrow CD34++CD38- hematopoietic progenitor cells, using a pre-colony-forming cell (pre-CFC) assay, which detects the effects of these cytokines on the initial phases of the differentiation of these primitive progenitors, which are unresponsive to interleukin (IL) 3 alone. Surprisingly, TNF-alpha was a very potent stimulator of the proliferation of CD34++CD38- cells and was the most potent synergistic factor for the IL-3-induced proliferation of these cells of all cytokines tested (IL-1, IL-6, granulocyte colony-stimulating factor, kit ligand). TNF-alpha was the only cytokine that, as a single added factor, induced substantial proliferation in CD34++CD38- cells in the presence of IL-3, except for kit ligand, which induced very limited proliferation. TNF-alpha, moreover, induced a high degree of resistance to the inhibitory effects of TGF-beta in a dose-dependent way. The inhibitory effects of IFN-gamma, however, were not affected by the presence of TNF-alpha. We hypothesize that in situations of the hematopoietic stress, TNF-alpha may abrogate the inhibitory effect of ambient TGF-beta in the bone marrow microenvironment to allow primitive stem cells to proliferate and differentiate in response to an increased demand for mature blood cells.

Interleukin 4 and interferon gamma costimulate the expansion of early human myeloid colony-forming cells. Proposal of a model for the regulation of myelopoiesis by interleukin 4 and interferon gamma and its integration with the regulation of the immune response

We have previously shown that interleukin 4 (IL-4) and interferon gamma (INF-gamma) reciprocally regulate the production of granulocytes and monocytes from mature monopotential hematopoietic progenitor cells, while at the level of the very primitive stem cells IFN-gamma is a selective inhibitor of proliferation and differentiation, and IL-4 has weak stimulatory effects. We investigated the effects of IL-4 and IFN-gamma on the expansion in suspension culture of myeloid colony-forming cells (CFCs) induced by either IL-3 or IL-1+IL-3, using on the one hand more differentiated CD34+HLA-DR strongly positive (HLA-DR++) and on the other hand more primitive Cd34+HLA-DR weakly positive (HLA-DR+/-) human bone marrow cells. It is shown that both IL-4 and IFN-gamma stimulate the IL-3- and IL-3+IL-1-induced expansion of the number of CFCs in the HLA-DR+/- population. In the presence, but not in the absence of IL-1, additive effects of IL-4 and IFN-gamma were seen. We could not demonstrate any IL-3-like effect by IL-4 on early human hematopoietic progenitors. No expansion of CFC number was seen in the HLA-DR++ population. Based on these data and on data which we have published previously, a model for the regulation of myelopoiesis by IL-4 and IFN-gamma is proposed. In this model, IL-4 and IFN-gamma, which are both immune recognition induced inflammatory cytokines, both stimulate the expansion and recruitment of early myeloid progenitors, whereas at the level of their terminal differentiation, the balance between both cytokines determines whether preferentially monocytes/macrophages (IFN-gamma) or granulocytes (IL-4) are being produced. At the level of the most primitive cells, the inhibitory action of IFN-gamma might prevent differentiative exhaustion of the stem cell compartment in situations of hematopoietic stress.

Mean corpuscular hemoglobin is not increased in Fmr1 knockout mice

A slight increase in mean corpuscular hemoglobin (MCH) has been reported in erythrocytes from human fragile X patients. As it is difficult to perform case-controlled studies in patients with fragile X syndrome, we studied MCH in erythrocytes from transgenic mice with an Fmr1 knockout. None of the knockout mice showed increased MCH levels when compared with normal littermates. We conclude that it is unlikely that the FMR1 gene product has an effect on MCH.

Interferon gamma selectively inhibits very primitive CD342+CD38- and not more mature CD34+CD38+ human hematopoietic progenitor cells

To assess the effects of interferon gamma (IFN-gamma) on very primitive hematopoietic progenitor cells, CD34(2+)CD38- human bone marrow cells were isolated and cultured in a two-stage culture system, consisting of a primary liquid culture phase followed by a secondary semisolid colony assay. CD34(2+)CD38- cells needed at least the presence of interleukin 3 (IL-3) and kit ligand (KL) together with either IL-1, IL-6, or granulocyte-colony-stimulating factor (G-CSF) in the primary liquid phase in order to proliferate and differentiate into secondary colony-forming cells (CFC). Addition of IFN-gamma to the primary liquid cultures inhibited cell proliferation and generation of secondary CFC in a dose-dependent way. This was a direct effect since it was also seen in primary single cell cultures of CD34(2+)CD38- cells. The proliferation of more mature CD34+CD38+ cells, however, was not inhibited by IFN-gamma, demonstrating for the first time that IFN-gamma is a specific and direct hematopoietic stem cell inhibitor. IFN-gamma, moreover, preserves the viability of CD34(2+)CD38- cells in the absence of other cytokines. IFN-gamma could, therefore, play a role in the protection of the stem cell compartment from exhaustion in situations of hematopoietic stress and may be useful as stem cell protecting agent against chemotherapy for cancer.

Transforming growth factor-beta regulates the cell cycle status of interleukin-3 (IL-3) plus IL-1, stem cell factor, or IL-6 stimulated CD34+ human hematopoietic progenitor cells through different cell kinetic mechanisms depending on the applied stimulus

The immediate cell kinetic response of highly purified human bone marrow progenitor cells (CD34+ sorted fraction) to the inhibitory effects of transforming growth factor-beta (TGF-beta) was studied using the BrdU-Hoechst flow-cytometric technique. The progenitor cells were stimulated with either interleukin-3 (IL-3) alone or with IL-3 in combination with IL-1, stem cell factor (SCF), or IL-6, and the inhibitory action of TGF-beta was evaluated in each phase of the first three consecutive cell cycles. Semisolid methylcellulose cultures were also performed to compare these initial events to the effects observed after 7, 14, and 21 days of incubation. Within the CD34+ compartment, the progenitor cells can be discriminated on a functional basis, i.e., in terms of TGF-beta sensitivity. Very primitive progenitors, recruited out of the G0 phase by IL-3 plus an early-acting factor (IL-1, SCF) are, upon addition of TGF-beta, arrested specifically in the G1 phase of the second cell cycle. In the clonogenic assays, the increased colony formation due to IL-1 or SCF was completely abolished by the counteracting effect of TGF-beta that diminished colony output back to the level of TGF-beta-plus-IL-3 supplemented colony growth. Addition of TGF-beta to CD34+ progenitors responding to IL-3 alone resulted in an overall retardation, but without an apparent specific accumulation of cells in any of the cell cycles. Finally, within the CD34+ compartment, there exists a subset of IL-3-responsive, but TGF-beta-insensitive, progenitor cells that were, upon addition of TGF-beta, not arrested at all. In conclusion, our results demonstrate that TGF-beta exerts different cell kinetic effects on CD34+ progenitor cell growth depending on the applied stimulus.

Differential regulation of the expression of CD38 and human leukocyte antigen-DR on CD34+ hematopoietic progenitor cells by interleukin-4 and interferon-gamma

We studied the effects of interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) on the expression of CD38 and human leukocyte antigen (HLA)-DR on purified CD34+ bone marrow progenitor cells. CD34+CD38- and CD34+HLA-DR- cells are largely nonoverlapping populations. After culture for 4 days in IFN-gamma, the expression of CD38 and HLA-DR is significantly increased and the disappearance of the CD38- and HLA-DR- populations is virtually complete. Moreover, IFN-gamma induces a population of CD34+ cells with a very high expression of CD38 (CD34+CD38++ cells), which were absent in the initial CD34+ population. IL-4 has no effect on the expression of CD38, but induces a limited but significant increase in the expression of HLA-Dr. After culture in IFN-gamma, CD34+ cells show a higher cloning efficiency of the colony-forming unit-macrophage (CFU-M) and burst-forming unit-erythroid (BFU-E) compared to cells cultured in medium alone. After culture in IL-4, a limited increase in CFU-granulocyte (CFU-G) and BFU-E is seen, whereas CFU-G, CFU-M, and BFU-E are increased after culture in IL-4 plus IFN-gamma. We further investigated the functional properties of the CD34+CD38++ cells generated in the presence of IFN-gamma. This cell population is highly enriched for BFU-E but partially depleted of CFU-M. Most of the CFU-M were found in the CD34+CD38+/-(CD34+CD38- and CD34+CD38+ cells) population.

Quantitative cell-cycle progression analysis of the first three successive cell cycles of granulocyte colony-stimulating factor and/or granulocyte-macrophage colony-stimulating factor-stimulated human CD34+ bone marrow cells in relation to their colony formation

The bromodeoxyuridine (BrdU)-Hoechst flow cytometric technique was applied to study the immediate cell kinetic response of highly purified human (h) bone marrow progenitor cells (CD(34+)-sorted fraction) to h granulocyte colony-stimulating factor (G-CSF) and/or h granulocyte-macrophage colony-stimulating factor (GM-CSF). The technique permits us to differentiate cycling from noncycling cells and to make a quantitative assessment of cell cycles after stimulation. Semisolid agar and single-cell liquid cultures were also performed to compare these initial events to the effects observed after 14 days of culture. The combination of G-CSF plus GM-CSF, acting synergistically in day 14 cultures, was found to have a subadditive effect in the first cell cycles, thereby indicating partial overlap of the different target cells. However, this combination accelerated transit through the cell cycle, as could be seen from the higher number of cells in the third cell cycle after 72 hours of stimulation. We conclude that, apart from the unresponsive cells, the CD34+ compartment consists of cells responsive to both G-CSF and GM-CSF, and cells responsive to either one of the CSFs alone, and that the combination of the two CSFs speeds up the cell cycle traverse rate for a significant fraction of the target cells that are initially responsive for both G-CSF and GM-CSF. The latter supports the hypothesis of an overlapping signalling pathway of G-CSF and GM-CSF.

Effects of interleukin-4 on myelopoiesis: localization of the action of IL-4 in the CD34+HLA-DR++ subset and distinction between direct and indirect effects of IL-4

We compared the myelopoietic effects of interleukin-4 (IL-4) on CD34+HLA-DR+ and on CD34+HLA-DR++ bone marrow progenitor cells stimulated by either granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-3 (IL-3). IL-4 stimulates G-CSF-induced colony-forming unit-granulocyte (CFU-G) and inhibits all colony types induced by GM-CSF and IL-3 in the HLA-DR++ population, but not in the HLA-DR+ population. In CD34+HLA-DR+ cells, however, a stimulation of G-CSF-supported CFU-G was also seen with sequential application of IL-4 in liquid cultures followed by G-CSF in agar cultures. In order to confirm that these are direct effects of IL-4, single-cell culture experiments were performed with CD34+HLA-DR++ cells. In these cultures IL-4 stimulates G-CSF-induced CFU-G and only inhibits colony-forming unit-macrophage (CFU-M) regardless of the CSF used to generate them.

Interferon-gamma and interleukin-4 reciprocally regulate the production of monocytes/macrophages and neutrophils through a direct effect on committed monopotential bone marrow progenitor cells

We studied the direct effects of interferon-gamma (IFN-gamma) in single cell colony assays of CD34+HLA-DR++ bone marrow progenitor cells stimulated by either granulocyte-colony-stimulating factor (G-CSF), interleukin(IL)-3, granulocyte/macrophage-colony-stimulating factor (GM-CSF), combinations of these CSF or medium conditioned by the 5637 human bladder carcinoma cell line. In this culture system IFN-gamma stimulated monocytic colonies (CFU-M) no matter which CSF or CSF combination was used to support them and inhibited granulocytic colonies (CFU-G) if they were generated in the presence of G-CSF. IL-4 antagonized the myelopoietic effects of IFN-gamma: the IFN-gamma-induced suppression of G-CSF-supported CFU-G, as well as the stimulation of CFU-M, were reversed by IL-4. In all cultures, IFN-gamma had a limited, but statistically non-significant, inhibitory effect on CFU-GM, which was not affected by the presence of IL-4. These data show that IFN-gamma and IL-4 reciprocally regulate the generation of myeloid cells involved in humoral (neutrophils) and cellular (macrophages) immune responses through a direct effect on monopotential myeloid progenitor cells.

Improved BrdUrd-Hoechst bivariate cell kinetic analysis by helium-cadmium single laser excitation

In laser based flow cytometers, UV excitation of Hoechst 33258 and propidium iodide (PI) or ethidium bromide (EB) is performed with 351/364 nm high power lines of UV-capable argon ion lasers, which are expensive and short-lived. In this paper we note for the first time that helium-cadmium lasers emitting 10 to 30 mW at 325 nm are even more superior for cell kinetic bivariate bromodeoxyuridine (BrdUrd)/Hoechst PI or EB cell cycle analysis. HeCd single laser UV excitation gives comparable CVs for cell cycle distributions, and almost normal G2M/G1 ratios of 1.9 to 2.0 for all cell cycles. This is shown for synchronous and asynchronous cell populations on a FACStar+ and an Ortho Cytofluorograf. Therefore we recommend helium-cadmium lasers as low-power, cheap, and long-lived UV excitation sources for the cytochemically simple but high resolution multiparameter BrdUrd-Hoechst cell kinetic analysis.

Stromal populations and fibrosis in human long-term bone marrow cultures

An immunofluorescence study of the adherent layer of human long-term bone marrow cultures (HLTBMC) revealed the following surface markers on the different stromal cell populations: stromal fibroblastic cells CD10+, FIB86.3+, CD13+, CD71+; adipocytes CD10+, FIB86.3-, CD13+, CD71-/+; and macrophages CD10-/+, FIB86.3+, CD13+, CD71-/+, CD14+, CD33+, CD25+, HLA-DR+, CD4+, CD19+, CD45+. The markers of the stromal fibroblastic cells in HLTBMC were similar to those of twice-passaged fibroblasts not only from bone marrow and spleen, but also from a hemopoietic non-supportive organ such as the skin. Some of the cultured human umbilical vein endothelial cells used as controls were found to be CD25+, demonstrating for the first time the interleukin-2 receptor p55 chain on normal non-hemopoietic cells. The stromal fibroblastic cells are overrepresented compared to the small non-macrophage hemopoietic cell population in the adherent layer of HLTBMC. In addition, silver staining revealed an increased reticulin content in most of the HLTBMC. An excessive growth of stromal fibroblastic cells and an excessive deposition of their product, the reticulin fibers, are the hallmark of myelofibrosis. The finding of equivalent observations in HLTBMC suggests that the hitherto unexplained, premature quenching of hemopoiesis in HLTBMC might at least partly be due to mechanisms similar to those operating in myelofibrosis in vivo.

DNA ploidy and the expression of tissue-carcinoembryonic antigen in grade III carcinoma of the breast

A series of 50 Stage I and II, Grade III ductal carcinomas of the breast was characterized by DNA flow cytometry and further analyzed with a monoclonal antibody for carcinoembryonic antigen (CEA). The antigen was detected with the indirect immunoperoxidase technique on paraffin sections and on cytologic smears of the cell suspensions that were used for flow cytometric DNA analysis. A significant higher incidence of CEA-positivity in cytologic smears and tissue sections was found in DNA-diploid tumors (13/18 and 12/18, respectively) than in DNA-aneuploid tumors (13/22 and 12/32, respectively) (P less than 0.05 and P less than 0.025, respectively).

Aberrant Ki-67 expression in normal bone marrow revealed by multiparameter flow cytometric analysis

Ki-67 is a commercially available monoclonal antibody that reacts with a nuclear antigen detectable in proliferating cells only. Since its first description, it has been widely used as a "universal" proliferation marker and few groups have questioned the validity of the initially described reactivity, although this was tested only on very restricted experimental models. We wanted to check its reactivity on normal bone marrow (BM) samples using a multiparameter flow cytometric analysis. Although we were able to reproduce the findings of Ki-67 positivity on cultured and stimulated cells, we could not detect any convincing Ki-67 positivity on nuclei of normal BM samples. These samples all had a noticeable proliferating compartment as evidenced by their DNA content. These data are in contrast with the data we obtained starting from stressed marrows and marrows cultured in the presence of hematopoietic growth factors, where we found a marked Ki-67 positivity. This discrepancy suggests that bone marrow cells, growing and proliferating under steady-state conditions and guided by natural control mechanisms, may lose their Ki-67 expression upon exiting the progenitor compartment and entering the differentiating compartment.

Cimetidine induced pancytopenia. Effect on human CFU-MIX colony formation

We describe a 26 year-old male with a pancytopenia possibly due to cimetidine. Using progenitor cell culture techniques we investigated the mechanism of this bone marrow toxicity. Our results show a cimetidine dose-dependent inhibition of normal human CFU-GM colony formation as described by Fitchen and Koeffler in 1980. No differences in growth inhibition were found between the patients' recovery marrow and the controls. Toxicity on normal human CFU-MIX colony formation was, however, far more pronounced. At concentrations as low as 5 micrograms/ml the numbers of CFU-MIX colonies were decreased by almost 20% and more than 30% in cultures of two normal bone marrow samples. A significant decrease in CFU-MIX colony size was measured even at therapeutic levels (0.5 micrograms/ml). No obvious decrease in CFU-GM colony size was noticed at low concentrations. Experiments with T-cell- and monocyte-depleted bone marrow samples gave similar results: a pronounced inhibition of the CFU-MIX colony formation at low concentrations of cimetidine whereas the CFU-GM formation was less affected. It is therefore very unlikely that Accessory cells play part in the cimetidine induced CFU-MIX inhibition. Our results suggest the existence of H2 histamine receptors on human CFU-MIX (= multipotent progenitor cell). Blocking these receptors prevents the multipotent progenitor cell from going into the DNA-synthesis phase of the cell cycle.

Flow cytometric detection of multifocal DNA aneuploid cell populations in mastectomy specimens containing a primary breast carcinoma

DNA flow cytometry was used to study the presence of DNA aneuploid cell populations in macroscopically normal glandular tissue in mastectomy specimens from 30 patients with breast cancer. In the 13 patients with a DNA diploid primary tumor, no DNA aneuploidy could be found in any of the 39 distant specimens assessed. However, DNA aneuploid cell populations were demonstrated in four of the 17 (23%) patients with a primary DNA aneuploid carcinoma and in seven out of 54 (13%) distant tissue samples (P = 0.02). In all cases the DNA index of the DNA aneuploid cells found in the distant samples was identical to that of the primary tumor. The replicate aneuploid DNA indices and histologic controls taken in parallel very strongly suggest that these distant DNA aneuploid cell populations are metastases.

1,3'-Diethyl-4,2'-quinolylthiacyanine iodide as a "thiazole orange" analogue for nucleic acid staining

Flow cytometric evaluation of reticulocytes has become a valuable and more precise alternative for the microscopically determined reticulocyte count. Until now, the most promising results are obtained with the "thiazole orange" (TO) nucleic acid dye. We report on the use of a "thiazole orange" analogue, 1,3'-diethyl-4,2'-quinolylthiacyanine iodide (DEQTC), which gives comparable results and is commercially available at low cost.

Flow cytometric analysis of T-lymphocyte subpopulations in B-cell chronic lymphocytic leukemia: correlation with clinical stage

Several authors have studied the T-lymphocyte subpopulations in B-cell chronic lymphocytic leukemia (B-CLL), but previous studies were performed after preceding enrichment procedures, which are known to cause selective losses of certain subpopulations. To correct for this deficiency we used flow cytometric analysis, which enabled us to measure subpopulations directly on total blood samples. We studied T-lymphocyte subsets with OKT monoclonal antibodies in 45 patients with B-CLL. Serum levels of IgG, IgA and IgM were assayed simultaneously and findings were correlated with clinical stage (Rai classification). The absolute number of CD4-positive cells decreased in more advanced Rai stages, while the absolute number of CD8-positive cells increased, resulting in a progressive reduction in CD4/8 ratio. Results from patients in stages with equal prognosis (Rai I and II, Rai III and IV) were similar and when these results were grouped the observed differences were highly significant and clearly correlated with all prognostic groups.