Increase In Colony-forming Cells Research Articles

Therapeutic Targeting of CD163 on Hematopoietic Progenitor Cells By Novel Monoclonal Antibody TBI 304H Demonstrates an Increase in Erythropoiesis in Humanized Mice

▪Hemoglobin (Hb) is known to stimulate erythropoiesis, a process that may be mediated by CD163. CD163 is a receptor for the hemoglobin-haptoglobin (Hb-Hp) complex expressed on monocyte/macrophages as well as a subpopulation of human CD34+ hematopoietic progenitor cells (HPCs). We have demonstrated that administration of ligands to the CD163 receptor can measurably stimulate erythropoiesis in human CD34+ cell-engrafted severe-combined immunodeficiency (SCID) mice. To better elucidate the role of CD163 in hematopoiesis, we investigated the effects of the natural ligand to CD163 (Hb-Hp) as well as a stimulatory antibody, TBI 304H, on HPCs in vivo. SCID mice engrafted with human CD34+ cells were used as a model system were used to investigate the effect of Hb and anti-CD163 monoclonal antibodies (TBI 304 and TBI 304H) on human hematopoiesis in vivo. In an initial study, NOD-SCID IL2R gammanull (NSG) mice were engrafted with human CD34+ cells and animals with < 30% human CD45+ cells in the peripheral blood were administered 2 mg Hb/mouse, or 100 or 500 µg/mouse TBI 304 every 4 days for a total of four doses. At study termination on day 14, bone marrow cells (BMCs) were examined by flow cytometry and CD34+ cells were recovered from the BMCs for enumeration in colony-forming assays. Hemoglobin administration resulted in an increase of human CD34+ cells ranging from 4% to 7% of BMCs and a corresponding 57% increase in colony-forming cells (CFCs) over control animals. In contrast, the monoclonal antibody (mAb), TBI 304, produced a dose-dependent decrease in CD34+ and colonies, possibly reflecting a depletion of CD34+/CD163+ cells as a result of overstimulation due to the much longer circulating half-life of the mAb compared to Hb.. To confirm this hypothesis, human CD34+ cell engrafted animals were given only a single dose of 10 or 100 µg/mouse of TBI 304 and BMCs were examined earlier on day 7. TBI 304 provided a 3.5-fold increase in human CD34+ cells as well as a 1.8 to 6.7-fold increase in bone marrow erythroid lineage engraftment (huGlyA+, huCD36+ and huCD71+) and a 2-fold increase in colony-forming cells. The ability of TBI 304 to stimulate erythropoiesis in preclinical models led to the creation of an anti-CD163 mAb suitable for human clinical use. TBI 304H was generated by grafting the complementarity-determining regions derived from TBI 304 onto a humanized IgG4 framework without altering antigen specificity. An IgG4 framework, as an antibody without Fc effector function, was deemed the most suitable for an agonistic mAb. In the single dose, 7 day Hu-SCID model human CD34+ cells were mobilized from the mouse bone marrow by TBI 304H, as reflected by dose dependent decreases in huCD34+, huCD71+, and huGlyA+ cells in the mouse marrow. At the highest dose tested (500 µg/mouse) the decrease in human HPCs was similar to that found in animals administered Hb (2 mg/mouse). In this model, human hematopoiesis derived from the engrafted human CD34+ cells is not sustained and these date may reflect a mobilization of human HPCs through stimulation by an anti-CD163 antibody. Therapure has received U.S. FDA approval to conduct a Phase I trial of the novel therapeutic antibody TBI 304H. The Phase I clinical trial is a single-center, open-label, intra-subject escalating dose study, which will evaluate the safety, tolerability and pharmacokinetics of TBI 304H following administration to subjects experiencing chemotherapy-induced anemia. DisclosuresMatthews:Therapure Biopharma: Employment. Eberle-Ayres:Therapure Biopharma: Employment. Lu:Therapure Biopharma: Employment. Singh:Therapure Biopharma: Employment. Cutler:Therapure Biopharma: Employment. Bell:Therapure Biopharma: Employment.

The Hemoglobin-Haptoglobin Receptor (CD163) Is Expressed by a Subpopulation of Erythroid and Granulo-Macrophagic Progenitors and Can Be Stimulated in Vitro and in Vivo by Physiological and Pharmacological Ligands to Stimulate Hematopoiesis

AbstractAbstract 1221The receptor for the hemoglobin (Hb)-haptoglobin (Hp) complex, CD163, is expressed on the surface of a subpopulation of hematopoietic stem/progenitor cells (HPCs) (Matthews et al, 2006). The purpose of the studies presented here were two-fold – to demonstrate that the CD34+CD163+ double positive population could be isolated from normal adult bone marrow cells and these cells were functional as HPCs and, in addition, that these cells could be stimulated in vivo by ligands to CD163 to affect hematopoiesis. To investigate the clonogenic potential of CD34+/CD163+ HPCs, bone marrow CD34+ cells were examined for CD163 co-expression, sorted by fluorescence activated cell sorting (FACS) and plated into colony-forming assays (CFAs). 4.2% ± 1.4% (n=4) of CD34+ cells were found to co-express CD163 and this population consisted of two distinct sub-populations, CD34++ (hi)CD163+ and CD34+(lo)CD163+, each of which represented approximately half of the total CD34+CD163+ population. All three sorted populations (CD34+(all)CD163−, CD34++(hi) CD163+, CD34+(lo)CD163+) were plated into CFAs (n=4) and were assessed for erythroid and myeloid colony formation. The clonogenic efficiency of CD34++(hi)CD163+ had a 2.5-fold increase in the number CFU-E and CFU-GM when compared to both CD34+ (total) CD163− and CD34+(lo) CD163+ cells. In contrast, CD34+(hi an low)CD163+cells produced fewer BFU-E.To determine how the expression of CD163 expression on progenitor cells may play a role in hematopoiesis, we investigated the effects of the natural ligand to CD163 (Hb/Hp) as well as an agonistic antibody to CD163 (TBI 304) on HPCs in vivo. NOD-scid IL2R gammanull (NSG) mice (HuMurine Technologies) were engrafted with human CD34+cells and animals with < 30% human CD45+ cells in the peripheral blood were administered either 2 mg Hb/mouse, or 100 or 500 μg/mouse TBI 304 every 4 days. At study termination (day 14), bone marrow cells (BMC) were examined by flow cytometry and enriched for CD34+ cells for enumeration in CFAs. Hb administration resulted in an increase of human CD34+cells ranging from 4% to 7% of BMC and a corresponding 57% increase in colony-forming cells (CFC) when compared to control (PBS-administered) animals. In contrast, TBI 304 produced a dose dependent decrease in CD34+ and CFC, possibly reflecting a depletion of CD34+/CD163+ cells from overstimulation due to the longer circulating antibody. To investigate this, human CD34+ cell engrafted animals were given a single dose of 10 or 100 μg/mouse of TBI 304 and bone marrow cells were examined on day 7. TBI 304 provided a 3.5-fold increase in human CD34+ cells as well as a 1.8 to 6.7-fold increase in bone marrow erythroid lineage engraftment (huGlyA+, huCD36+ and huCD71+) and a 2-fold increase in erythroid and myeloid colony-forming cells. No overall toxicities were observed with the administration of TBI 304 or Hb.We have demonstrated that CD163 is expressed on a population of CD34+ hematopoietic progenitor cells, these cells have increased hematopoietic progenitor activity in vitro and that administration of physiological or pharmacological agonists of the CD163 receptor can measurably stimulate hematopoiesis in vivo. Disclosures:Matthews:Therapure Biopharma: Employment. Bell:Therapure Biopharma: Employment.

Myeloid Dendritic Cells Contribute to Hematopoietic Progenitor Mobilization by G-CSF.

AbstractAbstract 2319Granulocyte-colony stimulating factor (G-CSF) is the prototypic agent used to mobilize hematopoietic stem and progenitor cells (HSPCs) into the blood where they can then be harvested for stem cell transplantation. G-CSF acts in a non-cell-intrinsic fashion to induce HSPC mobilization. We recently showed that G-CSF signaling in a CD68+ monocyte/macrophage lineage cell within the bone marrow initiates the HSPC mobilization cascade (Christopher et al., 2011). Consistent with this finding, two other groups showed that ablation of monocytes/macrophages induces HSPC mobilization (Winkler et al., 2010; Chow et al., 2011). CD68 marks a heterogeneous cell population that includes monocytes, macrophages, myeloid dendritic cells, and osteoclasts. To further define the relevant cell population(s) for HSPC mobilization by G-CSF, we first examined the role of osteoclasts. Receptor activator of NF-kappaB (RANK) signaling is required for osteoclast development. Osteoprotegerin (OPG) is a decoy receptor for RANK ligand, and treatment with OPG-Fc (a stabilized form of OPG) results in osteoclast ablation in mice. We treated mice with 100 μg of OPG-Fc and documented complete osteoclast ablation by histomorphometry. Osteoclast ablation did not result in constitutive HSPC mobilization, nor did it affect G-CSF-induced HSPC mobilization. To further assess the role of osteoclasts, we transplanted RANK−/− fetal liver cells into irradiated Csf3r−/− (G-CSF receptor deficient) recipients. Since RANK is required for osteoclast development, the osteoclasts in these bone marrow chimeras lack the G-CSFR, while other hematopoietic cells (including monocytes/macrophages) are G-CSFR sufficient. Again, G-CSF-induced HSPC mobilization in these mice was normal. Based on these data, we conclude that osteoclasts are dispensable for HSPC mobilization by G-CSF.We next quantified changes in monocytic/macrophage cell populations in the bone marrow after G-CSF treatment (250 μg/kg per day for 5 days) using a novel multi-color flow cytometry assay that includes CD115, F4/80, MHC class II, Gr-1, B220, and CD11c. Using this assay, we observed a significant decrease in macrophages (11.8 ± 3.6-fold) and, surprisingly, myeloid dendritic cells (MDCs; 5.5 ± 1.2-fold) in the bone marrow with G-CSF treatment. To further assess the role of MDCs, we used transgenic mice expressing the diphtheria toxin receptor under the control of the CD11c promoter (CD11c-DTR) to conditionally ablate MDCs. To avoid systemic toxicity, we transplanted CD11c-DTR bone marrow into congenic wild type recipients prior to MDC ablation. The resulting bone marrow chimeras were treated with diphtheria toxin (DT; 400 ng per day for 6 days), which resulted in a 92% reduction in MDCs. Ablation of MDCs resulted in a significant increase in colony-forming cells in the blood and spleen (figure 1A). Moreover, MDC ablation significantly increased mobilization of colony-forming cells and c-Kit+lineage−Sca-1+ (KLS) cells by G-CSF (figures 1B and 1C). Taken together, these data suggest that myeloid dendritic cells, but not osteoclasts, contribute to HSPC mobilization by G-CSF. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Comparative in vitro analysis of different hematopoietic cell populations from human cord blood: in search of the best option for clinically oriented ex vivo cell expansion

Ex vivo expansion of hematopoietic stem and progenitor cells has become a priority in the experimental hematology arena. In this study we have obtained different hematopoietic cell populations from umbilical cord blood and simultaneously assessed their proliferation and expansion kinetics. Our main goal was to determine which one of these cell populations would be more suitable for clinical-grade ex vivo expansion. By using immunomagnetic-negative selection and cell sorting, five cell populations were obtained: unseparated mononuclear cells (MNCs; I); two lineage-negative cell populations, one enriched for CD34+ CD38+ cells (II) and the other enriched for CD34+ CD38- cells (III); and two CD34+ cell fractions purified by fluorescence-activated cell sorting, one containing CD34+ CD38+ cells (IV) and the other containing CD34+ CD38- cells (V). The kinetics of such populations were analyzed in both relative and absolute terms. No expansion was observed in Population I; in contrast, significant increments in the numbers of both progenitor and stem cells were observed in cultures of Populations II to V. Population V (reaching 12,800-fold increase in total cells; 1280-fold increase in CD34+ cells; 490-fold increase in colony-forming cells; and 12-fold increase in long-term culture-initiating cells) showed the highest proliferation and expansion potentials. Our study suggests that the cell fraction containing greater than 98% CD34+ CD38- cells would be the ideal one for large-scale ex vivo expansion; however, based on our data, it seems that, except for MNCs, all other cell populations could also be used as input cell fractions.

Bone marrow CD34+ cells expanded on human brain endothelial cells reconstitute lethally irradiated baboons in a variable manner

Increased cell dose has a positive impact on the therapeutic outcome of bone marrow (BM) hematopoietic stem cell (HSC) transplant. However, methods to successfully expand BM HSCs have yet to be achieved. It has been shown previously that ex vivo expansion of BM cells using porcine microvascular endothelial cells can rescue a baboon from a lethal dose of radiation. However, in a prior study, baboons that received CD34+ cell doses less than 4 × 106 cells/kg body weight failed to achieve hematopoietic reconstitution. In our present study we used human brain endothelial cells (HUBECs) and cytokines to expand BM cells, and examined their ability to provide hematopoietic reconstitution in three lethally irradiated baboons following autologous transplant as a surrogate preclinical model. After ex vivo culture, the grafts represented a 1.8- to 2.1-fold expansion of CD34+ cells, a 3.7- to 13.2-fold increase of colony-forming cells, and a 1.9- to 3.2-fold increase of cobblestone area-forming cells, in comparison to the input cell numbers. Despite transplanting CD34+ cell grafts displaying a comparable degree of expansion, there was an obvious variability in the kinetics of hematopoietic reconstitution. The variation in hematopoietic reconstitution cannot be fully explained by the properties tested in expanded CD34+ cells, and warrant caution against taking into account such attributes as cell dose, expression of adhesion molecules, and migration as a measure of successful expansion of HSCs.

Bone Marrow CD34+ Cells Expanded On Human Brain Endothelial Cells Reconstitutes Lethally Irradiated Baboons in a Variable Manner.

Abstract 3214Poster Board III-151Increased cell dose has a positive impact on the therapeutic outcome of bone marrow (BM) transplantation. However, methods to successfully expand hematopoietic stem cells (HSC) from BM have yet to be achieved. It has been shown previously that ex vivo expansion of BM cells using porcine microvascular endothelial cells can rescue a baboon from a lethal dose of radiation (Brandt et al. Blood 1999). However, in prior studies baboons that received CD34+ cell doses less than 4 × 106 cells/kg body weight failed to achieve hematopoietic engraftment. In our current studies we have used human brain endothelial cells (HUBECs) and cytokines to expand BM cells and examined their ability to provide hematopoietic reconstitution in three lethally irradiated baboons following autologous transplantation. After ex vivo culture, the grafts represented a 1.8- to 2.1-fold expansion of CD34+ cells, a 3.7-fold to 13.2-fold increase of colony-forming cells (CFC), and a 1.9-fold to 3.2-fold increase of cobblestone area-forming cells (CAFC) in comparison to the input cell numbers. The animal (PA6873) which received expanded product of a suboptimal dose of CD34+ cells (1.6 × 106/kg) achieved only myeloid engraftment (day 24). Out of 3 baboons transplanted two displayed myeloid engraftment, one animal achieved both myeloid and platelet engraftment and the third animal (PA6888) failed to achieve engraftment. The animal (PA6893) which received the expanded product of 4.9 × 106/kg CD34+ cells achieved myeloid engraftment (WBC > 500/ml blood) by day 8 and platelet engraftment (>20,000/μl) by day 39. The WBC recovery of this baboon was comparable but the platelet recovery was delayed (31 day vs. 39 day) in comparison to that experienced by an animal that received a large number of unexpanded CD34+ cells (26 × 106 /kg). Interestingly, despite the grafts of all three animals having a similar degree of CD34+ cell expansion, similar progenitor cell (CFC, CAFC) expansion, a similar pattern of cell adhesion molecule expression and similar migration capacity across an SDF1 gradient, the hematopoietic reconstitution capacity of each graft differed greatly. Prior studies using human BM cells in non-contact HUBEC co-cultures in NOD/SCID mice demonstrated no such variability. Our current data indicates three possibilities for the variations in hematopoietic reconstitution observed in a baboon model. One possibility is that there might be cell autonomous biological variation of HUBEC expanded BM grafts. The second possibility is the expanded graft may have contained variable numbers of contaminating endothelial cells (HUBEC) contributing to variations in hematopoietic reconstitution. Transplantation of vascular endothelial cells without HSC rescue has been shown to enhance hematopoietic recovery following radiation in mice (Chute et al. Blood 2007). Biological variation amongst the hosts is unlikely since identical pre-transplant conditioning and post-transplant care was provided to all three baboons. In addition, since only non-adherent cells were harvested from the co-culture, it is possible that more primitive repopulating HSCs embedded within the endothelial monolayer might have been excluded from the graft. Taken together, our findings highlight inherent differences in the hematopoietic reconstitution capacity of expanded BM grafts in xenotransplantation studies and large animal models. DisclosuresNo relevant conflicts of interest to declare.

Effects of HOXB4 Overexpression on Ex Vivo Expansion and Immortalization of Hematopoietic Cells from Different Species

Overexpression of the human HOXB4 has been shown to induce the expansion and self-renewal of murine hematopoietic stem cells. In preparation for clinical studies, we wished to investigate the effects of HOXB4 on cells from other species, in particular preclinical large animals such as dogs and nonhuman primates. Thus, we transduced CD34(+) cells from nonhuman primates, dogs, and humans with a HOXB4-expressing gammaretroviral vector and a yellow fluorescent protein-expressing control vector. Compared with the control vector, HOXB4 overexpression resulted in a much larger increase in colony-forming cells in dog cells (28-fold) compared with human peripheral blood, human cord blood, and baboon cells (two-, four-, and fivefold, respectively). Furthermore, we found that HOXB4 overexpression resulted in immortalization with sustained growth (>12 months) of primitive hematopoietic cells from mice and dogs but not from monkeys and humans. This difference correlated with increased levels of retrovirally overexpressed HOXB4 in dog and mouse cells compared with human and nonhuman primate cells. The immortalized cells did not show any evidence of insertional mutagenesis or chromosomal abnormalities. Competitive congenic transplantation experiments showed that HOXB4-expanded mouse cells engrafted well after 1 or 3 months of expansion, and no leukemia was observed in mice. Our findings suggest that the growth promoting effects of HOXB4 are critically dependent on HOXB4 expression levels and that this can result in important species-specific differences in potency. Disclosure of potential conflicts of interest is found at the end of this article.

Effects of 5-aza-2′-deoxycytidine on proliferation, differentiation and p15/INK4b regulation of human hematopoietic progenitor cells

The demethylating agents 5-azacytidine and 5-aza-2'-deoxycytidine (DAC) have been shown to induce differentiation and inhibit growth of leukemic myeloid cells at low concentrations. However, the effect of DAC in changing the differentiation and proliferation behavior of normal human myeloid progenitors has rarely been investigated. Therefore, we established an in vitro model of normal hematopoietic differentiation, using CD34+ cells from mobilized peripheral blood, to study proliferation and colony formation, expression of several myeloid maturation markers and of the inhibitor of cyclin-dependent kinases p15/INK4b. Upon DAC treatment, cell growth was significantly decreased in a dose-dependent manner, without an increase in cytotoxicity. DAC treatment also resulted in a substantial increase of lysozyme-positive cells, which could be enhanced by G-CSF, a modest increase of myeloperoxidase+ and CD15+ cells, as well as an increase of colony-forming cells (CFU-GM) compared to control cells. p15/INK4b protein expression was strongly upregulated upon myeloid maturation, and additional DAC treatment did not change p15 expression or the methylation status of the p15 promoter at the noncytotoxic concentrations used. Taken together, these data indicate a role of DAC in changing myeloid progenitor cell expansion and differentiation. This model appears suitable also for global analyses of multiple differentially methylated genes.

Reculturing of Cells from Primary CFU-C Colonies

This study was aimed at investigating whether cells of CFU-C derived colonies could form secondary colonies. Bone marrow cultures of volumes of agar medium between 25 microliter and 75 microliter contained in glass capillaries were stimulated with mouse lung-conditioned medium (MLCM) containing granulocyte/macrophage colony-stimulating factor (GM-CSF). Agar gels with colonies of up to greater than or equal to 20 were blown out into identical culture medium, completely dispersed on a whirl-mix to single cell suspensions, and used for establishing secondary agar cultures. In these secondary cultures considerable numbers of secondary granulocytic, mixed granulocytic/macrophage and macrophage colonies as well as numerous clusters arose. In contrast, when single colonies were recultured, only few secondary cell aggregates were formed. When primary cultures containing up to greater than or equal to 20 cell aggregates were used for serial reculture at intermittent intervals of 3 and 4 days, a 2-7-fold increase of colony-forming cells was found in tertiary cultures as was monitored by 7 day colony counts. And by use of different kinds of CSF-containing media, an over 4-fold increase of secondary over primary colonies was obtained with bovine lung-conditioned medium (BLCM) in primary and L-cell-conditioned medium (LCCM) in secondary 7 day cultures. Primary capillary cultures were found to be devoid of CFU-S. Also, setting up bone marrow cultures in petri dishes and stimulating with MLCM, growth of primary as well as secondary colonies was obtained. The results indicate some self-renewal potential of CFU-C in vitro.