Ex-vivo expansion of bone marrow progenitor cells for hematopoietic reconstitution following high-dose chemotherapy for breast cancer

Evaluation of umbilical cord blood CD34 (+) hematopoietic stem cell expansion in co-culture with bone marrow mesenchymal stem cells in the presence of TEPA

BACKGROUND

During the last three decades hematopoietic stem cells (HSC) have become a standard protocol for the treatment of many hematologic malignancies and non-malignant disorders. Umbilical cord blood (UCB), as a source of HSCs, has many advantages compared with other sources. One major drawback in using this source in treatment of adult patients is the low HSC dose available. Ex vivo expansion of HSCs is a solution to overcome this limitation. In this study we used TEPA, as a Cu chelator, and human bone marrow (BM) mesenchymal stem cells (MSCs) to investigate expansion rate of UCB-HSCs.

MATERIALS AND METHODS

CB-HSCs were isolated using miniMACS magnetic separation system. We cultured the enriched CD34(+)cells in various conditions: culture condition A, supplemented only with recombinant cytokines; culture condition B, supplemented with BM-MSCs as a cell feeder layer and recombinant cytokines; culture condition C, supplemented with recombinant cytokines and TEPA; culture condition D, supplemented with recombinant cytokines, BM-MSCs as a cell feeder layer and TEPA. In order to evaluate the HSC expansion, we performed cell count, analysis of CD34(+) expression by flow cytometry, and colony-forming cell assay on Day 10 after culture.

RESULTS

The most fold increase in CD34(+) cell, total cell, and total colony numbers was observed in culture condition D (110.11 ± 15.3, 118.5 ± 21, and 172.9 ± 44.7, respectively) compared to other conditions.

CONCLUSION

The results showed that co-culture of HSCs with BM-MSCs in the presence of copper chelating agent (TEPA) could dramatically increase expansion rate of UCB-HSCs. Therefore, this strategy could be useful for HSC expansion.

Bone repair cells for craniofacial regeneration

Reconstruction of complex craniofacial deformities is a clinical challenge in situations of injury, congenital defects or disease. The use of cell-based therapies represents one of the most advanced methods for enhancing the regenerative response for craniofacial wound healing. Both somatic and stem cells have been adopted in the treatment of complex osseous defects and advances have been made in finding the most adequate scaffold for the delivery of cell therapies in human regenerative medicine. As an example of such approaches for clinical application for craniofacial regeneration, Ixmyelocel-T or bone repair cells are a source of bone marrow derived stem and progenitor cells. They are produced through the use of single pass perfusion bioreactors for CD90+ mesenchymal stem cells and CD14+ monocyte/macrophage progenitor cells. The application of ixmyelocel-T has shown potential in the regeneration of muscular, vascular, nervous and osseous tissue. The purpose of this manuscript is to highlight cell therapies used to repair bony and soft tissue defects in the oral and craniofacial complex. The field at this point remains at an early stage, however this review will provide insights into the progress being made using cell therapies for eventual development into clinical practice.

Cellular therapies supplement: strategies for improving transplant efficiency in the context of cellular therapeutics

The field of hematopoietic stem cell transplantation (HSCT) has overcome many obstacles that have led to our current clinical ability to utilize cells collected from marrow, mobilized peripheral blood, or umbilical cord blood for the treatment of malignant and nonmalignant hematologic diseases. It is in this context that it becomes evident that future progress will lie in our development of an understanding of the biology by which the process of HSCT is regulated. By understanding the cellular components and the mechanisms by which HSCT is either enhanced or suppressed it will then be possible to design therapeutic strategies to improve rates of engraftment that will have a positive impact on immune reconstitution post-HSCT. In this review we focus primarily on allogeneic hematopoietic stem cell transplantation (allo-HSCT), the current challenges associated with allo-HSCT, and some developing strategies to improve engraftment in this setting.

Ex vivo expansion of human hematopoietic stem and progenitor cells

Despite progress in our understanding of the growth factors that support the progressive maturation of the various cell lineages of the hematopoietic system, less is known about factors that govern the self-renewal of hematopoietic stem and progenitor cells (HSPCs), and our ability to expand human HSPC numbers ex vivo remains limited. Interest in stem cell expansion has been heightened by the increasing importance of HSCs in the treatment of both malignant and nonmalignant diseases, as well as their use in gene therapy. To date, most attempts to ex vivo expand HSPCs have used hematopoietic growth factors but have not achieved clinically relevant effects. More recent approaches, including our studies in which activation of the Notch signaling pathway has enabled a clinically relevant ex vivo expansion of HSPCs, have led to renewed interest in this arena. Here we briefly review early attempts at ex vivo expansion by cytokine stimulation followed by an examination of our studies investigating the role of Notch signaling in HSPC self-renewal. We will also review other recently developed approaches for ex vivo expansion, primarily focused on the more extensively studied cord blood-derived stem cell. Finally, we discuss some of the challenges still facing this field.

[Ex vivo expansion of hematopoietic stem cells: concept and clinical benefit]

A new discipline was born and grew up over the last 4 decades of 20th century: Experimental Hematology. In addition to yield the concept of Stemness, a paradigm later applied for the other tissues than hematopoietic one, it provided the results allowing a preclinical development and a therapeutic exploitation. The concept of ex vivo expansion of hematopoietic cells for transplantation is directly issued from this knowledge. It enabled us to realize that a critical quantity of different sub-populations of stem and progenitor cells are necessary to obtain a rapid and sustained hematopoietic reconstitution. These principles, transposed to human cells (originating from: bone marrow, peripheral blood, cord blood) required some important technological innovations (conception of the specific media, recombinant technology of cytokine production...), to achieve, after several attempts, the first efficient clinical trials (at the moment for cells mobilized in peripheral blood). This goal remains to be achieved for cord blood cells too. The developments in this field as well as its actual state are the subjects of this review.

Fibroblast growth factor andex vivoexpansion of hematopoietic progenitor cells

Fibroblast growth factor (FGF) belongs to a family of heparin-binding polypeptides and shows multiple functions including cell proliferation, differentiation, survival and motility. The expression of FGF receptors is widely distributed on different hematopoietic progenitor cells and stromal cells, and FGFs play an important role in hematopoietic stem cell homeostasis. FGFs have been shown to sustain the proliferation of hematopoietic progenitor cells, maintaining their primitive phenotype. Basic FGF (bFGF, FGF-2) stimulates the formation of an adherent stromal cell layer in human long-term bone marrow cultures, and promotes hematopoietic cell development. FGF-2 has also been shown to synergize with other hematopoietic growth factors to enhance in vitro colony formation by several classes of hematopoietic progenitor cells. Results of ex vivo expansion and clinical trials to date suggest that hematopoietic cells cultured under stroma-free cytokine combination conditions may be insufficient to restore hematopoiesis after a myeloablative conditioning regimen, although some recent trials demonstrated an improvement in engraftment and a reduction of the period of pancytopenia, especially neutrophils and platelets, after transplantation. A recent study by our group demonstrated that FGF-2 is effective in supporting the generation of megakaryocytic progenitor cells during ex vivo expansion. These observations could be useful in reducing the long period of severe thrombocytopenia that occurs frequently after umbilical/placental cord blood transplantation. The development of more effective amplifying systems for hematopoietic stem/progenitor cells can be expected since FGFs have multiple functions in hematopoiesis.

Placental/umbilical cord blood-derived mesenchymal stem cell-like stromal cells support hematopoietic recovery of X-irradiated human CD34+ cells

AIMS

The potential of human mesenchymal stem cell-like stroma prepared from placental/umbilical cord blood for hematopoietic regeneration by X-irradiated hematopoietic stem cells is herein assessed.

MAIN METHODS

Placental/umbilical cord blood-derived mesenchymal stem cell-like stromal cells were applied to a regenerative ex vivo expansion of X-irradiated human CD34(+) cells in a serum-free liquid culture supplemented with a combination of interleukine-3 plus stem cell factor plus thrombopoietin.

KEY FINDINGS

The total number of cells and of lineage-committed myeloid hematopoietic progenitor cells generated in the co-culture of both non-irradiated and X-irradiated cells with stromal cells was significantly higher than those in the stroma-free culture. In addition, the number of CD34(+) cells and CD34(+)/CD38(-) cells, immature hematopoietic stem/progenitor cells also increased more than the stroma-free culture. The stromal cells produced various types of cytokines, although there was little difference between the co-cultures of non-irradiated and X-irradiated cells with stromal cells. Furthermore, when X-irradiated cells came in contact with stromal cells for 16 h before cytokine stimulation, a similar degree of hematopoiesis was observed, thus suggesting the critical role of cell-to-cell interaction.

SIGNIFICANCE

The present results showed the potential efficacy of human mesenchymal stem cell-like stroma for hematopoietic regeneration from irradiated hematopoietic stem/progenitor cells.

Synergistic actions of hematopoietic and mesenchymal stem/progenitor cells in vascularizing bioengineered tissues

Poor angiogenesis is a major road block for tissue repair. The regeneration of virtually all tissues is limited by angiogenesis, given the diffusion of nutrients, oxygen, and waste products is limited to a few hundred micrometers. We postulated that co-transplantation of hematopoietic and mesenchymal stem/progenitor cells improves angiogenesis of tissue repair and hence the outcome of regeneration. In this study, we tested this hypothesis by using bone as a model whose regeneration is impaired unless it is vascularized. Hematopoietic stem/progenitor cells (HSCs) and mesenchymal stem/progenitor cells (MSCs) were isolated from each of three healthy human bone marrow samples and reconstituted in a porous scaffold. MSCs were seeded in micropores of 3D calcium phosphate (CP) scaffolds, followed by infusion of gel-suspended CD34⁺ hematopoietic cells. Co-transplantation of CD34⁺ HSCs and CD34⁻ MSCs in microporous CP scaffolds subcutaneously in the dorsum of immunocompromized mice yielded vascularized tissue. The average vascular number of co-transplanted CD34⁺ and MSC scaffolds was substantially greater than MSC transplantation alone. Human osteocalcin was expressed in the micropores of CP scaffolds and was significantly increased upon co-transplantation of MSCs and CD34⁺ cells. Human nuclear staining revealed the engraftment of transplanted human cells in vascular endothelium upon co-transplantation of MSCs and CD34⁺ cells. Based on additional in vitro results of endothelial differentiation of CD34⁺ cells by vascular endothelial growth factor (VEGF), we adsorbed VEGF with co-transplanted CD34⁺ and MSCs in the microporous CP scaffolds in vivo, and discovered that vascular number and diameter further increased, likely owing to the promotion of endothelial differentiation of CD34⁺ cells by VEGF. Together, co-transplantation of hematopoietic and mesenchymal stem/progenitor cells may improve the regeneration of vascular dependent tissues such as bone, adipose, muscle and dermal grafts, and may have implications in the regeneration of internal organs.

Hematopoietic growth factors for hematopoietic stem cell mobilization and expansion

During inflammation and cytopenia, increased levels of hematopoietic growth factors (HPGFs) induce mobilization and proliferation of hematopoietic stem cells and hematopoietic progenitor cells (HPCs), resulting in spatial and quantitative in vivo expansion of the hematopoietic tissue. Exogenous administration of recombinant HPGFs, particularly granulocyte colony-stimulating factor (G-CSF), is routine for mobilization of stem cells, followed by collection and transplantation of autologous or allogeneic stem cells. In this review, we summarize experience using different HPGFs and HPGF combinations for stem cell mobilization, such as G-CSF, granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), stem cell factor (SCF), and others. Preclinical and clinical studies of so-called early- and late-acting HPGFs for ex vivo expansion of HPCs are discussed, also with respect to the unresolved question whether expansion of repopulating stem cells can be achieved in vitro.

Regeneration of Megakaryocytopoiesis and ThrombopoiesisIn Vitrofrom X-Irradiated Human Hematopoietic Stem Cells

In the present study, we investigated whether X-irradiated hematopoietic stem cells can be induced to undergo megakaryocytopoiesis and thrombopoiesis in vitro using cytokine combinations that have been demonstrated to be effective for conferring increased survival on irradiated human CD34(+) megakaryocytic progenitor cells (colony-forming unit megakaryocytes; CFU-Meg), such as thrombopoietin (TPO), interleukin 3 (IL3), stem cell factor and FLT3 ligand. Culture of nonirradiated CD34(+) cells in serum-free medium supplemented with multiple cytokine combinations led to an approximately 200- to 600-fold increase in the total cell numbers by day 14 of culture. In contrast, the growth of X-irradiated cells was observed to be one-sixth to one-tenth that of the nonirradiated cultures. Similarly, total megakaryocytes were increased by 50- to 130-fold, while culture of X-irradiated cells yielded one-fourth to one-eighth of the control numbers. At this time, CD41(+) particles, which appeared to be platelets, were produced in the medium harvested from nonirradiated and irradiated cultures. Although radiation suppressed cell growth and megakaryocytopoiesis, there were no significant differences in thrombopoiesis between the two types of culture. These results suggest that X-irradiated CD34(+) cells can be induced to undergo nearly normal terminal maturation through megakaryocytopoiesis and thrombopoiesis by stimulation with appropriate cytokine combinations.

Bioreactor expansion of human adult bone marrow-derived mesenchymal stem cells

Supplementation of mesenchymal stem cells (MSCs) during hematopoietic stem cell (HSC) transplantation alleviates complications such as graft-versus-host disease, leading to a speedy recovery of hematopoiesis. To meet this clinical demand, a fast MSC expansion method is required. In the present study, we examined the feasibility of using a rotary bioreactor system to expand MSCs from isolated bone marrow mononuclear cells. The cells were cultured in a rotary bioreactor with Myelocult medium containing a combination of supplementary factors, including stem cell factor and interleukin-3 and -6. After 8 days of culture, total cell numbers, Stro-1(+)CD44(+)CD34(-) MSCs, and CD34(+)CD44(+)Stro-1(-) HSCs were increased 9-, 29-, and 8-fold, respectively. Colony-forming efficiency-fibroblast per day of the bioreactor-treated cells was 1.44-fold higher than that of the cells without bioreactor treatment. The bioreactor-expanded MSCs showed expression of primitive MSC markers endoglin (SH2) and vimentin, whereas markers associated with lineage differentiation, including osteocalcin (osteogenesis), type II collagen (chondrogenesis), and C/EBP-alpha (CCAAT/enhancer-binding protein-alpha) (adipogenesis), were not detected. Upon induction, the bioreactor-expanded MSCs were able to differentiate into osteoblasts, chondrocytes, and adipocytes. We conclude that the rotary bioreactor with the modified Myelocult medium reported in this study may be used to rapidly expand MSCs.

Mesenchymal stem cells feeder layer from human umbilical cord blood for ex vivo expanded growth and proliferation of hematopoietic progenitor cells

Ex vivo expansion of hematopoietic stem cells was suggested as the best way of overcoming problems caused by limited hematopoietic cell number for cord blood transplantation. In this study, we quantified and characterized an ex vivo expansion capacity of umbilical cord blood (UCB)-derived mesenchymal stem cells (MSCs) as a cell feeder layer for support of UCB-derived committed hematopoietic progenitor cells (HPCs) in the absence or presence of recombinant cytokines. The UCB-derived MSCs used in the study differentiated into osteoblast, chondrocytes, and adipocytes under proper conditions. Frequencies in colony forming unit-granulocyte, macrophage, colony forming unit-granulocyte, erythrocyte, macrophage, megakaryocyte, burst forming unit-erythrocyte, and colony forming unit-erythrocyte increased to 3.46-, 9.85-, 3.64-, and 2.03-folds, respectively, only in culture supplemented by UCB-derived MSCs as a cell feeder layer without recombinant cytokines (culture condition C). Identified expansion kinetics in all kinds of committed HPCs showed plateaus at 7 culture days, suggesting some consumable components were required for the expansion. Physiological importance and different roles for different committed HPCs of UCB-derived MSCs as a cell feeder layer were revealed by a distinguished expansion capacity for colony forming unit-megakaryocyte. The preferred maintenance of CD33(-)CD34(+) in culture condition C was also identified. The presence of cobblestone-like areas as hematopoietic microenvironment and various cell feeder layer-originated hematopoietic cytokines including interleukin-1beta and granulocyte, macrophage-colony stimulating factor were suggested as underlying mechanisms for the identified expansion capacity. The present numeric and biological information about intrinsic expansion capacity for UCB-derived committed HPCs will increase further biological and clinical applications of UCB-derived MSCs.

Ex Vivo Expansion of Megakaryocyte Progenitor Cells: Cord Blood Versus Mobilized Peripheral Blood

Thrombocytopenia is a problematic and potentially fatal occurrence after transplantation of cord blood stem cells. This problem may be alleviated by infusion of megakaryocyte progenitor cells. Here, we compared the ability of hematopoietic progenitor cells obtained from cord blood and expanded in culture to that of mobilized peripheral blood cells. The CD34(+) cells were plated for 10 days in presence of thrombopoietin (TPO) alone and combined with stem cell factor (SCF), Flt3-ligand (FL), interleukin-3 (IL-3), IL-6, and IL-11. Cells were analyzed for the CD41 and CD42b expression and for their ploidy status. Ex vivo produced platelets were enumerated. We show that (1) TPO alone was able to induce differentiation of CD34(+) cells into CD41(+) cells, with limited total leucocyte expansion; (2) the addition of SCF to TPO decreased significantly CD41(+) cell percentage in CB, but not in MPB; and (3) in CB, the addition of FL, IL-6, and IL-11 to TPO increased the leukocyte expansion with differentiation and terminal maturation into MK lineage. In these conditions, high numbers of immature CD34(+)CD41(+) MK progenitor cells were produced. Our results thereby demonstrate a different sensitivity of CB and MPB cells to SCF, with limited CB MK differentiation. This different sensitivity to SCF (produced constitutively by BM stromal cells) could explain the longer delay of platelet recovery after CB transplant. Nevertheless, in CB, the combination of TPO with FL, IL-6, and IL-11 allows generation of a suitable number of immature MK progenitor cells expressing both CD34 and CD41 antigens, which are supposed to be responsible for the platelet recovery after transplantation.

The comparison of different protocols for expansion of umbilical-cord blood hematopoietic stem cells

Hematopoiesis is maintained by the activity of multipotent stem cells, which have the dual capacity to self-renew and to differentiate into all of the blood cell lineages. The major challenge of stem cells based regenerative therapy is to expand ex vivo the primitive compartment to increase transplantable stem cells number. The present study was designed to evaluate several culture systems for in vitro maintenance of umbilical cord blood stem cells. The influences of different growth conditions such as stromal feeder layer, cytokines supplement and placental conditioned medium (PCM) have been evaluated over a relatively short period of time on CD34(+) cell expansion and maintenance of clonogenic progenitors. When cells were expanded on feeder layer in the presence of added cytokines and PCM on average a 2.96-fold increase of CD34(+)CD71(-) and a 3.13-fold increase of CD34(+)HLA-DR(-) was observed. The total number of colony forming cells (35 +/- 2.65) indicated also that the yield of clonogenic progenitors obtained with a combination of all factors was two folds higher than each of these factors alone and ten time above control (3.67 +/- 2.52). In conclusion, the results of our study clearly show that the ex vivo expansion of hematopoietic progenitor cells obtained from human umbilical cord blood is dependent on controlled experimental conditions, which might be helpful when designing culture systems for clinical applications.

Ex vivo expansion of neutrophil precursor cells from mobilized peripheral blood cells: similar results in cancer patients and normal donors

BACKGROUND

Infusion of ex vivo differentiated myeloid progenitors may reduce or abrogate severe neutropenia following mobilized peripheral blood transplantation. We compared the ex vivo expansion of myeloid progenitor cells starting from cancer patients (CP) and from normal donors (ND) and evaluated the influence of the CD34(+) cell mobilization on the capacities of cells to be expanded.

METHODS

The ex vivo-expanded cells were evaluated for their phenotype, the presence of primary and secondary granules and their functional capacities (oxidative burst activity and phagocytosis).

RESULTS

We did not observe significant differences between ND and CP for the total leukocyte and CD34(+) cell expansions nor for the myeloid progenitor production. In CP as well as in ND, the expanded cells were functionally competent.

DISCUSSION

This suggests that the capacities of CD34(+) cells to proliferate and differentiate ex vivo are not impaired by prior chemotherapy and/or disease status. On the other hand, we did not observe any significant correlation between the number of mobilized CD34(+) cells before apheresis and the cell expansion. In conclusion, the ex vivo expansion of CP and ND cells is comparable and achievable even with a low CD34(+) cell number in mobilized peripheral blood.

Homing efficiency and hematopoietic reconstitution of bone marrow-derived stroma cells expanded by recombinant human macrophage-colony stimulating factor in vitro

The increasing recognition of the properties of marrow stromal cells has spawned a major switch in our perception of their nature and the potential therapeutic applications that have been envisioned and implemented. Yet, several aspects of bone marrow stromal cell biology remain in question. This report describes the ability of recombinant human macrophage colony-stimulating factor (rhM-CSF) to maintain proliferation and differentiation of bone marrow stromal cells ex vivo. Our results demonstrated that M-CSF was essential for proliferation and differentiation of bone marrow-derived stromal cells and exerted its effects in a dose-dependent manner. The number of colony-forming unit (CFU) fibroblasts increased by 25% after incubation with rhM-CSF. In vitro expanded bone marrow stromal cells were easy to passage and differentiated to adipocyte and chondroblast cells under appropriate culture conditions. Furthermore, these expanded stromal cells to support CD34+ hematopoietic stem cells, as demonstrated by their ability to form CFU-Mix, burst-forming units-erythroid, and CFU-granulocyte macrophage colonies after 3 weeks of culture. The homing efficiency of in vitro expanded or fresh isolated bone marrow-derived stromal cells, which were labeled with carboxy fluorescein diacetate succinimidyl ester, to bone marrow was also investigated. Homing assays demonstrated that freshly isolated CD45+-depleted bone marrow cells were able to home to bone marrow in a dose-dependent manner, although some cells were found in the spleen, liver, and lung. However, their ability to home was dramatically reduced with culture time and was completely lost after five to seven passages in vitro. Animal studies showed that freshly isolated or rhM-CSF-induced bone marrow stromal cells promoted hematopoietic reconstitution in lethally irradiated mice. The ability to easily expand human stromal cells, which support survival and proliferation of CD34+ cells, has many important clinical applications for hematopoietic disorders.

The impact of progenitor enrichment, serum, and cytokines on the ex vivo expansion of mobilized peripheral blood stem cells: a controlled trial

The aim of this study was to verify, and possibly improve, culture conditions to expand human mobilized peripheral blood stem cells (PBSCs). We investigated the role of three parameters: A) the culture medium (serum-free versus serum-dependent); B) the initial cell population (Ficoll-separated mononucleated cells versus CD34(+)-selected cells), and C) the low concentration of recombinant cytokines, flt3 ligand, and thrombopoietin in association with a basic cocktail of stem cell factor, interleukin (IL)-6, IL-3, GM-CSF, and erythropoietin. Eighteen leukapheresis samples were monitored in static culture for 15 days. The expansion potential was assessed at day 10 and 15 by total nuclear cells, colony-forming-units (CFUs) (burst-forming units-erythroid [BFU-E], colony-forming units-granulocyte-macrophage [CFU-GM], and colony-forming units-granulocyte-erythroid-macrophage-megakaryocyte [CFU-GEMM]), and flow cytometry immunophenotyping (CD34(+)/CD38(-), CD38(+), CD33(+), CD41(+), GlyA(+) progenitor cells). The results, evaluated by multivariate analysis of variance, emphasize that some variables affected the outcome of stem and progenitor cell expansion. CD34(+) enrichment increased expansion of total nuclear cells, number of CD38(+) and CD33(+) late precursors, and number of the CFU-GM compartment. Interestingly, however, quantitative expansion of GlyA(+) and the early progenitor cells (CD34(+)/CD38(-), CFU-GEMM, BFU-E) are favored by the use of unselected mononucleated cells. Regarding the role of serum, no significant difference was observed except for expansion of total nuclear cells, CFU-GM, and BFU-E. Cytokine combinations, in particular the use of flt3 ligand, stimulated expansion of almost all the cellular subsets, reaching a statistical significance for total nuclear cells and CFU-GM. Our study indicates that progenitor and late precursor multilineage cell compartments of mobilized PBSCs may be significantly expanded in short-term cultures by well-defined experimental conditions. Furthermore, these data might be useful when evaluating ex vivo expansion of hematopoietic cells for clinical purposes.

Basic fibroblast growth factor-stimulated ex vivo expansion of haematopoietic progenitor cells from human placental and umbilical cord blood

We investigated whether basic fibroblast growth factor (bFGF) is effective in inducing ex vivo expansion of CD34+ haematopoietic progenitor cells derived from human placental and umbilical cord blood. bFGF significantly promoted the clonal growth of various haematopoietic progenitor cells, including granulocyte-macrophage colony-forming units (CFU-GM), mixed colony-forming units (CFU-Mix) and megakaryocyte colony-forming units (CFU-Meg) under semisolid culture conditions, with an optimal bFGF concentration of 30 ng/ml. CD34+ cells were then cultured in serum-free liquid medium containing various combinations of early-acting cytokines, including thrombopoietin (TPO), stem cell factor (SCF), interleukin 3 (IL-3) and flt3-ligand (FL), with or without bFGF, for 6 and 12 d. Without bFGF, TPO + IL-3, TPO + SCF + FL and TPO +SCF + IL-3 + FL dramatically increased the total numbers of erythroid progenitors, CFU-GM and CFU-Mix by d 12 of culture respectively. However, the addition of bFGF did not promote further proliferation of these progenitors, except for the erythroid progenitors, by d 6 when stimulated with all four cytokines. In contrast, total CFU-Meg numbers were approximately doubled when these cultures were supplemented with bFGF, producing 100- to 120-fold increases compared with the baseline control cultures. These results suggest that bFGF is effective in supporting the generation of megakaryocytic progenitor cells during ex vivo expansion.

Augmentation of umbilical cord blood (UCB) transplantation with ex vivo-expanded UCB cells: results of a phase 1 trial using the AastromReplicell System

Allogeneic stem cell transplantation with umbilical cord blood (UCB) cells is limited by the cell dose a single unit provides recipients. Ex vivo expansion is one strategy to increase the number of cells available for transplantation. Aastrom Biosciences developed an automated continuous perfusion culture device for expansion of hematopoietic stem cells (HSCs). Cells are expanded in media supplemented with fetal bovine serum, horse serum, PIXY321, flt-3 ligand, and erythropoietin. We performed a phase 1 trial augmenting conventional UCB transplants with ex vivo-expanded cells. The 28 patients were enrolled on the trial between October 8, 1997 and September 30, 1998. UCB cells were expanded in the device, then administered as a boost to the conventional graft on posttransplantation day 12. While expansion of total cells and colony-forming units (CFUs) occurred in all cases, the magnitude of expansion varied considerably. The median fold increase was 2.4 (range, 1.0-8.5) in nucleated cells, 82 (range, 4.6-266.4) in CFU granulocyte-macrophages, and 0.5 (range, 0.09-2.45) in CD34+ lineage negative (lin-) cells. CD3+ cells did not expand under these conditions. Clinical-scale ex vivo expansion of UCB is feasible, and the administration of ex vivo-expanded cells is well tolerated. Augmentation of UCB transplants with ex vivo-expanded cells did not alter the time to myeloid, erythroid, or platelet engraftment in 21 evaluable patients. Recipients of ex vivo-expanded cells continue to have durable engraftment with a median follow-up of 47 months (range, 41-51 months). A randomized phase 2 study will determine whether augmenting UCB transplants with ex vivo-expanded UCB cells is beneficial.

The improved survival of hematopoietic cells cultured with a fusion protein of insulin-like growth factor II (IGF-II) and interleukin 3 (IL-3) is associated with increases in Bcl-xL and phosphatidylinositol-3 kinase activity

We compared the antiapoptotic activity of a recombinant chimera of insulin-like growth factor II (IGF-II) and interleukin (IL)-3 with the corresponding equimolar mixture of the individual components based on changes in several factors associated with survival in the CD34+ human hematopoietic cell line TF-1. Propidium iodide-stained cells analyzed by fluorescein-activated cell sorter indicated that the chimera was more effective than the corresponding equimolar mixture in decreasing the amounts of apoptotic cells and increasing the proportion of cells in the S-phase of the cell cycle. The chimera was more effective in increasing the antiapoptotic protein Bclx(L) and produced a significant increase in signal transducer and activator of transcription-5 phosphorylation and in phosphatidylinositol-3 kinase (PI-3K) activity. The PI-3K inhibitor LY294002 specifically inhibited cell survival in the presence of the chimera, suggesting a key role of this enzyme in the potentiation of survival caused by the linkage of IGF and IL-3. This potentiation of survival and its preferential inhibition by LY294002 were also observed in a nontransformed, primary culture of human umbilical cord endothelial cells.

Investigation into an engraftment defect induced by culturing primitive hematopoietic cells with cytokines

BACKGROUND

Strategies for transplanting primitive hematopoietic progenitor (PHP) cells are under development that require in vitro manipulation of cells for several hours to several days prior to transplantation. This applies to gene-therapy protocols involving transduction with adenoviral or lentiviral vectors (typically 1 day of ex vivo culture) or retroviral vectors (up to 3 days of culture).

METHODS

Human mobilized peripheral blood (MPB) CD34(+) cells were cultured with the cytokines thrombopoietin mimetic peptide (mTPO), flt3 ligand (FL), and c-kit ligand (KL). Equal numbers of CD34(+) cells, either uncultured or cultured for various time periods up to 5 days, were tested for engraftment in sublethally irradiated 8-10 week-old NOD/SCID mice. Cells were also compared for expression and function of several key surface molecules.

RESULTS

At a limiting dose of 1 million cells, mice receiving uncultured cells had a mean of 20% CD45(+) (human) cells in their BM 6 weeks post-transplantation, versus 3% for mice receiving 3-5 day cultured cells. Analysis of 10 surface molecules, CD11a, CD18, CD29, CD49d, CD49e, CXCR-4, CD62L, CD31, CD43, and CD44 over a 5-day culture period showed that their expression levels were either maintained or up-regulated on CD34(+) cells and the primitive Thy-1(+) subset. Similar percentages of uncultured and 3-day cultured MPB CD34(+) cells bound to plates coated with vascular cell adhesion molecule-1 (VCAM-1) under both static and physiological flow conditions, and chemotaxis of cultured cells towards stromal-derived factor-1 (SDF-1) was not impaired, suggesting that VLA-4 and CXCR-4 were functional on cultured cells. CD34(+) Thy-1(+) MPB cells cultured with cytokines expressed increasing levels of Fas receptor beginning at 20 h in culture, with peak expression levels after 3 days (mean Day 0 expression, 39%; mean Day 3 expression, 86%), without increased apoptosis. Including inhibitors of caspases in the media of cells cultured for 24-48 h significantly improved their engraftment in a SCID-hu bone-engraftment model.

DISCUSSION

Increased susceptibility to apoptosis upon in vivo injection may contribute to impaired engraftment of in vitro manipulated cells. Inhibitors of apoptosis may increase their engrafting capacity in clinical settings.

Expansion of megakaryocyte progenitors from cryopreserved leukocyte concentrates of human placental and umbilical cord blood in short-term liquid culture

Long-term severe thrombocytopenia following human placental and umbilical cord blood (CB) transplantation is a significant clinical problem. We studied the ex vivo expansion of megakaryocytic progenitor cells (CFU-Meg) from cryopreserved/thawed leukocyte concentrates (LC) of CB prepared by the Tokyo Cord Blood Bank protocol. The LC cells were cultured in serum-free culture medium supplemented with a combination of early-acting cytokines including thrombopoietin (TPO), flt3-ligand (FL), and stem cell factor (SCF). Combination of TPO plus FL, TPO plus SCF, and all of these cytokines together resulted in 8.9-, 7.7-, and 8.4-fold increases in CFU-Meg, respectively, by Day 5 of culture. Our results showed that this simple expansion strategy has the potential for expanding CFU-Meg from cryopreserved/thawed LC cells from CB.

Cultivation of hematopoietic stem and progenitor cells: biochemical engineering aspects

The ex vivo expansion of hematopoietic cells is one of the most challenging fields in cell culture. This is a rapidly growing area of tissue engineering with many potential applications in bone marrow transplantation, transfusion medicine or gene therapy. Over the last few years much progress has been made in understanding hematopoietic differentiation, discovery of cytokines, isolation and identification of cellular subtypes and in the development of a variety of bioreactor concepts. All this has led to a number of (preliminary) clinical trials that gave a hint of the benefits that can be obtained from the use of expanded hematopoietic cells in therapy. Moreover, as we understand the complexity and the regulation of hematopoiesis, it becomes obvious that highly sophisticated cultivation techniques and bioreactor concepts are needed: a new challenge for bioprocess engineering in cell culture.

Reinjection of ex vivo-expanded primate bone marrow mononuclear cells strongly reduces radiation-induced aplasia

To assess the therapeutic efficacy of ex vivo-expanded hematopoietic cells in the treatment of radiation-induced pancytopenia, we have set up a non-human primate model. Two ex vivo expansion protocols for bone marrow mononuclear cells (BMMNC) were studied. The first consisted of a 7-day culture in the presence of stem cell factor (SCF), Flt3-ligand, thrombopoietin (TPO), interleukin-3 (IL-3), and IL-6, which induced preferentially the expansion of immature hematopoietic cells [3.1 +/- 1.4, 10.0 +/- 5.1, 2.2 +/- 1.9, and 1.0 +/- 0.3-fold expansion for mononuclear cells (MNC), colony-forming units-granulocyte-macrophage (CFU-GM), burst-forming units erythroid (BFU-E), and long-term culture initiating cells (LTC-IC) respectively]. The second was with the same cytokine combination supplemented with granulocyte colony-stimulating factor (G-CSF) with an increased duration of culture up to 14 days and induced mainly the production of mature hematopoietic cells (17.2 +/- 11.7-fold expansion for MNC and no detectable BFU-E and LTC-IC), although expansion of CFU-GM (13.7 +/- 18.8-fold) and CD34+ cells (5.2 +/- 1.4-fold) was also observed. Results showed the presence of mesenchymal stem cells and cells from the lymphoid and the megakaryocytic lineages in 7-day expanded BMMNC. To test the ability of ex vivo-expanded cells to sustain hematopoietic recovery after radiation-induced aplasia, non-human primates were irradiated at a supralethal dose of 8 Gy and received the product of either 7-day (24 h after irradiation) or 14-day (8 days after irradiation) expanded BMMNC. Results showed that the 7-day ex vivo-expanded BMMNC shortened the period and the severity of pancytopenia and improved hematopoietic recovery, while the 14 day ex vivo-expanded BMMNC mainly produced a transfusion-like effect during 8 days, followed by hematopoietic recovery. These results suggest that ex vivo expanded BMMNC during 7 days may be highly efficient in the treatment of radiation-induced aplasia.

Effects of amifostine on the proliferation and differentiation of megakaryocytic progenitor cells

This study investigated the effects of amifostine, a clinically usable radioprotector or chemoprotector, on the proliferation and differentiation of normal and X-irradiated cluster of differentiation 34 positive (CD34+) megakaryocytic progenitor cells (colony-forming unit in megakaryocytes, CFU-Meg) from human placental and umbilical cord blood (CB) in vitro. Amifostine significantly accelerated megakaryocyte colony formation in a plasma clot culture supplemented with recombinant human thrombopoietin because of an increase in immature CFU-Meg-derived large megakaryocyte colony formation. An analysis of the cells that were harvested from the culture showed that amifostine induced a 70- and an 83-fold increase in the total cell and CFU-Meg numbers, respectively, and produced hyperploid megakaryocytes of more than 8 N ploidy. The radioprotective effect of amifostine on the clonal growth of X-irradiated CD34+ CFU-Meg was observed by treatment before or after irradiation. These findings suggest that the action of amifostine extends from immature CFU-Meg to the terminal differentiation of megakaryopoiesis, and its radioprotective effect is shown in megakaryopoiesis and thrombopoiesis.

[Effects of glycosaminoglycans on the in vitro colony formation of CD34+ megakaryocytic progenitor cells in human placental/umbilical cord blood]

The in vitro effect of various glycosaminoglycans (GAGs) on the clonal growth of CD34+ megakaryocytic progenitor cells (CFU-Megs) isolated from human placental/umbilical cord blood (CB) was evaluated in human plasma containing semisolid culture stimulated by recombinant human thrombopoietin (TPO). The GAGs, including hyaluronic acid from human umbilical cords (HA-h), pig skins (HA-p) and rooster combs (HA-r), or keratan sulfate (KS), various chondroitin sulfates (CS-A, B, C, D, E), and heparan sulfate (HS), were tested. Each GAG alone did not affect the clonal growth of CFU-Meg. In the presence of TPO, adding of HA-p or HS (100 micrograms/ml) resulted in an approximately 1.3-fold increase, in the total number of colonies, due to an increase in large megakaryocyte colonies. In contrast, CS-E led to a marked decrease in CFU-Meg growth. At the end of the culture, the total number of cells increased 3.0-fold of the initial value of the control, but adding HA-p or HS showed an approximately 9.1-fold or 18.3-fold increase. Similarly, the total number of CFU-Meg detected in the harvested cells increased to 4.8-fold of the initial value, while, an approximately 18.3-fold or 38.8-fold increase was observed in the culture containing HA-p or HS, respectively. Flow cytometric analysis of the harvested cells showed no significant difference in the expression of surface antigens and DNA ploidy distribution of megakaryocytes between the control and GAG treatments. These results suggest that HA-p and HS promote the proliferation of immature CB CD34+ CFU-Meg in the presence of TPO.

IL-10 increases the number of CFU-GM generated by ex vivo expansion of unmanipulated human MNCs and selected CD34+ cells

BACKGROUND

Ex vivo expansion strategies with different cytokine combinations are currently used by several groups as a means of increasing the number of HPCs for a variety of special clinical applications. Because there is little information on the potential role of IL-10 in such ex vivo expansion models, the effect of this cytokine on the generation of myeloid progenitor cells in suspension cultures was investigated.

STUDY DESIGN AND METHODS

On the basis of data from the literature and from new experiments, the combination of SCF and IL-3 at concentrations of 100 ng per mL and 100 U per mL, respectively, was chosen as the standard cocktail. The addition of IL-10 to such cultures resulted in a marked and dose-dependent potentiation of myeloid progenitor cell production.

RESULTS

Using unmanipulated leukapheresis components from 13 individuals (including lymphoma and cancer patients and normal donors), the expansion multiple of CFU-GM after 14 days as compared with pre-expansion values was 9.54 +/- 2.31 times by SCF/IL-3 and 46.38 +/- 7.37 times by the combination of SCF/IL-3 and 100 ng per mL of IL-10 (p<0.001). IL-10 also potentiated CFU-GM generation from selected CD34 PBMNCs (n = 9) with an expansion of 17.22 +/- 7.04 times versus 45.67 +/- 16.78 times using the SCF/IL-3 and SCF/IL-3/IL-10 combination, respectively (p<0.05). Moreover, expansion-promoting effects of IL-10 were observed in liquid cultures containing MNCs from bone marrow (n = 4) and cord blood (n = 3), but did not reach statistical significance because of the small number of samples.

CONCLUSION

These results suggest IL-10 as a useful cytokine to optimize progenitor cell-expansion strategies for clinical application.

Signal through gp130 activated by soluble interleukin (IL)-6 receptor (R) and IL-6 or IL-6R/IL-6 fusion protein enhances ex vivo expansion of human peripheral blood-derived hematopoietic progenitors

This study was designed to investigate the effects of a combination of soluble interleukin (sIL)-6 receptor (R) and IL-6 on the ex vivo expansion of human peripheral blood (PB)-derived hematopoietic progenitor cells in a short-term serum-free liquid suspension culture system, using PB-derived CD34(+)IL-6R(+/-) cells as a target. In combination with stem cell factor (SCF), IL-3, and sIL-6R/IL-6, the expansion efficiency (EE) for granulocyte/macrophage colony-forming unit (CFU-GM) reached a peak level on day 10 of incubation. On the other hand, the EE for erythroid burst (BFU-E) and mixed colony-forming unit (CFU-Mix) reached a peak level on day 7 of incubation. Among the cytokine combinations tested, SCF + IL-3 + sIL-6R/IL-6 + flt3 ligand (FL) most effectively expanded CFU-GM and CFU-Mix. The maximum EEs for CFU-GM and CFU-Mix were 208-fold and 42-fold, respectively. While the EE for BFU-E was 70-90-fold in the presence of SCF + IL-3 + sIL-6R/IL-6, FL significantly augmented the EE for CFU-GM and CFU-Mix. In contrast, thrombopoietin (TPO) significantly augmented the EE for CFU-Mix. Interestingly, in combination with IL-3 and SCF, newly generated IL-6R/IL-6 fusion protein (FP) expanded PB-derived BFU-E and CFU-Mix twice more effectively than a combination of sIL-6R and IL-6. These results demonstrated that human PB-derived committed progenitors were effectively expanded in vitro using sIL-6R/IL-6 or FP, in combination with IL-3, SCF and/or FL or TPO, and that FP may transduce a stronger intracellular signal than a combination of sIL-6R and IL-6.

Ex vivo-expanded hematopoietic cell graft recipients exhibit T cell repertoire diversity similar to that seen after conventional stem cell transplants

The feasibility of using ex vivo-expanded hematopoietic progenitor cells to reconstitute hematopoiesis after high-dose chemotherapy is presently being examined. Early studies have shown that myeloid and erythroid hematopoiesis can be successfully reconstituted after high-dose chemotherapy and ex vivo-expanded hematopoietic cell transplantation. The lymphoid reconstitution, however, has not been addressed previously. In this study, we examined the diversity of the T cell receptor V beta chain (TCRBV) repertoires in 5 breast cancer patients who were transplanted with ex vivo-expanded bone marrow mononuclear cells as the only source of hematopoietic graft. Using the TCRBV third complementarity determining region (CDR3) fingerprinting methodology, it is shown that CD4(+) and CD8(+) T cell subsets after ex vivo-expanded hematopoietic cell graft transplants exhibit TCRBV diversities that are similar in complexity when compared to those seen after conventional autologous peripheral blood stem cell transplants (PBSCT). No apparent difference in the extent of CDR3 diversity was found between ex vivo expanded and conventional autologous PBSCT recipients when the CD4(+) and CD8(+) subsets were further separated into CD45RA(+) "naïve" and CD45RO(+) "memory" subsets. The diversity of the CD45RA(+) naïve subsets was as complex as that of the CD45RO(+) memory subsets. These results indicate that T cell repertoire diversification is not further compromised when ex vivo-expanded hematopoietic cells are used instead of autologous peripheral blood stem cells as the only source of graft.

Ig heavy chain CDR3 size diversities are similar after conventional peripheral blood and ex vivo expanded hematopoietic cell transplants

It is largely unknown whether the immune repertoire can be reconstituted successfully after high-dose chemotherapy and transplantation using ex vivo expanded hematopoietic stem cell (HSC) grafts. It is critically important for the transplant outcome that immune repertoire reconstitution progresses after ex vivo expanded HSC graft transplants at least as efficiently as that seen after conventional HSC transplants. Previously, we showed that the T cell receptor V beta (TCRVB) third complementarity determining region (CDR3) diversification after ex vivo expanded bone marrow (BM) HSC graft transplants was similar to that seen after conventional peripheral blood stem cell transplants (PBSCTs). In the present study, the CDR3 diversity of the six immunoglobulin (Ig) heavy chain variable region gene (V(H)) families was examined in five breast cancer patients who were transplanted with ex vivo expanded BM HSCs as the only source of stem cells. For comparison, 12 healthy adults and four conventional PBSCT recipients were also studied. Using both CDR3 fingerprinting and single strand conformation polymorphism (SSCP) methodologies, it is shown that the contribution of the V(H) families to the overall repertoire among healthy adults is highly variable and not always proportional to V(H) family member size. After both ex vivo expanded HSC transplants and conventional PBSCTs, the V(H) CDR3 repertoires were limited in size diversity at 6 weeks post transplant. By 6 months, however, V(H) families displayed a repertoire diversity that was as complex as that seen in healthy adults. No difference was seen between ex vivo expanded HSC graft transplant recipients and conventional PBSCT recipients in V(H) repertoire diversity. In one patient there was a follow-up analysis 12 months after ex vivo expanded graft transplant, and the diversity of the V(H) families was maintained. In all patients, the amino acid size of the CDR3 regions fell within adult limits at all time points post transplant. These results indicate that B cell repertoire regeneration after ex vivo expanded hematopoietic cell graft transplants is similar to that seen after conventional PBSCT.

Ex vivo expansion of transplantable human hematopoietic stem cells: where do we stand in the year 2000?

Ex vivo expansion of hematopoietic precursors, progenitors and stem cells represents the modern era of cellular therapeutics in the 21st century. For the last 10 years, increasing means for identifying and purifying hematopoietic stem cells and cytokines have facilitated and improved the development of ex vivo stem cell expansion technology. However, technology has not yet reached a stage where ex vivo-expanded hematopoietic progenitors and stem cells can be used routinely for replacement therapy. Lessons learned over the past 10 years from investigations focused at developing optimal ex vivo stem cell expansion systems have continued to a much greater understanding of stem cell biology. This knowledge has led to novel attempts at ex vivo expansion of hematopoietic precursors, progenitors, and stem cells, and should facilitate development of a new generation of cellular therapeutics. This review addresses recent progress toward development of clinically useful protocols for stem cell expansion. In addition, we discuss the results of a limited number of clinical trials that address the efficacy of such procedures. Three major areas of ex vivo stem cell expansion that impact clinical feasibility are discussed, including: (1) selection of an optimal stem cell population for expansion, (2) definition of the desired characteristics of the expanded stem cell population to be used for engraftment, and (3) development of new reagents and procedures for expansion and infusion of hematopoietic progenitors and stem cells.

Ex vivo expansion of CD34-positive peripheral blood progenitor cells from patients with non-Hodgkin's lymphoma: no evidence of concomitant expansion of contaminating bcl2/JH-positive lymphoma cells

The aim of the present study was to evaluate the capacity to expand of hematopoietic stem cell (HSC) samples from eight patients with NHL, and to follow in parallel the fate of tumor cells in four of eight samples still containing bcl2/JH+ tumor cells after CD34+ or CD19-/20-/34+ cell selection. The presence of bcl2/JH+ cells was also investigated after expansion in four of eight samples, two of which were bcl2/JH at harvesting and two which were initially bcl2/JH+ but became bcl2/JH (below the level of PCR detection) after cell selection, to assess a possible reappearance of occult tumor cells after expansion culture. We used culture conditions that we previously had established to allow high level expansion of normal precursors, progenitors and LTC-ICs. In this study, particular attention was given to the role of Flt3-ligand, known to favor the growth of B cells. The expansion conditions were: 1.5 x 10(3) cells/ml in serum-free medium containing stem cell factor (SCF), interleukin-3 (IL-3), IL-6, granulocyte-stimulating factor (G-CSF), erythropoietin (Epo) +/- Flt3-ligand (Flt3-L) for 10 days. After culture, total cells, CFU-GMs, BFU-Es and LTC-ICs were expanded to a mean of 833-, 6.6-, 4.6-, and 1.8-fold, respectively with the cocktail of cytokines not including Flt3-L. When Flt3-L was added, the mean expansion values were 1095-, 31-, 15- and three-fold, respectively. Residual bcl2/JH+ cells present in four of eight samples before expansion were not detected after expansion. Similarly, no tumor cells reappeared after expansion of the two samples which had become negative after selection, as well as in the two samples which were bcl2/JH- at harvesting. These results suggest first that ex vivo expansion of hematopoietic stem cells in patients with non-Hodgkin's lymphoma is feasible without incurring the parallel risk of amplifying tumor cells; second, that Flt3-L did not stimulate the growth of tumor cells while it clearly favored the growth of normal progenitors.