Ex vivo expansion of haemopoietic progenitor cells

Over the last few years, techniques have become available that allow the extensive proliferation of haemopoietic progenitor cells in ex vivo culture systems. The most commonly used method involves a simple liquid suspension culture system supplemented with a range of cytokines. Alternatively, more complex systems have been devised in which the formation of a stromal layer is required. Large increases in total cell numbers and committed progenitor cells can be readily obtained and, with some techniques, significant expansion of primitive haemopoietic cells has been demonstrated. Although these strategies have several potential applications, few clinical studies have been performed. It has been shown that infusion of ex vivo cultured cells is well tolerated with no associated toxicity. However, it is still unclear whether these culture systems sustain sufficient numbers of long-term repopulating cells to secure durable engraftment following myeloablative therapy. In gene therapy studies, ex vivo expansion of stem cells should improve the efficiency of gene transduction to enable the production of genetically modified cells that are capable of expressing the gene of interest for extended periods of time.     

Ex vivo generation of functional dendritic cells from mobilized CD34+ hematopoietic stem cells

Gene engineering to enhance tumour immunogenicity and elicit curative responses against established tumours and tumour recurrences has become an attractive prospect. Gene engineering enables new genes to be selectively inserted into the genome of a tumour cell, or the construction of new fusion plasmids coding tumour antigens and immunomodulatory molecules. The rationale behind current research is to enhance the immune recognition of tumour antigens through their association with the molecules on which immune recognition depends. The immunotherapy data obtained in many experimental tumour systems provide a realistic assessment of the potential and limits of this technological approach. Experimental vaccination of rodents has been shown to induce a significant immune memory, even against poorly immunogenic tumours, that can prevent tumour growth and cure initial metastases, but is poorly effective against established tumours. Its use in tumour prevention is a fresh dawning perspective.     

Ex vivo expansion of genetically marked rhesus peripheral blood progenitor cells results in diminished long-term repopulating ability

The possibility of primitive hematopoietic cell ex vivo expansion is of interest for both gene therapy and transplantation applications. The engraftment of autologous rhesus peripheral blood (PB) progenitors expanded 10 to 14 days were tracked in vivo using genetic marking. Stem cell factor (SCF)/granulocyte colony-stimulating factor (G-CSF)-mobilized and CD34-enriched PB cells were divided into two equal aliquots and transduced with one of two retroviral vectors carrying the neomycin-resistance gene (neo) for 4 days in the presence of interleukin-3 (IL-3), IL-6, and SCF in the first 5 animals, IL-3/IL-6/SCF/Flt-3 ligand (FLT) in 2 subsequent animals, or IL-3/IL-6/SCF/FLT plus an autologous stromal monolayer (STR) in the final 2. At the end of transduction period, one aliquot (nonexpanded) from each animal was frozen, whereas the other was expanded under the same conditions but without vector for a total of 14 days before freezing. After total body irradiation, both the nonexpanded and expanded transduced cells were reinfused. Despite 5- to 13-fold higher cell and colony-forming unit (CFU) doses from the expanded fraction of marked cells, there was greater short- and long-term marking from the nonexpanded cells in all animals. In animals receiving cells transduced and expanded in the presence of IL-3/IL-6/SCF/FLT, engraftment by the marked expanded cells was further diminished. This discrepancy was even more pronounced in the animals who received cells transduced and expanded in the presence of FLT and autologous stroma, with no marking detectable from the expanded cells. Despite lack of evidence for expansion of engrafting cells, we found that the addition of FLT and especially STR during the initial brief transduction period increased engraftment with marked cells into a clinically relevant range. Levels of marked progeny cells originating from the nonexpanded aliqouts were significantly higher than that seen in previous 4 animals receiving cells transduced in the presence of IL-3/IL-6/SCF, with levels of 10% to 20% confirmed by Southern blotting from the nonexpanded IL-3/IL-6/SCF/FLT/STR graft compared with 0.01% in the original IL-3/IL-6/SCF cohort. These results suggest that, although expansion of PB progenitors is feasible ex vivo, their contribution towards both short- and long-term engraftment is markedly impaired. However, a brief transduction in the presence of specific cytokines and stromal support allows engraftment with an encouraging number of retrovirally modified cells.     

Increased recruitment of hematopoietic progenitor cells underlies the ex vivo expansion potential of FLT3 ligand

The ligand for flt-3 (FLT3L) exhibits striking structural homology with stem cell factor (SCF) and monocyte colony-stimulating factor (M-CSF) and also acts in synergy with a range of other hematopoietic growth factors (HGF). In this study, we show that FLT3L responsive hematopoietic progenitor cells (HPC) are CD34+CD38-, rhodamine 123dull, and hydroperoxycyclophosphamide (4-HC) resistant. To investigate the basis for the capacity of FLT3L to augment the de novo generation of myeloid progenitors from CD34+CD38- cells, single bone marrow CD34+CD38- cells were sorted into Terasaki wells containing serum-free medium supplemented with interleukin-3 (IL-3), IL-6, granulocyte colony-stimulating factor (G-CSF), SCF (4 HGF) +/- FLT3L. Under these conditions, FLT3L recruited approximately twofold more CD34+CD38- cells into division than 4 HGF alone. The enhanced proliferative response to FLT3L was evident by day 3 and was maintained at all subsequent time points examined. In accord with these findings, we also show that transduction of CD34+CD38- cells with the LAPSN retrovirus is enhanced by FLT3L. The results of these experiments therefore indicate that increased recruitment of primitive HPC into cell cycle underlies the ex vivo expansion potential of FLT3L and also its ability to improve retroviral transduction of HPC.     

Ex vivo culture of peripheral blood CD34+ cells: effects of hematopoietic growth factors on production of neutrophilic precursors

A major potential application for ex vivo culture of hematopoietic progenitor cells is the treatment of cytopenia following high-dose chemotherapy and hematopoietic transplantation. We have previously postulated that infusion of a sufficient number of neutrophil postprogenitor cells generated by ex vivo culture of CD34+ cells may be able to abrogate neutropenia. In this article, we describe further development of an efficient stromal-free, cytokine-dependent, static culture system for generation of these cells. Our previous studies indicated that maximal production of nucleated cells and myeloid progenitor cells from PB CD34+ cells occurred with multiple hematopoietic growth factor (HGF), notably the 6-HGF combination of interleukin (IL)-1, IL-3, IL-6, granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage-CSF (GM-CSF), and stem cell factor (SCF). In the present study, we determine the contribution of each of these 6 HGF in generation of neutrophilic precursors. SCF, G-CSF, and IL-3 were found to be the most important HGF for production of neutrophilic cells. The 4-HGF combination of IL-3, IL-6, G-CSF, and SCF was optimized by performing dose-response experiments and shown to be as potent as 6 HGF for production of nascent CFU-GM and neutrophilic precursors.     

Ex vivo generation of human anti-pre-B leukemia-specific autologous cytolytic T cells

In contrast to other neoplasms, antigen-specific autologous cytolytic T cells have not been detected in patients with human pre-B-cell leukemias. The absence of efficient B7 family (B7-1/CD80; B7-2/CD86) -mediated costimulation has been shown to be a major defect in tumor cells' capacity to function as antigen-presenting cells. We show here the generation of autologous anti-pre-B-cell leukemia-specific cytolytic T-cell lines from the marrows of 10 of 15 patients with pre-B-cell malignancies. T-cell costimulation via CD28 is an absolute requirement for the generation of these autologous cytolytic T cells (CTL). Although costimulation could be delivered by either bystander B7 transfectants or professional antigen-presenting cells (indirect costimulation), optimal priming and CTL expansion required that the costimulatory signal was expressed by the tumor cell (direct costimulation). These anti-pre-B-cell leukemia-specific CTL lysed both unstimulated and CD40-stimulated tumor cells from each patient studied but did not lyse either K562 or CD40-stimulated allogeneic B cells. Cytolysis was mediated by the induction of tumor cell apoptosis by CD8+ T cells via the perforin-granzyme pathway. Although we were able to generate anti-leukemia-specific CTL from the bone marrow, we were unable to generate such CTL from the peripheral blood of these patients. These studies show that antigen-specific CTL can be generated from the bone marrow of patients with pre-B-cell leukemias and these findings should facilitate the design of adoptive T-cell-mediated immunotherapy trials for the treatment of patients with B-cell precursor malignancies.     

In vivo telomere dynamics of human hematopoietic stem cells

Aging in vivo and cell division in vitro are associated with telomere shortening. Several lines of evidence suggest that telomere length may be a good predictor of the long term replicative capacity of cells. To investigate the natural fate of chromosome telomeres of hematopoietic stem cells in vivo, we measured the telomere length of peripheral blood granulocytes from 11 fully engrafted bone marrow transplant recipients and from their respective donors. In 10 of 11 donor-recipient pairs, the telomere length was significantly reduced in the recipient and the extent of reduction correlated inversely with the number of nucleated cells infused. These data provide internally controlled in vivo evidence that, concomitantly with their proliferation, hematopoietic stem cells lose telomere length; it is possible that, as a result, their proliferative potential is reduced. These findings must be taken into account when developing new protocols in which few stem cells are used for bone marrow transplantation or for gene therapy.     

Ex vivo transduction of corneal epithelial progenitor cells using a retroviral vector

An in vivo model was used to determine whether bone hyperemia precedes increased intracortical porosity induced by disuse. Twenty-four adult male roosters (age 1 yr) were randomly assigned to intact-control, 7-days-sham-surgery, 7-days-disuse, and 14-days-disuse groups. Disuse was achieved by isolating the left ulna diaphysis from physical loading via parallel metaphyseal osteotomies. The right ulna served as an intact contralateral control. Colored microspheres were used to assess middiaphyseal bone blood flow. Bone blood flow was symmetric between the left and right ulnae of the intact-control and sham-surgery groups. After 7 days of disuse, median (+/-95% confidence interval) standardized blood flow was significantly elevated compared with the contralateral bone (6.5 +/- 5.2 vs. 1.0 +/- 0.8 ml x min-1 x 100 g-1; P = 0.03). After 14 days of disuse, blood flow was also elevated but to a lesser extent. Intracortical porosity in the sham-surgery and 7-days-disuse bones was not elevated compared with intact-control bones. At 14 days of disuse, the area of intracortical porosity was significantly elevated compared with intact control bones (0.015 +/- 0.02 vs. 0. 002 +/- 0.002 mm2; P = 0.03). We conclude that disuse induces bone hyperemia before an increase in intracortical porosity. The potential interaction between bone vasoregulation and bone cell dynamics remains to be studied.     

Calcium kinetic investigations and their clinical use

Pool sizes and internal fluxes of minerals can be quantitatively determined by tracer-kinetic investigations and compartmental analysis. Investigations performed in 252 patients revealed characteristic patterns for calcium pools and fluxes with respect to disease. The method provides a useful diagnostic tool in the early detection of metabolic bone disorders and in problems of differential diagnostics.     

Inhibition of interleukin-1beta-converting enzyme in human hematopoietic progenitor cells results in blockade of cytokine-mediated apoptosis and expansion of their proliferative potential

This article describes the stabilization/solidification (S/S) of a steel industry waste, using a common type-F fly ash from a coal power station as the main binder. The waste, which contains hazardous levels of metals, may be stabilized by a conventional S/S to achieve permissible Pb, Cd, and Zn concentrations in the Toxicity Characteristic Leaching Procedure (TCLP) leachates of S/S solids. On the other hand, the stabilization of Cr(VI), also present in the waste, requires a reducing pretreatment stage with ferrous sulfate to attain TCLP leachates within limits. A bibliographic study on the stabilization of Cr(VI)-containing wastes is included in the paper, along with a discussion on the lowest Cr concentration in TCLP and aqueous (DIN) leachates.     

Ex vivo expansion with stem cell factor and interleukin-11 augments both short-term recovery posttransplant and the ability to serially transplant marrow

The characterization of many cytokines involved in the control of hematopoiesis has led to intense investigation into their potential use in ex vivo culture to expand progenitor numbers. We have established the optimum ex vivo culture conditions that allow substantial amplification of transient engrafting murine stem cells and which, simultaneously, augment the ability to sustain serial bone marrow transplantation (BMT). Short-term incubation of unfractionated BM cells in liquid culture with stem cell factor (SCF) and interleukin-11 (IL-11) produced a 50-fold amplification of clonogenic multipotential progenitors (CFU-A). Following such ex vivo expansion, substantially fewer cells were required to rescue lethally irradiated mice. When transplanted in cell doses above threshold for engraftment, BM cells expanded ex vivo resulted in significantly more rapid hematopoietic recovery. In a serial transplantation model, unmanipulated BM was only able to consistently sustain secondary BMT recipients, but BM expanded ex vivo has sustained quaternary BMT recipients that remain alive and well more than 140 days after 4th degree BMT. These results show augmentation of both short-term recovery posttransplant and the ability to serially transplant marrow by preincubation in culture with SCF and IL-11.     

A potential molecular approach to ex vivo hematopoietic expansion with recombinant epidermal growth factor receptor-expressing adenovirus vector

Ex vivo expansion of hematopoietic stem cell (HSC) is an attractive technology for its potency of a variety of clinical applications. Such a technology has been achieved to some extent with combinations of various cytokines or continuous perfusion cultures. However, much more improvement is required especially for expansion of primitive hematopoietic progenitors. We propose here a novel molecular approach that might have the potential to compensate the current expansion. We designed an adenovirus vector to transiently express human epidermal growth factor receptor (EGFR), which is known to transduce only a mitogenic, but not a differentiation signal to mouse bone marrow cells on human purified CD34+ peripheral blood (PB) cells, and tried to expand these cells with EGF ex vivo. Because we found that exposure of CD34+ PB cells to cytokines induced surface expression of adenovirus-internalization receptor and rendered these cells permissive to adenovirus infection, we infected these cells with the adenovirus vector carrying EGFR gene in the presence of cytokines. Two-color flow cytometric analysis demonstrated that 60.3% +/- 22.4% of CD34+ cells expressed the adenovirus-mediated EGFR. Moreover, long-term culture-initiating cell assay showed that adenovirus vector could transduce more primitive progenitors. Subsequently, we tried to expand these cells in suspension culture with EGF for 5 days. Methylcellulose clonal assay showed that EGF induced 5.0- +/- 2.4-fold proliferation of the colony-forming unit pool during 5 days of expansion. The simple procedure of efficient adenovirus gene delivery to immature hematopoietic cells proved promising, and this technique was potentially applicable for a novel strategy aiming at ex vivo expansion of hematopoietic progenitors.     

The in vivo balance between B cell clonal expansion and elimination is regulated by CD95 both on B cells and in their micro-environment

In congenital nephrogenic diabetes insipidus, the renal collecting ducts are resistant to the antidiuretic action of arginine vasopressin or to its antidiuretic analog 1-deamino[8-D-arginine] vasopressin (dDAVP). This is a rare, but now well described entity secondary to either mutations in the AVPR2 gene that codes for the vasopressin antidiuretic (V2) receptor or to mutations in the AQP2 gene that codes for the vasopressin-dependent water channel. A majority (> 90%) of congenital nephrogenic diabetes insipidus patients have AVPR2 mutations: Of 115 families with congenital nephrogenic diabetes insipidus, 105 families had AVPR2 mutations, and 10 had AQP2 mutations. When studied in vitro, most AVPR2 mutations lead to receptors that are trapped intracellularly and are unable to reach the plasma membrane. A minority of the mutant receptors reach the cell surface but are unable to bind vasopressin or to trigger an intracellular adenosine 3:5-cyclic phosphate signal properly. Most of the reported mutations are secondary to a complete loss of function of the receptor, and only a few mutations have been associated with a mild phenotype. These advances provide diagnostic tools for physicians caring for these patients because, when the disease causing mutation has been identified, carrier and perinatal testing could be done by mutation analysis.     

Engraftment of ex vivo expanded and cycling human cord blood hematopoietic progenitor cells in SCID mice

The ability of human hematopoietic cells to engraft SCID mice provides a useful model in which to study the efficiency of retroviral gene transfer and expression in primitive stem cells. In this regard, it is necessary to determine whether SCID mice can be engrafted by cycling human hematopoietic progenitor cells. Human cord blood cells from 12 different donors were cultured in vitro for 6 days with interleukin-3 and stem cell factor. Phenotypic analysis indicated that hematopoietic cells were induced to cycle and the number of progenitors was expanded, thus making them targets for retroviral gene transfer. The cells were then transferred to SCID mice. Human hematopoietic progenitor cell engraftment was assessed up to 7 weeks later by growth of human progenitor cells in soft agar. After in vitro culture under conditions used for retroviral gene transfer, human cord blood hematopoietic cells engrafted the bone marrow and spleen of SCID mice. Interestingly, cultured cord blood cells engrafted after intraperitoneal but not after intravenous injection. Furthermore, engraftment of cord blood cells was observed in mice receiving no irradiation before transfer of the human cells, suggesting that competition for space in the marrow is not a limiting factor when these cells have been cultured. Administration of human cytokines after transfer of human cord blood cells to SCID mice was also not required for engraftment. Thus, engraftment of SCID mice with human hematopoietic cells cultured under conditions suitable for gene transfer may provide an in vivo assay for gene transfer to early human hematopoietic progenitor cells.     

In vitro expansion of hematopoietic progenitor cells induces functional expression of Fas antigen (CD95)

Fas antigen (Fas Ag; CD95) is a cell surface molecule that can mediate apoptosis. Bcl-2 is a cytoplasmic molecule that prolongs cellular survival by inhibiting apoptosis. To investigate the role of both molecules in hematopoiesis, we evaluated the expression of Fas Ag and Bcl-2 on CD34+ hematopoietic progenitor cells expanded in vitro. CD34+ cells isolated from bone marrow were cultured in iscove's modified Dulbecco's medium supplemented with 10% fetal calf serum, 1% bovine serum albumin, 50 ng/mL stem cell factor, 50 ng/mL interleukin-3 (IL-3), 50 ng/mL IL-6, 100 ng/mL granulocyte colony-stimulating factor, and 3 U/mL erythropoietin for 7 days. Colony-forming unit of granulocytes/macrophages (CFU-GM) and burst-forming unit of erythroids (BFU-E) were expanded 6.9-fold and 8.8-fold in number at day 5 of culture, respectively. Freshly isolated CD34+ cells did not express Fas Ag, whereas approximately half of them expressed Bcl-2. CD34+ cells cultured with hematopoietic growth factors gradually became positive for Fas Ag and rapidly lost Bcl-2 expression. Furthermore, apoptosis was induced in the cultured CD34+ population when anti-Fan antibody (IgM; 1 microgram/mL) was added, as shown by significant decrease in the number of viable cells, morphologic changes, induction of DNA fragmentation, and significant decrease in the number of clonogenic progenitor cells including CFU. GM and BFU-E. These results indicate that functional expression of Fas Ag is induced on CD34+ cells expanded in vitro in the presence of hematopoietic growth factors. Induction of Fas Ag and downregulation of Bcl-2 may be expressed as part of the differentiation program of hematopoietic cells and may be involved in the regulation of hematopoiesis.