In vitro expansion of CD34+ cells from peripheral blood of myeloma and lymphoma patients

We studied the feasibility of in vitro expansion of CD34+ cells from patients with multiple myeloma (MM) or follicular non Hodgkin lymphoma (NHL). CD34+ cells were selected from peripheral blood (PB) using avidinbiotin immunoadsorption columns: purified CD34+ cells from three MM and five NHL patients were expanded. First, CD34+ cells (2 MM, 4 NHL) were grown for 14 days in 5 ml of IMDM plus 12.5% horse serum (HS), 12.5% fetal calf serum (FCS) and a commonly used combination of cytokines: IL1alpha, IL3, IL6, SCF, GM-CSF, G-CSF (10 ng/ml each) and EP (4 UI/ml). In these conditions, at day 14, average increase in CD34+, CFU-GM and total cell numbers were, respectively: x 6.0 x 23 and x 2,113 fold with 20 to 35% of granulocytic cells. In terms of CD34+ cell, CFU-GM and total cell outputs, MM cultures were comparable to NHL cultures, but MM cultures seemed to produce less granulocytic cells than NHL cultures. Next, in vitro expansion of PB CD34+ cells was tested in culture media suitable for clinical use. Two cultures (1 MM, 1 NHL) were carried out for 14 days in 20 ml of X-Vivo 10 medium, 2% human serum, IL1alpha, IL3, IL6, SCF, GM-CSF, G-CSF (6 ng/ml each) and EP (2 UI/ml). Increase in CD34+, CFU-GM and total cell numbers in these conditions were, respectively: x 5.7 and x 19.7, x 11.9 and x 40.9, x 424 and x 408 fold, with at least 75% of granulocytic cells in both cultures. We conclude that, although further improvements are necessary, in vitro expansion of PB CD34+ cells can presumably be carried out successfully for MM patients as well as for NHL patients, including in conditions suitable for clinical use.     

The ex vivo expansion capacity of normal human bone marrow cells is dependent on experimental conditions: role of the cell concentration, serum and CD34+ cell selection in stroma-free cultures

The present study was conducted to establish defined culture conditions for ex vivo expansion of normal human bone marrow cells. We investigated the role of three experimental expansion parameters: the cell concentration in the initial culture medium, the role of animal serum, human plasma and serum-free substitute, and the expansion potential of mononucleated cells (MNC) versus CD34+ cells. Cells were cultured in suspension with stem cell factor (SCF), IL3, IL6 and Erythropoietin (Epo) for 10 days. 1) Reducing the cell concentration from 3 x 10(4) to 1.5 x 10(3)/ml increased total cell expansion almost 20 fold, progenitor expansion more than 3 fold, and the maintenance of long term culture-initiating cells (LTC-IC). 2) In medium containing a serum-free substitute, total and CD34+ cell expansion was 3 times greater than in medium containing 1-10% human AB plasma or 25% animal serum. 3) The expansion potential of selected CD34+ cells was significantly greater than that of the total MNC population. However, taking into account the cell loss due to CD34+ selection, the overall results for quantitative expansion in relation to the initial number of MNCS favor the use of non-selected MNCS. 4) SCF + IL3 + IL6 was clearly the best combination of early cytokines for LTC-IC maintenance, with or without lineage-restricted cytokines, whereas the presence of IL1 beta in any combination augmented the decrease in LTC-IC. Addition of G-CSF to the medium resulted in 1 log increase in total cell expansion and a 2-fold increase in CFU-GM expansion. Addition of Epo always induced a dramatic proliferation of erythroid cells (up to 2000 fold) as well as of CFU-GM (up to 4 fold), without exhausting the LTC-IC pool. We concluded that the expansion of hemopoietic cells for clinical purposes needs establishment of controlled, reproducible and reliable culture conditions.     

Cell culture bags allow a large extent of ex vivo expansion of LTC-IC and functional mature cells which can subsequently be frozen: interest for a large-scale clinical applications

The aim of this study was to evaluate the ex vivo expansion of normal CD34+ cells in gas-permeable polypropylene bags suitable for clinical use. Cells were cultured for 14 days in serum-free medium supplemented with SCF, IL3, IL6, FLT3-1, G-CSF + MGDF or Epo. The bags supported the expansion of hematopoietic cells in a similar manner to small scale well or flask systems, allowing mean expansions of up to 2193-fold for total nucleated cells, 140-fold for CFU-GM and 66-fold for LTC-IC. Increasing the initial cell concentration from 5 x 10(3) to 1 x 10(5)CD34+ cells/ml induced the production of granulocytic cells with terminal differentiation while simultaneously decreasing the overall extent of expansion of the white blood cells produced. We tested the phagocytic activity and oxidative metabolism of the white blood cells produced. The percentage of phagocytic cells was 39+/-0.5% in expanded cultures derived from fractions initiated at 5 x 10(3), 10(4) or 10(5) cells/ml and 45+/-6% in cultured cells obtained from starting fractions containing 5 x 10(4) cells/ml, as compared to 58+/-4% in normal controls. A study of the potential for oxygen-dependent microbe killing showed that the expanded cells produced H2O2, although in lesser quantities than control cells. We subsequently investigated the possibility of freezing expanded cells. Total cell recovery after thawing was 45+/-4%, while recoveries of progenitors and stem cells ranged from 65 to 90%, without any influence of the initial cell concentration. This new approach could be of major interest for clinical practice, as it would allow evaluation of the quality of a graft prior to its infusion and employs experimental conditions which meet the criteria for potential clinical use.     

A successful case report of one and one half ventricle repair for pure pulmonary stenosis in a 4-year-old girl]

We tested two positive selection techniques for separation of CD34+ cells from bone marrow and analyzed the yields of CD34+ cells, BFU-E, CFU-GM, CFU-MK and LTC-IC after selection and expansion. An immunoadsorption procedure (CellPro) and an immunomagnetic (Baxter) CD34+ cell separation method were employed to purify the same bone marrow samples from seven normal subjects. Mean yields of CFU-GM and CFU-MK and absolute numbers of LTC-ICs were not different in the two purified cell populations. In contrast, the mean recovery of BFU-E was significantly lower for the immunoadsorption (21 +/- 14%) than for the immunomagnetic technique (44 +/- 27%). After separation, CD34+ cells were evaluated in 10-day liquid cultures for their expansion capacity in terms of total cells and progenitors. The expansion capacity of progenitors such as CFU-GM, CFU-MK and especially BFU-E selected by immunoadsorption was higher than the capacity of progenitors obtained by immunomagnetism, although final total and progenitor cell numbers are similar. Our results suggest that the populations separated by the two techniques differ mainly in the expansion capacity of progenitors and in the recovery of BFU-E after the selection procedure. These differences between two methods, which already are widely employed in research and in clinical transplantation, should be taken into account when considering the aims of the experiments.     

Synergy of growth factors during mobilization of peripheral blood precursor cells with recombinant human Flt3-ligand and granulocyte colony-stimulating factor in rabbits

The potential of recombinant human (rh)Flt3 ligand (FL), alone or in combination with other recombinant growth factors, to mobilize peripheral blood precursor cells (PBPCs) was examined in an animal model. Adult outbred New Zealand White rabbits received subcutaneous injections daily for 14 days in a standardized protocol; whole blood cell counts and colony-forming unit-granulocyte/macrophage (CFU-GM) colonies were measured 3 times weekly during the injection period and for an additional observation period of 14 days. Two animals in each group were treated as follows: 200 or 500 microg/kg FL, 10 microg/kg granulocyte colony-stimulating factor (G-CSF), 10 or 75 microg/kg stem cell factor (SCF), 10 microg/kg G-CSF + 500 microg/kg FL, 10 microg/kg G-CSF + 75 microg/kg SCF + 500 microg/kg FL. Both G-CSF and FL induced a sustained and dose-dependent increase in the leukocyte count to a maximum of 5-fold. They were additive in combination, leading to a tenfold increase in white blood cell counts. No consistent pattern was observed for platelet counts or red blood cells. No toxic side effects were seen. Both G-CSF and FL mobilized CFU-GM in a dose-dependent fashion to a 59-fold increase for G-CSF and 116-fold for FL. Maximum mobilization occurred on day 4 with G-CSF and on day 11 with FL. G-CSF + FL in combination acted synergistically, inducing a 503-fold increase of CFU-GM over baseline. The addition of SCF to this combination did not alter leukocyte counts or CFU-GM mobilization. Our results indicate that FL is a potent and safe agent for the mobilization of PB-PCs and is synergistic with G-CSF.     

Stromal factors support the expansion of the whole hemopoietic spectrum from bone marrow CD34+DR- cells and of some hemopoietic subsets from CD34+ and CD34+DR+ cells

Ex vivo expanded bone marrow CD34+DR- cells could offer a graft devoid of malignant cells able to promptly reconstitute hemopoiesis after transplant. We investigated the specific expansion requirements of this subpopulation compared to the more mature CD34+ and CD34+DR+ populations. The role of stromal factors was assessed by comparing the expansion obtained when the cells were cultured in (1) long-term bone marrow culture (LTBMC) medium conditioned by an irradiated human BM stroma (CM), (2) medium supplemented with 15% FBS (FBSM) and (3) non-conditioned LTBMC medium (LTM) for 21 days. The effect of the addition of G-CSF (G) and/or of MIP-1alpha (M) to a combination of IL-3, SCF, IL-6 and IL-11 (3, S, 6, 11) was analyzed. Compared to CD34+DR- cells, CD34+ and CD34+DR+ cells gave rise to a similar number of viable cells and to a lower progenitor expansion. The expansion potential of CD34+ and CD34+DR+ cells was equivalent in CM and in FBSM except for both the emergence of CD61 + megakaryocytic cells and LTC-IC maintenance which were improved by culture in CM. In contrast, expansion from CD34+DR- cells was enhanced by CM for all the parameters tested. Compared to FBSM, CM induced a higher level of CFU-GM and BFU-E expansion and allowed the emergence of CD61+ cells. HPP-CFC were maintained or expanded in CM but decreased in FBSM. Compared to input, the number of LTC-IC remaining after 21 days of CD34+DR- expansion culture was strongly decreased in FBSM and variably maintained or expanded in CM. Comparison with LTM indicated that stroma conditioning is responsible for this effect. G-CSF significantly improved CFU-GM and HPP-CFC expansion from CD34+DR- cells without being detrimental to the LTC-IC pool. The growth of CD61+ cells was significantly enhanced by G-CSF in CM. Addition of MIP-1alpha had no significant effect either on progenitor expansion or on LTC-IC, regardless of culture medium. We conclude that factors present in stroma- conditioned medium are necessary to support the expansion of the whole spectrum of hematopoietic cells from CD34+DR- cells and to support the expansion of cell subsets from CD34+ and CD34+DR+.     

Randomized comparison of progenitor-cell mobilization using chemotherapy, stem-cell factor, and filgrastim or chemotherapy plus filgrastim alone in patients with ovarian cancer

PURPOSE: This was the first randomized study to investigate the efficacy of peripheral-blood progenitor cell (PBPC) mobilization using stem-cell factor (SCF) in combination with filgrastim (G-CSF) following chemotherapy compared with filgrastim alone following chemotherapy. PATIENTS AND METHODS: Forty-eight patients with ovarian cancer were treated with cyclophosphamide and randomized to receive filgrastim 5 microg/kg alone or filgrastim 5 microg/kg plus SCF. The dose of SCF was cohort-dependent (5, 10, 15, and 20 microg/kg), with 12 patients in each cohort, nine of whom received SCF plus filgrastim and the remaining three patients who received filgrastim alone. On recovery from the WBC nadir, patients underwent a single apheresis. RESULTS: SCF in combination with filgrastim following chemotherapy enhanced the mobilization of progenitor cells compared with that produced by filgrastim alone following chemotherapy. This enhancement was dose-dependent for colony-forming unit-granulocyte-macrophage (CFU-GM), burst-forming unit-erythrocyte (BFU-E), and CD34+ cells in both the peripheral blood and apheresis product. In the apheresis product, threefold to fivefold increases in median CD34+ and progenitor cell yields were obtained in patients treated with SCF 20 microg/kg plus filgrastim compared with yields obtained in patients treated with filgrastim alone. Peripheral blood values of CFU-GM, BFU-E, and CD34+ cells per milliliter remained above defined threshold levels longer with higher doses of SCF. The higher doses of SCF offer a greater window of opportunity in which to perform the apheresis to achieve high yields. CONCLUSION: SCF (15 or 20 microg/kg) in combination with filgrastim following chemotherapy is an effective way of increasing progenitor cell yields compared with filgrastim alone following chemotherapy.     

Thrombopoietin directly and potently stimulates multilineage growth and progenitor cell expansion from primitive (CD34+ CD38-) human bone marrow progenitor cells: distinct and key interactions with the ligands for c-kit and flt3, and inhibitory effects of TGF-beta and TNF-alpha

Thrombopoietin (Tpo) is a primary regulator of megakaryocyte and platelet production. However, studies in c-mpl-deficient mice suggest that Tpo might also play an important role in early hemopoiesis. Here, the direct ability of Tpo to stimulate stroma-independent growth, multilineage differentiation, and progenitor cell expansion from single primitive CD34+ CD38- human bone marrow cells was investigated. Tpo alone stimulated limited clonal growth, but synergized with c-kit ligand (KL), flt3 ligand (FL), or IL-3 to potently enhance clonogenic growth. Whereas KL and FL in combination stimulated the clonal growth of only 3% of CD34+ CD38- cells, 40% of CD34+ CD38- cells were recruited by KL+FL+Tpo, demonstrating that Tpo promotes the growth of a high fraction of CD34+ CD38- progenitor cells. Additional cytokines (IL-3, IL-6, and erythropoietin (Epo)) did not significantly enhance clonal growth above that observed in response to KL+FL+Tpo. In contrast, Tpo enhanced clonogenic growth in response to KL+FL+IL-3+IL-6+Epo by as much as 80%, implicating a key role for this cytokine in early hemopoiesis. Importantly, we also demonstrate that the majority of Tpo-recruited CD34+ CD38- progenitor cells have a multilineage differentiation potential, and that Tpo promotes prolonged expansion of multipotent progenitors. Specifically, whereas progenitor cells were reduced in cultures containing only KL+FL, addition of Tpo resulted in 40-fold expansion of multipotent progenitors following a 14-day incubation. Finally, we identified inhibitors of Tpo-induced progenitor cell growth, in that TGF-beta as well as TNF-alpha almost completely abrogated the growth of CD34+ CD38- progenitor cells in response to Tpo alone as well as KL+FL+Tpo.     

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.     

Responses of circulating urea cycle and branched-chain amino acids to feeding in adult and aged Fischer-344 rats

The goal of our study was to identify cytokine combinations that would result in simultaneous ex vivo expansion of both the megakaryocyte (Mk) and granulocyte lineages, since these cell types have the potential to reduce the periods of thrombocytopenia and neutropenia following chemotherapy. We investigated the effects of cytokine combinations on expansion of the Mk (CD41a+ cells and colony forming unit [CFU]-Mk) and granulocyte (CD15+ cells and CFU-granulocyte/monocyte [GM]) lineages. Peripheral blood CD34+ cells were cultured in serum-free medium with interleukin 3 (IL-3), stem cell factor (SCF), and various combinations of thrombopoietin (TPO), IL-6, GM-CSF, and/or G-CSF. The Mk lineage was primarily influenced by TPO in our cultures, although Mk and CFU-Mk numbers were increased when TPO was combined with IL-6. The primary stimulator of the granulocyte lineage was G-CSF, although many synergistic and additive effects were observed with addition of other factors. Expansion of CFU-GM increased upon addition of more cytokines. The cytokine combination of IL-3, SCF, TPO, IL-6, GM-CSF and G-CSF produced the greatest number of granulocytes and CFU-GM. The minimum cytokines necessary for expansion of both the Mk and granulocyte lineages included TPO and G-CSF, since no other factors examined could increase Mk and granulocyte numbers to the same extent. The number of hematopoietic progenitors produced in our culture system should be sufficient for successful engraftment following myelosuppressive therapy if produced on a scale of about one liter.     

Flt3 ligand enhances the yield of primitive cells after Ex vivo cultivation of CD34+ CD38dim cells and CD34+ CD38dim CD33dim HLA-DR+ cells

Flt3 ligand (FL) has been proposed as a possible modulator of early hematopoietic cell growth. The purpose of this study was to analyze the impact of FL on ex vivo expansion of hematopoietic cells obtained from adult donors. We sought to precisely identify hematopoietic populations responsive to FL and to quantitate the ability of FL to enhance the survival and/or proliferation of early hematopoietic precursors in a stroma-free culture system. Towards that end, four CD34+ subsets were isolated and their response to FL was characterized. In methylcellulose, FL significantly increased colony formation by CD34+ CD38dim cells but not CD34+ CD38+ cells. In suspension culture, the enhancement of cell expansion by FL was 10 times greater with the CD34+ CD38dim fraction than the CD34+ CD38+ fraction. FL stimulated the generation of colony-forming unit-granulocyte-macrophage (CFU-GM) from the CD34+CD38dim fraction by 14.5- +/- 5.6-fold. To determine if CD34+ CD38dim cells responded uniformly to FL, the population was subdivided into a CD34+ CD38dim CD33dim HLA-DR+ (HLA-DR+) fraction and a CD34+ CD38dim CD33(dim) HLA-DRdim (HLA-DRdim) fraction. FL was far more effective at stimulating cell and progenitor growth from the HLA-DR+ fraction. To determine if FL enhanced or depleted the number of precommitted cells in expansion culture, CD34+ CD38dim and HLA-DR+ fractions were incubated in liquid culture and analyzed by flow cytometry. Inclusion of FL enhanced the absolute number of primitive CD34+ CD33dim cells and CD34+ HLA-DRdim cells after 5 to 12 days of cultivation. To confirm immunophenotypic data, the effect of FL on long-term culture-initiating cells (LTCIC) was determined. After 2 weeks of incubation of CD34+ CD38dim or HLA-DR+ cultures, LTCIC recoveries were significantly higher with FL in 5 of 6 trials (P < . 05). For HLA-DR+ cells, LTCIC recoveries averaged 214% +/- 87% of input with FL and 24% +/- 16% without FL. In contrast, HLA-DRdim LTCIC could not be maintained in stroma-free culture. We conclude that less than 10% of CD34+ cells respond vigorously to FL and that those cells are contained within the HLA-DR+ fraction. FL stimulates the expansion of total cells, CD34+ cells, and CFU-GM and enhances the pool of early CD34+ CD33(dim) cells, CD34+ HLA-DRdim cells, and LTCIC. These data indicate that it is possible to expand hematopoietic progenitors from adult donors without losing precursors from the precommitted cell pool.     

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.     

Short-term effects of early-acting and multilineage hematopoietic growth factors on the repair and proliferation of irradiated pure cord blood (CB) CD34+ hematopoietic progenitor cells

PURPOSE: Hematopoietic growth factor(s) (GF) may exert positive effects in vitro or in vivo on the survival of hematopoietic stem and progenitor cells after accidental or therapeutic total body irradiation. METHODS AND MATERIALS: We studied the clonogenic survival and DNA repair of irradiated (0.36, 0.73, and 1.46 Gy) CD34+ cord blood (CB) cells after short-term incubation (24 h) with GFs. CD34+ cells were stimulated with basic fibroblast growth factor (bFGF), stem cell factor/c-kit ligand (SCF), interleukin-3 (IL-3), IL-6, leukemia inhibitory factor (LIF), and granulocyte-monocyte colony stimulating factor (GM-CSF) alone or in combination in short-term serum-free liquid suspension cultures (LSC) immediately after irradiation and then assayed for clonogenic progenitors. DNA repair was evaluated by analysis of DNA strand breaks using the comet assay. Survival of CFU-GM, BFU-E, and CFU-Mix was determined and dose-response curves were fitted to the data. RESULTS: The radiobiological parameters (D[0] and n) showed significant GF(s) effects. Combination of IL-3 with IL-6, SCF or GM-CSF resulted in best survival for CFU-GM BFU-E and CFU-Mix, respectively. Combinations of three or more GFs did not increase the survival of clonogenic CD34+ cells compared to optimal two-factor combinations. The D[0] values for CFU-GM, BFU-E, and CFU-Mix ranged between 0.56-1.15, 0.41-2.24, and 0.56-1.29 Gy, respectively. As for controls, the curves remained strictly exponential, i.e., all survival curves were strictly exponential without any shoulder (extrapolation numbers n=1 for all tested GF(s). DNA repair capacity of CD34+ cells determined by comet assay, was measured before, immediately after irradiation, as well as 30 and 120 min after irradiation at 1 Gy. Notably, after irradiation the 2-h repair of cytokine-stimulated and unstimulated CD34+ cells was similar. CONCLUSION: Our data indicate that increased survival of irradiated CB CD34+ cells after short-term GF treatment is mediated through proliferative GF effects on the surviving fraction but not through improved DNA repair capacity.     

Recombinant human c-Mpl ligand (thrombopoietin) not only acts on megakaryocyte progenitors, but also on erythroid and multipotential progenitors in vitro

To determine the hematopoietic actions of recombinant human c-Mpl ligand (thrombopoietin [TPO]), we studied its effects on the proliferation and differentiation of highly purified CD34+ blood progenitors in plasma-containing and serum-free culture. TPO alone promoted the growth of small megakaryocyte colonies (CFU-Meg) in numbers two to three times greater than those produced by interleukin (IL)-3. The combination of TPO and stem cell factor (SCF) exerted a significant synergistic effect on CFU-Meg formation. In the presence of TPO and IL-3 or granulocyte/macrophage-colony stimulating factor (GM-CSF), a significant number of mixed colonies (CFU-Mix) were observed. The combination of TPO and Epo did not increase the number of CFU-Meg, but did support erythroid-burst (BFU-E) and CFU-Mix colony formation. Interestingly, the combination of TPO with cytokines known to have burst-promoting activity (BPA), including IL-3, GM-CSF, IL-9, and SCF, increased the number of BFU-E and CFU-Mix in the presence of Epo. The BPA of TPO was further investigated by delayed addition of Epo on day 6 after incubation with TPO from day 0. None of the BFU-E or CFU-Mix survived, indicating that TPO acted as a costimulant exclusively for Epo. Moreover, a neutralizing anti-human Mpl receptor polyclonal antibody completely abrogated the BPA of TPO, demonstrating that this effect was mediated through the Mpl receptor. Finally, experiments in single-cell clone sorting and serum-free culture clearly demonstrated that a combination of TPO and Epo directly supported BFU-E and CFU-Mix. These results suggest that TPO acts not only in megakaryocytopoiesis but also in the early stage of hematopoiesis.     

Thrombopoietin requires additional megakaryocyte-active cytokines for optimal ex vivo expansion of megakaryocyte precursor cells

Little is known concerning the interaction of thrombopoietin (TPO) with other megakaryocyte-active cytokines in directing the early events of megakaryocyte development. Culture of CD34(+) cells in interleukins (IL) -1, -6, -11, plus stem cell factor (SCF; S) results in a 10- to 12-fold expansion in total cell numbers, whereas total CD41(+) megakaryocytes are expanded approximately 120-fold over input levels. Addition of TPO to IL-1, -6, -11, S generates a biphasic proliferation of CD41(+) cells, accelerates their rate of production, and results in an ex vivo expansion of more than 200-fold. The addition of Flt-3 ligand (FL) increases CD41+ cell expansion to approximately 380-fold over input levels. In the absence of TPO, approximately 95% of the expanded cells show the phenotype of promegakaryoblasts; TPO and/or FL addition increases CD41 antigen density and ploidy in a subpopulation of promegakaryoblasts. A moderate (approximately sevenfold) expansion of megakaryocyte progenitor cells (colony-forming unit-megakaryocyte) occurs in the presence of IL-1, -6, -11, S, and the addition of TPO to this cocktail yields an approximately 17-fold expansion. We conclude that early proliferative events in megakaryocyte development in vitro are regulated by multiple cytokines, and that TPO markedly affects these early developmental steps. However, by itself, TPO is neither necessary nor sufficient to generate a full proliferative/maturational in vitro response within the megakaryocyte compartment. TPO clearly affects terminal differentiation and the development of (some) high-ploidy human megakaryocytes. However, its limited in vitro actions on human cell polyploidization suggest that additional megakaryocyte-active cytokines or other signals are essential for the maximal development of human megakaryocytes.     

Preservation of mucosal and systemic adjuvant properties of ISCOMS in the absence of functional interleukin-4 or interferon-gamma

We have developed an efficient and rapid method to analyze transduction in human hematopoietic cells and to select them. We constructed two retroviral vectors using the recombinant humanized S65T green fluorescent protein (rHGFP) gene. Transduced cells appeared with specific green fluorescence on microscopy or fluorescence-activated cell sorting (FACS) analysis. The rHGFP gene was placed under the control of two different retroviral promotors (LTR) in the LGSN vector and in the SF-GFP vector. Amphotropic retroviruses were tested on NIH/3T3 fibroblasts or human hematopoietic (K562, TF-1) cell lines. Then CD34+ cells isolated from cord blood were infected three times after a 48-h prestimulation with IL-3, IL-6, SCF or with IL-3, IL-6, SCF, GM-CSF, Flt3-L and TPO. After 6 days of expansion, a similar number of total CD34(+)-derived cells, CD34+ cells and CFC was obtained in non-transduced and transduced cells, demonstrating the absence of toxicity of the GFP. A transduction up to 46% in total CD34(+)-derived cells and 21% of CD34+ cells was shown by FACS analysis. These results were confirmed by fluorescence of colonies in methyl-cellulose (up to 36% of CFU-GM and up to 25% of BFU-E). The FACS sorting of GFP cells led to 83-100% of GFP-positive colonies after 2 weeks of methyl-cellulose culture. Moreover, a mean gene transfer efficiency of 8% was also demonstrated in longterm culture initiating cells (LTC-IC). This rapid and efficient method represents a substantial improvement to monitor gene transfer and retroviral expression of various vectors in characterized human hematopoietic cells.     

Expansion in bioreactors of human progenitor populations from cord blood and mobilized peripheral blood

Umbilical cord blood (UCB) and mobilized peripheral blood (MPB) provide an alternate source to bone marrow for transplantation. Expansion in vitro of stem/progenitor cell populations from these sources may provide adult-sized grafts otherwise not attainable because of the limited cell numbers available in the case of UCB or because of numerous rounds of apheresis required for sufficient MPB cells. We asked whether continuous perfusion culture could be employed in ex vivo expansion to produce clinically relevant numbers of stem/progenitor cells from these sources. To evaluate MPB, 1-10 million leukocytes, from patients who had received either granulocyte colony-stimulating factor (G-CSF) or cyclophosphamide and granulocyte-macrophage colony-stimulating factor (GM-CSF), were inoculated into bioreactors, with or without irradiated, allogeneic stroma. The growth factor combination in the perfusion medium consisted of interleukin-3 (IL-3), stem cell factor (SCF), GM-CSF and erythropoietin (Epo). Under the best conditions tested, total cell numbers, granulocyte-macrophage colony-forming units (CFU-GM), and long-term culture-initiating cell (LTC-IC) populations were expanded by about 50-, 80-, and 20-fold, respectively, over 14 days. At low cell inocula (1 million), the presence of stroma enhanced the expansion of total cells and CFU-GM but not of LTC-IC. When SCF was not included in the medium, both total cells and CFU-GM expanded to a much lesser extent, but again the expansion of LTC-IC was not affected. At the higher cell inoculum (10 million), expansions of total cells and CFU-GM were equivalent with or without stroma. To evaluate UCB, cells were placed into bioreactors with or without irradiated, allogeneic stroma, and the bioreactors were perfused with medium containing the four standard growth factors. After 6-14 days, in several independent experiments, 20-24 million cells were harvested from bioreactors perfused with SCF-containing medium, irrespective of the presence or absence of preformed stroma. Similarly, in reactors perfused with SCF-containing medium (with or without stroma), an average 40- to 60-fold expansion of CFU-GM was obtained, yielding an average of 1.5-1.8 x 10(5) CFU-GM per reactor. Harvested cells were thus up to 40-fold enriched in CFU-GM in comparison to the inoculum. In the absence of SCF, cell expansions averaged 1.5- to 2-fold, and CFU-GM were expanded only 10- to 14-fold by day 14. As before, the presence of preformed stroma did not affect either cell or CFU-GM yields, provided the cell inoculum was at least 4.5 million cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Colony formation of human fetal CD34+ hematopoietic cells

Manipulations to enhance engraftment of donated cells may be advantageous in transplantation of fetal hematopoietic cells (FHC). By assessing the formation of colonies, CD34+ enrichment was evaluated with and without cytokine stimulation (interleukins 3 and 6, stem cell factor, granulocyte-macrophage colony-stimulating factor). Cord blood cells and bone marrow cells served as controls. In FHC, cytokine stimulation and CD34+ enrichment always enhanced the formation of CFU-GM (colony-forming units--granulocytes, macrophages) and CFU-GEMM (colony-forming units-granulocytes, erythroid cells, macrophages, megakaryocytes). However, BFU-E (burst-forming units--erythroid cells) in FHC remained unchanged after cytokine stimulation and CD34+ enrichment. In FHC, the addition of cytokines and the enrichment of CD34+ cells usually contributed equally to enhance CFU-GM and CFU-GEMM colony formation. CD34-negative FHC produced the same number or more BFU-E and half the number of CFU-GM and CFU-GEMM as compared with crude cells. This CD34-negative cell population also responded to cytokine stimulation. Such findings may indicate that purification of CD34+ cells is not meaningful in fetal transplantation.     

K+ channel antisense oligodeoxynucleotides inhibit cytokine-induced expansion of human hemopoietic progenitors

Primitive human hemopoietic progenitor cells identified by surface membrane markers CD33-CD34+ are capable of expansion into lineage-restricted precursors following in vitro stimulation by hemopoietic regulators such as stem cell factor (SCF) and interleukin-3 (IL-3). In search of ionic currents involved in cytokine-induced progenitor cell growth and differentiation, human umbilical cord blood CD33-CD34+ cells were subjected to perforated patch-clamp recordings following overnight incubation with SCF and/or IL-3. An inward rectifying potassium channel (Kir) was found in 33% of control unstimulated cells, in 34% of cells incubated with IL-3, in 31% of cells incubated with SCF and in 75% of cells incubated with IL-3 plus SCF. Kir activity increased with elevation of extracellular potassium and was blocked by extracellular Cs+ or Ba2+ Antisense oligodeoxynucleotides directed against Kir blocked both mRNA and functional expression of Kir channels. Kir antisense also inhibited the in vitro expansion of cytokine-stimulated CD33-CD34+ cells into erythroid (BFU-E) and myeloid (GM-CFU) progenitors in 7-day suspension cultures. Extracellular Cs+ or Ba2+ induced a similar degree of inhibition (40-60%) of progenitor cell generation. These findings strongly suggest an essential role for Kir in the process of cytokine-induced primitive progenitor cell growth and differentiation.     

The effects of Flk-2/flt3 ligand as compared with c-kit ligand on short-term and long-term proliferation of CD34+ hematopoietic progenitors elicited from human fetal liver, umbilical cord blood, bone marrow, and mobilized peripheral blood

The Flk-2/flt3 ligand (FL) was evaluated and compared with c-kit ligand (KL) for its in vitro proliferative effects on CD34+ cells from human fetal liver, umbilical cord blood, bone marrow, and mobilized peripheral blood. Using a 7-day liquid culture system, FL in combination with interleukin-3 (IL-3), interleukin-6 (IL-6), and granulocyte colony-stimulating factor (G-CSF) was comparable with KL in combination with IL-3, IL-6, and G-CSF for the expansion of hematopoietic progenitors. When FL-containing cultures were assayed after 21 or 28 days, a greater number of progenitors were generated as compared with KL-containing cultures. Using bone marrow microvascular endothelial cells as support stroma, cultures supplemented with FL generated a greater number of progenitors in both the nonadherent and adherent layers at day 35. These data suggest that FL ligand, in combination with other cytokines, can be used for short-term ex vivo expansion of hematopoietic progenitors and facilitates the preservation and possible expansion of primitive cells capable of long-term generation of progenitors.