Ex-vivo expansion of hematopoietic progenitor cells: preliminary results in breast cancer

Ex Vivo Expansion of Hematopoietic Stem Cells to Improve Engraftment in Stem Cell Transplantation

The efficient use of hematopoietic stem cells (HSC) for transplantation is often limited by the relatively low numbers of HSC collected. The ex vivo expansion of HSC for clinical use is a potentially valuable and safe approach to increase HSC numbers thereby increasing engraftment and reducing the risk of morbidity from infection. Here, we describe a protocol for the robust ex vivo expansion of human CD34(+) HSC isolated from umbilical cord blood. The protocol described can efficiently generate large numbers of HSC. We also describe a flow cytometry-based method using high-resolution division tracking to characterize the kinetics of HSC growth and differentiation. Utilizing the guidelines discussed, it is possible for investigators to use this protocol as presented or to modify it for their specific needs.

Novel Techniques for Ex Vivo Expansion of Cord Blood: Clinical Trials

Cord blood (CB) provides an excellent alternative source of hematopoietic progenitor cells (HPC) for patients lacking human leukocyte antigen-matched peripheral blood or bone marrow graft for transplantation. However, due to the limited cell dose in CB graft, it is associated with prolonged time to engraftment, risk of graft rejection, infections, and treatment-related mortality. To increase the cell dose, a variety of ex vivo expansion techniques have been developed. Results of traditional methods of CB expansion using cytokines alone were disappointing. Expanding CB cells with mesenchymal progenitor cells led to sizeable increase in graft content and improved engraftment. Other methods used HPC-differentiation blockers, such as nicotinamide analogs, copper chelators, inducing constitutive Notch signaling, or an aryl hydrocarbon receptor antagonist (StemReginin1). Many of these methods lead to substantial expansions of total nucleated cells and CD34(+) cells, and significantly improved time to neutrophil or platelet engraftment in patients transplanted with the expanded products compared to the recipients of unmanipulated CBT. These studies differ not only in the expansion method but also with regards to the cytokines used, patient population, conditioning regimens, and transplantation practices, to name a few. Some of these methods employed expansion of a portion of CB unit in the setting of single CBT, while others in the setting of double CBT. Here, we review various procedures used for CB expansion and highlight some of the key differences. Novel methods of improving engraftment that aim at improving bone marrow homing potential of CB cells are not reviewed.

Survival of cord blood haematopoietic stem cells in a hyaluronan hydrogel for ex vivo biomimicry

Haematopoietic stem cells (HSCs) and haematopoietic progenitor cells (HPCs) grow in a specified niche in close association with the microenvironment, the so-called 'haematopoietic niche'. Scaffolds have been introduced to overcome the liquid culture limitations, mimicking the presence of the extracellular matrix (ECM). In the present study the hyaluronic acid scaffold, already developed in the laboratory, has been used for the first time to maintain long-term cultures of CD34⁺ haematopoietic cells obtained from human cord blood. One parameter investigated was the impact on ex vivo survival of CD34⁺ cord blood cells (CBCs) on the hyaluronic acid surface, immobilized with peptides containing the RGD motif. This peptide was conjugated by coating the hyaluronan hydrogel and cultured in serum-free liquid phase complemented with stem cell factor (SCF), a commonly indispensable cytokine for haematopoiesis. Our work demonstrated that these hyaluronan hydrogels were superior to traditional liquid cultures by maintaining and expanding the HPCs without the need for additional cytokines, and a colonization of 280-fold increment in the hydrogel compared with liquid culture after 28 days of ex vivo expansion.

Ex vivo expansion of haematopoietic stem cells to improve engraftment in stem cell transplantation

The efficient use of haematopoietic stem cells (HSC) for transplantation is often limited by the relatively low numbers of HSC collected. The ex vivo expansion of HSC for clinical use is a potentially valuable and safe approach to increase HSC numbers thereby increasing engraftment and reducing the risk of morbidity from infection. Here we describe a protocol for the robust ex vivo expansion of human CD34(+) HSC isolated from umbilical cord blood. The protocol described can efficiently generate large numbers of HSC. We also describe a flow cytometry-based method using high resolution division tracking to characterise the kinetics of HSC growth and differentiation. Utilising the guidelines discussed, it is possible for investigators to use this protocol as presented or to modify it for their specific needs.

Overcoming the barriers to umbilical cord blood transplantation

Umbilical cord blood (UCB) transplantation (UCBT) has seen a marked increase in utilization in recent years, especially in the pediatric population; however, graft failure, delayed engraftment and profound delay in immune reconstitution leads to significant morbidity and mortality in adults. The lack of cells available for post-transplant therapies, such as donor lymphocyte infusions, has also been considered a disadvantage. To overcome the cell-dose barrier, the combination of two UCB units is becoming commonplace in adolescent and adult populations, and is currently being studied in pediatrics as well. In some studies, the use of two UCB units appears to have a positive impact on outcomes; however, engraftment is still suboptimal. A possible additional way to improve outcome and extend applicability of UCBT is via ex vivo expansion. Studies to develop optimal expansion conditions are still in the exploratory phase; however, recent studies suggest expanded UCB is safe and can improve outcomes. The ability to transplant across HLA disparities, rapid procurement time and decreased graft-versus-host disease (GvHD) seen with UCBT makes it a promising stem cell source and, while barriers exist, consistent progress is being made to overcome them.

Ex vivo expansion of cord blood

A marked increase in the utilization of umbilical cord blood (UCB) transplantation has been observed in recent years; however, the use of UCB as a hematopoietic stem cell (HSC) source is limited primarily by the number of progenitor cells contained in the graft. Graft failure, delayed engraftment and profound delay in immune reconstitution lead to significant morbidity and mortality in adults. The lack of cells available for post transplant therapies, such as donor lymphocyte infusions, has also been considered to be a disadvantage of UCB. To improve outcomes and extend applicability of UCB transplantation, one potential solution is ex vivo expansion of UCB. Investigators have used several methods, including liquid suspension culture with various cytokines and expansion factors, co-culture with stromal elements and continuous perfusion systems. Techniques combining ex vivo expanded and unmanipulated UCB are being explored to optimize the initial engraftment kinetics as well as the long-term durability. The optimal expansion conditions are still not known; however, recent studies suggest that expanded UCB is safe. It is hoped that by ex vivo expansion of UCB, a resulting decrease in the morbidity and mortality of UCB transplantation will be observed, and that the availability of additional cells may allow adoptive immunotherapy or gene transfer therapies in the UCB setting.

Pre-clinical development of cord blood-derived progenitor cell graft expanded ex vivo with cytokines and the polyamine copper chelator tetraethylenepentamine

BACKGROUND

We have previously demonstrated that the copper chelator tetraethylenepentamine (TEPA) enables preferential expansion of early hematopoietic progenitor cells (CD34+CD38-, CD34+CD38-Lin-) in human umbilical cord blood (CB)-derived CD34+ cell cultures. This study extends our previous findings that copper chelation can modulate the balance between self-renewal and differentiation of hematopoietic progenitor cells.

METHODS

In the present study we established a clinically applicative protocol for large-scale ex vivo expansion of CB-derived progenitors. Briefly, CD133+ cells, purified from CB using Miltenyi Biotec's (Bergisch Gladbach, Germany) CliniMACS separation device and the anti-CD133 reagent, were cultured for 3 weeks in a clinical-grade closed culture bag system, using the chelator-based technology in combination with early-acting cytokines (SCF, thrombopoietin, IL-6 and FLT-3 ligand). This protocol was evaluated using frozen units derived from accredited cord blood banks.

RESULTS

Following 3 weeks of expansion under large-scale culture conditions that were suitable for clinical manufacturing, the median output value of CD34+ cells increase by 89-fold, CD34+CD38- increase by 30-fold and CFU cells (CFUc) by 172-fold over the input value. Transplantation into sublethally irradiated non-obese diabetic (NOD/SCID) mice indicated that the engraftment potential of the ex vivo expanded CD133+ cells was significantly superior to that of unexpanded cells: 60+/-5.5% vs. 21+/-3.5% CD45+ cells, P=0.001, and 11+/-1.8% vs. 4+/-0.68% CD45+CD34+ cells, P=0.012, n=32, respectively.

DISCUSSION

Based on these large-scale experiments, the chelator-based ex vivo expansion technology is currently being tested in a phase 1 clinical trial in patients undergoing CB transplantation for hematological malignancies.

Ex vivo expansion of umbilical cord blood

The efficacy of cord blood (CB) transplantation is limited by the low cell dose available. Low cell doses at transplant are correlated with delayed engraftment, prolonged neutropenia and thrombocytopenia and elevated risk of graft failure. To potentially improve the efficacy of CB transplantation, approaches have been taken to increase the cell dose available. One approach is the transplantation of multiple cord units, another the use of ex vivo expansion. Evidence for a functional and phenotypic heterogeneity exists within the HSC population and one concern associated with ex vivo expansion is that the expansion of lower 'quality' hematopoietic progenitor cells (HPC) occurs at the expense of higher 'quality' HPC, thereby impacting the reserve of the graft. There is evidence that this is a valid concern while other evidence suggests that higher quality HPC are preserved and not exhausted. Currently, ex vivo expansion processes include: (1) liquid expansion: CD34+ or CD133+ cells are selected and cultured in medium containing factors targeting the proliferation and self-renewal of primitive hematopoietic progenitors; (2) co-culture expansion: unmanipulated CB cells are cultured with stromal components of the hematopoietic microenvironment, specifically mesenchymal stem cells (MSC), in medium containing growth factors; and (3) continuous perfusion: CB HPC are cultured with growth factors in 'bioreactors' rather than in static cultures. These approaches are discussed. Ultimately, the goal of ex vivo expansion is to increase the available dose of the CB cells responsible for successful engraftment, thereby reducing the time to engraftment and reducing the risk of graft failure.

An effective and simple expansion system for megakaryocyte progenitor cells using a combination of heparin with thrombopoietin and interleukin-11

Transfusion of ex vivo expanded megakaryocyte (MK) progenitor cells has been suggested to shorten the time of platelet recovery in the thrombocytopenia induced by radiotherapy or chemotherapy. Here, we report an effective and simple expansion system of MK progenitor cells from cord blood (CB) CD34(+) cells using a combination of thrombopoietin (TPO), interleukin (IL)-11, and heparin. When the CB CD34(+) cells were cultured in a liquid expansion system in the presence of TPO + recombination human (rh)IL-11 + heparin for 7 days, the number of CB CD34(+)/CD41a(+) cells was significantly increased compared to control groups (p < 0.05). When the suspension cells collected from 7-day liquid culture were replated in semisolid cultures, increased large MK colonies were observed in the culture with combination of TPO + IL-11 + heparin compared to those of control groups. In vivo, transfusion of CD34(+) cells expanded with TPO + IL-11 + heparin into irradiated nonobese diabetic/severe combined immunodeficient mice significantly accelerated platelet recovery. These data indicate that heparin as effective cofactor for TPO and IL-11 promotes expansion of MK progenitor cells from CB CD34(+) cells. This expansion system is simple and effective and could be used for the treatment of thrombocytopenia after radiotherapy or chemotherapy.

Ex vivo expansion of megakaryocyte precursor cells in autologous stem cell transplantation for relapsed malignant lymphoma

To evaluate the impact of ex vivo expanded megakaryocyte (MK) progenitors on high-dose chemotherapy-induced thrombocytopenia, we conducted a phase II study in 10 patients with relapsed lymphoma. Two fractions of peripheral blood progenitor cells (PBPC) were cryopreserved, one with enough cells for at least 2 x 10(6) CD34+ cells/kg and a second obtained after CD34+ selection. Ten days before autologous stem cell transplantation, the CD34+ fraction was cultured with MGDF+SCF for 10 days. After BEAM (BCNU, cyclophosphamide, cytarabine, and melphalan) chemotherapy, patients were reinfused with standard PBPC and ex vivo expanded cells. No toxicity was observed after reinfusion. The mean fold expansion was 9.27 for nucleated cells, 2 for CD34+ cells, 676 for CD41+ cells, and 627 for CD61+ cells. The median date of platelet transfusion independence was day 8 (range: 7-12). All patients received at least one platelet transfusion. In conclusion, ex vivo expansion of MK progenitors was feasible and safe, but this procedure did not prevent BEAM-induced thrombocytopenia. Future studies will determine if expansion of higher numbers of CD34+ cells towards the MK-differentiation pathway will translate into a functional effect in terms of shortening of BEAM-induced thrombocytopenia.

Ex vivo expansion of neutrophil precursor cells from fresh and cryopreserved cord blood cells

BACKGROUND

Neutropenia following cord blood (CB) transplantation may be abrogated by infusion of granulopoietic progenitor cells. The purpose of this study was to determine whether myeloid progenitors can be obtained by ex vivo expansion of cryopreserved cord blood aliquots, and whether these progenitors present the morphologic, biologic and functional properties of myeloid progenitors at various stages of differentiation.

METHODS

The cells, plated for 7 days in serum-free medium with SCF, IL-3, G-CSF, Flt3-ligand and thrombopoietin in various combinations were assessed for the expression of CD34, CD38 and CD13. Maturation of cells into the myeloid lineage was evaluated by the expression of CD15, CD11b and CD16 and by the presence of primary (myeloperoxidase) and secondary granules (lactoferrin). The capacity of cells to phagocyte latex beads was evaluated to assess their functionality.

RESULTS

We have shown that a). CD34+ cells isolated from thawed samples were able to produce expansions similar to fresh samples. b). The best combination for the expansion of neutrophil precursor cells was S3FG; c). in these conditions, all stages of myeloid progenitors were represented, but few mature cells were observed. d). However, when the cells were plated on a BM stroma to try to reproduce conditions occurring during transplant, they acquired rapidly the characteristics of mature segmented cells. e). The ex vivo generated granulocytes were able to phagocyte latex beads.

DISCUSSION

In conclusion, it seems reasonable to systematically aliquot CB samples before cryopreservation. Some aliquots can then be thawed, enriched in CD34+ cells and ex vivo differentiated into myeloid lineage, while the other aliquots are conserved to be infused without manipulation.

Ex vivo expansion of normal progenitor cells from acute myeloid leukemia cell-contaminated CD34+ peripheral blood progenitor cells after mafosfamide purging

The rationale for purging of autologous acute myeloid leukemia (AML) grafts is to eradicate contaminating leukemic cells that might contribute to relapse. However, in vitro purging generally delays post-transplant hematopoietic recovery, thus increasing treatment-related complication rates. Theoretically, this prolonged aplasia might be shortened by the additional transplantation of ex vivo-generated progenitor cells. Therefore, we investigated whether nonleukemic progenitors could be expanded ex vivo from AML cell-contaminated CD34(+) peripheral blood progenitor cell (PBPC) preparations. Nonleukemic CD34(+)-selected PBPC and AML cells (Kasumi-1, KG-1, primary AML blasts) were cultured in cytokine-supplemented liquid culture for up to 19 days. Cells were used either unmanipulated or following in vitro purging with mafosfamide (30, 50, 75 microg/ml). Ex vivo-generated cells were assessed by flow cytometry, progenitor cell assays, and polymerase chain reaction. Without prior purging, ex vivo culture markedly amplified AML cells as well as nonleukemic CD34(+) PBPC (day 12: Kasumi-1, 18.5 +/- 0.6-fold; KG-1, 52.2 +/- 2.6-fold; CD34(+), 74.1 +/- 5.6-fold). Co-culture with leukemic cells did not affect CD34(+) cell growth and vice versa. Following in vitro purging, CD34(+) PBPC were expanded even at the highest mafosfamide dose (day 19: 25 +/- 15-fold), whereas leukemic cells were markedly depleted (approx. 1.5 log). Furthermore, normal colony-forming units (CFU) could be effectively recovered (day 19: 10 +/- 3.1% of prepurging input CFU), whereas CFU-L were depleted to undetectable levels in six of seven experiments. Finally, leukemic cells were undetectable following ex vivo co-culture of purged cells (CD34(+) PBPC plus 10% Kasumi-1 cells or primary blasts), but were clearly detectable without purging. Taken together, these data demonstrated that ex vivo expansion of normal progenitors from mafosfamide-purged AML cell-contaminated grafts might be feasible.

Both CD34+38+ and CD34+38- cells home specifically to the bone marrow of NOD/LtSZ scid/scid mice but show different kinetics in expansion

Human hemopoietic stem cells (HSC) have been shown to engraft, differentiate, and proliferate in the hemopoietic tissues of sublethally irradiated NOD/LtSZ scid/scid (NOD/SCID) mice. We used this model to study homing, survival, and expansion of human HSC populations from different sources or phenotype. We observed that CD34+ cells homed specifically to bone marrow (BM) and spleen, but by 3 days after injection, survived only in the BM. These BM-homed CD34+ cells proliferated intensively and gave rise to a 12-fold, 5.5-fold, and 4-fold expansion in 3 days for umbilical cord blood, adult mobilized peripheral blood, and adult BM-derived cells, respectively. By injection of purified subpopulations, it was demonstrated that both CD34+38+ and CD34+38- umbilical cord blood HSC homed to the BM and expanded. Importantly, kinetics of expansion were different: CD34+38+ cells started to increase in cell number from day 3 onwards, and by 4 wk after injection, virtually all CD34+ cells had disappeared. In contrast, CD34+38- cells remained quiescent during the first week and started to expand intensively from the third week on. In this paper, we have shown that homing, survival, and expansion of stem cells are three independent phenomena important in the early phase of BM engraftment and that kinetics of engraftment differ between CD34+38+ and CD34+38- cells.

Umbilical cord blood cells capable of engrafting in primary, secondary, and tertiary xenogeneic hosts are preserved after ex vivo culture in a noncontact system

This report describes stroma-based and stroma-free cultures that maintain long-term engrafting hematopoietic cells for at least 14 days ex vivo. Umbilical cord blood (UCB) CD34(+) cells were cultured in transwells above AFT024 feeders with fetal-liver-tyrosine-kinase (FL) + stem cell factor (SCF) + interleukin 7 (IL-7), or FL + thrombopoietin (Tpo). CD34(+) progeny were transplanted into nonobese diabetic-severe combined immunodeficiency (NOD-SCID) mice or preimmune fetal sheep. SCID repopulating cells (SRC) with multilineage differentiation potential were maintained in FL-SCF-IL-7 or FL-Tpo containing cultures for up to 28 days. Marrow from mice highly engrafted with uncultured or expanded cells induced multilineage human hematopoiesis in 50% of secondary but not tertiary recipients. Day 7 expanded cells engrafted primary, secondary, and tertiary fetal sheep. Day 14 expanded cells, although engrafting primary and to a lesser degree secondary fetal sheep, failed to engraft tertiary recipients. SRC that can be transferred to secondary recipients were maintained for at least 14 days in medium containing glycosaminoglycans and cytokines found in stromal supernatants. This is the first demonstration that ex vivo culture in stroma-noncontact and stroma-free cultures maintains "long-term" engrafting cells, defined by their capacity to engraft secondary or tertiary hosts. (Blood. 2001;97:3441-3449)

Xenotransplantation of immunodeficient mice with mobilized human blood CD34+ cells provides an in vivo model for human megakaryocytopoiesis and platelet production

The study of megakaryocytopoiesis has been based largely on in vitro assays. We characterize an in vivo model of megakaryocyte and platelet development in which human peripheral blood stem cells (PBSCs) differentiate along megakaryocytic as well as myeloid/lymphoid lineages in sublethally irradiated nonobese diabetic/severe combined immunodeficient (NOD-SCID) mice. Human hematopoiesis preferentially occurs in the bone marrow of the murine recipients, and engraftment is independent of exogenous cytokines. Human colony-forming units-megakaryocyte (CFU-MK) develop predominantly in the bone marrow, and their presence correlates with the overall degree of human cell engraftment. Using a sensitive and specific flow cytometric assay, human platelets are detected in the peripheral blood from weeks 1 to 8 after transplantation. The number of circulating human platelets peaks at week 3 with a mean of 20 x 10(9)/L. These human platelets are functional as assessed by CD62P expression in response to thrombin stimulation in vitro. Exogenous cytokines have a detrimental effect on CFU-MK production after 2 weeks, and animals treated with these cytokines have no circulating platelets 8 weeks after transplantation. Although cytokine stimulation of human PBSCs ex vivo led to a significant increase in CFU-MK, CD34+/41+, and CD41+ cells, these ex vivo expanded cells provided only delayed and transient platelet production in vivo, and no CFU-MK developed in vivo after transplantation. In conclusion, xenogeneic transplantation of human PBSCs into NOD/SCID mice provides an excellent in vivo model to study human megakaryocytopoiesis and platelet production.

Influence of medium components on ex vivo megakaryocyte expansion

Reinfusion of ex vivo-expanded autologous megakaryocytes together with a stem cell transplantation may be useful to prevent or reduce the period of chemotherapy-induced thrombocytopenia. In this study, we analyzed several serum-containing and serum-free media to identify the most suitable medium for megakaryocyte expansion. Moreover, two thrombopoietin (Tpo)-mimetic peptides were tested to evaluate whether they could replace Tpo in an expansion protocol. To analyze the effects of different media on megakaryocyte expansion, we used an in vitro liquid culture system. For this purpose, CD34(+) cells were isolated from peripheral blood and cultured for 8 days in the presence of Tpo and interleukin-3 (IL-3). The presence of megakaryocytes was analyzed by flow cytometric analysis after staining for CD41 expression. For our standard culture procedure, megakaryocyte medium (MK medium) supplemented with 10% AB plasma was used. Addition of 5% or 2.5% AB plasma yielded higher numbers of megakaryocytes, implying the presence of inhibitory factors in plasma. However, some plasma components are required for optimal megakaryocyte expansion because addition of less than 1% AB plasma or addition of human serum albumin instead of AB plasma resulted in the formation of lower numbers of megakaryocytes. Two commercially available serum-free media were also tested: Cellgro and Stemspan. If CD34(+) cells were cultured in Cellgro medium similar numbers of megakaryocytes were obtained as when CD34(+) cells were cultured in MK medium supplemented with 10% AB plasma. In MK medium with 2.5% AB plasma, higher numbers of megakaryocytes were cultured than in MK medium supplemented with 10% AB plasma. Therefore, Cellgro medium is not the best alternative medium. In cultures with Stemspan medium, higher numbers of megakaryocytes were obtained compared to MK medium with 10% AB plasma. Stemspan is thus a good alternative for MK medium. Two Tpo-mimetic peptides, AF13948 and PK1M, were tested for their ability to replace Tpo. In cultures with AF13948, comparable numbers of megakaryocytes were obtained as in the presence of Tpo, but in cultures with PK1M the number of megakaryocytes was lower. This study shows that high concentrations of plasma in medium inhibits megakaryocyte formation, but some plasma components are required for optimal megakaryocyte expansion. For an ex vivo expansion protocol, it is worthwhile to test several media, because the number of megakaryocytes differs widely with the medium used.

Umbilical cord blood progeny cells that retain a CD34+ phenotype after ex vivo expansion have less engraftment potential than unexpanded CD34+ cells

BACKGROUND

Because of the limitation of cell numbers associated with cord blood harvests, there is a need to determine the efficacy of using ex vivo-expanded cord blood cells in a transplantation setting. In this study, limiting-dilution analysis was used in nonobese diabetic mice with severe combined immunodeficiency (NOD/SCID) to compare the engraftment potential of progeny cells expressing the CD34+ phenotype after expansion with that of uncultured CD34+ cells.

STUDY DESIGN AND METHODS

Cord blood CD34+ cells were cultured in Iscove's modified Dulbecco medium supplemented with 10-percent fetal calf serum (FCS) and IL-6, SCF, megakaryocyte growth and development factor, and Flt3 ligand. The resulting ex vivo-expanded products were assessed for total numbers of nucleated cells, CD34+ cells, and CFUs and long-term culture-initiating cell activity. The engraftment potentials of cultured progeny CD34+ cells and uncultured CD34+ cells were determined by using NOD/SCID mice.

RESULTS

After 14 days of culture, total nucleated cell counts increased over input values by 180 +/- 59-fold, CD34+ cell numbers by 44 +/- 13-fold, CFU activity by 23 +/- 5-fold, and long-term culture-initiating cell activity by 20 +/- 6-fold (mean +/- SD; n = 6). The frequency of SCID-repopulating cells (SRC) in mice transplanted with uncultured products was 1 per 20,000 CD34+ cells (95% CI, 1:10,000-1:38,000) and that in mice receiving ex vivo-expanded products was 1 per 418,000 progeny CD34+ cells (95% CI, 1:158,000-1:1,100,000). Taken together, these data indicated that, after 2 weeks of culture, there was a modest twofold increase in the total number of SRCs. However, the levels of human CD45 cell engraftment in NOD/SCID recipients of progeny CD34+ cells were significantly lower than those in mice receiving equivalent numbers of uncultured CD34+ cells (p<0.05).

CONCLUSION

Umbilical cord blood progeny cells retaining a CD34+ phenotype after ex vivo expansion have less engraftment potential than do unexpanded CD34+ cells.

High-dose chemotherapy with hematopoietic stem-cell transplantation for breast cancer: current status, future trends

High-dose chemotherapy with hematopoietic stem-cell transplantation (HDC/HSCT) has been extensively studied as a potential treatment for breast cancer. A literature search of MEDLINE from January 1990 through December 1999 identified 497 published full papers. Of these articles, 120 reported the results of clinical trials, 78 were reviews, and 299 reported on issues related to the technology of peripheral stem cells, supportive care, and toxicity. The phase II data must be interpreted with caution, as it is subject to selection bias; transplant recipients tended to be younger, rigorously staged, and selected to be chemotherapy responsive. There continues to be controversy regarding the role of high-dose therapy in this disease. Only a few fully published randomized trials are available; these studies were powered only to detect large differences in survival and no benefit was shown. Several large controlled trials are either in progress or are too early for definitive analysis. This review analyzes the current literature on HDC/HSCT for breast cancer, identifying prognostic factors and discussing ongoing research designed to improve antitumor effects.

Ex vivo expanded unselected peripheral blood: progenitor cells reduce posttransplantation neutropenia, thrombocytopenia, and anemia in patients with breast cancer

The safety and efficacy of administering ex vivo expanded peripheral blood progenitor cells (PBPC) to patients with breast cancer who undergo high-dose chemotherapy and PBPC transplantation was investigated. Unselected PBPC were cultured in gas-permeable bags containing 1-L serum-free media, granulocyte colony-stimulating factor, stem cell factor, and pegylated megakaryocyte growth and development factor for 9 days. Cell dose cohorts were assigned to have between 2 and 24 × 109 PBPC cultured at 1, 2, or 3 × 106 cells/mL. Twenty-four patients received high-dose chemotherapy followed by infusion of the cultured PBPC and at least 5 × 106 CD34+ uncultured cryopreserved PBPC per kilogram. No toxicities resulted from infusions of the ex vivo expanded PBPC. The study patients had shorter times to neutrophil (P = .0001) and platelet (P = .01) recovery and fewer red cell transfusions (P = .02) than 48 historical controls who received the same conditioning regimen and posttransplantation care and at least 5 × 106CD34+ PBPC per kilogram. Improvements in all these endpoints were significantly correlated with the expanded cell dose. Nine of 24 (38%) patients recovered neutrophil counts above 500/μL by day 5 or 6 after transplantation, whereas none of the controls had neutrophil recovery before the eighth day. Seven (29%) patients had neutropenia for 3 or fewer days, and 9 (38%) patients did not experience neutropenic fevers or require broad-spectrum antibiotics. Therefore, ex vivo expanded PBPC are capable of ameliorating posttransplantation neutropenia, thrombocytopenia, and anemia in patients receiving high-dose chemotherapy.

Ex vivo expanded unselected peripheral blood: progenitor cells reduce posttransplantation neutropenia, thrombocytopenia, and anemia in patients with breast cancer

The safety and efficacy of administering ex vivo expanded peripheral blood progenitor cells (PBPC) to patients with breast cancer who undergo high-dose chemotherapy and PBPC transplantation was investigated. Unselected PBPC were cultured in gas-permeable bags containing 1-L serum-free media, granulocyte colony-stimulating factor, stem cell factor, and pegylated megakaryocyte growth and development factor for 9 days. Cell dose cohorts were assigned to have between 2 and 24 × 109 PBPC cultured at 1, 2, or 3 × 106 cells/mL. Twenty-four patients received high-dose chemotherapy followed by infusion of the cultured PBPC and at least 5 × 106 CD34+ uncultured cryopreserved PBPC per kilogram. No toxicities resulted from infusions of the ex vivo expanded PBPC. The study patients had shorter times to neutrophil (P = .0001) and platelet (P = .01) recovery and fewer red cell transfusions (P = .02) than 48 historical controls who received the same conditioning regimen and posttransplantation care and at least 5 × 106CD34+ PBPC per kilogram. Improvements in all these endpoints were significantly correlated with the expanded cell dose. Nine of 24 (38%) patients recovered neutrophil counts above 500/μL by day 5 or 6 after transplantation, whereas none of the controls had neutrophil recovery before the eighth day. Seven (29%) patients had neutropenia for 3 or fewer days, and 9 (38%) patients did not experience neutropenic fevers or require broad-spectrum antibiotics. Therefore, ex vivo expanded PBPC are capable of ameliorating posttransplantation neutropenia, thrombocytopenia, and anemia in patients receiving high-dose chemotherapy.

Clinical applications of CD34(+) peripheral blood progenitor cells (PBPC)

Recently, a number of devices have been developed for the positive selection of CD34(+) peripheral blood progenitor cells (PBPC) for clinical use in autologous or allogeneic transplantation. The rationale for CD34(+) selection is based on clinical studies showing a two- to five-log reduction of contaminating tumor cells in patients with breast cancer, multiple myeloma and low-grade lymphoma. In addition, a three- to five-log reduction of T cells can be obtained by CD34(+) selection in both autologous grafts for patients with autoimmune disease resistant to conventional therapy and allogeneic grafts to reduce the incidence and severity of acute graft-versus-host disease. Transplantation of positively selected autologous CD34(+) PBPC results in a rapid and stable neutrophil and platelet engraftment in patients who received an infused dose of at least 2.0 x 10(6) CD34(+) cells/kg. Results from randomized trials suggest that time to engraftment is not different compared to unmanipulated PBPC autografts. However, close monitoring for infectious complications (e.g., cytomegalovirus disease) is required. Allogeneic CD34(+) PBPC have also been successfully transplanted and, using novel technologies, megadoses of purified CD34(+) PBPC can be obtained and used to overcome histocompatibility differences betweeen allogeneic donor and patient resulting in stable engraftment, even in a haploidentical setting. Additional randomized phase III trials are required to determine whether tumor cell purging or lymphocyte depletion by CD34(+) cell selection will have a significant impact on progression-free and overall survival in both autologous and allogeneic transplantation.

Selection and use of chemotherapy with hematopoietic growth factors for mobilization of peripheral blood progenitor cells

Peripheral blood progenitor cells (PBPCs) have become the preferred means of stem cell support for high-dose chemotherapy in recent years. The biology of PBPC mobilization is complex and may be influenced by several variables. Signals from both stromal and hemopoietic cells may induce downregulation of adhesion molecules and upregulate the expression of metalloproteinases. Cytokines alone can mobilize PBPCs but a synergistic effect has been shown when they are used in conjunction with chemotherapy. Disease-specific mobilization strategies appear to have the advantage of less toxicity, greater stem cell yield, and enhanced antitumor activity. Studies have demonstrated that the number of peripheral blood CD34+ cells can be used as a predictor for the timing of apheresis and for estimating PBPC yield. Similarly the CD34+ cell dose is the strongest predictor of hematologic recovery after PBPC transplant. Age, prior radiotherapy, marrow involvement, and prior chemotherapy (especially with alkylating agents) are important factors influencing the yield of stem cells.

Effective ex vivo generation of granulopoietic postprogenitor cells from mobilized peripheral blood CD34(+) cells

OBJECTIVE

Neutropenia following high-dose chemotherapy and peripheral blood progenitor cell (PBPC) transplantation might be abrogated by an additional transplantation of ex vivo generated granulopoietic postprogenitor cells (GPPC). Therefore, the ex vivo expansion of CD34(+) PBPC was systematically studied aiming for optimum GPPC production.

MATERIALS AND METHODS

CD34(+) PBPC were cultured in serum-free medium comparing different (n = 32) combinations of stem cell factor (S), interleukin 1 (1), interleukin 3 (IL-3) (3), interleukin-6 (6), erythropoietin (E), granulocyte colony-stimulating factor (G), granulate-macrophage colony-stimulating factor (GM), daniplestim (D, a novel IL-3 receptor agonist), and Flt3 ligand (FL) under various culture conditions. Ex vivo generated cells were assessed by flow cytometry, morphology, and progenitor cell assays.

RESULTS

Addition of G +/- GM but not GM alone to cultures stimulated with S163E effectively induced the generation of GPPC. GPPC production was maximum after 12 to 14 days. Best expansion rates were observed when cells were cultured at 1.5x10(4)/mL in 21% O(2). Modifications of culture conditions were either less or equally effective (i.e., modification of starting cell concentrations, low oxygen, addition of serum albumin or autologous plasma, repetitive feeding). Comparison of different cytokine combinations revealed that the optimum GPPC expansion cocktail consisted of S6GD+FL (day 12: 130-fold cellular expansion, 32% myeloblasts/promyelocytes, 49.4% myelocytes/metamyelocytes, 12.4% bands/segmented), which furthermore expanded CD34(+) cells (3.4-fold) and clonogenic progenitors (13.4-fold).

CONCLUSION

Using the S6DG+FL expansion cocktail, GPPC could be effectively produced ex vivo starting from positively selected CD34 PBPC, possibly enabling amelioration or even abrogation of posttransplant neutropenia.

Effective ex vivo generation of megakaryocytic cells from mobilized peripheral blood CD34(+) cells with stem cell factor and promegapoietin

OBJECTIVE

The additional transplantation of ex vivo-generated megakaryocytic cells might enable the clinician to ameliorate or abrogate high-dose chemotherapy-induced thrombocytopenia. Therefore, the ex vivo expansion of CD34(+) PBPC was systematically studied aiming for an optimum production of megakaryocytic cells.

MATERIALS AND METHODS

CD34(+) PBPC were cultured in serum-free medium comparing different (n = 23) combinations of stem cell factor (SCF) (S), IL-1beta (1), IL-3 (3), IL-6 (6), erythropoietin (EPO) (E), thrombopoietin (TPO) (T) and promegapoietin (PMP, a novel chimeric IL-3/TPO receptor agonist). Ex vivo-generated cells were assessed by flow cytometry, morphology, and progenitor cell assays.

RESULTS

Addition of TPO to cultures stimulated with S163E, a potent progenitor cell expansion cocktail previously described by our group, effectively induced the generation of CD61(+) cells (day 12: 31.4 +/- 7.9%). The addition of PMP tended to be more effective than TPO +/- IL-3. Whereas EPO was not required to maximize TPO- or PMP-induced megakaryocytic cell production, the use of IL-6 and IL-1beta augmented cellular expansion as well as CD61(+) cell production rates in the majority of cytokine combinations studied. Thus, the most effective CD61(+) cell expansion cocktail consisted of S163 + PMP which resulted in 65.9 +/- 3.0% CD61(+) at day 12 and an overall production of 40.7 +/- 4.5 CD61(+) cells per seeded CD34(+) PBPC. However, the basic 2-factor combination S + PMP also allowed for an effective CD61(+) cell production (day 12 CD61(+) cell production: 15.1 +/- 1.6). Moreover, maximum amplification of CFU-Meg was observed after 7 days using this two-factor cocktail (12.9 +/- 2.6-fold). The majority of CD61(+) cells generated in TPO- or PMP-based medium were low-ploidy 4N and 8N cells, and ex vivo-generated CD61(+), CD41(+), and CD42b(+) cells were mainly double positive for FACS-measured intracellular von Willebrand Factor (vWF) (76.7 +/- 3.3%, 58.8 +/- 4.4%, and 82.7 +/- 2.5%, respectively).

CONCLUSIONS

Taken together, this study demonstrates that megakaryocytic cells can be effectively produced ex vivo with as little as two-factors (SCF + PMP), an approach that might be favorably employed in a clinical expansion trial aiming to ameliorate high-dose chemotherapy-induced thrombocytopenia.