Large volume ex vivo expansion of CD34-positive hematopoietic progenitor cells for transplantation

Development and clinical translation considerations for the next wave of gene modified hematopoietic stem and progenitor cells therapies

INTRODUCTION

Consistent and reliable manufacture of gene modified hematopoietic stem and progenitor cell (HPSC) therapies will be of the utmost importance as they become more mainstream and address larger populations. Robust development campaigns will be needed to ensure that these products will be delivered to patients with the highest quality standards.

AREAS COVERED

Through publicly available manuscripts, press releases, and news articles - this review touches on aspects related to HSPC therapy, development, and manufacturing.

EXPERT OPINION

Recent advances in genome modification technology coupled with the longstanding clinical success of HSPCs warrants great optimism for the next generation of engineered HSPC-based therapies. Treatments for some diseases that have thus far been intractable now appear within reach. Reproducible manufacturing will be of critical importance in delivering these therapies but will be challenging due to the need for bespoke materials and methods in combination with the lack of off-the-shelf solutions. Continued progress in the field will manifest in the form of industrialization which currently requires attention and resources directed toward the custom reagents, a focus on closed and automated processes, and safer and more precise genome modification technologies that will enable broader, faster, and safer access to these life-changing therapies.

An objective flow cytometry method to rapidly determine cord blood potency in cryopreserved units

BACKGROUND

Cord blood banks have to determine the regenerative potential of cord blood units (CBUs) on a representative sample of the cryopreserved product before release to the transplant center. Potency can be measured by using a colony-forming unit (CFU) method, which delays the release of CBU by 7 to 14 days. To accelerate CBU qualification, we have developed a rapid method to assess the response of CD34 cells to interleukin (IL)-3. Flow cytometry was used to measure IL-3-induced STAT5 phosphorylation within CD34-cells. This IL-3 test was compared to the CFU method, as well as the aldehyde dehydrogenase (ALDH) enzyme-based assay.

STUDY DESIGN AND METHODS

Ten cryopreserved CBUs were analyzed for their contents in CD34 and CD45 viable cells, total CFUs, ADLHbright cells, and IL-3-responsive CD34+ cells. Extreme and mild warming event scenarios were simulated on CBUs and used as poor-quality samples. Segments, tubes, and bags from five CBUs were compared for their potency using IL-3 and CFU methods.

RESULTS

The IL-3 test was accurate in identifying the samples handled following standard operating procedures and those subjected to extreme warming events. Based on these results, a threshold of 55% of IL-3-responsive CD34 cells was established to identify good-quality samples. The IL-3 test was also the most sensitive to detect samples subjected to milder warming events.

CONCLUSIONS

Our new method for determining CBU functionality is rapid, unbiased, and robust. The IL-3 test described herein fulfills the requirements for validation, and we intend to implement this method in our cord blood bank facility.

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.

Mesenchymal stem cells in ex vivo cord blood expansion

Umbilical cord blood (CB) is becoming an important source of haematopoietic support for transplant patients lacking human leukocyte antigen matched donors. The ethnic diversity, relative ease of collection, ready availability as cryopreserved units from CB banks, reduced incidence and severity of graft versus host disease and tolerance of higher degrees of HLA disparity between donor and recipient, are positive attributes when compared to bone marrow or cytokine-mobilized peripheral blood. However, CB transplantation is associated with significantly delayed neutrophil and platelet engraftment and an elevated risk of graft failure. These hurdles are thought to be due, at least in part, to low total nucleated cell and CD34(+) cell doses transplanted. Here, current strategies directed at improving TNC and CD34(+) cell doses at transplant are discussed, with particular attention paid to the use of a mesenchymal stem cell (MSC)/CB mononuclear cell ex vivo co-culture expansion system.

Ex-vivo expansion of CFU-GM and BFU-E in unselected PBMC cultures with Flt3L is enhanced by autologous plasma

BACKGROUND

Previous ex-vivo expansion studies in our laboratory, comparing unselected and CD34(+)-selected PBMC, have shown no advantage for CD34(+) cell selection, in terms of the expansion achieved. Our goal was to develop procedures for consistent generation of large numbers of hematopoietic progenitor and post-progenitor cells from unselected PBMC.

METHODS

Unselected PBMC, collected from cancer patients undergoing apheresis prior to high-dose chemotherapy and autologous stem cell rescue, were expanded ex vivo in static cultures, without a stromal layer, in the presence of Flt3 ligand (Flt3L), a recombinant GM-CSF/IL-3 fusion protein (PIXY321), G-CSF and GM-CSF for 10 days.

RESULTS

The addition of 2% autologous plasma to this cytokine combination enhanced expansion of total cell numbers (3.2 fold versus 1.9 fold; p < 0.01), colony-forming units granulocyte-macrophage (CFU-GM) (22.0 fold versus 8.1 fold, p < 0.01) and burst-forming units erythroid (BFU-E) (17.6 fold versus 7.0 fold, 0.01 < p < 0.02). The optimal seeding density for a given specimen was inversely related to the frequency of CD34(+) cells in the sample. CFU-GM expansion with the Flt3L-containing cytokine cocktail was equivalent to that obtained with IL-3, IL-6, G-CSF and SCF, whether or not the cultures were supplemented with autologous plasma. In plasma-free cultures, BFU-E expansion was significantly higher with IL-3, IL-6, G-CSF and SCF than with Flt3L, PIXY321, G-CSF and GM-CSF. In the presence of autologous plasma, however BFU-E expansion was higher in the Flt3L-containing media. In comparison studies, autologous plasma suppressed BFU-E expansion in SCF-containing cultures. Consistent with our colony assay results, dual-parameter flow cytometric analysis of the expanded cell population revealed that supplementation with autologous plasma yielded a significant increase in the numbers of myeloid progenitors in Flt3L-containing cultures.

DISCUSSION

Unselected PBMC from cancer patients can be effectively expanded ex vivo in Flt3L, PIXY321, G-CSF and GM-CSF, supplemented with autologous plasma, yielding high numbers of myeloid and erythroid progenitors.

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.

Protocols for hematopoietic stem cell expansion from umbilical cord blood

The reconstitution of adult stem cells may be a promising source for the regeneration of damaged tissues and for the reconstitution of organ dysfunction. However, there are two major limitations to the use of such cells: they are rare, and only a few types exist that can easily be isolated without harming the patient. The best studied and most widely used stem cells are of the hematopoietic lineage. Pioneering work on hematopoietic stem cell (HSC) transplantation was done in the early 1970s by ED. Thomas and colleagues. Since then HSCs have been used in allogenic and autologous transplantation settings to reconstitute blood formation after high-dose chemotherapy for various blood disorders. The cells can be easily harvested from donors, but the cell number is limited, especially when the HSCs originate from umbilical cord blood (UCB). It would be desirable to set up an ex vivo strategy to expand HSCs in order to overcome the cell dose limit, whereby the expansion would favor cell proliferation over cell differentiation. This review provides an overview of the various existing HSC expansion strategies-focusing particularly on stem cells derived from UCB-of the parameters that might affect the outcome, and of the difficulties that may occur when trying to expand such cells.

Clinically relevant expansion of hematopoietic stem cells with conserved function in a single-use, closed-system bioprocess

The clinical potential of umbilical cord blood-derived stem and progenitor cells has been demonstrated in various animal and human transplantation studies. However, the need for increased numbers of appropriate umbilical cord blood-derived cells continues to limit the development and success of these therapies. Ex vivo expansion has been widely studied as a method to overcome this limitation. We describe the use of a clinically relevant single-use, closed-system bioprocess capable of generating greater numbers of hematopoietic stem and progenitor cells that maintain in vivo and in vitro developmental potential. In addition to expanded numbers of CD34+ cells, CD34(+)CD38(-) cells, colony-forming cells, and long-term culture-initiating cells, the bioprocess generated > or =3.3-fold more long-term nonobese diabetic/severe combined immunodeficient repopulating cells (quantitatively determined using limiting dilution analysis) than present at input. Interestingly, these cells were also capable of multilineage engraftment and were shown to maintain their engraftment potency on a per long-term nonobese diabetic/severe combined immunodeficient repopulating cell basis compared with input noncultured cells. The developmental capacity of bioprocess-generated cells was further demonstrated by their ability to repopulate secondary nonobese diabetic/severe combined immunodeficient recipients. In vitro lineage analysis confirmed that bioprocess-generated cells could differentiate into myeloid and natural killer, B, and T cell lymphoid lineages. This in-depth analysis describes a bioprocess that generates human hematopoietic stem and progenitor cells with conserved hematopoietic activity, establishes analysis criteria for in vitro hematopoietic stem cell expansion studies, and serves as a foundation to test the therapeutic utility of cultured hematopoietic stem cells in large animals and humans.

Superior ex vivo cord blood expansion following co-culture with bone marrow-derived mesenchymal stem cells

One factor limiting the therapeutic efficacy of cord blood (CB) hematopoietic progenitor cell (HPC) transplantation is the low cell dose of the graft. This is associated with an increased incidence of delayed or failed engraftment. Cell dose can be increased and the efficacy of CB transplantation potentially improved, by ex vivo CB expansion before transplantation. Two ex vivo CB expansion techniques were compared: (1) CD133+ selection followed by ex vivo liquid culture and (2) co-culture of unmanipulated CB with bone-marrow-derived mesenchymal stem cells (MSCs). Ex vivo culture was performed in medium supplemented with granulocyte colony-stimulating factor, stem cell factor and either thrombopoietin or megakaryocyte growth and differentiation factor. Expansion was followed by measuring total nucleated cell (TNC), CD133+ and CD34+ cell, colony-forming unit and cobblestone area-forming cell output. When compared to liquid culture, CB-MSC co-culture (i) required less cell manipulation resulting in less initial HPC loss and (ii) markedly improved TNC and HPC output. CB-MSC co-culture therefore holds promise for improving engraftment kinetics in CB transplant recipients.

Ex vivo expansion of hematopoietic stem cells derived from umbilical cord blood in rotating wall vessel

Expansion of umbilical cord blood mononuclear cells (UCB MNCs) was carried out in a rotating wall vessel (RWV) bioreactor and tissue culture flasks (T-flasks) in serum-containing medium supplemented with relatively low doses of purified recombinant human cytokines (5.33 ng/ml IL-3, 16 ng/ml SCF, 3.33 ng/ml G-CSF, 2.13 ng/ml GM-CSF, 7.47 ng/ml FL and 7.47 ng/ml TPO) for 8 days. The cell density, pH and osmolality of the culture medium in the two culture systems were measured every 24h. Flow cytometric assay for CD34+ cells was carried out at 0, 144 and 197 h and methylcellulose colony assays were performed at 0, 72, 144 and 197 h. The pH and osmolality of the medium in the two culture systems were maintained in the proper ranges for hematopoietic stem cells (HSCs) and progenitors culture. The RWV bioreactor, combined with a cell-dilution feeding protocol, was efficient to expand UCB MNCs. At the end of 200 h culture, the total cell number was multiplied by 435.5+/-87.6 times, and CD34+ cells 32.7+/-15.6 times, and colony-forming units of granulocyte-macrophage (CFU-GM) 21.7+/-4.9 times. While in T-flasks, however, total cells density changed mildly, CD34+ cells and CFU-GM decreased in number. It is demonstrated that the RWV bioreactor can provide a better environment for UCB MNCs expansion, enhance the contact between HSCs and accessory cells and make the utilization of cytokines more effective than T-flask.

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.

Clinical-scale production of granulocyte progenitor and post-progenitor cells using daniplestim, leridistim, Progenipoietin, Promegapoietin and autologous plasma

BACKGROUND

Supplementation of PBPC autografts with ex vivo expanded PBMC may significantly reduce or eliminate the period of neutropenia associated with high-dose chemotherapy.

METHODS

Unmanipulated growth-factor mobilized PBMC were expanded in media containing daniplestim, leridistim, Promegapoietin, and Progenipoietin (DLPP) and 2% autologous plasma at 4 x 10(5) PBMC/mL, first in 25 cm(2) T-flasks, with sampling on Days 7, 10, 13 and 15, and then in 1264 cm(2) Nunclon Cell Factories, with sampling on Days 7 and 13.

RESULTS

In T25-flasks, maximal CFU-GM expansion ([38.2 +/- 9.5]-fold) occurred on Day 10, whereas maximal total cell expansion ([6.7 +/- 1.1]-fold) occurred on Day 15. Production of CD15(+)CD11b(-) and CD15(+)CD11b(+) granulocytic post-progenitors (3.0 +/- 0.4 x 10(6) and 3.7 +/- 0.9 x 10(6), respectively) was also maximal at Day 15. Compared with the previously studied combination of Flt3L, PIXY321, G-CSF, GM-CSF and Epo, the DLPP cocktail performed similarly, with the exception of yielding larger GM colonies at Day 10 and fewer granulocyte post-progenitors on Day 15. In Cell Factories, CFU-GM were expanded (31.6 +/- 14.5)-fold, while total nonadherent cells were expanded (2.6 +/- 0.5)-fold. The two stack Cell Factory cultures seeded with 1.0 x 10(8) unselected PBMC produced approximately 3.3 x 10(6) CFU-GM and 1.3 x 10(8) myeloid post-progenitors.

DISCUSSION

Whereas expansion of cell numbers, CFU-GM and granulocytic post-progenitors in Cell Factories mirrored that achieved in T25-flasks, future preclinical studies with the DLPP cytokine combination may be performed in small volumes, with subsequent translation to the larger volume Cell Factories. Sufficient expansion can be achieved using the DLPP cytokine combination in the Cell Factories to provide the numbers of progenitors required for clinical trials.

Bioreactors for hematopoietic cell culture

Hematopoietic cell culture, or ex vivo expansion of hematopoietic cells, is an enabling technology with many potential applications in bone-marrow transplantation, immunotherapy, gene therapy, and the production of blood products. Hematopoietic cultures are complex, with many different cell types of different stages of development present at any given point in time and never in steady state. Moreover, these cells interact strongly with each other and the environment through cytokines (growth factors) and adhesion molecules, as well as through their metabolism. Despite these significant challenges, cell products produced in bioreactors have shown promise in recent phase 1 clinical trials.

Ex vivo expansion of hematopoietic progenitor cells and mature cells

Hematopoietic cells have the potential for providing benefit in a variety of clinical settings. These include cells for support of patients undergoing high-dose chemotherapy, as a target for replacement gene therapy, and as a source of cells for immunotherapy. The limitation to many of these applications has been the total absolute number of defined target cells. Therefore many investigators have explored methods to culture hematopoietic cells in vitro to increase the numbers of these cells. Studies attempting to expand hematopoietic stem cells, progenitor cells, and mature cells in vitro have become possible over the past decade due to the availability of recombinant growth factors and cell selection technologies. To date, no studies have demonstrated convincing data on the expansion of true stem cells, and so the focus of this review is the expansion of committed progenitor cells and mature cells. A number of clinical studies have been preformed using a variety of culture conditions, and several studies are currently in progress that explore the use of ex vivo expanded cells. These studies will be discussed in this review. There are evolving data that suggest that there are real clinical benefits associated with the use of the expanded cells; however, we are still at the early stages of understanding how to optimally culture different cell populations. The next decade should determine what culture conditions and what cell populations are needed for a range of clinical applications.

Progress in haematopoietic stem cell transplantation for multiple myeloma

High-dose myeloablative treatment followed by autologous haematopoietic stem cell transplantation has significantly improved survival of patients younger than 65 years of age with multiple myeloma as compared with conventional chemotherapy. However, all patients seem to relapse and molecular remissions are rare. Results of allogeneic transplantation, still hampered by high transplant-related mortality, have improved dramatically over the last 5-6 years and this is an option for patients younger than 50-55 years old. The relapse rate is lower than with autologous transplantation and molecular remissions are frequent. Some patients are still in complete haematological remission more the 10 years following transplantation. Autologous transplantation followed by nonmyeloablative allogeneic transplantation is on trial and may be a way to eventually cure a fraction of younger patients with multiple myeloma.

Suppressive effects of TNF-alpha, TGF-beta1, and chemokines on megakaryocytic colony formation in CD34+ cells derived from umbilical cord blood compared with mobilized peripheral blood and bone marrow

CD34+ cells from human umbilical cord blood (CB) were isolated and investigated for megakaryocytic (MK) colony formation in response to recombinant human (rh) stimulatory and suppressive cytokines and compared with their counterparts in normal BM and G-CSF-mobilized peripheral blood (mPBL). First, we observed that IL-11 by itself at any dosage had no stimulator activity on MK colony formation derived from CD34+ cells in CB, mPBL, and BM. IL-3, steel factor (SLF), or thrombopoietin (Tpo) alone stimulated numbers of colony-forming unit-megakaryocyte (CFU-MK) in a dose-dependent fashion. Maximum growth of MK progenitor cells was noted in the presence of a combination of cytokines: IL-11, IL-3, SLF, and Tpo. The frequency of CFU-MK in CB and mPBL was significantly greater than that in BM, and the size of colonies in CB and mPBL was significantly greater than that in BM, and the size of colonies was larger as well. In addition, an increased number of big mixed colonies containing MK were observed in CB and mPBL. In the presence of IL-11, IL-3, SLF, and Tpo, CFU-MK derived from CB, mPBL, and BM was suppressed by tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta1 (TGF-beta1). CFU-MK derived from normal BM was inhibited by some chemokines evaluated, whereas CFU-MK derived from CB was suppressed only by platelet factor-4 (PF-4), IFN-inducible protein-10 (IP-10), Exodus-1, Exodus-2, and Exodus-3, but to a lesser degree. In CB, unlike granulocyte-macrophage (CFU-GM), erythroid (BFU-E), high-proliferative potential (HPP-CFC), or multipotential (CFU-GEMM) progenitors, at least a subpopulation of MK progenitors are in S-phase. Therefore, CB MK progenitors respond to the suppressive effects of some members of the chemokine family. Similar results were noted for burst-forming unit-MK (BFU-MK). Our results indicate that CB and mPBL are rich sources of MK progenitors and that MK progenitors in CB are responsive to the suppressive effects of TNF-alpha and TGF-beta1 and some members of the chemokine family.

Conditions that enable human hematopoietic stem cell engraftment in all NOD-SCID mice

BACKGROUND

Transplantation of human hematopoietic stem cells is the only true test of their long-term repopulation potential. Models are readily available to evaluate murine hematopoietic stem cells, but few exist that allow reliable quantification of human stem cells. The non-obese diabetic-severe combined immunodeficient (NOD-SCID) mouse model enables quantification of human hematopoietic stem cells, but the conditions that permit human engraftment in all animals have yet to be defined. The aims of the project were, therefore, to describe the variables that allow human engraftment in the NOD-SCID mouse model and the techniques that accurately quantify this engraftment.

METHODS

NOD-SCID mice that had or had not received 250, 325, or 400 cGy irradiation received cord blood (CB) mononuclear or CD34+ cells i.v. or i.p. Mice were killed 6 weeks after transplantation, and the bone marrow, spleen, and thymus were harvested. Four-color flow cytometric analysis, semi-quantitative PCR, myeloid and erythroid progenitor, and stem cell assays were used to monitor human engraftment.

RESULTS

A 250 or 325 cGy and i.v. injection of CB mononuclear or CD34+ cells is required to detect multilineage human engraftment in the bone marrow, spleen, or thymus of NOD-SCID mice. Four-color flow cytometric analysis and semi-quantitative PCR enable accurate detection of 0.1% human cells. Progenitor and stem cell assays provide functional information about the engrafted cells.

CONCLUSIONS

Successful development of the NOD-SCID mouse model and techniques to assess human engraftment now allow it to be used reliably to analyze the effects of short-term cytokine exposure on the long-term repopulating capacity of CB stem cells.

Physiologically significant effects of pH and oxygen tension on granulopoiesis

OBJECTIVE

Granulocyte differentiation in the bone marrow (BM) takes place in regions with lower pH and O(2) tension (pO(2)) than those in the BM sinuses. This suggests that granulopoiesis will be enhanced at subvascular pH and pO(2).

MATERIALS AND METHODS

The effects of pH AND pO2 on granulocyte proliferation, differentiation, and granulocyte colony-stimulating factor receptor (G-CSFR) expression were evaluated using mobilized peripheral blood CD34(+) cells directed down the granulocytic pathway with stem cell factor, interleukin 3, interleukin 6, and G-CSF.

RESULTS

Cell expansion was enhanced at subvascular pH, with twice as many total cells and CD15(bright)/CD11b(+) late neutrophil precursors (myelocytes, metamyelocytes, bands) produced at pH 7.07 to 7.21 as was produced at pH 7.38. Low pH accelerated the rate of differentiation concomitant with this increase in proliferation. Also, total, CD15(bright)/CD11b(-) (promyelocytes, early myelocytes), and CD15(bright)/CD11b(+) cell expansion was enhanced at lower pO(2), with twice as many of each cell type produced at 5% O(2) as at 20% O(2). The effects of low pH and low pO(2) were additive, such that generation of total, CD15(bright)/CD11b(-), and CD15(bright)/CD11b(+) cells was 3.5-, 2.4-, and 4.0-fold greater at pH 7.21 and 5% O(2) than at the standard hematopoietic culture conditions of pH 7.38 and 20% O(2). Low pH resulted in faster upregulation of G-CSFR surface expression, whereas pO(2) had no effect on G-CSFR expression.

CONCLUSION

These data provide compelling evidence that pH and pO(2) gradients within the BM play significant roles in regulating hematopoiesis. More rapid granulocytic cell proliferation and differentiation at low pH may be explained in part by more rapid G-CSFR expression. The ability to alter cell development by manipulating pH and pO(2) has important implications for optimizing ex vivo production of neutrophil precursors.

Engraftment of primates with G-CSF mobilized peripheral blood CD34+ progenitor cells expanded in G-CSF, SCF and MGDF decreases the duration and severity of neutropenia

We used a primate model of autologous peripheral blood progenitor cell (PBPC) transplantation to study the effect of in vitro expansion on committed progenitor cell engraftment and marrow recovery after transplantation. Four groups of baboons were transplanted with enriched autologous CD34+ PBPC collected by apheresis after five days of G-CSF administration (100 microg/kg/day). Groups I and III were transplanted with cryopreserved CD34+ PBPC and Groups II and IV were transplanted with CD34+ PBPC that had been cultured for 10 days in Amgen-defined (serum free) medium and stimulated with G-CSF, megakaryocyte growth and development factor (MGDF), and stem cell factor each at 100 etag/ml. Group III and IV animals were administered G-CSF (100 microg/kg/day) and MGDF (25 microg/kg/day) after transplant, while animals in Groups I and II were not. For the cultured CD34+ PBPC from groups II and IV, the total cell numbers expanded 14.4 +/- 8.3 and 4.0 +/- 0.7-fold, respectively, and CFU-GM expanded 7.2 +/- 0.3 and 8.0 +/- 0.4-fold, respectively. All animals engrafted. If no growth factor support was given after transplant (Groups II and I), the recovery of WBC and platelet production after transplant was prolonged if cells had been cultured prior to transplant (Group II). Administration of post-transplant G-CSF and MGDF shortened the period of neutropenia (ANC < 500/microL) from 13 +/- 4 (Group I) to 10 +/- 4 (Group III) days for animals transplanted with non-expanded CD34+ PBPC. For animals transplanted with ex vivo-expanded CD34+ PBPC, post-transplant administration of G-CSF and MGDF shortened the duration of neutropenia from 14 +/- 2 (Group II) to 3 +/- 4 (Group IV) days. Recovery of platelet production was slower in all animals transplanted with expanded CD34+ PBPC regardless of post-transplant growth factor administration. Progenitor cells generated in vitro can contribute to early engraftment and mitigate neutropenia when growth factor support is administered post-transplant. Thrombocytopenia was not decreased despite evidence of expansion of megakaryocytes in cultured CD34+ populations.

The use of Teflon cell culture bags to expand functionally active CD8+ cytotoxic T lymphocytes

We have investigated the ability of Teflon cell culture (TCC) bags, compared to conventional tissue culture flasks and plates, to support the expansion of human CD8+ T cells in response to an allogeneic stimulus. TCC bags, which are compatible with good manufacturing practice (GMP), facilitated CD8+ T cell growth as well as conventional culture vessels and resulted in cytotoxic T cells which were able to kill allogeneic targets. Growth characteristics were compared by investigating the number, immunophenotype and cell cycle properties of the cells generated. The kinetics of cell growth were not significantly different over the first 14 days of culture in each vessel type, with the cell counts being highest at day 10 in all cases. However, the TCC bags resulted in a significantly higher proportion of cells with the morphology of typical lymphocytes than tissue culture flasks after 14 and 18 days in culture. There were no significant differences in the percentage of typical lymphocytes expanded in TCC bags compared to those expanded in plates. Expanded CD8+ cells maintained their initial level of expression of CD3, CD11a, CD18 and T cell receptor (alphabeta heterodimer, TCR (alphabeta)) but increased expression of CD45RO, CD95 and of activation markers HLA-DR and CD25 in each culture vessel. Studies of cell cycle parameters showed that each vessel supported CD8+ T cell stimulation, as demonstrated by significantly higher levels of S phase than fresh PBMN cells. The cells generated in TCC bags were able to kill allogeneic targets and also possessed natural killer (NK) cell activity. Thus, TCC bags are able to support the expansion of CD8+ T lymphocytes as well as flasks or tissue culture plates and are applicable to lymphocyte expansion for use in immunotherapy.

Differential kinetics of primitive hematopoietic cells assayed in vitro and in vivo during serum-free suspension culture of CD34+ blood progenitor cells

So far, blood progenitor cells (BPC) expanded ex vivo in the absence of stromal cells have not been demonstrated to reconstitute hematopoiesis in myeloablated patients. To characterize the fate of early hematopoietic progenitor cells during ex vivo expansion in suspension culture, human CD34(+)-enriched BPC were cultured in serum-free medium in the presence of FLT3 ligand (FL), stem cell factor (SCF) and interleukin 3 (IL-3). Both CD34 surface expression levels and the percentage of CD34+ cells were continuously downregulated during the culture period. We observed an expansion of colony-forming units granulocyte-macrophage (CFU-GM) and BFU-E beginning on day 3 of culture, reaching an approximate 2-log increase by days 5 to 7. Limiting dilution analysis of primitive in vitro clonogenic progenitors was performed through a week 6 cobblestone-area-forming cell (CAFC) assay, which has previously been shown to detect long-term bone marrow culture-initiating cells (LTC-IC). A maintenance or a slight (threefold) increase of week 6 CAFC/LTC-IC was found after one week of culture. To analyze the presence of BPC mediating in vivo engraftment, expanded CD34+ cells were transplanted into preirradiated NOD/SCID mice at various time points. Only CD34+ cells cultured for up to four days successfully engrafted murine bone marrow with human cells expressing myeloid or lymphoid progenitor phenotypes. In contrast, five- and seven-day expanded human BPC did not detectably engraft NOD/SCID mice. When FL, SCF and IL-3-supplemented cultures were performed for seven days on fibronectin-coated plastic, or when IL-3 was replaced by thrombopoietin, colony forming cells and LTC-IC reached levels similar to those of control cultures, yet no human cell engraftment was recorded in the mice. Also, culture in U-bottom microplates resulting in locally increased CD34+ cell density had no positive effect on engraftment. These results indicate that during ex vivo expansion of human CD34+ cells, CFC and LTC-IC numbers do not correlate with the potential to repopulate NOD/SCID mice. Our results suggest that ex vivo expanded BPC should be cultured for limited time periods only, in order to preserve bone-marrow-repopulating hematopoietic stem cells.

Proliferation and Survival of Mammary Carcinoma Cells Are Influenced by Culture Conditions Used for Ex Vivo Expansion of CD34+Blood Progenitor Cells

Malignant cell contamination in autologous transplants is a potential origin of tumor relapse. Ex vivo expansion of CD34+ blood progenitor cells (BPC) has been proposed as a tool to eliminate tumor cells from autografts. To characterize the influence of culture conditions on survival, growth, and clonogenicity of malignant cells, we isolated primary mammary carcinoma cells from pleural effusions and ascites of patients with metastatic breast cancer and cultured them in the presence of stem cell factor (SCF), interleukin-1β (IL-1β), IL-3, IL-6, and erythropoietin (EPO), ie, conditions previously shown to allow efficient ex vivo expansion of CD34+ BPC. In the presence of serum, tumor cells proliferated during a 7-day culture period and no significant growth-modulatory effect was attributable to the presence of hematopoietic growth factors. When transforming growth factor-β1 (TGF-β1) was added to these cultures, proliferation of breast cancer cells was reduced. Expansion of clonogenic tumor cells was seen in the presence of SCF + IL-1β + IL-3 + IL-6 + EPO, but was suppressed by TGF-β1. Cocultures of tumor cells in direct cellular contact with hematopoietic cells showed that tumor cell growth could be stimulated by ex vivo expanded hematopoietic cells at high cell densities (5 × 105/mL). In contrast, culture under serum-free conditions resulted in death of greater than 90% of breast cancer cells within 7 days and a further decrease in tumor cell numbers thereafter. In the serum-free cultures, hematopoietic cytokines and cellular contact with CD34+ BPC could not protect the tumor cells from death. Therefore, ex vivo expansion of CD34+ BPC in serum-free medium provides an environment for efficient purging of contaminating mammary carcinoma cells. These results have clinical significance for future protocols in autologous progenitor cell transplantation in cancer patients.

Proliferation and Survival of Mammary Carcinoma Cells Are Influenced by Culture Conditions Used for Ex Vivo Expansion of CD34+Blood Progenitor Cells

Malignant cell contamination in autologous transplants is a potential origin of tumor relapse. Ex vivo expansion of CD34+ blood progenitor cells (BPC) has been proposed as a tool to eliminate tumor cells from autografts. To characterize the influence of culture conditions on survival, growth, and clonogenicity of malignant cells, we isolated primary mammary carcinoma cells from pleural effusions and ascites of patients with metastatic breast cancer and cultured them in the presence of stem cell factor (SCF), interleukin-1β (IL-1β), IL-3, IL-6, and erythropoietin (EPO), ie, conditions previously shown to allow efficient ex vivo expansion of CD34+ BPC. In the presence of serum, tumor cells proliferated during a 7-day culture period and no significant growth-modulatory effect was attributable to the presence of hematopoietic growth factors. When transforming growth factor-β1 (TGF-β1) was added to these cultures, proliferation of breast cancer cells was reduced. Expansion of clonogenic tumor cells was seen in the presence of SCF + IL-1β + IL-3 + IL-6 + EPO, but was suppressed by TGF-β1. Cocultures of tumor cells in direct cellular contact with hematopoietic cells showed that tumor cell growth could be stimulated by ex vivo expanded hematopoietic cells at high cell densities (5 × 105/mL). In contrast, culture under serum-free conditions resulted in death of greater than 90% of breast cancer cells within 7 days and a further decrease in tumor cell numbers thereafter. In the serum-free cultures, hematopoietic cytokines and cellular contact with CD34+ BPC could not protect the tumor cells from death. Therefore, ex vivo expansion of CD34+ BPC in serum-free medium provides an environment for efficient purging of contaminating mammary carcinoma cells. These results have clinical significance for future protocols in autologous progenitor cell transplantation in cancer patients.

Ex vivo expansion and differentiation of unselected peripheral blood progenitor cells in serum-free media

The ability to expand and differentiate unselected PBPC was investigated. Cells were grown in serum-free media containing stem cell factor, GCSF and megakaryocyte growth and development factor (pegylated PEG-rHuMGDF) with or without supplemental serum. Optimal proliferation occurred when PBPC were cultured without prior Ficoll-Paque separation in serum-free media. Cell yields after 17 days of culture were proportional to the percentage of CD34+ cells in the starting population and were 1170+/-302-fold higher than the starting numbers of CD34+ cells. Granulocyte-macrophage colony-forming units increased over 12 days of culture, whereas the numbers of erythroid colony-forming cells peaked between 4 and 7 days. Elimination of PEG-rHuMGDF from cell cultures resulted in significantly lower yields of myeloid and erythroid colony-forming cells and total cell numbers. Cell differentiation into neutrophils was indicated by progressive increases in CD11b, CD15, and CD66b expression. Expanded neutrophils phagocytosed and killed bacteria as efficiently as neutrophils from normal donors. Large-scale expansion studies yielded similar proliferation and differentiation results as parallel small-scale cultures. Therefore, unselected PBPC can be efficiently expanded and differentiated into large numbers of functional mature neutrophils.

Stirred culture of peripheral and cord blood hematopoietic cells offers advantages over traditional static systems for clinically relevant applications

The ability to culture hematopoietic cells in readily characterizable and scalable stirred systems, combined with the capability to utilize serum-free medium, will aid the development of clinically attractive bioreactor systems for transplantation therapies. We thus examined the proliferation and differentiation characteristics of peripheral blood (PB) mononuclear cells (MNC), cord blood (CB) MNC, and PB CD34(+) cells in spinner flasks and (control) T-flask cultures in both serum-containing and serum-free media. Hematopoietic cultures initiated from all sources examined (PB MNC, CB MNC, and PB CD34(+) cells) grew well in spinner vessels with either serum-containing or serum-free medium. Culture proliferation in spinner flasks was dependent on both agitator design and RPM as well as on the establishment of critical inoculum densities (ID) in both serum-containing (2 x 10(5) MNC/mL) and serum-free (3 x 10(5) MNC/mL) media. Spinner flask culture of PB MNC in serum-containing medium provided superior expansion of total cells and colony-forming cells (CFC) at high ID (1.2 x 10(6) cells/mL) as compared to T-flask controls. Serum-free spinner culture was comparable, if not superior, to that observed in serum-containing medium. This is the first report of stirred culture of PB or CB MNC, as well as the first report of stirred CD34(+) cell culture. Additionally, this is the first account of serum-free stirred culture of hematopoietic cells from any source.

Minimal residual disease in autologous hematopoietic harvests from breast cancer patients

The increasing use of high-dose chemotherapy with autologous hematopoietic transplantation for the treatment of solid malignancies has raised concern about the role of tumor cells contaminating the grafts. Minimal residual disease (MRD) in autologous grafts has became a dynamic and intensively studied field in oncology. This review discusses the current status of MRD in breast cancer autografts and presents existing data on detection methodology, clinical relevance, biologic characteristics and purging techniques.

A Prospective Randomized Trial of Buffy Coat Versus CD34-Selected Autologous Bone Marrow Support in High-Risk Breast Cancer Patients Receiving High-Dose Chemotherapy

High-dose chemotherapy with hematopoietic progenitor cell support is administered increasingly to selected categories of patients with high-risk malignancies. Bone marrow and/or peripheral blood progenitor cells (PBPCs) are commonly cryopreserved with the cryoprotectant dimethyl sulfoxide (DMSO), which can cause a variety of systemic side effects when the graft is thawed and infused. The progenitor cells thought to be responsible for hematopoietic recovery express the CD34 antigen and constitute 1% to 3% of the marrow cells and 0.5% of the PBPC fraction. Transplantation of a CD34+ graft would markedly reduce the volume and thus the amount of DMSO required, thereby decreasing the infusion-related toxicities. In this study, 89 high-risk breast cancer patients received high-dose therapy and were randomized to receive an autologous CD34+ marrow graft (Arm A) versus a standard buffy coat fraction (Arm B). After marrow infusion, significant increases in diastolic and systolic blood pressure, as well as significant decreases in heart rate, were documented in Arm B compared to Arm A patients (P < .001). None of the patients in Arm A experienced any clinically serious adverse events associated with the marrow infusion compared to 6% of the Arm B patients. The median time to neutrophil engraftment was 13 days for Arm A and 11 days for Arm B patients (P = .218). The median time to platelet engraftment was 27 days for Arm A and 20 days for Arm B patients (0.051). There were no other significant differences between the two arms of the study with respect to thrombocytopenia-related complications or immune function reconstitution. Additionally, patients on Arm A who received ≥1.2 × 106 CD34+ cells/kg had no delay in platelet recovery (22 days), compared to patients on Arm B, who also received greater than 1.2 × 106 CD34+ cells/kg (20 days) (P = .604). In conclusion, this prospective randomized study demonstrates that breast cancer patients who receive high-dose therapy with autologous CD34+ marrow support have reduced marrow infusion-related toxicity, comparable time to neutrophil engraftment and immune function recovery posttransplant, and for those who receive <1.2 × 106 CD34+ cells/kg, comparable time to platelet engraftment compared to women who receive buffy coat fractions of marrow.

A Prospective Randomized Trial of Buffy Coat Versus CD34-Selected Autologous Bone Marrow Support in High-Risk Breast Cancer Patients Receiving High-Dose Chemotherapy

High-dose chemotherapy with hematopoietic progenitor cell support is administered increasingly to selected categories of patients with high-risk malignancies. Bone marrow and/or peripheral blood progenitor cells (PBPCs) are commonly cryopreserved with the cryoprotectant dimethyl sulfoxide (DMSO), which can cause a variety of systemic side effects when the graft is thawed and infused. The progenitor cells thought to be responsible for hematopoietic recovery express the CD34 antigen and constitute 1% to 3% of the marrow cells and 0.5% of the PBPC fraction. Transplantation of a CD34+ graft would markedly reduce the volume and thus the amount of DMSO required, thereby decreasing the infusion-related toxicities. In this study, 89 high-risk breast cancer patients received high-dose therapy and were randomized to receive an autologous CD34+ marrow graft (Arm A) versus a standard buffy coat fraction (Arm B). After marrow infusion, significant increases in diastolic and systolic blood pressure, as well as significant decreases in heart rate, were documented in Arm B compared to Arm A patients (P < .001). None of the patients in Arm A experienced any clinically serious adverse events associated with the marrow infusion compared to 6% of the Arm B patients. The median time to neutrophil engraftment was 13 days for Arm A and 11 days for Arm B patients (P = .218). The median time to platelet engraftment was 27 days for Arm A and 20 days for Arm B patients (0.051). There were no other significant differences between the two arms of the study with respect to thrombocytopenia-related complications or immune function reconstitution. Additionally, patients on Arm A who received ≥1.2 × 106 CD34+ cells/kg had no delay in platelet recovery (22 days), compared to patients on Arm B, who also received greater than 1.2 × 106 CD34+ cells/kg (20 days) (P = .604). In conclusion, this prospective randomized study demonstrates that breast cancer patients who receive high-dose therapy with autologous CD34+ marrow support have reduced marrow infusion-related toxicity, comparable time to neutrophil engraftment and immune function recovery posttransplant, and for those who receive <1.2 × 106 CD34+ cells/kg, comparable time to platelet engraftment compared to women who receive buffy coat fractions of marrow.

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.

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.

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.

Phage presentation and affinity selection of a deletion mutant of human interleukin-3

A deletion derivative of the cytokine human interleukin-3 (hIL-3(15-125), comprising amino acids 15-125 of the native protein) was produced as a fusion to the filamentous phage surface protein pIII. The cytokine was detected in association with phage particles by protein immunoblotting. Compared to an equivalent quantity of soluble-cytokine, phage-presented hIL-3(15-125) exhibited reduced biological activity in a hIL-3-dependent cell proliferation assay. The reduction in activity was attributable to presence of phage particles in the assay, rather than directly owing to physical incorporation of the cytokine into the phage particle. Owing to the position of the amber codon in the phagemid vector, the phagemid-produced free hIL-3(15-125) species (designated hIL-3(15-125) epsilon) had 20 amino acids appended to its C-terminus; hIL-3(15-125) epsilon did not exhibit reduced bioactivity. hIL-3(15-125)-presenting phage were affinity-selected with either a hIL-3-reactive polyclonal antibody or with cells expressing the heterodimeric hIL-3 receptor. These data are consistent with the use of phage-display technology for the affinity selection of hIL-3 variants with modified biological properties.

Neutrophil maturation of CD34+ cells from peripheral blood and bone marrow in serum-free culture medium with PIXY321 and granulocyte-colony stimulating factor (G-CSF)

Bone marrow (BM) or peripheral blood (PB) CD34+ cells were cultured for 12 days in serum-free culture medium containing PIXY321 (IL-3/ GM-CSF fusion protein) with or without periodic supplements of granulocyte-colony stimulating factor (G-CSF). The cultures were evaluated at day 12 for total cell proliferation (fold increase from day 0), neutrophil differentiation by flow cytometry, using dual staining with CD15-FITC and CD11b-PE, and morphology using Wright-Giemsa and granule staining. In cultures containing PIXY321 where 6000 U/ml of G-CSF was added days 0 and 6, there was no significant difference (p > or = 0.05) in cell proliferation or the percent of CD15+/CD11b+ cells when compared with cultures with PIXY321 alone. ELISA analysis showed G-CSF levels had declined by 90% after 3 days of culture. Further studies were performed to assess the benefit of supplementing lower concentrations of G-CSF (600 U/ml) at more frequent intervals. A significant increase (p < or = 0.05) in cell proliferation and percent CD15+/CD11b+ was observed when G-CSF was added on days 0, 3, 6, and 9 (every 3 days) as compared with those cultures with PIXY321 alone. CD34+ cell proliferation without G-CSF was 19.6 +/- 4.8-fold, with G-CSF added on days 0 and 6 was 28.7 +/- 6.4-fold, and with G-CSF added on days 0, 3, 6, and 9 was 45.9 +/- 10.6-fold. Percent of CD15+/CD11b+ cells was 19.0 +/- 4.6%, 38.2 +/- 7.2%, and 58.5 +/- 6.5%, respectively, in these cultures. We observed more CD15+/CD11b+ cells, myelocytes/metamyelocytes, and secondary granule staining in cultures with G-CSF added on day, 0, 3, 6, and 9 as compared with cultures with G-CSF added on days 0 and 6 or no G-CSF added. We conclude that PIXY321 and G-CSF act synergistically on the in vitro proliferation and neutrophil differentiation of BM and PB CD34+ cells and that frequent supplements of G-CSF facilitate neutrophil differentiation.

Engraftment and Development of Human CD34+-Enriched Cells From Umbilical Cord Blood in NOD/LtSz-scid/scid Mice

Understanding the repopulating characteristics of human hematopoietic stem/progenitor cell fractions is crucial for predicting their performance after transplant into high-risk patients following high-dose therapy. We report that human umbilical cord blood cells, 78% to 100% of which express the hematopoietic progenitor cell surface marker CD34, can consistently engraft, develop, and proliferate in the hematopoietic tissues of sublethally irradiated NOD/LtSz-scid/scid mice. Engraftment and development of CD34+ cells is not dependent on human growth factor support. CD34+ cells home to the mouse bone marrow (BM) that becomes the primary site of human hematopoietic development containing myeloid, lymphoid, erythroid, and CD34+ progenitor populations. Myeloid, and in particular lymphoid cells possessing more mature cell surface markers, comprise the human component of mouse spleen and peripheral blood, indicating that development proceeds from primary hematopoietic sites to the periphery. Repopulation of secondary recipients with human cells by BM from primary recipients demonstrates the maintenance of substantial proliferation capacity of the input precursor population. These data suggest that the cells capable of initiating human cell engraftment (SCID-repopulating cells) are contained in the CD34+ cell fraction, and that this mouse model will be useful for assaying the developmental potential of other rare human hematopoietic cell fractions in vivo.

Engraftment and Development of Human CD34+-Enriched Cells From Umbilical Cord Blood in NOD/LtSz-scid/scid Mice

Understanding the repopulating characteristics of human hematopoietic stem/progenitor cell fractions is crucial for predicting their performance after transplant into high-risk patients following high-dose therapy. We report that human umbilical cord blood cells, 78% to 100% of which express the hematopoietic progenitor cell surface marker CD34, can consistently engraft, develop, and proliferate in the hematopoietic tissues of sublethally irradiated NOD/LtSz-scid/scid mice. Engraftment and development of CD34+ cells is not dependent on human growth factor support. CD34+ cells home to the mouse bone marrow (BM) that becomes the primary site of human hematopoietic development containing myeloid, lymphoid, erythroid, and CD34+ progenitor populations. Myeloid, and in particular lymphoid cells possessing more mature cell surface markers, comprise the human component of mouse spleen and peripheral blood, indicating that development proceeds from primary hematopoietic sites to the periphery. Repopulation of secondary recipients with human cells by BM from primary recipients demonstrates the maintenance of substantial proliferation capacity of the input precursor population. These data suggest that the cells capable of initiating human cell engraftment (SCID-repopulating cells) are contained in the CD34+ cell fraction, and that this mouse model will be useful for assaying the developmental potential of other rare human hematopoietic cell fractions in vivo.

Hematopoietic stem cell expansion

This review addresses two issues: (1) cytokine-mediated expansion of functional end cells for the abrogation of short term neutropenia and thrombopenia following high dose chemotherapy and (2) cytokine-driven increase in absolute numbers of functional stem cells. The literature suggests that the short term exposure of CD34+ cells to cytokines produces mature progenitors which in turn give rise to functional neutrophils and platelets. The expansion of functional stem cells is a more complex issue, as primitive stem cells are quiescent and their growth requirements are less clearly defined.

Optimization of CD34+ cell selection using immunomagnetic beads: implications for use in cryopreserved peripheral blood stem cell collections

Isolation of CD34+ cells from bone marrow, umbilical cord blood, and mobilized peripheral blood stem cell (PBSC) collections has many potential clinical benefits. The aim of this study was to evaluate the use of the ISOLEX 300 system to select hematopoietic precursors and determine the effectiveness at depleting contaminating tumor cells from cryopreserved/thawed PBSC. Median recovery of CD34+ cells and CFU-GM colonies was 71% and 51.5%, respectively, using a protocol optimized for our laboratory. A mean 2.9 log10 decrease in contaminating breast carcinoma cells was seen after the selection process. Selected CD34+ cells underwent a second round of cryopreservation/thawing while retaining 85.6% viability and 72.3% recovery of CFU-GM colonies.

Peripheral blood stem cells for autografting

High-dose therapy with autologous hematopoietic progenitor cell support is effective treatment for patients with a variety of high-risk malignancies. Accelerating of marrow recovery from near-lethal or lethal toxicity with hematopoietic cell support improves the safety and cost effectiveness of the high-dose regimens. Peripheral blood progenitor cells will soon replace marrow as the major source of hematopoietic support. This chapter reviews the techniques of peripheral blood progenitor cell collection, mobilization, purification (for tumor removal), and ex vivo expansion.