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

Curative approaches for sickle cell disease: A review of allogeneic and autologous strategies

Despite sickle cell disease (SCD) first being reported >100years ago and molecularly characterized >50years ago, patients continue to experience severe morbidity and early mortality. Although there have been substantial clinical advances with immunizations, penicillin prophylaxis, hydroxyurea treatment, and transfusion therapy, the only cure that can be offered is hematopoietic stem cell transplantation (HSCT). In this work, we summarize the various allogeneic curative approaches reported to date and discuss open and upcoming clinical research protocols. Then we consider gene therapy and gene editing strategies that may enable cure based on autologous HSCs.

CD26 protease inhibition improves functional response of unfractionated cord blood, bone marrow, and mobilized peripheral blood cells to CXCL12/SDF-1

Hematopoietic stem cell transplantation (HSCT) is an important treatment option for patients with malignant and nonmalignant hematologic diseases. Methods to improve transplant efficiency are being explored with the intent to improve engraftment and immune reconstitution post-HSCT. A current approach under investigation involves treatment of donor cells with inhibitors that target the protease CD26, a negative regulator of the chemokine CXCL12/stromal cell-derived factor-1. CD26 inhibitor treatment has been shown to improve the functional response of CD34(+) cord blood (CB) cells, but not CD34(+) granulocyte colony-stimulating factor-mobilized peripheral blood stem cells, to CXCL12/stromal cell-derived factor-1. The effect of CD26 inhibitors on unfractionated CB, bone marrow, or granulocyte colony-stimulating factor-mobilized peripheral blood mononuclear cells has not been evaluated previously. We observed that although CB had greater CD26 expression than bone marrow or mobilized peripheral blood, treatment with a CD26 inhibitor (Diprotin A) resulted in increased responsiveness to stromal cell-derived factor-1 for all three mononuclear cell sources tested. This suggests that clinical therapeutic benefit might be gained by using CD26 inhibitors as a strategy to improve engraftment of unfractionated mobilized peripheral blood cells as well as CB cells.

A journey to produce platelets in vitro

Allogeneic platelet transfusions protect patients from bleeding episodes and also make aggressive medical procedures such as those involving marrow transplants requiring chemotherapy and/or radiotherapy possible. These patients are dependent upon an unfailing supply of platelets that can sometimes be in short supply due to high demands coupled with an extremely short expiration date for platelet products of only 5 days. One approach that is under investigation to overcome platelet shortages is to harness the extraordinary capabilities of stem cells to proliferate and differentiate into various cell types and to use this ability to specifically produce clinical scale quantities of functional platelets in bioreactors. To accomplish such an enormous and complex task requires an appreciation of the regulatory mechanisms that occur during the development of megakaryocytes (MKs) and the subsequent biogenesis of functional platelets from mature MKs. This means understanding the complex network of intracellular and extracellular regulatory mechanisms that act at each phase of a developmental process that ushers stem cells along the MK lineage to produce billions of platelets per day in a healthy individual.

Nicotinamide, a SIRT1 inhibitor, inhibits differentiation and facilitates expansion of hematopoietic progenitor cells with enhanced bone marrow homing and engraftment

Strategies that increase homing to the bone marrow and engraftment efficacy of ex vivo expended CD34(+) cells are expected to enhance their clinical utility. Here we report that nicotinamide (NAM), a form of vitamin B-3, delayed differentiation and increased engraftment efficacy of cord blood-derived human CD34(+) cells cultured with cytokines. In the presence of NAM, the fraction of CD34(+)CD38(-) cells increased and the fraction of differentiated cells (CD14(+), CD11b(+), and CD11c(+)) decreased. CD34(+) cells cultured with NAM displayed increased migration toward stromal cell derived factor-1 and homed to the bone marrow with higher efficacy, thus contributing to their increased engraftment efficacy, which was maintained in competitive transplants with noncultured competitor cells. NAM is a known potent inhibitor of several classes of ribosylase enzymes that require NAD for their activity, as well as sirtuin (SIRT1), class III NAD(+)-dependent-histone-deacetylase. We demonstrated that EX-527, a specific inhibitor of SIRT1 catalytic activity, inhibited differentiation of CD34(+) cells similar to NAM, while specific inhibitors of NAD-ribosylase enzymes did not inhibit differentiation, suggesting that the NAM effect is SIRT1-specific. Our findings suggest a critical function of SIRT1 in the regulation of hematopoietic stem cell activity and imply the clinical utility of NAM for ex vivo expansion of functional CD34(+) cells.

Ex vivo rapamycin treatment of human cord blood CD34+ cells enhances their engraftment of NSG mice

Since cord blood (CB) has become a commonly used source of transplantable hematopoietic stem (HSC) and hematopoietic progenitor cells (HPC), there has been a need to overcome the limited HSC and HPC numbers available to transplant from a single CB, especially for adult recipients. Our laboratory previously demonstrated that Rheb2 overexpression significantly impaired the repopulating ability of HSC. Since overexpression of Rheb2 leads to increased signaling through mTOR, we examined the effect of the mTOR inhibitor rapamycin ex vivo on cytokine expanded CD34(+) CB cells for the engraftment of these cells in non-obese diabetic, severe combined immunodeficient, IL-2 receptor γ chain null (NSG) mice. We observed significant enhancement in engraftment of the CB treated ex vivo with cytokines in the presence of rapamycin prior to transplant, effects seen in primary as well as secondary transplants. These pre-clinical results suggest a positive role for rapamycin during ex vivo culture of CB SCID repopulating cells/HSC.

GSK-3β inhibition promotes engraftment of ex vivo-expanded hematopoietic stem cells and modulates gene expression

Glycogen synthase kinase-3β (GSK-3β) has been identified as an important regulator of stem cell function acting through activation of the wingless (Wnt) pathway. Here, we report that treatment with an inhibitor of GSK-3β, 6-bromoindirubin 3'-oxime (BIO) delayed cell cycle progression by increasing cell cycle time. BIO treatment resulted in the accumulation of late dividing cells enriched with primitive progenitor cells retaining the ability for sustained proliferation. In vivo analysis using a Non-obese diabetic/severe combined immunodeficient (NOD/SCID) transplantation model has demonstrated that pretreatment with BIO promotes engraftment of ex vivo-expanded hematopoietic stem cells. BIO enhanced the engraftment of myeloid, lymphoid and primitive stem cell compartments. Limiting dilution analysis of SCID repopulating cells (SRC) revealed that BIO treatment increased human chimerism without increasing SRC frequency. Clonogenic analysis of human cells derived from the bone marrow of transplant recipient mice demonstrated that a higher level of human chimerism and cellularity was related to increased regeneration per SRC unit. Gene expression analysis showed that treatment with BIO did not modulate the expression of canonical Wnt target genes upregulated during cytokine-induced cell proliferation. BIO increased the expression of several genes regulating Notch and Tie2 signaling downregulated during ex vivo expansion, suggesting a role in improving stem cell engraftment. In addition, treatment with BIO upregulated CDK inhibitor p57 and downregulated cyclin D1, providing a possible mechanism for the delay seen in cell cycle progression. We conclude that transient, pharmacologic inhibition of GSK-3β provides a novel approach to improve engraftment of expanded HSC after stem cell transplantation.

Hematopoietic stem cells in research and clinical applications: The "CD34 issue"

In this paper, experimental findings concerning the kinetics of hematopoietic reconstitution are compared to corresponding clinical data. Although not clearly apparent, the transplantation practice seems to confirm the basic proposals of experimental hematology concerning hematopoietic reconstitution resulting from successive waves of repopulation stemming from different subpopulations of progenitor and stem cells. One of the "first rate" parameters in clinical transplantations in hematology; i.e. the CD34+ positive cell dose, has been discussed with respect to the functional heterogeneity and variability of cell populations endowed by expression of CD34. This parameter is useful only if the relative proportion of stem and progenitor cells in the CD34+ cell population is more or less maintained in a series of patients or donors. This proportion could vary with respect to the source, pathology, treatment, processing procedure, the graft ex vivo treatment and so on. Therefore, a universal dose of CD34+ cells cannot be defined. In addition, to avoid further confusion, the CD34+ cells should not be named "stem cells" or "progenitor cells" since these denominations only concern functionally characterized cell entities.

Effect of ex vivo culture of CD34+ bone marrow cells on immune reconstitution of XSCID dogs following allogeneic bone marrow transplantation

Successful genetic treatment of most primary immunodeficiencies or hematological disorders will require the transduction of pluripotent, self-renewing hematopoietic stem cells (HSC) rather than their progeny to achieve enduring production of genetically corrected cells and durable immune reconstitution. Current ex vivo transduction protocols require manipulation of HSC by culture in cytokines for various lengths of time depending upon the retroviral vector that may force HSC to enter pathways of proliferation, and possibly differentiation, which could limit their engraftment potential, pluripotentiality and long-term repopulating capacity. We have compared the ability of normal CD34(+) cells cultured in a standard cytokine cocktail for 18hours or 4.5 days to reconstitute XSCID dogs following bone marrow transplantation in the absence of any pretransplant conditioning with that of freshly isolated CD34(+) cells. CD34(+) cells cultured under standard gamma-retroviral transduction conditions (4.5 days) showed decreased engraftment potential and ability to sustain long-term thymopoiesis. In contrast, XSCID dogs transplanted with CD34(+) cells cultured for 18hours showed a robust T cell immune reconstitution similar to dogs transplanted with freshly isolated CD34(+) cells, however, the ability to sustain long-term thymopoiesis was impaired. These results emphasize the need to determine ex vivo culture conditions that maintain both the engraftment potential and "stem cell" potential of the cultured cells.

Inhibition of CD26 in human cord blood CD34+ cells enhances their engraftment of nonobese diabetic/severe combined immunodeficiency mice

CD26, a surface serine dipeptidylpeptidase IV (DPPIV) expressed on different cell types, cleaves the amino-terminal dipeptide from some chemokines, including stromal-derived factor-1 (SDF-1/CXCL12). SDF-1/CXCL12 plays important roles in hematopoietic stem cell (HSC) homing, engraftment, and mobilization. Inhibition of CD26 peptidase activity enhances homing, engraftment, and competitive repopulation in congenic mouse bone marrow cell transplants. Our studies evaluated a role for CD26 in in vivo engraftment of HSCs from human umbilical cord blood (CB) into nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. Pretreating purified CD34(+) human CB cells with Diprotin A, a DPPIV inhibitor, for 15 min significantly enhanced engraftment. Treatment did not affect differentiation of CD34(+) cells in vivo, as measured phenotypically by human markers CD33, CD38, CD19, and CD34. We found that the percentage of CD26(+) cells within the more immature cells (CD34(+)CD38()) was significantly higher than in the more mature population (CD34(+)CD38(+)). These results suggest that inhibition of CD26 may be one way to enhance engraftment of limiting numbers of stem cells during CB transplantation.

CD26 inhibition on CD34+ or lineage- human umbilical cord blood donor hematopoietic stem cells/hematopoietic progenitor cells improves long-term engraftment into NOD/SCID/Beta2null immunodeficient mice

Given the tremendous need for and potential of umbilical cord blood (CB) to be utilized as a donor source for hematopoietic stem cell (HSC) transplantation in adults, there is a strong push to overcome the constraints created by the limited volumes and subsequent limited HSC and hematopoietic progenitor cell (HPC) numbers available for HSC transplantation from a single collection. We have previously described the use of CD26 inhibitor treatment of donor cells as a method to increase the transplant efficiency of mouse HSCs and HPCs into a mouse recipient. To study the use of CD26 inhibitors as a method of improving the transplantation of human CB HSCs and HPCs, we utilized the nonobese diabetic/severe combined immunodeficient/beta 2 microglobulin null (NOD/SCID/B2m(null)) immunodeficient mouse model of HSC transplantation. We report here significant improvements in the engraftment of long-term repopulating cells following the treatment of either CD34(+) or lineage negative (lin()) donor CB with the CD26 inhibitor, Diprotin A, prior to transplant. These results establish a basis on which to propose the use of CD26 inhibitor treatment of donor CB units prior to transplantation for the purpose of improving transplant efficiency and subsequently patient outcome.

Marking of peripheral T-lymphocytes by retroviral transduction and transplantation of CD34+ cells in a canine X-linked severe combined immunodeficiency model

A retrovirus vector containing an enhanced green fluorescent protein complimentary DNA (EGFP cDNA) was used to mark and dynamically follow vector-expressing cells in the peripheral blood of bone marrow transplanted X-linked severe combined immunodeficient dogs. CD34(+) cells isolated from young normal dogs were transduced, using a 2 day protocol, with an amphotropic retroviral vector that expressed enhanced green fluorescent protein (EGFP) and the canine common gamma chain (gammac) cDNAs. Following transplantation of the transduced cells, normal donor peripheral blood lymphocytes (PBL) appeared by 1 month post-bone marrow transplant (BMT) and rescued three of five treated dogs from their lethal immunodeficiency. PCR and flow cytometric analysis of post-BMT PBL documented the peripheral EGFP expressing cells as CD3(+) T cells, which varied from 0% to 28%. Sorting of EGFP(+) and EGFP(-) peripheral blood T cells from two dogs, followed by vector PCR analysis, showed no evidence of vector shutdown. EGFP expression in B cells or monocytes was not detected. These marking experiments demonstrate that the transduction protocol did not abolish the lymphoid engraftment capability of ex vivo transduced canine CD34(+) cells and supports the potential utility of the MSCV retroviral vector for gene transfer to XSCID affected canine hematopoietic progenitor cells (HPC).

Short-term pretreatment with low-dose hydrogen peroxide enhances the efficacy of bone marrow cells for therapeutic angiogenesis

Therapeutic angiogenesis can be induced by the implantation of bone marrow cells (BMCs). Hydrogen peroxide (H(2)O(2)) has been shown to increase VEGF expression and to be involved in angiogenesis. We tested the hypothesis that pretreatment with H(2)O(2) enhances the efficacy of BMCs for neovascularization. H(2)O(2) pretreatment was done by incubating mouse BMCs in 5 microM H(2)O(2) for 30 min, followed by washing twice with PBS. The H(2)O(2)-pretreated and untreated BMCs were then studied in vitro and in vivo. RT-PCR analysis showed that expression of VEGF and Flk-1 mRNA was significantly higher in H(2)O(2)-pretreated BMCs than in untreated BMCs after 12 and 24 h of culture (P<0.01). Pretreatment with H(2)O(2) also effectively enhanced the VEGF production and endothelial differentiation from BMCs after 1 and 7 days of culture (P<0.05). To estimate the angiogenic potency in vivo, H(2)O(2)-pretreated or untreated BMCs were intramuscularly implanted into the ischemic hindlimbs of mice. After 14 days of treatment, many of the H(2)O(2)-pretreated BMCs were viable, showed endothelial differentiation, and were incorporated in microvessels. Conversely, the survival and incorporation of the untreated BMCs were relatively poor. Microvessel density and blood flow in the ischemic hindlimbs were significantly greater in the mice implanted with H(2)O(2)-pretreated BMCs than in those implanted with untreated BMCs (P<0.05). These results show that the short-term pretreatment of BMCs with low-dose H(2)O(2) is a novel, simple, and feasible method of enhancing their angiogenic potency.

Growth kinetics of progenitor cell-enriched hematopoietic cell populations in long-term liquid cultures under continuous removal of mature cells

BACKGROUND

During long-term culture of primitive hematopoietic cells large numbers of mature cells are generated that, on the one hand, consume nutrients and cytokines present in the medium and, on the other hand, may produce or elicit the production of soluble factors that limit the growth of primitive cells. Thus it is possible that under standard culture conditions hematopoietic stem and progenitor cells are unable to display their true proliferation and expansion potentials.

METHODS

Hematopoietic cell populations, enriched for CD34+ cells, were obtained from both umbilical cord blood (UCB) and mobilized peripheral blood (MPB), and cultured in cytokine-supplemented liquid culture, under continuous removal of mature cells by means of weekly re-selection of primitive, lineage-negative (Lin-) cells. Proliferation and expansion capacities of such cells were determined weekly for a 42-day culture period.

RESULTS

As expected, based on our previous studies in standard liquid cultures, throughout the culture period there was a continuous decrease in the proportion of progenitor cells; however, after every re-selection on days 7, 14 and 21, there was a significant enrichment for both CD34+ cells and colony-forming cells (CFC). As a result of such an enrichment, the cumulative increase in the numbers of total cells and CFC in cultures with two, three or four selections was significantly higher than the increments observed in standard cultures, in which only a single selection was performed on day 0. Cultures of UCB cells showed consistently higher levels of both total cells and CFC than cultures of MPB cells.

DISCUSSION

Taken together, these results indicate that continuous removal of mature cells from liquid cultures of primitive progenitors results in higher increments in the levels of both total cells and CFC.

In vitro expanded cells contributing to rapid severe combined immunodeficient repopulation activity are CD34+38-33+90+45RA-

Expansion of hematopoietic stem cells could be used clinically to shorten the prolonged aplastic phase after umbilical cord blood (UCB) transplantation. In this report, we investigated rapid severe combined immunodeficient (SCID) repopulating activity (rSRA) 2 weeks after transplantation of CD34(+) UCB cells cultured with serum on MS5 stromal cells and in serum- and stroma-free cultures. Various subpopulations obtained after culture were studied for rSRA. CD34(+) expansion cultures resulted in vast expansion of CD45(+) and CD34(+) cells. Independent of the culture method, only the CD34(+)33(+)38(-) fraction of the cultured cells contained rSRA. Subsequently, we subfractionated the CD34(+)38(-) fraction using stem cell markers CD45RA and CD90. In vitro differentiation cultures showed CD34(+) expansion in both CD45RA(-) and CD90(+) cultures, whereas little increase in CD34(+) cells was observed in both CD45RA(+) and CD90(-) cultures. By four-color flow cytometry, we could demonstrate that CD34(+)38(-)45RA(-) and CD34(+)38(-)90(+) cell populations were largely overlapping. Both populations were able to reconstitute SCID/nonobese diabetic mice at 2 weeks, indicating that these cells contained rSRA activity. In contrast, CD34(+)38(-)45RA(+) or CD34(+)38(-)90(-) cells contributed only marginally to rSRA. Similar results were obtained when cells were injected intrafemorally, suggesting that the lack of reconstitution was not due to homing defects. In conclusion, we show that after in vitro expansion, rSRA is mediated by CD34(+)38(-)90(+)45RA(-) cells. All other cell fractions have limited reconstitutive potential, mainly because the cells have lost stem cell activity rather than because of homing defects. These findings can be used clinically to assess the rSRA of cultured stem cells.

G-CSF- and GM-CSF-induced upregulation of CD26 peptidase downregulates the functional chemotactic response of CD34+CD38− human cord blood hematopoietic cells

OBJECTIVE

Cytokine treatment with granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), and stem cell factor (SCF) is a mainstay of current and future clinical and research protocols for peripheral blood stem cell mobilization, therapeutic care after hematopoietic stem cell transplantation (HSCT), and ex vivo hematopoietic stem and progenitor cell (HSC/HPC) expansion. We have previously shown that the peptidase CD26 (DPPIV/dipeptidylpeptidase IV) negatively regulates HSC/HPC and that inhibition of CD26 improves the chemotactic ability and trafficking of HSC/HPC. We set out to establish whether short-term in vitro G-CSF, GM-CSF, or SCF treatment upregulates CD26 and thereby has a detrimental effect on the chemotactic potential of HSC/HPC that could be reversed by CD26 inhibitor treatment.

MATERIALS AND METHODS

CD34+ or CD34+CD38- cells, a population enriched in HSC, were isolated from human umbilical cord blood and subjected to G-CSF, GM-CSF, or SCF treatment. We then evaluated CD26 expression, CD26 activity, and CXCL12 (SDF-1)-induced migration in the presence or absence of a CD26 inhibitor, Diprotin A.

RESULTS

Treatment with G-CSF and GM-CSF but not SCF upregulates CD26 expression and activity resulting in a CD26 inhibitor-reversible downregulation of CXCL12-induced chemotactic response.

CONCLUSIONS

Short-term in vitro G-CSF and GM-CSF treatment upregulates the peptidase CD26, resulting in downregulation of the functional ability of CD34+CD38- cells to respond to the chemokine CXCL12. This suggests that current and future clinical protocols utilizing G-CSF and GM-CSF may have unforeseen detrimental effects on the trafficking of HSC/HPC during HSCT that can be overcome through the use of CD26 inhibitors.

Dynamic changes in cellular and microenvironmental composition can be controlled to elicit in vitro human hematopoietic stem cell expansion

OBJECTIVE

The absence of effective strategies for the ex vivo expansion of human hematopoietic stem cells (HSCs) limits the development of many cell-based therapies. Prior attempts to stimulate HSC expansion have focused on media supplementation using cytokines and growth factors. In these cultures, cellular and microenvironmental compositions change with time. In this study, the impact of controlling these dynamic changes on HSC output is determined.

MATERIALS AND METHODS

Cord blood-derived lin(-) cells were cultured for 8 days in serum-free medium supplemented with stem cell factor, Flt3 ligand, and thrombopoietin. Functional, phenotypic, and molecular (gene and protein) analyses were used to characterize dynamic changes in cellular and microenvironmental composition. The effects of these changes and the mechanism behind their effects on HSC expansion were assessed using a selection/media exchange-based global culture manipulation (GCM) technique.

RESULTS

We show that the direct secretion of negative regulators by culture-generated lin(+) cells, and the indirect stimulation of cells to secrete negative regulators by culture-conditioned media, limits in vitro HSC generation. The GCM strategy was able to abrogate these effects to produce elevated numbers of LTC-ICs (14.6-fold relative to input), migrating rapid NOD/SCID repopulating cells (12.1-fold), and long-term NOD/SCID repopulating cells (5.2-fold).

CONCLUSIONS

Cellular and microenvironmental changes that occur during all in vitro HSC cultures can significantly affect HSC output through the direct or indirect secretion of negative regulators. This study provides insight into the mechanisms regulating HSC fate in vitro and describes a novel methodology to regulate overall in vitro microenvironmental dynamics to enable the generation of clinically relevant numbers of HSCs.

Stem cell factor improves SCID-repopulating activity of human umbilical cord blood-derived hematopoietic stem/progenitor cells in xenotransplanted NOD/SCID mouse model

Poor in vivo homing capacity of hematopoietic stem/progenitor cells (HS/PCs) from umbilical cord blood (UCB) can be reversed by short-term ex vivo manipulation with recombinant human stem cell factor (rHuSCF). This study was designed to evaluate the effect of ex vivo manipulation of UCB-derived HS/PCs with rHuSCF on human cell engraftment rates in xenotransplanted NOD/SCID mouse model. The human cell engraftment rates in xenotransplanted primary and secondary NOD/SCID mice were characterized using four-color flow cytometric analysis and progenitor assay. Grafts of rHuSCF-treated UCB CD34(+) cells resulted in significantly higher levels of human cell engraftment than that of nontreated ones in both xenotransplanted primary and secondary NOD/SCID recipients. Fresh UCB CD34(+) cells did not express either of the matrix metalloproteinase (MMP) family members MMP-2 or MMP-9. rHuSCF-treated UCB CD34(+) cells expressed significant levels of MMP-2 and MMP-9. Pretreatment of UCB CD34(+) cells with the specific MMP inhibitor completely blocked human cell engraftment in xenotransplanted NOD/SCID recipients. Our results indicate that ex vivo manipulation of human HS/PCs with rHuSCF might provide an optimal approach to develop more effective stem cell-based therapies in situations where engraftment is delayed due to limiting HS/PCs number, for example, UCB transplantation.

Simultaneous Maintenance of Human Cord Blood SCID-Repopulating Cells and Expansion of Committed Progenitors at Low O2 Concentration (3%)

In the present work, we tested the hypothesis that liquid cultures (LCs) of cord blood CD34+ cells at an appropriate low O2 concentration could simultaneously allow colony-forming cell (CFC) expansion and nonobese diabetic/severe combined immunodeficiency mice-repopulating cell (SRC) maintenance. We first found that 3% was the minimal O2 concentration, still allowing the same rate of CFC expansion as at 20% O2. We report here that 7-day LCs of cord blood CD34+ cells at 3% O2 maintain SRC better than at 20% O2 and allow a similar amplification of CFCs (35- to 50-fold) without modifying the CD34+ cell proliferation. Their phenotypic profile (antigens: HLA-DR, CD117, CD33, CD13, CD11b, CD14, CD15, and CD38) was not modified, with exception of CD133, whose expression was lower at 3% O2. These results suggest that low O2 concentrations similar to those found in bone marrow participates in the regulation of hematopoiesis by favoring stem cell-renewing divisions. This expansion method that avoids stem cell exhaustion could be of paramount interest in hematopoietic transplantation by allowing the use of small-size grafts in adults.

Clonogenic assay with established human tumour xenografts: correlation of in vitro to in vivo activity as a basis for anticancer drug discovery

Pluripotent cells can be grown in clonogenic assays. The tumour stem-cell fraction, which accounts for <0.4% of the total cells, and which is considered the most relevant cell type in the development of metastases and recurrences, is able to divide and to form colonies in a semisolid matrix (agar or methylcellulose). Major applications of the tumour clonogenic assay (TCA) are chemosensitivity testing of tumours and xenografts, and for assessments within drug discovery programmes. Of critical relevance for the usefulness of the TCA is whether it can predict sensitivity or resistance towards clinically used agents. When we compared the response of human tumours established as xenografts in nude mice in the TCA in vitro to that of the clinical response, 62% of the comparisons for drug sensitivity, and 92% of the comparisons for drug resistance were correct. The same percentage of true/false observations was found when tumours were tested after serial passage in nude mice in the TCA in vitro and their response compared to in vivo activity in corresponding xenografts (60% and 90%, respectively). The highest correct predictive values were, however, found when the clinical response of tumours was compared to their explants established in the nude mouse and treated in vivo. Of 80 comparisons performed, we observed a correct prediction for tumour resistance in 97% and for tumour sensitivity in 90%. In our opinion, the TCA with established human tumour xenografts has an important role in current drug discovery strategies. We therefore included the TCA as secondary assay in our approach to anticancer drug discovery and found that a number of novel agents were active; these are now in advanced preclinical development or clinical trials. Thus, the tumour clonogenic assay has proven predictive value in the chemosensitivity testing of standard and experimental anticancer drugs.

Low angiogenic potency induced by the implantation of ex vivo expanded CD117+stem cells

Ex vivo expansion of stem cells might be a feasible method of resolving the problem of limited cell supply in cell-based therapy. The implantation of expanded CD34+endothelial progenitor cells has the capacity to induce angiogenesis. In this study, we tried to induce angiogenesis by implanting expanded CD117+stem cells derived from mouse bone marrow. After 2 wk of culture with the addition of several growth factors, the CD117+stem cells expanded ∼20-fold and had an endothelial phenotype with high expression of CD34 and vascular endothelial-cadherin. However, >70% of these ex vivo expanded cells had a senescent phenotype by β-galactosidase staining, and their survival and incorporation were poor after implantation into the ischemic limbs of mice. Compared with the PBS injection only, the microvessel density and the percentage of limb blood flow were significantly higher after the implantation of 2 × 105freshly collected CD117+cells ( P < 0.01) but not after the implantation of 2 × 105expanded CD117+cells ( P > 0.05). These data indicate that ex vivo expansion of CD117+stem cells has low potency for inducing therapeutic angiogenesis, which might be related to the cellular senescence during ex vivo expansion.

Sustained transgene expression by human cord blood derived CD34+ cells transduced with simian immunodeficiency virus agmTYO1-based vectors carrying the human coagulation factor VIII gene in NOD/SCID mice

BACKGROUND

Gene therapy is being studied as the next generation therapy for hemophilia and several clinical trials have been carried out, albeit with limited success. To explore the possibility of utilizing autologous bone marrow transplantation of genetically modified hematopoietic stem cells for hemophilia gene therapy, we investigated the efficacy of genetically engineered CD34+ cell transplantation to NOD/SCID mice for expression of human factor VIII (hFVIII).

METHODS

CD34+ cells were transduced with a simian immunodeficiency virus agmTYO1 (SIV)-based lentiviral vector carrying the enhanced green fluorescent protein (eGFP) gene (SIVeGFP) or the hFVIII gene (SIVhFVIII). CD34+ cells transduced with SIV vectors were transplanted to NOD/SCID mice. Engraftment of transduced CD34+ cells and expression of transgenes were studied.

RESULTS

We could efficiently transduce CD34+ cells using the SIVeGFP vector in a dose-dependent manner, reaching a maximum (99.6 +/- 0.1%) at MOI of 5 x 10(3) vector genome/cell. After transducing CD34+ cells with SIVhFVIII, hFVIII was produced (274.3 +/- 20.1 ng) from 10(6) CD34+ cells during 24 h in vitro incubation. Transplantation of SIVhFVIII-transduced CD34+ cells (5-10 x 10(5)) at a multiplicity of infection (MOI) of 50 vector genome/cell into NOD/SCID mice resulted in successful engraftment of CD34+ cells and production of hFVIII (minimum 1.2 +/- 0.9 ng/mL, maximum 3.6 +/- 0.8 ng/mL) for at least 60 days in vivo. Transcripts of the hFVIII gene and the hFVIII antigen were also detected in the murine bone marrow cells.

CONCLUSIONS

Transplantation of ex vivo transduced hematopoietic stem cells by non-pathogenic SIVhFVIII without exposure of subjects to viral vectors is safe and potentially applicable for gene therapy of hemophilia A patients.

Ex vivo manipulation of umbilical cord blood-derived hematopoietic stem/progenitor cells with recombinant human stem cell factor can up-regulate levels of homing-essential molecules to increase their transmigratory potential

OBJECTIVE

The cause of delayed hematopoietic reconstitution after umbilical cord blood transplantation (UCBT) remains controversial. We hypothesized that hematopoietic stem/progenitor cells (HS/PCs) from UCB have some defects of the homing-related molecules responsible for their slow engraftment.

MATERIALS AND METHODS

A homing-related molecule repertoire expressed on HS/PCs from fresh and cryopreserved UCB, mobilized peripheral blood (mPB), and bone marrow (BM) were compared using sensitive, four-color fluorescence-activated cell sorting analysis. Purified CD34+ cells were subjected to ex vivo transmigration through double-coated transwell filter inserts, and an in vivo homing assay was performed in xenotransplanted NOD/SCID mice.

RESULTS

UCB-derived CD34(bright) cells expressed significantly lower levels of CD49e, CD49f, and CXCR-4 than their mPB and BM counterparts. CD34+ cells from UCB (and BM) exhibited significantly lower ex vivo transmigration than those from mPB, which were largely blocked by neutralizing antibodies to CD49e or CD49f. Recombinant human tumor necrosis factor-alpha treatment enhanced ex vivo transmigration of CD34+ cells from UCB and BM by inducing expression of the matrix metalloproteinases MMP-2/MMP-9. Short-term treatment of UCB-derived CD34+ cells with rHu-stem cell factor (rHuSCF) up-regulated levels of the homing-related molecules with their increased ex vivo transmigratory and in vivo homing potential.

CONCLUSION

Our results indicate that disadvantageous transmigratory behavior of HS/PCs from UCB, which might partly explain the delayed reconstitution after UCBT, can be reversed by ex vivo manipulation with rHuSCF.

Retrovirus vector production and transduction: modulation by the cell cycle

In this study, the cell cycle modulation of retrovirus vector production and transduction was analysed. Retrovirus vector expression was found to be similar in all phases of the cell cycle and, in contrast to some other virus promoters shown previously to be upregulated by G(2)/M arrest, Moloney murine leukaemia virus LTR-driven expression was upregulated neither by G(2)/M growth arrest nor by G(1)/S growth arrest. In contrast, cultures enriched for S phase cells produced more infectious virions, apparently by modulation of stages consequent to provirus expression. In terms of retrovirus transduction, limitations appear to be slow progression through the cell cycle and short half-life of the virus. Synchronization of cells prior to mitosis can increase transduction efficiency. Cell cycle modulation can be used to modify retrovirus vector production and transduction and can allow short transduction periods.

Ex vivo expansion of human umbilical cord blood CD34+ cells in a collagen bead-containing 3-dimensional culture system

Self-renewal of stem cells depends on several critical factors, including the hematopoietic microenvironment, interactions with supporting stromal cells, features of the extracellular matrix, hematopoietic growth factors, and cytokines. Our study investigated the role of artificial 3-dimensional microenvironments as a means of replicating a more physiologic milieu in expansion of cord blood CD34+ cells. In the 3-dimensional model, hematopoietic cells inside collagen beads are exposed to cytokines added to a culture medium. We found that amplification of CD34+ cells with a clonogenic assay, fluorescence-activated cell sorter analysis, and bone marrow repopulation of NOD/SCID mice showed greater clonogenic ability of cells cultured by the 3-dimensional method compared with the 2-dimensional method. The present study demonstrated that 3-dimensional matrix support may be useful for extended periods in expansion and preservation of stem cells or progenitor cells in vitro.

Clinical application of hematopoietic progenitor cell expansion: current status and future prospects

In the past decade, we have witnessed significant advances in ex vivo hematopoietic stem cell culture expansion, progressing to the point where clinical trials are being designed and conducted. Preclinical milestone investigations provided data to enable expansion of portions of hematopoietic grafts in a clinical setting, indicating safety and feasibility of this approach. Data derived from current clinical trials indicate successful reconstitution of hematopoiesis after myeloablative chemoradiotherapy using infusion of ex vivo-expanded perfusion cultures. Future avenues of exploration will focus upon refining preclinical and clinical studies in which cocktails of available cytokines, novel molecules and sophisticated expansion systems will explore expansion of blood, marrow and umbilical cord blood cells.

Nonobese diabetic-severe combined immunodeficient mice transplantation of volume-reduced and thawed umbilical cord blood transplants following closed-system immunomagnetic cell selection

BACKGROUND

Protocols for the expansion of human umbilical cord blood (UCB) progenitors begin with the selection of CD34+ cells from stored frozen and thawed units. Use of an immunomagnetic selection procedure within a closed blood bag system for volume-reduced UCB transplants was evaluated, and the influence of CD34 cell selection on in vivo engraftment potential was studied.

STUDY DESIGN AND METHODS

Eleven thawed buffy coat-processed UCB units were processed within a standard blood bag with a washing solution. In six independent experiments, the same dosage of 2 x 104 CD34+ cells from paired selected and nonselected samples was transplanted into NOD-SCID mice. In two experiments, cells from the negative fraction were also transplanted.

RESULTS

The purity of CD34+ cells after selection was correlated with the removal of supernatant after the first washing step and therefore with adequate removal of damaged or dead cells (r=0.86, p < 0.01). Mice transplanted with unselected UCB cells had more human cells within their marrow than animals transplanted with selected cells (8.6 +/- 5.9% selected group vs. 19.8 +/- 14.2% unselected group; p=0.04), whereas no engraftment could be observed transplanting cells from the two negative fractions. A higher percentage of human CD45+ cells in the unselected group were found to be positive for CD38, CD14, CD33, and CD19, indicating a higher potential for these unselected progenitors to differentiate into myeloid cells and B cells.

CONCLUSIONS

Processing of volume-reduced and thawed UCB transplants within a closed-bag system before immunomagnetic CD34+ cell selection allows for the preparation of CD34+ cells of significant purity at technically useful cell recoveries. However, these experiments indicate a potential impairment of engraftment capacity for the CD34+ cell-enriched fraction.

Targeted beta-globin gene conversion in human hematopoietic CD34(+ )and Lin(-)CD38(-)cells

Chimeric oligonucleotides have been used successfully to correct point and frameshift mutations in several cell types, as well as in animal and plant models. However, their application to primitive human blood cells has been limited. In this investigation, chimeric oligonucleotides designed to direct a site-specific nucleotide exchange in the human beta-globin gene (an A to T substitution within codon 6) were introduced into normal human CD34(+) and Lin(-)CD38(-) cells via microinjection. This A to T nucleotide exchange introduces the single site mutation responsible for sickle cell anemia. In 23% of experimental samples, gene conversion was detected in the progeny of microinjected CD34(+) and Lin(-)CD38(-) cells that were cultured for at least 4 weeks. In addition, gene conversion was detected in the erythroid progeny of Lin(-)CD38(-) cells at the mRNA level. Conversion rates as high as 10-15% in 11% (five of 44) of experimental samples were confirmed by allele-specific PCR and sequence analysis of genomic DNA from the progeny of microinjected Lin(-)CD38(-) cells. Given that as few as 10% normal hematopoietic cells are sufficient to keep patients free of sickle cell disease, the level of conversion we have achieved in some samples may well be of therapeutic benefit in patients with sickle cell disease.