[Ex vivo expansion of hematopoietic stem cells: concept and clinical benefit]

HIV-1 Tat protein inhibits the hematopoietic support function of human bone marrow mesenchymal stem cells

Most HIV-1-infected patients experience hematopoiesis suppression complications. Bone marrow mesenchymal stem cells (BMSCs) are involved in regulation of hematopoietic homeostasis, so we investigated the role of Tat, a protein released by infected cells in bone marrow and impacted differentiation potential of mesenchymal stem cells, in the BMSC hematopoietic support function. BMSCs were treated with HIV-1 Tat protein (BMSC_Tat-p), transfected with HIV-1 Tat mRNA (BMSC_Tat-m) or treated with solvent (PBS) (BMSC_con) for 20 days. Then, the hematopoietic support function of BMSC_Tat-p, BMSC_Tat-m and BMSC_con was analyzed via ex vivo expansion of hematopoietic stem cells (HSCs) grown on the BMSCs and via in vivo cotransplantation of HSCs and BMSCs. In addition, the hematopoiesis-supporting gene expression patterns of BMSC_Tat-p, BMSC_Tat-m and BMSC_con were compared. The results showed that BMSC_Tat-p and BMSC_Tat-m displayed reduced expansion, a decline in the number of colony forming units (CFUs) and a decreased proportion of the primitive subpopulation of hematopoietic stem cells under coculture conditions compared with BMSC_con. The ability of BMSC_Tat-p to support hematopoietic recovery was also impaired, which was further confirmed by the patterns in gene expression analysis. In conclusion, Tat treatment reduced the function of BMSCs in hematopoietic support, likely by downregulating the expression of a series of hematopoietic cytokines.

Inhibition of T cell protein tyrosine phosphatase enhances interleukin-18-dependent hematopoietic stem cell expansion

The clinical application of hematopoietic progenitor cell-based therapies for the treatment of hematological diseases is hindered by current protocols, which are cumbersome and have limited efficacy to augment the progenitor cell pool. We report that inhibition of T-cell protein tyrosine phosphatase (TC-PTP), an enzyme involved in the regulation of cytokine signaling, through gene knockout results in a ninefold increase in the number of hematopoietic progenitors in murine bone marrow (BM). This effect could be reproduced using a short (48 hours) treatment with a pharmacological inhibitor of TC-PTP in murine BM, as well as in human BM, peripheral blood, and cord blood. We also demonstrate that the ex vivo use of TC-PTP inhibitor only provides a temporary effect on stem cells and did not alter their capacity to reconstitute all hematopoietic components in vivo. We establish that one of the mechanisms whereby inhibition of TC-PTP mediates its effects involves the interleukin-18 (IL-18) signaling pathway, leading to increased production of IL-12 and interferon-gamma by progenitor cells. Together, our results reveal a previously unrecognized role for IL-18 in contributing to the augmentation of the stem cell pool and provide a novel and simple method to rapidly expand progenitor cells from a variety of sources using a pharmacological compound.

A stromal-free, serum-free system to expand ex vivo hematopoietic stem cells from mobilized peripheral blood of patients with hematologic malignancies and healthy donors

BACKGROUND AIMS

The number of hematopoietic stem cells (HSCs) is critical for transplantation. The ex vivo expansion of mobilized peripheral blood (MPB) HSCs is of clinical value for reconstitution to meet clinical need.

METHODS

This study proposed a simple, defined, stromal-free and serum-free culture system (SF-HSC medium) for clinical use, which is composed of Iscove's modified Dulbecco's medium, cytokine cocktails and serum substitutes. This study also characterized the cellular properties of expanded MPB CD133(+) HSCs from patients with hematologic malignancies and healthy donors by surface antigen, colony-forming cell, long-term culture-initiating cell, gene expression and in vivo engraftment assays.

RESULTS

The expanded fold values of CD45(+) white blood cells and CD34(+), CD133(+), CD34(+)CD38(-), CD133(+)CD38(-), CD34(+)CD133(+), colony-forming and long-term culture-initiating cells at the end of 7-day culture from CD133(+) MPB of hematologic malignancies were 9.4-fold, 5.9-fold, 4.0-fold, 35.8-fold, 21.9-fold, 3.8-fold, 11.8-fold and 6.7-fold, and values from healthy donor CD133(+) MPB were 20.7-fold, 14.5-fold, 8.5-fold, 83.8-fold, 37.3-fold, 6.2-fold, 19.1-fold and 14.6-fold. The high enrichment of CD38(-) cells, which were either CD34(+) or CD133(+), sustained the proliferation of early uncommitted HSCs. The expanded cells showed high levels of messenger RNA expression of HOBX4, ABCG2 and HTERT and had the in vivo ability to re-populate NOD/SCID mice.

CONCLUSIONS

Our results demonstrated that an initial, limited number of MPB CD133(+) HSCs could be expanded functionally in SF-HSC medium. We believe that this serum-free expansion technique can be employed in both basic research and clinical transplantation.

Combination of low O(2) concentration and mesenchymal stromal cells during culture of cord blood CD34(+) cells improves the maintenance and proliferative capacity of hematopoietic stem cells

The physiological approach suggests that an environment associating the mesenchymal stromal cells (MSC) and low O(2) concentration would be most favorable for the maintenance of hematopoietic stem cells (HSCs) in course of ex vivo expansion of hematopoietic grafts. To test this hypothesis, we performed a co-culture of cord blood CD34(+) cells with or without MSC in presence of cytokines for 10 days at 20%, 5%, and 1.5% O(2) and assessed the impact on total cells, CD34(+) cells, committed progenitors (colony-forming cells-CFC) and stem cells activity (pre-CFC and Scid repopulating cells-SRC). Not surprisingly, the expansion of total cells, CD34(+) cells, and CFC was higher in co-culture and at 20% O(2) compared to simple culture and low O(2) concentrations, respectively. However, co-culture at low O(2) concentrations provided CD34(+) cell and CFC amplification similar to classical culture at 20% O(2) . Interestingly, low O(2) concentrations ensured a better pre-CFC and SRC preservation/expansion in co-culture. Indeed, SRC activity in co-culture at 1.5% O(2) was higher than in freshly isolated CD34(+) cells. Interleukin-6 production by MSC at physiologically low O(2) concentrations might be one of the factors mediating this effect. Our data demonstrate that association of co-culture and low O(2) concentration not only induces sufficient expansion of committed progenitors (with respect to the classical culture), but also ensures a better maintenance/expansion of hematopoietic stem cells (HSCs), pointing to the oxygenation as a physiological regulatory factor but also as a cell engineering tool.

Definitive setup of clinical scale procedure for ex vivo expansion of cord blood hematopoietic cells for transplantation

We recently developed a clinical grade ex vivo cord blood expansion procedure enabling a massive amplification of hematopoietic progenitors without any loss of stem cell potential. This procedure, based on day 14 liquid cultures of cord blood CD34(+) cells, in medium Macopharma HP01 and in the presence of stem cell factor (SCF; 100 ng/ml), fms-related tyrosine kinase 3-ligand (Flt-3L; 100 ng/ml), megakaryocyte growth and developmental factor (MGDF; 100 ng/ml), and granulocyte colony-stimulating factor (G-CSF; 10 ng/ml) had to be modified due to the commercially unavailability of clinical grade MGDF molecule. So MGDF was replaced by thrombopoietin (TPO) in fivefold lower dose (20 ng/ml), and culture time was reduced to 12 days. That way, a mean expansion fold of 400, 80, and 150 was obtained for total cells, CD34(+) cells, and colony-forming cells (CFCs), respectively. This amplification was associated with a slight enhancing effect on stem cells [Scid repopulating cells (SRCs)]. These are the ultimate preclinical modifications of a clinical grade expansion protocol, which is already employed in an ongoing clinical trial.

Systematic investigation of oxygen and growth factors in clinically valid ex vivo expansion of cord blood CD34(+) hematopoietic progenitor cells

BACKGROUND AIMS

Cord blood is considered to be a superior source of hematopoietic stem and progenitor cells for transplantation, but clinical use is limited primarily because of the low numbers of cells harvested. Ex vivo expansion has the potential to provide a safe, effective means of increasing cell numbers. However, an absence of consensus regarding optimum expansion conditions prevents standard implementation. Many studies lack clinical applicability, or have failed to investigate the combinational effects of different parameters.

METHODS

This is the first study to characterize systematically the effect of growth factor combinations across multiple oxygen levels on the ex vivo expansion of cord blood CD34(+) hematopoietic cells utilizing clinically approvable reagents and methodologies throughout.

RESULTS

Optimal fold expansion, as assessed both phenotypically and functionally, was greatest with thrombopoietin, stem cell factor, Flt-3 ligand and interleukin-6 at an oxygen level of 10%. With these conditions, serial expansion showed continual target population expansion and consistently higher expression levels of self-renewal associated genes.

CONCLUSIONS

This study has identified optimized fold expansion conditions, with the potential for direct clinical translation to increase transplantable cell dose and as a baseline methodology against which future factors can be tested.

Ex vivo-expanded bone marrow stem cells home to the liver and ameliorate functional recovery in a mouse model of acute hepatic injury

BACKGROUND

Stem cell transplantation provides a theoretical approach for liver regeneration medicine; it may promote liver regeneration and self-repair. However, the transplantation of bone marrow-mesenchymal stem cells expanded ex vivo as a therapy for liver disease has rarely been investigated. This study aimed to explore whether bone marrow stem cells expanded ex vivo home to the liver and foster hepatic recovery after CCl4 injury.

METHODS

Bone marrow cells from BALB/c mice were expanded ex vivo by multiple-passage cultivation, characterized by cytoflow immunofluorescence, and pre-labeled with PKH26 before intravenous infusion into animals treated with CCl4. The integration of bone marrow cells into the liver was examined microscopically, and plasma hepatic enzymes were determined biochemically.

RESULTS

Cultured bone marrow cells exhibited antigenic profiles comparable to those of primary medullary stem cells. Double immunofluorescence showed colocalization of these cells with proliferative activity and albumin expression in the liver of CCl4-treated mice. Densitometry showed increased in situ cell proliferation (50+/-14 vs 20+/-3 cells/high-power field, P<0.05) and albumin expression (149+/-25 vs 20+/-5 cells/high-power field, P<0.05) in the liver, as well as reduced serum aminotransferase levels (P<0.05) and better survival rates (P<0.05) in animals receiving cultured bone marrow cells relative to controls.

CONCLUSIONS

Ex vivo-expanded bone marrow cells are capable of relocating to and proliferating in the chemically-injured liver. Transplantation of these pluripotent stem cells appears to improve serum indices of liver function and survival rate in mice after CCl4-induced hepatic damage.

Clinical-scale cultures of cord blood CD34(+) cells to amplify committed progenitors and maintain stem cell activity

We developed a clinical-scale cord blood (CB) cell ex vivo procedure to enable an extensive expansion of committed progenitors--colony-forming cells (CFCs) without impairing very primitive hematopoietic stem cells (HSCs). CD34(++) cells, selected from previously cryopreserved and thawed CB units, were cultured in two steps (diluted 1:4 after 6 days) in the presence of stem cell factor (SCF), fms-related tyrosine kinase 3 ligand (Flt-3L), megakaryocyte growth and development factor (MGDF) (100 ng/ml each), granulocyte-colony stimulating factor (G-CSF) (10 ng/ml) in HP01 serum-free medium. HSC activity was evaluated in a serial transplantation assay, by detection of human cells (CD45, CD33, CD19 and CFC of human origin) in bone marrow (BM) of primary and secondary recipient NOD/SCID mice 6-8 weeks after transplantation. A wide amplification of total cells (∼350-fold), CD34(+) cells (∼100-fold), and CFC (∼130-fold) without impairing the HSC activity was obtained. The activity of a particular HSC subpopulation (SRC(CFC)) was even enhanced.Thus, an extensive ex vivo expansion of CFCs is feasible without impairing the activity of HSCs. This result was enabled by associating antioxidant power of medium with an appropriate cytokine cocktail (i.e., mimicking physiologic effects of a weak oxygenation in hematopoietic environment).

Thrombopoietin to replace megakaryocyte-derived growth factor: impact on stem and progenitor cells during ex vivo expansion of CD34+ cells mobilized in peripheral blood

BACKGROUND

The first protocol of ex vivo expansion that enabled almost total abrogation of postmyeloablative chemotherapy neutropenia was based on a three-cytokine cocktail (stem cell factor [SCF], granulocyte-colony-stimulating factor [G-CSF], pegylated-megakaryocyte growth and development factor [PEG-MGDF]) in a serum-free medium. Since the clinical-grade molecule MGDF is no longer available on the market, we evaluated its substitution by thrombopoietin (TPO).

STUDY DESIGN AND METHODS

CD34+ cells of myeloma patients were expanded for 10 days in serum-free cultures with SCF, G-CSF, or MGDF (100 ng/mL) or with TPO (2.5, 10, 20, 50, and 100 ng/mL) instead of MGDF. Day 10 amplifications of total nucleated cells, CD34+ cells, committed progenitors (CFCs), the capacity of engraftment of NOD/SCID mice (SCID repopulating cells [SRCs]), and the immunophenotype of cells in expansion product (CD13, CD14, CD33, CD41, CD61) were analyzed.

RESULTS

TPO in doses of 2.5 and 10 ng/mL exhibits an effect comparable to that of MGDF (100 ng/mL) on total, CD34+, and CFCs amplification. Compared to MGDF, TPO (starting at 10 ng/mL) enhances two- to threefold the percentage of megakaryocyte lineage cells (CD41+ and CD61+). Finally, TPO maintains or even enhances (depending on dose) SRC activity.

CONCLUSIONS

The use of TPO instead of MGDF in our protocol is feasible without any negative effect on progenitor cell expansion. Furthermore, applied in dose of 10 or 100 ng/mL it could enhance both the stem cell activity and the percentage of megakaryocyte lineage cells in expansion product.

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.