Ex vivo expansion of immature 4-hydroperoxycyclophosphamide-resistant progenitor cells from G-CSF-mobilized peripheral blood

Replication of bone marrow differentiation niche: comparative evaluation of different three-dimensional matrices

The comparative evaluation of different 3D matrices-Matrigel, Puramatrix, and inverted colloidal crystal (ICC) scaffolds-provides a perspective for studying the pathology and potential cures for many blood and bone marrow diseases, and further proves the significance of 3D cultures with direct cell-cell contacts for in vitro mimicry of the human stem cell niche.

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

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

Impaired survival of bone marrow hematopoietic progenitor cells in cyclic neutropenia

Cyclic neutropenia (CN) is a congenital hematopoietic disorder characterized by remarkably regular oscillations of blood neutrophils from near normal to extremely low levels at 21-day intervals. Recurring episodes of severe neutropenia lead to repetitive and sometimes life-threatening infections. To investigate the cellular mechanism of CN, the ultrastructure and the proliferative and survival characteristics of bone marrow-derived CD34(+) early progenitors, CD33(+)/CD34(-) myeloid progenitors, and CD15(+) neutrophil precursors from CN patients and healthy volunteers were studied. The ultrastructural studies showed profound apoptotic features in bone marrow progenitor cells in CN. Colony-forming assays demonstrated a 75% decrease in the number of early myeloid-committed colonies compared with controls. Long-term culture-initiating cell assays demonstrated a 6-fold increase in production of primitive progenitor cells in CN. To determine whether accelerated apoptosis might account for the underproduction of myeloid progenitors, the hematopoietic subpopulations were labeled with fluorescein isothiocyanate-annexin V and analyzed by flow cytometry. Short-term culture of CN cells resulted in apoptosis of approximately 65% of CD34(+) cells, 80% of CD33(+)/CD34(-) cells, and more than 70% of CD15(+) cells, as compared with 20%, 7%, and 15% apoptosis in respective control subpopulations. Evidence of accelerated apoptosis of bone marrow progenitor cells was observed in all 8 patients participating in the study, regardless of the stage in the CN cycle in which bone marrow aspirations were obtained. Granulocyte colony-stimulating factor therapy of CN patients significantly improved survival of bone marrow progenitor cells. These data indicate that ineffective production of neutrophils is due to accelerated apoptosis of bone marrow myeloid progenitor cells in CN.

Expansion and transduction of nonenriched human cord blood cells using HS-5 conditioned medium and FLT3-L

Cord blood (CB) stem cell transplantations have been associated with delayed hematopoietic engraftment. This has most likely been due to the limited numbers of hematopoietic short-term repopulating cells in CB. Ex vivo expansion of CB has been attempted, and expansion of CD34-enriched CB has been successful; however, CD34 enrichment procedures are in general associated with substantial cell loss. Thus, we have studied culture conditions for expansion of nonenriched CB. Nonenriched CB cells were cultured for 21 days in the presence of conditioned medium from the HS-5 stromal cell line and FLT3-L or alternatively in the presence of FLT3-L, stem cell factor (SCF), megakaryocite growth and development factor (MGDF), and granulocyte colony-stimulating factor (G-CSF) (FSMG), either on fibronectin fragment CH-296-coated dishes or on uncoated dishes. With all four culture conditions, the number of mononuclear cells initially decreased until day 7 and then increased until the end of the expansion cultures. Overall expansion using HS-5 and FLT3-L resulted in superior expansion of MNC and CFU-C (44-/34-fold) for both cultures with and without CH-296 compared to FSMG (18-/17-fold). Expansion on CH-296 was less efficient than expansion on tissue culture-treated wells without CH-296 for both conditions. We then studied the best time for transduction on nonenriched CB. In contrast to enriched CD34 cells, we found for both conditions, HS-5/FLT3-L and growth factor cocktail, higher transduction efficiencies when cells were transduced on day 7 as compared to day 2. Gene transfer rates up to 45% were achieved with both conditions, which corresponded with the increased number of cells in S phase on day 7 compared to day 2. We conclude that HS-5 and FLT-3L allow efficient expansion and transduction of nonenriched CB.

Tumor necrosis factor-alpha and TNF-beta inhibit clonogenicity of mobilized human hematopoietic progenitors

We studied the effect of tumor necrosis factors (TNF-alpha and TNF-beta) on the clonogenicity of peripheral blood progenitor cells (PBPC) mobilized by granulocyte colony-stimulating factor (G-CSF). The cells were obtained by nine leukaphereses in patients with malignancies undergoing peripheral blood stem cell transplantation (PBSCT). Flow cytometry was performed to evaluate the number of CD34+ cells in peripheral blood and leukapheresis products. PBPC were grown in semisolid medium supplemented with human growth factors in the absence or presence of TNF at concentrations ranging from 0.1 to 10 ng/ml. Colonies were scored on day 14. TNF-alpha and TNF-beta suppressed colony formation in all cases studied. TNF-alpha inhibited the growth of colony-forming units-granulocyte-macrophage (CFU-GM) at 1 and 10 ng/ml and burst-forming units-erythroid (BFU-E) at 10 ng/ml (p < 0.05), and TNF-beta inhibited the growth of CFU-GM and BFU-E at 1 and 10 ng/ml (p < 0.05). Thus, G-CSF-mobilized hematopoietic PBPC are highly sensitive to both TNF-alpha and TNF-beta. This finding should be taken in account when PBPC are handled ex vivo.

Dissecting the marrow microenvironment

Cloned human stromal cell lines representing functionally distinct cellular components of the marrow microenvironment were generated to serve as tools for identifying gene products that regulate hematopoiesis. Oligonucleotide arrays, or "gene chips" were used to provide a comprehensive comparison of gene expression among the cell lines. One line, designated HS-5, was found to secrete large amounts of cytokines, and conditioned media from this line was found to support the ex vivo expansion of both immature and mature progenitors. In contrast, a second line, designated HS-27a, does not secrete known cytokines but does support cobblestone area formation by CD34+/38lo cells. HS-27a, but not HS-5, was also found to express hJagged1, a ligand for Notch1, which may function to influence cell fate decisions of hematopoietic precursors. Both cell lines are currently being used to identify other gene products that regulate hematopoiesis and to generate reagents that will allow more formal evaluation of the putative role of hJagged1 in hematopoietic cell fate decisions.