The Biology and Clinical Uses of Blood Stem Cells

Factors associated with successful mobilization of peripheral blood progenitor cells in 200 patients with lymphoid malignancies

Peripheral blood progenitor cells (PBPC) were mobilized and harvested in 200 patients treated for non-Hodgkin's lymphoma (n = 148), Hodgkin's disease (n = 22) and multiple myeloma (n = 30). The variables predicting the collection of a minimal (>2.5 x 10(6)/kg) or a high (>10 x 10(6)/kg) CD34+ cell count were analysed. Patients were mobilized with haemopoietic growth factors following either standard chemotherapy (n = 49) or high-dose cyclophosphamide, given alone (n = 55) or combined with high-dose VP16 (n = 86). 10 patients received haemopoietic growth factors only. The first mobilization resulted in a PBPC harvest with enough CD34+ cells in 179/200 patients (90%). High-dose cyclophosphamide, with or without VP16, did not mobilize a higher progenitor cell yield than standard chemotherapy. When performing multiple regression analysis in the 190 patients who received chemotherapy-containing mobilization, only the number of previous chemotherapy regimens and the exposure to fludarabine predicted for a failure to collect a minimal PBPC count (P=0.06 and 0.0008 respectively). The target to collect a high CD34+ cell count was negatively associated with the number of previous chemotherapy regimens (P=0.002). When only non-Hodgkin's lymphoma patients were considered for multivariate analysis, low-grade histology with fludarabine appeared to be associated with poor PBPC cell yield (P=0.08 and 0.005 respectively). This data confirms that PBPC harvest should be planned early in the disease course in transplant candidates, and can be obtained after a standard course of chemotherapy.

Nonobese Diabetic/Severe Combined Immunodeficiency (NOD/SCID) Mouse as a Model System to Study the Engraftment and Mobilization of Human Peripheral Blood Stem Cells

Mobilized CD34+ cells from human peripheral blood (PB) are increasingly used for hematopoietic stem-cell transplantation. However, the mechanisms involved in the mobilization of human hematopoietic stem and progenitor cells are largely unknown. To study the mobilization of human progenitor cells in an experimental animal model in response to different treatment regimens, we injected intravenously a total of 92 immunodeficient nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice with various numbers of granulocyte colony-stimulating factor (G-CSF) –mobilized CD34+ PB cells (ranging from 2 to 50 × 106cells per animal). Engraftment of human cells was detectable for up to 6.5 months after transplantation and, depending on the number of cells injected, reached as high as 96% in the bone marrow (BM), displaying an organ-specific maturation pattern of T- and B-lymphoid and myeloid cells. Among the different mobilization regimens tested, human clonogenic cells could be mobilized from the BM into the PB (P= .019) with a high or low dose of human G-CSF, alone or in combination with human stem-cell factor (SCF), with an average increase of 4.6-fold over control. Therefore, xenotransplantation of human cells in NOD/SCID mice will provide a basis to further study the mechanisms of mobilization and the biology of the mobilized primitive human hematopoietic cell.

Activation of the sodium/hydrogen exchanger via the fibronectin-integrin pathway results in hematopoietic stimulation

The proliferative response of hematopoietic cells is regulated by many factors, including the presence and type of growth factors, the cellular microenvironment, and the physiochemical conditions prevailing in the tissue milieu. A process fundamental to all cells is the regulation of the intracellular acid-base conditions. One of the mechanisms by which intracellular pH (pHi) is regulated is through the sodium/hydrogen exchanger, a ubiquitous membrane protein which exploits the intra- and extracellular sodium ion gradient to drive hydrogen ions out of the cell. However, activation of the exchanger via mitogenic and nonmitogenic signals leads to an increase in pHi which, in turn, may directly or indirectly result in a proliferative response. It has been shown that interaction of fibronectin with its integrin receptor subunits alpha4 and alpha5 can result in activation of the Na+/H+ exchanger. In this report, we demonstrate that when mouse bone marrow cells are physically brought together in a preculture system we designate as high cell density culture (HCDC), in a small volume and at the same cellularity as that in the marrow, hematopoietic stem and progenitor cell populations are stimulated with no additional stimulation in the presence of growth factors. Neutralizing antibodies to the growth factors added to HCDC had little, if any, effect on the degree of stimulation. However, when antibodies to fibronectin or the alpha4 integrin subunit were added to HCDC, inhibition was observed, indicating that the observed hematopoietic stimulation occurred via the fibronectin-integrin pathway. Addition of 5 microM 5-(N,N-hexamethylene) amiloride (5-HMA), a specific inhibitor of the Na+/H+ exchanger, also resulted in inhibition of in vitro hematopoiesis. Since the exchanger was implicated, we then measured the pHi of normal and HCDC-treated bone marrow cells in the absence and presence of 5-HMA by flow cytometry using the fluorescent pH-sensitive indicator, carboxy SNARF-1 AM. It was found that cells subjected to HCDC exhibited a higher pH than normal fresh cells. In each case, the pH was lowered in the presence of 5-HMA. Furthermore, addition of antibodies to fibronectin or the alpha4 integrin subunit to HCDC also reduced the pH, to a similar level to that found for 5-HMA. Our results demonstrate, for the first time, that a hematopoietic stem and progenitor cell proliferative response can be initiated by activation of the Na+/H+ exchanger, leading to an increase in pHi, via cell-cell interaction through the fibronectin-integrin pathway. This pathway could, therefore, be significant not only in normal hematopoietic regulation, but also under pathophysiological conditions.

Nonobese Diabetic/Severe Combined Immunodeficiency (NOD/SCID) Mouse as a Model System to Study the Engraftment and Mobilization of Human Peripheral Blood Stem Cells

Mobilized CD34+ cells from human peripheral blood (PB) are increasingly used for hematopoietic stem-cell transplantation. However, the mechanisms involved in the mobilization of human hematopoietic stem and progenitor cells are largely unknown. To study the mobilization of human progenitor cells in an experimental animal model in response to different treatment regimens, we injected intravenously a total of 92 immunodeficient nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice with various numbers of granulocyte colony-stimulating factor (G-CSF) –mobilized CD34+ PB cells (ranging from 2 to 50 × 106cells per animal). Engraftment of human cells was detectable for up to 6.5 months after transplantation and, depending on the number of cells injected, reached as high as 96% in the bone marrow (BM), displaying an organ-specific maturation pattern of T- and B-lymphoid and myeloid cells. Among the different mobilization regimens tested, human clonogenic cells could be mobilized from the BM into the PB (P= .019) with a high or low dose of human G-CSF, alone or in combination with human stem-cell factor (SCF), with an average increase of 4.6-fold over control. Therefore, xenotransplantation of human cells in NOD/SCID mice will provide a basis to further study the mechanisms of mobilization and the biology of the mobilized primitive human hematopoietic cell.

Mobilization and transplantation of Philadelphia chromosome-negative peripheral blood progenitor cells in patients with CML

Mobilization and transplantation of peripheral blood progenitor cells (PBPCs) was investigated in patients with stage IA or stage IIA chronic myelogenous leukaemia (CML) using combination chemotherapy with idarubicin, cytosine arabinoside and etoposide (ICE) followed by simultaneous administration of rhG-CSF and rhIL-2 or rhG-CSF alone. 17 patients (stage IA: 12; stage IIA: five) were mobilized. Chemotherapy, cytokine priming and collection of PBPCs were well tolerated. Using large-volume aphereses, a median number of 10.6 x 10(7)/kg b.w. of MNC were harvested, which yielded between 0.15 and 21.0 x 10(6) CD34+ cells/kg b.w. High numbers of CD34+ HLA-DR- cells could be obtained. Autologous transplantation of mostly Ph- apheresis products was performed in 16/17 patients after high-dose chemotherapy, 10 patients achieved a complete or major cytogenetic remission (stage IA: seven; stage IIA: three), but six patients did not respond cytogenetically. Median follow-up after transplantation was 18+ months. Our data show that this very efficient treatment modality for PBPC mobilization in CML was safe and able to induce major and sustained cytogenetic responses in the majority of patients.

A newly discovered class of human hematopoietic cells with SCID-repopulating activity

The detection of primitive hematopoietic cells based on repopulation of immune-deficient mice is a powerful tool to characterize the human stem-cell compartment. Here, we identify a newly discovered human repopulating cell, distinct from previously identified repopulating cells, that initiates multilineage hematopoiesis in NOD/SCID mice. We call such cells CD34neg-SCID repopulating cells, or CD34neg-SRC. CD34neg-SRC are restricted to a Lin-CD34-CD38- population without detectable surface markers for multiple lineages and CD38 or those previously associated with stem cells (HLA-DR, Thy-1 and CD34). In contrast to CD34+ subfractions, Lin-CD34-CD38- cells have low clonogenicity in short-and long-term in vitro assays. The number of CD34neg-SRC increased in short-term suspension cultures in conditions that did not maintain SRC derived from CD34+ populations, providing independent biological evidence of their distinctiveness. The identification of this newly discovered cell demonstrates complexity of the organization of the human stem-cell compartment and has important implications for clinical applications involving stem-cell transplantation.

Delineation of cell cycle state and correlation to adhesion molecule expression of human CD34+ cells from steady-state bone marrow and peripheral blood mobilized following G-CSF-supported chemotherapy

Treatment with a combination of chemotherapy and G-CSF leads to the release of hematopoietic stem cells from the bone marrow (BM) to the peripheral blood (PB), where they can be harvested for transplantation. Premobilization BM CD34+ cells were reported to proliferate actively, while virtually none of the mobilized PB CD34+ cells were in the S/G2M phase. We were interested in elucidating the cell cycle state further and in investigating the role of adhesion molecule expression on marrow-adherent and circulating CD34+ cells during different phases of the cell cycle. Consecutive premobilization BM and leukapheresis product (LP) samples were obtained from 14 patients following G-CSF-supported chemotherapy. Steady-state BM and LP CD34+ selected cells were triple-stained for CD34, for DNA using the intercalating dye 7-aminoactinomycin D, and for Ki-67, cyclins, or adhesion antigens. Ki-67 is expressed in all phases of the cell cycle except G0 and was found in 69.14%+/-3.46% (mean +/- standard error [SE]) of BM CD34+ cells and 62.78%+/-3.37% of LP CD34+ cells, while in BM significantly more CD34+/Ki-67+ cells were in the S/G2M phase of the cell cycle than in LP (8.6%+/-0.9% versus 1.8%+/-0.3%, respectively, p = 0.0001). Therefore, most circulating mobilized CD34+ cells are in the G1 phase, similar to their steady-state BM counterparts. Cyclin A became detectable in the 2n DNA peak. As expected, a higher proportion of CD34+/cyclin A+/S/G2M cells was found in BM than in LP (p < 0.05). Antigen density of the cyclins D3 and D2 tended to be higher on LP than on BM CD34+ cells, while D1 was found at low levels in similar density. The adhesion antigens CD18, CD49b, CD49d, CD49e, CD58, and CD62L were expressed in a significantly higher proportion of S/G2M-phase than in G0/G1-phase CD34+ cells. The strongest association to the proliferative status was observed for CD49d, which was coexpressed by 85.9% +/-2.6% (BM) or 90.8%+/-2.5% (LP) of CD34+/S/G2M cells, whereas a distinct CD34+/CD49d-/S/G2M population could not be detected. The average coexpression of the other antigens was 57% (CD49e, CD18) or lower. Our results demonstrate that the majority of PB CD34+ cells mobilized following G-CSF-supported chemotherapy and steady-state BM CD34+ cells are in the late G1 phase of the cell cycle and show a correlation between the expression of adhesion receptors and cell cycle status of CD34+ cells in both BM and LP.

Hematopoietic progenitor cell collection and neoplastic cell contamination in breast cancer patients receiving chemotherapy plus granulocyte-colony stimulating factor (G-CSF) or G-CSF alone for mobilization

BACKGROUND

We compared hematopoietic progenitor cell (HPC) collection and neoplastic cell contamination in breast cancer patients given cyclophosphamide (CTX) plus granulocyte-colony stimulating factor (G-CSF) or G-CSF alone for mobilization.

PATIENTS AND METHODS

In 57 stage II-III breast cancer patients, CD34+ cells, colony-forming units-granulocyte macrophage (CFU-GM), early HPC and breast cancer cells were counted in HPC collections obtained after CTX plus G-CSF (n = 27) or G-CSF-alone mobilization (n = 30).

RESULTS

The CD34+ cell collection was about two-fold greater after CTX plus G-CSF mobilization (11.0 +/- 7.9 vs. 5.8 +/- 3.5 x 10(6)/kg, P < 0.001). Similarly, the total number of CFU-GM, CD34+CD38- cells and of week-5 cobblestone area forming cells (CAFC) collected was significantly higher in patients mobilized with CTX plus G-CSF. Breast cancer cells were found in the apheresis products of 22% of patients mobilized with CTX plus G-CSF and in 10% of patients mobilized with G-CSF alone (P = 0.36). Of seven patients who failed G-CSF-alone mobilization and eventually underwent chemotherapy plus G-CSF mobilization, none had cytokeratin-positive cells after G-CSF mobilization, whereas four out of seven had cytokeratin-positive cells after chemotherapy plus G-CSF (P = 0.07 by chi 2 test).

CONCLUSION

The CTX plus G-CSF mobilization protocol was associated with a significantly higher HPC collection. However, this benefit was not accompanied by a reduction in the incidence of tumor-contaminated HPC graft.

Hematopoietic growth factors and transfusion medicine

At least 20 different hematopoietic drugs (see Table 1) are currently under investigation. These most likely will impact on all aspects of transfusion therapy. Which agents to use and in what combinations will be the subject of scrutiny for many years to come as scientists try to recreate and enhance the process of hematopoiesis. Perhaps someday blood cells and hematopoietic progenitor cells can be manufactured for therapy with genetically selected phenotypes to avoid immune destruction and rejection. If this comes to pass, blood donations as we know them today, as a valuable adjunct to medical care, will fade into history, supplanted by the use of hematopoietic growth factors.

Preferential photoinactivation of leukemia cells by aluminum phthalocyanine

The efficacy of chloroaluminum phthalocyanine (AlPc) for photodynamic therapy (PDT) has been evaluated in vitro on acute myeloid leukemia (AML) cells, normal peripheral blood leukocytes (PBL) and mobilized peripheral blood stem cells (mPBSC). The selectivity of the treatment has been evaluated by mixing PBL and TF-1, an erythroleukemic cell line. Upon photoradiation, this photosensitizer leads to a significant and preferential photokilling of leukemia cells in comparison to normal cells. The use of stimulated lymphocytes in PBL/TF-1 mixtures instead of resting cells also leads to a preferential killing towards TF-1 although activated PBL are more affected than resting PBL. The analysis of AlPc intracellular emission by flow cytometry shows that the uptake of the dye by leukemia cells is faster. This good efficacy towards AML and the observed lower phototoxicity towards normal cells (PBL, normal progenitors) suggest that this phthalocyanine is a potential bone marrow purging agent.

Identification of sequence-tagged transcripts differentially expressed within the human hematopoietic hierarchy

Hematopoiesis is regulated by a complex gene expression program. To gain further insight into the molecular mechanisms underlying this process in humans, we sampled the transcriptional activity of the CD34+ hematopoietic progenitor line KG1a by single-pass sequencing the 5' ends of 1018 clones from a unidirectional cDNA library. Searches of public databases with the resulting expressed sequence tags (ESTs) identified 101 clones that showed no sequence similarity to any of the existing entries and that were therefore considered to derive from previously undescribed genes. Of the remaining 917 ESTs, 553 (a total of 485 distinct transcripts) corresponded to known genes. A further 279 KG1a ESTs matched or exhibited sequence similarity to ESTs or genomic sequences from humans and other species. Among the latter were putative human orthologs of developmental and cell cycle control genes from Caenorhabditis elegans, Drosophila, and yeast, as well as genes whose predicted amino acid sequences showed similarity to mammalian transcription factors. Hybridization of selected novel KG1a ESTs to globally amplified cDNAs prepared from single primary human hematopoietic precursors and homogeneous populations of terminally maturing hematopoietic cells revealed transcripts that are expressed preferentially at a specific stage or in a particular lineage within the hematopoietic hierarchy. Thus, included in the KG1a EST dataset are candidates for new human genes that may play roles in hematopoietic differentiative progression and lineage commitment.

High CD34+ Cell Counts Decrease Hematologic Toxicity of Autologous Peripheral Blood Progenitor Cell Transplantation

Optimal numbers of CD34+ cells to be reinfused in patients undergoing peripheral blood progenitor cell (PBPC) transplantation after high-dose chemotherapy are still unknown. Hematologic reconstitution of 168 transplantations performed in patients with lymphoproliferative diseases was analyzed according to the number of CD34+ cells reinfused. The number of days from PBPC reinfusion until neutrophil recovery (>1.0 × 109/L) and unsustained platelet recovery (>50 × 109/L) were analyzed in three groups defined by the number of CD34+ cells reinfused: a low group with less than or equal to 2.5 × 106 CD34+ cells/kg, a high group with greater than 15 × 106 CD34+cells/kg, and an intermediate group to which the former two groups were compared. The 22 low-group patients had a significantly delayed neutrophil (P < .0001) and platelet recovery (P < .0001). The 41 high-group patients experienced significantly shorter engraftment compared with the intermediate group with a median of 11 (range, 8 to 16) versus 12 (range, 7 to 17) days for neutrophil recovery (P = .003), and a median of 11 (range, 7 to 24) versus 14 (range, 8 to 180+) days for platelet recovery (P< .0001). These patients required significantly less platelet transfusions (P = .002). In a multivariate analysis, the amount of CD34+ cells reinfused was the only variable showing significance for neutrophil and platelet recovery. High-group patients had a shorter hospital stay (P = .01) and tended to need fewer days of antibotic administration (P = .12). In conclusion, these results suggest that reinfusion of greater than 15 × 106 CD34+ cells/kg after high-dose chemotherapy for lymphoproliferative diseases further shortens hematopoietic reconstitution, reduces platelet requirements, and may improve patients' quality of life.

High CD34+ Cell Counts Decrease Hematologic Toxicity of Autologous Peripheral Blood Progenitor Cell Transplantation

Optimal numbers of CD34+ cells to be reinfused in patients undergoing peripheral blood progenitor cell (PBPC) transplantation after high-dose chemotherapy are still unknown. Hematologic reconstitution of 168 transplantations performed in patients with lymphoproliferative diseases was analyzed according to the number of CD34+ cells reinfused. The number of days from PBPC reinfusion until neutrophil recovery (>1.0 × 109/L) and unsustained platelet recovery (>50 × 109/L) were analyzed in three groups defined by the number of CD34+ cells reinfused: a low group with less than or equal to 2.5 × 106 CD34+ cells/kg, a high group with greater than 15 × 106 CD34+cells/kg, and an intermediate group to which the former two groups were compared. The 22 low-group patients had a significantly delayed neutrophil (P < .0001) and platelet recovery (P < .0001). The 41 high-group patients experienced significantly shorter engraftment compared with the intermediate group with a median of 11 (range, 8 to 16) versus 12 (range, 7 to 17) days for neutrophil recovery (P = .003), and a median of 11 (range, 7 to 24) versus 14 (range, 8 to 180+) days for platelet recovery (P< .0001). These patients required significantly less platelet transfusions (P = .002). In a multivariate analysis, the amount of CD34+ cells reinfused was the only variable showing significance for neutrophil and platelet recovery. High-group patients had a shorter hospital stay (P = .01) and tended to need fewer days of antibotic administration (P = .12). In conclusion, these results suggest that reinfusion of greater than 15 × 106 CD34+ cells/kg after high-dose chemotherapy for lymphoproliferative diseases further shortens hematopoietic reconstitution, reduces platelet requirements, and may improve patients' quality of life.

Anti–VLA4/VCAM-1—Induced Mobilization Requires Cooperative Signaling Through the kit/mkit Ligand Pathway

Although a large body of data on mobilization have yielded valuable clues, the mechanism(s) dictating egress of stem/progenitor cells during baseline hematopoiesis and after their mobilization are poorly understood. We have previously provided functional in vivo evidence that cytoadhesion molecules, specifically the β1integrins, are involved in mobilization; however, the mechanism by which this was achieved was unclear. To provide further insights into the anti–very late antigen 4 (VLA4)/anti–vascular cell adhesion molecule 1 (VCAM-1)—induced mobilization, we used these antibodies to treat mutant mice with compromised growth factor receptor function. We found that mobilization by anti-VLA4 does not depend on a functional granulocyte colony-stimulating factor, interleukin-7 (IL-7), or IL-3α receptor. By contrast, the functional kit receptor is required, because W/Wv mice responded minimally, whereas Steel-Dickie (Sl/Sld) responded normally. Both Wv and Sl/Sld mice did not respond to anti–VCAM-1 treatment, in contrast to their +/+ littermates and despite normal levels of VCAM-1 expression in bone marrow cells. The defective response to anti–VCAM-1 in W/Wv mice was corrected after their transplantation with +/+ cells. mev/mev mice showed increased numbers of circulating progenitors before treatment and a heightened response after anti-VLA4 or anti–VCAM-1 treatment. Downmodulation of kit expression was detected in normal bone marrow cells after anti-VLA4 treatment. On the strength of the above findings we conclude that (1) anti–VLA4/VCAM-1—induced mobilization likely requires signaling for stimulation of cell migration; (2) this cooperative signaling involves the kit/kit ligand pathway, and provides a novel example of integrin/cytokine crosstalk; and (3) migration mediated through the kit/kit ligand pathway may be a common contributor to different mobilization stimuli. Dissection of the exact molecular pathways that lead to mobilization remains a future challenge.

Anti–VLA4/VCAM-1—Induced Mobilization Requires Cooperative Signaling Through the kit/mkit Ligand Pathway

Although a large body of data on mobilization have yielded valuable clues, the mechanism(s) dictating egress of stem/progenitor cells during baseline hematopoiesis and after their mobilization are poorly understood. We have previously provided functional in vivo evidence that cytoadhesion molecules, specifically the β1integrins, are involved in mobilization; however, the mechanism by which this was achieved was unclear. To provide further insights into the anti–very late antigen 4 (VLA4)/anti–vascular cell adhesion molecule 1 (VCAM-1)—induced mobilization, we used these antibodies to treat mutant mice with compromised growth factor receptor function. We found that mobilization by anti-VLA4 does not depend on a functional granulocyte colony-stimulating factor, interleukin-7 (IL-7), or IL-3α receptor. By contrast, the functional kit receptor is required, because W/Wv mice responded minimally, whereas Steel-Dickie (Sl/Sld) responded normally. Both Wv and Sl/Sld mice did not respond to anti–VCAM-1 treatment, in contrast to their +/+ littermates and despite normal levels of VCAM-1 expression in bone marrow cells. The defective response to anti–VCAM-1 in W/Wv mice was corrected after their transplantation with +/+ cells. mev/mev mice showed increased numbers of circulating progenitors before treatment and a heightened response after anti-VLA4 or anti–VCAM-1 treatment. Downmodulation of kit expression was detected in normal bone marrow cells after anti-VLA4 treatment. On the strength of the above findings we conclude that (1) anti–VLA4/VCAM-1—induced mobilization likely requires signaling for stimulation of cell migration; (2) this cooperative signaling involves the kit/kit ligand pathway, and provides a novel example of integrin/cytokine crosstalk; and (3) migration mediated through the kit/kit ligand pathway may be a common contributor to different mobilization stimuli. Dissection of the exact molecular pathways that lead to mobilization remains a future challenge.

Innovative Two-Step Negative Selection of Granulocyte Colony-Stimulating Factor–Mobilized Circulating Progenitor Cells: Adequacy for Autologous and Allogeneic Transplantation

A major obstacle in purifying either autologous or allogeneic hematopoietic stem cells from granulocyte colony-stimulating factor (G-CSF) mobilized circulating progenitor cells (CPC) is represented by the huge cellularity present in each apheretic product. To obtain a significant debulking of unwanted cells from the leukapheresis, we developed a modified protocol of immune rosetting whereby human ABO-Rh– compatible red blood cells (RBCs) are treated with chromium chloride and then coated with murine monoclonal antibodies (MoAbs) against leukocyte antigens. When experiments were performed with leukaphereses obtained from normal donors or from T-cell acute lymphoblastic leukemia (T-ALL) patients, RBCs were coated with murine MoAbs against human mature myeloid cells (CD11b) and T cells (CD6); whereas, in the case of patients with B-precursor ALL, B-cell non-Hodgkin's lymphoma (B-NHL), or multiple myeloma (MM), RBCs were coated with anti-CD11b only. After incubation with CPC, rosetting cells (myeloid precursor cells, granulocytes, monocytes, and T cells) were removed by Ficoll-Hypaque density gradient centrifugation with a blood cell processor apparatus, COBE (Lakewood, CO) 2991. After this step, a significant reduction of the initial cellularity was consistently obtained (range, 72% to 97%), whereas the median absolute recovery of the CD34+ cells was above 85% (range, 64 to 100), with a 10-fold relative enrichment ranging from 3% to 41%. In a second step, CPC can be further purged of contaminating T or B cells by incubation with lymphoid-specific magnetic microbeads (anti-CD2 and -CD7 to remove T cells; anti-CD19 to remove B cells) and elution through a type-D depletion column (composed of ferromagnetic fiber) inserted within a SuperMACS separator device (Miltenyi Biotech, Bergisch-Gladbach, Germany). By this approach, a highly effective (three to four logs) T-cell depletion was achieved in all experiments performed with normal donors or T-ALL patients (median loss of CD3+cells: 99.8% [range 99.2 to 100]) and an equally efficient B-cell depletion was obtained from B-precursor ALL, B-NHL, or MM patients. At the end of the procedure the T- or B-cell depleted fraction retained a high proportion of the initial hematopoietic CD34+ stem cells, with a median recovery above 70% (range 48% to 100%) and an unmodified clonogenic potential. In five patients (two follicular NHL and three ALL) the purified fraction of stem cells was found disease free at the molecular level as assessed by polymerase chain reaction (PCR) analysis of the t(14;18) chromosome translocation or clono-specific DNA sequences of IgH or T-cell receptor γ and δ chain genes. Purified autologous and allogeneic CPCs were transplanted in three and six patients, respectively, who showed a prompt and sustained hematologic engraftment. In conclusion, this method represents a simple and reproducible two-step procedure to obtain a highly efficient purging of T or B cells from G-CSF expanded and mobilized CPCs. This approach might lead to the eradication of the neoplastic clone in the autologous stem cell inoculum as well as for T-cell depletion during allogeneic transplantation.

Innovative Two-Step Negative Selection of Granulocyte Colony-Stimulating Factor–Mobilized Circulating Progenitor Cells: Adequacy for Autologous and Allogeneic Transplantation

A major obstacle in purifying either autologous or allogeneic hematopoietic stem cells from granulocyte colony-stimulating factor (G-CSF) mobilized circulating progenitor cells (CPC) is represented by the huge cellularity present in each apheretic product. To obtain a significant debulking of unwanted cells from the leukapheresis, we developed a modified protocol of immune rosetting whereby human ABO-Rh– compatible red blood cells (RBCs) are treated with chromium chloride and then coated with murine monoclonal antibodies (MoAbs) against leukocyte antigens. When experiments were performed with leukaphereses obtained from normal donors or from T-cell acute lymphoblastic leukemia (T-ALL) patients, RBCs were coated with murine MoAbs against human mature myeloid cells (CD11b) and T cells (CD6); whereas, in the case of patients with B-precursor ALL, B-cell non-Hodgkin's lymphoma (B-NHL), or multiple myeloma (MM), RBCs were coated with anti-CD11b only. After incubation with CPC, rosetting cells (myeloid precursor cells, granulocytes, monocytes, and T cells) were removed by Ficoll-Hypaque density gradient centrifugation with a blood cell processor apparatus, COBE (Lakewood, CO) 2991. After this step, a significant reduction of the initial cellularity was consistently obtained (range, 72% to 97%), whereas the median absolute recovery of the CD34+ cells was above 85% (range, 64 to 100), with a 10-fold relative enrichment ranging from 3% to 41%. In a second step, CPC can be further purged of contaminating T or B cells by incubation with lymphoid-specific magnetic microbeads (anti-CD2 and -CD7 to remove T cells; anti-CD19 to remove B cells) and elution through a type-D depletion column (composed of ferromagnetic fiber) inserted within a SuperMACS separator device (Miltenyi Biotech, Bergisch-Gladbach, Germany). By this approach, a highly effective (three to four logs) T-cell depletion was achieved in all experiments performed with normal donors or T-ALL patients (median loss of CD3+cells: 99.8% [range 99.2 to 100]) and an equally efficient B-cell depletion was obtained from B-precursor ALL, B-NHL, or MM patients. At the end of the procedure the T- or B-cell depleted fraction retained a high proportion of the initial hematopoietic CD34+ stem cells, with a median recovery above 70% (range 48% to 100%) and an unmodified clonogenic potential. In five patients (two follicular NHL and three ALL) the purified fraction of stem cells was found disease free at the molecular level as assessed by polymerase chain reaction (PCR) analysis of the t(14;18) chromosome translocation or clono-specific DNA sequences of IgH or T-cell receptor γ and δ chain genes. Purified autologous and allogeneic CPCs were transplanted in three and six patients, respectively, who showed a prompt and sustained hematologic engraftment. In conclusion, this method represents a simple and reproducible two-step procedure to obtain a highly efficient purging of T or B cells from G-CSF expanded and mobilized CPCs. This approach might lead to the eradication of the neoplastic clone in the autologous stem cell inoculum as well as for T-cell depletion during allogeneic transplantation.

Inhibition of human immunodeficiency virus type 1 replication in myelomonocytic cells derived from retroviral vector-transduced peripheral blood progenitor cells

Monocytes and macrophages (Mo/Mphi) contribute to the pathogenesis of human immunodeficiency virus type 1 (HIV-1) infection. A successful hematopoietic stem/progenitor cell (HSPC)-based gene therapy strategy for HIV-1 disease must protect Mo/Mphi as well as T cells from HIV-1-related pathology. In this report, we demonstrate that RevM10-transduced HSPCs isolated from cytokine-mobilized peripheral blood give rise to Mo/Mphi suppressing replication of Mphi-tropic HIV-1 isolates. A Moloney murine leukemia virus (MoMLV)-based retroviral vector encoding a bicistronic mRNA co-expressing RevM10 and the murine CD8alpha' chain (Lyt2) was used to transduce HSPCs. Following transduction, these cells were expanded and differentiated by short-term culture in methylcellulose containing various cytokines. In vitro differentiated Mo/Mphi were enriched by fluorescence activated cell sorting (FACS) for the co-expressed transgene (Lyt2) and myelomonocytic (CD33, CD14) surface markers. HIV-1 replication of two Mphi-tropic isolates (JR-FL, BaL) was inhibited in Mo/Mphi expressing RevM10 and Lyt2 relative to control cells expressing only Lyt2 but no functional RevM10 gene product. Cell proliferation and expression of lineage-specific surface markers was not altered in transduced, in vitro differentiated Mo/Mphi cells. This study supports the feasibility of HSPC-based gene therapy as a future treatment for HIV-1 disease.

Impaired Induction of the CD28-Responsive Complex in Granulocyte Colony-Stimulating Factor Mobilized CD4 T Cells

Use of the CD28/B7 costimulatory signal for T-cell activation was analyzed in granulocyte colony-stimulating factor (G-CSF) mobilized peripheral blood mononuclear cells (G-PBMCs) and in peripheral blood mononuclear cells obtained before administration of G-CSF (preG-PBMCs). CTLA4Ig inhibition of OKT3-stimulated proliferation was significantly lower in G-PBMCs compared with preG-PBMCs (39.9% ± 5.6% and 72.2% ± 5.4%, respectively; P < .001). Furthermore, as shown in electrophoretic mobility-shift assays, the inducible level of the T-cell transcription factor CD28 responsive complex (CD28RC) was suppressed in CD4 cells derived from G-PBMC. However, depletion of CD14 cells from G-PBMCs restored CD28RC induction to normal levels. Taken together, these findings suggest that the large number of CD14 monocytes in G-PBMCs may limit T-cell responsiveness by suppressing the induction of the CD28RC.

Impaired Induction of the CD28-Responsive Complex in Granulocyte Colony-Stimulating Factor Mobilized CD4 T Cells

Use of the CD28/B7 costimulatory signal for T-cell activation was analyzed in granulocyte colony-stimulating factor (G-CSF) mobilized peripheral blood mononuclear cells (G-PBMCs) and in peripheral blood mononuclear cells obtained before administration of G-CSF (preG-PBMCs). CTLA4Ig inhibition of OKT3-stimulated proliferation was significantly lower in G-PBMCs compared with preG-PBMCs (39.9% ± 5.6% and 72.2% ± 5.4%, respectively; P < .001). Furthermore, as shown in electrophoretic mobility-shift assays, the inducible level of the T-cell transcription factor CD28 responsive complex (CD28RC) was suppressed in CD4 cells derived from G-PBMC. However, depletion of CD14 cells from G-PBMCs restored CD28RC induction to normal levels. Taken together, these findings suggest that the large number of CD14 monocytes in G-PBMCs may limit T-cell responsiveness by suppressing the induction of the CD28RC.

Lymphoma Cell Burden in Progenitor Cell Grafts Measured by Competitive Polymerase Chain Reaction: Less Than One Log Difference Between Bone Marrow and Peripheral Blood Sources

A controversy persists in autologous transplantation as to which source of progenitor cells, bone marrow (BM) or peripheral blood (PB), contains the lowest number of contaminating lymphoma cells, and how mobilization procedures affect these numbers. To accurately measure the number of non-Hodgkin's lymphoma (NHL) cells harboring the bcl-2/immunoglobulin H (IgH) rearrangement in progenitor cell grafts, we developed a nested quantitative competitive polymerase chain reaction assay (QC-PCR). DNA from lymph nodes of four patients with NHL were cloned into the pSK(+) vectors to generate four internal controls (ICs) (two with major breakpoint region [MBR] and two with minor cluster region [mcr] rearrangements). The kinetics of amplification of ICs paralleled those of bcl-2/IgH rearranged genomic DNA. When used in a QC-PCR assay, these ICs were accurate at a 0.2-log level and provided reproducible results, as shown by low intrarun and interrun variability. An excellent correlation between predicted and observed lymphoma cell content (r = .99) was observed over a range of at least 5 logs of rearranged cells. This approach was used to measure involvement by NHL cells at the time of progenitor cell harvest in 37 autologous transplant patients. The number of bcl-2/IgH rearranged cells in BM, PB, and mobilized PB (mPB) was found to vary from 1 to 1.1 × 105 per million cells. The number of lymphoma cells present in BM was significantly higher than in PB (P = .0001), with a median difference in lymphoma cell content between BM and PB of 0.48 log of cells (range, −0.7 to 5 logs). In contrast, we found no difference in the concentration of bcl-2/IgH rearranged cells present in BM versus PB progenitor cells mobilized with cyclophosphamide and granulocyte colony-stimulating factor (G-CSF) (mPB) (P = .57). In conclusion, the QC-PCR assay described in this study could measure accurately and reproducibly the number of bcl-2/IgH rearranged cells among normal cells. Differences in levels of contamination by lymphoma cells between BM and PB were of less than one log (10-fold), and no differences in lymphoma cell concentrations were observed between BM and mobilized PB. As more cells are usually infused with mPB than with BM grafts, mPB progenitor cell grafts may actually be associated with higher levels of contamination by lymphoma cells. Furthermore, this QC-PCR assay should provide an important tool to assess the prognostic impact of lymphoma cell burden both in progenitor cell grafts and in vivo.

Lymphoma Cell Burden in Progenitor Cell Grafts Measured by Competitive Polymerase Chain Reaction: Less Than One Log Difference Between Bone Marrow and Peripheral Blood Sources

A controversy persists in autologous transplantation as to which source of progenitor cells, bone marrow (BM) or peripheral blood (PB), contains the lowest number of contaminating lymphoma cells, and how mobilization procedures affect these numbers. To accurately measure the number of non-Hodgkin's lymphoma (NHL) cells harboring the bcl-2/immunoglobulin H (IgH) rearrangement in progenitor cell grafts, we developed a nested quantitative competitive polymerase chain reaction assay (QC-PCR). DNA from lymph nodes of four patients with NHL were cloned into the pSK(+) vectors to generate four internal controls (ICs) (two with major breakpoint region [MBR] and two with minor cluster region [mcr] rearrangements). The kinetics of amplification of ICs paralleled those of bcl-2/IgH rearranged genomic DNA. When used in a QC-PCR assay, these ICs were accurate at a 0.2-log level and provided reproducible results, as shown by low intrarun and interrun variability. An excellent correlation between predicted and observed lymphoma cell content (r = .99) was observed over a range of at least 5 logs of rearranged cells. This approach was used to measure involvement by NHL cells at the time of progenitor cell harvest in 37 autologous transplant patients. The number of bcl-2/IgH rearranged cells in BM, PB, and mobilized PB (mPB) was found to vary from 1 to 1.1 × 105 per million cells. The number of lymphoma cells present in BM was significantly higher than in PB (P = .0001), with a median difference in lymphoma cell content between BM and PB of 0.48 log of cells (range, −0.7 to 5 logs). In contrast, we found no difference in the concentration of bcl-2/IgH rearranged cells present in BM versus PB progenitor cells mobilized with cyclophosphamide and granulocyte colony-stimulating factor (G-CSF) (mPB) (P = .57). In conclusion, the QC-PCR assay described in this study could measure accurately and reproducibly the number of bcl-2/IgH rearranged cells among normal cells. Differences in levels of contamination by lymphoma cells between BM and PB were of less than one log (10-fold), and no differences in lymphoma cell concentrations were observed between BM and mobilized PB. As more cells are usually infused with mPB than with BM grafts, mPB progenitor cell grafts may actually be associated with higher levels of contamination by lymphoma cells. Furthermore, this QC-PCR assay should provide an important tool to assess the prognostic impact of lymphoma cell burden both in progenitor cell grafts and in vivo.

Antibodies to VLA4 Integrin Mobilize Long-Term Repopulating Cells and Augment Cytokine-Induced Mobilization in Primates and Mice

Although the use of cytokine-mobilized peripheral blood stem cells has gained a significant momentum in clinical transplantation, the mobilization schemes practiced are guided by a great deal of empiricism. The mechanism(s) by which cytokines or chemokines, alone or in combination, bring about redistribution of stem/progenitor cells from bone marrow to peripheral blood are poorly understood. Likewise the fate of mobilized stem/progenitor cells and their biological properties are incompletely defined. One of the leading hypotheses to explain the mechanism of cytokine-induced mobilization encompasses the view that cytokines disrupt, directly or indirectly, cytoadhesive interactions of stem/progenitor cells with their bone marrow stroma. Compatible with this view are changes in the expression and/or function of several cytoadhesion molecules, especially integrins, postmobilization, and extensive in vitro experimentation supporting the concept of cytokine/integrin interactions. To provide a further insight on the cytokine/integrin interplay in vivo, we have combined cytokine treatments with anti-integrin treatments for mobilization in primates and mice. We found that anti-VLA4 treatment combined with either granulocyte colony-stimulating factor (G-CSF ) treatment or kit ligand treatment leads to significant enhancement of mobilization efficiency (fivefold to eightfold) well above the levels produced by either cytokine alone or anti-VLA4 treatment alone. Similar enhancement was seen when combinations of cytokines, ie, G-CSF plus kit ligand or G-CSF plus Flt3-ligand were used with anti-VLA4 in primates and mice. Furthermore, when anti-VLA4 was given in 5-Fluorouracil–treated primates, significant numbers of progenitor cells were circulating for several days during the recovery period only in the anti-VLA4 treated animals. These data suggest that (1) the effect of anti-VLA4 on mobilization, when used alone, is unlikely to be mediated by secondary cytokine elaboration in vivo; (2) three different cytokines and their combinations do not appear to influence the in vivo responsiveness to anti-VLA4 in coadministration schemes; (3) even if cytokine treatments on their own exert downmodulation of VLA4 function, the target progenitor cells influenced by anti-VLA4 or by cytokines may not necessarily overlap; and (4) augmentation of mobilization in cytokine/anti-VLA4 treatments is most likely caused by an amplification of the pool of target cells on which anti-VLA4 exerts its effects. Because cytokines or anti-VLA4 are each capable of mobilizing long-term repopulating cells and because we show with the present studies that anti-VLA4 in an autologous bone marrow cell transplantation setting does not cause any delay in engraftment, the combination of cytokine/anti-integrin treatment enhancing mobilization may have a clinical use.

Antibodies to VLA4 Integrin Mobilize Long-Term Repopulating Cells and Augment Cytokine-Induced Mobilization in Primates and Mice

Although the use of cytokine-mobilized peripheral blood stem cells has gained a significant momentum in clinical transplantation, the mobilization schemes practiced are guided by a great deal of empiricism. The mechanism(s) by which cytokines or chemokines, alone or in combination, bring about redistribution of stem/progenitor cells from bone marrow to peripheral blood are poorly understood. Likewise the fate of mobilized stem/progenitor cells and their biological properties are incompletely defined. One of the leading hypotheses to explain the mechanism of cytokine-induced mobilization encompasses the view that cytokines disrupt, directly or indirectly, cytoadhesive interactions of stem/progenitor cells with their bone marrow stroma. Compatible with this view are changes in the expression and/or function of several cytoadhesion molecules, especially integrins, postmobilization, and extensive in vitro experimentation supporting the concept of cytokine/integrin interactions. To provide a further insight on the cytokine/integrin interplay in vivo, we have combined cytokine treatments with anti-integrin treatments for mobilization in primates and mice. We found that anti-VLA4 treatment combined with either granulocyte colony-stimulating factor (G-CSF ) treatment or kit ligand treatment leads to significant enhancement of mobilization efficiency (fivefold to eightfold) well above the levels produced by either cytokine alone or anti-VLA4 treatment alone. Similar enhancement was seen when combinations of cytokines, ie, G-CSF plus kit ligand or G-CSF plus Flt3-ligand were used with anti-VLA4 in primates and mice. Furthermore, when anti-VLA4 was given in 5-Fluorouracil–treated primates, significant numbers of progenitor cells were circulating for several days during the recovery period only in the anti-VLA4 treated animals. These data suggest that (1) the effect of anti-VLA4 on mobilization, when used alone, is unlikely to be mediated by secondary cytokine elaboration in vivo; (2) three different cytokines and their combinations do not appear to influence the in vivo responsiveness to anti-VLA4 in coadministration schemes; (3) even if cytokine treatments on their own exert downmodulation of VLA4 function, the target progenitor cells influenced by anti-VLA4 or by cytokines may not necessarily overlap; and (4) augmentation of mobilization in cytokine/anti-VLA4 treatments is most likely caused by an amplification of the pool of target cells on which anti-VLA4 exerts its effects. Because cytokines or anti-VLA4 are each capable of mobilizing long-term repopulating cells and because we show with the present studies that anti-VLA4 in an autologous bone marrow cell transplantation setting does not cause any delay in engraftment, the combination of cytokine/anti-integrin treatment enhancing mobilization may have a clinical use.

Optimization of fibronectin-assisted retroviral gene transfer into human CD34+ hematopoietic cells

Efficient retroviral gene transfer into hematopoietic stem and progenitor cells can be achieved by co-localizing retrovirus and target cells on specific adhesion domains of recombinant fibronectin (FN) fragments. In this paper, we further optimize this technology for human CD34+ cells. Investigating the role of cytokine prestimulation in retrovirus-mediated gene transfer on plates coated with the recombinant FN CH-296 revealed that prestimulation of granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood (PB) CD34+ cells was essential to achieve efficient gene transfer into clonogenic cells. The highest gene transfer occurred by prestimulating PB CD34+ cells for 40 hr with a combination of stem cell factor (SCF), G-CSF, and megakaryocyte growth and development factor (MGDF) prior to retroviral infection on CH-296. Surprisingly, a prolonged simultaneous exposure of primary CD34+ PB cells to retrovirus and cytokines in the presence of CH-296 lowered the gene transfer efficiency. Gene transfer into cytokine prestimulated CD34+ bone marrow (BM) cells was not influenced by increasing the coating concentrations of a recombinant FN fragment, CH-296, nor was it adversely influenced by increasing the number of CD34+ target cells, suggesting that the amount of retroviral particles present in the supernatant was not a limiting factor for transduction of CD34+ BM cells on CH-296-coated plates. The polycation Polybrene was not required for efficient transduction of hematopoietic cells in the presence of CH-296. Furthermore, we demonstrated that repeated exposure of CH-296 to retrovirus containing supernatant, called preloading, can be employed to concentrate the amount of retroviral particles bound to CH-296. These findings establish a simple and short clinically applicable transduction protocol that targets up to 68% of BM or G-CSF-mobilized PB CD34+ cells and is capable of genetically modifying up to 17% of CD34+CD38-/dim PB cells.

Hematopoietic transplantation: state of the art

Bone marrow transplantation has developed from an experimental therapy for a small group of patients to a well-established form of treatment with well-defined indications for a large group of patients with hematological and non-hematological neoplasia. The availability of suitable donors has more than doubled due to large registries of persons volunteering for marrow donation. With improved techniques for histocompatibility typing, it has become possible to study the role of specific histoincompatibilities for graft-versus-host disease and graft-versus-leukemia reactions. The source of hematopoietic stem cells now comprises not only bone marrow, but also stem cells mobilized into the peripheral blood and stem cells from cord blood. Hematopoietic growth factors have found a large distribution in the mobilization of stem cells and support for hematological reconstitution. They are studied for the expansion of pools of stem cells. Reconstitution of antileukemia and antiviral activity has been achieved by adoptive immunotherapy using lymphocytes and dendritic cells cultured in vitro. The way from transplantation of bone marrow to cellular and genetic engineering leads to new indications such as treatment of severe autoimmune disease. Hematopoietic transplantation has come a long way and it still has possible new areas of application.

The Granulocyte Colony-Stimulating Factor Receptor Is Required for the Mobilization of Murine Hematopoietic Progenitors Into Peripheral Blood by Cyclophosphamide or Interleukin-8 But Not Flt-3 Ligand

Hematopoietic progenitor cells (HPC) can be mobilized from the bone marrow into the peripheral circulation in response to a number of stimuli including hematopoietic growth factors, cytotoxic agents, and certain chemokines. Despite significant differences in their biological activities, these stimuli result in the mobilization of HPC with a similar phenotype, suggesting that a common mechanism for mobilization may exist. In this study, the role of granulocyte colony-stimulating factor (G-CSF) in progenitor mobilization was examined using G-CSF receptor (G-CSFR)–deficient mice. In contrast to wild-type mice, no increase in circulating colony-forming cells (CFU-C), CD34+ lineage− progenitors, or day 12 colony-forming unit-spleen progenitors (CFU-S) was detected in G-CSFR–deficient mice after cyclophosphamide administration. This defect was not due to a failure to regenerate HPC following cyclophosphamide administration as the number of CFU-C in the bone marrow of G-CSFR–deficient mice was increased relative to wild-type mice. Likewise, no increase in circulating CFU-C was detected in G-CSFR–deficient mice following interleukin-8 (IL-8) administration. In contrast, mobilization of HPC in response to flt-3 ligand was nearly normal. These results show that the G-CSFR is required for mobilization in response to cyclophosphamide or IL-8 but not flt-3 ligand and suggest that the G-CSFR may play an important and previously unexpected role in HPC migration.

The Granulocyte Colony-Stimulating Factor Receptor Is Required for the Mobilization of Murine Hematopoietic Progenitors Into Peripheral Blood by Cyclophosphamide or Interleukin-8 But Not Flt-3 Ligand

Hematopoietic progenitor cells (HPC) can be mobilized from the bone marrow into the peripheral circulation in response to a number of stimuli including hematopoietic growth factors, cytotoxic agents, and certain chemokines. Despite significant differences in their biological activities, these stimuli result in the mobilization of HPC with a similar phenotype, suggesting that a common mechanism for mobilization may exist. In this study, the role of granulocyte colony-stimulating factor (G-CSF) in progenitor mobilization was examined using G-CSF receptor (G-CSFR)–deficient mice. In contrast to wild-type mice, no increase in circulating colony-forming cells (CFU-C), CD34+ lineage− progenitors, or day 12 colony-forming unit-spleen progenitors (CFU-S) was detected in G-CSFR–deficient mice after cyclophosphamide administration. This defect was not due to a failure to regenerate HPC following cyclophosphamide administration as the number of CFU-C in the bone marrow of G-CSFR–deficient mice was increased relative to wild-type mice. Likewise, no increase in circulating CFU-C was detected in G-CSFR–deficient mice following interleukin-8 (IL-8) administration. In contrast, mobilization of HPC in response to flt-3 ligand was nearly normal. These results show that the G-CSFR is required for mobilization in response to cyclophosphamide or IL-8 but not flt-3 ligand and suggest that the G-CSFR may play an important and previously unexpected role in HPC migration.