High dose ara-C combined with autologous peripheral blood stem cell transplantation in the treatment of acute myelogenous leukemia: the question is still not answered

Characterization of Clonogenic Progenitors in Autologous Peripheral Blood Stem Cell Grafts: Evaluation of a Simple In Vitro Assay Suitable for Routine Clinical Use

Autologous peripheral blood stem cell (PBSC) transplantation has a low treatment-related morbidity and mortality when using appropriate criteria for patient selection and graft quality evaluation. It will be important to use simple and standardised procedures for evaluation of progenitor cell numbers when considering autografting in patients with malignant or non-malignant disorders and increased risk of prolonged posttransplant cytopenia. We determined the number of clonogenic cells in PBSC autografts after 7 days of in vitro culture, and these results were compared with both the total number of colonies and the numbers of colony subsets in conventional 14 days colony assays (colony-forming unit granulocyte-erythrocyte-macrophage-megakaryocyte, CFU-GEMM; CFU-E, CFU-GM; CFU-megakaryocyte). The total colony number after 7 days of culture correlated significantly with (i) the CD34+ cell number; (ii) the total colony number as well as the numbers of erythroid, nonerythroid and mixed colonies in a conventional assay using 14 days of culture; (iii) the number of megakaryocyte colonies. The total colony number after 7 days of in vitro culture is a simple in vitro parameter that seems to reflect the proliferative capacity of various progenitor subsets in PBSC autografts. This simple analysis may be used in combination with other in vitro techniques (e.g. estimation of stem cell viability and CD34+ cell subset analysis) for pretransplant evaluation of autografts. However, the possible clinical use of this parameter has to be examined in prospective clinical studies.

Antitumor activity and mechanism of action of the iron chelator, Dp44mT, against leukemic cells

Iron chelators have been reported to induce apoptosis and cell cycle arrest in cancer cells. Recent studies suggest broad and selective antitumor activity of the new iron chelator, di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT; Whitnall et al., Proc Natl Acad Sci USA 2006;103:14901-14906). However, little is known concerning its effects on hematological malignancies. Using acute leukemia cells, the effect of Dp44mT on apoptosis, cell cycle, caspase-3 activation, and mitochondrial trans-membrane potential has been examined by flow cytometry. Dp44mT acted to induce a G(1)/S arrest in NB4 promyelocytic leukemia cells at low concentrations (0.5-2.5 microM), being far more effective than the clinically used chelator, desferrioxamine (DFO). Moreover, Dp44mT induced apoptosis of NB4 cells in a dose- and time-dependent manner with markedly less effect on nonproliferating cells. The apoptosis-inducing activity of Dp44mT was significantly more effective than DFO. Furthermore, this study also showed that Dp44mT had broad activity, inducing apoptosis in several types of acute leukemia and also multiple myeloma cell lines. Additional studies examining the cytotoxic mechanisms of Dp44mT showed that a reduction in the mitochondrial trans-membrane potential and caspase-3 activation could be involved in the mechanism of apoptosis. Our results suggest that Dp44mT possesses potential as an effective cytotoxic agent for the chemotherapeutic treatment of acute leukemia.

A distinct p53 protein isoform signature reflects the onset of induction chemotherapy for acute myeloid leukemia

PURPOSE

The antioncogene protein product p53 has not been studied previously in cancer patients during in vivo chemotherapy. This study examined the early p53 protein and gene expression during induction chemotherapy in acute myeloid leukemia (AML).

EXPERIMENTAL DESIGN

Leukemic cells were collected from five AML patients during their first 18 hours of induction chemotherapy and examined for p53 protein and gene expression by one- and two-dimensional gel immunoblot and high-density gene expression arrays.

RESULTS

Up-regulation of p53 protein expression was detected in AML patients posttreatment in vivo. One- and two-dimensional gel immunoblots showed two main forms of p53, denominated alpha p53 and delta p53, both recognized by various NH2-terminal directed antibodies. As a response to treatment, we detected rapid accumulation of alpha p53, with significantly altered protein expression levels already after 2 hours. The accumulation of alpha p53 was accompanied by increased transcription of putative p53 target genes and subsequent cytopenia in the patients.

CONCLUSION

Up-regulation of the p53 protein and target genes seems to be a prominent feature in induction chemotherapy of AML. The rapid shift from a shorter p53 protein form (delta) toward the full-length protein (alpha) underscores the complexity of p53 protein modulation in patients undergoing chemotherapy.

Chemotherapy plus G-CSF mobilized peripheral blood stem cell harvests from acute myeloid leukaemia patients contain large amounts of polyclonal myeloid linneg CD11cpos dendritic precursor cells

Dendritic cells (DC) are potent antigen-presenting cells that can induce effective tumour-specific T-cell responses. This study investigated leucapheresis products as source of DC precursors in 48 patients undergoing autologous peripheral blood stem cell (PBSC) transplantation for haematological malignancies. Strikingly, high-dose cytarabine and etoposide plus granulocyte colony stimulating factor (G-CSF) mobilized PBSC harvests from acute myeloid leukaemia (AML) patients containing the highest number of myeloid lin(neg)CD11c(pos) DC (mean: 7.04 x 106/kg, range: 1.46-19.67) which was 18.1-fold higher than in non-AML patients mobilized using chemotherapy (CT) regimens plus G-CSF. Clonality of purified lin(neg)CD11c(pos) DC from CT plus G-CSF mobilized AML patients (n = 8 ) was assessed using the human androgen-receptor locus methylation, disclosing a polyclonal pattern in five female patients. These cells displayed morphological and phenotypic features of myeloid DC precursors with expression of HLA-DR, HLA-ABC, CD86, CCR5 and CD54 molecules but lacking CD80, CD83, CD1a and CD40 antigens. Short-term culture with autologous leukaemic cell lysates plus tumour necrosis factor-alpha yielded maturated myeloid DC capable of triggering interleukin-2 and interferon-gamma production by autologous T-lymphocytes. These findings suggest that the use of post-remission CT and G-CSF as mobilizing regimen in AML patients generates PBSC containing high doses of polyclonal myeloid lin(neg)CD11c(pos) DC precursors, which could be used to design feasible immunotherapy protocols.

The ultimate source of human hematopoietic stem cells: thinking outside the marrow

The ability to reconstitute cellular components of the hematopoietic system has immense utility in several areas of clinical medicine. These include replacement of cells responsible for innate and acquired immunity, providing red cells for oxygen transport, and ultimately the ability to recover hematopoietic function by repopulating all lineages comprising the entire blood system. This latter property functionally defines the mammalian hematopoietic stem cell (HSC). Recently, human embryonic stem cells (ESCs) have been suggested to be a viable source of transplantable hematopoietic cells. Although the number of human ESCs is virtually unlimited, the ability to efficiently differentiate adequate numbers of cells that possess hematopoietic repopulating ability remains to be determined. Achieving this goal is confounded by the difficulty of experimentally generating murine hematopoietic cell types capable of in vivo reconstitution from mouse ESC, suggesting that similar limitations may arise using human counterparts. Although the use of human ESCs and adult somatic HSCs have their independent merits, a direct comparison between HSCs derived from each source using similar assays will ultimately be required to determine the best source for clinical use. Here we will summarize the results from efforts to differentiate and assay primitive hematopoietic cells derived from ESCs, and compare these findings to similar parameters using putative mammalian HSCs harvested from the adult.

Thawing of cryopreserved mobilized peripheral blood--comparison between waterbath and dry warming device

BACKGROUND

Thawing of cryopreserved mobilized peripheral blood (MPB) is routinely performed for autologous and allogeneic MPB transplantation. Usually thawing is achieved by submerging the cell bag in a waterbath (37 degrees C temperature). We compared the effectiveness of thawing cryopreserved MPB in a waterbath with an electric dry-warming device containing warmed gel pads (Sahara, Transmed).

METHODS

Two cryopreserved bags from each of 31 apheresis procedures were thawed in a waterbath and under dry conditions in parallel. Viability (dye exclusion), apoptosis/necrosis (annexin/propidiumiodide staining) and clonogenic potential (CFU-E plus BFU-E, CFU-GM) of the cells were tested after thawing.

RESULTS

Statistical analysis by Wilcoxon matched-pair test showed no significant difference between the thawing procedures in terms of the in vitro parameters tested.

DISCUSSION

Our results indicate that thawing of cryopreserved MPB using dry warming and water bath give similar viability, apoptosis/necrosis rate and clonogenic potential. Both procedures take about the same amount of time and are easy to perform. Nevertheless, the potentially decreased risk of bacterial contamination of either the cell product or the patient room, and guidelines of good clinical practice (GCP), favor the use of the dry warming procedure.

No differences in colony formation of peripheral blood stem cells frozen with 5% or 10% dimethyl sulfoxide

High-dose chemotherapy with autologous stem cell rescue usually requires cryopreservation of the cells. For several years, 10% dimethyl sulfoxide (DMSO) has been used as the standard cryoprotectant. Because DMSO infusion can lead to toxic clinical complications in a dose-related manner, we wanted to evaluate if reduction to 5% DMSO would be possible. We have compared colony formation in the myeloid, erythropoietic, and megakaryocyte lineages in peripheral blood progenitor cell (PBPC) samples cryopreserved in parallel with 5% and 10% DMSO. Twenty-seven PBPC samples from patients with malignant diseases were investigated after 3 months of cryopreservation in liquid N(2), and samples from 14 of these patients were investigated after 1 year. A significantly higher colony formation was demonstrated for colony-forming units-erythrocyte (CFU-E) and CFU-granulocyte, erythrocyte, macrophage, megakaryocyte (GEMM) both at 3 months and at 1 year in the 5% samples. For CFU-granulocyte-macrophage (GM) and CFU-megakaryocyte (Mk) no significant difference was demonstrated neither at 3 months nor at 1 year in samples frozen with 5% and 10% DMSO. Also, there was a statistically significant correlation between the CFU-total and CFU-Mk-total, indicating that the CFU-total might be used as an evaluation of megakaryocyte progenitors. Viability testing with the Trypan Blue exclusion test showed that cells cryopreserved in 5% DMSO had significantly higher viability than the cells cryopreserved in 10% DMSO. We conclude that 5% DMSO is at least as good for cryopreservation of small-volume PBPC samples as the conventional 10% DMSO, and our results suggest that the possibility of using 5% DMSO for cryopreservation of autologous PBPC grafts should be further investigated in clinical studies.

Prevention of leptin binding to its receptor suppresses rat leukemic cell growth by inhibiting angiogenesis

Leptin promotes the growth and viability of hematopoietic cells, and it also stimulates microvessel formation, indicating a role for leptin in angiogenesis. Acute myelocytic leukemia (AML) remains a disease with poor prognosis. Similar to solid tumors, it probably requires angiogenesis to ensure adequate supplies of nutrients. We studied rats with transplanted AML to test if a neutralizing anti-leptin receptor monoclonal antibody (mAb) (anti-OB-R) could inhibit leukemogenesis. At 4 weeks after transplantation, the bone marrow contained about 80% leukemic cells as assayed with a specific mAb and flow cytometry. Microscopic examination of bone marrow sections stained with an anti-von Willebrand mAb revealed a marked increase in microvessel density in the leukemic rats compared with controls. Treatment with anti-OB-R for 3 weeks more than halved the content of bone marrow leukemic cells with a concomitant, substantial decrease in angiogenesis. A parallel experiment using an irrelevant anticasein mAb showed no effect on either leukemic cell growth or angiogenesis. We could not detect surface expression of the leptin receptor on the leukemic cells, but on mononuclear cells from healthy rats. The anti-OB-R did not affect in vitro proliferation of leukemic cells whereas proliferation of the mononuclear cells was markedly impaired. The anti-OB-R had no effect on either leukemic cell growth or angiogenesis in leukemic fa/fa rats with a mutated leptin receptor. We conclude that leptin stimulates leukemic cell growth in vivo by promoting angiogenesis. Inhibition of binding of leptin to its receptor might be a new adjunct therapy in AML.

Serum levels of angiogenin, basic fibroblast growth factor and endostatin in patients receiving intensive chemotherapy for acute myelogenous leukemia

Angiogenesis seems to be important both in the pathogenesis of acute myelogenous leukemia (AML) and for the susceptibility of AML blasts to chemotherapy. Recent clinical studies even suggest that antiangiogenic therapy can induce disease control in patients with AML relapse. In this context we have investigated the profile of the systemic component of angiogenic regulation in AML by characterizing the serum levels of (i) the angiogenic regulators angiogenin, basic fibroblast growth factor (bFGF) and endostatin; (ii) the endothelial cell marker soluble (s) E-selectin. Patients with untreated AML had increased levels of angiogenin, endostatin and sE-selectin, whereas the levels of bFGF were not significantly altered. The systemic levels of the proangiogenic bFGF, the antiangiogenic endostatin and the endothelial cell marker sE-selectin showed significant correlations, whereas angiogenin and sE-selectin levels were not correlated. Furthermore, intensive chemotherapy resulted in decreased systemic levels of the 2 proangiogenic mediators angiogenin and bFGF, whereas endostatin levels remained high after treatment. Although angiogenin normally is a part of the acute phase reaction, its systemic levels were not altered when patients with chemotherapy-induced cytopenia developed complicating bacterial infections. Our results suggest that intensive chemotherapy can modulate the systemic component of angiogenic regulation in AML patients.

Peripheral blood stem cells differ from bone marrow stem cells in cell cycle status, repopulating potential, and sensitivity toward hyperthermic purging in mice mobilized with cyclophosphamide and granulocyte colony-stimulating factor

Peripheral blood stem cells (PBSCs) are increasingly used in autologous stem cell transplantations. We investigated the mobilizing effect of a combined cyclophosphamide (CTX) and granulocyte colony-stimulating factor (G-CSF) treatment on progenitor cells (STRA) and primitive stem cells (LTRA) in normal and splenectomized CBA/H mice. This combined treatment not only resulted in mobilization but also in expansion of hematopoietic stem cell subsets. The latter phenomenon was somewhat suppressed in splenectomized animals, but in these mice an enhanced mobilization of STRA and LTRA cells into the peripheral blood was observed. Furthermore, we studied the engraftment potential of mobilized PBSCs. Mice transplanted with PBSCs engrafted significantly better compared to mice transplanted with bone marrow stem cells from control and mobilized mice. The repopulation curve was characterized by a less-deep nadir indicating that the differences occur during the initial phase after transplantation. Contamination of autologous PBSC transplants with malignant cells is noticed frequently and is the basis for urging the use of purging modalities. Here we used hyperthermia and found that the mobilized progenitor cells in peripheral blood are more resistant to hyperthermia than those in the bone marrow (i.e., a survival of 11 +/- 5% after 90 min at 43 degrees C for peripheral blood progenitors, compared to 0.5 +/- 0.4% in bone marrow of mobilized animals and 1.6 +/- 0.5% in normal animals, respectively). Hyperthermic purging does not eliminate the superior repopulating features of a PBSC graft, as is demonstrated by an increased median survival time of lethally irradiated mice transplanted with purged PBSCs. In conclusion, our data demonstrate that CTX + G-CSF-mobilized PBSCs have an enhanced engraftment potential concomitantly with a decreased cycling activity and hence a decreased hyperthermic sensitivity. These findings support the use of these mobilized PBSCs for autologous stem cell transplantation and strengthen the basis for using hyperthermia as a purging modality.

Expression of Fc(epsilon)-receptors by human acute myelogenous leukemia (AML) blasts: studies of high- and low- (CD23) affinity receptor expression and the effects of IgE-mediated receptor ligation on functional AML blast characteristics

Acute myelogenous leukemia (AML) blasts derived from 20 patients were examined for expression of high- (Fc(epsilon)RI) and low-affinity (Fc(epsilon)RII, CD23) IgE Fc(epsilon)-receptors. Fc(epsilon)RI expression was not detected for any patient. In contrast, expression of CD23 (at least 15% of the blasts stained positive) was detected for 6 out of the 20 patients. Acute lymphoblastic leukemia (ALL) blasts derived from 12 patients did not express CD23 (<1% positive cells for all patients). The functional effects of Fc(epsilon)R-receptor ligation were also examined for 20 patients, including the five patients with highest CD23 expression (30-55% positive cells) and five patients with verified low CD23 expression (<or=7% positive cells). The presence of IgE during in vitro culture altered the functional characteristics (spontaneous and cytokine-dependent proliferation, colony formation, cytokine secretion, or spontaneous in vitro apoptosis) of AML blasts for a subset of both CD23-positive patients and certain patients with very low CD23 expression. This last observation suggests that Fc(epsilon)R are either expressed at a very low level or receptors are expressed only by a minor cell subset for these patients. We conclude that functional Fc(epsilon)R can be expressed by human AML cells.

Effects of vascular endothelial growth factor on acute myelogenous leukemia blasts

Vascular endothelial growth factor (VEGF) and its specific receptors are expressed by various malignant cells, including acute myelogenous leukemia (AML) blasts. In this study we performed a detailed characterization of VEGF effects on native human AML blasts derived from a large group of consecutive AML patients with high blast counts in peripheral blood. Exogenous VEGF had divergent effects on spontaneous proliferation and cytokine-dependent (GM-CSF, G-CSF, IL-3) proliferation. Increased, decreased, or unaltered proliferation was observed in the presence of VEGF for various patients, and the VEGF effect differed even in the same patient depending on which exogenous cytokine being present together with VEGF. Similarly, increased, decreased or unaltered interleukin-1beta (IL-1beta) and IL-6 secretion was detected when VEGF was added, and for certain patients the effect of VEGF differed between IL-1beta and IL-6. Exogenous VEGF could also modulate proliferation and differentiation of clonogenic AML progenitors. Constitutive AML blast secretion of VEGF was detected for 40% of patients. Leptin, Flt3-L, IL-4, IL-10, and IL-13 had divergent effects on VEGF release by AML blasts. These results suggest that VEGF can modulate AML blast functions in vivo for a subset of patients. Furthermore, the detection of VEGF in peripheral blood stem cell (PBSC) autografts suggests that VEGF may influence the proliferation and possibly also the survival of contaminating AML cells in PBSC autografts. We conclude that VEGF may influence the functional characteristics of AML cells. Our results suggest that VEGF is important in leukemic hematopoiesis, and the detection of VEGF in PBSC autografts indicates that VEGF may influence the functional phenotype of contaminating AML cells in these grafts.