Hematopoietic growth factors for the treatment of aplastic anemia

Granulocyte and granulocyte macrophage colony-stimulating factors as therapy in human and veterinary medicine

Granulocyte colony-stimulating factors (G-CSFs) and granulocyte macrophage colony-stimulating factors (GM-CSFs) are endogenous cytokines that regulate granulocyte colonies and play a major role in the stimulation of granulopoiesis (neutrophils, basophils and eosinophils) and in the regulation of microbicidal functions. There are numerous pathological conditions in which neutrophils are decreased, the most common being neutropenia associated with cancer chemotherapy, which increases the risk of serious microbial infections developing with the potential for high morbidity and mortality. New methods in molecular biology have led to the identification and cloning of CSF genes and biopharmaceutical production. Since then, CSFs have been widely used for the prevention and treatment of neutropenia associated with cancer chemotherapy, for mobilising haematopoietic cell precursors, and for other neutropenia-related pathologies. This review focuses on the use of CSFs within both human and veterinary medicine. Clinical applications, pharmacology, tolerability and the potential role of these factors in veterinary medicine are considered.

Diagnosis and treatment of children with aplastic anemia

BACKGROUND

Long-term survival rates among children diagnosed with severe aplastic anemia (SAA) are excellent due to the success of human leukocyte antigen (HLA)-identical related hematopoietic stem cell transplantation (HSCT), concurrent advances in immunosuppressive treatment (IST), and improved supportive care. The challenge in making treatment recommendations for children with SAA, therefore, is to balance the apparent chronicity and morbidity following IST, with the potential up-front toxicity and complications of HSCT.

METHODS

This review provides an update on the diagnosis and a risk-based treatment algorithm for children with acquired SAA. Recent experience using alternative donor HSCT and efforts to extend HSCT eligibility through advances in donor matching, de-escalation of conditioning regimens, and potential marrow graft engineering are highlighted. We discuss IST response rates, risks of relapse, and complications including clonal evolution.

CONCLUSIONS

While good treatment options exist for a majority of children diagnosed with SAA, novel non-transplantation treatments for unresponsive and relapsed patients without suitable transplant donors are needed. Further improvements in outcome will ultimately require a more complete understanding of the pathophysiology of aplastic anemia (AA).

Colony-stimulating factors in the management of neutropenia and its complications

Granulocyte colony-stimulating factor (CSF) and granulocyte-macrophage CSF are potent drugs used to increase neutrophil counts after myelosuppressive chemotherapy. However, in various indications, the use of CSFs has no clinical benefit with regard to morbidity or mortality from infectious complications, frequency of antibiotic use, or rate of hospitalization. Thus, the application of CSFs should be limited to indications with proven clinical benefits or evidence of cost-effectiveness. This review will provide an overview of the state-of-the-art use of CSFs in chemotherapy-associated neutropenia, transplantation, and bone marrow failure syndromes. In addition, recently developed drugs for accelerated hematopoietic recovery will be presented.

Bone marrow cytogenetic abnormalities of aplastic anemia

Cytogenetic abnormalities in association with aplastic anemia have been reported fairly infrequently. Clonal cytogenetic abnormalities at initial diagnosis are uncommon. A retrospective study was performed of the cytogenetic findings in patients with typical morphological and clinical features of severe aplastic anemia from a single institution for the years 1988 through 1998. A total of 30 cases of aplastic anemia, 16 men and 14 women, were identified. The median age was 60 with females being significantly older (67.5 years) in comparison to males (44 years). Bone marrow specimens failed to yield metaphases in 16 cases and normal karyotypes were detected in 11 cases. Cytogenetic abnormalities were detected in 3 cases. Clonal abnormalities, as defined, occurred in only 2 cases (6.7%). A review of the literature identified a total of 24 cases of aplastic anemia with abnormal cytogenetic findings. Overall, the most common chromosome abnormalities are trisomies of 6 and 8 and loss of chromosome 7. Trisomy 6 is more common at diagnosis while loss of chromosome 7 is more common after therapy.

A ligand-receptor signaling threshold model of stem cell differentiation control: a biologically conserved mechanism applicable to hematopoiesis

A major limitation to the widespread use of hematopoietic stem cells (HSC) is the relatively crude level of our knowledge of how to maintain these cells in vitro without loss of the long-term multilineage growth and differentiation properties required for their clinical utility. An experimental and theoretical framework for predicting and controlling the outcome of HSC stimulation by exogenous cytokines would thus be useful. An emerging theme from recent HSC expansion studies is that a net gain in HSC numbers requires the maintenance of critical signaling ligand(s) above a threshold level. These ligand-receptor complex thresholds can be maintained, for example, by high concentrations of soluble cytokines or by extracellular matrix- or cell-bound cytokine presentation. According to such a model, when the relevant ligand-receptor interaction falls below a critical level, the probability of a differentiation response is increased; otherwise, self-renewal is favored. Thus, in addition to the identity of a particular receptor-ligand interaction being important to the regulation of stem cell responses, the quantitative nature of this interaction, as well as the dynamics of receptor expression, internalization, and signaling, may have a significant influence on stem cell fate decisions. This review uses examples from hematopoiesis and other tissue systems to examine existing evidence for a role of receptor activation thresholds in regulating hematopoietic stem cell self-renewal versus differentiation events.

A ligand-receptor signaling threshold model of stem cell differentiation control: a biologically conserved mechanism applicable to hematopoiesis

A major limitation to the widespread use of hematopoietic stem cells (HSC) is the relatively crude level of our knowledge of how to maintain these cells in vitro without loss of the long-term multilineage growth and differentiation properties required for their clinical utility. An experimental and theoretical framework for predicting and controlling the outcome of HSC stimulation by exogenous cytokines would thus be useful. An emerging theme from recent HSC expansion studies is that a net gain in HSC numbers requires the maintenance of critical signaling ligand(s) above a threshold level. These ligand-receptor complex thresholds can be maintained, for example, by high concentrations of soluble cytokines or by extracellular matrix- or cell-bound cytokine presentation. According to such a model, when the relevant ligand-receptor interaction falls below a critical level, the probability of a differentiation response is increased; otherwise, self-renewal is favored. Thus, in addition to the identity of a particular receptor-ligand interaction being important to the regulation of stem cell responses, the quantitative nature of this interaction, as well as the dynamics of receptor expression, internalization, and signaling, may have a significant influence on stem cell fate decisions. This review uses examples from hematopoiesis and other tissue systems to examine existing evidence for a role of receptor activation thresholds in regulating hematopoietic stem cell self-renewal versus differentiation events.

Pharmacologic doses of granulocyte colony-stimulating factor affect cytokine production by lymphocytes in vitro and in vivo

Peripheral blood stem cell (PBSC) transplantation is successful in improving engraftment without increasing acute graft-versus-host disease (GVHD), despite much larger numbers of T cells in unmanipulated PBSCs than in bone marrow grafts. In mouse models and retrospective human studies, granulocyte colony-stimulating factor (G-CSF) therapy has been associated with less acute GVHD. We studied the effect of G-CSF on interferon (IFN)-γ and IL-4 expression in CD4+lymphocytes. CD4+ cells co-cultivated with G-CSF and stimulated with PHA or CD3 monoclonal antibodies showed significant decreases in IFN-γ and increases in IL-4 expression (n = 13;P < .01). G-CSF appeared to have a direct effect on CD4+ cells independent of monocytes present in the culture because purified CD4+ cells exposed to G-CSF, washed, and cocultivated with untreated monocytes demonstrated similar changes in IFN-γ and IL-4 expression, whereas untreated CD4+ cells cocultured with G-CSF–stimulated monocytes behaved as controls. We then studied peripheral blood mononuclear cells (PBMCs) from G-CSF–mobilized PBSC donors. When their PBMCs were cultured with PHA or CD3 monoclonal antibody, the percent of IFN-γ–expressing cells decreased by a mean of 55% and 42%, respectively, whereas the percent of IL-4–containing cells increased by a mean of 39% and 58%, respectively, following G-CSF stimulation. Increased apoptosis of IFN-γ–producing CD4+ cells was not responsible for the shift in TH1/TH2 subsets. G-CSF-R mRNA was present in both CD4+ and CD8+ cells. These results suggest that G-CSF decreases IFN-γ and increases IL-4 production in vitro and in vivo and likely modulates a balance between TH1 and TH2 cells, an effect that may be important in PBSC transplantation.

Pharmacologic doses of granulocyte colony-stimulating factor affect cytokine production by lymphocytes in vitro and in vivo

Peripheral blood stem cell (PBSC) transplantation is successful in improving engraftment without increasing acute graft-versus-host disease (GVHD), despite much larger numbers of T cells in unmanipulated PBSCs than in bone marrow grafts. In mouse models and retrospective human studies, granulocyte colony-stimulating factor (G-CSF) therapy has been associated with less acute GVHD. We studied the effect of G-CSF on interferon (IFN)-γ and IL-4 expression in CD4+lymphocytes. CD4+ cells co-cultivated with G-CSF and stimulated with PHA or CD3 monoclonal antibodies showed significant decreases in IFN-γ and increases in IL-4 expression (n = 13;P < .01). G-CSF appeared to have a direct effect on CD4+ cells independent of monocytes present in the culture because purified CD4+ cells exposed to G-CSF, washed, and cocultivated with untreated monocytes demonstrated similar changes in IFN-γ and IL-4 expression, whereas untreated CD4+ cells cocultured with G-CSF–stimulated monocytes behaved as controls. We then studied peripheral blood mononuclear cells (PBMCs) from G-CSF–mobilized PBSC donors. When their PBMCs were cultured with PHA or CD3 monoclonal antibody, the percent of IFN-γ–expressing cells decreased by a mean of 55% and 42%, respectively, whereas the percent of IL-4–containing cells increased by a mean of 39% and 58%, respectively, following G-CSF stimulation. Increased apoptosis of IFN-γ–producing CD4+ cells was not responsible for the shift in TH1/TH2 subsets. G-CSF-R mRNA was present in both CD4+ and CD8+ cells. These results suggest that G-CSF decreases IFN-γ and increases IL-4 production in vitro and in vivo and likely modulates a balance between TH1 and TH2 cells, an effect that may be important in PBSC transplantation.

Hematopoietic growth factors in the pathogenesis and for the treatment of aplastic anemia

The production and release of hematopoietic growth factors from bone marrow stromas established in vitro from patients with aplastic anemia is normal or increased. Addition of hematopoietic growth factors to aplastic anemia bone marrow cells results in only modest increases in colony growth, with the exception of granulocyte colony-stimulating factor (G-CSF), which corrects their impaired cloning efficiency to normal. Most clinical data on the use of hematopoietic growth factors in aplastic anemia have derived from uncontrolled and small single-arm studies or case reports. Sustained trilineage hematologic responses have not been observed when hematopoietic growth factors have been used alone or in combination. Serious side effects have been reported for most of the hematopoietic growth factors in patients with aplastic anemia, with the exception of G-CSF. There is a major concern that they may further increase the risk of clonal disorders such as myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Hematopoietic growth factors should not be used alone in newly diagnosed patients as specific treatment for aplastic anemia, and their use in combination with immunosuppressive therapy should be confined to multicenter, prospective randomized studies.

Chemotherapeutic neuropathy

Peripheral neurotoxicity is a dose-limiting side-effect for a number of effective chemotherapeutic agents, including platinum compounds, taxanes, and vinca alkaloids. New experimental chemotherapy drugs that cause neuropathy include suramin and Dolostatin-10. A better understanding of cellular mechanisms will lead to novel treatment strategies that will protect neurons without decreasing therapeutic efficacy.