Endogenous serum levels and surface receptor expression of GM-CSF and IL-3 in patients with myelodysplastic syndromes

Leukemia Cells and the Cytokine Network: Therapeutic Prospects

The network and balance of cytokines is of major importance in maintaining proper homeostasis of hematopoiesis. Abnormalities in this network may result in a variety of blood disorders; however, the role of this network is not clear in leukemia. The use of antineoplastic agents has improved the survival rate of some types of leukemia, and adjunctive therapy with cytokines may be helpful. Chemotherapeutic approaches are no longer the best choice because cytotoxicity may affect normal and leukemic cells, and leukemic cells may develop resistance to the chemotherapeutic agent. Induction of differentiation to a mature phenotype and the control of apoptotic-gene expression have provided other possible alternative therapies. Combined effects of cytokines and vitamin derivatives such as retinoic acid (RA) and 1, 25 dihydroxyvitamin D3 (VD3) were found more beneficial than any of these agents individually. These agents exhibit cooperative effects, potentiate each other's effects, or both. Therefore, understanding the hematopoietic actions of these agents, their interactions with their receptors, and their differentiation signaling pathways may result In the design of new therapies. However, the role of cytokines in apoptosis is controversial because in some cases they were found to increase tumor cell resistance to apoptosis-inducing agents. Recent studies in the molecular biology of gene regulation, transcription factors, and repressors have led to new possible approaches such as differentiation therapy for the treatment of leukemia. In addition, the development of drugs that act on the molecular level such as imatinib is just the beginning of a new era in molecular targeted therapy in which the drug acts specifically on the leukemic cell. There are many possible combinations of cytokines, retinoids, and VD3, and perhaps the best therapeutic combination is yet to be described. This minireview is an update on the role of cytokines and the therapeutic potential of combinations with agents such as RA, VD3, and other chemotherapeutic agents.

MDS: a stem cell disorder--but what exactly is wrong with the primitive hematopoietic cells in this disease?

Despite the various abnormalities identified in the immune system or the bone marrow microenvironment in patients with myelodysplastic syndrome (MDS), most of the investigation of this disorder has centered on the hematopoietic stem/progenitor compartment. It is generally written that MDS is a stem cell disorder, and there is certainly evidence supporting this view. However, whether it occurs in a cell with only myeloid multipotentiality (i.e., that involves megakaryocytic, erythroid and granulocytic/monocytic lineages) or occurs in a true stem cell is open to debate. The absence of an assay for human stem cells necessitates the use of surrogate markers for such cells, such as gene expression profiles, or the identification of specific genetic or epigenetic abnormalities that are found in multiple lineages. Clearly, the common cytogenetic and genetic abnormalities found in MDS are most indicative of a clonal myeloid disease similar to AML, rather than a lymphoid disease, and the often tri-lineage ineffective hematopoiesis and dysplasia are generally not found within the lymphoid compartment. Recent studies, using modern molecular detection techniques, have identified new recurring molecular lesions in these disorders but have not really unraveled its pathogenesis.

Different Radiosensitive Megakaryocytic Progenitor Cells Exist in Steady-State Human Peripheral Blood

CD34 antigen is a novel marker for human hematopoietic stem/progenitor cells. In the present study, two cell fractions, CD34low and CD34high, were prepared from steady-state human peripheral blood on the basis of CD34 antigen expression. The colony-forming unit megakaryocytes (CFU-Meg) contained in each cell fraction were compared for X-radiation sensitivity and cytokine action. The content of CD34+CD45+ cells in the CD34low and CD34high cell fractions was 74.8% and 88.8%, respectively, and the frequency of thrombopoietin (TPO)-supported CFU-Meg in the CD34low cell fraction was 1.9 times higher than that in CD34high. The CFU-Meg in CD34high were more radiosensitive than those in CD34low, indicating that steady-state human peripheral blood contains different types of CFU-Meg. However, no significant differences were observed between cell fractions in the radiation survival curves of CFU-Meg stimulated by TPO plus cytokines except granulocyte colony-stimulating factor (G-CSF). TPO plus interleukin 3 was the optimal combination for survival of both types of CFU-Meg after X irradiation. The present study also demonstrated that TPO plus G-CSF is able to increase the survival of irradiated CD34low CFU-Meg. These results suggest that two megakaryocytic progenitor populations with different radiosensitivity and cytokine responses are found in steady-state human peripheral blood.

Reconstitution of dendritic and natural killer-cell subsets after allogeneic stem cell transplantation: effects of endogenous flt3 ligand

Recovery of dendritic cells (DCs) and natural killer (NK) cells after allogeneic stem cell transplantation (SCT) is important for allograft responses and antitumor immunity and thus for treatment outcome. Regulation of this regenerative process is not well understood. We investigated the influence of endogenous cytokines on the recovery and diversification of DC and NK cell subsets up to 6 months after SCT. Reconstitution of circulating DCs and NK cells was rapid but accompanied by prolonged skewing of cell subsets. The speed of recovery of CD11c(+)CD123(low) DC1 exceeded that of CD11c(-) CD123(+) DC2, and correlated with plasma levels of flt3 ligand (FL), but not with granulocyte or granulocyte-macrophage colony-stimulating factors and stem cell factor. There was a 5-fold increase in interferon-gamma-producing CD56(high)CD16(-)/low NK cells and a corresponding reduction in the CD56(low)CD16(high) subset, accompanied by strongly reduced NK cell cytotoxicity. In vitro data implicate an inhibitory effect of cyclosporin A on NK cell differentiation and cytotoxicity. NK cell numbers did not correlate with plasma levels of FL or interleukin 15. Our results demonstrate that endogenous FL has distinct effects on the kinetics of reconstitution of DCs and NK cells and have potential implications for the modulation of immune responses after allogeneic SCT.

Leukemic cells and the cytokine patchwork

BACKGROUND

In leukemia, the clonal population is characterized by a hierarchical organization. Although the majority of the leukemic population is generated after post-determinic divisions, a subset of cells retain undifferentiated "blast" morphology. In addition, leukemic cells often have numerical or structural chromosomal abnormalities, aberrant gene expression patterns, and abnormal cell surface marker profiles. Despite these differences when compared to normal bone marrow and blood cells, leukemic cell survival and proliferation, just like that of normal progenitor cells, is influenced by hematopoietic growth factors. A major issue is whether differential regulation of normal and leukemic hematopoietic cells by cytokines can be exploited in antileukemic treatment or, in contrast, whether in vivo cytokine therapy may even be harmful to the patients.

PROCEDURE

Here we review the results of recent experimental and clinical observations that investigated the influence of cytokines on leukemic cell growth and differentiation in vitro and in vivo.

RESULTS

The majority of studies indicate that hematopoietic growth factors are involved in the regulation of proliferation and terminal differentiation of leukemic blast cells. Genetic aberrations involving cytokines or their receptors may contribute to leukemogenesis. Abundant interactions, cross-lineage stimulation, and aberrant response patterns seem to transform the complex cytokine network regulation of normal hematopoiesis into an even more interlaced "patchwork" that controls leukemic hematopoiesis.

CONCLUSIONS

Since hematopoietic growth factors are present in high serum concentrations in patients with acute leukemia and myelodysplastic syndromes, consequences of possible interactions should be kept in mind even when well-defined human recombinant factors in single application are to be involved in antileukemic protocols.

Biological and clinical significance of clonogenic assays in patients with myelodysplastic syndromes

Biological and clinical significance of growth pattern of hematopoietic progenitors were investigated in 117 patients with primary myelodysplastic syndromes (MDSs) at referral. Abnormal (i.e., "leukemic" or absent) growth of GM colonies (CFU-GM) and GM clusters was found in 47% of patients with "advanced" MDS (RAEB, RAEB-t, and CMML) and in 15% of "low-risk" (RA/RARS) patients. In vitro erythropoiesis was decreased in most of the patients, with significantly lower number of BFU-E in "advanced" MDS than in RA/RARS patients. Megakaryocyte progenitors (CFU-MK) were very low or absent in almost all the patients, regardless of the FAB type. Significant correlation was demonstrated between the number of BFU-E and hemoglobin concentration and between number of CFU-MK and platelet count. Growth capacity of GM progenitors appears to be in proportion to "myeloproliferative" capacity of the malignant clone. T-cell depletion had no influence on growth capacity of hematopoietic progenitors, nor did colony growth respond in a dose-dependent manner to different concentrations of LCM. Growth capacity of MDS hematopoietic progenitors was independent of Bournemouth score, of the presence and type of cytogenetic abnormality, and of the expression of CD95 and caspase-3 antigens on bone marrow cells. However, in patients with "abnormal" growth of GM progenitors, CD34 antigen expression was significantly higher than in patients with "normal" growth. "Abnormal" GM growth was found to be independently predictive regarding the survival and the risk for AML development. In contrast, the prognostic value of erythroid and megakaryocyte cultures was found to be limited.

Chronic myelomonocytic leukemia requires granulocyte-macrophage colony-stimulating factor for growth in vitro and in vivo

OBJECTIVE

Chronic myelomonocytic leukemia (CMML) is a heterogeneous disease with no effective treatments or cure. Several factors have been implicated in its pathogenesis. In the current study, we studied the dependence of CMML on granulocyte-macrophage colony-stimulating factor (GM-CSF).

MATERIALS AND METHODS

We used in vitro colony assays in methylcellulose where CMML cells were tested in the presence or absence of the specific GM-CSF antagonist E21R. We also developed an in vivo model in which CMML cells were tested for their ability to engraft into immunodeficient mice transgenic for human GM-CSF.

RESULTS

Bone marrow cells from seven of seven patients with CMML formed spontaneous colonies that were sensitive to E21R treatment, with reduction in colony growth by up to 92%. E21R also inhibited colony formation by CMML patient cells stimulated by exogenously added GM-CSF but not interleukin-3. In in vivo experiments we observed engraftment of CMML cells (but not normal cells) in immunodeficient mice transgenic for human GM-CSF. None engrafted in nontransgenic mice. Cell dose escalation showed that the optimal number was 0.5 to 1 x 10(8) peripheral blood mononuclear cells per mouse, which is equivalent to an infusion of 0.2 to 3.6 x 10(6) CD34(+) cells. Time course experiments showed that maximal engraftment occurred 6 weeks after injection.

CONCLUSIONS

These results demonstrate that in some CMML patients, GM-CSF produced by either autocrine or paracrine mechanisms is a major growth determinant. The results suggest that therapies directed at blocking this cytokine could control the growth of some CMML patients in vivo.

Randomized controlled trial of azacitidine in patients with the myelodysplastic syndrome: a study of the cancer and leukemia group B

PURPOSE

Patients with high-risk myelodysplastic syndrome (MDS) have high mortality from bone marrow failure or transformation to acute leukemia. Supportive care is standard therapy. We previously reported that azacitidine (Aza C) was active in patients with high-risk MDS.

PATIENTS AND METHODS

A randomized controlled trial was undertaken in 191 patients with MDS to compare Aza C (75 mg/m(2)/d subcutaneously for 7 days every 28 days) with supportive care. MDS was defined by French-American-British criteria. New rigorous response criteria were applied. Both arms received transfusions and antibiotics as required. Patients in the supportive care arm whose disease worsened were permitted to cross over to Aza C.

RESULTS

Responses occurred in 60% of patients on the Aza C arm (7% complete response, 16% partial response, 37% improved) compared with 5% (improved) receiving supportive care (P <.001). Median time to leukemic transformation or death was 21 months for Aza C versus 13 months for supportive care (P =.007). Transformation to acute myelogenous leukemia occurred as the first event in 15% of patients on the Aza C arm and in 38% receiving supportive care (P =.001). Eliminating the confounding effect of early cross-over to Aza C, a landmark analysis after 6 months showed median survival of an additional 18 months for Aza C and 11 months for supportive care (P =.03). Quality-of-life assessment found significant major advantages in physical function, symptoms, and psychological state for patients initially randomized to Aza C.

CONCLUSION

Aza C treatment results in significantly higher response rates, improved quality of life, reduced risk of leukemic transformation, and improved survival compared with supportive care. Aza C provides a new treatment option that is superior to supportive care for patients with the MDS subtypes and specific entry criteria treated in this study.

A hypothesis for the pathogenesis of myelodysplastic syndromes: implications for new therapies

To guide development of new clinical strategies, a review of recent investigations in the pathobiology of MDS was performed. Articles were identified through a Medline search. Studies, including reviews, are cited in the references. A multistep pathogenesis is proposed. (1) Targeted injury or mutation within hemopoietic stem cells may be followed by an immunologic response adversely affecting progenitor survival. (2) Accelerated proliferation and premature death of marrow cells is amplified by apoptogenic cytokines (TNF-alpha, Fas ligand). (3) Establishment of an abnormal clone associated with telomere shortening. (4) Disease progression associated with loss of tumor suppressor activity. Opportunities for therapeutic interventions are possible at each step. Comparisons between the proposed pathogenesis of MDS and severe aplastic anemia (SAA) are also presented. Leukemia (2000) 14, 2-8.

Cytokine priming of the granulocyte respiratory burst in myelodysplastic syndromes

Increased susceptibility to infections in patients with myelodysplastic syndromes (MDS) is thought to be due to neutropenia as well as functional abnormalities of neutrophils. In the present study we examined the effect of two different stimulants (fMLP, PMA) and three cytokines (alphaTNF, G-CSF and GM-CSF), both singly and in combination on granulocyte (RB) in 25 MDS patients compared to seven healthy controls. Single fMLP and PMA-stimulation showed similar results for both groups. Preincubation with cytokines enhanced fMLP-stimulated RB in most MDS patients and controls, but in patients to a significantly lesser extent when compared to the control group (p < or = 0,05). Combinations of alphaTNF + GM-CSF and alphaTNF + G-CSF were highly synergistic in priming fMLP-stimulated burst in both groups. But again, as with the single cytokine priming this effect was markedly reduced in MDS patients compared to controls (p < or = 0,05). A specific priming defect for one of the cytokines or a cytokine combination could not be demonstrated. Serum alphaTNF levels were measured in 18 and neutrophil alkaline phosphatase (NAP) index in 23 patients. Results did not correlate with variations of the RB in MDS patients. We conclude that reduced alphaTNF, GM-CSF and G-CSF priming of granulocyte RB is a frequent finding in MDS and may contribute to the enhanced susceptibility to bacterial infections.

What is ineffective erythropoiesis in myelodysplastic syndromes?

The anaemia of MDS is multifactorial with intramedullary ineffective erythropoiesis resulting from an imbalance between erythroid proliferation, differentiation and apoptosis in favour of initial hypercellularity with high cell death through to a lower cellularity, lower death state with the eventual evolution of the leukaemic clone in many patients. The fundamental molecular abnormality(ies) in MDS, which produce the milieu for the heterogeneous molecular insults described (e.g., oncogene mutations) remains elusive. Many questions such as why MDS red cells are macrocytic and what are the precise cellular and molecular mechanisms of ineffective erythropoiesis remain unanswered but future study of the erythroid lineage should provide molecular clues to the earliest abnormalities in the pathogenesis of MDS.

Sweet's syndrome (acute febrile neutrophilic dermatosis)

Acute febrile neutrophilic dermatosis, first described in 1964 by Robert Douglas Sweet, has been termed Sweet's syndrome. Classic Sweet's syndrome occurs in middle-aged women after a nonspecific infection of the respiratory or gastrointestinal tract. Raised erythematous plaques with pseudoblistering and occasionally pustules occur on the face, neck, chest, and extremities, accompanied by fever and general malaise. Involvement of the eyes, joints, and oral mucosa as well as internal manifestations of Sweet's syndrome in the lung, liver, kidneys, and central nervous system has been described. The disease is thought to be a hypersensitivity reaction. Parainflammatory (e.g., infections, autoimmune disorders, vaccination) and paraneoplastic (e.g., hemoproliferative disorders, solid malignant tumors) occurrence is found in approximately 25% of the cases and 2% are associated with pregnancy. Sweet's syndrome responds rapidly to systemic therapy with corticosteroids but recurs in about 25% of the cases. Alternative treatment modalities (e.g., potassium iodide, colchicine, dapsone, clofazimine, cyclosporine) have also been used. This article presents data from 38 patients with Sweet's syndrome and reviews its epidemiology, clinical spectrum, histologic features, laboratory results, differential diagnosis, pathogenic mechanisms, associated diseases, and treatment.

Immunological findings in patients with myelodysplastic syndrome

Activation of monocytes and granulocytes in vitro by cytokines, in vivo administration of cytokines, as well as in vivo cytokine production due to infectious and inflammatory diseases causes changes of the surface expression density of certain membrane molecules. In recent studies we attempted to determine the feasibility of using flow cytometric immunophenotyping as a tool to develop a sensitive parameter for detecting infections at an early stage of disease when clinical parameters are still negative. Since infections are an important factor determining the clinical course of myelodysplastic syndromes (MDS), early detection of infection might be beneficial for these immunocompromised patients. We indeed found activation-associated immunophenotypic changes of cell surface antigens on monocytes and granulocytes of clinically infection free MDS patients suggesting enhanced immune activity in these patients, most likely due to latent or beginning infections. In particular, analyses of the expression density of receptors for IgG (Fc gamma Rs), complement receptors, and certain activation-associated surface molecules such as the CD67 and the M5 molecule seem to be of clinical relevance. We will also discuss findings concerning changes of cytokine levels and functional alterations of immunologic parameters in MDS patients.