Cytokines for Patients With Myelodysplastic Syndromes
HGFs and cytokines are important peptide regulators of cell proliferation, differentiation and maturation, and programmed cell death (apoptosis). These regulators interact with specific receptors on the cell surface and trigger signal transductions. Although HGFs can act specifically on different lineages of hematopoietic cells, they can stimulate multiple lineages when targeting multipotent stem cells or early-stage progenitor cells, depending on the distribution pattern of their receptors.
G-CSF, GM-CSF, stem cell factor (SCF), EPO, thrombopoietin (TPO), several interleukins, and interferon (IFN) alpha and gamma are the cytokines that have been evaluated so far for the treatment of MDS. Growth factors have been widely used as part of the supportive therapy in patients with cytopenia of different etiology.
The prerequisite for introducing growth factors in the treatment of MDS is to correct cytopenias without increasing the risk of disease progression or leukemia transformation. Theoretically, growth factors can relieve symptoms and shorten recovery from cytopenia, therefore improving quality of life and possibly reducing complications and mortality secondary to cytopenia. There is no evidence that administration of growth factors can significantly prolong survival or induce remission in patients with MDS. Among cytokines, G-CSF and GM-CSF, EPO, and TPO specifically target myeloid, erythroid, and megakaryoid precursors, respectively. Other cytokines are less specific, may carry extramedullary activities, and are often associated with significant side effects when used at high doses. Cytokines exert their functions in an endocrine, autocrine, and/or paracrine fashion.
In the United States, G-CSF, GM-CSF, EPO, and IL-11 are currently the approved cytokines for the treatment of primary or secondary cytopenia. It should be noted that the use of growth factors and other cytokines in patients with MDS is still largely experimental. Benefits, side effects, and risk of disease progression caused by growth factors and cytokines always need to be carefully considered due to the very unstable genetic background of most patients with MDS.
The following are the possible rationales for using growth factors and cytokines in the treatment of hematological disorders:
- Induce proliferation of progenitor cells and facilitate recovery from cytopenia.
- Accelerate recovery from cytopenia, especially after intensive therapy.
- Induce differentiation of immature cells.
- Prevent apoptosis of essential normal progenitors.
- Modify bone marrow microenvironment.
- Increase sensitivity of leukemia cells to chemotherapeutic agents.
G-CSF and GM-CSF
G-CSF and GM-CSF have been extensively studied for the treatment of patients with MDS (Table 9). There is significant evidence that both of them may restore neutrophil counts in 80% to 90% of treated patients. Recombinant human G-CSF and GM-CSF are available and used primarily for patients with chemotherapy- and bone marrow transplantation-induced neutropenia, and occasionally in patients with aplastic anemia and MDS. Although these therapies improve quality of life and shorten recovery from neutropenia, the data have failed to show a clear effect on survival in patients with MDS.
Table 9. Hematopoietic Growth Factors Used in Patients With MDS
Author Cytokines Receptor Specificity Dose Cases Response
Saba G-CSF G-CSF-R myeloid 5-10 mcg/kg MC 80% to 100%
Cazzola GM-CSF GM-CSF-R myeloid 100-200 mcg/kg MC 63% to 100%
Estey et al GM-CSF GM-CSF-R myeloid 5-10 mcg/m2 29 14/29
Estey et al EPO EPO-R erythroid 50-150 mcg/kg MC 15% to 20%
N/A TPO c-mpl megakaryoid 0.6-2.4 mcg/kg N/A N/A
N/A SCF Flk-2,3 multipotent N/A N/A N/A
Nand et al IL-2 IL-2-R lymphoid 1 mU/day 10 0/10
Kurzrock et al IL-3 IL-3-R multipotent 30-1000 mcg/m2/day 24 8/24
Kurzrock et al IL-11 IL-11-R megakaryoid 10 mcg/kg/day 16 6/16
Maerevoet et al IFN-alpha IFN-alpha-R hematopoietic 0.5-3 mU, 3x/week 17 8/17
Maiolo et al IFN-gamma IFN-gamma-R lymphoid 0.1 mg/m2/day 30 13/30
G-CSF, granulocyte colony-stimulating factor; R, receptor; MC, multicenter; GM-CSF, granulocyte-macrophage colony-stimulating factor; EPO, erythropoietin; TPO, thrombopoietin; N/A, not available; SCF, stem cell factor; IL, interleukin; IFN, interferon
The doses of G-CSF and GM-CSF vary according to patients’ subtypes, responses, and study design (single-agent therapy or combination with other compounds). Both CSFs can be given subcutaneously and intravenously, at a starting dose of 5 mcg/kg to 10 mcg/kg for G-CSF and 100 mcg/m2 to 200 mcg/m2 for GM-CSF. Higher doses can be reached if the patient is tolerant. Some studies showed that a high dose of GM-CSF significantly increased blast count and inversely lowered platelets’ number. Such effects were not seen in patients with MDS who received low-dose GM-CSF (5 mcg/kg to 10 mcg/kg) while maintaining an optimal response rate (nearly 50%). Combination of G-CSF or GM-CSF with EPO may enhance the EPO-stimulated erythroid response,[64,65] as G-CSF or GM-CSF may increase the pool of erythroid burst-forming-units, which are then further stimulated by EPO.
Only the use of growth factors after chemotherapy or transplantation has shown, so far, promising results with significant shortening of the time to neutrophil count recovery and reduction of infection rates without evident increase in the risk of progression to leukemia. Treatment with growth factors at the beginning or after chemotherapy yields similar results. However, early administration may provide additional benefit by increasing the sensitivity of leukemia cells to chemotherapeutic agents. The risk of progression to leukemia by priming growth factors with chemotherapy remains questionable. The discrepancy probably arises from the differences in study design, patient selection (eg, the blast count), and the dose of growth factors.
The recommendations for using growth factors in patients with MDS are:
- Recommended after induction chemotherapy.
- Recommended for intermittent use.
- Recommended for use with blast-count monitoring.
- Not recommended as single agent for patients with blast count higher than 20.
- Not recommended for patients with high-risk MDS as single therapeutic agent.
EPO is a 30-kd glycoprotein produced by the kidneys, which induces proliferation and differentiation of precursors of the erythroid series, but has no effect on other lineages. Human recombinant EPO is commercially available and approved for treating the anemia associated with chronic renal failure and HIV-related anemia, in which the insufficient production of endogenous EPO is responsible for the cytopenic condition.
The effect of treatment with EPO has also been studied in patients with MDS. The response rates reported from multiple trials ranged from 10% to 60%, and varied according to MDS subtype, transfusion dependence, and the endogenous EPO level. Higher response rate can be achieved in patients who are not transfusion dependent, and especially in patients whose endogenous EPO levels are less than 200 mc/L.[68,69] However, the doses of EPO given to patients varied among the different studies. Pretreatment levels of endogenous EPO were not related to the intensity of MDS-associated anemia, indicating an underlying primary genetic defect that results in ineffective erythropoiesis rather than insufficiency of endogenous EPO. Even in patients who responded to EPO, anemia recurred after discontinuation of EPO.[70,71]
Priming by administration of either G-CSF or GM-CSF may augment the response rate to EPO, possibly due to a greater release of erythroid progenitors from physiologic reservoirs.[64,65] There is no obvious evidence that EPO increases the risk of leukemia transformation. Side effects, including fever, fluid retention, and flulike symptoms, are mild and tolerable. To summarize, EPO is effective in patients with MDS at low or intermediate risk, who are relatively transfusion independent, and with low endogenous EPO levels. When EPO is not effective as a single agent, G-CSF or GM-CSF can be added because of a possible synergistic effect.
Following discovery of G-CSF, GM-CSF, and EPO, efforts have been made to identify specific regulators of megakaryocytic precursors. In 1994, a gene encoding TPO was cloned, 4 years after the identification of its receptors, and called c-mpl. In vitro and in vivo studies indicated that TPO specifically acts on primitive progenitors of megakaryopoietic lineage, with weak effects on the erythroid lineage, due to the homologous motif shared with EPO. An in vitro study also showed that interleukin-3 (IL-3) and SCF enhanced the effect of pegylated TPO.
Clinical trials with TPO were not started in patients with MDS because of the capacity of TPO to induce anti-TPO antibodies. In addition, ex vivo studies suggested that TPO induced proliferation and differentiation of AML cell lines expressing surface c-mpl. Whether administration of TPO for the treatment of thrombocytopenia secondary to AML or MDS is safe requires further investigation.[76-78] Use of TPO is currently restricted to clinical trials and laboratory investigations.
Human IL-11 was cloned and mapped to human chromosome 19. This cytokine is a 19-kd glycoprotein produced by lymphocytes, fibroblasts, and epithelial cells. IL-11 induces proliferation, differentiation, and maturation of platelet progenitors by promoting entry of a G0 quiescent population of cells into active cell cycle and by shortening cell cycles. IL-11 also acts synergistically with other multipotent growth factors, such as IL-3 and SCF, for multilineage stimulation. Recombinant human IL-11 is the only thrombopoietic cytokine now approved for the treatment of thrombocytopenia associated with nonneoplastic disorders or induced by intensive chemotherapy. The recommended dose is 50 mcg/kg/day. Side effects include fever, mild anemia, arthralgia, and fluid retention.
In the case of hematologic malignancies, severe thrombocytopenia is a common and most serious problem, particularly with acute leukemia and MDS. Platelet transfusions have a short-lived effect and have to be repeated every 2-3 days. Recently, Kurzrock and colleagues reported a pilot study using lower doses of IL-11 in patients with MDS (RA, RARS, and RAEB) or aplastic anemia. In this study, 16 patients with thrombocytopenia (11 with MDS, 4 with aplastic anemia, and 1 with an autologous bone marrow transplantation) received at least 2 courses of daily IL-11 (10 mcg/kg/day subcutaneously). Each course consisted of a 2-week IL-11 treatment followed by a 2-week rest period.
Substantial recovery of platelets (doubling or tripling of platelets) was found in 6 patients (5 with MDS and 1 with aplastic anemia). Duration of the response was 12-30 weeks or longer, and treatment was well tolerated by the patients. These results are encouraging since there is a need for thrombopoiesis-promoting molecules for the treatment of neoplastic patients who are transfusion dependent. The recommended dose of 25 mcg/kg/day to 50 mcg/kg/day for IL-11 was also tested in patients with AML and MDS, but it was associated with significant toxicity and poor tolerance (MD Anderson Cancer Center, unpublished data, 2000). Further studies are needed to explore and evaluate the overall impact of IL-11 on the biologic and phenotypic characteristics of patients with neoplastic bone marrow failure.
Other Cytokines: Interleukin-3, Interleukin-2, and Interferons
IL-3 is a multipotent HGF produced by T cells, monocytes/macrophages, and stromal cells. In vitro, IL-3 induces proliferation, maturation, and stem cell renewal in multiple lineages of hematopoietic cells within the erythroid, myeloid, and megakaryoid lineage . Clinical studies of IL-3 as single agent for the treatment of MDS were reported by Kurzrock and colleagues in 1991, showing trilineage responses (myeloid, 33.3%; erythroid, 25%; and megakaryoid, 12.5%; respectively). Most patients tolerated infusion of IL-3 at a dose level of 30 mcg/m2/day to 1000 mcg/m2/day. Side effects were mainly low-grade fever and headache. A combined administration of IL-3 and EPO was also studied in patients with MDS, but it was associated with a significant IL-3-mediated toxicity that required a dose reduction in 13 of the 22 patients with MDS. The role of IL-3 for the treatment of MDS requires more and larger scale studies.
IL-2 is released by T lymphocytes upon activation and acts in an autocrine and/or paracrine manner. IL-2 stimulates proliferation and functions of lymphocytes and natural killer (NK) cells. The use of IL-2 for the treatment of MDS is based on the finding that patients with MDS have reduced NK and lymphokine activated killer cell activity. A phase 1 study showed that 1.25 mU/m2 of IL-2 was the maximal tolerated dose. Unfortunately, the slightly decreased dose of 1 mU/m2 showed no benefit in patients with MDS, even though it was associated with an improvement in NK cell activity.
IFN-alpha and IFN-gamma are well-known immunomodulators, used extensively for treatment of a number of diseases. Since the 1980s, IFN-alpha has been popular for treatment of patients with CML, where it achieved curative results, as reviewed by Talpaz and colleagues. The mechanisms of the antineoplastic effects of IFN remain unclear. Although promising for the treatment of CML, application of IFN for the treatment of patients with MDS is still questionable, even though different studies have shown that IFN-alpha or IFN-gamma treatment can achieve hematologic response rates as high as 30% to 40%.[62,63,84] The use of this cytokine in patients with MDS, together with IL-2 and IL-3, is, thus, restricted to clinical trials and should not be used as standard-of-care therapy.
In summary, the role of cytokines in the treatment of patients with MDS is mainly supportive, and it should not be forgotten that some of the cytokines may have questionable proleukemia effects. Conversely, lineage-specific cytokines such as G-CSF, GM-CSF, IL-11, and TPO may be safe as single-agent therapies in patients with low-risk MDS with benign or low-grade cytogenetic abnormalities. Combination treatments of these cytokines with chemotherapy or bone marrow transplantation may be beneficial.