A pilot study of rhuIL-11 treatment of refractory ITP

Structural Understanding of Interleukin 6 Family Cytokine Signaling and Targeted Therapies: Focus on Interleukin 11

Cytokines are small signaling proteins that have central roles in inflammation and cell survival. In the half-century since the discovery of the first cytokines, the interferons, over fifty cytokines have been identified. Amongst these is interleukin (IL)-6, the first and prototypical member of the IL-6 family of cytokines, nearly all of which utilize the common signaling receptor, gp130. In the last decade, there have been numerous advances in our understanding of the structural mechanisms of IL-6 family signaling, particularly for IL-6 itself. However, our understanding of the detailed structural mechanisms underlying signaling by most IL-6 family members remains limited. With the emergence of new roles for IL-6 family cytokines in disease and, in particular, roles of IL-11 in cardiovascular disease, lung disease, and cancer, there is an emerging need to develop therapeutics that can progress to clinical use. Here we outline our current knowledge of the structural mechanism of signaling by the IL-6 family of cytokines. We discuss how this knowledge allows us to understand the mechanism of action of currently available inhibitors targeting IL-6 family cytokine signaling, and most importantly how it allows for improved opportunities to pharmacologically disrupt cytokine signaling. We focus specifically on the need to develop and understand inhibitors that disrupt IL-11 signaling.

Platelet and peripheral white blood cell counts at diagnosis predict the response of adult immune thrombocytopenia to recombinant human interleukin-11: A retrospective, single-center, case-control study

This study evaluated the effectiveness of recombinant human interleukin-11 (rhIL-11) in the treatment of immune thrombocytopenia (ITP) and determined whether clinical and laboratory findings predicted the treatment response.This retrospective, single-center, case-control study included 103 adult patients with ITP treated between July 2010 and April 2014 at Jiangxi Province People's Hospital. About 49 patients in the pred+IL group received prednisone (conventional dose) combined with an rhIL-11 regimen, and 54 patients in the pred alone group received prednisone (conventional dose) alone. Demographic data, initial and follow-up platelet counts, proportions of patients achieving platelet counts ≥30 × 10/L (response) and ≥100 × 10/L (complete response) at different time points, and adverse reactions were compared between groups.Complete response rates were similar between groups overall but higher in the pred+IL group than in the pred alone group for newly diagnosed patients and those with severe ITP (P < .05). Proportions of patients achieving response or complete response at different time points were similar between groups overall but higher in the pred+IL group than in the pred alone group for newly diagnosed patients and those with severe ITP (P < .05). Posttreatment platelet count correlated negatively with platelet count at diagnosis and white blood cell (WBC) count at diagnosis in patients with newly diagnosed ITP (r = -0.337, P = .073 and r = -0.367, P = .050, respectively) or ITP with bleeding-related episodes (r = -0.357, P = .020 and r = -0.434, P = .004, respectively). No immediate or postinfusion severe adverse reactions were observed.rhIL-11 increased CR and improved hemostasis in patients with newly diagnosed or severe ITP. Platelet and WBC counts at diagnosis can predict the response to rhIL-11.

A panoramic review and in silico analysis of IL-11 structure and function

Human Interleukin (IL)-11 is a multifunctional cytokine, recognized for its thrombopoietic effects for more than two decades; clinically, IL-11 is used in the treatment of thrombocytopenia. IL-11 shares structural and functional similarities with IL-6, a related family member. In recent years, there has been a renewed interest in IL-11, because its distinct biological activities associated with cancers of epithelial origin and inflammatory disorders have been revealed. Although the crystal structure of IL-11 was resolved more than two years, a better understanding of the mechanisms of IL-11 action is required to further extend the clinical use of IL-11. This review will discuss the available structural, functional, and bioinformatics knowledge concerning IL-11 and will summarize its relationship with several diseases.

Downregulation of T-bet/GATA-3 ratio induced by IL-11 treatment is responsible for Th1/Th2 balance restoration in human immune thrombocytopenic purpura (ITP)

Abnormal cellular immunity induced by deranged Th1/Th2 profile has been revealed to play a critical role in the pathogenesis of immune thrombocytopenic purpura (ITP). Correction of the shifted Th1/Th2 balance represents a potential therapeutic approach to treat ITP. Here, we investigated the effects of IL-11 on the restoration of Th1/Th2 balance in the peripheral blood mononuclear cells (PBMCs) isolated from adult ITP patients. As shown here, we observed a higher ratio of T-bet/GATA-3 gene expression by quantitative real-time PCR in the PBMCs from ITP patients, consistent with the presence of an abnormally high Th1/Th2 ratio. Remarkably, upon IL-11 treatment, a reversal of T-bet/GATA-3 ratio in ITP was achieved and was shown to be responsible for the restoration of Th1/Th2 balance, with IL-11 at 100 ng/ml demonstrating the highest efficiency. T-bet and GATA-3 are the two transcriptional factors that have been indicated to be the master regulators for Th1 and Th2 lineage commitment, respectively. In the presence of 100 ng/ml IL-11, GATA-3 transcript abundance rose up to ~85-fold of that measured in untreated cells, whereas T-bet transcripts were lowered merely to ~41%, suggesting that GATA-3 was the major contributor for the reversal of T-bet/GATA-3 ratio. Thus, our findings may very well encourage the development of novel medicines that specifically target and correct the T-bet/GATA-3 imbalance identified in ITP.

Romiplostim: a novel thrombopoiesis-stimulating agent

PURPOSE

The pharmacology, pharmacokinetics, dosage and administration, efficacy, safety, effects on quality of life, and place in therapy of romiplostim are reviewed.

SUMMARY

Romiplostim is a second- generation thrombopoietic agent that stimulates the thrombopoietin receptor and platelet production without inducing production of autoantibodies. Romiplostim, a peptibody, bears no structural resemblance to endogenous thrombopoietin, thus minimizing the risk for development of thrombopoietin autoantibodies. Clinical trials have shown that romiplostim increases platelet counts compared with placebo in both splenectomized and non-splenectomized adult patients with chronic idiopathic thrombocytopenic purpura (ITP). Clinical trials with romiplostim are ongoing for patients with myelodysplastic syndrome and those receiving chemotherapy for treatment of malignancies. Romiplostim may confer an increased risk of bone marrow reticulin formation or fibrosis, malignancy, thrombosis, and thrombocytopenia that is more severe than the level present before initiation of romiplostim. While all patients receiving romiplostim in clinical trials experienced at least one adverse event, most were mild to moderate in severity. The most frequent adverse effects were ecchymosis, headache, and petechiae. Romiplostim is initiated at a dosage of 1 microg/kg subcutaneously once weekly and titrated to achieve platelet counts between 50 and 200 x 10(9) platelets/L, with a maximum dose of 10 microg/kg. Romiplostim is only available through the manufacturer's risk-management program. The current wholesale price of romiplostim is $1,062.50 for a single-use vial of 250 microg or $2,125 for a single-use vial of 500 microg. The extrapolated drug cost for weekly dosing for one year is approximately $55,250.

CONCLUSION

Romiplostim is a novel thrombopoietic-stimulating agent for use in patients with chronic ITP who have not responded to other therapies.

The role of interleukin-11 to prevent chemotherapy-induced thrombocytopenia in patients with solid tumors, lymphoma, acute myeloid leukemia and bone marrow failure syndromes

Thrombocytopenia occurs at various grades of severity in patients with malignancies undergoing myelosuppressive chemotherapy. In most instances, this is the major dose-limiting hematologic toxicity, especially in the treatment of potentially curable cancers. The standard preventive measure against chemotherapy-induced thrombocytopenia has been dose reduction and/or dose delay. This can often lead to poor outcomes, including reduced disease free periods and overall survival. With the availability of a platelet growth factor, recombinant human interleukin (IL)-11, an effective way to prevent chemotherapy-induced thrombocytopenia and accelerate platelet recovery, can now be provided to patients. The use of recombinant human IL-11 has also been extended to include patients with prolonged thrombocytopenia, such as those with bone marrow failure syndromes. With the use of recombinant human IL-11 in both malignant and non-malignant conditions, adverse reactions often seen with platelet transfusions, such as transfusion reactions, viral and bacterial infections and platelet refractoriness, can now be decreased or avoided.

Neonatal thrombocytopenia: what we do and don't know

The evaluation and management of thrombocytopenia is a frequent challenge for neonatologists, as it affects 22-35% of infants admitted to the neonatal intensive care unit. Multiple disease processes can cause neonatal thrombocytopenia, and these can be classified as those inducing early thrombocytopenia (< or =72 h of life) and those inducing late-onset thrombocytopenia (>72 h). Most cases of neonatal thrombocytopenia are mild to moderate, and do not warrant intervention. In approximately 25% of affected neonates, however, the platelets count is <50 x 10(9)/L, and therapy with platelet transfusions is considered to decrease the risk of hemorrhage. The existing evidence to establish platelet transfusion triggers in neonates is very limited, but it suggests that transfusing platelets to non-bleeding neonates with platelet counts >50 x 10(9)/L does not decrease the risk of intraventricular hemorrhage (IVH), and that 30 x 10(9)/L might be an adequate threshold for stable non-bleeding neonates. However, adequately powered multi-center studies are needed to conclusively establish the safety of any given set of neonatal transfusion guidelines.

The Pathophysiology of ITP Revisited: Ineffective Thrombopoiesis and the Emerging Role of Thrombopoietin Receptor Agonists in the Management of Chronic Immune Thrombocytopenic Purpura

Autoimmune thrombocytopenia (ITP) is characterized by autoantibody-mediated platelet destruction that can be demonstrated by shortened radiolabeled platelet survival. An additional role of ineffective thrombopoiesis was suggested by autologous platelet kinetic studies performed in the 1980s. Sera of patients with ITP have been demonstrated to inhibit megakaryocyte growth in culture supporting the concept of suboptimal platelet production as a contributing factor to the thrombocytopenia. The relatively modest rise in thrombopoietin (TPO) levels in thrombocytopenic patients with ITP has helped to identify the TPO receptor as a potential target for the treatment of ITP. Initial studies with recombinant TPO in patients with ITP were encouraging, and novel compounds designed to stimulate the TPO receptor and resultant pathways have been shown in randomized trials to be effective in raising the platelet count and sustaining it at safe levels. Adverse effects of these agents have been relatively mild, although rare serious events including increased bone marrow reticulin deposition, increased numbers of circulating blasts and thrombosis have occurred, and theoretic risks of stimulation of megakaryocytopoiesis and platelet activation remain a concern. As these agents become available it will be important to identify those patients who will most benefit from their use. The place of these drugs in the current management algorithms of ITP will evolve over time as results of clinical trials with these agents and experience with their use in the clinic clarify short-term and long-term efficacy and potential toxicities.

Idiopathic thrombocytopenic purpura and dysmegakaryocytopoiesis

Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disorder characterized with thrombocytopenia, primarily caused by platelet destruction. However, the studies of platelet kinetics show platelet turn over are normal or decreased, suggesting that reduced platelet production may lead to severity of ITP. We review recent research progress on abnormal cell events involved in megakaryocytopoiesis contributing to thrombocytopenia.

Cytokines for the Treatment of Thrombocytopenia

Multiple cytokines affect the cellular processes that occur during the transition of a hematopoietic stem cell (HSC) to a platelet. Thrombopoietin (TPO) is the physiological regulator of thrombopoiesis. Although a number of cytokines (interleukin [IL]-1, IL-3, and IL-6) were first evaluated for their ability to lessen the degree of thrombocytopenia occurring during a variety of clinical scenarios, their clinical development was abandoned due to their limited effectiveness or excessive toxicity. Clinical results with TPO and a truncated pegylated form of TPO, megakaryocyte growth and development factor (MGDF), were more promising, but the repeated use of MGDF resulted in the development of neutralizing antibodies. This adverse event halted the further clinical development of not only MGDF but also TPO. IL-11 also affects various stages of megakaryocytopoiesis and thrombopoiesis and its use has been shown to shorten the duration of chemotherapy-induced thrombocytopenia, which led to its approval by the US Food and Drug Administration (FDA). A growing number of new non-immunogenic peptides and non-peptide TPO agonists recently have entered clinical trials. These small molecules appear to be effective therapies and have acceptable toxicity, but additional clinical evaluation will be required prior to their approval for clinical use.

Treatment of immune thrombocytopenic purpura in adults

Idiopathic thrombocytopenic purpura (ITP) is a hematologic disorder characterized by the destruction of antibody-coated platelets in the reticuloendothelial system. Whereas 70% to 80% of children experience the acute form of the disease and recover within a few weeks or months after diagnosis, most adults have persistent disease and will require therapy. Principles of management are largely predicated on the extent of thrombocytopenia and symptoms of disease. Minimizing the toxicity associated with treatment while achieving hemostatic platelet counts are essential goals of treatment. Although there are numerous therapeutic options, neither consensus among experts nor clear algorithms to treat this complex disease exist. This article will review appropriate treatment options available for adult patients with ITP prior to splenectomy, at splenectomy, and following splenectomy. In addition to conventional agents such as corticosteroids and intravenous immune globulin (IVIg), the role of newer therapies with diverse mechanisms of action, such as rituximab, anti-D, and thrombopoietin (TPO)-like agents, will be highlighted. When used as either monotherapy or in combination with conventional therapeutics, these treatments may offer a more tolerable side effect profile and improved clinical benefit compared to existing drugs.

Suspects in the tale of lupus-associated thrombocytopenia

Immunologically mediated thrombocytopenia is a frequent clinical manifestation in patients with systemic lupus erythematosus (SLE). Autoantibodies targeting platelet membrane glucoproteins have a central role in peripheral platelet destruction. Autoantibodies against thrombopoietin are also present in about one-third of patients, but their pathogenetic role is obscure. Thirty-eight serum samples from SLE patients were tested for anti-platelet antibodies, anti-thrombopoietin antibodies and levels of circulating thrombopoietin. Bone marrow histology was also assessed. Thirty-nine per cent of sera displayed anti-thrombopoietin antibodies and 29% had circulating anti-platelet antibodies. Anti-thrombopoietin antibodies were associated with lower thrombopoietin concentrations, and lower mean platelet values in long-term follow-up. Anti-platelet antibodies were present in about 40% of thrombocytopenic and non-thrombocytopenic individuals but were absent in patients who had recovered from thrombocytopenia, supporting their pathogenetic role. Both autoantibodies were absent in control sera from patients with rheumatoid arthritis and primary Sjögren's syndrome. Decreased bone marrow cellularity, normal or low number of hypolobulated, pyknotic megakaryocytes and stromal alterations were prominent findings in thrombocytopenic SLE patients, suggesting a defect in megakaryopoiesis. These findings were not evident in specimens from patients with idiopathic thrombocytopenic purpura who had increased megakaryocytes, normal cellularity and absence of stromal alterations. In conclusion, peripheral destruction due to platelet autoantibodies, anti-thrombopoetin antibodies, lower effective circulating thrombopoetin and impaired compensatory response due to bone marrow damage interact in SLE and thrombocytopenia ensues.

Purification and Characterization of Recombinant Truncated Human Interleukin-11 Expressed as Fusion Protein in Escherichia coli

Mature human interleukin-11 (HuIL-11) is a cytokine consisting of 178 amino acid residues that results from scission of the N-terminal signal peptide, consisting of 21 amino acid residaues, from the corresponding nascent polypeptide. A DNA fragment encoding a truncated HuIL-11 (trHuIL-11), with an additional 5 amino acid residues removed from the N-terminus, was cloned into vector pGEX-2T between the BamHI site and the EcoRI site. Upon transformation with Escherichia coli BL21, the construct over-produced a glutathione S-transferase (GST)-fused protein in a soluble form after IPTG induction. The fusion protein was initially fractionated with butyl-Sepharose 4 fast flow column and by affinity chromatography using a GSH-Sepharose 4B column. On-site enzymatic release with thrombin gave the target protein at 96% purity as judged by SDS-PAGE and HPLC. Expression of the interleukin as a GST-fused protein thus greatly improved downstream processing. Subsequent biological activity assay suggested that trHuIL-11 had similar activity profile to the naturally produced sample and may be a promising candidate for further development as biopharmaceutical.

Low-dose interleukin-11 in patients with bone marrow failure: update of the M. D. Anderson Cancer Center experience

BACKGROUND

Recombinant interleukin (IL)-11 is a thrombopoietic growth factor. The purpose of this study was to assess the toxicity, safety and efficacy of low-dose recombinant IL-11 in patients with bone marrow failure (BMF).

PATIENTS AND METHODS

Patients with BMF due to myelodysplastic syndromes (MDS), graft failure, chemotherapy or aplastic anemia (AA) were treated. Patients were required to have a platelet count of <20 x 10(9)/l, or a platelet count of <50 x 10(9)/l with an absolute neutrophil count <1 x 10(9)/l, or a hemoglobin value <10 g/dl. Treatment consisted of daily IL-11 at a dose of 10 mug/kg subcutaneously followed by a 2-week rest period. Two induction courses were given. Responders could receive maintenance therapy.

RESULTS

Thirty-three patients (MDS, n=14; AA, n=16; prolonged thrombocytopenia following stem cell transplantation or chemotherapy, n=3) were evaluable. Their median age was 58 years (range 5-85). Three patients (9%) had poor risk cytogenetics. Nine patients (27%) responded to IL-11 (six MDS, three AA). Of these, three patients treated with IL-11 alone (n=1) or IL-11 together with other growth factors (n=2) showed multilineage recovery. The median time to response was 0.9 months (range 0.3-11). Factors associated with higher response rates in univariate analysis were age >50 years (P=0.008), diagnosis of MDS versus AA (P=0.025) and creatinine level >1 mg/dl (P=0.0004). The median response duration was 3 months (range 1.4-34.5+). Amongst responders, the median increment in platelet count was 111 x 10(9)/l (range 43-165). The most common side-effects were grade 1-2 lower extremity edema, conjunctival injections and fatigue. Grade 3 toxicities included arrhythmia (n=1) and transient ischemic attack (n=1). Ten patients (30%) had no side-effects.

CONCLUSIONS

Low-dose IL-11 has activity in patients with BMF and is generally well tolerated.

Evaluation and treatment of severe and prolonged thrombocytopenia in neonates

Thrombocytopenia is one of the most common hematologic problems in the neonatal intensive care unit (NICU). Despite its prevalence,several basic pathophysiologic questions remain unanswered. For instance, there is a lack of evidence-based guidelines for treatment,and the kinetic mechanisms (decreased platelet production,increased platelet consumption, or sequestration) responsible for most varieties of neonatal thrombocytopenia are not well defined.Moreover, a clear correlation between degree of thrombocytopenia and the resulting bleeding risk has not been demonstrated, and no transfusion-trigger studies have been conducted in neonates. As a consequence of these deficiencies in knowledge, there is great variability in platelet transfusion practices among NICUs. This article presents an overview of the evaluation of a neonate with severe thrombocytopenia and a review of current and projected therapeutic options.

Molecular and cellular biology of moderate-dose (1-10 Gy) radiation and potential mechanisms of radiation protection: report of a workshop at Bethesda, Maryland, December 17-18, 2001

Exposures to doses of radiation of 1-10 Gy, defined in this workshop as moderate-dose radiation, may occur during the course of radiation therapy or as the result of radiation accidents or nuclear/radiological terrorism alone or in conjunction with bioterrorism. The resulting radiation injuries would be due to a series of molecular, cellular, tissue and whole-animal processes. To address the status of research on these issues, a broad-based workshop was convened. The specific recommendations were: (1) RESEARCH: Identify the key molecular, cellular and tissue pathways that lead from the initial molecular lesions to immediate and delayed injury. The latter is a chronic progressive process for which postexposure treatment may be possible. (2) Technology: Develop high-throughput technology for studying gene, protein and other biochemical expression after radiation exposure, and cytogenetic markers of radiation exposure employing rapid and accurate techniques for analyzing multiple samples. (3) Treatment strategies: Identify additional biological targets and develop effective treatments for radiation injury. (4) Ensuring sufficient expertise: Recruit and train investigators from such fields as radiation biology, cancer biology, molecular biology, cellular biology and wound healing, and encourage collaboration on interdisciplinary research on the mechanisms and treatment of radiation injury. Communicate knowledge of the effects of radiation exposure to the general public and to investigators, policy makers and agencies involved in response to nuclear accidents/events and protection/treatment of the general public.

Recombinant human interleukin-11 improves thrombocytopenia in patients with cirrhosis

To elucidate the hematopoietic activity of recombinant human interleukin-11 (rhIL-11, [Neumega, Cambridge, MA]) in patients with cirrhosis and thrombocytopenia, we administered rhIL-11 at 50 microg/kg/d subcutaneously to 10 patients for 10 days with a 30-day follow-up period. All treated patients (n = 9) experienced a gradual, yet significant increase in their platelet count above the baseline value (P < or =.01) reaching the peak value (median, 93,000/microL; range, 60,000-206,000/microL) at a median of 13 days (range, 6-23 days). Eight patients (89%) had a significant increase of > or =50% over the baseline value (P <.05). Moreover, further increases to > or =60,000/microL, > or =80,000/microL, and > or =100,000/microL were observed in 100%, 78%, and 33% of the patients, respectively. A subsequent decline in platelet count was observed at a median of 19 days (range, 7-26 days) after the occurrence of peak concentration. A significant increase in neutrophil count was also demonstrated starting on the third day of treatment (P < or =.01). Concurrent with an increase in the serum level of fibrinogen, transaminase levels declined significantly during treatment period, while bilirubin levels continued to drop for up to 20 days after the initiation of treatment (P <.05). The most frequent effects were due to plasma volume expansion, including conjunctival redness and edema. In conclusion, rhIL-11 can improve platelet counts in patients with early cirrhosis and these patients could benefit from rhIL-11 treatment. However, given the high frequency of regimen-related toxicity, the use of rhIL-11 in patients with cirrhosis should be administered with caution.

Neurologic complications of cancer therapy

Neurologic complications of chemotherapy are relatively common. The diagnosis of chemotherapy-associated neurotoxicity remains a clinical one, and is largely based on the exclusion of other possible causes. The goal of this review is to describe the neurotoxicity associated with established chemothrerapeutic agents and with some of the newer biologic agents, monoclonal antibodies and targeted molecular therapies used in the treatment of cancer.

Marked improvement of thrombocytopenia in a murine model of idiopathic thrombocytopenic purpura by pegylated recombinant human megakaryocyte growth and development factor

OBJECTIVE

We examined the stimulatory effect of pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) on platelet production in male (NZW x BXSB) F(l) (W/B F(1)) mice, a murine model of idiopathic thrombocytopenic purpura.

MATERIALS AND METHODS

A cohort of 19- to 25-week-old, severely thrombocytopenic male W/B F(1) mice were given PEG-rHuMGDF at different dosing schedules. Before and at various times after therapy, platelet counts, reticulated platelets, platelet lifespan, and levels of platelet-associated immunoglobulin G were measured. Analysis of megakaryocytic cells was performed.

RESULTS

Treatment of male W/B F(1) mice with PEG-rHuMGDF (30 microg/kg/day) three times per week for several weeks resulted in sustained thrombocytosis, accompanied by increased megakaryocytopoiesis in both the bone marrow and spleen. The degree of the platelet response to PEG-rHuMGDF varied between individual mice, likely reflecting the heterogeneity of the disease. Production of new platelets in response to PEG-rHuMGDF was manifested by an increase in reticulated platelets. Levels of platelet-associated immunoglobulin G decreased inversely during periods of thrombocytosis. PEG-rHuMGDF therapy also improved thrombocytopenia in male W/B F(1) mice refractory to splenectomy. Platelet lifespan was not affected by PEG-rHuMGDF. Male W/B F(1) mice treated with pegylated murine MGDF, a homologue of PEG-rHuMGDF, had persistent thrombocytosis for at least 7 months, suggesting that antiplatelet antibody production was not enhanced.

CONCLUSIONS

PEG-rHuMGDF therapy potently stimulated platelet production, effectively ameliorating thrombocytopenia in a murine model of idiopathic thrombocytopenic purpura.

Thrombopoietin, but not cytokines binding to gp130 protein-coupled receptors, activates MAPKp42/44, AKT, and STAT proteins in normal human CD34+ cells, megakaryocytes, and platelets

OBJECTIVE

The development of megakaryocytes is regulated by thrombopoietin (TPO), which binds to the c-mpl receptor, and by several other cytokines such as interleukin (IL)-6, IL-11, leukemia inhibitory factor (LIF), cilliary neurotropic factor (CNTF), and oncostatin (OSM), which bind to gp130 protein-coupled receptors. We attempted to identify signal transduction pathways activated by these factors in normal human megakaryocytes.

MATERIALS AND METHODS

To better understand the role of these factors in normal human megakaryopoiesis we studied their effect on 1) purified human bone marrow-derived CD34+ cells, 2) human alpha(IIb)beta3+ cells (shown by immunophenotypical and morphological criteria to be megakaryoblasts), which had been expanded ex vivo from CD34+ cells in chemically defined artificial serum, and 3) gel-filtered human peripheral blood platelets. Further, in an attempt to correlate the influence of these factors on cell proliferation and survival with activation of signal transduction pathways, we evaluated their effect on the phosphorylation of MAPK p42/44 and activation of PI-3K-AKT and JAK-STAT proteins in these various cell types.

RESULTS

Using serum-free liquid cultures, we found that only TPO and IL-6 protected CD34+ cells and megakaryocytes from undergoing apoptosis (decrease in annexin-V binding, PARP cleavage, and activation of caspase-3). Moreover, only TPO when used alone and IL-6 only when used in combination with TPO, stimulated the growth of human colony-forming unit-megakaryocytes (CFU-Meg) in semisolid serum-free medium. We also observed that while TPO efficiently activated various signaling pathways in CD34+ cells, megakaryocytes, and platelets (MAPK p42/44, PI-3K-AKT, STAT proteins), IL-6 stimulated phosphorylation of STAT-1, -3, and -5 proteins only in CD34+ cells and megakaryoblasts. To our surprise, none of the other gp130 protein-related cytokines tested (IL-11, LIF, CNTF, and OSM) activated these signaling pathways in CD34+ cells, megakaryoblasts, or platelets.

CONCLUSIONS

Our signal transduction studies explain why TPO, by simultaneously activating several signaling pathways, is the most potent megakaryopoietic regulator and why of all five gp130 protein-related cytokines tested, only IL-6, through activation of STAT proteins, plays a role in normal human megakaryopoiesis.