Thrombopoietic cytokines in relation to platelet recovery after bone marrow transplantation

Suppression of Hematopoietic Primitive Cells in Patients with Secondary Failure of Platelet Recovery after Acute Graft-versus-Host Disease

Secondary failure of platelet recovery (SFPR) can occur after allogeneic hematopoietic stem cell transplantation (alloHSCT), and 20% of cases are related to acute graft-versus-host disease (aGVHD). The underlying mechanisms of this association are unclear, however. The aim of the present study was to investigate the potential mechanisms of SFPR secondary to aGVHD, which may provide a new therapeutic strategy for these patients. A total of 468 patients with malignant hematologic disease who underwent alloHSCT were included. Sixty-six patients developed SFPR after alloHSCT, and in 45 of these 66 patients (68.2%), SFPR was secondary to grade II-IV aGVHD (SFPR/aGVHD). Compared with patients with good graft function (GGF), patients with SFPR had poor overall survival (20.72% versus 88.01%; P < .0001). Grade II-IV aGVHD was identified as an independent risk factor for SFPR in multivariate analysis (hazard ratio, 9.512; P < .0001). We observed reduced erythroid and megakaryocyte colony formation in bone marrow (BM) samples isolated from SFPR/aGVHD patients, consistent with the lower frequency of megakaryocyte and erythrocyte progenitors in BM. Levels of the inflammatory cytokines IL-2R and TNF-R1 were significantly higher in the SFPR/aGVHD group compared with the GGF group (P = .002 and .001, respectively), as were the frequencies of proinflammatory T helper subsets. Furthermore, the pathways that regulate hematopoiesis and immune responses were universally underexpressed in CD34⁺ cells isolated from SFPR/aGVHD patients. Differentially expressed genes were significantly enriched in the hematopoietic cell lineage pathway and other pathways involved in both immune responses and megakaryopoiesis. In summary, we found that both the immune microenvironment and compromised proliferation of hematopoietic primitive cells contribute to the development of SFPR secondary to aGVHD, and our data provide new insight into the mechanisms of SFPR in the context of aGVHD.

Hyaluronan Depolymerization by Megakaryocyte Hyaluronidase-2 Is Required for Thrombopoiesis

Hyaluronan is the predominant glycosaminoglycan component of the extracellular matrix with an emerging role in hematopoiesis. Modulation of hyaluronan polymer size is responsible for its control over cellular functions, and the balance of hyaluronan synthesis and degradation determines its molecular size. Although two active somatic hyaluronidases are expressed in mammals, only deficiency in hyaluronidase-2 (Hyal-2) results in thrombocytopenia of unknown mechanism. Our results reveal that Hyal-2 knockout mice accumulate hyaluronan within their bone marrow and within megakaryocytes, the cells responsible for platelet generation. Proplatelet formation by Hyal-2 knockout megakaryocytes was disrupted because of abnormal formation of the demarcation membrane system, which was dilated and poorly developed. Importantly, peptide-mediated delivery of exogenous hyaluronidase rescued deficient proplatelet formation in murine and human megakaryocytes lacking Hyal-2. Together, our data uncover a previously unsuspected mechanism of how hyaluronan and Hyal-2 control platelet generation.

Thrombopoietic cytokines and platelet count in multiple myeloma

Cytokines like interleukin (IL)-6 and IL-1beta are both implicated in multiple myeloma (MM) pathogenesis and megakaryopoiesis. The dynamic interaction between thrombopoiesis and thrombopoietic cytokines in MM may affect platelet (PLT) counts. Sixty-eight patients with MM (30 female, 38 male; median age 58 (40-79), 38 newly diagnosed, 15 in plateau, and 15 relapse and/or refractory patients) and 21 controls were included in the study. Plasma levels of thrombopoietin (TPO), IL-1beta, IL-11 and IL-6 were measured by ELISA. PLT counts were not different between the control group and MM patients with various disease stages and activity. IL-6 and TPO levels were higher in MM patients than healthy subjects (p < 0.001). PLT counts were inversely correlated with TPO (r = -0.566; p < 0.001) and positively correlated with IL-6 (r = 0.263; p = 0.04) levels in MM patients. TPO and IL-6 levels were significantly correlated (r = 0.305; p < 0.001). Disease activity has no effect on plasma cytokine levels. TPO levels were higher in stage III than stage I (p = 0.05) and stage II (p = 0.03) patients in newly diagnosed MM. High TPO levels induced by IL-6 may sustain normal PLT counts despite bone marrow infiltration by plasma cells and decreased PLT half-life.

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.

Serum stem cell growth factor for monitoring hematopoietic recovery following stem cell transplantation

Stem cell growth factor (SCGF) is a novel cytokine for primitive hematopoietic progenitor cells. Although it has burst-promoting activity and granulocyte/macrophage colony-promoting activity in vitro, its significance in hematopoiesis in vivo has not been elucidated. In this study, we have established enzyme-linked immunosorbent assay (ELISA) to quantify human SCGF and measured serum cytokines in normal volunteers and 27 patients undergoing stem cell transplantation (SCT), including six autologous and 21 allogeneic transplants. SCGF levels gradually increased after SCT regardless of graft-versus-host disease or type of transplant. The maximum level of SCGF was observed during the rapid granulocyte recovery phase in patients subjected to an autologous transplantation, and during the granulocyte stabilization phase in allogeneic patients. SCGF levels in PBSCT patients began to rise earlier than in BMT patients. Two patients with no increment of SCGF after SCT showed delayed engraftment. The source of SCGF was further analyzed by RT-PCR and we found that SCGF was highly expressed in bone marrow (BM) CD34(+) and CD34(-)CD33(+) cells, but not in BM CD34(-)CD33(-) cells, BM stromal cells and peripheral blood cells. The cell population expressing SCGF in BM possess the colony-forming cell activity. Therefore, serum SCGF can be an indicator of hematopoietic recovery following SCT.

Hypoproteinemia in severe childhood atopic dermatitis: a serious complication

As a complication of atopic dermatitis (AD), the incidence of hypoproteinemia is increasing among infants with severe AD in Japan. It can be a life-threatening condition owing to hypovolemic shock as a result of hypoproteinemia and vascular infarction as a result of thrombocythemia. However, the pathophysiology of this condition remains unclear. The objectives of the present study were two-fold. The first objective was to determine the main route of protein loss, i.e. through the damaged skin or the gastrointestinal tract, or as a result of insufficient food intake. The second objective was to identify whether allergy or infection was the cause of severe skin inflammation. Fifteen patients with AD were enrolled who had serum protein levels of 3.2-5.8 g/dl. Specific immunoglobulin E (IgE) and skin test to allergens, stool eosinophils, alpha1-antitrypsin clearance, skin Staphylococcus aureus colonization and superantigens (SAgs) produced by the organism, serum SAg-specific IgE antibodies, serum interleukin (IL)-5, IL-6, IL-12, and interferon-gamma (IFN-gamma) were evaluated. Prominent serous skin discharge was seen in all of the patients and was found to have almost the same protein concentration as serum. Marked thrombocytosis, with a maximum of 1,060 x 103/ml, was seen. Skin culture revealed S. aureus colonization in all patients. SAg-producing S. aureus were found in 84.6% of the patients. The concentration of serum IL-5 was significantly increased and correlated well with the blood eosinophil count. Hence, the main route of protein loss was believed to be through damaged skin. The cause of severe inflammation was thought to be a combination of allergic inflammation and skin colonization by SAg-producing S. aureus. Serum cytokines showed a T helper 2 (Th2) T-cell-mediated pattern. To prevent hypovolemic shock, vascular occlusion, and growth retardation, it is of vital importance to diagnose hypoproteinemia at an early stage and start appropriate therapy.

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.

Platelet count and interleukin 6 gene polymorphism in healthy subjects

BACKGROUND

Interleukin 6 (IL-6) is thought to play important roles in the development of reactive thrombocytosis caused by inflammation by its stimulatory effect on megakaryocytopoiesis. A G/C polymorphism of the IL-6 gene at position -174 has been found to be associated to different transcription rates. Specifically, subjects with the CC genotype showed lower plasma IL-6 levels compared with GC or GG subjects. Given this difference in transcription rates of IL-6 we speculated on different platelet count according to this IL-6 polymorphism.

METHODS

The G/C polymorphism of the IL-6 gene at position -174, serum IL-6 concentration and platelet count were prospectively analyzed in 59 (25 women) consecutive healthy subjects.

RESULTS

Subjects who were homozygotes for the C allele at position -174 of the IL-6 gene (Sfa NI genotype) showed significantly lower platelet count than carriers of the G allele, despite similar age, sex, body mass index and proportion of smokers (205400 +/- 44088 vs 239818 +/- 60194, p = 0.047). This was in parallel to differences in peripheral white blood cell count (5807 +/- 1671 vs 6867 +/- 1192 x 10(9)/ml, p = 0.01).

CONCLUSION

This is the first description, to our knowledge, of a genetical influence on basal platelet counts, which appears to be partially dependent on a polymorphism of the IL-6 gene, even in the absence of inflammation.