No abstract

The growth of human eosinophil progenitors (CFU-Eo) and the modulation of growth by hydrocortisone were studied as functions of the presence of lymphocytes and monocytes in marrow cells under study; and the source of colony-stimulating factors, specifically, media conditioned by macrophage-like cell line, GCT; phytohemagglutinin-stimulated mononuclear cells (PHA-LCM); or the T cell line, MO. CFU-Eo growth was greatest in marrow containing accessory cells as compared to marrow depleted of accessory cells; and in marrow treated with phytohemagglutinin-stimulated leukocyte conditioned media (PHA-LCM) or MO (T cell line)-conditioned medium (MO-CM) as compared with GCT cell- conditioned medium (GCT-CM). Hydrocortisone reproducibly inhibited eosinophil progenitor growth in unfractionated marrow stimulated by GCT- CM. This effect was abrogated by admixing irradiated mononuclear cells or T lymphocytes with the target marrow or by adding interleukin 1 or interleukin 2 (IL-1, IL-2). Inhibition by hydrocortisone did not occur when monocyte and T lymphocyte depleted marrow was studied. Unlike GCT- CM, MO-CM and PHA-LCM stimulated equal proportions of eosinophil progenitors in nondepleted and accessory cell-depleted marrow and demonstrated less hydrocortisone inhibition. However, both GCT-CM and PHA-LCM produced in the presence of hydrocortisone stimulated significantly fewer CFU-Eos in both unfractionated and accessory cell- depleted marrow target populations. These results indicate that the growth of CFU-Eo and inhibition of growth by hydrocortisone is a direct function of a monocyte-T cell interaction and probably is mediated through effects on the production/release of eosinophil colony stimulating factor (Eo-CSF).

No abstract

AMG 531 is a novel thrombopoiesis-stimulating peptibody that acts by stimulating the thrombopoietin (TPO) receptor. We report efficacy data in splenectomized patients from a randomized, double blind, placebo-controlled Phase 3 study designed to evaluate the efficacy and safety of AMG 531 in patients with chronic ITP. Sixty-three splenectomized patients were enrolled (placebo, 21; AMG 531, 42), with a median age of 52 years (range 26 to 88) and a mean baseline platelet count 14.7x109/L. Subcutaneous AMG 531 or placebo was administered weekly for 24 weeks at a starting dose of 1μg/kg, and adjusted to maintain a target platelet count of 50–200x109/L. The primary study endpoint was the incidence of a durable platelet response, defined as a platelet count ≥50x109/L for ≥6 weeks during the last 8 weeks of the 24 week treatment period in the absence of rescue medications. Sixteen of the 42 splenectomized patients (38.1%) receiving AMG 531 achieved a durable platelet response compared to 0/21 (0.0%) receiving placebo (p=0.0013). Overall response, defined as either durable or transient platelet response (≥4 weekly platelet responses), was observed in 33/42 (78.6%) patients receiving AMG 531, compared to 0/21 (0%) placebo patients. The mean number of weekly platelet responses (platelet count ≥50x109/L) was significantly greater in patients receiving AMG 531 (12.3/24 weeks, 51%) compared to placebo (0.2/24 weeks, 1%) (p<0.0001). AMG 531 reduced the proportion of patients requiring ITP rescue medications, defined as either increase from baseline in dose of concurrent medication or use of new medication to increase platelet counts. Twelve of 21 (57.1%) placebo-treated patients received rescue medications compared to just 11/42 (26.2%) AMG 531-treated patients (p=0.0175). In addition, 12/12 (100.0%) AMG 531-treated patients compared to 1/6 (16.7%) placebo-treated patients either discontinued or reduced by >25% their concurrent ITP medications. AMG 531 was well-tolerated. There were 2 treatment-related serious adverse events; 1 patient with elevated bone marrow reticulin that returned to baseline 3 months after withdrawal of AMG 531, and 1 patient experienced thrombosis that was successfully treated allowing study continuation. No patient developed neutralizing antibodies against either AMG 531 or endogenous TPO. In summary, AMG 531 was well-tolerated, and effectively increased and sustained platelet counts in splenectomized patients with ITP. AMG 531-treated patients required less frequent rescue medications in comparison to those receiving placebo, and were able to reduce their use of concurrent therapies.

The growth of eosinophil progenitors (CFU-Eo) and its modulation by hydrocortisone (HC), mononuclear cells, interleukin 1 (IL-1), and interleukin 2 (IL-2) in three cases of eosinophilia are reported in this paper. One microM HC decreased the proportion of CFU-Eo in each of these three patients, and in each case, the addition of autologous mononuclear cells at a 1:1 ratio abrogated the effect of HC on CFU-Eo. As studied in two of the three cases, IL-1 and IL-2 were able to prevent the effect of HC. Further studies showed no effect of HC when monocyte T cell-depleted marrow cells were used as the target population. These results suggest that CFU-Eo production in eosinophilic states is subject to modulation by HC and T lymphocytes.