Summary. The`high and low responder phenomenon' of monocyte tissue factor (MTF) activity has been attributed to effects on monocytes by granulocytes, platelets and lipopolysaccharide (LPS). To study the possible contribution of plasma to the high and low responder phenomenon, we measured the MTF activity in isolated cryopreserved human monocytes from two donors (monocytes A and monocytes B) after incubation in a plasma environment depleted of granulocytes, platelets and LPS. In buffer only, MTF activity was 643 and 679 fM (fM final concentration of tissue factor), in normal pooled plasma, it was 1478 and 1615 fM (P 0´001), respectively, in monocytes A and in monocytes B. Incubation with individual plasma samples from healthy controls (n 43) gave a median MTF of 1355 fM (range 1044±1976 fM) and 1329 fM (range 858±1951 fM) respectively. A plasma consistently induced a higher or lower level of MTF activity in both monocytes: r 0´82 (P , 0´00001). Coumarin use did not influence the high and low responder phenomenon. In the absence of granulocytes, platelets and LPS, plasma determines the high and low responder phenomenon. This phenomenon is not influenced by coumarin treatment.
2514 The overall short term effectivity of Rituximab in the treatment of ITP is reported to be around 50%. In most studies the traditional CD20 dosing scheme of 4 weekly interspaced 375 mg/m2 doses is used although other single-arm studies suggest comparable effectivity of lower doses. To investigate alternative dosing schemes, we conducted an open label phase II multicenter trial and randomized 156 ITP patients that were refractory for corticosteroid treatment, between three schemes. Questions were: are higher CD20 peak levels of value and is dose saving a feasible approach in early responding patients? The treatment arms were: A) 375 mg/m2 once a week for 4 weeks, B) 750 mg/m2 once a week for 2 weeks and C) 375 mg/m2 once a week for 2 weeks, in early and sustained responding patients (= within 15 days and still responding at 43 days) and another 2 × 375 mg/m2 to patients not fulfilling these criteria. In retrospect, seven of the 156 patients appeared ineligible at randomization and were therefore excluded from all analyses. Here we report on the best response within 71 days as primary end point for the first 105 patients that were included, i.e. 35 per treatment arm Arm A (n=35) 4 × 375 mg/m2 Arm B (n=35) 2 × 750 mg/m2 Arm C (n=35) 2 or 4 × 375 mg/m2 Patient characteristics Male/female, % 37/63 49/51 43/57 WHO 0/1/2/not reported, % 86/6/–/9. 77/20/3/– 91/9/–/– Age in years, median (range) 56 (19–77) 56 (17–82) 41 (18–80) On stable corticosteroid, % 36 29 46 Splenectomized, % – 15 11 Baseline plt count × 109/l, median (range) 16 (3–31) 15 (1–30) 19 (2–30) Treatment outcome, % Early responses in Arm C 26 All best responses within 71d 46 42 51 CR: >150 × 109 plt/l 20 14 14 GR: >50 × 109 plt/l 20 14 23 MR: >30 × 109 plt/l AND >2 × baseline 6 14 14 No response 54 58 49 Treatment failure at 6 months, % (standard error) 57 (8) 60 (8) 54 (9) So far, on the basis of the within 71 days overall response data, no superior dosing scheme of CD20 can yet be discerned. Disclosures: No relevant conflicts of interest to declare.
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