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Platelet transfusion refractoriness results in adverse outcomes and increased health care costs. Managing refractoriness resulting from HLA alloimmunization necessitates the use of HLA antigen–matched platelets but requires a large platelet donor pool and does not guarantee full matching. We report the first randomized, double-blind, noninferiority, crossover trial comparing HLA epitope–matched (HEM) platelets with HLA standard antigen–matched (HSM) platelet transfusions. Alloimmunized, platelet-refractory, thrombocytopenic patients with aplastic anemia, myelodysplastic syndrome, or acute myeloid leukemia were eligible. HEM platelets were selected using HLAMatchMaker epitope (specifically eplet) matching. Patients received up to 8 prophylactic HEM and HSM transfusions provided in random order. The primary outcome was 1-hour posttransfusion platelet count increment (PCI). Forty-nine patients were randomized at 14 UK hospitals. For intention to treat, numbers of evaluable transfusions were 107 and 112 for HEM and HSM methods, respectively. Unadjusted mean PCIs for HEM and HSM methods were 23.9 (standard deviation [SD], 15) and 23.5 (SD, 14.1), respectively (adjusted mean difference, −0.1; 95% confidence interval [CI], −2.9 to 2.8). Because the lower limit of the 95% CI was not greater than the predefined noninferiority limit, the HEM approach was declared noninferior to the HSM approach. There were no differences in secondary outcomes of platelet counts, transfusion requirements, and bleeding events. Adequate 1-hour PCI was more frequently observed, with a mean number of 3.2 epitope mismatches, compared with 5.5 epitope mismatches for inadequate 1-hour increments. For every additional epitope mismatch, the likelihood of an adequate PCI decreased by 15%. Epitope-matched platelets should be considered to support HLA alloimmunized patients. This trial was registered at www.isrctn.com as #ISRCTN23996532.

The effect of variation in platelet function in platelet donors on patient outcome following platelet transfusion is unknown. This trial assessed the hypothesis that platelets collected from donors with highly responsive platelets to agonists in vitro assessed by flow cytometry (high-responder donors) are cleared more quickly from the circulation than those from low-responder donors, resulting in lower platelet count increments following transfusion. This parallel group, semirandomized double-blinded trial was conducted in a single center in the United Kingdom. Eligible patients were those 16 or older with thrombocytopenia secondary to bone marrow failure, requiring prophylactic platelet transfusion. Patients were randomly assigned to receive a platelet donation from a high- or low-responder donor when both were available, or when only 1 type of platelet was available, patients received that. Participants, investigators, and those assessing outcomes were masked to group assignment. The primary end point was the platelet count increment 10 to 90 minutes following transfusion. Analysis was by intention to treat. Fifty-one patients were assigned to receive platelets from low-responder donors, and 49 from high-responder donors (47 of which were randomized and 53 nonrandomized). There was no significant difference in platelet count increment 10 to 90 minutes following transfusion in patients receiving platelets from high-responder (mean, 21.0 × 109/L; 95% confidence interval [CI], 4.9-37.2) or low-responder (mean, 23.3 × 109/L; 95% CI, 7.8-38.9) donors (mean difference, 2.3; 95% CI, -1.1 to 5.7; P = .18). These results support the current policy of not selecting platelet donors on the basis of platelet function for prophylactic platelet transfusion.

Genetic variation is known to account for up to 70% of the wide variation in platelet function observed in healthy individuals. We have shown that platelet concentrates (PC) that are highly activated when collected by apheresis are produced from donors whose platelets are highly responsive to adenosine diphosphate (ADP) and collagen related peptide (CRP-XL) in vitro(high responder donors) with activation being measured by P-selectin expression and fibrinogen binding. The effect of this variation in donors on the outcome from platelet transfusion is unknown. The aim of the PROmPT trial (Platelet Responsiveness and Outcome from Platelet Transfusion, ISRCTN 56366401) was to test the hypothesis that PC following transfusion from high responder donors are cleared more rapidly from the circulation than PC from low responder donors. Method We established a cohort of 1,000 blood donors phenotyped for responsiveness to CRP (0.1-0.5 µg/mL) or ADP (10-7M) by flow cytometry. A sub-set of these individuals (26 high and 19 low responder donors) who reproducibly had global responses, i.e. not outliers for just one agonist, in the top and bottom 10% of the cohort were selected to supply apheresis platelets collected on the Terumo Trima system for the trial. The trial was designed as a parallel group, semi-randomised double-blinded trial in stable haematology patients who required prophylactic platelet transfusions. Based on 80% power, a 5% significance level, and a presumed 10% dropout, 100 patients (with the aim of 50 receiving a unit from high responders and 50 from low responders) were required to detect a mean difference of 7x109/L in the primary endpoint of the 1 hour (10-90 min) count increment (CI) between the high and low responder PC. Patients were randomised to receive a single PC from either a high or low responder donor when both were available. If only one type of PC was available then patients received that PC. Patients with factors known to affect platelet CI were excluded. In addition, 30 patients acted as controls, receiving non-trial PC from random donors. PCs were ABO and Rh compatible. Patients were followed up for 5 days or until their next platelet transfusion. Secondary outcomes included an assessment of bleeding score (modified WHO score) both by the patient and the clinician, 24 hour (12-36 hours) CI, as well as time to next platelet transfusion, and red cell transfusion requirements. CIs were adjusted for confounding factors that affect platelet increments, these were age and dose of PC, and body surface area. Results Baseline characteristics of patients were adequately balanced between groups. Fifty one patients received a PC from low responder donors, and 49 from high responder donors (47 of which were randomised and 53 non-randomised) and 30 patients received non-trial units (2 non trial transfusions were excluded from final analysis). There was no significant difference in the adjusted 1 hour CI, in patients receiving platelets from high or low responder donors (high response 21.04 versus low response 23.34x109/L; difference 2.30, 95%CI -1.09 to 5.69, p = 0.18) or the 24 hour platelet CI (high response 12.9 versus low response 14.31x109/L; difference 1.41, 95% CI -1.96 to 4.78, p = 0.41). There were no significant differences in all other secondary outcomes between patients receiving PC from high or low responder donors, including maximum bleeding scores (odds ratio 0.78, 95%confidence interval 0.29 to 2.16, p=0.64) and bleeding rates (number of days with Grade 2-4 bleed) (rate ratio was 0.70, 95% confidence interval 0.16 to 2.97, p = 0.63). In addition, there was no significant difference in 1 hour CI between patients receiving non-trial units and those from high (p = 0.28) or low responders (p = 0.95) or in any secondary outcomes. Conclusions Results from this trial suggest that in a setting of prophylactic transfusion, the platelet responsiveness of the donor does not affect platelet count increments, bleeding scores, inter-transfusion interval or red cell usage in recipients. Further studies will be required to determine whether PC derived from high responders may be more efficacious in patients who are actively bleeding at the time of transfusion. Disclosures No relevant conflicts of interest to declare.

Abstract 1 Background The effectiveness of prophylactic platelets (plts) to prevent bleeding in patients with hematological malignancies remains unclear. The aim of this trial was to test the hypothesis that a policy of no-prophylactic plt transfusions (PltTx) is as effective and safe as a policy of prophylactic PltTx. Methods TOPPS was a randomized, parallel group, open-label, non-inferiority trial that recruited from 14 UK and Australian hospitals (ISRCTN08758735). The primary outcome was proportion of patients with a clinically significant bleed, defined as ≥WHO Grade 2, up to 30 days (d) from randomization. Non-inferiority margin was defined as a 15% difference in proportion of patients experiencing the primary outcome. Adult patients were eligible if they had a hematological malignancy, were receiving chemotherapy or stem cell transplant (SCT) and expected to be thrombocytopenic for at least 5 days. Patients were randomized by centralized computer system to receive either prophylactic PltTx if plt count was Results Recruitment began August 2006 and closed in August 2011. Of 1093 patients screened, 600 patients were randomized (301 no-prophylaxis, 299 prophylaxis). Baseline characteristics were well matched. 70% patients in both arms received autologous SCT (autoSCT). The majority of patients in both arms had complete bleeding data recorded [median 30d (IQR 29 to 30) no-prophylaxis arm, median 30d (IQR 30 to 30) prophylaxis arm]. Two patients (1 in each arm) withdrew prior to any data collection. Most PltTx in both arms were given according to protocol (no-prophylaxis 450/504 (89%) vs prophylaxis 810/894 (91%). Fewer patients in the no-prophylaxis group received PltTx (176/300, 59%) vs. prophylaxis group (266/298, 89%) [OR 0.14 (95% CI 0.09 to 0.23]; and they also received fewer PltTx overall [no-prophylaxis mean 1.7 PltTx (SD 2.6) vs. prophylaxis mean 3.0 PltTxs (SD 3.2); rate ratio 0.62, 95% CI 0.51 to 0.74]. Average number of days with plt count A WHO grade 2–4 bleed occurred in 151/300 patients (50%) in the no-prophylaxis group compared to 128/298 (43%) in the prophylaxis group (adjusted difference in proportions 8.4%, 90% CI 1.7 to 15.2%: p-value for non-inferiority 0.06). This study therefore did not prove its main aim, that a no-prophylaxis policy is non-inferior to prophylaxis. The time to the first grade 2–4 bleed was significantly shorter in the no-prophylaxis group (Fig. 1). Patients in the no-prophylaxis group averaged 1.7d (SD 2.9) with a WHO grade 2–4 bleed during follow-up, vs. 1.2d (SD 2.0) in the prophylactic group [rate ratio 1.52, 95% CI 1.14 to 2.03]. Whilst there were more grade 3–4 bleeds in the no-prophylaxis group (6/300) compared to the prophylaxis group (1/298) this did not reach statistical significance (OR 6.05, 95% CI 0.73 to 279.72, p = 0.13). Only 2 of these 7 patients had a plt count For all patients, there was no significant difference between treatment groups in period of thrombocytopenia, number of days in hospital, or number of SAEsexperienced. Discussion This multicenter study has not shown that a no-prophylaxis PltTx policy is non-inferior to prophylaxis. Patients in the no-prophylaxis group had more days with a WHO grade 2 or above bleed, and a shorter time to first bleed. Further analysis is needed to determine whether these findings apply to all subgroups of patients. Despite a role for prophylactic platelet transfusions, rates of bleeding in patients remain high. Funding NHS Blood and Transplant & Australian Red Cross Blood Service Disclosures: No relevant conflicts of interest to declare.