Optimizing therapy with factor VIII/von Willebrand factor concentrates in von Willebrand disease

In von Willebrand disease, the main goals of treatment are to correct the dual defect of haemostasis caused by a reduced or abnormal von Willebrand factor (vWF), i.e. the prolonged bleeding time (BT) and the deficiency of factor VIII coagulant activity (FVIII:C). The synthetic vasopressin analogue, desmopressin (DDAVP), has reduced the need for transfusions in most of the mild forms of von Willebrand disease but DDAVP is ineffective in type 3 and in other severe cases of types 1 and 2 von Willebrand disease. For many years cryoprecipitate has been the mainstay of replacement therapy but, after the introduction of virucidal methods, concentrates containing FVIII/vWF have been considered much safer than cryoprecipitate and proposed in von Willebrand disease management. FVIII/vWF concentrates have been produced and tested by many authors but there is only one report describing four virus-inactivated FVIII/vWF concentrates evaluated in a cross-over randomized trial. According to these in vitro and pharmacokinetic data, the following information can be derived: (a) no FVIII/vWF concentrate had an intact multimeric structure similar to that of normal plasma or of cryoprecipitate; (b) all FVIII/vWF concentrates were equally effective in attaining normal and sustained levels of FVIII:C postinfusion, although peak levels were more delayed in the concentrate devoid of FVIII:C; (c) no FVIII/vWF concentrate consistently normalized the BT in a sustained fashion. On the other hand, clinical haemostasis can be achieved in the management of bleeding episodes and of surgery for most of von Willebrand disease cases regardless of whether the BT is corrected; in the few rare cases with mucosal bleeding not controlled by FVIII/vWF concentrates, infusion of DDAVP or platelet concentrates can be administered in addition.     

Characterization of factor VIII/von Willebrand factor concentrates using a modified method of von Willebrand factor multimer analysis

In order to provide patients with von Willebrand disease a factor VIII (FVIII)/von Willebrand factor (vWF) concentrate of reproducible quality, an SDS-agarose gel electrophoresis method has been established to determine the content of the high molecular weight multimers (band 11 and higher) of vWF. This method has been used to characterize the content of high molecular weight vWF multimers in Humate^® P/Haemate^® P, a commercial FVIII/vWF concentrate. The average content of high molecular weight vWF multimers of 47 batches of Humate^® P/Haemate^® P has been determined to be 84.1% of the corresponding bands in normal human plasma. Use of this multimer analysis method for the characterization of five further commercial products revealed clear differences with respect to the high molecular weight vWF multimer content. Furthermore, there is a linear correlation ( r ² = 0.73) between the content of high molecular weight vWF multimers and the specific activity of vWF (determined as vWF:RCoF/vWF:Ag). The method described here for analysis of the content of high molecular weight vWF multimers is a reliable and reproducible method to characterize this class of factor concentrates with respect to vWF multimer composition.     

Progress in large-scale purification of factor VIII/von Willebrand factor concentrates using ion-exchange chromatography

Background and Objectives We investigated and optimized the parameters of a chromatographic process suitable for industrial scale to obtain a highly purified factor VIII (FVIII)/von Willebrand factor (VWF) concentrate. Materials and Methods Several chromatographic runs were performed on the same production intermediate using different anion-exchange supports. The best matrix was selected and the final product was characterized. Once the chromatographic medium was chosen, the other parameters were evaluated to obtain the highest purified product and to modulate the VWF content in the FVIII/VWF complex. Results Fractogel EMD TMAE was the best support among those tested. It was the only one maintaining good results either with standard or double loading and flow rate conditions with respect to a typical industrial process. The chromatographic recovery of FVIII co-purified with VWF was at least 86% with a specific activity not lower than 140 IU/mg. The FVIII/VWF complex obtained is highly pure and, with the exception of immunoglobulin M (IgM), all investigated contaminant proteins are under the detection limit. Different concentrates characterized by variable FVIII/VWF ratios were purified by varying the chromatographic conditions. Conclusions Several highly purified products, suitable for haemophilia A and von Willebrand disease management, can be obtained, through the same chromatographic process, on an industrial scale.     

Influence of von Willebrand factor on the reactivity of human factor VIII inhibitors with factor VIII

In order to determine the difference in reactivity of factor (F) VIII inhibitors against the FVIII/von Willebrand factor (vWF) complex and against vWF-deficient FVIII, we investigated a panel of 10 antibodies to FVIII from multitransfused individuals with severe haemophilia A and other pathologies. Immunoblotting of purified FVIII and purified thrombin-cleaved FVIII revealed that in all cases inhibitor epitopes could be localized in the heavy chain (A2 subunit) while in four cases they were also present in the light chain. One of the FVIII inhibitors remained unclassified. The effect on FVIII:C of purified IgG from inhibitor plasmas was tested against a high purity FVIII/vWF concentrate and a monoclonally purified FVIII concentrate with only trace contents of vWF, by two different functional assays. Our results suggest that for those inhibitors showing A2 plus light chain (LC) reactivity, the IgG concentration required to inhibit 50% of FVIII activity in vitro is higher for the FVIII/vWF complex than for the vWF-deficient FVIII. We conclude that there might be a protective role of vWF (at least in vitro) against FVIII inhibitors with A2 and LC subunit specificity.     

von Willebrand factor containing factor VIII concentrates

There are several plasma derived von Wille-brand factors (vWF) containing factor (FVIII) concentrates that can be used in the treatment of von Willebrand disease (vWD). All concentrates are effective in attaining normal postinfusion levels or of FVIII:C but it is difficult to achieve normalization of the bleeding time even with concentrates containing almost all vWF multimers including those of high molecular weight. Haemate P (Centeon) may be considered as the golden standard concentrate available at present. However, the development of more purified vWF concentrates devoid of FVIII:C is the goal for future development.     

In vitro characterization of recombinant factor VIII concentrates reveals significant differences in protein content,activity and thrombin activation profile

Recombinant factor VIII (rFVIII) concentrates differ due to cell lines, culture conditions, presence of the B domain and authorized potency assays. This study characterizes three commercially available rFVIII concentrates: a second‐generation full length (A), a third‐generation full length (B) and a third‐generation B domain‐deleted (BDD) product (C). rFVIII concentrates were characterized for FVIII activity (FVIII:C) by one‐stage clotting and chromogenic assays, FVIII antigen (FVIII:Ag), thrombin activation profile and FXa‐generation assay. The rFVIII concentrates exhibited significant differences with regard to FVIII:C, FVIII:Ag and thrombin activation profile. Product A had significantly greater FVIII:C and FVIII:Ag relative to the measured values of products B and C. In addition, product A demonstrated faster and more complete activation by thrombin than the two others. BDD product C had the slowest measured thrombin activation rate. Product A exhibited a greater in vitro FXa generation than products B and C. We found no differences in FXa generation among all three products when FXa generation was normalized for FVIII:Ag. The greater FVIII:C and FVIII:Ag values for product A compared with that for products B and C are due to application of different authorized potency assays (one‐stage assay for A vs. chromogenic assay for B and C). The variation in thrombin activation profiles may arise from differences in cell line‐dependent posttranslational modifications of the various recombinant proteins.     

Inhibitor development in haemophilia A: the role of von Willebrand factor/factor VIII concentrates

Summary.  The presence of inhibitors that neutralize the function of factor VIII (FVIII) decreases the haemostatic efficacy of replacement clotting factor concentrate and increases morbidity among patients with haemophilia A. Certain genetic and environmental variables have been linked to a higher incidence of inhibitors. Conversely, the presence of von Willebrand factor (VWF) in some plasma-derived FVIII products may provide some measure of protection against inhibitor development, although the evidence is not conclusive. Clinical trials are needed to resolve this issue and determine the appropriate role of VWF-containing FVIII concentrates in the treatment of haemophilia A patients.     

Pharmacokinetics of von Willebrand factor and factor VIII coagulant activity in patients with von Willebrand disease type 3 and type 2

Nine patients with von Willebrand disease type 3, six with type 2B, one with type 2A, and one patient with type 1/2N were infused with one dose of ≈50 or 100 IU ristocetin cofactor activity (RCoF) per kg body weight of von Willebrand factor (vWF) (Human), a product with a very low content of factor VIII (FVIII). Blood samples were collected over 96 h. The data for RCoF and vWF antigen (vWF:Ag) were fitted to a 1-compartment model decay. The data for FVIII:C were fitted to a model with a linear time 'synthesis' term and a 1-compartment decay. Results in von Willebrand disease type 3 patients (nine patients; 10 infusions) indicated a volume of distribution of 39.9 and 39.8 mL kg⁻¹ for RCoF and vWF:Ag, respectively. The FVIII:C rate of synthesis was 6.4 U dL⁻¹ h⁻¹ (range: 4.4–8.8). The decay rates for FVIII:C, RCoF, and vWF:Ag were 0.041 (h⁻¹) [ t _1/2: 16.9 h]; 0.061 (h⁻¹) [ t _1/2: 11.3 h] and 0.006 (h⁻¹) [ t _1/2: 12.4 h], respectively. In patients with von Willebrand disease type 2 ( n  = 8) the RCoF mean volume of distribution was 46 mL kg⁻¹. The factor VIIIC mean rate of synthesis was 5.5 U dL⁻¹h⁻¹ and the decay rate 0.043 (h⁻¹) [ t _1/2: 16.1 h]. The rate of decay for RCoF and vWF:Ag were 0.050 (h⁻¹) [ t _1/2: 13.9 h] and 0.044 (h⁻¹) [ t _1/2: 15.7 h], respectively.     

Pharmacokinetics and hemostatic effect of different factor VIII/von Willebrand factor concentrates in von Willebrand's disease type III

Summary Four different plasma-derived concentrates composed of coagulation factor VIII (FVIII) and von Willebrand factor (vWF) of varying quality (Hemate-P, Behring; Profilate, Alpha; and FVIII-VHP-vWF, C.R.T.S Lille), or almost purified vWF (Facteur Willebrand, C.R.T.S Lille) and one recombinant FVIII concentrate (Recombinate, Baxter) were given, in doses of 30–60 IU VIII:C/kg or 70–110 IU RCof/kg, to five patients with von Willebrand's disease type III, in order to evaluate the role of the vWF in factor FVIII concentrates. All plasma concentrates except Profilate had a multimeric vWF pattern almost similar to that of normal plasma. Bleeding time (b.t.), VIII:C, vWF: Ag, ristocetin cofactor activity, and multimeric pattern of the plasma-vWF were followed for 72 h. Both Duke b.t. and the multimeric pattern in plasma normalized after infusion of Hemate-P, FVIII-VHP-vWF, and Facteur Willebrand and, to a lesser extent, after Profilate. As expected, in response to Recombinate there was no effect on primary hemostasis, and the half-life of FVIII procoagulant activity (VIII:C) was very short. Normalization of the vWF is important not only for improving the primary hemostasis, but also for maintaining the plasma FVIII concentration on a high level, both by reducing the elimination rate of infused FVIII and via a secondary release of endogenous FVIII. If a prompt hemostatic effect is required, we recommend a concentrate containing both FVIII and all vWF multimers, but for prophylactic treatment, pure vWF may be used.     

Further evidence for recessive inheritance of von Willebrand disease with abnormal binding of von Willebrand factor to factor VIII.

A new family with a bleeding diathesis and FVIII deficiency secondary to abnormal binding of von Willebrand factor (vWF) to factor VIII (FVIII) is described. Two propositi of this family, an 18-year-old male and a 33-year-old female, both with a history of epistaxis, bruising, bleeding from the gums, epistaxis, hemarthrosis, and hematoma, were analyzed. Also additional members of the same family with no bleeding history were also studied. The propositi showed normal vWF activities, low FVIII activity; one of them had been diagnosed as having hemophilia A and the other was a hemophilia A carrier. Both showed a very poor response to treatment with FVIII concentrates and desmopressin (DDAVP) but a good clinical response to cryoprecipitate. APTT was prolonged and no inhibitory activity was noticeable in their plasmas. Thirty-five units per kilogram body weight of Hemofil M was infused to both propositi and FVIII reached basal level within 60 minutes of the infusion. No FVIII response at all was observed in the female after intravenous DDAVP administration. However, the male who received the infusion of 35 U/kg body weight of Humate-P achieved a normal FVIII level that was maintained for 12 hours. Multimeric analysis of vWF was normal in all the members studied. Von Willebrand factor domain for FVIII binding was assayed in the two propositi and in six other members of the same family by using a non-isotopic and sensitive method, a modification of the one previously described, using the Hemofil M concentrate as exogenous FVIII. The data obtained showed that both propositi had similar binding to that observed by using plasma of a patient with severe von Willebrand disease. Furthermore, five siblings had a decreased binding of vWF to FVIII, when compared with plasma from normal individuals or patients with hemophilia A. We also observed that, for screening purpose, the ratio of bound FVIII/immobilized vWF (at saturation of the anti-vWF and offering of 1 U/ml of exogenous FVIII) distinguished two levels of abnormality (normal range 0.70-1.15, propositi 0.004-0.007, and remaining members affected 0.25-0.42). The most probable explanation is that the propositi are homozygous or double heterozygous, the other five siblings affected being heterozygous for a recessive vWF defect. This more accessible assay presented here may be of help in routine analysis for diagnosing this type of von Willebrand disease, which has important implications for therapy and genetic counseling.     

Early transfusion of factor VIII/von Willebrand factor concentrates seems to be effective in the treatment of gatrointestinal bleeding in patients with von Willebrand type III disease

The association between gastrointestinal angiodysplasia and von Willebrand disease was reported 30 years ago. The clinical course of patients with von Willebrand disease and angiodysplasia is characterized by numerous admissions to hospital for gastrointestinal bleeding necessitating transfusion with packed red cells, factor VIII and plasma. The management of these patients is problematic. Numerous treatments for the gastrointestinal bleeding have been proposed: surgery, electrocoagulation, laser photocoagulation, sclerotherapy, arteriography with embolization, immunoglobulins, oestrogens, and octreotide, but no treatment modality has been successful in all cases. We report a 66-year-old-female with small bowel angiodysplasia and von Willebrand type III disease in whom prompt administration of factor VIII/vWF concentrates was effective. Education of patients to recognize minimal gastrointestinal bleeding manifestations, periodical clinical visits and early infusion of factor VIII/vWF seems to be fundamental for the success of this therapy. A longer follow-up and the study of other patients are needed to confirm our observation.     

von Willebrand factor contributes to longer half‐life of PEGylated factor VIII in vivo

PEGylation of B‐domain deleted factor VIII (PEG‐FVIII‐BDD) prolongs the half‐life of the molecule by approximately twofold in animals (Mei et al., Blood 2010; 116 : 270). To investigate the role of von Willebrand factor (vWF) in the catabolism of PEG‐FVIII‐BDD in vivo, a FVIII‐BDD mutant (F8V), which is incapable of binding vWF, was generated by deleting the vWF‐binding region in the a3 domain of FVIIII‐BDD. F8V was expressed, purified and PEGylated by site‐specific conjugation. The biochemical and biological properties of F8V and PEGylated F8V (PEG‐F8V) were evaluated in vitro and in vivo. The specific activity of purified F8V by a chromogenic assay was similar to FVIII‐BDD and PEGylation had minimal impact on the specific activity of F8V in this assay. Analysis by Biacore indicated that both F8V and PEG‐F8V display greatly reduced vWF binding in vitro. Pharmacokinetic studies in FVIII knockout (HaemA) mice showed that the terminal half‐life (T_1/2) of F8V was dramatically reduced relative to FVIII‐BDD (0.6 h vs. 6.03 h). PEGylation of F8V promoted a significant increase in T_1/2, although PEGylation did not fully compensate for the loss in vWF binding. PEG‐F8V showed a shorter T_1/2 than PEG‐FVIII‐BDD both in HaemA mice (7.7 h vs. 14.3 h) and in Sprague‐Dawley male rats (2.0 ± 0.3 h vs. 6.0 ± 0.5 h). These data demonstrated that vWF contributes to the longer T_1/2 of PEG‐FVIII‐BDD. Furthermore, this suggests that the clearance of the FVIII:vWF complex, through vWF receptors, is not the sole factor which places an upper limit on the duration of PEG‐FVIII circulation in plasma.     

Immunoprotective effect of von Willebrand factor towards therapeutic factor VIII in experimental haemophilia A

The development of inhibitory anti-factor VIII (FVIII) antibodies in patients with haemophilia A following replacement therapy is associated with several types of risk factors. Among these, the purity of FVIII concentrates, and in particular the presence of von Willebrand factor (VWF), was controversially proposed to influence the immunogenicity of exogenous FVIII. We re-assessed in vivo and in vitro the immuno-protective effect of VWF towards FVIII. The immuno-protective effect of VWF towards FVIII was investigated in vivo, in a model of haemophilia A. We studied the endocytosis of FVIII by murine bone marrow-derived dendritic cells and evaluated the capacity of VWF to block the internalization of FVIII. We characterized the relevance of VWF for the accumulation of FVIII in the marginal zone of the spleen, a secondary lymphoid organ where the immune response to therapeutically administered FVIII initiates. Our results confirm that VWF reduces the immunogenicity of FVIII in FVIII-deficient mice. Paradoxically, VWF is important for the accumulation of FVIII in the marginal zone of the spleen. We propose that VWF exerts at least two non-mutually exclusive immunoprotective roles towards FVIII in haemophilic mice: VWF prevents the endocytosis of FVIII by professional antigen-presenting cells by blocking the interaction of FVIII with as yet unidentified endocytic receptor(s). Hypothetically, VWF, by virtue of increasing the half-life of FVIII in the circulation, may allow an increased contact time with tolerogenic marginal zone B cells in the spleen.     

In vitro reactivity of factor VIII inhibitors with von Willebrand factor in different commercial factor VIII concentrates

A relevant aspect in the treatment of patients with hemophilia A (HA) presenting inhibitor against factor VIII (FVIII) is the different antigenicity of FVIII used for replacement therapy. The aim of the study was to assess the effect of different products, with variable von Willebrand factor (vWF) concentration, in preventing the binding of inhibitor to FVIII. The reactivity of inhibitors from plasma of 18 patients with HA versus three commercial concentrates containing different amounts of vWF was compared. The results show that increasing amounts of vWF might have a protective effect on the transfused FVIII inactivation.     

Stability of factor VIII concentrates after reconstitution

Adjusted-dose continuous infusion of factor VIII (FVIII) has recently been shown to reduce the doses of the factor in patients undergoing surgery by 50-75%. The main limitation of this method has been the instability of factor concentrates. All manufacturers are recommending infusion of the concentrate within hours after reconstitution. We studied the stability of 15 different lyophillzed F VIII products. Reconstituted samples were stored for periods of 4, 24, and 72 hr and 1, 2, 3, and 4 weeks at temperatures of WC, 20-23°C, and 37°C in their original glass containers and in plastic tubes and then frozen. Assays were performed in duplicate, using a one-stage clotting method and a chromoge nlc assay for F VIII, wlth all samples from a single concentrate In the same run. Activation of the coagulation factor occurred In some concentrates, more often at 44°C than at 20-23°C or 3PC. The stability of all products was substantially better than that declared by the manufacturers. Several concentrates maintained factor activities above 80% of baseline for the entlre period of 4 weeks at 44°C or at 20-23°C. The results demonstrate that many of the F VIII concentrates may be used for continuous infusion. © 1994 Wiley-Liss, Inc.     

von Willebrand factor in factor VIII concentrates protects against neutralization by factor VIII antibodies of haemophilia A patients

We investigated the neutralization activity of factor VIII (FVIII) antibodies of 12 haemophilia A patients, acquired during treatment with plasma-derived FVIII concentrates. All plasma samples, drawn in a clinically stable situation before any immunotolerance treatment, contained anti-A2 domain and anti-light-chain FVIII antibodies. In nine patients' plasmas, containing relatively high amounts of FVIII light-chain antibodies (53-96%), a higher neutralization activity was found against recombinant FVIII concentrate (Recombinate) than against plasma-derived von Willebrand factor (vWF)-containing concentrate (Haemoctin SDH). No difference in neutralization of the two concentrates was found in two patients' plasmas with almost equal content of FVIII light- and heavy-chain antibodies, or one plasma with predominantly heavy-chain antibodies. These results suggest that haemophilia A patients with relatively high amounts of FVIII light-chain antibodies in plasma might benefit by infusion of FVIII concentrates containing vWF because vWF appears to have some protective effect on FVIII. This hypothesis should be tested by a clinical study.     

Potency measurement of factor VIII in recombinant concentrates

In preliminary studies on the stability of recombinant factor VIII (rFVIII) concentrates post reconstitution, a rise in potency to 200% of labelled values was observed in concentrates stored at 22 °C over 24 h. This was observed in potency estimates by the one-stage clotting, but not the two-stage clotting or chromogenic assays, and was not observed for intermediate-purity product derived from plasma (IPVIII). Use of human serum albumin (HSA), rather than the usual bovine material (BSA), to dilute product for the stability study abolished the rise in potency. Incorporating purified von Willebrand Factor (VWF) in the diluent buffer abolished the rise observed in BSA. A similar rise was observed upon incubating rFVIII in the presence of 10^?4 u of thrombin per mL in HSA buffer. Potency estimates using the HSA in the dilution buffer resulted in severe underpotency in relation to the label claim when using the two-stage clotting and the chromogenic assays, but not the one-stage clotting assay. Predilution in severe haemophilic plasma restored potency levels to those claimed. We conclude that (i) commercial preparations of BSA may be unsuitable for inclusion in buffers for rFVIII studies; (ii) FVIII in rFVIII concentrates is exquisitely sensitive to activation by thrombin, presumably as a result of the lack of VWF; (iii) accurate potency estimation in the two-stage assay systems requires VWF in the assay system.     

von Willebrand factor/factor VIII concentrate (Humate‐P) for management of elective surgery in adults and children with von Willebrand disease

Summary. von Willebrand disease (VWD) is the most common inherited bleeding disorder. Treatment guidelines recommend the use of von Willebrand factor/factor VIII (VWF/FVIII) concentrate for VWD patients with type 2 or 3 VWD undergoing surgery, and type 1 patients undergoing surgery who are unresponsive, or for whom desmopressin acetate is contraindicated. This prospective, open‐label, multinational study evaluated the safety, efficacy and optimal dosing of a VWF/FVIII concentrate (Humate‐P) in subjects with VWD undergoing elective surgery. Dosing was based on VWF ristocetin cofactor (VWF:RCo) and FVIII pharmacokinetic assessments performed before surgery. Pharmacokinetic assessments were completed in 33 adults and 9 children. Haemostatic efficacy was assessed on a 4‐point scale (excellent, good, moderate/poor or none). Overall effective haemostasis was achieved in 32/35 subjects. Median terminal VWF:RCo half‐life was 11.7 h, and median incremental in vivo recovery was 2.4 IU dL^?1 per IU kg^?1 infused. Major haemorrhage occurred after surgery in 3/35 cases despite achieving target VWF and FVIII levels. Median VWF/FVIII concentrate loading doses ranged from 42.6 IU VWF:RCo kg^?1 (oral surgery) to 61.2 IU VWF:RCo kg^?1 (major surgery), with a median of 10 (range, 2–55) doses administered per subject. Adverse events considered possibly treatment‐related (n = 6) were generally mild and of short duration. The results indicate that this VWF/FVIII concentrate is safe and effective in the prevention of excessive bleeding during and after surgery in individuals with VWD.     

ADAMTS13 content in plasma‐derived factor VIII/von Willebrand factor concentrates

Thrombotic thrombocytopenic purpura (TTP) is a microangiopathy syndrome caused by a congenital or acquired deficiency of ADAMTS13, a plasma metalloprotease that cleaves von Willebrand factor (VWF) and thus prevents the formation of platelet‐rich thrombi in the microcirculation. TTP can be fatal if not appropriately and timely treated with the infusion of fresh frozen plasma (FFP) or exchange plasmapheresis, that reverse the process of microangiopathy by removing anti‐ADAMTS13 autoantibodies and replacing functional ADAMTS13. The treatment of TTP with FFP is not free from risks and must be administered in hospitals or clinics, owing to the substantial amount of plasma volume infused or exchanged and the frequent need of catheter application. Moreover, most FFPs are not subjected to treatments to remove or inactivate blood‐borne infectious agents. A number of recent reports indicate that certain plasma‐derived VWF‐factor VIII (FVIII) concentrates are clinically effective in the treatment of congenital TTP. In this study, we measured ADAMTS13 levels in various plasma‐derived VWF‐FVIII concentrates, showing that Koate^®‐DVI (Grifols), contained relatively high amounts of ADAMTS13 and that Alphanate^® (Grifols) was the closest other product in terms of protease content. Koate^®‐DVI contains, on average (five lots tested), 0.091 ± 0.007 Units of ADAMTS13 activity per IU of FVIII. On the basis of this analysis and other reports of VWF‐FVIII concentrate utilization in congenital TTP, potential dosing, and future clinical developments are discussed. Am. J. Hematol. 88:895–898, 2013. © 2013 Wiley Periodicals, Inc.