Estimating the potential cost of a high dose immune tolerance induction (ITI) therapy relative to the cost of a combined therapy of a low dose ITI therapy with bypassing agent prophylaxis.

INTRODUCTION: The International Immune Tolerance Study (I-ITI) demonstrated comparable success rates between low (FVIII 50 IU/kg/TIW) and high dose (FVIII 200 IU/kg/day) regimens. While costlier, the high dose ITI regimen achieved shorter time-to-treatment success with fewer bleeding episodes compared to the low dose ITI regimen. Adding bypassing agent prophylaxis (BAP) to a low dose ITI regimen may reduce bleeding while still being less costly than high dose ITI. AIM AND METHODS: An economic model was developed to compare high dose ITI to low dose ITI with BAP. All model inputs were derived from clinical trials. The I-ITI study indicated a median time to negative inhibitor titre of 4.6 and 9.2 months and average number of bleeds/patient of 4.2 and 9.9 for the high and low dose regimens respectively. Based on the BAP trials, aPCC (85 U/kg/TIW) and rFVIIa (90 µg/kg/day) achieved a 62% and 45% reduction in bleeding frequency respectively. Cost analysis was from a US third party payer perspective and limited to drug costs. One-way, two-way and probabilistic sensitivity analyses were performed. RESULTS: Costs of low dose ITI with aPCC prophylaxis until negative inhibitor titre is achieved was 24.0% less compared to high dose ITI. Low dose ITI with rFVIIa prophylaxis cost 46.5% more compared to high dose ITI. Model results were robust in the majority of the sensitivity analyses. CONCLUSION: A low dose ITI regimen with aPCC prophylaxis may be cost saving compared to a high dose ITI regimen with the potential to reduce morbidity by lowering the risk for breakthrough bleeds.

Complications of haemophilia in babies (first two years of life): a report from the Centers for Disease Control and Prevention Universal Data Collection System.

AIM: To describe the prevalence and complications in babies ≤2 years with haemophilia. METHODS: We used a standardized collection tool to obtain consented data on eligible babies aged ≤2 years with haemophilia enrolled in the Centers for Disease Control and Prevention Universal Data Collection System surveillance project at US Hemophilia Treatment Centers (HTCs). RESULTS: Of 547 babies, 82% had haemophilia A, and 70% were diagnosed within one month of birth. Diagnosis was prompted by known maternal carrier status (40%), positive family history (23%), bleeding (35%) and unknown 2%; 81% bled during the first two years. The most common events were bleeding (circumcision, soft tissue, oral bleeding) and head injury. There were 46 episodes of intracranial haemorrhage (ICH) in 37 babies (7%): 18 spontaneous, 14 delivery related, 11 traumatic, 2 procedure related and 1 unknown cause. Of the 176 central venous access devices (CVADs) in 148 (27%) babies, there were 137 ports, 22 surgically inserted central catheters and 20 peripherally inserted central catheters. Ports had the lowest complication rates. Inhibitors occurred in 109 (20%) babies who experienced higher rates of ICH (14% vs. 5%; P = 0.002), CVAD placement (61% vs. 19%; P < 0.001) and CVAD complications (44% vs. 26%; P < 0.001). The most common replacement therapy was recombinant clotting factor concentrates. CONCLUSION: Bleeding events in haemophilic babies ≤2 years were common; no detectable difference in the rates of ICH by the mode of delivery was noted. Neonatal factor exposure did not affect the inhibitor rates. Minor head trauma, soft tissue and oropharyngeal bleeding were the leading indications for treatment.

Efficacy and safety of prophylactic treatment with plasma-derived factor XIII concentrate (human) in patients with congenital factor XIII deficiency.

UNLABELLED: Congenital factor XIII (FXIII) deficiency is an extremely rare, potentially life-threatening bleeding disorder. Routine prophylactic management is recommended for individuals with clinically relevant FXIII deficiency. This prospective, multicentre, open-label study evaluated the long-term efficacy and safety of prophylactic infusions of FXIII concentrate (human) 40 IU kg(-1) in patients with congenital FXIII deficiency. FXIII concentrate (human) was administered every 4 weeks for 12 months. Dosing was adjusted to maintain trough FXIII activity levels of 5-20%. Logistical and ethical constraints precluded use of a placebo control group. Annualized incidence of spontaneous bleeding was compared with historical rates; safety was assessed as a secondary objective. Forty-one patients were enrolled and completed the study. The annualized rate for spontaneous bleeding episodes requiring FXIII treatment was 0.000 episodes per patient-year (95% CI: 0.000; 0.097). The study met its primary endpoint: the upper limit of the 95% CI was substantially below the historical rate of 2.5 bleeding episodes per patient-year. Five spontaneous bleeding episodes (involving three patients; none requiring FXIII treatment) and eight trauma-related bleeding episodes (two requiring FXIII treatment) occurred. Five patients had surgery during the study, only one of whom required FXIII treatment for post-surgical bleeding. Most patients (≥ 85%) had trough FXIII activity levels ≥ 10%. No patient discontinued treatment due to an adverse event. No adverse events related to thromboembolism or viral transmission were reported. Prophylactic treatment with FXIII concentrate (human) was well tolerated and prevented spontaneous bleeding episodes that were serious enough to require treatment with FXIII-containing product. CLINICAL TRIAL REGISTRATION: www.clinicaltrials.gov/ct2/show/NCT00885742.

Pharmacokinetics and safety of plasma-derived factor XIII concentrate (human) in patients with congenital factor XIII deficiency.

UNLABELLED: Congenital factor XIII (FXIII) deficiency is a rare condition with substantial risk for life-threatening bleeding. Replacement of deficient FXIII with plasma-derived FXIII concentrate is a treatment option. The current 12-week study evaluated the steady-state pharmacokinetic (PK) and safety profile of prophylactic infusions of FXIII concentrate (human) in patients with congenital FXIII deficiency. Patients received FXIII concentrate (human) 40 IU kg(-1) on Days 0, 28, and 56. FXIII levels were assessed before and after each infusion; steady-state PK parameters were assessed up to 28 days after the infusion on Day 56. Treatment effectiveness in maintaining trough FXIII activity levels ≥ 5% over 28 days and safety parameters were also assessed. Fourteen patients received FXIII concentrate (human) and 13 completed the study. Post-infusion, FXIII activity levels increased to within the range found in patients without congenital FXIII deficiency without reaching supra-therapeutic levels. Non-baseline-adjusted trough FXIII activity levels were maintained at or above 10% at all post-baseline visits in all patients. Steady-state PK parameters were baseline-adjusted; maximum FXIII activity was 87.7% at 1.72 h post-infusion, subsequently declining to a minimum of 5.0%. The half-life was 6.6 days. FXIII concentrate (human) was generally well tolerated. Two patients had possibly treatment-related adverse events. There were no reports of thromboembolism, viral transmission, bleeding events or treatment-related hypersensitivity. These findings support use of FXIII concentrate (human) 40 IU kg(-1) every 28 days as an appropriate regimen for routine, long-term prophylaxis in children and adults with congenital FXIII deficiency. CLINICAL TRIAL REGISTRATION: www.clinicaltrials.gov/ct2/show/NCT00883090.

Further characterization of the thrombasthenia-related idiotype OG. Antiidiotype defines a novel epitope(s) shared by fibrinogen B beta chain, vitronectin, and von Willebrand factor and required for binding to beta 3.

A patient (OG) with Glanzmann thrombasthenia became refractory to platelet transfusion after the production of an immunoglobulin G (IgG) isoantibody (Ab1) specific for the integrin subunit beta 3. To determine the frequency at which the OG idiotype is found in the general population and in immune-mediated disease states, we developed a rabbit polyclonal antibody (Ab2) specific for affinity-purified OG anti-beta 3 Fab. The binding of Ab2 to Ab1 is inhibited by purified alpha IIb beta 3. Ab2 als binds to IgG specific for alpha IIb beta 3 obtained from one nonrelated Glanzmann thrombasthenia patient ES who has developed isoantibodies of similar specificity. On the other hand, Ab2 does not recognize alpha IIb beta 3-specific antibodies produced by two Glanzmann thrombasthenia patients, AF and LUC, who have developed isoantibodies with specificities distinct from that of the OG isoantibody. Moreover, Ab2 does not recognize alpha IIb beta 3-specific antibodies developed by three representative patients with (autoimmune) thrombocytopenic purpura or six representative patients with alloimmune thrombocytopenias, nor does it bind to IgG from any of 13 nonimmunized individuals. We have found that Ab2 also binds to selected protein ligands of alpha IIb beta 3 namely, fibrinogen, vitronectin, and von Willebrand factor, but not to other protein ligands or control proteins, such a fibronectin, type I collagen, and albumin. The epitope(s) recognized by Ab2 on each adhesive protein are either very similar or identical since each protein can inhibit the binding of Ab2 to any of the other proteins. The epitope on fibrinogen recognized by Ab2 resides in the B beta chain, and is likely contained within the first 42 amino acids from the NH2 terminus. Since OG IgG inhibits fibrinogen binding to alpha IIb beta 3, the specificity of the OG idiotype defines a novel binding motif for the integrin alpha IIb beta 3 that is shared by fibrinogen, vitronectin, and von Willebrand factor, but distinct from previously described RGD-containing sites on the fibrinogen, A alpha chain or the fibrinogen gamma chain COOH-terminal decapeptide site. Our findings reported here represent an excellent example of molecular mimicry in which an antigen-selected, IgG inhibitor of alpha IIb beta 3 function shares a novel recognition sequence common to three physiologic protein ligands of that receptor.

Comparison of kaolin and tissue factor activated thromboelastography in haemophilia.

A limitation of bypassing agent therapy for haemophilia patients with inhibitors is the absence of a laboratory assay, which predicts the clinical response to treatment. Recent investigations have demonstrated the potential for thromboelastography to assess the effects of bypassing agent therapy in this patient population. While tissue factor activation has been used in several prior studies, a recent multicentre study failed to demonstrate an expected concentration-response effect of rFVIIa and called into question the tissue factor activation methods that have been employed. A comparison of kaolin to two concentrations of tissue factor as the activation method for thromboelastography was investigated in patients with haemophilia. We performed kaolin and tissue factor activated thromboelastography on blood from inhibitor and non-inhibitor patients with and without addition of rFVIIa and rFVIII. The results demonstrate that kaolin leads to a longer R, K and angle than the higher dilution of tissue factor (1:17 000) at baseline (no factor) and after addition of rFVIIa for both the inhibitor and non-inhibitor patients. Kaolin led to a longer R and K in comparison to a low dilution of tissue factor (1:42 000) following the addition of rFVIIa in the inhibitor patients. The longer R and K allows for better discrimination of the effects of rFVIIa thus making kaolin the most sensitive activation method in this setting. Thus kaolin activated thromboelastography should be considered an effective, perhaps the most effective, activator when utilizing thromboelastography to assess the effects of rFVIIa in haemophilia patients with inhibitors.

Glycoprotein Ic-IIa functions as an activation-independent fibronectin receptor on human platelets.

Soluble fibronectin binds specifically to glycoprotein (GP) IIb-IIIa on thrombin-activated platelets, and this binding is not observed with platelets of patients with Glanzmann's thrombasthenia (GT) which lack GPIIb-IIIa. Here we report that GT platelets retain the ability to interact with fibronectin-coated surfaces. Adhesion to fibronectin does not require platelet activation and is inhibited by soluble fibronectin, antibodies specific for fibronectin, peptides containing the sequence Arg-Gly-Asp and polyclonal antibodies specific for band 3 of the chicken embryo fibroblast fibronectin receptor (anti-band 3). Using anti-band 3, we have purified a second fibronectin receptor from human platelets, a heterodimer composed of glycoproteins previously designated GPIc and GPIIa. The GPIc-IIa complex is found on both GT and normal platelets and appears to be identical to the GP138 kD-GP160 kD complex recently immunopurified by Giancotti et al. (1986. Exp. Cell Res. 163:47-62) and by Sonnenberg et al. (1987. J. Biol. Chem. 268:10376-10383). In this report, we provide the first evidence that GPIc-IIa actually mediates adhesion of platelets to fibronectin-coated surfaces. GPIc-IIa thus represents a second functional fibronectin receptor, distinct from GPIIb-IIIa, that is largely responsible for the adhesion of nonactivated platelets to fibronectin-coated surfaces.

On the association of the platelet-specific alloantigen, Pena, with glycoprotein IIIa. Evidence for heterogeneity of glycoprotein IIIa.

Neonatal alloimmune thrombocytopenic purpura associated with a new platelet-specific alloantigen Pena has been reported. We now provide direct evidence that the Pena determinant is associated with glycoprotein (GP) IIIa, but that it is distinct from epitopes that define the PlA system. By ELISA wherein monoclonal antibodies specific for GPIIb (Tab) and specific for GPIIIa (AP3) were used to capture and hold antigens from a platelet lysate prepared under conditions that generate free GPIIb and GPIIIa, anti-Pena reacted with GPIIIa held by AP3 but not with GPIIb held by Tab. In an alternative ELISA where purified GPIIIa from both PlA1-positive and PlA1-negative platelets were used individually as antigen, anti-Pena reacted with both allelic forms of GPIIIa. By radioimmuno-precipitation, anti-Pena precipitated a single surface-labeled membrane protein with electrophoretic characteristics in sodium dodecyl sulfate-polyacrylamide gels, under nonreduced or reduced conditions, identical to those of GPIIIa. By fluorocytometry, platelets from several donors, regardless of PlA phenotype, bound an amount of anti-Pena roughly equivalent to one-half that amount of anti-PlA1 bound by PlA1 homozygous (A1/A1) platelets and roughly equal to that amount of anti-PlA1 bound by PlA1 heterozygous (A1/A2) platelets. Using platelets from donors typed homozygous for PlA1 and Pena in a quantitative indirect binding assay, 14-24,000 molecules of anti-Pena and 41-51,000 molecules of anti-PlA1 were bound per platelet at saturation. Anti-Pena completely inhibited ADP-induced aggregation of Pena-positive platelets, regardless of PlA phenotype. These results indicate that the Pena determinant is associated with GPIIIa but distinct from PlA.

Pilot dose-finding and safety study of bivalirudin in infants <6 months of age with thrombosis.

BACKGROUND: Thrombosis is not uncommon in children with serious medical conditions. Unfractionated heparin, the most commonly used anticoagulant in the acute management of thrombosis, has significant pharmacologic limitations, especially in infants. Newer anticoagulants have improved properties relative to heparin, and this may enhance the outcome in children. OBJECTIVE: To determine dosing, and to assess the safety and efficacy of bivairudin for infants with thrombosis. METHODS: Infants <6 months old were chosen for this pilot study as they may most benefit from a direct thrombin inhibitor because of their physiologically low antithrombin levels. This was an open label, dose-finding and safety study. Patients received one of three bolus doses and one of two initial infusion doses with subsequent dosing adjusted utilizing the activated partial thromboplastin time. Safety was assessed by specific bleeding endpoints. Efficacy was determined by reassessing the initial imaging study at 48-72 h and by measurement of molecular markers of thrombin generation. RESULTS: Sixteen patients completed the study. All three bolus doses resulted in therapeutic anticoagulation, as did both initial infusion doses. A dose-response effect was noted for the continuous infusion but not the bolus dosing. Two patients met the study criteria for major bleeding, both with gross hematuria, which resolved with a reduction in the bivalirudin infusion rate. In terms of efficacy, 37.5% of patients had complete or partial resolution of their thrombosis by 48-72 h. There was a significant decrease in all three molecular markers of thrombin generation. CONCLUSION: This study demonstrates the potential utility of bivalirudin in the pediatric population.

Repertoire cloning of a human IgG inhibitor of alpha IIB beta 3 function. The OG idiotype.

A patient (OG) with Glanzmann thrombasthenia became refractory to platelet transfusion following the production of IgG antibodies (Ab1) specific for the integrin subunit beta 3. We generated recombinant VH and VL cDNA libraries using IgG-specific mRNA isolated from OG peripheral blood B-lymphocytes that had been selected for binding to antigen (alpha IIb beta 3 adsorbed to plastic dishes). These antigen-specific B-lymphocytes contain rearranged VH DNA segments that belong exclusively to the VH4 gene family. Recombinant Fab were expressed on the surface of filamentous phage coinfected with VH and VL segments cloned into the phagemid pHEN1 or the phage fd-tet-DOG1. To facilitate selection of the desired recombinant Ab1 Fab, we developed a rabbit polyclonal antibody specific for affinity-purified OG anti-beta 3 Fab (Ab2). Ab2 reacts specifically with Ab1, and this interaction is inhibited by purified alpha IIb beta 3. Following three rounds of phage selection on Ab2 adsorbed to plastic dishes and random reassociation of heavy and light chains, we isolated Ab1 Fab and tested their binding to alpha IIb beta 3. Five Id-positive Fab were selected for further characterization. These Fab use one of two VH genes (H21 or H23) complexed with one of three V lambda genes. Subsequent sequence data demonstrated that all three lambda genes are the same clone L22 which uses a germline V lambda gene segment. Fab using H23 bind to alpha IIb beta 3, while those using H21 do not. Based on sequence homology, both H21 and H23 use VH gene segments belonging to the VH4 gene family. Thus, the idiotype OG is restricted to the VH4 gene family and is the first sequenced prototype of human antibodies that bind close to or at a functional epitope(s) of alpha IIb beta 3.

Controversies in the treatment of pediatric immune thrombocytopenias.

Although pediatric immune thrombocytopenia (ITP) is common, there is no consensus on the optimal approach to therapy. Childhood ITP differs in its clinical course and trigger from adult immune thrombocytopenic purpura. There appear to be two clinical phenotypes among children with ITP: children with polyclonal autoantibody production triggered by an external exposure such as infection, and children with coexistent immune deficiency or dysregulation on a congenital or acquired basis. Treatment implications exist for each group. The first may be best managed by observation and conservative measures; for the latter, treatment could include normal intravenous gammaglobulin concentrate, anti-blood group D antigen (anti-Rh factor), or steroids. Early recognition of the thrombocytopenic child with immune dysfunction versus the normal child with a polyclonal response to a particular environmental antigen will result in better prognosis for both by selecting the appropriate therapy and minimizing long-term side effects.

Childhood immune thrombocytopenic purpura.

Childhood immune thrombocytopenic purpura (ITP) is acute and generally seasonal in nature, suggesting that infectious or environmental agents may trigger the immune response to produce platelet-reactive autoantibodies 4 to 8 weeks following an infection. In general, the patient is well apart from the diffuse bruising and petechiae indicative of a profound thrombocytopenia. Over a period of 6 months, the thrombocytopenia resolves in approximately 85% of children, while the remaining 15% with persistent platelet consumption are designated as chronic ITP patients. The peak age of acute ITP is 2 to 5 years of age, a period when children experience the greatest frequency of viral infections. Children with the chronic form of ITP mirror the adult phenotype, in that females predominate, and there is no seasonal fluctuation of the disease. Evidence from our laboratory suggests that the activated platelet itself may play a role in perpetuating autoantibody production and immune dysregulation associated with ITP. Current data on lymphocyte studies and cytokine alterations noted in response to the variety of regimens used in children with ITP suggest that acute ITP is accompanied by autoantibodies to GPIb and a cytokine profile that is proinflammatory in nature. Early recognition of the immune dysregulation driving acute versus chronic ITP will distinguish those children who might benefit from immunotherapy versus those who will recover without therapeutic intervention.

Alloimmunization to platelet antigens.

Alloantibodies to platelet-specific antigens can cause significant thrombocytopenia and bleeding in NATP and PTP. IVIG plays an important role in the therapeutic regimen of both of these disorders. Alloantibodies in the multiply transfused patient bind to HLA class I and platelet-specific antigens. IVIG has not improved response to random-donor platelets in refractory patients, but there may be a role for IVIG in critically ill and bleeding patients, in combination with HLA-matched platelets.

Clinical manifestations of the prothrombin G20210A mutation in children: a pediatric coagulation consortium study.

The prothrombin G20210A mutation is a common risk factor for thrombosis which increases the risk of deep vein thrombosis, stroke, and fetal loss. There are few publications of its clinical manifestations in children. Our objective was to determine the clinical manifestations of the prothrombin mutation in children. Via survey of pediatric hematologists, we collected data on children with thrombosis and the prothrombin mutation. Thirty-eight patients with a thrombotic event were identified as having the prothrombin mutation. Children with arterial thrombosis were younger, less than half had additional risk factors present at the time of the event, and had a high frequency of central nervous system thrombosis. Children with venous thrombosis were older, almost always had additional risk factors present, and had thrombosis occur most often in the extremities, although there were also a significant number of events in the central venous and cerebral circulation. There was a striking predilection for central nervous system events as 30% of all the events and 67% of the arterial events occurred there. In all, 14/38 children (37%) had central nervous system thrombosis. Unlike factor V Leiden and deficiencies of proteins C and S which cause venous thromboembolism, the prothrombin mutation in children is often associated with arterial thrombosis and with central nervous system events. In children with the prothrombin mutation and venous thrombosis, other risk factors are usually present. Therefore, children with arterial or venous thrombosis of any location should be evaluated for the presence of the prothrombin mutation.

Sequence analysis of monoclonal antibodies derived from a patient with idiopathic thrombocytopenic purpura.

Autoantibodies directed at the platelet membrane glycoprotein Ib (GPIb) can mediate a severe form of idiopathic thrombocytopenic purpura (ITP). The platelet-specific antibody from plasma of one patient (DM) with this form of ITP displays a public idiotype termed DMId. The DMId idiotype has been found in the plasma of several patients with ITP, usually in association with GPIb-specific autoantibodies. As a step in the understanding of the molecular genetics of this form of ITP we have determined the nucleotide sequences of expressed V region genes selected from a panel of five human lymphoblastoid cell lines derived from patient DM. Two of the lines secreted antibodies that bound GPIb, and three of the lines secreted antibodies that expressed DMId. The H chain sequences of the DMId-positive antibodies and of one of the GPIb-binding antibodies belong to the VH4 family. The second GPIb-binding antibody belongs to the VH1 family. All have multiple substitutions from previously published sequences giving these antibodies the appearance of having been antigen driven. These results are consistent with the hypothesis that autoantibodies in ITP arise from a "normal" immune response inappropriately directed at platelet antigens. Further, our results suggest that VH4 gene segments may be recruited preferentially into the DMId-positive, GPIb-specific autoantibody response.