FACTOR VIII AND FACTOR IX

July 18, 2002
13:00 to 17:00
Georgiana Room
Boston Park Plaza Hotel

Chairman:  D. DiMichele--USA
Co-Chairmen: J. Ingerslev--Denmark; C. Lee--UK; K. Mertens--The Netherlands;
J. Oldenburg--Germany; HM van den Berg--The Netherlands; A. Srivastava--India; JM Saint-Remy--Belgium

Completed and Submitted Reports-
Chair: D. DiMichele

The following report  was published in 2002:   

The North American Immune Tolerance Registry: Practices, Outcomes, Outcome Predictors. D.DiMichele, B.L. Kroner. Thromb Haemost 2002;87:52-7.

ISTH website publication:

The Design and Analysis of Pharmacokinetics: Studies of Coagulation Factors.
M. Lee, M. Morfini, S. Schulman, J. Ingerslev

Completed studies/Publications in progress:

The Design and Analysis of Pharmacokinetics: Studies of Coagulation Factors-- Summary.
M. Lee, M. Morfini, S. Schulman, J. Ingerslev

International Registry: Congenital FVII Deficiency
G. Mariani

Dr. Ingerslev reported on behalf of Dr. Mariani and the FVII Registry Study Group . Currently closed to new subject accrual, the registry now contains 514 subjects from 59 centers. Of these 198 are asymptomatic. Among the symptomatic patients, clinical manifestations are classified as follows: 29% severe; 42% moderate and 30% mild.

There have been DNA samples submitted on 335/514 subjects. All but one mutation have been characterized.

The planned analyses of the data include: 1) clinical phenotype genotype correlation; 2) association of FVII deficiency with thrombosis;3) phenotypic characterization of the severe deficiencies including the  incidence of CNS bleeds; 4) natural history of disease;  and 5) treatment practices. The first publication on the association of FVII deficiency with thrombosis has been submitted to Blood. Manuscripts in preparation  are on the topics of genotype/phenotype correlation and CNS bleeds. The subcommittee will continue to be apprised of this group’s excellent productivity.

Registries and Studies in Progress
Co- Chairs: M. van den Berg and A. Srivastava

Registry on FIX inhibitors associated with anaphylaxis- J. Lusher

Dr. Lusher gave an update  on the FIX inhibitor  registry  of Dr Warrier.
The most recent  update  in July 2002 included 85 patients were included.
Demographics  ( mean and range) of the group at the time of inhibitor development   are  as follows:

age 19.5 months (9-156)
exposure days 11 days (2-180)
peak inhibitor titer 30 BU/ml (1-960)
complete gene mutation 17/32 (53%)


All FIX products have been associated with inhibitor  development .  Among the 32 patients  on whom these data  are available, 21 attempts at ITI (66%) are noted  with only 2/21 successes (9.5%). Data on the other patients are not yet available, so this figure could increase slightly; nevertheless, this is a much lower success rate for immune  tolerance  than  achieved  for hemophilia A.

Part of the reason for this registry was to document  the prevalence  of nephrotic syndrome  occurring  during ITI. So far three cases  demonstrated  a clear  association.  In all,13 cases have been reported. The nephrotic syndrome occurred after  a median duration of ITI of 9 months. Eleven of 13 cases had  documented  prior  allergy  to factor IX. Renal biopsy was performed in 2. Both biopsies  revealed  membranous  glomerulonephritis. Immunohistochemical staining was negative  in one patient studied.

It was concluded that the prevalence of inhibitors with an allergic phenotype  in hemophilia B is low (2.3%), and only 10% of the patients  achieved  tolerance after ITI. Nephrotic syndrome has been reported in 13 cases. Professor Mannucci commented that  although the Milan protocol to study the immunology of this phenomenon is available on the ISTH website, no samples had been received to date. Physicians  are again urged to participate .

Update on the Gene Therapy Registry- K. High

Dr. K. High gave a gene therapy registry update  with respect  to the development of databases produced by authorities. The current NIH database on gene transfer is now on the OBA website:   http:// www.4.od.nih.gov/oba/rac/clinicaltrial.htm and contains  information on 10 trials on gene transfer in X-linked recessive disorders.
 
During the third and fourth quarters of 2002, the GeMCRIS database - intended for all but with restricted access to the the public and non-investigators through graded built-in  firewalls - will come into operation. It is currently being piloted by the NIH Clinical Research Center. This database  will serve MDs with access to rapid reporting of AE's.

Data exchange  with the GTPTS (longterm  follow up of gene therapy  trial subjects) tracking system of the FDA will occur.       

International IT study update- D. DiMichele

Dr. DiMichele   gave this presentation  on behalf of her two co- principal  investigators, Drs. Charles Hay and Evelien Mauser- Bunschoten. Most importantly,  after a delay due to the recombinant factor shortage, the study has now officially started (July 2002) and is open for enrollment. A broad outline of the study was presented. It is a two-arm prospective  randomized  trial  comparing IT success in subjects  treated with low-dose arm ITT (50 IU/kg 3 times a week) to those treated with a high-dose regimen of 200 IU/kg per week. The anticipated enrollment is 150 subjects. The hypothesis  is that the high-dose arm will achieve  more  rapid tolerance, but may not yield  a higher  overall success  rate. Subjects  can be included  if they have severe HA, are < 8 years old, have had an inhibitor for < 12 months, have historical peak titers of between  5-200 BU/ml, have a confirmed current  titer  of < 10 BU. Patients with current titers > 10 BU/ml can be enrolled but  will not be immediately randomized  until the titer falls below 10 BU/ml in the ensuing12 months. More information  about  the trial is available on the  Hemophilia Research Society  website as well as  on the study website: www.itistudy.com . There was a question about  whether the study should not also randomize  for product  type. Dr. DiMichele  remarked that  the study is not powered to determine the influence of this parameter on IT success; however, using a minimization strategy, both arms would include  an equal number of subjects  using vWf -containing, monoclonal  and recombinant products  so that this variable did not confound the analysis.

Proposed registry: FVIII inhibitors developing on continuous infusion- J.Oldenburg                     
 
Dr. Oldenburg briefly reviewed the increasing use of continuous  infusion (CI) for factor replacement   in hemophilia. He also mentioned that so far, 11 cases of inhibitors developing in such patients  had been reported. All except  one of them had >50 factor exposure days before developing inhibitors. Most of these patients  had mild hemophilia. The basis for this phenomenon  is not clear but could be related to altered  immunogenicity  of the FVIII molecule  during  the process of infusion. He proposed that it was therefore worth establishing a registry of these cases to gather data in an attempt to better understand its pathogenesis and its natural history.

In the discussion that followed, it was pointed out that unless there were control data available on similar patients treated with bolus infusion, it would be difficult to conclude whether these events were indeed due to CI. Suggestions were also made for modifications to the questionnaire so  as to include the time scale  in which these inhibitors appeared and their subsequent  profile.

Challenges in gene based-diagnosis : Proposed working group on standardization- J. Oldenburg

Dr. Oldenburg mentioned that gene-based diagnosis of hemophilia was being  increasingly  used in recent  times. Even though a very large number of a variety of mutations  had been documented in the databases, one-third of all new reports still included  novel mutations. In spite of the many different techniques being used for screening for mutations, including sequencing of the gene, the success rate for mutation detection varies between 85-98%. Establishing causality of disease due to these mutations requires expression studies, which are not widely available. Carrier detection in families with large deletions  can be difficult to detect  using molecular genetic methods. Dr. Oldenburg presented data on the use of fluorescent  in-situ hybridization (FISH) with probes  for exons 5, 25, 26 of the FVIII gene for detection of such defects. FISH was also useful in documenting somatic mosaicism.

Because of these problems and the need to establish  a uniform  diagnostic  approach, Dr. Oldengurg proposed that a network be established for standardizing the methodology for the gene-based diagnosis of hemophilia. The aim of such a group would be to define the criteria for assigning causality to a particular mutation and also to exchange samples that prove difficult to analyze.

In the discussion that followed, it was mentioned that while this was a good idea, the logistics of establishing such a network, particularly its funding, needed careful planning. It was suggested that a working party be formed to look into the feasibility of this proposal.

Standardization Issues
Co-chairs: K. Mertens/ JM Saint-Remy

The Mega 2 Standard.  N. Kirschbaum

Last year an extensive calibration program was completed on the new common working standard of the FDA and the European Pharmacopoeia. 100,000 vials of this material are available as an international, common working standard. In view of this major step toward harmonization in this area between US and Europe, it is unfortunate that it proved impossible to assign one single potency for both 1-stage and chromogenic assays. In Europe, this material is available as BRP batch 3 with a potency of 8.6 IU per vial for the chromogenic assay. In the US the same material is called Mega 2 and has an assigned potency of 8.6 IU per vial for the chromogenic assay and 11.3 IU per vial for the 1-stage assay. Dr. Kirschbaum presented stability studies conducted by the FDA on this material, demonstrating excellent longterm stability in both assay methods. She further reported on the standard performance of Mega 2 in the lot release of 43 batches of plasma-derived FVIII and on various lots of two recombinant products. In general there was good agreement with the labelled potency using Mega 2 in both chromogenic and 1-stage assays, with 90% of batch testing yielding potencies within a range of ±10% of the label value. The exception involved one of the recombinant products, for which 86% of batch testing by the chromogenic assay was within the ±10% range, but the use of the 1-stage assay resulted in only 45 % of batches testing within this range and another 45% testing in the range of ±10-20% of the label potency. Dr. Kirschbaum concluded that the introduction of Mega 2 will not imply any shift in product potency. Upon questions from the audience, she further explained that the situation of a dual potency for Mega 2, though apparently confusing, seems workable without causing major inconsistencies.

Proposal to replace WHO concentrate standard – T.W. Barrowcliffe

Together with the calibration of the US/European working standard, another batch of the same plasma-derived product has been processed and filled in ampoules ( N ) to serve as the 7th WHO standard for FVIII concentrate. Dr. Barrowcliffe presented a report of the calibration study involving 38 laboratories. All labs were instructed  to follow the ISTH/SSC recommendations, including the use of FVIII deficient plasma as a prediluent. Of the participants, 27 obtained data with the 1-stage assay, while 31 used the chromogenic assay. The candidate standard did not display any significant discrepancy (< 2%) between 1-stage and chromogenic assays, thus allowing the data to be averaged according to the general WHO policy. Interlaboratory agreement was much better than in the calibration of the current 6th International Standard, with an overall GCV value of 8.29%. The new candidate standard has been calibrated against the current 6th IS (recombinant) as well as its predecessor, the 5th IS (plasma-derived) and the two secondary standards, the US Mega-1 and the European BRP-2. Against these four references, the potency of the new IS was found to be 11.40, 10.66, 10.60 and 10.09 IU per ampoule, respectively. For the potency of the new IS, Dr. Barrowcliffe discussed three options: (1) 11.4 IU based on the current WHO 6th IS, (2) 10.8 IU based on all four references, and (3) 11.1 IU based on the mean of options 1 and 2. Option 1 seems preferable in terms of continuity of the FVIII concentrate unitage, but other options allow greater harmonization between other standards that are being used. The various options have recently been sent to the participants as well as to the FVIII-IX subcommittee members for an opinion. Dr. Barrowcliffe expects that a final recommendation will be submitted to the Subcommittee for a vote prior to the Birmingham meeting.

Effect of standard and assay method on FVIII measurement in recombinant and plasma-derived concentrates – J.D. Schreiber

A manufacturer's view on FVIII working standards was presented by Dr. Schreiber from Baxter (Vienna). One study compared the company's recombinant and two plasma-derived products employing 1-stage and chromogenic assays against several standards, including the Mega 2 working standard. Good agreement was found using Mega 2 in chromogenic assays at its established potency of 8.6 IU per vial. In the 1-stage assay, however, values were found suggesting that the potency of Mega 2 seems 15% higher than its established value. In a second study, therefore, an in-house standard was calibrated by six different Baxter laboratories. Good agreement between 1-stage and chromogenic assays could be achieved when the calibration was based on the average of Mega 1 and WHO 6th IS, but not on Mega 2. Dr. Schreiber concluded that this in-house standard can be used within Baxter worldwide with one single potency for both assay methods, and with reasonably low (approx. 8%) interlaboratory variability.

Second Refacto lab field study – J. Ingerslev

This study has been recently concluded and focused on the use of Refacto Lab Standard (RLS) to facilitate the measurement of B-domain deleted FVIII in post-infusion samples. In this study, which involved 35 labs worldwide, hemophilic plasma was spiked with Refacto at levels of 0.2, 0.6 and 0.9 IU/ml, and these samples were assayed against normal plasma and RLS as a standard. In the chromogenic assay (7 labs) the expected FVIII levels were found irrespective of the standard used. In the 1-stage assay (31 labs) FVIII was underestimated against the plasma standard, and this was totally corrected by using RLS as a reference. Dr. Ingerslev concluded that this approach should eliminate most of the discrepancies reported so far in assaying plasma of patients treated with this FVIII product.

Focus of future SSC concentrate studies – K. Mertens

The SSC concentrate studies have been running since 1995 and serve to inform participants on the performance of their in-house assay method on a variety of FVIII samples. Seven  studies have been performed involving 12 FVIII samples ranging from intermediate and high purity plasma-derived products to recombinant full-length and B-domain deleted FVIII. In these "field studies" inter-laboratory variability was much larger (overall CV's 10-20%) than in controlled calibration studies. A significant number of participants do not follow the SSC guidelines which imply using the chromogenic assay, FVIII deficient plasma as a prediluent and 1% of albumin for all other dilutions. Given the limited extent of improvment over time, the Subcommittee decided at its meeting in Paris to reconsider these activities. A new Steering Committee has been formed, consisting of Drs. U. Oswaldsson, J.D. Schreiber, M. Lee, S. Raut and K. Mertens (chairman). This group proposed to develop a more systematic study design, if possible. The participants' views will be sought as to potential options to expand the program in a way that should allow for the identification of major sources of variablility. In the meantime the studies will be resumed and further developments will be discussed at the Subcommittee Meeting in 2003.

General discussion on concentrate issues

In the general discussion Dr. Kotitschke (Biotest, Germany) presented some data on a collaborative study that will start shortly. This study will focus on the use of prediluents in a standardized chromogenic assay. For this purpose various FVIII deficient plasmas will be compared in the assay of a variety of FVIII products. The main question is how much von Willebrand factor the FVIII deficient plasma should contain in order to be a suitable prediluent. Finding an equivalent to hemophilic plasma would facilitate following the SSC guidelines. Dr. Kotitschke mentioned that 4 additional labs can still join this interesting study.

Proposal to replace WHO plasma standard – A. Hubbard

Upon the establishment of the current 4th IS, the Subcommittee has expressed some concern on the low FVIII activity content of this material (0.57 IU/ml). Dr. Hubbard presented extensive stability data showing that this plasma displays a FVIII activity loss of < 0.1% per year. Thus, the 4th IS is fully appropriate to be used, together with fresh normal plasma, in the calibration of the next IS. A candidate 5th IS has already been filled, and preliminary estimates indicate that its FVIII activity is approx. 0.7 IU/ml. Recruitment of study participants has recently started, and Dr. Hubbard expects that results will be available at the Subcommittee Meeting in 2003.

FVIII unitage and in vivo recovery – K. Mertens

This report involved a pharmacokinetic analysis of two plasma-derived products in a bioequivalence study. The study was designed according to the SSC guidelines, including the recommended sampling scheme, and a cross-over design. Post-infusion patient samples were analysed in a rigorously standardized manner in one single lab using both 1-stage and chromogenic assays, employing plasma and product standards in parallel. FVIII levels expressed in plasma units were consistently higher than in concentrate units, the difference being 12%. Results of chromogenic and 1-stage assays were virtually identical, irrespective of whether plasma or the product was used as a standard. As expected, the unitage had no impact on determination of half-life, but did affect the AUC and Cmax values. For some batches there was a slight discrepancy between the label potency and the re-assayed potency according to the SSC recommended method. These discrepancies, though minor, were reflected by apparently different in vivo recoveries in the cross-over analysis. Although these discrepancies are minor and without any clinical relevance, this study illustrates the impact of label potency assignment for pharmacokinetic studies, particularly if the infused product is to be used as a reference for post-infusion FVIII assays.

An improved method for assaying FVIII following B domain-deleted FVIII infusion - C. Wiseman & J. Lusher

A comparison was run using freshly prepared or frozen ReFacto Laboratory Standard (RLS). It was shown that more consistent results were obtained with the frozen preparation. For instance, intra-assay CVs of 7.7% were obtained with the frozen RLS as compared to up to 10.8% with the freshly prepared RLS. An inter-assay CV of 6.5% was obtained with the frozen preparation, while 7.5% was observed with the freshly prepared RLS. In addition, using the frozen RLS (kept at –80°C) saved considerable time. The use of a frozen RLS could reduce the discrepancy between the one-stage coagulation and the chromogenic assay and is now planned to be used to evaluate plasma samples of patients under ReFacto infusion.

Standardization of FVIII assays in post-infusion plasma – T.W. Barrowcliffe

A few studies have assessed FVIII assay discrepancies in post-infusion samples. A comparison of results obtained from different centres showed CVs of up to 15% for the one-stage coagulation assay and up to 20% when the chromogenic assay was used. One confounding variable could be the use of either plasma or FVIII concentrate standards, which are shown not to be interchangeable. For instance, in a FXa generation assay, it is shown that FVIII concentrates increase the rate of FX activation as compared to plasma, while the reverse is true in a thrombin generation assay. Several draft recommendations were put forward for consideration. For pharmacokinetic studies, the product may be diluted in FVIII deficient plasma in order to serve as a standard that facilitates like-versus-like analysis. For monitoring treatment in clinical situations, plasma standards may be used for patients treated with plasma-derived products, and possibly also with full-length recombinant products. As also suggested by Drs. Ingerslev and Wiseman, product standards may be particularly useful for B-domain-deleted FVIII; however, final recommendations await further discussion of these options at the 2003 Subcommittee meeting.

UK NEQAS study of FVIII measurement: a 92 laboratory survey - E. Preston

The evaluation of FVIII:C varies greatly from one laboratory to the other. A number of factors can play a role in this variation: use of different reference plasma samples, calibration and standard curves, as well as the coagulometer to cite but a few such variables. A survey was organized in the UK involving 92 laboratories. A standard reference preparation of FVIII was sent to centres which were asked to run the assay as "field evaluation," namely, using their own reagents and methodology. Large variations were observed. CVs of up to 70% were obtained whenever stored reference samples were used, while CVs of 50% were seen with freshly prepared reference curves. A second survey involved the sending of three plasma samples containing different titres of FVIII to 81 centres in the UK. Again, large variations were observed  in FVIII with ± 30% of the laboratories giving results out of the normal variation range. In addition, the interpretation of the results show that in many cases laboratories do not comply with the the ISTH classification of haemophilia A patients as severe (less than 1% FVIII), mild (1 to 5%) or moderate (more than 5%). This misinterpretation of results adds further confusion to diagnosis and may possibly exert an influence upon treatment. The reasons why laboratories do not follow the recommendations of the ISTH subcommittee were discussed, as well as possible remedies to this situation.

Need for Bethesda assay standardization - A. Macartney & G. Savidge

Many variables can affect the titration of inhibitors in plasma samples. Two of such variables are the source of FVIII and the source of diluent for plasma samples. An assessment of Bethesda titre was carried out using different FVIII preparations, either recombinant (B-domain deleted (BDD) FVIII), or plasma-derived products. Significantly higher titres of inhibitors were obtained using the BDD FVIII in particular. Next, the question of the diluent was examined by comparing reagents obtained from different sources, i.e., plasma of severe haemophilia A patients or plasma artificially depleted in FVIII. It was shown that such diluents vary greatly in terms of content of von Willebrand factor (VWF), and remarkably also of residual FVIII antigen. The IL diluent which contained no detectable functional or antigenic VWF, and no FVIII antigen, gave the highest inhibitor titres using the BDD FVIII preparation. Addition of VWF significantly reduced the inhibitor titre in a dose-dependent manner. This suggests that BDD FVIII might be particularly suitable for the evaluation of inhibitor titres and that VWF may play a role in the detection assay for inhibitor. Further studies are required to understand the precise relationships between these parameters, including the specificity of inhibitor antibodies. The presenters recommended that the Subcommittee pursue the standardization of the Bethesda assay.

Standardization of inhibitor assays. - S. Kitchen

An NIBSC attempt at standardization of inhibitor assay was carried out by distributing two potential standards, each consisting of a human monoclonal anti-FVIII antibody, and one consisting of a polyclonal rabbit antibody against human FVIII. The two human antibodies were derived from the peripheral memory B cells of two haemophilia A patients with inhibitor. The rabbit antiserum was generated by repeated SC injections of human recombinant FVIII in adjuvant. Three plasma samples from patients with inhibitors were assayed. All three inhibitor samples were sent to 15 centres which were asked to run a standard Bethesda assay. Results demonstrated an intralaboratory variability of between 30 and 50% using each of the two human monoclonal antibody standards, regardless of whether the one-stage or chromogenic assay was used. The rabbit polyclonal antiserum resulted in decreased interlab variability of ± 25%.  The reasons for such variations were discussed and probably relate to the use of different reagents, such as dilution buffer. Dr. Kitchen asked for feedback as to whether a larger study should be launched using the polyclonal rabbit antibody inhibitor standard. If so, he asked for feedback as to the optimal titer for such material. The chair asked Dr. Kitchen to prepare a report containing background information accompanied by his specific questions. The chair will distribute this report to Subcommittee members for feedback in the next few months so that further study can be undertaken prior to the 2003 meeting.

Factor VIII Measurement: Is a New Paradigm Possible?-
Co-chairs: J. Ingerslev and J. Oldenburg

Dr. K. Mann summarised his work on models of coagulation by introducing the audience to the three principal substrates  and models  adopted in his lab: 1) purified systems, 2) whole blood, and 3)computerised simulation of coagulation. The series of events in coagulation  recorded through the quantification of  thrombin activation markers  (TAT complexes ) all occured before less than 5% of the clotting  reaction had taken place. Levels of anticoagulants  such as TFPI and AT modified the time-course of thrombin formation considerably. Dose titration, with the addition of exogenous  factor VIII to haemophilia A plasma, demonstrated a tendency toward  normalisation  of thrombin generation  with the addition of very small  amounts of F VIII. Early data suggested differences in TAT generation profiles  with the addition of similar cconcentrations of  different recombinant  clotting factor concentrates.  Dr. Mann postulated that, since the clotting response was the composite outcome of multiple genetic and environmental  factors, modeling could be used to tailor therapy to the needs of an individual  hemophilia patient and alter the current  practice of uniform global factor replacement strategies.

Dr. J. Ingerslev ,on behalf of his colleague B. Sørensen,  introduced their dynamic whole blood clotting method which is based based on thrombelastography  using a novel software system for the handling  of continuous  data during coagulation. Coagulation is activated by small amounts of TF. In this system severe haemophilia A and B patients  display  a severely diminished coagulation signal; however, heterogeneity is found among patients with less than 1% F VIII clotting activity,  some patients demonstrating minimal clot formation late in the process and others  showing  a much earlier signal  of coagulation of higher velocity . The incremental addition of small amounts of F VIII ranging from 0.5% to 5% of normal  plasma  concentration  dramatically improved  the coagulation profile to close to normal. Dr Ingerslev was asked  about  the longterm stability of clots formed in his assay at low FVIII concentrations . He did not have any data at present, but plans to study this question in the future.

Dr. T. Barrowcliffe reported on the results of a joint study from NIBSC and the Royal Free Hospital. The group studied thombin generation in F VIII deficient plasma, with and without the addition of varying amounts of F VIII concentrate. In general, this model was also sensitive to very low concentrations  of F VIII which were capable of generating large amounts of thrombin. The subsequent  addition of higher  factor VIII concentrations  primarily  influenced the time to thrombin generation rather than altering the maximum thrombin generation potential . The concentration of FIXA significantly  affected this assay.

Dr. A. Giles (Biomerieux), on behalf of Drs. Shima and Yoshioka, updated the Subcommittee on the use of waveform PTT analysis, including a summary of the published studies on hemophilic plasma using this technology. In principle, waveform analysis consists of extracting the photometer data from a clot-based PTT  and calculating the first and second derivatives of the signal. Using this technique, derived profiles of coagulation in haemophilia could be established. A large phenotypic variation in the second derivative was seen among severe (<1%) haemophilia plasmas.  Dose-response relationships were established using F VIII deficient plasma spiked to various theoretical levels.  A small study on the use of this method in the study of the hemostatic response in patients with hemophilia A and inhibitors was also presented. Dr. Giles concluded by saying that with the newest coagulation instruments one can obtain more information than with just an APTT or a PT. Although  he agreed that whole blood models of coagulation may prove to be more physiologic in the evaluation of hemostasis in hemophilia, both at baseline and after factor replacement, he believes that there is also a role for the waveform PTT technology in the assessment of the clotting response.

In conclusion, the different methods presented were all consistent in demonstrating that 1) severe haemophilia A plasmas display  a heterogeneous pattern of clot formation and thrombin generation; 2) clot  formation /thrombin generation is significantly improved by very small incremental increases in F VIII, with some clotting profiles returning to normal or near normal with the addition of less than 5% of factor VIII.  All methods demonstrate potential as possible alternative strategies  to the currently used plasma–based  assay methods. A workshop is planned prior to the next subcommittee meeting to coordinate the systematic study of these techniques. More data on their use in the evaluation of hemostasis in hemophilia is expected in 2003.

Factor VIII Dosing: Developing Future Strategies-
Co- Chairs: C. Lee and D.DiMichele

Report on the WHO/WFH workshop on the delivery of treatment in hemophilia - C. Lee

Dr. Lee reported on the proceedings from the joint WHO/WFH sponsored meeting held in London in February, 2002. The goal of this meeting was to identify the barriers to and development of strategies for extending hemophilia therapy to the developing world. Participants included Drs. C. Lee (UK), E. Berntorp ( pharmacokinetics)(Sweden) and S. Schulman(continuous infusion)(Sweden), K. Fischer (prophylaxis)(Netherlands),M. Escobar (historical data on dosing)(US) and D. DiMichele (immune tolerance dosing)(US), A. Chuansumrit (Thai strategies in health care delivery)(Thailand), A. Srivastava ( global needs and economics)( India), V. Boulyjenkov and J. Emmannuel (WHO) and Line Robbillard (WFH). Much discussion at the meeting focused on defining optimal and minimum effective dosing. The rationale for not necessarily  normalizing factor levels included 1) redundancy in the clotting cascade; 2) factor shortages;  and 3) national economics and heath care budget appropriations. The goal of therapy in the developing world  was discussed and suggested by Dr. Srivastava to be functionality, not perfect joint health.  Identified strategies for optimizing dosing included 1) individual pharmacokinetic analysis; 2) better assays for assessing hemostasis in vivo; 3) more frequent dosing; and 4) the concomitant use of antifibrinolytics. IT was determined not  to be an ethical use of clotting factor resources in the developing world. The identified barriers to optimizing therapy included 1)unavailability of PK variability  relative to ethnicity; 2)vial size limitations; and 3) limitations of factor delivery systems. Although  no formal recommendations were possible at this time, ongoing meetings  on this topic are planned and will be reported regularly to the ISTH as part of a coordinated project with the FVIII/IX Subcommitttee.

A dose-finding study in dogs using B-domainless FVIII- M. van den Berg

Although this study will proceed, it was unable to be initiated prior to this meeting. Dr van den Berg plans to present  preliminary  results at the 2003 Subcommittee  meeting.

Dose response in hemophilia: Orthopedic outcome in the developing world- A. Srivastava

Dr. Srivastava presented  his proposal for a study to be conducted in the developing world. The study proposes to document orthopedic  outcomes using existing factor replacement strategies currently practiced in the developing world.  The optimal orthopedic outcome identified  by this study was functional independence.  The goals of the study are 1) to document  orthopedic  outcome  on the various dosing regimens  used to treat children in a representative group of participating countries; and 2) to develop a cost effective model for treatment in the developing world. Eligibility criteria will include 1) severe (<1%) hemophilia; 2) age of 2-10 yrs. ( currently still being defined however); 3)no inhibitor; and 4) well documented care. An enrollment of 250-500 subjects  is expected with a 5 yr. follow-up period planned. Participating countries currently include 1) India, 2) Malaysia, 3) Singapore, 4) Iran, 5) Brazil, 6) Venezuela, 7) Thailand, and 8) South Africa. Dosing strategies among these countries vary from 50-500 u/kg/yr. Data to be collected include 1) clinical joint scores (to be standardized by distributing the CDC video), 2) radiologic joint scores ( Pettersson), and 3) functional independence scores (WeeFIM modification).  After some discussion, the subcommittee endorsed Dr Srivastava’s proposal. An update on the progress of this study will be presented  in 2003.

Proposed international survey of FVIII replacement in surgery- A. Srivastava

As a follow-up to data presented last year, Dr Srivastava reviewed the published literature on the data supporting the 1995 WHO/WFH  guidelines on factor support required for surgical peri- and post operative hemostasis.(Haemophilia, 1995 (suppl 8-13)). He found the data lacking and proposes to conduct an international survey to establish current practices relative to surgical morbidity and mortality, and to ultimately develop a consensus on acceptable outcomes and the dosing strategies needed to achieve these outcomes. The questionnaire will have two components: 

Component A: Current standards of practice with respect to a) factor dosing in surgery, b) use of CI vs bolus dosing, c) duration of factor replacement,  d) target factor levels for surgery and post-op period, e) frequency of factor level monitoring, and f) variation in practice relative to type of surgery being performed.

Component B: Outcome data using these practices.
He received input from the group with respect to monitoring thrombotic complications and inclusion of data on mild/carrier patients. He will modify the data collection tool and resubmit it to the Subcommittee for final comment prior to sending it out. He will seek external funding for data analysis. An update is expected in 2003.

International prophylaxis group- V. Blanchette

After a review of the published literature on prophylaxis, Dr. Blanchette reported on the activities of the newly established International Prophylaxis Group, the goals of which are 1) to acquire further data on the optimal delivery of prophylaxis; 2) to disseminate this information worldwide; and 3) to continue to define standards  for cost effective prophylactic factor dosing and outcome measurement.  Annual meetings  on specific topics are planned.  These topics will include 1) development of a unified MRI scoring system, 2) development of a unified clinical scoring system, 3) further development of QOL instruments  and studies . A Steering Committtee and Expert Advisory Group have been identified. The Hospital for Sick Children (HSC) in Toronto will function as the Study Coordinating Center. The group is funded through a multi-industry grant. Dr Blanchette will continue to report on the group’s activities to both this Subcommittee as well as to the Pediatric Subcommitttee of the WFH.

Dr DiMichele concluded the meeting.