2003; baxter - Supplements - Haematologica

[Round Table on Immune Tolerance Treatment]review paperAntibody reactivity to factorVIIa may impede the effect ofby-passing agents in patientswith hemophilia Bhaematologica 2003; 88(suppl. n. 12):29-33http://www.haematologica.org/free/immunotolerance2001.pdfJAN ASTERMARK, ERIK BERNTORPDepartment for Coagulation Disorders, University of Lund,Malmö, SwedenWe studied patients with hemophilia B and highrespondingfactor IX inhibitors to detect possiblecross-reactivity with other vitamin K-dependent procoagulantfactors due to the structural similarity ofthe proteins. The aim was to explain why the hemostaticeffect of by-passing agents such as activatedprothrombin complex concentrates (aPCC) andrecombinant factor VIIa is inadequate in somepatients. Immunoglobulins (Igs) from three patientswere separately purified on protein A sepharose andthen subjected to immunoaffinity chromatographyon factor IX- and factor VIIa sepharose. All three Igfractions, but not commercially available Ig, containedantibodies that bound to both gels. The Igfractions and the immunoaffinity purified anti-factorIX and VIIa antibodies inhibited thrombin formationin a plasma system using Feiba‚ (12 mU/mL) asactive enzyme, but had little effect in the presenceof NovoSeven‚ (18 U/mL). Minor inhibition of factorXa formation also occurred in a system containingpurified proteins. The divergent effect of the twoproducts may be due to the availability of varyingamounts of factor VIIa for neutralization by the antibodies.Our findings are of unknown clinical significancebut may suggest characterization of the antibodyprofile of individual inhibitor patients to optimizethe type and dose of the agent used to treatsevere bleeds.©2003, Ferrata Storti FoundationKey words: hemophilia B, inhibitors, antibodies,by-passing agents, factor VIIa.Correspondence: Jan Astermark, M.D. Ph.D., Department forCoagulation Disorders, University Hospital, SE-205 02 Malmö,Sweden. Phone: international +46.40.332392. Fax: international+46.40.336255. E-mail:jan.astermark@medforsk.mas.lu.seDevelopment of inhibitory antibodies inpatients with hemophilia still representsa major challenge in regard to both eradicationof the inhibitor and treatment of bleedingepisodes. 1,2 In the case of major bleeds, bypassingagents such as activated prothrombincomplex concentrates (e.g. Feiba ® ‚ and Autoplex® , Baxter) or recombinant factor VIIa(NovoSeven‚ ® Novo-Nordisk) are needed andboth agents seem to be effective in 80-90% of allhemorrhages in inhibitor patients. However,some patients still do not achieve an adequatehemostatic response. 3-7 The reason for this is notyet known.Factor IX is structurally very similar to the othervitamin K-dependent procoagulant factors i.e.factor VII, factor X and prothrombin. 8 In addition,inhibitory antibodies that may develop inpatients with hemophilia in response to giventreatment are known to be synthesized by differentclones. Thus, from a structural point ofview, it would not be surprising if antibodiesagainst factor IX in patients with hemophilia Bwere to cross-react with one or more of the othervitamin K-dependent coagulation factors andthereby to some extent possess the capacity toreduce the hemostatic effect of factor VIIaand/or activated prothrombin complex concentrates(aPCCs). We conducted an investigationto ascertain whether Ig fractions from hemophiliaB patients with high-responding factor IXinhibitors exhibit antibody reactivity to other vitaminK-dependent proteins including factorVIIa. We also evaluated the effect of these antibodieson the formation of factor Xa and thrombinin vitro before and after immunoaffinitychromatography.Materials and MethodsMaterialsRecombinant factor VIIa (NovoSeven ® ) wasfrom Novo Nordisk A/S. Recombinant albuminfreefactor VIII was kindly provided by Dr. V. Foster,Baxter, and BeneFIX ® and Feiba ® were purchasedfrom the same company. Purified recombinantfactor VIIa was a generous gift from Dr.Persson, Novo Nordisk A/S. Intravenous immu-haematologica vol. 88(supplement n. 12):september 2003