title: Changes in the amino acid sequence of the recombinant human factor VIIa analog, vatreptacog alfa, are associated with clinical immunogenicity.
abstract: BACKGROUND
  Vatreptacog alfa, a recombinant human factor VIIa (rFVIIa) analog developed to improve the treatment of bleeds in hemophilia patients with inhibitors, differs from native FVIIa by three amino acid substitutions. In a randomized, double-blind, crossover, confirmatory phase III trial (adept(™) 2), 8/72 (11%) hemophilia A or B patients with inhibitors treated for acute bleeds developed anti-drug antibodies (ADAs) to vatreptacog alfa.
  
  
  OBJECTIVE
  To characterize the formation of anti-vatreptacog alfa ADAs in hemophilia patients with inhibitors.
  
  
  METHODS
  This was a post hoc analysis of adept(™) 2. Immunoglobulin isotype determination, specificity analysis of rFVIIa cross-reactive antibodies, epitope mapping of rFVIIa single mutant analogs and pharmacokinetic (PK) profiling were performed to characterize the ADAs.
  
  
  RESULTS
  Immunoglobulin isotyping indicated that the ADAs were of the immunoglobulin G subtype. In epitope mapping, none of the rFVIIa single mutant analogs (V158D, E296V or M298Q) contained the complete antibody epitope, confirming that the antibodies were specific for vatreptacog alfa. In two patients, for whom PK profiling was performed both before and after the development of ADAs, vatreptacog alfa showed a prolonged elimination phase following ADA development. During the follow-up evaluation, the rFVIIa cross-reactivity disappeared after the last vatreptacog alfa exposure, despite continued exposure to rFVIIa as part of standard care.
  
  
  CONCLUSIONS
  Results from the vatreptacog alfa phase III trial demonstrate that the specific changes made, albeit relatively small, to the FVIIa molecule alter its clinical immunogenicity.
authors.affiliation: Haemophilia Comprehensive Care Centre, Faculty of Health Sciences, University of the Witwatersrand and National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: J N
authors.initials: JN
authors.lastname: Mahlangu
authors.affiliation: Novo Nordisk A/S, Bagsvaerd, Denmark.
authors.forename: K N
authors.initials: KN
authors.lastname: Weldingh
authors.affiliation: Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA, USA.
authors.forename: S R
authors.initials: SR
authors.lastname: Lentz
authors.affiliation: Maimonides Medical Centre, New York, NY, USA.
authors.forename: S
authors.initials: S
authors.lastname: Kaicker
authors.affiliation: Haemophilia Centre, National Blood Centre, Kuala Lumpur, Malaysia.
authors.forename: F A
authors.initials: FA
authors.lastname: Karim
authors.affiliation: Department of Transfusion Medicine, Nagoya University Hospital, Nagoya, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Matsushita
authors.affiliation: Hemophilia Center, Oregon Health and Science University, Portland, OR, USA.
authors.forename: M
authors.initials: M
authors.lastname: Recht
authors.affiliation: Department of Hematooncology and Bone Marrow Transplantation, Medical University of Lublin, Lublin, Poland.
authors.forename: W
authors.initials: W
authors.lastname: Tomczak
authors.affiliation: Department of Disorders of Haemostasis and Internal Medicine, Institute of Hematology and Transfusion Medicine, Warsaw, Poland.
authors.forename: J
authors.initials: J
authors.lastname: Windyga
authors.affiliation: Novo Nordisk A/S, Bagsvaerd, Denmark.
authors.forename: S
authors.initials: S
authors.lastname: Ehrenforth
authors.affiliation: Novo Nordisk A/S, Bagsvaerd, Denmark.
authors.forename: K
authors.initials: K
authors.lastname: Knobe
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000918:Antibody Specificity; D000937:Antigen-Antibody Reactions; D003429:Cross Reactions; D000939:Epitopes / Q000737:chemistry / Q000276:immunology; D015942:Factor VIIa / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000493:pharmacokinetics; D006681:HLA-D Antigens / Q000032:analysis / Q000235:genetics; D006467:Hemophilia A / Q000097:blood; D006470:Hemorrhage / Q000188:drug therapy / Q000209:etiology; D006801:Humans; D007074:Immunoglobulin G / Q000096:biosynthesis / Q000276:immunology; D007518:Isoantibodies / Q000096:biosynthesis* / Q000276:immunology; D009500:Neutralization Tests; D017434:Protein Structure, Tertiary / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000493:pharmacokinetics; D013329:Structure-Activity Relationship
chemical_list: D000939:Epitopes; D006681:HLA-D Antigens; D007074:Immunoglobulin G; D007518:Isoantibodies; D011994:Recombinant Proteins; C000596433:vatreptacog alfa; D015942:Factor VIIa
keywords: antibodies; antibody formation; hemophilia; immunoglobulin isotypes; recombinant factor VIIa; vatreptacog alfa