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T‐cell responses in two unrelated hemophilia A inhibitor subjects include an epitope at the factor VIII R593C missense site
Author(s) -
JAMES E. A.,
VAN HAREN S. D.,
ETTINGER R. A.,
FIJNVANDRAAT K.,
LIBERMAN J. A.,
KWOK W. W.,
VOORBERG J.,
PRATT K. P.
Publication year - 2011
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/j.1538-7836.2011.04202.x
Subject(s) - missense mutation , epitope , medicine , chemistry , immunology , mutation , antibody , biochemistry , gene
Summary. Background: Development of neutralizing anti‐factor (F)VIII antibodies (‘inhibitors’) is a serious clinical problem in hemophilia A. Increased inhibitor risk has been associated with certain FVIII missense substitutions, including R593C in the A2 domain. Objectives: The aim of the present study was to identify T‐cell epitopes in FVIII and characterize T‐cell responses in two unrelated hemophilia A subjects sharing F8‐R593C and HLA‐DRB1*1101 genotypes. We hypothesized that the hemophilic substitution site coincides with an important T‐cell epitope. Patients/methods: The binding affinities of peptides for recombinant HLA‐DR proteins were measured and compared with epitope prediction results. CD4+ T cells were stimulated using peptides and stained with fluorescent, peptide‐loaded tetramers. Results: The inhibitor subjects, but not HLA‐matched controls, had high‐avidity HLA‐DRB1*1101‐restricted T‐cell responses against FVIII 589–608 , which contains the hemophilic missense site. Antigen‐specific T cells secreted Th1 and Th2 cytokines and proliferated in response to FVIII and FVIII 592–603 . FVIII 589–608 bound with physiologically relevant (micromolar) IC 50 values to recombinant DR0101, DR1101 and DR1501 proteins. Conclusions: Hemophilia A patients with R593C missense substitutions and these HLA haplotypes had an increased incidence of inhibitors in our cohorts, supporting a paradigm in which presentation of FVIII epitopes containing the wild‐type R593 influences inhibitor risk in this hemophilia A sub‐population.