CD4+ T-cell epitopes associated with antibody responses after intravenously and subcutaneously applied human FVIII in humanized hemophilic E17 HLA-DRB1*1501 mice

Abstract

Today it is generally accepted that B cells require cognate interactions with CD4 IntroductionThe most serious complication in replacement therapy with FVIII products is the development of neutralizing antibodies against FVIII (FVIII inhibitors), which is observed in approximately 25% to 30% of patients with severe hemophilia A. 1 Although several genetic 2 and nongenetic 3 factors that contribute to the risk for patients to develop these antibodies have been identified, why some patients develop antibodies while others do not remains largely unknown.Today it is generally accepted that B cells require cognate interactions with CD4 ϩ T cells to develop high-affinity antibodies against protein antigens. 4,5 In line with this perception, several lines of evidence have supported the involvement of CD4 ϩ T cells in the generation of antibody responses against FVIII in patients with hemophilia A and in murine hemophilia models. 6,7 CD4 ϩ T cells express T-cell receptors that recognize antigen-derived peptides (CD4 ϩ T-cell epitopes) presented by MHC class II molecules, which are expressed on specialized antigen-presenting cells. 8 Structural features of both the MHC class II molecule and the peptide determine the specificity of CD4 ϩ T cells that can bind to the MHC class II-peptide complex. 8,9 The conditions under which CD4 ϩ T cells interact with this complex determine whether the immune system reacts with nonresponsiveness, is activated to develop specific antibodies, or is tolerized to suppress antibody responses. 9,10 Therefore, it is crucial to understand which FVIII peptides are presented by MHC class II complexes under conditions of FVIII replacement therapy and how CD4 ϩ T cells interact with MHC class II-FVIII peptide complexes expressed by antigenpresenting cells. The available information on FVIII peptides presented in the context of specific human MHC class II molecules is limited. Several studies used peripheral blood cells of patients and healthy controls 11 to identify CD4 ϩ T-cell epitopes in the A2 domain, 12 A3 domain, 13 and C2 domain of FVIII. 14 However, these studies lack information on the specific MHC class II molecules associated with the FVIII peptides identified. Jacquemin et al identified T-cell epitopes of FVIII using CD4 ϩ T-cell clones isolated from a mild hemophilia A patient carrying an Arg2150His mutation in the C1 domain of FVIII. 15 All clones recognized FVIII peptides encompassing residue Arg2150. Peptides were presented by HLA-DRB1*0401/HLA-DRB4*01 or HLA-DRDRB1*1501/ HLA-DRB5*0101. One of the peptides identified was a promiscuous epitope that bound to several different HLA-DR proteins. James et al used MHC class II tetramers to analyze FVIII-specific CD4 ϩ T cells obtained from a mild hemophilia A patient carrying an Ala2201Pro mutation in the C2 domain of FVIII. 16 Responses of CD4 ϩ T cells to sequences containing Ala2201 (wild-type), Pro2201 (hemophilic), and other predicted T-cell epitopes were evaluated and resulted in the identification of an HLA-DRB1*0101 restricted T-ce...

von Willebrand factor binds to the surface of dendritic cells and modulates peptide presentation of factor VIII

“…Interestingly, this peptide is presented by multiple MHC class II alleles 9,10 and has also been described as a functional T-cell epitope in humanized E17 HLA-DRB1*1501 mice. 39 These observations raise the possibility that VWF modulates CD4 + Tcell responses by affecting FVIII peptide presentation by antigen-presenting cells. The potential modulating effect of VWF on FVIII immunogenicity has been the subject of intense discussion.…”

A major determinant of the immunogenicity of factor VIII in a murine model is independent of its procoagulant function

“…44 Although it has been difficult to identify T-cell epitopes that are clearly associated with fVIII inhibitor formation, Steinitz et al recently identified 8 dominant T-cell epitopes associated with antibody production in a humanized MHC class II murine hemophilia A model. 45 Studies with model small immunogens indicate that nearly the entire surface of a protein is potentially antigenic. 46 Consistent with this, analysis of B-cell epitopes in the C2 domain after immunization of fVIII Ϫ/Ϫ mice with fVIII found a continuous spectrum of overlapping epitopes.…”

T cells from hemophilia A subjects recognize the same HLA-restricted FVIII epitope with a narrow TCR repertoire

“…Finally, Steinitz et al performed comprehensive T-cell epitope mapping using humanized HLA-DRA*01-DRB1*15:01 transgenic HA mice, identifying 8 HLA-DRA*01-DRB1*15:01-restricted epitopes in FVIII. 27 MHCII tetramer-guided epitope mapping (TGEM) has proved useful in mapping HLA-restricted T-cell epitopes. [28][29][30] FVIII-specific T cells have been cloned from tetramer-positive cells and by limiting dilution, 31 providing definitive evidence of antigen specificity.…”