Identification of T-cell epitopes in clotting factor IX and lack of tolerance in inbred mice

Abstract

Summary. Immune responses to the factor IX protein pose problems for hemophilia B patients who develop antibodies against factor IX and for potential future treatment with gene therapy. To better define the response to human factor IX, we analyzed T-cell responses to human factor IX in factor IX knockout mice on BALB/c and C57BL/6 (B6) backgrounds, both strains having CD4þ T cells that proliferate in response to human factor IX. Surprisingly, wild-type mice have similar factor IX-recognizing CD4þ T cells. We defined a dominant CD4þ epitope for each strain (CVETGVKITVVAGEH for BALB/c and LLELDEPLVLNSYVTPIC for B6) that was recognized by both factor IX knockout and wild-type mice. While human factor IX did not cross-react with the mouse homologs of these epitopes, immunization with peptides from murine factor IX stimulated proliferation in factor IX knockout mice and wild-type mice, demonstrating a failure to delete murine factor IX-specific T cells in normal mice.

Immune deviation by mucosal antigen administration suppresses gene-transfer–induced inhibitor formation to factor IX

“…A representative example is shown in Figure 1A. Splenocytes from hemophilia B mice on a C57BL/6 background proliferated upon stimulation with peptide 2A-58 (NKYNNHDIALLELDEPLV-LNS), which is consistent with data published by Greenwood et al, 25 who identified immunodominant CD4 ϩ T-cell epitopes for hF.IX in C57BL/6 and BALB/c mice. Combined data from our study and the Greenwood et al 25 study show that peptides containing immunodominant CD4 ϩ T-cell epitopes in C57BL/6 (H-2 b ), BALB/c (H-2 d ), and C3H/HeJ (H-2 k ) mice are clustered in a sequence of hF.IX that is part of the catalytic domain of the serine protease ( Figure 1B).…”

Factor IX variants improve gene therapy efficacy for hemophilia B

“…44 These 3 residues are located outside the F.IX regions recently recognized containing T-cell epitopes in mice of distinct strains immunized to human F.IX. 45 Together these data suggested that it is unlikely that these changes in F.IX amino acid are located in highly immunogenic regions. Since all 3 residues that were substituted in these studies are conserved in the canine F.IX, further experiments in outbred large-animal models of hemophilia B are warranted to determine the risk of antibody to each F.IX variant.…”

Correction of factor IX deficiency in mice by embryonic stem cells differentiated in vitro

“…Second, when injected into the liver parenchyma, PEPs are able to engraft robustly and restore wild-type hepatocellular function in F-IX-deficient mice. F-IX-deficient mice (18,19) have a phenotype that is similar to hemophilia B in humans, characterized by a severe bleeding diathesis caused by absence of F-IX protein (20,21). F-IX has a short half-life requiring continuous replacement, and, consequently, any substantial production of mouse F-IX in the deficient mice indicates hepatocyte function derived from the engrafted PEPs.…”