Sensitization of CD4+ T Cells to Coagulation Factor VIII: Response in Congenital and Acquired Hemophilia Patients and in Healthy Subjects

Abstract

SummaryAntibodies (Ab) that inhibit factor VIII (fVIII) may develop in patients with hemophilia A and rarely in individuals without congenital fVIII deficiency (acquired hemophilia). Synthesis of fVIII inhibitors requires CD4+ T cells. We investigated the proliferative response of blood CD4+ cells from 11 patients with congenital or acquired hemophilia and 12 healthy subjects, to recombinant human fVIII, and to pools of overlapping synthetic peptides spanning the sequences of individual fVIII domains. All patients had CD4+ cells that responded to fVIII. The intensity of the responses fluctuated over time: several patients had brief periods when they did not respond to fVIII. All healthy subjects had transient CD4+ responses to fVIII, that were significantly lower than those of hemophilia patients. Also, healthy subjects responded to fVIII less frequently and for shorter periods than hemophilia patients. All patients and healthy subjects recognized several fVIII domains: the A3 domain was recognized most strongly and frequently. The transient sensitization of CD4+ cells to fVIII in healthy subjects suggests that inadequate tolerization of CD4+ cells to fVIII, due to lack of endogenous fVIII, is an important factor in the development of clinically significant anti-fVIII antibodies in hemophilia A.

CD4+ T-cell clones specific for wild-type factor VIII: a molecular mechanism responsible for a higher incidence of inhibitor formation in mild/moderate hemophilia A

“…13,14 The epitopes recognized by such T cells were located by incubating T cells with peptides overlapping the whole FVIII molecule. 14 In severe hemophilia A patients, FVIII-specific T cells recognizing a large array of peptides covering the entire FVIII molecule were detected. However, stimulation with FVIII peptides also identified FVIII-specific CD4 ϩ T cells in the blood of hemophilia A patients without inhibitor and in healthy individuals.…”

“…There was only a limited quantitative difference between healthy individuals and hemophilia A patients with or without inhibitor in proliferation of FVIIIspecific T cells. 14 Different hypotheses can be formulated to account for the limited difference reported between individuals with and without inhibitor with regard to FVIII-specific T cells. First, it is plausible that stimulation with peptides does not provide a full evaluation of the size of the T-cell population recognizing each individual peptide, which could lead to an underestimation of the number of FVIII-specific T cells in patients with inhibitor.…”

“…13 The epitopes recognized by such T cells were studied using synthetic peptides covering the entire FVIII molecule. 14 Epitopes were mapped in all domains of the FVIII molecule. Surprisingly, T cells proliferating in response to FVIII peptides were also identified in hemophilia A patients without inhibitor and in healthy individuals.…”

“…Only minor qualitative or quantitative differences were identified between FVIII-specific T cells from healthy individuals and from hemophilia A patients with or without inhibitor. 14 Thus, the cellular regulatory mechanisms behind the development of inhibitors to FVIII in some hemophilia A patients remain to be elucidated.…”

Anti-Erythropoietin Antibodies and Pure Red Cell Aplasia

“…Furthermore, they are mostly of the IgG4 isotype, they recognize conformational epitopes, and they have neutralizing activity. Interestingly, analyses of the T cell response in patients with anti-factor VIII antibodies could only show minor differences between factor VIII-specific T cells from healthy individuals and from hemophilia A patients with or without inhibitor (27). Furthermore, despite extensive studies, predisposing factors for the development of anti-factor VIII antibodies remain mostly unknown.…”