Hemophilia A is a genetic disorder characterized by a deficient factor VIII (FVIII) activity. Among patients receiving FVIII replacement therapy, a significant number develop antibodies inhibiting FVIII procoagulant activity (called inhibitors). Development of inhibitors severely complicates the course of the disease, dramatically decreasing the efficacy of FVIII replacement therapy. The problem of inhibitors is one of the most complex in hemophilia A treatment, because a great variety of inhibitors directed against different epitopes in the FVIII molecule is found in individual patients. At present, there is no effective solution for this problem, and any developments in this area are greatly appreciated by clinicians.
The novel study by Villard and colleagues in this issue (page 949) appears promising, as it demonstrates that peptide surrogates, mimicking epitopes recognized by inhibitors, may block their inhibitory activity, thereby allowing restoration of a normal procoagulant activity of FVIII. To prove their concept, Villard et al used the human monoclonal inhibitory antibody Bo2C11 specific for the C2 domain of FVIII as a model for inhibitors. The authors showed that selected dodecapeptides neutralized the Bo2C11 inhibitory activity in the functional test. Moreover, these peptides were efficient in preventing inhibition of FVIII activity by Bo2C11 in a murine FVIII-knockout model of hemophilia A, suggesting that peptide decoys may also be used in vivo. Remarkably, the phage display technology used by the authors allowed selection of peptides that lack sequence homology with FVIII and therefore do not interfere with FVIII function.
But a number of issues should be addressed in order to evaluate the potential of peptide decoys for hemophilia A treatment: peptide half-life in vivo should be improved; the polyclonal nature of inhibitors and differences in inhibitors spectra among patients require designing mixtures of peptides which mimic different FVIII epitopes. In summary, the study of Villard et al outlines a novel approach to the solution of inhibitor problems in hemophilia A.
