Ligand Mediated Targeting of FVIII Inhibitor Specific Primary B Cells Via Surface Immunoglobulin.

Hemophilia A is an X-linked bleeding disorder. Mutations in the Factor VIII (FVIII) gene result in reduced or non-functional expression of FVIII. In hemophilia A recombinant (rFVIII) or plasma derived (pdFVIII) preparations are substituted to restore coagulation activity. However, a major problem of current treatment in hemophilia A is the development of an antibody response (inhibitors) to FVIIII. Various Immune Tolerance Therapies (ITTs) are being applied to overcome the FVIII specific immune response. In this study, phage displayed random peptide libraries were screened with various patients’ plasma samples. We recently reported about the identification of a conformational epitope in the A2 subunit of FVIII. Phages as well as corresponding synthetic peptides specifically block inhibitor binding and crossreact with heterologous plasma. Peptide ligands specifically stained primary B cells (CD19+/CD27+ double positive cells) of the inhibitor patient, but not of a healthy control by FACS analysis. To increase the potential of small synthetic peptide ligands as tools for the development of novel inhibitor elimination strategies, the peptide was expressed in a multimeric form in an eukaryotic expression system. In multimeric form the peptide ligand is highly stable and reveals better inhibitor blocking capacities than the synthetic peptide we sowed before. The multimer now serves as basis for the construction of LECs (Ligand Effector Conjugates) for the specific targeting and destruction of inhibitor specific B cells.