Reduction of the immune response to factor VIII mediated through tolerogenic factor VIII presentation by immature dendritic cells

Summary. Background: The development of neutralizing antibodies to factor FVIII (FVIII) represents the most serious complication in the treatment of hemophilia A. Objective: We have explored the potential of using immature dendritic cells (iDCs) to present FVIII in a tolerogenic manner to T cells. Methods: The iDCs were isolated from hemophilic murine bone marrow and pulsed with canine cFVIII (cFVIII-iDCs) in the presence or absence of the NFκB pathway blocking compound Andrographolide (Andro-cFVIII-iDCs). Three weekly intravenous infusions of one million cFVIII pulsed-iDCs were administered to a group of five hemophilic Balb/c mice. Anti-FVIII antibody levels were monitored by functional Bethesda assay after four weekly intravenous challenges with 2 IU of cFVIII. Results: We have shown that cFVIII in the presence or absence of Andro is efficiently taken up by iDCs and that this process does not result in the maturation of DCs or the activation of co-cultured T cells. Following repeated infusion of the cFVIII-iDCs and Andro-cFVIII-iDCs into hemophilic mice, which were subsequently challenged with cFVIII, long-term reductions of FVIII inhibitors of 25% and 40%, respectively, were documented. Studies of cytokine release and T-cell phenotypes indicate that the mechanisms responsible for reducing immunologic responsiveness to cFVIII appear to involve an expansion of Foxp3 T regulatory cells in the case of cFVIII-iDC infusion and the elaboration of the immunosuppressive cytokines IL-10 and TGF-β following andrographolide-treated cFVIII-iDCs. Conclusions: This study shows that tolerogenic presentation of cFVIII to the immune system can significantly reduce immunogenicity of the protein.