Current efforts to improve FVIII products focus on the extension of half-life by chemical and/or molecular modifications of the protein. However, any modification of FVIII might induce neo-epitopes that could be associated with an increase in immunogenicity of the modified FVIII. To test AZD9291 mouse for neo-epitope formation in modified FVIII, we have developed a new mouse model for HA that carries the human FVIII cDNA as
a transgene [10]. Human FVIII transgenic mice are immunologically tolerant to native human FVIII and respond with a vigorous immune response to unrelated proteins. Currently, we are testing the hypothesis that modifications of human FVIII that induce neo-epitopes cause anti-FVIII antibody formation in the new transgenic mouse model. Almost all studies addressing this issue have utilized the intravenous infusion of recombinant human FVIII into HA mice. Thus, while the inbred nature of the mouse strains removes the complexity of the genetic background in human populations, the immune response is to a xenoprotein. This has implications with regard to antigen presentation that are addressed in the companion report detailed earlier. After repeated IV infusions of FVIII, most, if not all, haemophilic mice will develop antibodies to FVIII [26]. This contrasts with the ∼25% incidence of inhibitor development seen in human
haemophiliacs. Over the past few years, a variety of approaches has been used for inducing tolerance to FVIII in Cetuximab manufacturer haemophilic mice. These strategies have included attempts to induce Ruxolitinib price both central and peripheral tolerance mechanisms (Table 2). Central tolerance, the deletion of high-affinity FVIII-specific T cells and the generation of FVIII-specific regulatory T
cells, has been achieved by the intrathymic injection of FVIII in neonatal mice [27]. In addition, the intravenous delivery to neonates of retroviral and lentiviral vectors expressing FVIII has also been shown to result in tolerance [28,29]. Interestingly, these studies, both of which used transgenes regulated by liver-specific promoters, came to contrasting conclusions with regard to the levels of FVIII required to mediate tolerance in these very young animals. After the IV infusion of FVIII, the protein is endocytosed and processed by APCs in the spleen. The optimal presentation of FVIII peptides by cognate MHC class II receptors to FVIII-specific T cells requires the participation of pairs of co-stimulatory molecules on APCs and T cells (e.g. CD80/86-CD28, CD40-CD40L) to generate activating signalling cascades within the CD4+ T cells. Blockade of these co-stimulatory interactions results in a tolerogenic response to FVIII, presumably through the generation of functionally incompetent, anergic T cells.