To date, the gene therapy approaches for either FVIII or FIX have directed protein synthesis to various somatic cells [34,35]. These approaches have targeted the ultimate replacement of FVIII or FIX in plasma where FVIII and IX normally carry out their support in haemostasis but do not become activated until vascular injury perturbs the need for activation of haemostasis locally.

These approaches are intended for those patients who do not have inhibitory antibodies. In some cases, the development of inhibitory antibody may reduce the Tanespimycin research buy number of cells producing FVIII or IX. A recent new strategy has been developed by two research groups – one under the direction of Morty Poncz at Children’s Hospital of Philadelphia, and three research groups in Milwaukee at the Blood Research institute under the direction of Qizhen Shi and Bob Montgomery and at the

Medical College of Wisconsin under the direction of David Wilcox. The Philadelphia group uses the GPIbα-promoter with FVIII, and the Milwaukee groups use the αIIb-promoter with both FVIII and FIX. Most of this discussion will be focused on the studies in Milwaukee. Ever since the discovery that FVIII and von Willebrand factor (VWF) are two separate proteins that circulate in blood as a non-covalent complex, there have been studies to characterize the importance of this relationship. As both FVIII and VWF are released in parallel after DDAVP, we explored the DDAVP response in severe haemophilia and severe von Willebrand’s disease after replacement Oxalosuccinic acid therapy and found that

the DDAVP releasable pool of FVIII Erlotinib was dependent on both VWF and FVIII being synthesized in vivo [36]. Studies then demonstrated that if FVIII was expressed in an endothelial cell or a megakaryocyte, the FVIII was stored together with VWF in the Weibel-Palade body and α-granule respectively [27,37,38]. This brought up the feasibility of using platelet-directed expression of FVIII as a means of gene therapy for haemophilia A. Transgenic mice and bone marrow transduced with the FVIII cDNA under the control of the platelet αIIb-promoter resulted in platelets with FVIII co-localized with VWF in platelet α-granules. Not only was this approach effective for cessation of bleeding in the FVIII KO mouse, but this approach was also effective even in the presence of high titre inhibitory antibodies to FVIII [27]. Furthermore, bone marrow transduced with a lentiviral 2bF8-construct conferred the same protection as the transgenic approach [39], and the presence of inhibitory antibodies did not preclude the engraftment and subsequent efficacy of 2bF8-lentiviral transduced HSC [40]. Using double KO mice with neither FVIII nor VWF, FVIII storage and release were present in the platelet from both mice, but the amount of stored FVIII was significantly increased in the presence of VWF.