Production of functional coagulation factor VIII from iPSCs using a lentiviral vector

New approaches to gene and cell therapy for hemophilia

Hemophilia is considered suitable for gene therapy because it is caused by a single gene abnormality, and therapeutic coagulation factor levels may vary across a broad range. Recent success of hemophilia B gene therapy with an adeno-associated virus (AAV) vector in a clinical trial showed the real prospect that, through gene therapy, a cure for hemophilia may become a reality. However, AAV-mediated gene therapy is not applicable to patients with hemophilia A at present, and neutralizing antibodies against AAV reduce the efficacy of AAV-mediated strategies. Because patients that benefit from AAV treatment (hemophilia B without neutralizing antibodies) are estimated to represent only 15% of total patients with hemophilia, the development of basic technologies for hemophilia A and those that result in higher therapeutic effects are critical. In this review, we present an outline of gene therapy methods for hemophilia, including the transition of technical developments thus far and our novel techniques.

Gene therapy for hemophilia

Hemophilia is an X-linked inherited bleeding disorder consisting of two classifications, hemophilia A and hemophilia B, depending on the underlying mutation. Although the disease is currently treatable with intravenous delivery of replacement recombinant clotting factor, this approach represents a significant cost both monetarily and in terms of quality of life. Gene therapy is an attractive alternative approach to the treatment of hemophilia that would ideally provide life-long correction of clotting activity with a single injection. In this review, we will discuss the multitude of approaches that have been explored for the treatment of both hemophilia A and B, including both in vivo and ex vivo approaches with viral and nonviral delivery vectors.

Replacing bad (F)actors: hemophilia

Hemophilia A and B are bleeding disorders that result from functional deficiencies in specific circulating blood clotting factors termed factor VIII (FVIII) and factor IX (FIX), respectively, and collectively display an incidence of 1 in 4000 male births. Stem cell transplantation therapies hold the promise of providing a cure for hemophilia, but currently available transplantable stem cell products do not confer endogenous FIX or FVIII biosynthesis. For this reason, stem cell-based approaches for hemophilia have focused primarily on genetic engineering of pluripotent or multipotent stem cells. While pluripotent stem cells have been branded with high expectation and promise, they remain poorly characterized in terms of clinical utility and safety. In contrast, adult-lineage-restricted stem cells are established agents in the clinical armamentarium. Of the clinically established stem cell types, hematopoietic stem cells (HSCs) are the most utilized and represent the standard of care for several genetic and acquired diseases. Furthermore, HSCs are ideal cellular vehicles for gene therapy applications because they self-renew, repopulate the entire blood lineage while concurrently amplifying the transgene copy number >10(6) fold, and also have direct access to the bloodstream. Current research on HSC transplantation gene therapy approaches for hemophilia A and B is focused on the following: (1) identification of safe and efficient methods of nucleic acid transfer, (2) optimization of transgene product expression, (3) minimization of conditioning-regimen-related toxicity while maintaining HSC engraftment, and (4) overcoming preexisting immunity. Based on the existing data and current rate of progress, clinical trials of HSC transplantation gene therapy for hemophilia are predicted to begin in the coming years.