With respect to the targeting of HSCs, recombinant retroviral vectors, and most recently lentiviral vectors, have been the system of choice for proof-of-concept studies in a variety of animal models

With respect to the targeting of HSCs, recombinant retroviral vectors, and most recently lentiviral vectors, have been the system of choice for proof-of-concept studies in a variety of animal models. In addition to recombinant retroviral vectors, other nonviral technologies are being investigated for genetic modification of HSCs. transfer into HSCs, ii) Clasto-Lactacystin b-lactone optimization of the coagulation factor VIII transgene for high expression, iii) minimization of conditioning regimen-related toxicity with HSC engraftment and iv) overcoming complications due to pre-existing factor VIII immunity. Herein, we review the state of the art in HSC transplantation gene therapy of hemophilia A. == Clinical Gene Therapy of Hemophilia A == Loss of circulating factor VIII (fVIII) activity due to mutations Clasto-Lactacystin b-lactone within the fVIII gene results in the X-linked, recessive bleeding disorder hemophilia A. The clinical presentation is usually a moderate to severe bleeding phenotype that correlates with the patient’s residual plasma fVIII activity level. Hemophilia A has been targeted by numerous academic and commercial entities as a primary candidate for gene transfer-based therapies for several reasons. First, modest increases in fVIII levels ( 1% of normal levels) can alleviate spontaneous bleeding episodes. Second, many different cell types are capable Clasto-Lactacystin b-lactone of synthesizing functional fVIII protein and virtually any tissue or cell type with access to the bloodstream can be targeted for gene transfer. Third, gene therapy should be more economical and less invasive than protein alternative therapy given that it would consist of limited (possibly only one) treatment events. There have been 3 phase 1 clinical trials of gene therapy for hemophilia A conducted to date and each employed a different gene-transfer strategy (for review see Doering and Spencer, 2010 [1]). The first trial, sponsored by Transkaryotic Therapies, Inc., involvedex vivogene modification of autologous dermal fibroblasts and transplantation into the greater or smaller omentum of twelve male patients [2]. Although no severe adverse events were observed in this trial, designed to assess safety, sustained fVIII levels above 1% of normal were not achieved. In a second study, sponsored Rabbit Polyclonal to CD91 by Chiron Corporation, retroviral particles made up of a human B-domain deleted (BDD) fVIII transgene were introduced into thirteen male hemophilia A patients via peripheral vein infusion [3]. Again, fVIII levels above 1% of normal were not maintained and the trial was halted. The third trial, sponsored by GenStar Therapeutics, Inc., consisted of a single patient being infused with high-capacity adenoviral particles made up of the full-length human fVIII cDNA. Following administration of viral vector, the patient designed transient chills, fever, back pain, and headaches preceding the onset of thrombocytopenia and transaminitis. This patient did achieve fVIII levels >1% of normal that were maintained for several months, but as predicted based on the non-integrating property of adenoviruses, the fVIII activity eventually declined. The trial was halted due to the significant side effects observed. In summary, not only have there been no milestones of success in previous trials, to our knowledge, there are no approved or ongoing clinical trials utilizing gene transfer to treat hemophilia A. == Clinical Hematopoietic Stem Cell (HSC) Therapy == Hematopoietic stem cells first were discovered in the late 1940’s as a result of the finding that spleen cells could safeguard mice from Clasto-Lactacystin b-lactone exposure to lethal doses of radiation [4,5]. A comprehensive review of the history of HSC transplantation (HSCT) has been documented by E. D. Tomas, recipient of the Nobel Prize in Physiology or Medicine in 1990 for his pioneering work in this field [6]. Subsequently, HSCs have been implemented in the treatment of several genetic and acquired diseases including leukemia, non-Hodgkin’s lymphoma, aplastic anemia, and sickle-cell disease. Annually, more than 20,000 clinical HSCTs are performed. The ability of HSCs to reconstitute all cellular hematopoietic lineages, including myeloid, lymphoid, and erythroid populations through a combination of self-renewal and cellular differentiation endows them with unique clinical power. Engrafted HSCs are capable of contributing to hematopoiesis for the duration of the.