A study in the February 2009 issue of Molecular Therapy presented an innovative approach to gene therapy for hemophilia. The technique involves “hijacking” a particular gene and manipulating it to serve a new purpose. In this case, the gene responsible for the production of albumin (a water-soluble protein found in high concentration in plasma)—the most abundantly expressed gene in the liver--is changed to produce other important therapeutic proteins. One of those is factor VIII (FVIII), a clotting protein that is deficient or lacking in people with hemophilia A.
Vital to this technology are RNA (ribonucleic acid) molecules, which are subsequently “spliced” into the albumin gene. Then, instead of producing albumin, the gene directs the production of another much-needed therapeutic protein, such as FVIII and apolipoprotein A-I (apoA-I), the primary protein found in so-called “good cholesterol.” The procedure corrected hemophilia A in mice. Further, the spliced genes were only expressed in liver cells, not in other cells, so an immune response was not triggered.
“We instructed the liver to make more apoA-I protein than it normally does, and in separate experiments we instructed the liver to make the correct form of Factor VIII instead of a mutated form. We also added an RNA molecule that makes a monoclonal antibody that is not normally produced in liver,” said Gerard J. McGarrity, PhD, VIRxSYS Executive Vice President of Scientific and Clinical Affairs. “The work is at an early stage, but we are definitely teaching old genes some new tricks.”
The technique, called spliceosomal-mediated RNA trans-splicing (SMaRT™), has been patented by VIRxSYS Corporation, a Gaithersburg, MD-based biotechnology company specializing in gene therapy. The lead author of the study was Madaiah Puttaraju, PhD, of VIRxSYS. Some parts of the study were performed under a cooperative research and development agreement between VIRxSYS and the National Heart, Lung, and Blood Institute of the National Institutes of Health.
While the technique is still undergoing development, the results of these animal tests were encouraging enough that the company expects to begin human clinical trials in 2010.
Source: Wang J, Mansfield SG, Cote CA, et al. Trans-splicing Into Highly Abundant Albumin Transcripts for Production of Therapeutic Proteins in Vivo. Mol Therapy. 2009; 17(2):343-51.