Mutations Boost Bioavailability Of Factor IX Gene Therapy

NEW YORK (Reuters Health) - Injecting mice with a variant version of the factor IX (FIX) gene results in a two- to five-fold increase in circulating levels of the factor compared with those resulting from the wild-type gene, according to researchers at the Children's Hospital of Philadelphia.

Human studies have shown gene therapy for hemophilia with wild-type FIX is safe, but results in subtherapeutic circulating levels of the clotting factor, Dr. Valder R. Arruda and colleagues note in the March 15th issue of Blood. Biopsies in animals and humans have demonstrated that the factor collects in both intracellular and extracellular space.

The safety of the therapy depends on the vector dose, Dr. Arruda noted in an interview with Reuters Health, so he and his colleagues sought to find a way to increase the FIX dose without increasing vector exposure.

Collagen IV is the main extracellular bonding site for FIX and blocking FIX binding to collagen IV does not affect its clotting activity. The researchers conducted a series of experiments in mice using a FIX variant mutated in two sites to interfere with collagen IV binding.

Animals injected with a viral vector carrying the variant FIX gene had two- to five-fold higher circulating FIX levels than those injected with wild-type FIX gene. Clotting activity remained the same. The researchers tested another variant, which had been shown to have higher protein-specific activity than wild-type FIX, and found it increased clotting activity two- to six-fold.

Dr. Arruda said that he and his colleagues are now planning studies in dogs with FIX genes engineered to carry both variants.

In an accompanying editorial, Dr. Francesco Bernardi of Ferrara University in Italy notes that "the combination of protein molecular biology and biochemistry with viral vector technology provides a promising strategy to improve the efficacy for a variety of gene-based therapies in hematology."

Source: Blood 2005;105:2316-2323. [ Google search on this article ]

MeSH Headings: Biological Therapy : Genetic Engineering : Genetic Techniques : Investigative Techniques : Therapeutics : Gene Therapy : Analytical, Diagnostic and Therapeutic Techniques and Equipment