Results so far suggest the experimental vector does not trigger the T-cell mediated immune response seen in a previous hemophilia B gene therapy trial.
The third and highest dose of the novel gene-vector combination is scheduled to be infused into the fifth and sixth study participants by mid-January. Investigators will then decide whether to expand the trial to include four more adults with severe hemophilia B. Study participants were all recruited at UCL/Royal Free Hospital through the efforts of co-author Edward G.D. Tuddenham, M.D.
Davidoff and Nathwani noted that hemophilia B has been the main focus of gene therapy efforts for disorders affecting the liver because the threshold required for therapeutic effect is modest. In patients with severe hemophilia B whose baseline level of Factor IX is less than 1 percent, generating expression of just 5 percent has the potential to dramatically affect their quality of life, reducing disabling and painful episodes of bleeding and eliminating the need for costly infusions of the protein.
Factor IX is needed for normal clot formation. A mutation in the gene that carries instructions for assembling the protein leaves about 1 in 30,000 individuals at risk for disabling episodes of internal and external bleeding. The gene is carried on the X chromosome, and the disorder is almost exclusively a male disease.
The trial vector was made at the Children's Good Manufacturing Practices (GMP), LLC, facility, on the St. Jude campus. The GMP operates under government-approved manufacturing guidelines and produces the highly specialized medicines and vaccines that pharmaceutical companies are reluctant to pursue.
The other authors are Cecilia Rosales and Jenny McIntosh (both of UCL); Anne Riddell (KD Haemophilia Centre and Thrombosis Unit
|SOURCE St. Jude Children's Research Hospital|
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