Persistent delivery of factor IX in mice: Gene therapy for hemophilia using implantable microcapsules

Severe hemophilia B is a life-threatening, life long condition caused by ab sence of or defective coagulation factor IX, Gene therapy could provide an alternative treatment to repeated injection of plasma-derived concentrate o r recombinant factor IX, We have previously described the use of implantabl e microcapsules containing recombinant myoblasts to deliver human factor IX in mice. This study reports the generation of improved myoblast-specific e xpression vectors. Mouse myoblast clones transfected with the various vecto rs secreted factor IX in vitro, at rates between 70 and 1000 ng/10(6) cells /day, The recombinant myoblast clones were then encapsulated and implanted into mice. Immunocompetent mice implanted with encapsulated myoblasts had u p to 65 ng of factor IX per milliliter in their plasma for up to 14 days, a fter which antibodies to human factor IX became detectable, and this coinci ded with decreased factor LX in mouse plasma. In immunodeficient mice, howe ver, factor IX delivery was maintained at a constant level for at least 6 w eeks (end of experiment). Interestingly, the highest-secreting myoblast clo ne in vitro did not deliver the highest level of hFIX in vivo. This discrep ancy observed between performance in vitro and in vivo may have important i mplications for the development of gene therapy protocols based on recombin ant cells.