REPLACING THE FIRST EPIDERMAL GROWTH FACTOR-LIKE DOMAIN OF FACTOR-IX WITH THAT OF FACTOR-VII ENHANCES ACTIVITY IN-VITRO AND IN CANINE HEMOPHILIA-B

Using the techniques of molecular biology, we made a chimeric Factor I X by replacing the first epidermal growth factor-like domain with that of Factor VII. The resulting recombinant chimeric molecule, Factor IX VIIEGF1, had at least a twofold increase in functional activity in the one-stage clotting assay when compared to recombinant wild-type Facto r TX. The increased activity was not due to contamination with activat ed Factor IX, nor was it due to an increased rate of activation by Fac tor VIIa-tissue factor or by Factor XIa. Rather, the increased activit y was due to a higher affinity of Factor IXVIIEGF1 for Factor VIIIa wi th a K-d for Factor VIIIa about one order of magnitude lower than that of recombinant wild-type Factor IXa. In addition, results from animal studies show that this chimeric Factor IX, when infused into a dog wi th hemophilia B, exhibits a greater than threefold increase in clottin g activity, and has a biological half-life equivalent to recombinant w ild-type Factor IX.