CIRCULATING HUMAN FACTOR-IX PRODUCED IN KERATIN PROMOTER TRANSGENIC MICE - A FEASIBILITY STUDY FOR GENE-THERAPY OF HEMOPHILIA-B

It has previously been suggested that keratinocytes might provide a su itable target cell for delivery of factor IX to the systemic circulati on for gene therapy of haemophilia B. Here, an investigation of the us e of cellular gene promoters specific for keratinocytes was undertaken to examine whether factor IX could be passed from the epidermis to th e systemic circulation, Utilizing two bovine cytokeratin gene promoter s, BKIII and BKVI, three lines of transgenic mice were generated with targeted expression of human factor IX in the epidermis. All three tra nsgenic mouse lines secreted epidermally derived human factor IX into the blood system, Most effective factor IX expression (46 ng/ml steady -state levels of circulating human factor IX) was obtained utilizing t he BKVI gene promoter, the human homologue of K10, which is expressed exclusively in differentiated keratinocytes, localized distal to the b asement membrane, This report demonstrates, for the first time, that h uman factor IX can be efficiently synthesized and secreted from kerati nocytes in situ, and can cross the epidermal basement membrane to reac h the systemic circulation, The transgenic mouse model will provide a good in vivo system with which to optimize the efficiency of different keratin gene promoter constructs for delivery of therapeutic gene pro ducts to the serum, especially for those promoters, such as K10, which are not effectively expressed in vitro.