EXPRESSION AND CHARACTERIZATION OF BIOLOGICALLY-ACTIVE HUMAN EXTRACELLULAR-SUPEROXIDE DISMUTASE IN MILK OF TRANSGENIC MICE

We have targeted the expression of recombinant human extracellular sup eroxide dismutase, a glycosylated tetrameric metalloprotein, to the ma mmary gland of transgenic mice. This was achieved by using regulatory elements from either the murine whey acidic protein gene or the ovine beta-lactoglobulin gene to control expression of human extracellular s uperoxide dismutase cDNA. Whey acidic protein regulatory sequences dir ected high level mammary gland-specific expression of the recombinant gene and secretion of biologically active extracellular superoxide dis mutase into the milk. The produced recombinant protein was fully activ e, it was in tetrameric form, it showed heparin affinity, and its mass was similar to that of the native enzyme. In addition, the in vivo pl asma clearance in a rabbit model was similar to the previously studied native and recombinant forms. To our knowledge, this is the first exa mple of efficient production of a tetrameric, protease-susceptible met alloprotein in milk of transgenic animals. Production at equivalent le vels in transgenic farm animals would yield sufficient extracellular s uperoxide dismutase for therapeutic purposes.