Method for the production of biologically active polypeptides in a mammal's

A process for the production of erythropoietin in milk of a transgenic non-human mammal said process comprising the steps of:

• a) obtaining a mammary gland specific expression system comprising in operable linkage:
• 1) expression regulatory elements from a milk protein gene or a mammary tumor virus,
• 2) a DNA sequence encoding a signal sequence,
• 3) a DNA sequence encoding a fragment of a non-EPO protein, where the fragment is sufficient to reduce or prevent the formation of side effects associated with ectopic expression or leakage of erythropoietin, or a DNA sequence encoding a non-EPO protein, wherein the protein reduces or prevents the formation of side effects associated with ectopic expression or leakage of erythropoietin, and a
• 4) a DNA sequence encoding erythropoietin, whereby elements 3) and 4) are linked in frame forming a fusion protein,
• b) producing a transgenic non-human mammal comprising introducing the expression system of step a) into a non-human mammalian zygote or embryo, and maturing said zygote or embryo into a transgenic non-human mammal,
• c) expressing said fusion protein such that the fusion protein is secreted into the milk of said mammal,
• d) collecting said milk from the mammal or a female descendant of said mammal,
• e) isolating said recombinant fusion protein from said milk,
• f) releasing erythropoietin from said fusion protein, and
• g) purifying said erythropoietin.