http://www.uniprot.org/uniprot/O95390

From the looks of it it is a secreted protein with disulfide bonds that is processed by proteases cleaving it at a particular point and other enzymes adding sugar residues at particular points. You're gonna need to make it in a eukaryote through the secretory pathway and it probably needs a suite of modifying enzymes to cleave and glycosylate it properly, but I don't know if those enzymes are widespread in the eukaryotes or animal-specific. You can always make it in animal cells but that's expensive compared to fermentation tanks. It also must make its way INTO circulation, implying injection, and I haven't been able to see how much plasma was injected and if that indicates occasional infusions or regular injections given how quickly it degrades.

EDIT: see downstream reply to ChristianKl for updated information after I followed the citations and looked at the actual papers after work. Looks like the protein is easier to make than I expected (and indeed a lot of eukaryotic proteins CAN be made in bacteria if you have the industrial-scale equipment to do the proper post-processing), but extremely expensive at this time.

You basically CANNOT give proteins other than digestive enzymes orally.

And I do indeed suspect they'll find some downside to this somewhere, likely in either cancer rates or metabolic issues.

I should go after the actual papers later today or something...