Products made by transgenic animals. Several products are currently being developed by the three main companies involved in transgenic animal production of biopharmaceuticals:
PPL Therapeutics in Scotland, Pharming in the Netherlands, and Genzyme Transgenics in the US. PPL primarily uses sheep and
rabbits to produce alpha-1 antitrypsin, bile salt stimulated lipase, collagen, superoxide dismutase, factors VIII and IX,
fibrinogen, human serum albumin, blood-coagulation factor XIV, calcitonin, and some smaller peptides. Pharming focuses on
cattle for its production of alpha glucosidase, C-1 esterase inhibitor, collagen, fibrinogen, factors VIII and IX, and lactoferrin.
Genzyme is using goats to produce alpha-1 proteinase inhibitor, antithrombin III, beta interferon, calcitonin, human serum
albumin and growth hormone, tPA, and a malaria vaccine.
Some recombinant proteins expressed in the milk of transgenic mammals are too big for bacteria or yeasts to handle. For example,
the molecular weight of collagen is 130,000 daltons, and fibrinogen is a whopping 400,000 daltons!
Advantages: Shorter development cycles than animals; easy storage of seed banks; easy scale-up; good expression levels (up to 1 kg purified
recombinant protein/acre of crop); well-understood genetics; no plant viruses known to infect humans (so viral characterization
unnecessary); low-cost production ($10–20/gram of product).
Disadvantages: Potential for new contaminants (soil fungi and bacteria, plant-sourced impurities and metaboliytes, pesticides, herbicides);
posttranslational modifications differ from those made by animal cells; contain possible allergens; unresolved public issues.
Products made by transgenic plants. Integrated Protein Technologies is the division of Monsanto that is using genetic engineering technology to produce therapeutic
proteins in transgenic corn. In late March 2000, IPT had six recombinant protein products in Phase II clinical trials. Dow
AgroSciences is another player in this arena.
CropTech Corporation is using transgenic tobacco to produce human lysosomal enzymes, among other things. Human glucocerebrosidase
is currently produced by mammalian cell culture. Patients with Gaucher's disease receive the drug every two weeks for life,
costing an average $160,000 a year and making it one of the most expensive drugs on the world market, partly due to manufacturing
costs. CropTech researchers have introduced the gene for glucocerebrosidase into tobacco and shown that an active enzyme is
produced in the leaves. Leaves from a single tobacco plant could make enough enzyme for one dose. In addition to tobacco,
corn, and other crops, duckweed is being investigated as a potential plant source of therapeutic proteins.
ProdiGene already sells recombinant avidin and beta-glucuronidase produced in transgenic corn plants as research and diagnostic
reagents through a partnership with Sigma-Aldrich. The company also partnered with Genencor to produce industrial enzymes,
and with EPIcyte to produce therapeutic antibodies. ProdiGene is also working to produce vaccines for hepatitis and transmissible
gastroenteritis virus in edible form. Edible vaccines are also being produced by the Boyce Thompson Research Center, which
genetically modified potatoes and tomatoes to produce recombinant vaccines for cholera, Norwalk virus, and hepatitis B.