The Skaggs Institute
for Chemical Biology

Expression of Therapeutic Proteins in Eukaryotic Algae

S.P. Mayfield, D. Barnes, M.V. Beligni, A. Manuell, M. Muto, S.P. Fletcher

Antibody-based therapeutics have had great success during the past few years and continue to be one of the fastest growing sectors of drug development. Such therapeutics offer one of the few options available for treatment of viral infections, and antibodies have great potential as drugs for treatment of diseases associated with bioterrorism, such as anthrax and smallpox.

Using the unicellular eukaryotic alga Chlamydomonas reinhardtii, we have developed a system for expressing recombinant proteins. Algae are an ideal system for the production of therapeutic proteins; transgenic algae can be generated in a short time, and the cost of proteins produced in algae is a fraction of the cost of proteins produced by using traditional mammalian cell cultures. Currently, all monoclonal antibodies are produced by culturing mammalian cells, and capital costs for production facilities can run into the hundreds of millions of dollars. Because of these high capital and media costs, monoclonal antibodies are some of the most expensive drugs on the market.

To develop an efficient algal-based expression system, we have constructed strains of C reinhardtii that express a number of variants of human monoclonal antibodies. We have produced several forms of an antibody to herpes simplex virus and have shown that these antibodies assemble in the algae to form fully functional molecules that bind herpes simplex proteins. We have produced antibodies specific for the CD19 protein of lymphoma tumors, and we are exploring the ability of these antibodies to bind and neutralize CD19-positive tumor cells. Recently, we generated a series of transgenic algae that express antibodies to the microorganism that causes anthrax. In the near future, we hope to test these molecules for their ability to neutralize anthrax organisms.

We have also produced a number of other types of therapeutic proteins, including serum amyloids and interleukins. Treatment with serum amyloids and Interleukins may be effective therapies for diseases of the bowel, and production of a these proteins in algae makes oral delivery of the therapeutic proteins possible, because algae are safe to eat. Recently, we achieved expression of therapeutic proteins that accounted for 5% of total protein produced, levels that make production of proteins in algae economically practical for any type of therapeutic protein. Our challenge now is to produce and purify sufficient quantities of therapeutic proteins to begin animal-based testing.

Publications

Barnes, D., Franklin, S., Schultz, J., Henry, R., Brown, E., Coragliotti, A., Mayfield, S.P. Contribution of 5′ - and 3′ -untranslated regions of plastid mRNAs to the expression of Chlamydomonas reinhardtii chloroplast genes. Mol. Genet. Genomics 274:625, 2005.

Beligni, M.V., Yamaguchi, K., Mayfield, S.P. Chloroplast elongation factor Ts pro-protein is an evolutionarily conserved fusion with the S1 domain-containing plastid-specific ribosomal protein-7. Plant Cell 16:3357, 2004.

Beligni, M.V., Yamaguchi, K., Mayfield, S.P. The translational apparatus of Chlamydomonas reinhardtii chloroplast. Photosynth. Res. 82:315, 2004.

Manuell, A.L., Yamaguchi, K., Haynes, P.A., Milligan, R.A., Mayfield, S.P. Composition and structure of the 80S ribosome from the green alga Chlamydomonas reinhardtii: 80S ribosomes are conserved in plants and animals. J. Mol. Biol. 351:266, 2005.

Mayfield, S.P., Franklin, S.E. Expression of human antibodies in eukaryotic micro-algae. Vaccine 23:1828, 2005.

Somanchi A., Barnes, D., Mayfield, S.P. A nuclear gene of Chlamydomonas reinhardtii, Tba1, encodes a putative oxidoreductase required for translation of the chloroplast psbA mRNA. Plant J. 42:341, 2005.