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The Skaggs Institute
for Chemical Biology


Scientific Report 2006




Expression of Therapeutic Antibodies in Eukaryotic Algae


S.P. Mayfield, M.V. Beligni, A. Manuell, M. Muto, M. Tran, D. Siefker

With the advent of genomics and proteomics technologies, the discovery of new protein therapeutics has greatly accelerated during the past few years. Although these discoveries enable us to treat more diseases, protein-based therapeutic agents are expensive, limiting the development of these new drugs and reducing the number of patients with access to them. Currently, most protein therapeutic agents, and all therapeutic antibodies (i.e., monoclonal antibodies), are produced by culturing mammalian cells. Capital costs for production facilities can run into the hundreds of millions of dollars, and culture media are also expensive, making monoclonal antibodies the most expensive drugs on the market.

To expand our repertoire of protein-based therapeutic agents and to help reduce the cost of these drugs, we have developed eukaryotic algae as a system for expression of therapeutic proteins. Using this system, we have expressed a human antibody that was developed to block the effects of anthrax toxins and reduce mortality due to anthrax. This antibody is a human IgG1 that was identified in serum samples from soldiers who had been vaccinated against anthrax. The antibody binds to anthrax protective antigen 83 at high affinity and was previously shown to prevent anthrax toxins from entering cells in both cell-based assays and animal models. The antibody, 83K7C, was developed at Alexion Antibody Technologies, San Diego, California, and Alexion has provided 83K7C purified from mammalian cells so that we can directly compare the activities of antibodies expressed in mammalian cells with those of antibodies expressed in algae.

Genes that encode the heavy- and light-chain proteins of 83K7C were transformed into the eukaryotic green alga Chlamydomonas reinhardtii, and a transgenic line was produced in which both proteins accumulated. Comparison of 83K7C proteins expressed in the mammalian system with those expressed in the algal system indicated that both heavy- and light-chain proteins accumulate at the expected sizes in both systems. We also found that heavy- and light-chain proteins assembled into correct functional antibodies in algae and that the 83K7C expressed in algae were able to bind their target antigen, protective antigen 83 of anthrax toxin, at affinities similar to those of the Alexion antibody. These data establish that antibodies expressed in algae can form functional antigen-binding molecules and that 83K7C expressed in algae binds with affinity similar to that of 83K7C expressed in mammalian cells. The next phase of this project is to purify enough 83K7C expressed in algae to begin cell-based and animal trials for anthrax neutralization with the antibody. These tests should begin within the next year.

In addition to expressing the anthrax antibody, we are also expressing other therapeutic antibodies, including those used as anticancer agents. CD19 is a cell marker found on B-cell cancers, including those related to childhood lymphomas. We have expressed an antibody to CD19 in our algal system. This successful expression will enable us to engineer unique anticancer antibodies, including antibody-toxin fusion proteins that can only be made in this system.

Publications

Fletcher, S.P., Muto, M., Mayfield, S.P. Optimization of recombinant protein expression in the chloroplast of green algae. In: Transgenic Microalgae as Green Cell Factories. León, A., Gaván, A., Fernández, E. (Eds.). Landes Bioscience, Austin, TX, in press.

Franklin, S.E., Mayfield, S.P. Recent developments in the production of human therapeutic proteins in eukaryotic algae. Expert Opin. Biol. Ther. 5:225, 2005.

Manuell, A.L., Mayfield, S.P. A bright future for Chlamydomonas. Genome Biol. 7:327, 2006.

 

Stephen P. Mayfield, Ph.D.
Professor
Associate Dean, Kellogg School of Science and Technology

Mayfield Web Site