Codon Optimization in the Production of Recombinant Biotherapeutics: Potential Risks and Considerations
Biotherapeutics are increasingly becoming the mainstay in the treatment of a variety of human conditions, particularly in oncology and hematology. The production of therapeutic antibodies, cytokines, and fusion proteins have markedly accelerated these fields over the past decade and are probably the major contributor to improved patient outcomes. Today, most protein therapeutics are expressed as recombinant proteins in mammalian cell lines. An expression technology commonly used to increase protein levels involves codon optimization. This approach is possible because degeneracy of the genetic code enables most amino acids to be encoded by more than one synonymous codon and because codon usage can have a pronounced influence on levels of protein expression. Indeed, codon optimization has been reported to increase protein expression by > 1000-fold. The primary tactic of codon optimization is to increase the rate of translation elongation by overcoming limitations associated with species-specific differences in codon usage and transfer RNA (tRNA) abundance. However, in mammalian cells, assumptions underlying codon optimization appear to be poorly supported or unfounded. Moreover, because not all synonymous codon mutations are neutral, codon optimization can lead to alterations in protein conformation and function. This review discusses codon optimization for therapeutic protein production in mammalian cells.
I would like to thank Stephen Chappell and Daiki Matsuda for critical reading of the manuscript and valuable comments, Kathryn Crossin for helpful discussions on how codon optimization might lead to lost opportunities during therapeutic protein development, and Daniel Ivansson for a series of thoughtful discussions that sparked my interest in this topic.
Compliance with Ethical Standards
No funding has been received for the conduct of this study and/or preparation of this manuscript.
Conflict of interest
Vincent Mauro declares no conflict of interest.
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