Expression without boundaries: Cell-free protein synthesis in pharmaceutical research

Proteins are an increasingly important class of new drugs. Pharmaceutical proteins are usually expressed in cell based systems in the development phase and in production, and although cell free methods have recently emerged they have not been used widely for therapeutic protein development or production. Cell free expression methodology is well suited for pharmaceutical protein expression and engineering and will probably become more commonly used in the future. Cell free expression allows protein engineering in high throughput format, flexible strategies for glycosylation and chemical conjugation, and allows easy use of unnatural amino acids as building blocks of proteins. Thus, cell free expression can be used to modify protein solubility, stability, and pharmacokinetics of therapeutic proteins. Likewise, it is potentially useful in protein development for biomaterial matrices, nanoparticles, and vaccines. This review illustrates the potential of cell free expression in pharmaceutical protein research and development while highlighting both advantages and limitations of the method.