Feathered bioreactor: transforming a chicken egg into a recombinant protein biomanufacturing foundry

The limitations of conventional small-molecule drugs in treating complex chronic and inherited disorders have driven demand for recombinant protein therapeutics offering superior target specificity and mechanistic precision. However, existing production platforms remain inadequate: bacterial systems lack post-translational processing machinery; yeast and insect systems produce non-human glycans; and mammalian cell-based systems, while biologically capable, require infrastructure that renders therapeutics inaccessible in resource-limited settings. This review examines the transgenic chicken egg as a compelling manufacturing alternative, whose oviduct epithelium can be reprogrammed through Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated protein 9 (CRISPR/Cas9) mediated primordial germ cell editing to secrete recombinant proteins directly into albumen at clinically meaningful yields. The chicken egg's predominant human-compatible N-acetylneuraminic acid (Neu5Ac) glycosylation, natural sterility, and simplified protein matrix collectively address the biological and economic shortcomings of conventional platforms. Regulatory approval of egg-derived biopharmaceuticals, including Kanuma and Epovet, validates this approach. Outstanding challenges, including incomplete sialylation and extended flock-establishment timelines, are critically discussed, along with strategies to overcome them.