Key issues in the selection of an expression system for vaccine antigens

Three criteria by which the appropriate host cell is chosen for the expression of a recombinant-derived vaccine antigen are efficacy, safety, and scale-up. Efficacy for a vaccine antigen refers to the ability of the host cell to produce a vaccine antigen capable of eliciting a protective immune response. A concern for safety of a vaccine antigen relates to residual DNA in the final product, especially when derived from continuous mammalian cell lines as opposed to microbial cells. Since tens (or hundreds) of millions of doses of a widely used vaccine might be injected into healthy infants and young children during the lifetime of the product, safety is a critical issue, such that the use of a microbial expression system might be preferable to the use of a continuous cell line in certain circumstances.