A rationally designed oral vaccine induces immunoglobulin A in the murine gut that directs the evolution of attenuated Salmonella variants.

The ability of gut bacterial pathogens to escape immunity by antigenic variation-particularly via changes to surface-exposed antigens-is a major barrier to immune clearance. However, not all variants are equally fit in all environments. It should therefore be possible to exploit such immune escape mechanisms to direct an evolutionary trade-off.