A new strategy for the design of potentially safer vaccines is reported in Nature Communications this week. Vaccines based on bacterial minicells may eliminate risks associated with those containing attenuated bacteria, which may still cause disease in children or patients with a weak immune system.

Efficient vaccines deliver antigens, substances that cause an immune response, into immune cells via a bacterial protein injection system known as the type III secretion system (T3SS). However, the T3SS requires energy and is hence only active in live bacteria. Bacterial minicells are the result of aberrant bacterial cell divisions. Although they contain no DNA and cannot replicate, bacterial minicells do contain proteins that sustain some cellular functions. Jorge Galan and collaborators genetically modified minicells of Salmonella Typhimurium so that they contain a functional T3SS. The team went on to show that these minicells could be used to deliver antigens to immune cells via the T3SS and to elicit an immune response in mice.