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From 2013.igem.org

Original Technical Design

E. coli Nissle 1917 will be engineered to secrete granulocyte colony-macrophage stimulating factor (GM-CSF) to attract dendritic cells (DCs). GM-CSF is a well-studied immunostimulant used in multiple clinical vaccines. The modular nature of this secretion system allows the bacteria to also secrete adjuvants and other immunostimulants to provoke a variety of immune responses. The bacteria will target dendritic cells via cell surface expression of the anti-DEC-205 single-chain variable fragment (scFv), which targets the DC endocytic protein DEC-205 and facilitates bacterial uptake by the DC. Once enside the dendritic cell endosome, the acidic conditions will activate the expression of the listeriolysin O (LLO) protein in the bacteria, which will shear the endosome and allow the cancer cell markers expressed in the bacteria to enter to DC cytosol. Expression of the LLO protein is inhibited in neutral and basic conditions by an antisense RNA to the RBS of the composite LLO sequence, functionally creating a genetic pH switch for LLO expression. Cytosolic presence of cancer cell antigens allows them to be expressed on DC major histocompatibility complex (MHC) Class I molecules, which are critical to activate a Cytotoxic T Lymphocyte (CTL) response.  

The aDEC-205 scFv and the pH switch for LLO expression were later delegated as future tasks to improve vaccine safety and efficiency.