Salmonella-mediated delivery of Francisella type VI secretion system proteins as antigens to induce protective immunity

PROJECT SUMMARY/ABSTRACT Bacterial pathogens employ a myriad of mechanisms to invade the host, evade immune responses and inflict damage. Arguably the most pathogenic bacterium known is Francisella tularensis, which boasts a mortality rate upwards of 60%, is transmitted via aerosols, and can be made antibiotic resistant through rudimentary methods. Based on these characteristics, F. tularensis is one of only three bacteria of highest concern for weaponization by the Centers for Disease Control and Prevention. Although these bacteria have been studied since the early 1900s, we still lack a protective and non-toxic vaccine. These intracellular bacterial pathogens employ a contractile toxin secretion apparatus called the type VI secretion system (T6SS) to inject effector proteins into host cells to facilitate invasion into the cytosol and proliferation. Deleting any component of the T6SS apparatus or the effector proteins that it secretes renders Francisella avirulent. In this application, we propose to use an established antigen delivery strain of Salmonella to insert Francisella T6SS proteins directly into phagocytic cells to induce protective immunity. The protective immunity enhanced Salmonella vaccines (PIESVs) are composed of S. Typhmurium strains that simultaneously induce antigen expression and self-destruct within 8-10 cell divisions in the host. This results in antigen delivery into phagocytic cells within lymphoid tissue and has been used extensively as an antigen delivery platform. We will construct PIESV strains that express T6SS proteins and determine if they can elicit protective immunity in a mouse model for Francisella infection. These studies will provide insight into antigens that are protective against subsequent infection.