Project 2 - Targeting lactoferrin receptors for a gonococcal vaccine This goal of this project is to develop a broadly cross-protective vaccine against Neisseria gonorrhoeae, the bacteria responsible for the common sexually-transmitted disease, gonorrhea. The emergence of strains of N. gonorrhoeae that are resistant to most antibiotics has raised the specter of untreatable gonorrhea, adding urgency for the development and implementation of effective vaccines for prevention of this infection and its sequelae. N. gonorrhoeae is human-specific pathogen that exclusively resides in genitourinary tract, or less frequently, in the upper respiratory tract, of its human host. Our approach is to target the surface components responsible for mediating iron acquisition from the host iron binding proteins, transferrin (Tf) and lactoferrin (Lf), since these two systems have been shown to be essential for survival of the bacteria and their ability to cause infection in a human male urethral infection model. Since the bacteria cannot survive without these receptor proteins, they will not be able to escape vaccine coverage by loss of the receptors, thus could be eliminated from vaccinated individuals if we are successful in developing a fully cross-protective vaccine against all variants of the receptor proteins. This project is focused on using structure-guided antigen design to generate engineered antigens targeting both the surface lipoprotein, lactoferrin binding protein B (LbpB), and the integral outer membrane transport protein, lactoferrin binding protein A (LbpA), that will collectively induce a broadly cross-protective immune response against all known variants of these proteins. Our novel integrated vaccine design and evaluation pipeline approach will use libraries of antigenic variants in immunoassays and strain libraries in colonization and infection models to evaluate the cross-reactive and cross protective properties of the immune response to guide the selection of combinations of antigens. We will determine the global sequence diversity of the target antigens (LbpB and LbpA) and then develop non-binding mutants of representative variant LbpBs that are predicted to collectively provide a broad cross-protective immune response against all LbpB variants. We will evaluate the immunological properties of the negatively charged regions in the C-lobe of LbpB, determine the impact of their removal and determine the optimum combination of LbpA epitopes that can be displayed on the LbpB C-lobe that induces a broadly cross-protective response against LbpA. The final step will be to integrate the results from an established NIH grant focused on developing antigens targeting transferrin binding protein B and A (TbpB and TbpA) and determine the optimum combination of engineered TbpB and LbpB antigens displaying epitopes from TbpA and LbpA to induce a broadly cross- protective immune response against all four antigens. Studies in our normal and transgenic mice indicate that antigens targeting TbpB or TbpA can reduce colonization, thus the prospects of developing a vaccine that will eliminate bacteria expressing any of the four target antigens are promising. 1
