Transgenic mouse models of disease to test an innovative OMV-based vaccine for protection against the pathogenic Neisseriae

The human-specific pathogen Neisseria gonorrhoeae (Ngo) causes the sexually transmitted infection gonorrhea. Ngo frequently causes infections localized to the urogenital tract in both males and females, though manifestations such as pelvic inflammatory disease, ectopic pregnancy and infertility can result from untreated infection. Rapid evolution of drug resistance by Ngo has led to its identification as an urgent threat and hastens the need to identify an efficacious vaccine. Our vaccine strategy targets conserved outer membrane transport proteins that provide critical growth-supporting functions during human infection. The outer membrane transport system (TbpA/B) that enables Ngo to employ human transferrin as an iron source is necessary for and produced during human infections. The highly conserved zinc transporters (TdfH and TdfJ) are also expressed in vivo. We have observed that antibodies that target these receptors will both starve the bacteria of these essential nutrients and facilitate bacterial engulfment by opsonophagocytosis and complement-dependent killing. While surface-exposed, these proteins are not targeted when in the context of standard outer membrane vesicle (OMV)-based vaccines because they are not expressed during normal in vitro growth conditions. When they are present, their binding to their respective host proteins can inhibit the immune response. In this application, we propose to generate OMV vaccines that express binding-defective derivatives of these proteins and test their ability to protect against infection in ‘humanized’ transgenic mice that express the human ligands for these transport systems. We hypothesize that a vaccine that elicits a response against each of these surface antigens will fully protect against all gonococcal infections, and expect that they will also prevent meningococcal infection due to high levels of sequence identity in these transporters between the species. These studies are significant because development of a cross- protective vaccine to prevent diseases caused by the pathogenic Neisseriae are critically needed and the approach that we propose has the potential to protect against both species, making it more generally acceptable than an Ngo-focused vaccine. These studies are innovative because OMVs from recombinant strains that lack immune-regulatory components will be used to elicit a response that targets multiple binding-defective but otherwise highly conserved proteins required for infection, and because these are being tested using state-of-the-art, unique animal models in which the human metal binding proteins that the neisserial proteins target are endogenously expressed. The specific aims of this proposal are: Aim 1: Use transgenic mice producing human transferrin, calprotectin and psoriasin to discern in which infected tissues their neisserial outer membrane transport systems contribute to colonization and disease. Aim 2: Exploit a combination of immunization with iron and zinc-starved gonococci and a unique repertoire of neisserial outer membrane transporter- specific polyclonal and monoclonal antibodies to understand how these contribute to protection against Neisseria disease. Aim 3: Employ OMVs from genetically engineered LOS-modified, Rmp- and Opa-deficient Ngo strains that overproduce the outer membrane transporters to elicit cross-protective immune responses in transgenic animals. Overall, these innovative studies will target essential nutrient acquisition systems to develop an effective pan-Neisseriae vaccine.