Efficacy of novel reservoir-host targeted bait formulations against a tick-borne pathogen

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Lyme disease is the most common tick-borne illness in the US. Currently, there are no vaccines available to prevent Lyme disease and antibacterial therapy is the treatment of choice. The disease is caused by a spirochete, Borrelia burgdorferi, which is maintained in nature through an enzootic cycle involving a tick vector and a variety of vertebrate hosts. Regulation of gene expression in B. burgdorferi in response to environmental cues prevalent in these highly divergent hosts is critical for pathogen survival and transmission between the tick vector and vertebrate hosts. Deletion of Borrelia host-adaptation Regulator (BadR) and site-specific replacement of 8 critical residues of Carbon Storage Regulator A result in dysregulated borrelial strains that hyper-express a variety of lipoproteins. Purified Borrelial Lipoproteins (PBLs) from these strains confer protection when administered via parenteral route against challenge with B. burgdorferi infected Ixodes scapularis nymphs. Consistent with the RFA-AI-19-037 “Targeted Prevention of Tickborne Diseases”, this proposal is directed at evaluating PBLs from hyper-expression borrelial mutants as a bait-formulation to develop a reservoir-targeted approach to interrupt the natural history of B. burgdorferi infection using experimental (C3H/HeN) and reservoir (Peromyscus leucopus, white-footed mouse) mouse models of Lyme disease. Use of PBLs in their native conformation circumvents the need to express these antigens as recombinant proteins in heterologous systems or limitations in their reconstitution to reflect their proportions on the borrelial surface. The central hypothesis of this proposal is that oral administration of PBLs protects reservoir hosts against Bb challenge via ticks and interferes with the natural history of infection via Ixodes scapularis ticks. This hypothesis will be tested with 3 specific aims. In Specific Aim 1, correlates of protective immunity induced by PBLs against B. burgdorferi will be determined. Humoral immune response, levels of borrelicidal antibodies and levels of protection against B. burgdorferi challenge via ticks induced in C3H/HeN or P. leucopus mice following oral or parenteral administration of PBLs will be compared. In Specific Aim 2, the levels of PBL-induced reduction in B. burgdorferi burden in ticks will be determined. The ability of naïve tick larvae and nymphs fed on PBL-immunized mice to acquire and transmit B. burgdorferi to naïve mice will be ascertained to establish a strategy to interfere with the natural history of infection. In Specific Aim 3, several adjuvants and novel strains of B. burgdorferi expressing lipoproteins with properties to increase the potency of a single dose, oral, reservoir bait vaccine will be evaluated. These studies are novel in exploiting the components of genetically defined borrelial mutants in conjunction with adjuvants that increase the potency of PBLs administered as bait formulations to interfere with natural life cycle of Lyme disease pathogen. Overall, the proposed strategies will help in developing a vaccine platform exploiting genetically modified avirulent organisms or their components to block one or more tick-borne pathogens.