Efficacy of Purified Borrelial Lipoproteins (PBL) as an oral formulation in reducing transmission of Lyme spirochetes from reservoir hosts to Ixodes scapularis ticks

Abstract

Blocking transmission of Borrelia burgdorferi (Bb), the causative agent of Lyme disease (LD), from reservoir hosts to humans via Ixodes scapularis ticks represents an alternative strategy to reduce LD incidence. Here, we evaluated Purified Borrelial Lipoproteins (PBL) with a combination of adjuvants, for their ability to limit Bb transmission using C3H/HeN mice and Peromyscus leucopus reservoir models. Immunization with PBL as oral gavage, either alone or nanoparticle-encapsulated, elicited increased antibody responses and reduced pathogen burden in fed larvae and select host tissues. A formulation combining PBL with a recombinant fusion protein adjuvant consisting of Cholera Toxin B subunit, Outer surface protein A, and two-tandem repeats of an M-cell-targeting peptide (rCOM) induced durable protective immunity for up to 10 months in C3H/HeN mice. This oral regimen significantly reduced Bb burden in host tissues, in fed larvae from vaccinated hosts, molted nymphs, and nymph-challenged naive mice. Immunization with PBL+rCOM elevated peripheral levels of Bb-specific IgG isotypes and increased antigen-specific T cell responses producing IFN-{gamma} and IL-4 at days 28 and 65 post-immunization. Significant protective responses were observed in P. leucopus, including strong antibody responses, reduced Bb burden in tissues and reduced Bb transmission to naive larvae, independent of sex but influenced by challenge dose. Sodium chloride content in oral formulation modulated vaccine induced protective responses. Notably, Bb burden in infected nymphs was reduced during the bloodmeal on vaccinated hosts with decreased pathogen transmission to both vertebrate hosts. These findings support PBL+rCOM as a promising oral, reservoir-targeted, transmission-blocking biologic for controlling Lyme disease. Lay AbstractNumerous vertebrate hosts serve as reservoirs of pathogens that are transmitted to humans via the bite of blood feeding vectors such as ticks. Lyme disease, caused by Borrelia burgdorferi (Bb), is the most common tick-borne disease in the US. Bb is transmitted to humans following the bite of infected Ixodes scapularis ticks. In nature, ticks acquire Bb and other pathogens from a variety of reservoir hosts, notably Peromyscus leucopus. Therefore, strategies that limit pathogen burden in reservoir hosts or block their transmission via ticks are options to prevent human infectious diseases, circumventing need for human vaccines and therapeutics. An oral, reservoir host-targeted, pathogen-derived, biologic prepared by extracting immunogenic lipoproteins (Purified Borrelial Lipoproteins) from Bb and combining them with a mucosal adjuvant derived by fusing Cholera-Toxin B subunit, Outer surface protein A of Bb and 2 repeats of an M-cell targeting peptide was tested in C3H/HeN mice and Peromyscus leucopus hosts. Single or two dose regimens via the oral route resulted in significant increases in peripheral Bb specific antibody responses, select T cell responses, blocking the transmission of Bb to naive Is larvae, reducing pathogen burden in vaccinated hosts, and interfering with the infectious cycle of the agent of Lyme disease.