Broadly Protective Multivalent OspA Vaccine against Lyme Borreliosis, Developed Based on Surface Shaping of the C-Terminal Fragment.

The development of vaccines for prevention of diseases caused by pathogenic species can encounter major obstacles if high sequence diversity is observed between individual strains. Therefore, development might be restricted either to conserved antigens, which are often rare, or to multivalent vaccines, which renders the production more costly and cumbersome. In light of this complexity, we applied a structure-based surface shaping approach for the development of a Lyme borreliosis (LB) vaccine suitable for the United States and Europe. The surface of the C-terminal fragment of outer surface protein A (OspA) was divided into distinct regions, based primarily on binding sites of monoclonal antibodies (MAbs). In order to target the six clinically most relevant OspA serotypes (ST) in a single protein, exposed amino acids of the individual regions were exchanged to corresponding amino acids of a chosen OspA serotype. Six chimeric proteins were constructed, and, based on their immunogenicity, four of these chimeras were tested in mouse challenge models. Significant protection could be demonstrated for all four proteins following challenge with infected ticks (OspA ST1, OspA ST2, and OspA ST4) or with in vitro-grown spirochetes (OspA ST1 and OspA ST5). Two of the chimeric proteins were linked to form a fusion protein, which provided significant protection against in vitro-grown spirochetes (OspA ST1) and infected ticks (OspA ST2). This article presents the proof-of-concept study for a multivalent OspA vaccine targeting a wide range of pathogenic LB Borrelia species with a single recombinant antigen for prevention of Lyme borreliosis.

The Ixodes ricinus salivary gland proteome during feeding and B. Afzelii infection: New avenues for an anti-tick vaccine.

INTRODUCTION: Borrelia burgdorferi sensu lato, the causative agents of Lyme borreliosis, are transmitted by Ixodes ticks. Tick saliva proteins are instrumental for survival of both the vector and spirochete and have been investigated as targets for vaccine targeting the vector. In Europe, the main vector for Lyme borreliosis is Ixodes ricinus, which predominantly transmits Borrelia afzelii. We here investigated the differential production of I. ricinus tick saliva proteins in response to feeding and B. afzelii infection. METHOD: Label-free Quantitative Proteomics and Progenesis QI software was used to identify, compare, and select tick salivary gland proteins differentially produced during tick feeding and in response to B. afzelii infection. Tick saliva proteins were selected for validation, recombinantly expressed and used in both mouse and guinea pig vaccination and tick-challenge studies. RESULTS: We identified 870 I. ricinus proteins from which 68 were overrepresented upon 24-hours of feeding and B. afzelii infection. Selected tick proteins were successfully validated by confirming their expression at the RNA and native protein level in independent tick pools. When used in a recombinant vaccine formulation, these tick proteins significantly reduced the post-engorgement weights of I. ricinus nymphs in two experimental animal models. Despite the reduced ability of ticks to feed on vaccinated animals, we observed efficient transmission of B. afzelii to the murine host. CONCLUSION: Using quantitative proteomics, we identified differential protein production in I. ricinus salivary glands in response to B. afzelii infection and different feeding conditions. These results provide novel insights into the process of I. ricinus feeding and B. afzelii transmission and revealed novel candidates for an anti-tick vaccine.

Identification of novel conserved Ixodes vaccine candidates; a promising role for non-secreted salivary gland proteins.

Ixodes ricinus and Ixodes scapularis are the main vectors for the causative agents of Lyme borreliosis and a wide range of other pathogens. Repeated tick-bites are known to lead to tick rejection; a phenomenon designated as tick immunity. Tick immunity is mainly directed against tick salivary gland proteins (TSGPs) and has been shown to partially protect against experimental Lyme borreliosis. TSGPs recognized by antibodies from tick immune animals could therefore be interesting candidates for an anti-tick vaccine, which might also block pathogen transmission. To identify conserved Ixodes TSGPs that could serve as a universal anti-tick vaccine in both Europe and the US, a Yeast Surface Display containing salivary gland genes of nymphal I. ricinus expressed at 24, 48 and 72 h into tick feeding was probed with either sera from rabbits repeatedly exposed for 24 h to I. ricinus nymphal ticks and/or sera from rabbits immune to I. scapularis. Thus, we identified thirteen TSGP vaccine candidates, of which ten were secreted. For vaccination studies in rabbits, we selected six secreted TSGPs, five full length and one conserved peptide. None of these proteins hampered tick feeding. In contrast, vaccination of guinea pigs with four non-secreted TSGPs - two from the current and two from a previous human immunoscreening - did significantly reduce tick attachment and feeding. Therefore, non-secreted TSGPs appear to be involved in the development of tick immunity and are interesting candidates for an anti-tick vaccine.