Tick Midgut Thrombin Inhibitor as a Vaccine Target

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DESCRIPTION (provided by applicant): We seek in this proposal to develop a tick vaccine to block tick feeding and pathogen transmission to the vertebrate host. Ticks can harbor bacterial, viral and protozoan pathogens and infected ticks transmit pathogens to the mammalian host during feeding, causing human and cattle disease worldwide. Ixodid ticks are obligate hematophagous arthropods that feed on vertebrate hosts for 4-10 days to obtain their bloodmeal, an event essential to complete their life cycle. Molecules critical for tick feeding can serve as vaccine targets to block tick feeding and pathogen transmission. Since it is well understood that ticks must impair host coagulation cascades, especially at the vector-host interface, in order to obtain the bloodmeal successfully, there has been a clamor to define anticoagulation mechanisms of tick saliva. As a result, in the last decade or so anticoagulants have been described, both by our group and others, in the saliva or salivary glands of diverse tick species. The elaboration of structurally and functionally related anticoagulant molecules in the salivary gland proteome, a critical adaptation to resist host immune pressures, has however posed a bottleneck in the successful development of these salivary anticoagulants as tick vaccines. We now offer an approach to circumvent the bottleneck and draw attention to a less examined facet of tick anticoagulation strategies, i.e, the role of the tick gut in thwarting host coagulation. Ixodes scapularis, the blacklegged tick, is the predominant vector of multiple human pathogens including Borrelia burgdorferi the agent of Lyme disease in North America and will serve as a model tick in this proposal. We provide preliminary evidence that the gut of I. scapularis expresses a potent inhibitor of Thrombin, a key component of the host pro-coagulation cascade. We postulate that the thrombin inhibitor in the tick gut plays a critical role in preventing the ingested blood from clotting, keeping the blood meal fluid to facilitate the process of repletion. The tick gut thrombin inhibitor therefore provides a novel vaccine target to thwart tick feeding and block consequent pathogen transmission. We also reason that unlike the salivary anticoagulants, the gut anticoagulant representing a concealed antigen, may not have evolved to circumvent host immune responses; hence easier to neutralize. To test and validate the postulate of this proposal, we will, in Phase I studies, characterize the tick gut thrombin inhibitor, henceforth referred to as Gotti (G Gut of T ut Tick T ick Thrombin I hrombin Inhibitor) and address the vaccine potential of Gotti in the context of tick feeding and Borrelia transmission in a murine model of Lyme disease. Future studies will determine the ability of Gotti to serve as a vaccine to block transmission of other tick-transmitted pathogens. PUBLIC HEALTH RELEVANCE: Success towards developing vaccines to block tick feeding with the goal of thwarting disease transmission has remained elusive. This proposal will focus on Ixodes scapularis the vector of multiple pathogens, including Borrelia burgdorferi the agent of Lyme disease in the North America. We will examine the vaccine potential of Gotti, an I. scapularis midgut anticoagulant that may be critical to enable tick feeding. Gotti being a concealed antigen (not normally seen by the host) may not have evolved to escape the host immune responses and may be easier to exploit as a vaccine target to block tick feeding and the consequent pathogen transmission.