Developing a manufacturable tridecavalent vaccine for controlling infestations by cattle ticks

Abstract

Vaccines formulated with 4 to 10 among 13 tick salivary antigens are validated in cattle and dogs, however, their manufacturing with good cost-benefit is unfeasible due to the large number of their components. Furthermore, some targets are poor immunogens because they contain insufficient T helper cell epitopes (HTLs) and thus provide weak coverage of bovine class II alleles. This project seeks to solve these two weaknesses of a multivalent vaccine to control ticks in cattle. With a proprietary vector that co-expresses up to 3 target genes in a single fermentation, we will construct four formulations with the following plasmids: (A) 2 plasmids, each with 6 chimeric fusion proteins derived from the intact sequences of the 13 antigens; (B) 2 plasmids likewise, except that sequences of the 7 largest antigens are truncated with domain minimization to focus immunity to regions vulnerable to neutralizing antibodies; (C) a 5th plasmid expresses genes consisting of multiple linear B cell epitopes (L-BCLs) from the antigens; (D) 9 individual "priority" antigens resulting in 3 fermentations will also be produced. Except for formulation "D", fusions and order of resulting chimeras and L-BCLs will be optimized for half-life and protein stability in E. coli and solvent accessibility of L-BCLs. Importantly, all genes used to generate formulations A-D bear tags that improve immunogenicity of the encoded proteins: the role of the DC-binding tag is well established; a 2nd tag is a novel carrier that provides at least 2 HTLs for almost all DRB3 alleles of commercial breeds of cattle. They also bear one of the 13 tick antigens as a tag to facilitate expression, as well as a histidine tag for eventual purification steps; however, all resulting recombinant protein formulations will be delivered as bacterins. Effects on immunogenicity and on tick biology will be assessed with standard protocols and results will be compared with those obtained with the 13 antigens delivered as individual, tagless proteins and with empty bacterins. Alum is the adjuvant in all formulations. To replicate the field situation of tick vaccines, as well as assess the suppressive potential of tick saliva on immunity or, conversely, the immunity-enhancing potential of immune complexes formed between vaccine-induced antibodies and proteins of tick saliva, hosts will be exposed to ticks after the 1st immunization. Results will guide future experiments, but in this project we will examine tick guts for deposits of complement components. Some antigens are antimicrobial peptides, so we will examine if the vaccines make ticks vulnerable to entomopathogens. This project innovates by: producing a multicomponent vaccine, in demand to address complexity of parasites; using tick salivary antigens to generate good immune memory and delivered as bacterins to dispense with antigen purification; ensuring broad vaccine coverage of the MHC-II diversity of commercial cattle breeds and possibly creating synergism between host immunity and entomopathogens to control ticks. (AU)