Swine T-Cells and Specific Antibodies Evoked by Peptide Dendrimers Displaying Different FMDV T-Cell Epitopes

Dendrimeric peptide constructs based on a lysine core that comprises both B- and T-cell epitopes of foot-and-mouth disease virus (FMDV) have proven a successful strategy for the development of FMD vaccines. Specifically, BT dendrimers displaying two copies of the major type O FMDV antigenic B-cell epitope located on the virus capsid [VP1 (140–158)], covalently linked to a heterotypic T-cell epitope from either non-structural protein 3A [3A (21–35)] or 3D [3D (56–70)], named BT-3A and BT-3D, respectively, elicit high levels of neutralizing antibodies (nAbs) and IFN-γ-producing cells in pigs. To assess whether the inclusion and orientation of T-3A and T-3D T-cell epitopes in a single molecule could modulate immunogenicity, dendrimers with T epitopes juxtaposed in both possible orientations, i.e., constructs BTT-3A3D and BTT-3D3A, were made and tested in pigs. Both dendrimers elicited high nAbs titers that broadly neutralized type O FMDVs, although BTT-3D3A did not respond to boosting, and induced lower IgGs titers, in particular IgG2, than BTT-3A3D. Pigs immunized with B a control dendrimer displaying two B-cell epitope copies and no T-cell epitope, gave no nABs, confirming T-3A and T-3D as T helper epitopes. The T-3D peptide was found to be an immunodominant, as it produced more IFN-γ expressing cells than T-3A in the in vitro recall assay. Besides, in pigs immunized with the different dendrimeric peptides, CD4 T-cells were the major subset contributing to IFN-γ expression upon in vitro recall, and depletion of CD4 cells from PBMCs abolished the production of this cytokine. Most CD4IFN-γ cells showed a memory (CD42E3) and a multifunctional phenotype, as they expressed both IFN-γ and TNF-α, suggesting that the peptides induced a potent Th1 pro-inflammatory response. Furthermore, not only the presence, but also the orientation of T-cell epitopes influenced the T-cell response, as BTT-3D3A and B groups had fewer cells expressing both cytokines. These results help understand how BT-type dendrimers triggers T-cell populations, highlighting their potential as next-generation FMD vaccines.Spanish Ministry of Science, Innovation and Universities grants AGL2014-48923-C2 and AGL2017-89097-C2-2-R (to FS and DA) and AGL2016-349 76445-R to EB), as well as by Comunidad de Madrid co-financed with ECFEDER funds (S2013/ABI-350 2906-PLATESA and P2018/BAA-4370 to FS and EB) and by Generalitat de Catalunya (2009SGR492 to DA). Work at Centro de Biologı́a Molecular “Severo Ochoa” and at UPF was supported by Fundación Ramón Arece