Resumen de Synthetic dendrimer peptide vaccines against Foot-and-Mouth Disease Virus
Foot-and-mouth disease (FMD) is a highly contagious disease affecting cloven-hoofed animals that is produced by a virus belonging Picornaviridae family: FMD virus (FMDV). Although the mortality rate is low, FMD is very feared in farm industry and animal health since in case of an outbreak, massive culling of infected or suspected animals is carried out, causing a fatal economic impact. Current vaccines based on inactivated viruses are being used for disease control in endemic countries. Nevertheless, the several drawbacks of these vaccines, have led the FMD-free countries to apply non-vaccination policies, increasing the risk of disease reintroduction and severe outbreaks. Therefore, the development of safer and effective vaccines is a major priority for FMD control. Synthetic dendrimer peptides are among the different strategies to develop new FMD vaccines. Our laboratory, is using a dendrimer peptide, termed B2T-3A, as a vaccine model. B2T-3A harbors two copies of the major antigenic B-cell site [VP1 (140-158)], which is the main target for neutralizing antibodies (nAb), covalently linked to a promiscuous and heterotypic T-helper epitope from the non-structural protein 3A [3A (21-35)]. The administration of two doses of 2 mg of B2T-3A, protects pigs from FMDV experimental challenge. Interestingly, the modular design of this dendrimer peptide allows modifications aimed at improving its immunogenicity and its vaccine performance, some of which have been explored in this Thesis, as detailed below. i) The immunogenicity of dendrimer peptides derived from B2T-3A either synthesized with a different chemistry or harboring different FMDV T-cell epitopes previously identified in pig, have been characterized. The peptide B2T-TB2 –displaying two B2T-3A molecules covalently linked tail-to-tail- induced the highest nAb titers. For this reason, the immunogenicity of this construction was analyzed in pig.
ii) The immunization of pigs with a single dose of B2T-TB2 or B2T-3A, induced high levels of IgG1 and IgG2 specific antibodies along nAb. Also, a strong and specific response of T-cells expressing IFN-γ, the main pro-inflammatory cytokine, was detected upon in vitro recall of peripheral blood mononuclear cells (PBMCs). After the boost, nAb and IFN-γ-producing cells could be detected up to 5 months post-immunization.
iii) One single dose of B2T-3A, of 2 mg or 0.5 mg, protects pigs upon homologous FMDV experimental challenge.
iv) The dendrimer peptide B2T-3D, harboring a T-helper epitope from FMDV 3D protein [3D (56-70)], and dendrimers with both T-cell epitopes covalently link in tandem in both orientations (B2T-3A3D and B2T-3D3A), were selected to study their immunogenicity and the duration of the immune response in pigs. B2T-3D induced nAb titers and IFN-γ-producing cells similar to those of B2T-3A. The peptides harboring a copy of each of the T-cell epitopes (B2T-3A3D and B2T-3D3A) elicited a strong response of IFN-γ-producing cells, mainly due to the epitope T-3D, suggesting that this epitope is immunodominant over T-3A.
v) IFN-γ-producing cells activated by these peptides were, mainly, CD4+ T-cells although a minor contribution of CD8+ T-cells was as well observed.
vi) The majority of CD4+IFN-γ+ cells showed a memory (CD4+2E3-) and a multifunctional phenotype, as they expressed IFN-γ and TNF-α, suggesting that the peptides induced a potent Th1 pro-inflammatory response.
All-in-all, these results strengthen the value and future use of synthetic dendrimer peptides as alternative FMDV vaccines.
