Conventional foot-and-mouth disease (FMD) vaccines exhibit several limitations, such as the slow induction of antibodies, short-term persistence of antibody titers, as well as low vaccine efficacy and safety, in pigs. Despite the importance of cellular immune response in host defense at the early stages of foot-and-mouth disease virus (FMDV) infection, most FMD vaccines focus on humoral immune response. Antibody response alone is insufficient to provide full protection against FMDV infection; cellular immunity is also required. Therefore, it is necessary to design a strategy for developing a novel FMD vaccine that induces a more potent, cellular immune response and a long-lasting humoral immune response that is also safe. Previously, we demonstrated the potential of various pattern recognition receptor (PRR) ligands and cytokines as adjuvants for the FMD vaccine. Based on these results, we investigated PRR ligands and cytokines adjuvant-mediated memory response in mice. Additionally, we also investigated cellular immune response in peripheral blood mononuclear cells (PBMCs) isolated from cattle and pigs. We further evaluated target-specific adjuvants, including Mincle, STING, TLR-7/8, and Dectin-1/2 ligand, for their role in generating ligand-mediated and long-lasting memory responses in cattle and pigs. The combination of Mincle and STING-stimulating ligands, such as trehalose-6, 6′dibehenate (TDB), and bis-(3′-5′)-cyclic dimeric guanosine monophosphate (c-di-GMP), induced high levels of antigen-specific and virus-neutralizing antibody titers at the early stages of vaccination and maintained a long-lasting immune memory response in pigs. These findings are expected to provide important clues for the development of a robust FMD vaccine that stimulates both cellular and humoral immune responses, which would elicit a long-lasting, effective immune response, and address the limitations seen in the current FMD vaccine.

Currently available commercial foot-and-mouth disease (FMD) vaccines have various limitations, such as the slow induction and short-term maintenance of antibody titers. Therefore, a novel FMD vaccine that can rapidly induce high neutralizing antibody titers to protect the host in early stages of an FMD virus infection, maintain high antibody titers for long periods after one vaccination dose, and confer full protection against clinical symptoms by simultaneously stimulating cellular and humoral immunity is needed. Here, we developed immunopotent FMD vaccine strains A-3A and A-HSP70, which elicit strong initial cellular immune response and induce humoral immune response, including long-lasting memory response. We purified the antigen (inactivated virus) derived from these immunopotent vaccine strains, and evaluated the immunogenicity and efficacy of the vaccines containing these antigens in mice and pigs. The immunopotent vaccine strains A-3A and A-HSP70 demonstrated superior immunogenicity compared with the A strain (backbone strain) in mice. The oil emulsion-free vaccine containing A-3A and A-HSP70 antigens effectively induced early, mid-term, and long-term immunity in mice and pigs by eliciting robust cellular and humoral immune responses through the activation of co-stimulatory molecules and the secretion of proinflammatory cytokines. We successfully derived an innovative FMD vaccine formulation to create more effective FMD vaccines.

Current foot-and-mouth disease (FMD) vaccines have significant limitations, including side effects due to oil emulsions at the vaccination site, a narrow spectrum of protective efficacy, and incomplete host defenses mediated by humoral immunity alone. To overcome these limitations, new FMD vaccines must ensure improved safety with non-oil-based adjuvants, a broad spectrum of host defenses within/between serotypes, and the simultaneous induction of cellular and humoral immunity. We designed a novel, immune-potent, recombinant protein rpHSP70-AD that induces robust cellular immunity and elicits a broad spectrum of host defenses against FMD virus (FMDV) infections. We demonstrated that an oil emulsion-free vaccine containing rpHSP70-AD mediates early, mid-term, and long-term immunity and drives potent host protection against FMDV type O and A, suggesting its potential as an FMD vaccine adjuvant in mice and pigs. These results suggest a key strategy for establishing next-generation FMD vaccines, including novel adjuvants.

Vaccination prevents and controls foot-and-mouth disease (FMD). However, the current FMD vaccine remains disadvantageous since it cannot overcome maternally-derived antibody (MDA) interference in weeks-old animals, which suppress active immunity via vaccination. To address this, we developed the immune-enhancing O PA2-C3d and A22-C3d FMD vaccine strains that can stimulate receptors on the surface of B cells by inserting C3d (a B cell epitope) into the VP1 region of O PA2 (FMDV type O) and A22 (FMDV type A). We purified inactivated viral antigens from these vaccine strains and evaluated their immunogenicity and host defense against FMDV infection in mice. We also verified its efficacy in inducing an adaptive immune response and overcome MDA interference in MDA-positive (MDA(+), FMD-seropositive) and -negative (MDA(−), FMD-seronegative) pigs. These results suggest a key strategy for establishing novel FMD vaccine platform to overcome MDA interference and induce a robust adaptive immune response.

The cell envelopes of many Gram-positive bacteria contain wall teichoic acids (WTAs). Staphylococcus aureus WTAs are composed of ribitol phosphate (RboP) or glycerol phosphate (GroP) backbones substituted with D-alanine and N-acetyl-D-glucosamine (GlcNAc) or N-acetyl-D-galactosamine (GalNAc). Two WTA glycosyltransferases, TarM and TarS, are responsible for modifying the RboP WTA with ␣-GlcNAc and ␤-GlcNAc, respectively. We recently reported that purified human serum anti-WTA IgG specifically recognizes ␤-GlcNAc of the staphylococcal RboP WTA and then facilitates complement C3 deposition and opsonophagocytosis of S. aureus laboratory strains. This prompted us to examine whether anti-WTA IgG can induce C3 deposition on a diverse set of clinical S. aureus isolates. To this end, we compared anti-WTA IgG-mediated C3 deposition and opsonophagocytosis abilities using 13 different staphylococcal strains. Of note, the majority of S. aureus strains tested was recognized by anti-WTA IgG, resulting in C3 deposition and opsonophagocytosis. A minority of strains was not recognized by anti-WTA IgG, which correlated with either extensive capsule production or an alteration in the WTA glycosylation pattern. Our results demonstrate that the presence of WTAs with TarS-mediated glycosylation with ␤-GlcNAc in clinically isolated S. aureus strains is an important factor for induction of anti-WTA IgG-mediated C3 deposition and opsonophagocytosis.