Mincle and STING-Stimulating Adjuvants Elicit Robust Cellular Immunity and Drive Long-Lasting Memory Responses in a Foot-and-Mouth Disease Vaccine

Abstract

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.

Advanced Foot-And-Mouth Disease Vaccine Platform for Stimulation of Simultaneous Cellular and Humoral Immune Responses

“…Purified antigen was prepared in BHK-21 cells infected with recombinant immunopotent FMDV A-3A and A-HSP70 constructed for the swift phenotype of P1 (referred sequence) by reverse genetics according to the method described by Lee et al, with modifications [ 10 , 11 ]. For viral infection, the culture medium was replaced with serum-free Dulbecco’s modified Eagle’s medium (DMEM; HyClone, Logan, UT, USA) and the cells were inoculated with the virus by incubating for 1 h at 37 °C in a 5% CO 2 atmosphere.…”

“…The mouse experiment was conducted according to the method described in Lee et al [ 11 ]. Age- and sex-matched wild-type C57BL/6 mice (6–7-week-old females) were purchased from KOSA BIO Inc. (Gyeonggi, Korea).…”

“…To evaluate the potential of A-HSP70 as a FMDV vaccine strain and to investigate its ability to induce cellular and humoral immune responses and long-term immunity, target animal experiments using pigs were conducted to generate preliminary data according to the method described by Lee et al [ 11 ]. For the target animal experiment, FMD antibody-seronegative animals from a pig farm were used (the pigs were 10–12 weeks old).…”

“…To detect SP antibodies in the sera, PrioCHECK FMDV type A (Prionics AG, Switzerland) was used as described by Lee et al [ 11 ]. Absorbance in the ELISA plate was converted to a percent inhibition (PI) value.…”

“…A virus neutralization test was performed based on the guidelines set forth by the World Organization for Animal Health (OIE) manual [ 13 ], as described by Lee et al [ 11 ]. Briefly, the sera were heat-inactivated at 56 °C for 30 min in a water bath.…”