Inoculation of Swine with Foot-and-Mouth Disease SAP-Mutant Virus Induces Early Protection against Disease

Abstract

Foot-and-mouth disease virus (FMDV) leader proteinase (L pro ) cleaves itself from the viral polyprotein and cleaves the translation initiation factor eIF4G. As a result, host cell translation is inhibited, affecting the host innate immune response. We have demonstrated that L pro is also associated with degradation of nuclear factor B (NF-B), a process that requires L pro nuclear localization. Additionally, we reported that disruption of a conserved protein domain within the L pro coding sequence, SAP mutation, prevented L pro nuclear retention and degradation of NF-B, resulting in in vitro attenuation. Here we report that inoculation of swine with this SAP-mutant virus does not cause clinical signs of disease, viremia, or virus shedding even when inoculated at doses 100-fold higher than those required to cause disease with wild-type (WT) virus. Remarkably, SAP-mutant virus-inoculated animals developed a strong neutralizing antibody response and were completely protected against challenge with WT FMDV as early as 2 days postinoculation and for at least 21 days postinoculation. Early protection correlated with a distinct pattern in the serum levels of proinflammatory cytokines in comparison to the levels detected in animals inoculated with WT FMDV that developed disease. In addition, animals inoculated with the FMDV SAP mutant displayed a memory T cell response that resembled infection with WT virus. Our results suggest that L pro plays a pivotal role in modulating several pathways of the immune response. Furthermore, manipulation of the L pro coding region may serve as a viable strategy to derive live attenuated strains with potential for development as effective vaccines against foot-and-mouth disease.

Synonymous Deoptimization of Foot-and-Mouth Disease Virus Causes Attenuation In Vivo while Inducing a Strong Neutralizing Antibody Response

“…When the dose of virus was increased to 10 6 PFU, two out of three animals (animals 8 and 9) developed clinical signs at 3 to 4 dpi with lymphopenia (Fig. 7, lines) associated with the appearance of vesicles, but disease was less severe than that observed for WT FMDV, even at doses at least 10 times lower (13). One animal (animal 7) developed clinical signs only by 7 dpi and never had lymphopenia.…”

“…in the rear heel bulb with different doses of the deoptimized virus. Animals were inoculated with 10 3 , 10 5 , 10 6 , or 10 7 PFU/ animal of A12-deopt virus ( Table 2), doses that we had previously shown caused clinical disease in swine inoculated with the WT virus (13).…”

“…Substitutions of two conserved amino acid residues in this domain in FMDV A12 generated an attenuated mutant virus in cell culture and in swine. Interestingly, when the attenuated strain was tested as a vaccine candidate in swine, animals were completely protected even when challenged as early as 2 days postvaccination (13). However, since only two amino acid residues were replaced, reversion of the SAP mutant to virulence poses a considerable risk.…”

“…A porcine IFN-␣ (poIFN-␣) double-capture enzyme-linked immunosorbent assay (ELISA) previously developed in our laboratory was used to quantify IFN-␣ protein in the supernatants of infected cells (13 Mouse experiments. Six-to 7-week-old female C57BL/6 mice were purchased from Jackson Laboratory (Bar Harbor, ME) and were acclimated for 1 week.…”

Constitutively Active IRF7/IRF3 Fusion Protein Completely Protects Swine against Foot-and-Mouth Disease

“…At 14 dpc, all pigs were euthanized. Clinical scores were determined by recording the presence of vesicular lesions in each toe and in the snout and/or mouth (maximum score ϭ 17); lesions restricted to the site of inoculation were not counted (29). Experiment 2.…”