Transiently Transfected Mammalian Cell Cultures: An Adaptable and Effective Platform for Virus-like Particle-Based Vaccines against Foot-and-Mouth Disease Virus.

RNA viruses, such as foot-and-mouth disease virus (FMDV), have error-prone replication resulting in the continuous emergence of new viral strains capable of evading current vaccine coverage. Vaccine formulations must be regularly updated, which is both costly and technically challenging for many vaccine platforms. In this report, we describe a plasmid-based virus-like particle (VLP) production platform utilizing transiently transfected mammalian cell cultures that combines both the rapid response adaptability of nucleic-acid-based vaccines with the ability to produce intact capsid epitopes required for immunity. Formulated vaccines which employed this platform conferred complete protection from clinical foot-and-mouth disease in both swine and cattle. This novel platform can be quickly adapted to new viral strains and serotypes through targeted exchanges of only the FMDV capsid polypeptide nucleic acid sequences, from which processed structural capsid proteins are derived. This platform obviates the need for high biocontainment manufacturing facilities to produce inactivated whole-virus vaccines from infected mammalian cell cultures, which requires upstream expansion and downstream concentration of large quantities of live virulent viruses.

Detection of African swine fever virus utilizing the portable MatMaCorp ASF detection system.

African swine fever (ASF) has emerged as a major threat to domestic and wild suid populations, and its continued spread threatens commercial swine production worldwide. The causative agent of ASF, African swine fever virus (ASFV), possesses a linear, double stranded DNA genome. Traditional detection of ASFV relies on laboratory-based virus isolation or real-time PCR of samples, typically blood or spleen, obtained from suspect cases. While effective, these methodologies are not easily field deployable, a major limitation during disease outbreak and response management scenarios. In this report, we evaluated the MatMaCorp Solas 8® ASFV detection system, a field deployable DNA extraction and fluorescent detection device, for its ability to extract and detect ASFV from multiple sample types obtained from domestic swine experimentally infected with ASFV strain Georgia. We found that the MatMaCorp Solas 8® ASFV detection device, and affiliated MagicTip™ DNA extraction and C-SAND™ assay kits, readily detected ASFV in blood and spleen, as well as other sample types, including pinna, liver, skin, muscle and bone marrow.

Generation and characterization of genetically stable heterohybridomas producing foot-and-mouth disease virus-specific porcine monoclonal antibodies.

This report covers the methodology for generation of stable heterohybridoma clones producing Foot-and-mouth disease virus (FMDV) reactive porcine monoclonal antibodies (mAbs). Swine received five inoculations of an inactivated O1 Manisa FMDV vaccine prior to the harvest of splenocytes. Due to the lack of a species-specific hybridoma fusion partner, the Sp2/0 murine myeloma cell line was utilized for the formation of porcine-murine heterohybridoma clones. Twenty-nine FMDV-reactive parental clones were generated. Following sub-cloning and monitoring of reactivity over 20 serial passages, eleven subclones derived from unique parental origins were characterized and are reported herein. This methodology demonstrated the production of porcine mAbs by fusion of porcine splenocytes from immunized pigs with murine myeloma cells to generate heterohybridomas. The porcine immune response may differ from the murine immune response in relation to recognized epitopes. Therefore, application of this methodology may provide valuable resources for swine immunology and enhance the understanding of the mechanisms for antibody based protection from diseases in swine.

Evaluation of modified Vaccinia Ankara-based vaccines against foot-and-mouth disease serotype A24 in cattle.

To prepare foot-and-mouth disease (FMD) recombinant vaccines in response to newly emerging FMD virus (FMDV) field strains, we evaluated Modified Vaccinia virus Ankara-Bavarian Nordic (MVA-BN®) as an FMD vaccine vector platform. The MVA-BN vector has the capacity to carry and express numerous foreign genes and thereby has the potential to encode antigens from multiple FMDV strains. Moreover, this vector has an extensive safety record in humans. All MVA-BN-FMD constructs expressed the FMDV A24 Cruzeiro P1 capsid polyprotein as antigen and the FMDV 3C protease required for processing of the polyprotein. Because the FMDV wild-type 3C protease is detrimental to mammalian cells, one of four FMDV 3C protease variants were utilized: wild-type, or one of three previously reported mutants intended to dampen protease activity (C142T, C142L) or to increase specificity and thereby reduce adverse effects (L127P). These 3C coding sequences were expressed under the control of different promoters selected to reduce 3C protease expression. Four MVA-BN-FMD constructs were evaluated in vitro for acceptable vector stability, FMDV P1 polyprotein expression, processing, and the potential for vaccine scale-up production. Two MVA-BN FMD constructs met the in vitro selection criteria to qualify for clinical studies: MVA-mBN360B (carrying a C142T mutant 3C protease and an HIV frameshift for reduced expression) and MVA-mBN386B (carrying a L127P mutant 3C protease). Both vaccines were safe in cattle and elicited low to moderate serum neutralization titers to FMDV following multiple dose administrations. Following FMDV homologous challenge, both vaccines conferred 100% protection against clinical FMD and viremia using single dose or prime-boost immunization regimens. The MVA-BN FMD vaccine platform was capable of differentiating infected from vaccinated animals (DIVA). The demonstration of the successful application of MVA-BN as an FMD vaccine vector provides a platform for further FMD vaccine development against more epidemiologically relevant FMDV strains.

Versatility of the adenovirus-vectored foot-and-mouth disease vaccine platform across multiple foot-and-mouth disease virus serotypes and topotypes using a vaccine dose representative of the AdtA24 conditionally licensed vaccine.

We investigated the serotype- and topotype versatility of a replication-deficient human adenovirus serotype 5 vectored foot-and-mouth disease (FMD) vaccine platform (AdtFMD). Sixteen AdtFMD recombinant subunit monovalent vaccines targeting twelve distinct FMD virus (FMDV) serotype/topotypes in FMD Regional Pools I-VII were constructed. The AdtA24 serotype conditionally licensed vaccine served as the basis for vaccine design and target dose for cattle clinical trials. Several vaccines contained an additional RGD motif genetic insertion in the adenovector fiber knob, and/or a full-length 2B gene insertion in the FMDV P1 gene cassette. In 13 of the 22 efficacy studies conducted, naïve control and AdtFMD vaccinated cattle were challenged intradermolingually at 2 weeks post-vaccination using a FMDV strain homologous to the AdtFMD vaccine strain. Each of the 16 AdtFMD vaccines were immunogenic based on the presence of homologous neutralizing antibodies in the serum of approximately 90% of total vaccinates (n = 375) on the day of challenge. Importantly, for 75% of vaccines tested, the effective dose that conferred 100% protection against clinical FMD was identical to or in some cases lower than, the minimum protective dose for the conditionally licensed AdtA24 vaccine formulated with ENABL® adjuvant. Results also confirmed the capability of the AdtFMD vaccine platform to differentiate infected from vaccinated animals (DIVA) across the five FMDV serotypes evaluated. Collectively, this comprehensive set of FMD cattle vaccine dose ranging studies highlights the serotype- and topotype versatility of the AdtFMD vaccine platform for further development, licensure, and application in FMD outbreak control and disease eradication efforts.