A DNA-Modified Live Vaccine Prime–Boost Strategy Broadens the T-Cell Response and Enhances the Antibody Response against the Porcine Reproductive and Respiratory Syndrome Virus

Abstract

The Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) induces reproductive disorders in sows and respiratory illnesses in growing pigs and is considered as one of the main pathogenic agents responsible for economic losses in the porcine industry worldwide. Modified live PRRSV vaccines (MLVs) are very effective vaccine types against homologous strains but they present only partial protection against heterologous viral variants. With the goal to induce broad and cross-protective immunity, we generated DNA vaccines encoding B and T antigens derived from a European subtype 1 strain that include T-cell epitope sequences known to be conserved across strains. These antigens were expressed either in a native form or in the form of vaccibodies targeted to the endocytic receptor XCR1 and CD11c expressed by different types of antigen-presenting cells (APCs). When delivered in skin with cationic nanoparticles and surface electroporation, multiple DNA vaccinations as a stand-alone regimen induced substantial antibody and T-cell responses, which were not promoted by targeting antigens to APCs. Interestingly, a DNA-MLV prime–boost strategy strongly enhanced the antibody response and broadened the T-cell responses over the one induced by MLV or DNA-only. The anti-nucleoprotein antibody response induced by the DNA-MLV prime–boost was clearly promoted by targeting the antigen to CD11c and XCR1, indicating a benefit of APC-targeting on the B-cell response. In conclusion, a DNA-MLV prime–boost strategy, by enhancing the potency and breadth of MLV vaccines, stands as a promising vaccine strategy to improve the control of PRRSV in infected herds.

A DNA Prime Immuno-Potentiates a Modified Live Vaccine against the Porcine Reproductive and Respiratory Syndrome Virus but Does Not Improve Heterologous Protection

“…We showed in ref. [9] that an improvement of the T-cell response breadth was achieved by a DNA-MLV prime-boost strategy, versus DNA-only or MLV-only. We selected DNA plasmids from the ones that were used in that study (see Material and Method section).…”

“…All sequences were codon-optimized according to the porcine species, synthesized by GenScript (Piscataway, NJ, USA) and cloned in a pUMVC4a vector (Aldevron, Fargo, ND, USA). The four VB plasmids encoding PRRSV AG are pXCL1-N, pXCL1-GP4GP5M, pXCL1-NSP1β1 (AA1 to 202 of NSP1β), and pXCL1-NSP1β2 (AA182 to 383 of NSP1β) and are further described in submitted manuscript 1 [9]. The NSP1β sequence had to be separated into two parts to allow expression of the chimera.…”

“…The NSP1β sequence had to be separated into two parts to allow expression of the chimera. Vaccibody constructs encoding for RdRp did not lead to detectable expression upon transfection in HEK293 cells and therefore were not used [9]. Plasmid productions for immunization were prepared using endotoxin-free NucleoBond ® EF kit (Nagel Macherey GmbH, Düren, Germany) according to the manufacturer’s instructions and were stored at −20 °C until use.…”

“…Interestingly, T-cell epitopes from different PRRSV ORFs have been described that are conserved through European distant strains [8]. In a parallel study, in order to enhance and broaden the T-cell mediated immunity induced by MLVs, we used a DNA-MLV prime-boost strategy with plasmids encoding PRRSV antigens (PRRSV-AG) including conserved T-cell epitopes (NSP1β, RdRp, M-derived antigens) as well as the B cell immuno-dominant nucleoprotein N from a recent Western European strain [9]. We found that the DNA prime broadened the T-cell response and potently enhanced the anti-N IgG response induced by MLV.…”

Modeling Economic Effects of Vaccination Against Porcine Reproductive and Respiratory Syndrome: Impact of Vaccination Effectiveness, Vaccine Price, and Vaccination Coverage

“…Besides the commercially available inactivated vaccines and modified-live virus vaccines (MLV), new techniques for administration have been explored and developed and research on the use of DNA vaccines to further improve efficacy of MLV vaccines has been conducted (7)(8)(9). However, current vaccines fail to provide complete protection against heterologous field strains and commercially available vaccines only partially prevent or mitigate the disease and show limited effectiveness in the field (10)(11)(12)(13).…”