Abstract
Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically important swine pathogens, which causes reproductive failure in sows and respiratory disease in piglets. A major hurdle to control PRRSV is the ineffectiveness of the current vaccines to confer protection against heterologous strains. Since both GP4 and M genes of PRRSV induce neutralizing antibodies, in this study we molecularly bred PRRSV through DNA shuffling of the GP4 and M genes, separately, from six genetically different strains of PRRSV in an attempt to identify chimeras with improved heterologous cross-neutralizing capability. The shuffled GP4 and M genes libraries were each cloned into the backbone of PRRSV strain VR2385 infectious clone pIR-VR2385-CA. Three GP4-shuffled chimeras and five M-shuffled chimeras, each representing sequences from all six parental strains, were selected and further characterized in vitro and in pigs. These eight chimeric viruses showed similar levels of replication with their backbone strain VR2385 both in vitro and in vivo, indicating that the DNA shuffling of GP4 and M genes did not significantly impair the replication ability of these chimeras. Cross-neutralization test revealed that the GP4-shuffled chimera GP4TS14 induced significantly higher cross-neutralizing antibodies against heterologous strains FL-12 and NADC20, and similarly that the M-shuffled chimera MTS57 also induced significantly higher levels of cross-neutralizing antibodies against heterologous strains MN184B and NADC20, when compared with their backbone parental strain VR2385 in infected pigs. The results suggest that DNA shuffling of the GP4 or M genes from different parental viruses can broaden the cross-neutralizing antibody-inducing ability of the chimeric viruses against heterologous PRRSV strains. The study has important implications for future development of a broadly protective vaccine against PRRSV.
Highlights
Porcine reproductive and respiratory syndrome (PRRS), characterized by reproductive failure in sows and respiratory disease in piglets [1], is arguably the most economically important global swine disease in the past two decades [2,3,4,5]
To insert the shuffled GP4 fragments into the backbone porcine reproductive and respiratory syndrome virus (PRRSV) infectious clone pIR-VR2385-CA, two flanking fragments (1104 bp and 1957 bp, respectively) amplified from the pIRVR2385-CA plasmid DNA were linked to the shuffled GP4 fragments by a fusion PCR
The unique restriction enzyme sites Bsr GI and Xba I present in the flanking fragments were used to clone the fusion product into the backbone PRRSV infectious clone plasmid pIR-VR2385-CA to produce the GP4 shuffled PRRSV infectious cDNA library
Summary
Porcine reproductive and respiratory syndrome (PRRS), characterized by reproductive failure in sows and respiratory disease in piglets [1], is arguably the most economically important global swine disease in the past two decades [2,3,4,5]. Two major genotypes of PRRSV have been identified: the European type (type 1) and the North American type (type 2) that share approximately 55–70% nucleotide sequence identity [7,12,13,14,15]. The extensive antigenic and genetic variations among field strains of PRRSV are largely responsible for the poor cross-protection of the current vaccines against heterologous strains [18,19,20]. As the majority of field strains circulating in swine herds worldwide are genetically different from the MLVs, it is imperative to develop a second generation vaccine that can effectively protect against both homologous and heterologous strains [25,26,27]
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