In previous studies, we had identified important T-cell epitopes present in the NSP9 and NSP10 of PRRSV. The identified epitopes are highly conserved and we have shown that they are “seen” (recognized) by the immune system of the pig when infected by PRRSV (24). The degree of conservation of these epitopes suggests that they may be highly useful in the rational design of broadly efficacious vaccines against PRRSV. Furthermore, we have shown that a major component of protective immunity conferred by live vaccines is mediated by cell-mediated-immunity (CMI). Thus, if animals are preferentially immunized against conserved epitopes of NSPs, it is possible that such immunization could result in a highly “pan-strain specific” protective immunity which would establish protection against infection with a broader number of diverse PRRSV strains. We rationalize that in order to design a broadly protective PRRSV vaccine, it is necessary to identify proteins and their well conserved epitopes derived from genomic regions that are unlikely to readily mutate due to functional and structural constraints. Inducing CMI against the well conserved T cell epitopes should then control replication of a wide range of wt PRRSV strains.
In this NPB application (#13-186), we proposed to approach a rapid but thorough characterization of those genomic regions for cross (broad) protection by the development of a novel research tool: a self-propagating (def. self-propagating = infectious) replicon (SPR) of PRRSV. A replicon consists of a genetic construct that includes only the complete set of NSPs (i.e. the constituents of the replication machinery) of PRRSV but none of the structural ones, and coupled to the glycoprotein (G) of vesicular stomatitis virus (VSV) that would provide the ability of the replicon to bud as an enveloped (infectious) particle as has been shown previously for Semliki Forest virus. We postulated that this SPR, when used to infect pigs, will be able replicate in swine cells in vivo and therefore expose the pig’s immune system to the totality of non-structural antigens of PRRSV without causing any wt PRRSV infection or pathogenic effects as no infectious PRRSV can be produced by this novel genetic construct. The advantages of producing such SPR were multifold: (i) it would likely stimulate the immune system of the pig in a manner similar to the most effective platform: the modified live vaccines (MLVs); (ii) it would help elucidate and accurately quantify the level and broadness of protection contributed exclusively by the PRRSV NSPs in the absence of the structural proteins; (iii) the broad cell tropism of SPR would likely provide significant advantage for more robust immune response as the ability of this SPR to infect different cell types in vivo will be determined by the VSV G protein, thus significantly amplifying its tropism as opposed to the restricted tropism exhibited by the PRRSV MLVs; and (iv) it would provide a basic live, harmless immunogen to which we could later increase its immunogenic potential by inserting additional epitope(s) or individual structural antigen(s), eventually serving as a self-replicating virus-like immunogen that would stimulate further the immune system without producing any PRRSV infectious particle.
Contact information:
Asit K. Pattnaik, School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln, 109 MOLR Beadle Center, 4240 Fair Street, Lincoln, NE 68583-0900, Phone: 402-472-1067; Fax: 402-472-8722; e-mail: [email protected]
