Validation of a PRRSV live-virus potentiated by replication-competent expression of porcine interferons

Authors: Miller, Laura; Anderson, Sarah; FLEMING, DAMARIUS - Orise Fellow; JENNINGS, JARDON - Tennessee State University; Lager, Kelly; VAN GEELAN, ALBERT - Animal And Plant Health Inspection Services (APHIS), National Wildlife Center; SANG, YONGMING - Tennessee State University

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 5/19/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Introduction Although several PRRSV vaccines are currently available, based on different field isolates, they show limited cross-protective efficacy. In contrast to traditional methods of attenuation of PRRSV through repetitive cell culture passage, interferon genes were cloned into a PRRS DNA-launched reverse genetics system to generate vaccine candidates with specific changes. This recombinant virus was evaluated in vitro and in vivo to determine the effects of transgene expression on the virus, the cell, and the host animal. This vaccine platform is designed to directly overcome PRRSV-induced suppression of the pig's IFN signaling and associated immune response, in a manner similar to the atypical, IFN-inducing PRRSV strain A2MC2 [1-3]. Thus it may enhance vaccine efficacy against both homologous and heterologous PRRSV strains. Initial studies have shown the vaccine prototype efficacy is comparable to a commercially available PRRSV MLV vaccine. Materials and Methods The pCMV-P129 infectious cDNA clone was constructed from the virulent PRRSV-2 (Linage 8) field virus P129, isolated in Indiana in 1995. The infectious clone pKermit (Zoetis) [4] contains the GFP gene within an additional dedicated sgRNA expression cassette. The virus “Kermit” is derived from pKermit and causes infected cells to fluoresce with green light. In this study, the GFP gene was replaced with genes encoding a cohort of optimized antiviral interferons (IFNs) including each of IFN-a, IFN-ß and IFN-' subtypes. The IFN cohort-expressing virus (PRRSV-P129-IFNmix) was tested with or without an adjuvant and compared with a commercial MLV vaccine, Ingelvac PRRS® ATP (MLV-ATP). The vaccine challenge study used outbred pigs (5-wk-old, n = 10/group) (Table 1.) Table 1: Experimental design for the PRRSV-P129-IFNmix challenge study Group N Vaccine ToFA (5ug/ml) Montanide gel 10% Challenge 1 10 Sham + NADC-34 2 10 Sham + + NADC-34 3 10 PRRSV-P129-IFNmix + NADC-34 4 10 PRRSV-P129-IFNmix + + NADC-34 5 10 PRRSV-P129-IFNmix NADC-34 6 10 Sham NADC-34 7 10 MLV-ATP NADC-34 PRRSV dose: 2 ml/pig IM at 1 x 104 TCID50/ml; Sham: cell culture medium; Adjuvant: 10% Montanide T M IMS, Seppic; MLV-ATP: Ingelvac PRRS® ATP vaccine; ToFA: an acetyl-CoA carboxylase-a inhibitor. Results The PRRSV-P129-IFNmix virus had a higher replication rate and generated 0.5-2 logs more vaccine virus than the MLV-ATP vaccine during the 4-wk vaccination period. After the pigs were challenged with NADC-34 strain, all PRRSV-P129-IFNmix treatments were more effective in suppression of the challenged virus regardless of inclusion of the adjuvant (ADJ, 10% Montanide™ IMS, Seppic) [5]. The febrile response in pigs vaccinated with the attenuated PRRSV-P129-IFNmix are similar to the commercial ATP vaccine, particularly post challenge. The PRRSV-P129-IFNmix groups had a statistically non-significant difference across the range of high gross lung lesion scores from the MLV-ATP vaccine. The weekly weight gain in pigs vaccinated with the attenuated PRRSVp129-IFNmix vaccine candidates in comparison to the commercial ATP vaccine. The MLV-ATP group had better weight gain pre-challenge, but the groups with the tested vaccine candidates, particularly the MLV-PRRSVp129-IFNmix-ADJ, had greater weight gain post challenge. At -42 DPI all treatment groups were PRRSV antibody negative and PRRSV-free at vaccination. At challenge (0 DPI), the control and non-vaccinated groups were PRRSV antibody negative, while each vaccinated group was antibody positive. At 14 DPI, all challenged groups had antibody titers that were significantly higher than the non-vaccinated, non-challenged sham group; and the vaccinated groups were significantly different from the non-vaccinated groups. Acknowledgments We thank Jay G. Calvert (Zoetis) for the gift of the PRRSV infectious cDNA clone (pKermit). This work was supported by USDA NIFA