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Immune responses and protection by vaccine and various vaccine adjuvant candidates to virulent porcine reproductive and respiratory syndrome virus.

Author(s): Charerntantanakul W, Platt R, Johnson W, Roof M, Vaughn E, Roth JA

Affiliation(s): Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA.

Publication date & source: 2006-01-15, Vet Immunol Immunopathol., 109(1-2):99-115. Epub 2005 Sep 13.

Publication type: Randomized Controlled Trial; Research Support, Non-U.S. Gov't

Various vaccine adjuvant candidates were assessed with the modified-live porcine reproductive and respiratory syndrome virus (MLV PRRSV) (Ingelvac PRRS MLV) vaccine. Their influence on humoral-mediated immune (HMI) and cell-mediated immune (CMI) responses as well as protection from virulent PRRSV challenge (MN-184) was evaluated. Ninety seronegative pigs were randomly divided into nine groups of 10 pigs. One group received MLV vaccine alone. Five groups received MLV vaccine with either bacterial endotoxin-derived adjuvant (ET), mixed open reading frame 5 (ORF5) peptides derived from various PRRSV isolates, porcine interferon alpha (IFNalpha), polyinosinic-polycytidylic acid stabilized with polylysine and carboxymethylcellulose (poly-ICLC), or porcine interleukin-12 (IL-12). One group did not receive MLV vaccine but was immunized with ORF5 peptides conjugated with cholera toxin (ORF5 peptide/CT). Two groups served as challenged and unchallenged non-vaccinated controls. Four-color flow cytometry was utilized to simultaneously identify three major porcine T-cell surface markers (CD4, CD8, and gammadelta TCR) and detect activation marker CD25 (alpha chain of IL-2 receptor) or intracellular IFNgamma. The MLV PRRSV vaccine alone successfully primed CD4(-)CD8(+)gammadelta- T-cells as demonstrated by a significant increase in %IFNgamma+ cells when live PRRSV was used as a recall antigen. Booster immunizations of mixed ORF5 peptides and co-administration of IL-12 with MLV PRRSV vaccine significantly enhanced IFNgamma expression by some T-cell subsets (CD4(-)CD8(+)gammadelta+ and CD4(-)CD8(-)gammadelta+ for mixed ORF5 peptides and CD4(+)CD8(+)gammadelta- and CD4(-)CD8(+)gammadelta+ for IL-12). All groups receiving MLV-vaccine with or without adjuvants had reduced lung lesions after challenge. The group immunized with only ORF5 peptide/CT did not have significant T-cell recall responses and was not protected from challenge. Expression of IFNgamma by several T-cell subsets correlated with reduced lung lesions and viremia, whereas expression of CD25 did not. Expression of surface CD25 did not correlate with IFNgamma production. PRRSV ELISA s/p ratio prior to challenge also correlated with reduced lung lesions and viremia. In conclusion, booster immunizations of the mixed ORF5 peptides and co-administration of IL-12 effectively enhanced the CMI response to MLV vaccine. However, neither adjuvant significantly contributed to reducing clinical effects when compared to MLV alone.

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