PCV2 vaccine for swine elicits strong cell-mediated immune response

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A porcine circovirus type 2 (PCV2) vaccine from Zoetis produces a robust and lasting cell-mediated immune response — the type of response that’s essential for protecting pigs against PCV2 disease.

Zoetis researchers evaluated cell-mediated immunity in pigs vaccinated with Fostera^® Gold PCV MH,¹ the new vaccine that protects against Mycoplasma hyopneumoniae (M. hyo) in  addition to PCV2. They compared results to those from pigs given another commercial PCV2 vaccine and to control pigs that received only saline. The groups were treated as follows:

• Fostera Gold PCV MH split dose: 1 ml at 3 and 6 weeks of age
• Fostera Gold PCV MH one dose: 2 ml at 3 weeks of age
• Circumvent^® PCV-M G2 split dose: 1 ml at 3 and 6 weeks of age
• Controls: 1 ml saline at 3 and 6 weeks of age

Three weeks after the last vaccination was administered, pigs were challenged with virulent PCV2d because it’s the most prevalent PCV2 genotype in US herds.

Higher T-cell response

“Pigs in both groups vaccinated with Fostera Gold PCV MH had a higher T-cell response than pigs vaccinated with Circumvent PCV-M G2 (Figure 1),” said Meggan Bandrick, DVM, PhD, research scientist.

“In contrast, Circumvent PCV-M G2 induced very little detectable cell-mediated immunity,” she reported.

Bandrick explained that “A higher T-cell response after vaccination is associated with a longer duration of immunity,² which is especially important with persistent viruses like PCV2.”

The new vaccine’s duration of immunity against PCV2 is 23 weeks, she said, and noted that the vaccine’s duration of immunity against M. hyo is also 23 weeks.³

Cell-mediated immunity was evaluated with an enzyme-linked immunosorbant spot assay. The assay detected the number of lymphocytes isolated from blood that responded to the vaccines by secreting the cytokine interferon gamma (IFN-γ) when exposed to PCV2 antigen. “The strength of the PCV2-specific, IFN-γ response correlates with protective immunity,”  she said.

Serology demonstrated that pigs vaccinated with either regimen of Fostera Gold PCV MH or the other vaccine developed antibodies against PCV2, as expected, Bandrick noted.

Why cell-mediated immunity matters

Assessments of vaccine responses tend to focus on antibody response, also known as  humoral immunity, instead of cell-mediated immunity — often because antibodies are  easier to measure. However, both types of immunity are important, the scientist continued.

“Antibodies, which are made from B cells, recognize and help neutralize circulating virus,  but they can’t get to viruses that have gotten into cells. That’s where cell-mediated immunity comes in. T cells not only help B cells produce effective antibodies, they kill virus-infected cells and help clear infection,” she said.

Adjuvants differ

Why one vaccine induces stronger cell-mediated immunity than another is largely due  to the vaccine’s adjuvant — the substance added to vaccines to boost the immune response, Bandrick continued.

“The adjuvant in Fostera Gold PCV MH is MetaStim^®, which elicits an antibody response as well as a strong cell-mediated response. It’s also smooth and injection-site reactions to the vaccine are rare and negligible,” she said.

Besides MetaStim, the new vaccine contains PCV2a and 2b. It’s the only commercial vaccine in the US with two PCV2 genotypes, and its efficacy against 2d was demonstrated in a large field trial.⁴ Following PCV2d, PCV2b then 2a are the most prevalent PCV2 genotypes  circulating in US herds,⁵ Bandrick said.

Research with over 160 known PCV2 strains indicated that a vaccine with two PCV2 genotypes should provide the broadest coverage available against current and circulating  PCV2 viruses,⁶ she said.

“Fostera Gold PCV MH has several strong characteristics. It will provide broad genotype  coverage, induce a robust cell-mediated response and has a duration of immunity that lasts through the production stage. These attributes provide pork producers with excellent  protection against PCV2 disease,” Bandrick said.

All trademarks are the property of Zoetis Services LLC or a related company or a licensor unless otherwise noted. Circumvent is a registered trademark of Merck Animal Health.

1 Data on file, Study Report No. B820R-US17-747, Zoetis LLC.
2 Pulendran B, et al. Review: Translating Innate Immunity into Immunological Memory: Implications for Vaccine Development. Cell. 2006;124:849-863.
3 Data on file, Study Report No. B824R-US15-505, Zoetis LLC.
4 Data on file, Study Report No. 16PRGBIO01-01, Zoetis LLC.
5 Personal communication between Darin Madson, PhD, and Rick Swalla, DVM.
6 Data on file, Study Report No. WO1, EpiCC PCV2 Analysis, Zoetis LLC.

DISCOVERIES, Issue 9
Discoveries is a series of  research news reports written by the editors of Pig Health Today on behalf of the US Pork Business of Zoetis.

FSTRA-00103
August 2021