Cellular and humoral immunity following vaccination with two different PCV2 vaccines (containing PCV2a or PCV2a/PCV2b) and challenge with virulent PCV2d.

Abstract

Porcine Circovirus type 2 (PCV2) associated disease is one of the most economically important swine diseases worldwide. Vaccines reduce PCV2 disease by inducing humoral immunity (neutralizing antibodies) and cell-mediated immunity (CMI) but may be improved by optimizing the immune response they induce. This study evaluated immune responses to a trivalent inactivated Porcine Circovirus (PCV) Type 1-Type 2a chimera (cPCV2a), cPCV2b and Mycoplasma hyopneumoniae (MH) (an experimental serial of Fostera® Gold PCV MH, also marketed as Circomax® Myco) vaccine or a bivalent recombinant PCV2a baculovirus expressed ORF2 capsid plus MH vaccine (Circumvent® PCV-M G2). Treatment Groups (T) received two doses of placebo (T01), one full or two split doses of the trivalent vaccine (T02, T03) or two split doses of the bivalent vaccine (T04) where two doses were given, there was a three-week period between administrations. All pigs were challenged with a virulent field isolate of PCV2d. CMI was measured as PCV2-specific IFN-γ secreting cells in blood and lymph node. Humoral immunity was measured as PCV2 antibodies. Vaccine efficacy was determined as viremia and fecal shedding of virus. There was a robust antibody response in T02 and T04 post the second vaccination and all vaccinated groups post challenge. There was a robust PCV2-specific IFN-γ response following the 1st dose in T02 and T03 and after the second dose in T02. T04 induced a low but detectable PCV2-specific IFN-γ response only after the 2nd dose. Among lymph node cells (study day 52), there was a significantly higher PCV2-specific, IFN-γ response to replicase and PCV2d capsid peptides in T01, consistent with active viral replication in non-vaccinated pigs. The trivalent chimeric vaccine induced robust CMI and protective efficacy, following a one dose regimen or splitting the dose into two vaccine administrations.