Immune responses after administration of innovative Mycoplasma hyopneumoniae bacterins in pigs (SAPHIR Communication)

Vaccination against M. hyopneumoniae is widely used, but available vaccines provide only partial protection. This study aimed to screen innovative bacterins based on a highly virulent M. hyopneumoniae field strain for their ability to induce potent immune responses. Nine groups, each consisting of 6 M. hyopneumoniae-free piglets, were primo- (D0; 39 days of age) and booster (D14) vaccinated with 7 different experimental bacterins, a commercial bacterin as a positive control or PBS as a negative control. The experimental bacterin was formulated either with dmLT (group A), DDA:TDB liposomes (B), DPPC:DC-Chol liposomes+C-di.AMP (C), DPPC:DC-Chol liposomes+CpG ODN, resiquimod and Pam3Cys-SK4 (TLR ligands; D), PLGA:CTAB microparticles+TLR ligands (E), O/W emulsion+TLR ligands (F) and DOPC:Chol liposomes+TLR4 agonist and QS-21 (G). The specific immune response was assessed by the levels of specific antibodies in serum and in bronchoalveolar lavage fluid (BALf), and by T-cell specific responses measuring TNF, IFN-γ and IL-17 in CD4 T cells. On D28, 6/6 pigs from groups B, C, D, F, G and the commercial vaccine group, and 2/6 pigs from group E were seropositive. Group B, C and the commercial vaccine group had significantly higher OD-values for IgG in serum than group A and the negative control group, and the OD-value from group E was significantly lower compared to group C and the commercial vaccine group (P≤0.05). Serum IgA ELISA results did not differ over time or among groups. In group F, 1/6 pigs tested positive for M. hyopneumoniae specific IgA in BALf on D28. At D14, there was an upregulation of both TNF and IFN-γ double positive as well as IL-17+ CD4 T cells in the commercial vaccine and F groups. At D28, a strong TNF and IFN-γ response was observed in CD4 T cells from groups B and F, while a significant IL-17 response was seen in cells from the group E compared to the negative control group. Formulation B, E and F seem to be promising M. hyopneumoniae vaccine candidates.