RESUMO
Natural planned exposure (NPE) remains one of the most common methods in swine herds to boost lactogenic immunity against rotaviruses. However, the efficacy of NPE protocols in generating lactogenic immunity has not been investigated before. A longitudinal study was conducted to investigate the dynamics of genotype-specific antibody responses to different doses (3, 2 and 1) of Rotavirus A (RVA) NPE (genotypes G4, G5, P[7] and P[23]) in gilts and the transfer of lactogenic immunity to their piglets. Group 1 gilts received three doses of NPE at 5, 4 and 3 weeks pre-farrow (WPF), group 2 received two doses at 5 and 3 WPF, group 3 received one dose at 5 WPF, and group 4 received no NPE (control group). VP7 (G4 and G5) and truncated VP4* (P[7] and P[23]) antigens of RVA were expressed in mammalian and bacterial expression systems, respectively, and used to optimize indirect ELISAs to determine antibody levels against RVA in gilts and piglets. In day-0 colostrum samples, group 1 had significantly higher IgG titers compared to the control group for all four antigens, and either significantly or numerically higher IgG titers than groups 2 and 3. Group 1 also had significantly higher colostrum IgA levels than the control group for all antigens (except G4), and either significantly or numerically higher IgA levels compared to groups 2 and 3. In piglet serum, group 1 piglets had higher IgG titers for all four antigens at day 0 than the other groups. Importantly, RVA NPE stimulated antibodies in all groups regardless of the treatment doses and prevented G4, G5, P[7] and P[23] RVA fecal shedding prior to weaning in piglets in the absence of viral challenge. The G11 and P[34] RVA genotypes detected from pre-weaning piglets differed at multiple amino acid positions with parent NPE strains. In conclusion, the results of this study suggest that the group 1 NPE regimen (three doses of NPE) resulted in the highest anti-RVA antibody (IgG and IgA) levels in the colostrum/milk, and the highest IgG levels in piglet serum.
RESUMO
Introduction: African swine fever virus (ASFV) is a pathogen of great economic importance given that continues to threaten the pork industry worldwide, but there is no safe vaccine or treatment available. Development of a vaccine is feasible as immunization of pigs with some live attenuated ASFV vaccine candidates can confer protection, but safety concerns and virus scalability are challenges that must to be addressed. Identification of protective ASFV antigens is needed to inform the development of efficacious subunit vaccines. Methods: In this study, replication-incompetent adenovirus-vectored multicistronic ASFV antigen expression constructs that covered nearly 100% of the ASFV proteome were generated and validated using ASFV convalescent serum. Swine were immunized with a cocktail of the expression constructs, designated Ad5-ASFV, alone or formulated with either Montanide ISA-201™ (ASFV-ISA-201) or BioMize® adjuvant (ASFV-BioMize). Results: These constructs primed strong B cell responses as judged by anti-pp62-specific IgG responses. Notably, the Ad5-ASFV and the Ad5-ASFV ISA-201, but not the Ad5-ASFV BioMize®, immunogens primed significantly (p < 0.0001) higher anti-pp62-specific IgG responses compared with Ad5-Luciferase formulated with Montanide ISA-201™ adjuvant (Luc-ISA-201). The anti-pp62-specific IgG responses underwent significant (p < 0.0001) recall in all the vaccinees after boosting and the induced antibodies strongly recognized ASFV (Georgia 2007/1)-infected primary swine cells. However, following challenge by contact spreaders, only one pig nearly immunized with the Ad5-ASFV cocktail survived. The survivor had no typical clinical symptoms, but had viral loads and lesions consistent with chronic ASF. Discussion: Besides the limited sample size used, the outcome suggests that in vivo antigen expression, but not the antigen content, might be the limitation of this immunization approach as the replication-incompetent adenovirus does not amplify in vivo to effectively prime and expand protective immunity or directly mimic the gene transcription mechanisms of attenuated ASFV. Addressing the in vivo antigen delivery limitations may yield promising outcomes.