Immunization of pigs with replication-incompetent adenovirus-vectored African swine fever virus multi-antigens induced humoral immune responses but no protection following contact challenge

Michelle D Zajac; Jessie D Trujillo; Jianxiu Yao; Rakshith Kumar; Neha Sangewar; Shehnaz Lokhandwala; Huldah Sang; Kylynn Mallen; Jayden McCall; Leeanna Burton; Deepak Kumar; Emily Heitmann; Tristan Burnum; Suryakant D Waghela; Kelli Almes; Juergen Richt; Tae Kim; Waithaka Mwangi

doi:10.3389/fvets.2023.1208275

Immunization of pigs with replication-incompetent adenovirus-vectored African swine fever virus multi-antigens induced humoral immune responses but no protection following contact challenge

Front Vet Sci. 2023 Jun 19:10:1208275. doi: 10.3389/fvets.2023.1208275. eCollection 2023.

Authors

Michelle D Zajac¹, Jessie D Trujillo¹, Jianxiu Yao¹, Rakshith Kumar¹, Neha Sangewar¹, Shehnaz Lokhandwala¹, Huldah Sang¹, Kylynn Mallen¹, Jayden McCall¹, Leeanna Burton¹, Deepak Kumar¹, Emily Heitmann¹, Tristan Burnum¹, Suryakant D Waghela², Kelli Almes¹, Juergen Richt¹, Tae Kim¹, Waithaka Mwangi¹

Affiliations

¹ Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, United States.
² Department of Veterinary Pathobiology, Texas A&M University, College Station, TX, United States.

Abstract

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.

Keywords: African swine fever (ASFV); IgG; histopathology; natural transmission model; polyvalent Ad5 vectored vaccine; real-time quantitative polymerase chain reaction (RT-qPCR).

Grants and funding

This research was funded by the Agriculture and Food Research Initiative Competitive Grant No. 2016-67015-25041 from the USDA National Institute of Food and Agriculture, Median Diagnostics, Inc., the NBAF Transition Funds, and The Article Publishing Charge (APC) was funded by the Agriculture and Food Research Initiative Competitive Grant No. 2016-67015-25041 from the USDA National Institute of Food and Agriculture.