ASFV antigens selected from genotype I immunised pigs are immunogenic, but do not protect against genotype II challenge

Abstract

African swine fever virus (ASFV) has caused recent outbreaks of viral haemorrhagic fever in domestic pigs and wild boar in Africa, Asia, Europe, Oceania and North America. Control measures for African swine fever are limited in most countries to biosecurity at the farm gate followed by movement restrictions and selective or complete culling of pigs on affected premises. Modified live vaccines are being trialled in several countries, however development of safe and effective African swine fever subunit vaccines has been restricted by a poor understanding of the key antigens required for protection, particularly for the panzootic genotype II viruses. The cellular immune response is thought to be critical for protection against African swine fever and therefore to develop an effective subunit vaccine that stimulates an anti-ASFV T-cell response we screened lymphocytes from pigs which survived challenge with Georgia 2007/1. Using an overlapping peptide library corresponding to 168 annotated open reading frames and 24 potential minor open reading frames we identified seventeen proteins which strongly stimulated secretion of interferon gamma in an ELISpot assay. The phenotype of the T cells which were stimulated by these pools of peptides were then investigated by flow cytometry. Proteins stimulating predominantly CD8⁺ T cells were incorporated into bivalent replication deficient adenovirus vectors and tested as potential vaccine candidates in immunisation and challenge experiments in pigs.