Abstract
African swine fever virus (ASFV) affects pigs causing a haemorrhagic fever and up to 100 % lethality. Live vaccines were used in the 1960’s following outbreaks, but caused severe side-effects and to date there is no treatment or vaccine available for ASFV (Manso-Ribero et al. 1963). An emerging alternative to standard vaccination with live attenuated strains is the use of recombinant vaccines, which can be used to deliver target antigens without the concern of reversion to virulence and subsequent clinical disease. Mycobacterium bovis Bacillus Calmette–Guérin (BCG) is a live attenuated vaccine against Tuberculosis which remains the world’s most extensively used vaccine, with a safe and reliable track record. The studies described here aimed to develop a recombinant vaccine for ASFV using BCG (rBCG) expressing ASFV antigens. A mycobacterial toolbox that conforms to the BioBrick™ standards was generated in the process. This toolbox formed the basic minimal requirements for expression in any mycobacterial species, either integrative or episomal, and was complemented with a series of compatible and comparable mycobacterial promoters of varying strengths. This will allow researchers to individually tailor a plasmid to their specific requirements. This new synthetic biology approach to generate a designer rBCG vaccine allows for a rational optimization of the vaccine by probing the immune response to different antigens expressed at different levels. However, this study highlighted the unpredictability and instability of the mycobacterial vaccine vehicle. Following deletions of the promoter/gene region in the rBCG expressing the ASFV p30 antigen, the ASFV baculovirus-expressed p30 protein was then used in conjunction with BCG for in vitro studies and cytokine analysis of the porcine 3D4 (IPAM) and human THP-1 cell lines, in order to assess the adjuvant effect of the BCG and the ensuing immunological response.