A recombinant pseudorabies virus surface - displaying the classical swine fever E2 protein induces specific antibodies rapidly

Pseudorabies virus (PRV) and classical swine fever virus (CSFV) are both economically important pathogens threatening the pig industry in many countries. The triple-gene-deleted variant of PRV, herein referred to as rPRVTJ-delgE/gI/TK, has exhibited pronounced efficacy and safety profiles. This underscores its viability as a prospective vaccine vector. However, the generation of specific anti-E2 antibodies necessitates elevated immunization doses and extended durations when the extracellular domain of the E2 protein of CSFV is secreted via the recombinant rPRVTJ-delgE/gI/TK vector. To enhance the presentation of exogenous antigens by antigen-presenting cells (APCs), we engineered the E2 protein expressed on the surface of PRV particles in this study. The recombinant virus expressing the E2 protein with a heterogonous transmembrane domain was generated in the backbone of rPRVTJ-delgE/gI/TK and designated as rPRVTJ-UL44-E2. The E2 gene was fused to the 3′ terminus of the UL44 gene utilizing P2A, a self-cleaving peptide sequence. The electron microscopy showed that the E2 protein was anchored on the surface of the viral particles of rPRVTJ-delgE/gI/TK-E2. The insertion of the E2 gene did not alter the native biological characteristics of the viral vector. Rabbits immunized with 10⁷ median tissue culture infective doses (TCID₅₀) of rPRVTJ-UL44-E2 exhibited a rapid seroconversion to anti-E2 specific antibodies within 7 days post-immunization (dpi). All the rabbits immunized with the rPRVTJ-UL44-E2 had generated antibodies specific to E2 prior to the administration of the booster immunization. However, the immunized rabbits were not protected from the CSFV C-strain challenge. Nevertheless, this strategy has notably achieved rapid induction of E2-specific non-neutralizing antibodies. These findings provide insights that the design of rPRVTJ-UL44-E2 requires optimization, thereby indicating a promising avenue for augmenting vaccine-induced immune responses.