Co-expression of the hepatitis B surface and core antigens using baculovirus multiple expression vectors.

The hepatitis B (HB) virus DNA sequences coding for the pre-core (preC) or C antigens (HBpcAg, HBcAg) have been inserted into the baculovirus plasmid transfer vector, pAcYM1, such that the HB viral sequences are under the control of the polyhedrin promoter of Autographa californica nuclear polyhedrosis virus (AcNPV). Spodoptera frugiperda cells infected with either of the derived recombinant plasmids in the presence of infectious AcNPV DNA yielded recombinant, polyhedrin-negative viruses that expressed high levels of the respective HBpcAg or HBcAg (representing approx. 5 to 10% and approx. 40% of the stained cellular proteins, respectively). The particulate 27 nm HBcAgs have been purified to homogeneity from infected cell extracts by density gradient centrifugation. Dual expression transfer vectors containing the HBcAg gene sequences and the coding sequences of the HB viral S antigen (HBsAg), each gene under the control of its own copy of the polyhedrin promoter, have also been constructed and used to derive recombinant viruses. The recombinant with the HB C and S genes expressed high levels of the HBcAg (approx. 40% of the cellular proteins) and low levels of the HBsAg (approx. 2% of the stained cellular proteins). Dual expression, occluded, recombinant baculoviruses that make HBsAg, as well as the AcNPV polyhedrin protein, have been prepared that are highly infectious for Trichoplusia ni caterpillars, allowing reproducible preparation of the antigen in larvae. Using radioimmunoassays (RIAs) and ELISAs, the recombinant HBcAg (RIA) and HBsAg (ELISA) have been used to identify human antibodies to HB virus with results that compare favourably with the data obtained with non-recombinant antigens.