The position of heterologous epitopes inserted in hepatitis B virus core particles determines their immunogenicity

Abstract

The nucleocapsid (HBcAg) of the hepatitis B virus (HBV) has been suggested as a carrier moiety for vaccine purposes. We investigated the influence of the position of the inserted epitope within hybrid HBcAg particles on antigenicity and immunogenicity. For this purpose, genes coding for neutralizing epitopes of the pre-S region of the HBV envelope proteins were inserted at the amino terminus, the amino terminus through a precore linker sequence, the truncated carboxy terminus, or an internal site of HBcAg by genetic engineering and were expressed in Escherichia coUl. All purified hybrid HBc/pre-S polyproteins were particulate. Aminoand carboxy-terminal-modified hybrid HBc particles retained HBcAg antigenicity and immunogenicity. In contrast, insertion of a pre-S(1) sequence between HBcAg residues 75 and 83 abrogated recognition of HBcAg by 5 of 6 anti-HBc monoclonal antibodies and diminished recognition by human polyclonal anti-HBc. Predictably, HBcAg-specific immunogenicity was also reduced. With respect to the inserted epitopes, a pre-S(1) epitope linked to the amino terminus of HBcAg was not surface accessible and not immunogenic. A pre-S(1) epitope fused to the amino terminus through a precore linker sequence was surface accessible and highly immunogenic. A carboxy-terminal-fused pre-S(2) sequence was also surface accessible but weakly immunogenic. Insertion of a pre-S(l) epitope at the internal site resulted in the most efficient anti-pre-S(1) antibody response. Furthermore, immunization with hybrid HBc/pre-S particles exclusively primed T-helper cells specific for HBcAg and not the inserted epitope. These results indicate that the position of the inserted B-cell epitope within HBcAg is critical to its immunogenicity.

Comparison of antibody responses to different forms of HIV-1 core antigens by epitope mapping

“…Taken together, these data clearly show that the insertion of heterologous epitopes in core-like particles modified and determined their immunogenicity. Such an observation was also made and a similar conclusion reached when neutralizing epitopes of the pre-S region of the hepatitis B virus envelope were inserted at different places of the viral core protein [Schödel et al, 1992].…”

Specific deletions in the hepatitis B virus core open reading frame in patients with chronic active hepatitis B

“…Another consequence of these deletions would be loss of the HBe2 determinant because the remaining amino acids would constitute <90% of the full length protein. Schodel et al [1992] have demonstrated that insertion of a pre-S(l) epitope sequence into the core gene, which resulted in expression of the epitope between amino acids 75 and 83 of the HBcAg, dramatically reduced both the antigenicity and immunogenicity of the capsid protein. Such reduction was not observed if the foreign epitope was inserted at the 5' or 3' ends of the core gene.…”

Differentiation of core gene products of the hepatitis B virus in infected liver tissue using monoclonal antibodies

“…Our finding that practically all core protein in hepatocytes of chronic HBV carriers is assembled in core particles is also relevant to the host immune responses. The particulate core protein is more immunogenic than the denatured forms [Schödel et al, 1992]. In athymic mice only the particulate form of HBcAg was able to induce a T cell-independent antibody response [Milich et al, 1986].…”