Panagiota Maravelia[1], Lars Frelin[1], Neetu Jagya[1], Georg Verch[2], Yi Ni[2], Stephan Urban[2], Matti Sällberg[1]
Affiliates: [1] Division of Clinical Microbiology, Laboratory Medicine, Karolinska Institutet, Stockholm, Sweden. [2] Molecular Virology, University of Heidelberg, Heidelberg, Germany.

It is generally thought that chronic infections caused by the hepatitis B and D viruses (HBV/HDV) can be controlled, or cleared, by the host immunity. During the chronic HBV infection a severe T cell dysfunction, or tolerance, is induced by the virus. In addition, the neutralizing antibodies to the major surface (S) antigen determinant are blocked by the circulating HBV surface antigen (HBsAg). However, as preS1 constitutes only a smaller portion of the circulating HBsAg, these antibodies are attractive to improve the neutralizing ability of the host. Collectively, it is difficult to activate, or reactivate, HBV-specific immune responses in this impaired and complex immunological setting. We therefore used different genotypes (gts) of the HDV capsid antigen, HDAg, as heterologous antigens that induce only healthy T cells in chronic HBV infection, linked to preS1 sequences to circumvent the impaired HBV-specific immunity.

We designed 10 DNA vaccine candidates containing various combinations of preS1 sequences and HDAg. The DNA vaccines were evaluated for the induction of both antibodies and specific T cells in C57BL/6 mice after intramuscular immunization. Immune responses were monitored by ELISA/ELISPOT and the induced antibodies were further evaluated by an in vitro neutralization assay.

We could show that HDAg-specific T cells were genotype-specific in mice, thereby both HDV gt1 and gt2 strains need to be included in the vaccine. The various vaccine candidates differed in their ability to induce broadly cross-reactive preS1 antibodies and to neutralize HBV in vitro. We identified one vaccine candidate that induced preS1 antibodies which cross-reacted with the HBV genotypes A-F, and T cells targeting both HDV gts 1 and 2. In addition, this candidate was the most effective in inducing in vitro neutralizing antibodies to HBV. This unique therapeutic vaccine candidate used the concept of engaging healthy heterologous T cells to induce both HBV- and HDV-specific immune responses in patients chronically infected by HBV.

We conclude that this can be a good vaccine candidate for future combination of immunotherapies against chronic HBV and possibly also HDV infection.