Design of therapeutic vaccines against chronic hepatitis B virus (HBV) infection in preclinical models

• Research unit: EU RFP
• Project number: 98.0175

Key words (German)

Hepatitis B; therapeutischer Impfstoff; preklinische Modelle

Alternative project number (English)

EU project number: BIO4CT980002

Research programs (English)

EU-programme: 4. Frame Research Programme - 4.1 Biotechnology

Short description (English)

See abstract

Partners and International Organizations (English)

Coordinator: Universität Ulm (D)

Abstract (English)

In this project, we studied immunopotentiating reconstituted influenza virosomes (IRIV) as a carrier system for either the CHO-derived HBsAg antigen or HBsAg-encoding DNA.

1 Delivery of the CHO derived HBV antigen
In Epaxal BernaÔ, the first commercially available virosomal vaccine, it is expected that the inactivated hepatitis A virus is spontaneously adsorbed to IRIV particles. The antigen is believed to be attached to the IRIV by interacting with phospholipids which seem to be the natural receptor on hepatocytes. In a first phase, we studied this binding and the importance of adsorption of the antigen to the IRIV for the induction of a good immune response. Using the monolayer expansion method we could show binding of hepatitis A virions to a model membrane. On the other hand, we tested the immunogenicity of antigens using different virosomal carrier systems. As a model antigen we immunized mice with streptavidine bound to biotinylated virosomes, mixed with virosomes or given alone. A coadministration of the antigen together with IRIV enhanced the humoral immune response about 4-fold compared to antigen alone. A binding of the antigen via the biotinylated virosomes induced an about 45-fold higher antibody immune response than the antigen given alone. These datas demonstrate the importance of a physical association of the antigen with the carrier system (1).
We optimized our antigen carrier system by removing some B-cell epitopes from the virosomes. Using this modified virosome delivery system, a very good antibody response and a significant cellular immune response to HBsAg was elicited in mice.
Based on these results we prepared a virosome HBV vaccine formulation under GMP conditions, including the necessary documentation, according to the guidelines for preclinical evaluation of new vaccines from the European Agency for the Evaluation of Medicinal products (EMEA). Phase I clinical trials have begun using this formulation.
In woodchuck challenge experiments it was shown, that CHO-derived surface antigens from HBV protected animals against WHV infection. The virosome delivery technique was ineffective in this system as CHO-derived HBsAg formulated into an IRIV vaccine neither primed an immune response to surface antigen, nor protected woodchucks against a subsequent WHV challenge infection. Since we bound very high amount of antigen to the virosomes it is possible, that this henced the binding of the carrier system to the antigen presenting cells and therefore also its immunogenicity

2 Delivery of DNA vaccines
We studied the use of virosomes as a delivery system for DNA. To accomplish this, charged lipids were intercalated into the virosome bilayer. The positive results we obtained in in vitro experiments could not, however, be reproduced in animal trials. Alternative methods for the loading of DNA into virosomes are currently under evaluation.
DNA vaccines are most commonly expressed under control of the CMV promoter. We demonstrated that efficient DNA vaccines can be constructed that express HBsAg under control of the desmin promoter (2).

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 98.0175