Quantification, epitope mapping and genotype cross-reactivity of hepatitis B preS-specific antibodies in subjects vaccinated with different dosage regimens of BM32

BACKGROUND: Chronic hepatitis B virus (HBV) infections are a global health problem. There is a need for therapeutic strategies blocking continuous infection of liver cells. The grass pollen allergy vaccine BM32 containing the preS domain of the large HBV surface protein (LHBs) as immunogenic carrier induced IgG antibodies in human subjects inhibiting HBV infection in vitro. Aim of this study was the quantification, epitope mapping and investigation of HBV genotype cross-reactivity of preS-specific antibodies in subjects treated with different dosage regimens of BM32 METHODS: Hundred twenty eight grass pollen allergic patients received in a double-blind, placebo-controlled trial five monthly injections of placebo (aluminum hydroxide, n= 34) or different courses of BM32 (2 placebo + 3 BM32, n= 33; 1 placebo + 4 BM32, n= 30; 5 BM32, n= 31). Recombinant Escherichia coli-expressed preS was purified. Overlapping peptides spanning preS and the receptor-binding sites from consensus sequences of genotypes A-H were synthesized and purified. Isotype (IgM, IgG, IgA, IgE) and IgG subclass (IgG1-IgG4) responses to preS and peptides were determined by ELISA at baseline, one and four months after the last injection. IgG1 and IgG4 subclass concentrations specific for preS and the receptor-binding site were measured by quantitative ELISA.

FINDINGS: Five monthly injections induced the highest levels of preS-specific IgG consisting mainly of IgG1 and IgG4, with a sum of median preS-specific IgG1 and IgG4 concentrations of >135 μg/ml reaching up to 1.8 mg/ml. More than 20% of preS-specific IgG was directed against the receptor-binding site. BM32-induced IgG cross-reacted with the receptor-binding domains from all eight HBV genotypes A-H.

INTERPRETATION: BM32 induces high levels of IgG1 and IgG4 antibodies against the receptor binding sites of all eight HBV genotypes and hence might be suitable for therapeutic HBV vaccination.

FUNDING: This study was supported by the PhD program IAI (KPW01212FW), by Viravaxx AG and by the Danube-ARC funded by the Government of Lower Austria. Rudolf Valenta is a recipient of a Megagrant of the Government of the Russian Federation, grant No 14.W03.31.0024.