Immune therapy of hepatitis B virus chronic infection

Immune responses to recombinant Mycobacterium smegmatis expressing fused core protein and preS1 peptide of hepatitis B virus in mice

Attenuated strains of bacteria have been developed as potential live vectors to express homologous or heterologous antigens of many pathogens for inducing protective immune responses. The non-pathogenic and rapidly growing Mycobacterium smegmatis can be transformed effectively by genes for pathogenic antigens, and has been used as a valuable vector for the development of live vaccines. However, little is known on whether M. smegmatis could be transformed with the genes for HBV antigens and could express those genes, and whether vaccination with recombinant M. smegmatis could induce humoral and cellular immune responses in vivo. Both the core protein and preS1 peptide of the hepatitis B virus (HBV) are immunogenic and can induce cellular and humoral immune responses. This made them ideal platform for the development of new vaccines. In the present study, both recombinant M. smegmatis and DNA vaccines were generated to express the CS1 antigen, a fusion protein that comprises truncated core protein (amino acids 1-155) and preS1 peptide (amino acids 1-55) of HBV. Following vaccination of BALB/c mice with the live recombinant M. smegmatis, the CS1-based DNA vaccine, or controls, antigen-specific humoral and cellular immune responses were characterized. Vaccination with live recombinant M. smegmatis induced a stronger cellular immune response and a longer period of humoral immune response than with the DNA vaccination. These results indicate that the recombinant M. smegmatis can express efficiently immunogenic CS1 antigen of HBV in vivo, and may be used for the prevention of HBV infection.

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Recombinant hepatitis B core antigen carrying preS1 epitopes induce immune response against chronic HBV infection

Many studies have provided evidence that core antigen of hepatitis B virus (HBcAg) is extremely immunogenic, HBcAg can be function as both a T-cell-dependent antigen and a T-cell-independent antigen, and thus may be a promising candidate for therapeutic vaccine for control of chronic HBV infection. HBcAg is also an effective carrier for heterologous peptide epitopes. The preS1 is a surface protein of HBV and is immunogenic at the T and B cell level. The amino acid sequence 21-47 of preS1 is crucial for HBV binding to human hepatocytes as well as to PBMC and haematopoietic cell lines of the B cell lineage. Here we expressed a chimeric protein named HBVCS1, created by fusing the preS1 sequence 3-55 to the carboxyl terminus of the truncated HBcAg sequence 1-155 in E. coli. Analysis of its antigenicity and immunogenicity revealed that both HBc and preS1 epitopes are surface accessible, and that fusion of preS1 did not affect the HBc antigenicity and immunogenicity of the truncated HBc sequence. HBVCS1 induced strong anti-HBc and moderate anti-preS1 immune responses as well specific T-cell response in Balb/c mice. HBVCS1 vaccination reduced of the titer of HBsAg and HBV DNA in sera of HBV-Tg mice. These results indicate that HBVCS1 may have potential as a therapeutic vaccine for treatment of HBV chronic infection.

CpG oligodeoxynucleotides with hepatitis B surface antigen (HBsAg) for vaccination in HBsAg-transgenic mice

DNA motifs containing unmethylated CpG dinucleotides within the context of certain flanking sequences enhance both innate and antigen-specific immune responses, due in part to the enhanced production of Th1-type cytokines. Here we explored the ability of CpG-containing oligodeoxynucleotides combined with recombinant hepatitis B surface antigen (HBsAg) to induce Th1 responses in mice that are transgenic for this antigen and that represent a model for asymptomatic hepatitis B virus chronic carriers. This was compared to hepatitis B virus-specific DNA-mediated immunization, which we have previously shown to induce the clearance of the transgene expression product and the down-regulation of hepatitis B virus mRNA in this transgenic mouse lineage. In control nontransgenic C57BL/6 mice, three immunizations with HBsAg and CpG triggered the production of anti-HBs antibodies and of HBs-specific T cells that secrete gamma interferon but do not display any HBsAg-specific cytotoxic activity. In the HBsAg-transgenic mice, immunization with HBsAg and CpG oligodeoxynucleotides, but not with CpG alone, induced the clearance of HBsAg circulating in the sera, with a concomitant appearance of specific antibodies, and was able to regulate the hepatitis B virus mRNA constitutively expressed in the liver. Finally, adoptive transfer experiments with CD8(+) T cells primed in C57BL/6 mice with HBsAg and CpG oligodeoxynucleotide-based immunization show that these cells were able to partially control transgene expression in the liver and to clear the HBsAg from the sera of recipient transgenic mice without an antibody requirement. CpG oligodeoxynucleotides motifs combined with HBsAg could therefore represent a potential therapeutic approach with which to treat chronically infected patients.

Vaccination of chronic hepatitis B virus carriers with preS2/S envelope protein is not associated with the emergence of envelope escape mutants

PreS2/S vaccination of chronic hepatitis B virus (HBV) carriers led to a reduction in HBV replication or clearance of virus in 30% of treated patients. This study assessed whether vaccinotherapy of chronic HBV carriers induced the selection of escape mutants in the envelope 'a' determinant and whether envelope genetic variability might affect the response to vaccination. No amino acid differences were observed in the 'a' determinant between sequences obtained before and after treatment (five responders and seven non-responders). However, alignment with HBV prototype sequences revealed seven amino acid changes. Two mutations (T140S and P127L) diverged from subtype variations. In the complete envelope sequence (five non-responders and five responders), ten amino acid modifications were detected between sequences obtained before and after treatment. The absence of any common mutations did not enable the definition of a hot spot of mutations implicated in the response to vaccination. Moreover, vaccinotherapy does not induce the selection of escape mutants in the 'a' determinant.