[show abstract][hide abstract] ABSTRACT: Regulatory T (Treg) cells represent one of the main mechanisms of regulating self-reactive immune cells. Treg cells are thought to play a role in down-regulating immune responses to self or allogeneic antigens in the periphery. Although the function of Treg cells has been demonstrated in many experimental settings, the precise mechanisms and antigen specificity often remain unclear. In a hepatitis B e antigen-T-cell receptor (HBeAg-TCR) double transgenic mouse model, we observed a phenotypically unique (TCR+) CD4- /CD8- CD25(+/-) GITR(high) PD-1(high) FoxP3-) HBeAg-specific population that demonstrates immune regulatory function. This HBeAg-specific double-negative regulatory cell population proliferates vigorously in vitro, in contrast to any other known regulatory population, in an interleukin-2-independent manner.
[show abstract][hide abstract] ABSTRACT: Previous studies demonstrated that the primary APCs for the hepatitis B core Ag (HBcAg) were B cells and not dendritic cells (DC). We now report that splenic B1a and B1b cells more efficiently present soluble HBcAg to naive CD4(+) T cells than splenic B2 cells. This was demonstrated by direct HBcAg-biotin-binding studies and by HBcAg-specific T cell activation in vitro in cultures of naive HBcAg-specific T cells and resting B cell subpopulations. The inability of DC to function as APCs for exogenous HBcAg relates to lack of uptake of HBcAg, not to processing or presentation, because HBcAg/anti-HBc immune complexes can be efficiently presented by DC. Furthermore, HBcAg-specific CD4(+) and CD8(+) T cell priming with DNA encoding HBcAg does not require B cell APCs. TLR activation, another innate immune response, was also examined. Full-length (HBcAg(183)), truncated (HBcAg(149)), and the nonparticulate HBeAg were screened for TLR stimulation via NF-kappaB activation in HEK293 cells expressing human TLRs. None of the HBc/HBeAgs activated human TLRs. Therefore, the HBc/HBeAg proteins are not ligands for human TLRs. However, the ssRNA contained within HBcAg(183) does function as a TLR-7 ligand, as demonstrated at the T and B cell levels in TLR-7 knockout mice. Bacterial, yeast, and mammalian ssRNA encapsidated within HBcAg(183) all function as TLR-7 ligands. These studies indicate that innate immune mechanisms bridge to and enhance the adaptive immune response to HBcAg and have important implications for the use of hepadnavirus core proteins as vaccine carrier platforms.
The Journal of Immunology 07/2009; 182(11):6670-81. · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: Hepatitis B virus (HBV) expresses two structural forms of the nucleoprotein, the intracellular nucleocapsid (hepatitis core antigen [HBcAg]) and the secreted nonparticulate form (hepatitis e antigen [HBeAg]). The aim of this study was to evaluate the ability of HBcAg- and HBeAg-specific genetic immunogens to induce HBc/HBeAg-specific CD4(+)/CD8(+) T-cell immune responses and the potential to induce liver injury in HBV-transgenic (Tg) mice. Both the HBcAg- and HBeAg-specific plasmids primed comparable immune responses. Both CD4(+) and CD8(+) T cells were important for priming/effector functions of HBc/HBeAg-specific cytotoxic T-lymphocyte (CTL) responses. However, a unique two-step immunization protocol was necessary to elicit maximal CTL priming. Genetic vaccination did not prime CTLs in HBe- or HBc/HBeAg-dbl-Tg mice but elicited a weak CTL response in HBcAg-Tg mice. When HBc/HBeAg-specific CTLs were adoptively transferred into HBc-, HBe-, and HBc/HBeAg-dbl-Tg mice, the durations of the liver injury and inflammation were significantly greater in HBeAg-Tg recipient mice than in HBcAg-Tg mice. Importantly, liver injury in HBc/HBeAg-dbl-Tg mice was similar to the injury observed in HBeAg-Tg mice. Loss of HBeAg synthesis commonly occurs during chronic HBV infection; however, the mechanism of selection of HBeAg-negative variants is unknown. The finding that hepatocytes expressing wild-type HBV (containing both HBcAg and HBeAg) are more susceptible to CTL-mediated clearance than hepatocytes expressing only HBcAg suggest that the HBeAg-negative variant may have a selective advantage over wild-type HBV within the livers of patients with chronic infection during an immune response and may represent a CTL escape mutant.
Journal of Virology 12/2008; 83(3):1379-92. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: The hepatitis B core antigen (HBcAg) has been proposed as a useful particulate carrier platform for poorly immunogenic peptidic and carbohydrate B cell epitopes. However, biochemical and immunologic impediments have plagued this technology. Specifically, the "assembly" problem characterized by the low yield of unstable hybrid particles resulting from the insertion of foreign sequences and the "pre-existing immunity" problem due to the fact that the HBcAg is derived from a human pathogen have limited the development of this carrier technology. As a means of addressing the "pre-existing immunity" problem we have used the core proteins from the rodent hepdnaviruses. A number of advantages to the use of the rodent hepadnaviral core proteins as opposed to the HBcAg for vaccine design were defined including: equal or superior immunogenicity at the T and B cell levels; the use of the rodent core proteins does not compromise the anti-HBc diagnostic assay; the efficacy of the rodent core proteins as vaccine carriers will not be limited by pre-existing anti-HBc antibodies that are present in previously and currently HBV-infected persons; and the HBcAg-specific tolerance present in HBV chronic carriers can be circumvented by the use of the rodent core proteins.
[show abstract][hide abstract] ABSTRACT: The hepatitis B virus core protein (HBcAg) is a uniquely immunogenic particulate antigen and as such has been used as a vaccine carrier platform. The use of other hepadnavirus core proteins as vaccine carriers has not been explored. To determine whether the rodent hepadnavirus core proteins derived from the woodchuck (WHcAg), ground squirrel (GScAg), and arctic squirrel (AScAg) viruses possess immunogen characteristics similar to those of HBcAg, comparative antigenicity and immunogenicity studies were performed. The results indicate that (i) the rodent core proteins are equal in immunogenicity to or more immunogenic than HBcAg at the B-cell and T-cell levels; (ii) major histocompatibility complex (MHC) genes influence the immune response to the rodent core proteins (however, nonresponder haplotypes were not identified); (iii) WHcAg can behave as a T-cell-independent antigen in athymic mice; (iv) the rodent core proteins are not significantly cross-reactive with the HBcAg at the antibody level (however, the nonparticulate "eAgs" do appear to be cross-reactive); (v) the rodent core proteins are only partially cross-reactive with HBcAg at the CD4+ T-cell level, depending on MHC haplotype; and (vi) the rodent core proteins are competent to function as vaccine carrier platforms for heterologous, B-cell epitopes. These results have implications for the selection of an optimal hepadnavirus core protein for vaccine design, especially in view of the "preexisting" immunity problem that is inherent in the use of HBcAg for human vaccine development.
Journal of Virology 12/2005; 79(21):13641-55. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: The particulate hepatitis core protein (HBcAg) represents an efficient carrier platform with many of the characteristics uniquely required for the delivery of weak immunogens to the immune system. Although the HBcAg is highly immunogenic, the existing HBcAg-based platform technology has a number of theoretical and practical limitations, most notably the "preexisting immunity" and "assembly" problems. To address the assembly problem, we have developed the core protein from the woodchuck hepadnavirus (WHcAg) as a new particulate carrier platform system. WHcAg appears to tolerate insertions of foreign epitopes at a greater number of positions than HBcAg. For example, both within the external loop region and outside the loop region a total of 17 insertion sites were identified on WHcAg. Importantly, the identification of an expanded number of insertion sites was dependent on additional modifications to the C terminus that appear to stabilize the various internal insertions. Indeed, 21 separate C-terminal modifications have been generated that can be used in combination with the 17 insertion sites to ensure efficient hybrid WHcAg particle assembly. This combinatorial technology is also dependent on the sequence of the heterologous insert. Therefore, the three variables of insert position, C terminus, and epitope sequence are relevant in the design of hybrid WHcAg particles for vaccine purposes.
Journal of Virology 12/2005; 79(21):13656-66. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: The function of the hepatitis B virus (HBV) precore or HBeAg is largely unknown because it is not required for viral assembly, infection, or replication. However, the HBeAg does appear to play a role in viral persistence. It has been suggested that the HBeAg may promote HBV chronicity by functioning as an immunoregulatory protein. As a model of chronic HBeAg exposure and to examine the tolerogenic potential of the HBV precore and core (HBcAg) proteins, HBc/HBeAg-transgenic (Tg) mice crossed with T cell receptor (TCR)-Tg mice expressing receptors for the HBc/HBeAgs (i.e., TCR-antigen double-Tg pairs) were produced. This study revealed three phenotypes of HBe/HBcAg-specific T-cell tolerance: (i) profound T-cell tolerance most likely mediated by clonal deletion, (ii) T-cell clonal ignorance, and (iii) nondeletional T-cell tolerance mediated by clonal anergy and dependent on the structure, location, and concentration of the tolerogen. The secreted HBeAg is significantly more efficient than the intracellular HBcAg at eliciting T-cell tolerance. The split T-cell tolerance between the HBeAg and the HBcAg and the clonal heterogeneity of HBc/HBeAg-specific T-cell tolerance may have significant implications for natural HBV infection and especially for precore-negative chronic hepatitis.
Journal of Virology 04/2005; 79(5):3016-27. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: A unique characteristic of the hepatitis B virus is the production of a secreted form (precore or HBeAg) of the structural nucleocapsid (core or HBcAg). By using T cell receptor (TCR) transgenic (Tg) and TCR x HBc/HBeAg double- and triple-Tg pairs, we demonstrate that HBeAg elicits T cell tolerance, whereas HBcAg is nontolerogenic in this system. In fact, TCR x HBc double-Tg mice spontaneously seroconvert to IgG anti-HBc positivity at an early age. However, the presence of HBeAg in the serum of TCR x HBc x HBe triple-Tg mice prevents anti-HBc seroconversion. HBeAg mediates its immunoregulatory effect by eliciting tolerance in HBc/HBeAg-specific T cells. The results suggest that hepadnaviruses have retained a secretory form of the nucleoprotein because it functions as a T cell tolerogen and regulates the immune response to the intracellular nucleocapsid. This HBeAg-mediated immune regulation may predispose to chronicity during perinatal infections and prevent severe liver injury during adult infections.
Proceedings of the National Academy of Sciences 11/2004; 101(41):14913-8. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: The recent success of a Plasmodium falciparum malaria vaccine consisting of circumsporozoite (CS) protein (CSP) T and B cell epitopes has rekindled interest in the development of a pre-erythrocytic vaccine. Our goal was to design an efficient delivery system for known neutralizing epitopes.
Well-characterized CSP-specific neutralizing B cell epitopes and a 'universal' T cell epitope were combined with a particulate carrier platform, the hepatitis B core antigen (HBcAg), to produce a novel pre-erythrocytic vaccine candidate.
The vaccine candidate V12.PF3.1 is a potent immunogen in mice, eliciting unprecedented levels (greater than 106 titers) of sporozoite-binding antibodies after only two doses. The antisporozoite antibodies are long-lasting and represent all IgG isotypes, and antibody production is not genetically restricted. CSP-specific CD4+ T cells are also primed by V12.PF3.1 immunization in a majority of murine strains. Furthermore, the hybrid HBcAg-CS particles can be produced inexpensively in bacterial expression systems.
These characteristics suggest that V12.PF3.1 represents an efficient and economical P. falciparum vaccine candidate for use separately or in combination with other formulations.
[show abstract][hide abstract] ABSTRACT: This report reviews and extends data on the use of hepatitis B virus (HBV) core (HBcAg) particles as a carrier moiety for B-cell epitopes of the HBV envelope proteins1–4. Virus-neutralizing epitopes of the HBV pre-S region were inserted at the N-terminus, the N-terminus through a precore linker sequence, the C-terminus and an internal position of HBcAg by genetic engineering in Escherichia coli. The hybrid HBc/pre-S proteins were purified and their antigenicity and immunogenicity analysed. All purified HBc/pre-S particles were particulate. Pre-S epitopes inserted at the N-terminus through a precore polylinker, the truncated C-terminus and at the internal position between HBcAg amino acids 75 and 81 were accessible on the particle surface. N-terminal fusions required the presence of the linker sequence to become surface accessible and immunogenic. Fusions to the N- and C-termini of HBcAg did not interfere with HBcAg antigenicity and immunogenicity. In contrast, insertion at the internal site abrogated recognition of HBcAg by five out of six monoclonal antibodies and diminished recognition by human polyclonal anti-HBc antibodies as well as HBcAg immunogenicity. A pre-S(2) sequence fused to the C-terminus of HBcAg was surface accessible and weakly immunogenic. Pre-S(1) sequences fused to the N-terminus through a precore linker were surface accessible and highly immunogenic. The same sequence fused to the core methionine was not surface accessible or immunogenic. Insertion of the same pre-S(1) sequence at an internal position of HBcAg resulted in the most efficient anti-pre-S(1) antibody response. Hybrid HBc/pre-S particles were also expressed in avirulent aroA or Δcya Δcrp Salmonella typhimurium and Salmonella dublin. Oral immunization of mice with Salmonella expressing C-terminally fused hybrid HBc/pre-S(2) particles resulted in high-titred serum anti-HBc antibodies and low-titred anti-pre-S(2) antibodies. Oral immunization with Δcya Δcrp S. typhimurium expressing internally fused HBc/pre-S hybrid elicited high titred serum anti-pre-S(1) antibodies.
[show abstract][hide abstract] ABSTRACT: Summary The hepatitis B virus (HBV) nucleocapsid antigen (HBcAg) was investigated as a carrier moiety for the immunodominant circumsporozoite (CS) protein repeat epitopes of Plasmodiumfakiparum and the rodent malaria agent P. berghei. For this purpose hybrid genes coding for (NANP)4 (C75CS2) or (DP4NPN)2 (C75CS1) as internal inserts in HBcAg (between amino acids 75 and 81) were constructed and expressed in recombinant Salmonella typhimurium. The resulting hybrid HBcAg-CS polypeptides purified from S. typhimurium were particulate and displayed CS and HBc antigenicity, however, the HBc antigenicity was reduced compared to native recombinant HBcAg. Immunization of several mouse strains with HBcAg-CS1 and HBcAg-CS2 particles resulted in high titer, P. berghei- or P.fakiparum-specific anti-CS antibodies representing all murine immunoglobulin G isotypes. The possible influence of carrier-specific immunosuppression was examined, and preexisting immunity to HBcAg did not significantly affect the immunogenicity of the CS epitopes within HBcAg-CS1 particles. Similarly, the choice of adjuvant did not significantly alter the immunogenicity of HBcAg-CS hybrid particles. Immunization in complete or incomplete Freund's adjuvant or alum resulted in equivalent anti-HBc and anti-CS humoral responses. Examination of T cell recognition of HBcAg-CS particles revealed that HBcAg-specific T cells were universally primed and CS-specific T cells were primed if the insert contained a CS-specific T cell recognition site. This indicates that the internal site in HBcAg is permissive for the inclusion of heterologous pathogen-specific T as well as B cell epitopes. Most importantly, 90 and 100% of BALB/c mice immunized with HBcAg-CS1 particles were protected against a P. berghei challenge infection in two independent experiments. Therefore, hybrid HBcAg-CS particles may represent a useful approach for future malaria vaccine development.