B and T cell epitopes of glycoprotein D of herpes simplex virus type 1

Expression of recombinant herpes simplex virus type 2 glycoprotein D by high-density cell culture of Spodoptera frugiperda

Herpes simplex virus type 2 (HSV-2) is the major cause of genital herpes in humans. The glycoprotein D of HSV-2 (gD2) is a promising subunit vaccine candidate for the treatment of genital herpes. The aim of the present study was to express a biologically active recombinant gD2 in eukaryotic baculovirus system in quantities sufficient for further studies. Human cDNA encoding a gD2 protein with 393 amino acids was subcloned into the pFastBac HTb vector and the recombinant protein was expressed in Spodoptera frugiperda (Sf9) cells by high-density cell culture. In a stirred bioreactor, the key limiting factors including glucose concentration, glutamine concentration and dissolved oxygen (DO) were optimized for high-density cell growth. The Sf9 cell density could reach 9.6×10⁶ cells/mL and the yield of recombinant gD2 protein was up to 192 mg/L in cell culture under the optimal conditions of 15 mM glucose, 0.4 g/L glutamine and 40% DO. Production of significant amounts of pure, full-length gD2 opened up the possibility to investigate novel functions of gD2. Moreover, the purified recombinant gD2 protein revealed a partial prophylactic immune function in genital herpes of guinea pigs infected with HSV-2.

Stepwise identification of HLA-A*0201-restricted CD8+ T-cell epitope peptides from herpes simplex virus type 1 genome boosted by a StepRank scheme

Identification of immunodominant epitopes is the first step in the rational design of peptide vaccines aimed at T-cell immunity. To date, however, it is yet a great challenge for accurately predicting the potent epitope peptides from a pool of large-scale candidates with an efficient manner. In this study, a method that we named StepRank has been developed for the reliable and rapid prediction of binding capabilities/affinities between proteins and genome-wide peptides. In this procedure, instead of single strategy used in most traditional epitope identification algorithms, four steps with different purposes and thus different computational demands are employed in turn to screen the large-scale peptide candidates that are normally generated from, for example, pathogenic genome. The steps 1 and 2 aim at qualitative exclusion of typical nonbinders by using empirical rule and linear statistical approach, while the steps 3 and 4 focus on quantitative examination and prediction of the interaction energy profile and binding affinity of peptide to target protein via quantitative structure-activity relationship (QSAR) and structure-based free energy analysis. We exemplify this method through its application to binding predictions of the peptide segments derived from the 76 known open-reading frames (ORFs) of herpes simplex virus type 1 (HSV-1) genome with or without affinity to human major histocompatibility complex class I (MHC I) molecule HLA-A*0201, and find that the predictive results are well compatible with the classical anchor residue theory and perfectly match for the extended motif pattern of MHC I-binding peptides. The putative epitopes are further confirmed by comparisons with 11 experimentally measured HLA-A*0201-restrcited peptides from the HSV-1 glycoproteins D and K. We expect that this well-designed scheme can be applied in the computational screening of other viral genomes as well.

Liposomal gD ectodomain (gD1-306) vaccine protects against HSV2 genital or rectal infection of female and male mice

Herpes simplex virus type 2 (HSV2) is the most common causative agent of genital herpes, with infection rates as high as 1 in 6 adults. The present studies were done to evaluate the efficacy of a liposomal HSV2 gD(1-306) vaccine (L-gD(1-306)-HD) in an acute murine HSV2 infection model of intravaginal (female) or intrarectal (male or female) challenge. Two doses of L-gD(1-306)-HD containing 60 microg gD(1-306)-HD and 15 microg monophosphoryl lipid A (MPL) per dose provided protection against HSV2 intravaginal challenge (86-100% survival, P< or =0.0003 vs. control liposomes; P=0.06 vs. L-gD(1-306)-HD without MPL). Both male and female mice (BALB/c and C57BL/6) immunized with L-gD(1-306)-HD/MPL were significantly protected against HSV2 intrarectal challenge, with higher survival rates compared to controls (71-100%, P< or =0.007). L-gD(1-306)-HD/MPL also provided increased survival when compared to a liposomal peptide vaccine, L-gD(264-285)-HD/MPL (male BALB/c, P</=0.001; female BALB/c and male C57BL/6, P=0.06). Mice given L-gD(1-306)-HD/MPL also had minimal disease signs, reduced viral burden in their spinal cords and elevated neutralizing antibody titers in the females. The vaccine also stimulated gD(1-306)-HD specific splenocytes of both male and female mice with significantly elevated levels of IFN-gamma compared to IL-4 (P< or =0.01) indicating that there was an enhanced Th1 response. These results provide the first evidence that the L-gD(1-306)-HD vaccine can protect both male and female mice against intrarectal HSV2 challenge.

Protective immunity to genital herpes simplex virus type 1 and type 2 provided by self-adjuvanting lipopeptides that drive dendritic cell maturation and elicit a polarized Th1 immune response

Genital herpes simplex virus type 1 and type 2 (HSV-1 and HSV-2) infections are a significant health problem worldwide. While it is believed that CD4+ Th1 cells are among the effectors to herpes immunity, developing an epitope-based clinical vaccine capable of inducing an effective anti-herpes CD4+ Th1-mediated protection is still under investigation. Few molecules achieve this target without the aid of external immuno-adjuvant. The present study was undertaken to examine the immunogenicity in mice of five CD4+ T cell epitope peptides (gD1-29, gD49-82, gD146-179, gD228-257, and gD332-358), recently identified from the HSV-1 glycoprotein D (gD), covalently linked to a palmitic acid moiety (lipopeptides) using the high-yielding chemoselective ligation method and delivered subcutaneously in free-adjuvant saline. Their protective efficacy was evaluated in a progestin-induced susceptibility mouse model of genital herpes following intravaginal challenge with either HSV-1 or HSV-2. Four out of five gD lipopeptides effectively induced virus-specific CD4+ Th1 responses associated with a reduction of virus replication in the genital tract and protection from overt signs of genital disease. A cocktail of three highly immunogenic lipopeptides provoked maturation of dendritic cells, induced interferon gamma (IFN-gamma)-producing CD4+ T cells, and protected against both HSV- 1 and HSV-2 infections. Depletion of specific T cell subsets from lipopeptideimmunized mice before intravaginal HSV challenges demonstrated that CD4+ T cells were primarily responsible for this protection. The strength of induced T cell immunity, together with the ease of construction and safety of these totally synthetic self-adjuvanting lipopeptides, provide a molecularly defined formulation that could combat genital herpes and other human viral infections for which induction of Th1 immunity is crucial.

Immunological properties of a DNA plasmid encoding a chimeric protein of herpes simplex virus type 2 glycoprotein B and glycoprotein D

A DNA plasmid containing a chimeric sequence encoding both herpes simplex virus type 2 (HSV-2) glycoprotein B (gB) and glycoprotein D (gD) external domains (pcgDB) was used to immunize BALB/c mice against genital HSV-2 infection. To determine the efficacy of this vaccine, groups of mice immunized with the pcgDB plasmid were compared with animals immunized with plasmids corresponding to the individual proteins (pcgBt or pcgDt), administered separately or in combination (pcgBt + pcgDt). We studied the response of the different mouse groups to viral challenge by analyzing clinical disease (vaginitis), serum antibody levels, as well as lymphoproliferative responses and cytokine production by spleen cells. Increased IFN-gamma levels correlated with prolonged survival in mice immunized with the plasmid pcgDB, relative to mice immunized with plasmids coding for the individual proteins alone or in combination. Our results show that immunization with the plasmid encoding the chimeric protein is advantageous over separate proteins. These findings may have important implications for the development of multivalent DNA vaccines against HSV and other complex pathogens.

Identification of novel immunodominant CD4+ Th1-type T-cell peptide epitopes from herpes simplex virus glycoprotein D that confer protective immunity

The molecular characterization of the epitope repertoire on herpes simplex virus (HSV) antigens would greatly expand our knowledge of HSV immunity and improve immune interventions against herpesvirus infections. HSV glycoprotein D (gD) is an immunodominant viral coat protein and is considered an excellent vaccine candidate antigen. By using the TEPITOPE prediction algorithm, we have identified and characterized a total of 12 regions within the HSV type 1 (HSV-1) gD bearing potential CD4(+) T-cell epitopes, each 27 to 34 amino acids in length. Immunogenicity studies of the corresponding medium-sized peptides confirmed all previously known gD epitopes and additionally revealed four new immunodominant regions (gD(49-82), gD(146-179), gD(228-257), and gD(332-358)), each containing naturally processed epitopes. These epitopes elicited potent T-cell responses in mice of diverse major histocompatibility complex backgrounds. Each of the four new immunodominant peptide epitopes generated strong CD4(+) Th1 T cells that were biologically active against HSV-1-infected bone marrow-derived dendritic cells. Importantly, immunization of H-2(d) mice with the four newly identified CD4(+) Th1 peptide epitopes but not with four CD4(+) Th2 peptide epitopes induced a robust protective immunity against lethal ocular HSV-1 challenge. These peptide epitopes may prove to be important components of an effective immunoprophylactic strategy against herpes.

Mass spectrometric and chemical stability of the Asp-Pro bond in herpes simplex virus epitope peptides compared with X-Pro bonds of related sequences

The mass spectrometric analysis of the immunodominant epitope region (273-284) of herpes simplex virus type 1 (HSV-1) glycoprotein D (gD) showed a favoured fission at the Asp-Pro peptide bond. The fast atom bombardment collision induced dissociation (FAB-CID) study of closely related X-Pro peptides documented that neither the length nor the amino acid composition of the peptide has a significant influence on this preferential cleavage. At the same time the DP bond proved to be sensitive to acidic conditions in the course of peptide synthesis. These observations prompted us to compare the chemical and mass spectrometric stability of a new set of nonapeptides related to the 273-284 epitope region of gD, i.e. SALLEDPVG and SALLEXPVG peptides, where X = A, K, I, S, F, E or D, respectively. The chemical stability of these peptides during acidic hydrolysis was investigated by electrospray ionization mass spectrometry (ESI-MS) and the products were identified by ESI-MS and on-line high performance liquid chromatography-mass spectrometry (HPLC-MS). The mass spectrometric fragmentation and bond stability of the untreated peptide samples were also studied using ESI-MS and liquid secondary ion mass spectrometry (LSIMS). Both the chemical hydrolysis and the mass spectrometric fragmentation showed that the Asp-Pro bond could easily be cleaved, while the KP bond proved to be stable under both circumstances. On the other hand, the XP bond (X = A, I, S, F or E) fragmented easily under the mass spectrometric conditions, but was not sensitive to the acidolysis.

Identification of the core residues of the epitope of a monoclonal antibody raised against glycoprotein D of herpes simplex virus type 1 by screening of a random peptide library

Random peptide libraries (RPL) displayed on the surface of a filamentous bacteriophage can be used to identify peptide ligands that interact with target molecules. We have used a 15-amino acid residue RPL displayed on bacteriophage M13 to identify the core residues within the epitope of a monoclonal antibody (mAb) A16 which interacts with a continuous epitope restricted to amino acid residues 9 to 19 in the N-terminal region of glycoprotein D of herpes simplex virus type 1 (gD-1). The single peptide sequence obtained after three rounds of selection contained identical residues at three positions compared to the authentic gD-1 sequence. Synthetic peptides were prepared based on the sequence of the original epitope and the phage-derived epitope. The binding constants (Ka) with mAb A16 were determined using surface plasmon resonance (SPR) biosensor technology. The RPL-derived peptide and peptide 9-19 of gD-1 had approximately the same affinity for mAb A16. This suggests that those residues within the epitope that are essential for binding were identified. The synthesis of shorter versions of the RPL-derived peptide restricted the binding region to seven amino acid residues. These results show that minimal information retrieved from the screening of an RPL combined with peptide synthesis can characterize the epitope of an mAb with high resolution. Immunization of mice with the phage-derived peptide protected against a challenge with a lethal dose of herpes simplex virus type 1 equally well as the gD-1 derived peptide.

The influence of branched polypeptide carriers on the immunogenicity of predicted epitopes of HSV-1 glycoprotein D

To investigate the role of synthetic polypeptide carriers in inducing an epitope-specific immune response relevant for vaccine design, peptides comprising two distinct regions of herpes simplex virus type I glycoprotein D (1-23 and 273-284) have been conjugated to the branched polypeptides with polylysine backbone, poly[L-Lys-(DL-Alam)] (AK), or poly[L-Lys-(Leui-DL-Alam)] (LAK) and to keyhole limpet haemocyanin (KLH). The magnitude, fine specificity and isotype distribution of the conjugate-, peptide-and carrier-specific antibody responses were characterized in immunized BALB/c and CBA mice. Conjugates containing the polypeptide carrier AK were the most effective in inducing HSV gD-peptide-specific antibody responses while KLH peptide conjugates resulted in conjugate-specific antibody responses without measurable peptide specificity. The efficacy of AK-peptide conjugates was verified by the dominant appearance of peptide-specific antibodies belonging to functionally efficient IgG isotopes, accompanied by low levels of carrier specific antibody responses. Preimmunization of BALB/or CBA mice with AK conjugates comprising the 1-23 or 276-284 HSV peptides resulted in prolonged survival of animals infected with a lethal dose of infectious HSV-1. The potency of these conjugates in eliciting a protective immune response shows a close correlation with the relative levels of conjugate-induced virus-specific antibodies and the neutralizing activity of sera as measured in preimmunized survivors.

T cell responses to synthetic peptides of herpes simplex virus type 1 glycoprotein D in naturally infected individuals

To locate T cell determinants of glycoprotein D (gD) of herpes simplex virus type 1 (HSV-1), proliferation assays of lymphocytes obtained from 10 healthy HSV-seropositive individuals were performed using 34 overlapping gD peptides as antigens. Despite large differences between individual responses to the peptides both in number of stimulating peptides and gD regions, three regions (1-54, 110-214, and 290-314) induced a response in 50% or more of the HSV-seropositives. T cells were less frequently stimulated by peptides of region 210-294. No correlation was found between serological data and proliferative responses to the peptides. The diversity in T cell response to the peptides suggests a lack of immunodominance, implying that a single peptide/region of gD, or a combination of peptides, will not be sufficient to serve as a basis for a future HSV-1 vaccine.