Neutralizing antibodies induced by recombinant vaccinia virus expressing varicella-zoster virus gpIV

Immune response to vaccinia virus recombinants expressing glycoproteins gE, gB, gH, and gL of Varicella-zoster virus

Immunogenicity of Varicella-zoster virus glycoproteins gE, gB, gH, and gL expressed by recombinant vaccinia viruses (VV) separately or simultaneously was determined in mice and guinea pigs by ELISA, Western blotting, radioimmunoprecipitation, plaque reduction assay, and skin test. Single VV-gE and VV-gB recombinants and double VV-gH/gL recombinant elicited specific antibodies with VZV neutralizing activity in mice. Co-expression of gE and gB by one recombinant VV resulted in an increased antibody response in comparison with immunization with single recombinants or their mixtures. Unlike anti-gB and anti-gH/gL antibodies, the gE-specific antibodies had no virus neutralizing activity in absence of complement, and when used alone, they even caused considerable increase of VZV infectious units. Moreover, immune sera containing anti-gE antibodies antagonized complement independent virus-neutralizing activity of anti-gB- and anti-gH/gL-positive sera. The ability to induce delayed hypersensitivity reaction to VZV antigens was observed after immunization of guinea pigs with gE- and/or gB-expressing VVs.

Humoral immunoresponse to varicella-zoster virus pernasally coadministered with Escherichia coli enterotoxin in mice

It is evaluated whether Escherichia coli enterotoxin is useful for induction of immunity to varicella-zoster virus (VZV) as a mucosal adjuvant in mice. When a commercially available live varicella vaccine (Oka strain) and toxin were administered simultaneously via a nasal route three times at 2 or 6 month intervals, an antibody neutralizing VZV was detected in half or all of the mice vaccinated, respectively. The antibody specific to the vaccine strain of VZV reacted to five proteins, molecular weights of which were 110 K, 100 K, 62 K, 54 K and 46 K. These proteins were composed of glycosylated products of all kinds of glycoproteins. These results suggest that although a nasal administration of the vaccine without the adjuvant has little immunogenicity in mice, the simultaneous administration of the live vaccine and the toxin over a long period induces a specific humoral immunity to VZV.

Mutational analysis of the role of glycoprotein I in varicella-zoster virus replication and its effects on glycoprotein E conformation and trafficking

The contributions of the glycoproteins gI (ORF67) and gE (ORF68) to varicella-zoster virus (VZV) replication were investigated in deletion mutants made by using cosmids with VZV DNA derived from the Oka strain. Deletion of both gI and gE prevented virus replication. Complete deletion of gI or deletions of 60% of the N terminus or 40% of the C terminus of gI resulted in a small plaque phenotype as well as reduced yields of infectious virus. Melanoma cells infected with gI deletion mutants formed abnormal polykaryocytes with a disrupted organization of nuclei. In the absence of intact gI, gE became localized in patches on the cell membrane, as demonstrated by confocal microscopy. A truncated N-terminal form of gI was transported to the cell surface, but its expression did not restore plaque morphology or infectivity. The fusogenic function of gH did not compensate for gI deletion or the associated disruption of the gE-gI complex. These experiments demonstrated that gI was dispensable for VZV replication in vitro, whereas gE appeared to be required. Although VZV gI was dispensable, its deletion or mutation resulted in a significant decrease in infectious virus yields, disrupted syncytium formation, and altered the conformation and distribution of gE in infected cells. Normal cell-to-cell spread and replication kinetics were restored when gI was expressed from a nonnative locus in the VZV genome. The expression of intact gI, the ORF67 gene product, is required for efficient membrane fusion during VZV replication.

Varicella-zoster virus glycoproteins E and I expressed in insect cells form a heterodimer that requires the N-terminal domain of glycoprotein I

Varicella-zoster virus (VZV) glycoproteins E and I (gE and gI), which are major components of the virion envelope, form a noncovalently linked complex. To understand their properties and functions, we expressed and purified soluble forms of gE and gI in the baculovirus system. Extracellular domains of gE and gI were cloned into baculoviruses, using either native or insect-derived signal peptides. Each recombinant virus yielded soluble protein in culture medium although a higher level of secretion was achieved with insect-derived signal peptides in recombinant gE baculoviruses. A soluble gE-gI complex was formed by co-infecting insect cells with recombinant gE and gI baculoviruses and detected by immunoprecipitation followed by Western blotting analyses. By gel filtration and cross-linking studies, we showed that the VZV gE-gI complex expressed in insect cells is a heterodimer. Interestingly, two recombinant gI proteins in which signal peptides were replaced with insect-derived signal peptides did not associate with gE. Amino-terminal sequencing and site-specific mutational studies showed that the replacement of only the signal peptides did not prevent complex formation but alterations in the processed amino-terminus of gI abrogated its ability to complex with gE. These findings indicate that the mature amino-terminus of gI is required for gE-gI complex formation by the external domains of VZV gE and gI.

Assays for antibodies to varicella-zoster virus

Anti-varicella-zoster virus serum antibody assays and their use in vaccine development are described. Of particular interest are FAMA and neutralization assays and the gpELISA. These and other assays are compared and summarized in terms of characteristics including biologic relevance, sensitivity, specificity, and suitability for different laboratory and clinical applications.

New varicella vaccines

The live attenuated varicella vaccine, which is available for the prevention of chickenpox, was produced by a classic technology that also has been used for polio, measles, mumps, and rubella vaccines. There are many newer technologies that have been applied to the research and development of other vaccines. Each of these other approaches offers potential advantages and disadvantages relative to the current varicella vaccine.

Boosting immune response with a candidate varicella-zoster virus glycoprotein subunit vaccine

A varicella-zoster virus (VZV) seropositive individual was immunized with 100 micrograms of purified VZV TgpI-511 glycoprotein subunit antigen formulated with monophosphoryl lipid A. Serum samples were obtained during a 40-day period post-immunization (PI) and analysed by immunoprecipitation and virus neutralization tests. The results from immunoprecipitation studies revealed an increase in VZV anti-gpI antibody titer as early as 6 days PI which continued to rise during 40 days PI. In addition, virus neutralization tests showed a 21.0% VZV neutralization 6 days PI with an increase to a 96.7% VZV neutralization 40 days PI. These results suggested that the candidate VZV glycoprotein subunit vaccine (TgpI-511) was capable of boosting the production of neutralizing antibodies in the immunized VZV seropositive human subject.

Combined use of complement and anti-immunoglobulin in an enhanced neutralization assay for antibodies to varicella-zoster virus

An enhanced neutralization assay was developed to permit the sensitive, specific, and reproducible measurement of antibodies to varicella-zoster virus (VZV). Optimal neutralization was achieved using a combination of guinea pig complement (C') and rabbit anti-human IgG. This provided 625-, 160- and 13- to 64-fold increases in dilution endpoints of human post-zoster serum, varicella-zoster immune globulin and representative sera from recipients of live attenuated varicella vaccine, respectively, above those measured in the absence of C' and anti-IgG. The specificity of the assay was shown by the absorption of serum neutralization capacity with VZV-specific antigen and the lack of concordance between antibody titers to VZV with those to either herpes simplex virus type-2 or cytomegalovirus. The antibody status of recipients of live attenuated varicella vaccine was established from the amount of neutralizing activity produced at a single optimal serum dilution.

Antibody-binding sites on truncated forms of varicella-zoster virus gpI(gE) glycoprotein

Varicella-zoster virus (VZV)-seropositive human sera were shown to be reactive with the truncated VZV gpI(gE) candidate subunit vaccine (TgpI-511). To identify the location of antibody-binding sites (epitopes) on TgpI-511, three truncated forms of TgpI-511 glycoprotein (TgpI-124, TgpI-160, TgpI-316) DNA encoding the N-terminal region of this glycoprotein with amino acid residues of 124, 160 and 360, respectively, were inserted into the vaccinia virus genome. Infection of cells with recombinant vaccinia viruses resulted in the secretion of all three truncated gpI(gE) as well as TgpI-511 from the infected cells. Immunoprecipitation of these truncated glycoproteins with VZV-seropositive human sera and gpI(gE)-specific monoclonal antibodies identified the location of four new antibody-binding sites on the VZV TgpI-511 glycoprotein. In addition, tunicamycin treatment and O-glycanase digestion revealed the presence of both N-linked and O-linked oligosaccharides on TgpI-511. These results revealed the location of new epitopes on VZV TgpI-511 and demonstrated that the epitopes on TgpI-511 were recognized by human sera from VZV-seropositive individuals.

Antigenicity of a candidate varicella-zoster virus glycoprotein subunit vaccine

A 1642 bp DNA fragment, encoding the N-terminal region and 511 amino acid residues of varicella-zoster virus (VZV) glI gene, was inserted into vaccinia virus genome. The expression of recombinant vaccinia virus (designated VVTgpI-511) yielded the synthesis of a 60 kDa protein species which was processed to a secretory 76 kDa polypeptide (designated TgpI-511). The antigenicity of this protein was examined by subcutaneous inoculation of one rabbit with 100 micrograms purified TgpI-511 in the Ribi adjuvant system. The animal was boosted 3 weeks after the initial inoculation and antisera were tested 7 days after the last injection by immunoprecipitation and neutralization tests. The results showed that rabbit antibodies to TgpI-511 (RAnti-TgpI-511) were reactive with purified TgpI-511 as well as native gpI in VZV-infected cells. In addition, TgpI-511 was capable of eliciting complement-dependent VZV neutralizing antibodies. These results suggested that the purified preparation of TgpI-511 may have the potential to be used as a candidate VZV subunit vaccine.

Specific lysis of targets expressing varicella-zoster virus gpI or gpIV by CD4+ human T-cell clones

Varicella-zoster virus (VZV)-specific CD4-positive T cells are known to lyse targets expressing VZV antigen, but little is known of the glycoprotein specificity or phenotype of these cells. To test the ability of T cells to distinguish between gpI and gpIV (which share an antibody-defined epitope), we prepared clones from blood from four healthy individuals by limiting dilution. Among 68 T-cell clones from four donors which were VZV specific in tests of proliferation, 30 lysed autologous Epstein-Barr virus-transformed lymphoblasts which had been superinfected with a recombinant vaccinia virus which included the whole VZV gpI sequence. These clones were characterized as major histocompatibility complex class II restricted by inhibition of their cytotoxicity with HLA-DR and CD4 monoclonal antibodies. Twenty-one clones lysed targets expressing gpIV. Fifteen of these clones lysed targets expressing gpI and gpIV. Four clones with gpI-gpIV specificity were examined in detail, and their dual specificity was confirmed by cold target inhibition. These four clones failed to kill target cells infected with a mutant gpIV recombinant vaccinia virus from which amino acid residues 212 to 354 had been deleted. This region includes one of the two gpIV decapeptides which have 50% homology with amino acids 111 to 121 of gpI. Our data confirm that T-cell-receptor-associated structures are required for specific lysis of VZV targets and indicate that (i) gpI-specific CD4 cytotoxic T cells outnumber gpIV-specific T cells in blood and (ii) 50% of gpI-specific T-cell clones also lyse gpIV-expressing targets.