Protection of non-human primates against rabies with an adenovirus recombinant vaccine.

Rabies remains a major neglected global zoonosis. New vaccine strategies are needed for human rabies prophylaxis. A single intramuscular immunization with a moderate dose of an experimental chimpanzee adenovirus (Ad) vector serotype SAd-V24, also termed AdC68, expressing the rabies virus glycoprotein, resulted in sustained titers of rabies virus neutralizing antibodies and protection against a lethal rabies virus challenge infection in a non-human primate model. Taken together, these data demonstrate the safety, immunogenicity, and efficacy of the recombinant Ad-rabies vector for further consideration in human clinical trials.

Adenovirus-based vaccines: comparison of vectors from three species of adenoviridae.

In order to better understand the broad applicability of adenovirus (Ad) as a vector for human vaccine studies, we compared four adenovirus (Ad) vectors from families C (Ad human serotype 5 [HAdV-5; here referred to as AdHu5]), D (HAdV-26; here referred to as AdHu26), and E (simian serotypes SAdV-23 and SAdV-24; here referred to as chimpanzee serotypes 6 and 7 [AdC6 and AdC7, respectively]) of the Adenoviridae. Seroprevalence rates and titers of neutralizing antibodies to the two human-origin Ads were found to be higher than those reported previously, especially in countries of sub-Saharan Africa. Conversely, prevalence rates and titers to AdC6 and AdC7 were markedly lower. Healthy human adults from the United States had readily detectable circulating T cells recognizing Ad viruses, the levels of which in some individuals were unexpectedly high in response to AdHu26. The magnitude of T-cell responses to AdHu5 correlated with those to AdHu26, suggesting T-cell recognition of conserved epitopes. In mice, all of the different Ad vectors induced CD8(+) T-cell responses that were comparable in their magnitudes and cytokine production profiles. Prime-boost regimens comparing different combinations of Ad vectors failed to indicate that the sequential use of Ad vectors from distinct families resulted in higher immune responses than the use of serologically distinct Ad vectors from the same family. Moreover, the transgene product-specific antibody responses induced by the AdHu26 and AdC vectors were markedly lower than those induced by the AdHu5 vector. AdHu26 vectors and, to a lesser extent, AdC vectors induced more potent Ad-neutralizing antibody responses. These results suggest that the potential of AdHu26 as a vaccine vector may suffer from limitations similar to those found for vectors based on other prevalent human Ads.

Human immunodeficiency virus type 1-specific immune responses in primates upon sequential immunization with adenoviral vaccine carriers of human and simian serotypes.

Two triple immunization vaccine regimens with adenoviral vectors with E1 deleted expressing Gag of human immunodeficiency virus type 1 were tested for induction of T- and B-cell-mediated-immune responses in mice and in nonhuman primates. The vaccine carriers were derived from distinct serotypes of human and simian adenoviruses that fail to elicit cross-neutralizing antibodies expected to dampen the effect of booster immunizations. Both triple immunization regimens induced unprecedented frequencies of gamma interferon-producing CD8(+) T cells to Gag in mice and monkeys that remained remarkably stable over time. In addition, monkeys developed Gag-specific interleukin-2-secreting T cells, presumably belonging to the CD4(+) T-cell subset, and antibodies to both Gag and the adenoviral vaccine carriers.

Oral vaccination of mice with adenoviral vectors is not impaired by preexisting immunity to the vaccine carrier.

Adenovirus vectors with E1 deleted of the human serotype 5 (AdHu5) and the chimpanzee serotype 68 (AdC68) expressing the glycoprotein of the Evelyn Rokiniki Abelseth strain of rabies virus were tested upon oral application for induction of systemic and mucosal transgene product-specific antibody responses in mice. Both vectors induced systemic and mucosal antibodies to rabies virus, including virus-neutralizing antibodies and protection against a severe intracerebral challenge with a mouse-adapted strain of rabies virus. Pre-existing immunity of AdHu5 virus, which dampens induction of transgene product-specific immunity elicited by AdHu5 vectors given systemically did not impair the response induced by oral vaccination. Oral priming-boosting regimens with either heterologous or homologous adenoviral vectors used sequentially increased both mucosal and systemic antibody titers to rabies virus [corrected]

T helper cell-independent antibody responses to the transgene product of an e1-deleted adenoviral vaccine require NK1.1 T cells.

Mice lacking CD4(+) T cells due to a knock-out mutation respond to vaccination with a replication-defective adenoviral recombinant expressing the glycoprotein of rabies virus with a long-lasting virus-neutralizing antibody response. The vaccine-induced B cells secrete antibodies that are mainly of IgG isotypes. The response can be enhanced upon booster immunization, indicating the induction of B cell memory in the absence of CD4(+) T cells. The antibody response is independent of CD8(+) T cells but requires the presence of CD3(+) cells carrying the NK1.1 markers.

Replication-defective vector based on a chimpanzee adenovirus.

An adenovirus previously isolated from a mesenteric lymph node from a chimpanzee was fully sequenced and found to be similar in overall structure to human adenoviruses. The genome of this virus, called C68, is 36,521 bp in length and is most similar to subgroup E of human adenovirus, with 90% identity in most adenovirus type 4 open reading frames that have been sequenced. Substantial differences in the hexon hypervariable regions were noted between C68 and other known adenoviruses, including adenovirus type 4. Neutralizing antibodies to C68 were highly prevalent in sera from a population of chimpanzees, while sera from humans and rhesus monkeys failed to neutralize C68. Furthermore, infection with C68 was not neutralized from sera of mice immunized with human adenovirus serotypes 2, 4, 5, 7, and 12. A replication-defective version of C68 was created by replacing the E1a and E1b genes with a minigene cassette; this vector was efficiently transcomplemented by the E1 region of human adenovirus type 5. C68 vector transduced a number of human and murine cell lines. This nonhuman adenoviral vector is sufficiently similar to human serotypes to allow growth in 293 cells and transduction of cells expressing the coxsackievirus and adenovirus receptor. As it is dissimilar in regions such as the hexon hypervariable domains, C68 vector avoids significant cross-neutralization by sera directed against human serotypes.

A method that allows easy characterization of tumor-infiltrating lymphocytes.

A method was developed to compare the lymphocytic infiltrates in regressing vs. progressing experimental mouse tumors using a model for human papillomavirus-16 (HPV-16) oncoprotein-linked cancer. Tumor cells mixed with matrigel, composed of natural matrix substances that provide a basement membrane structure for adherent cells, were inoculated into mice vaccinated with an efficacious vaccine to the E7 oncoprotein or a vaccine to a control antigen. The tumor cells remained within the solidified gel and recruited a cellular infiltrate that could readily be analyzed upon removal of the gelatinous mass containing progressing or regressing tumors. The results show that tumors recruit activated CD8(+) T cells regardless of their antigen specificity. In regressing tumors expressing an appropriate target antigen for the vaccine-induced CD8(+) T cells, a strong increase of the tumor antigen-specific T cell population was observed over time. Progressing tumors that lacked the target antigen for the activated CD8(+) T cell population did not show this selective enrichment.

Viral recombinant vaccines to the E6 and E7 antigens of HPV-16.

Most cancerous lesions of the uterine cervix are linked to persistent infections with human papillomaviruses (HPV), most notably HPV-16 or -18. Vaccine-induced immune responses to the HPV early antigens E6 and E7, which contribute to cell transformation and are thus expressed in these cervical cancers, could potentially eradicate malignant cells. We generated recombinant vaccines based on E1-deleted adenovirus human strain 5 or on vaccinia virus strain Copenhagen expressing either the E6 or E7 oncoproteins of HPV-16. The different vaccines were compared in two experimental mouse tumor models employing Balb/c or C57Bl/6 mice. Data presented here demonstrate that depending on the model either CD4(+) or CD8(+) T cells provide protection to tumor cell challenge, resulting in striking differences in the efficacy of the four vaccines under investigation.

Induction of genital immunity by DNA priming and intranasal booster immunization with a replication-defective adenoviral recombinant.

Mice immunized through different routes such as i.m., intradermally, or intratracheally with a DNA vaccine to rabies virus developed high titers of serum Ab but only borderline levels of mucosal Abs determined from vaginal secretions. DNA vaccines given by either route enhanced vaginal IgA and IgG2a secretion upon a subsequent intranasal booster immunization with an E1-deleted adenoviral recombinant expressing the same Ag of rabies virus. DNA vaccine priming reduced the Ab response to the adenoviral Ags and counterbalanced the impaired B cell response to the rabies virus Ag expressed by the adenoviral recombinant in mice preimmune to adenovirus. The vaginal B cell response could further be enhanced by using the Th2-type cytokines IL-4 or IL-5 as genetic adjuvants concomitantly with the DNA vaccine before intranasal booster immunization with the recombinant vaccine.

A monoclonal antibody to a multiphosphorylated, conformational epitope at the carboxy-terminus of p53.

Mutations of the gene encoding the tumor suppressor protein p53 are the most common molecular alterations of cancer cells found in about half of all human tumors. Mutations which cluster in well-defined hot spots change the structure of the protein thus affecting its ability to bind to DNA. Post-translational modifications, primarily phosphorylation, might also influence how p53 binds to DNA or folds to its active tetrameric form. However, the lack of appropriate biochemical markers to characterize the status of phosphorylation in different cell types and in cells at different stages of tumor progression has prohibited such investigations. To generate a sensitive and phosphorylation-specific monoclonal antibody (mAb), we chemically synthesized the C-terminal 23 amino acid stretch of human p53 in a double-phosphorylated form. The peptide 371-393, carrying phosphate groups on Ser378 and Ser392, was co-synthesized with a turn-inducing spacer and peptide 31D, an immunodominant T-helper cell epitope in mice of the H-2k haplotype. After immunization and fusion of splenocytes with myeloma cells, a number of mAbs were obtained, from which mAb p53-18 emerged as a highly sensitive reagent. By enzyme-linked immunosorbent assay, p53-18, a mAb of the IgM isotype, recognized phosphorylated p53, expressed in insect cells infected with a recombinant baculovirus but not p53 expressed in Escherichia coli. Moreover, murine p53 from insect cells could be immune purified with mAb p53-18. Mass spectrometry following tryptic digestion of the purified protein and liquid chromatography of the fragments verified the presence of phosphate groups at both Ser375 and Ser389. From the corresponding human protein fragments, mAb p53-18 bound to the immunizing peptide phosphorylated on Ser378 and on Ser392, but failed to cross-react with the unphosphorylated peptide, or peptides phosphorylated individually on either Ser378 or Ser392. The binding to the unphosphorylated peptide could be restored, however, if the peptide conformation was stabilized to that of an alpha-helix. The immunogenic nature of the multiphosphorylated C-terminus of p53 is indicated by the finding that human sera, mostly from cancer patients, preferentially recognized the double-phosphorylated peptide over the monophosphorylated or unphosphorylated analogs. Antibody p53-18 appears to be a highly useful biochemical marker to detect low levels of p53 protein in different tissues, and to be a key tool to characterize the phosphorylation status of the C-terminus of p53 protein originated from various sources.

The effect of interferon-gamma on genetic immunization.

The effect of co-inoculation of a plasmid vector expressing the rabies virus glycoprotein and an additional vector encoding mouse interferon (IFN)-gamma on the development of an antigen specific B and T helper cell response was tested upon intramuscular inoculation of mice. The effect of IFN-gamma was dependent on the promoter driving expression of the viral antigen. The immune responses to antigen-expressing vector carrying a viral promoter such as the SV40 early promoter or the major histocompatibility (MHC) class I promoter were reduced in presence of IFN-gamma while the B and T helper cell response to a vector expressing the antigen under the control of the MHC class II promoter was not affected by this cytokine.

The effects of post-translational side-chain modifications on the stimulatory activity, serum stability and conformation of synthetic peptides carrying T helper cell epitopes.

Peptides 31D and VF13, corresponding to the rabies virus nucleo- and glycoproteins, respectively, vigorously stimulate T helper cells of the appropriate specificity. Earlier we showed how internal and external glycosylation affects the major histocompatibility complex molecule (MHC)-binding ability and conformation of these T-cell epitopes (Otvos et al. (1994) Biochim. Biophys. Acta 1224, 68-76; Otvos et al. (1995) Biochim. Biophys. Acta 1267, 55-64). In the current report, we examined the T-helper cell stimulatory ability after introduction of a new set of post-translational modifications. To obtain general information concerning the effects of amino acid side-chain modifications on other biochemical properties of protein fragments, we studied the serum stability and the conformation of the 31D and VF13 peptides. We found that the extent of the reduction of the T-cell stimulatory activity depends upon the location in the sequence of the host amino acid residue. Generally, beta-linked sugars in mid-chain positions had a greater inhibitory effect than alpha-linked sugars attached to identical amino acids. In a case where mid-chain glycosylation just marginally reduced the T-cell stimulatory activity, the beta-linked glycopeptide was significantly more resistant to serum proteases. This finding suggests that addition of beta-linked carbohydrates might be superior to the addition of alpha-linked sugars for vaccine development, and generally for peptide agonist drug design. In addition, data presented here provide the first documentation that phosphorylation and sulfation of tyrosine residues may retain the MHC-binding ability and T-cell stimulatory activity of class II epitopes. The sulfated and the phosphorylated 31D peptides exhibited considerably increased serum stability compared to the unmodified parent peptide. Finally, all post-translational modifications destabilized the dominant alpha-helical or turn structures of the peptides presented in aqueous trifluoroethanol mixtures. While the circular dichroism spectra of the alpha- and beta-linked VF13 glycopeptides with monosaccharides were almost indistinguishable, the structure of the glycopeptides depended upon the length of the sugar moiety. Significantly, incorporation of sulfate or phosphate groups resulted in identical peptide conformations.

Poly (DL-lactide-co-glycolide) microspheres as carriers for peptide vaccines.

Peptides carrying an immunodominant T-helper cell epitope delineated from the rabies virus nucleoprotein either alone or in combination with a linear B-cell epitope from the same protein were incorporated into three different formulations of poly(DL-lactide-co-glycolide) (PLG) which were distinct in their composition, and consequently in their peptide release rates. In vitro peptides incorporated into any of the PLG formulations stimulated a peptide-specific T-cell line. Upon subcutaneous immunization of mice, the PLG formulation that showed the fastest peptide release rate induced the best immune response. This immune response was in magnitude comparable or even superior to that induced by peptide emulsified in complete Freund's adjuvant.

A replication-defective human adenovirus recombinant serves as a highly efficacious vaccine carrier.

In this manuscript, an E1 and E3 deleted adenoviral recombinant expressing the rabies virus glycoprotein (G protein) under the control of the cytomegalovirus early promoter was tested for induction of a rabies virus-specific immune response in mice. The construct was found to induce neutralizing antibodies and cytolytic T cells to rabies virus. Mice vaccinated with the adenoviral construct either by the systemic route or by application into the airways were protected against a subsequent infection with a virulent strain of rabies virus. The efficacy of the replication-defective construct was far superior to that of a well-characterized vaccinia rabies glycoprotein recombinant.

Genetic immunization.

Genetic immunization, the latest addition to the field of vaccinology, has shown, in a number of animal models, to be an efficacious approach to induce protective immunity to infectious diseases. The advantages of DNA vaccines are their ease of construction, the low expanse of mass production, their high temperature stability, and their ability to induce a full spectrum of exceptionally long-lasting immune responses including cytolytic T cells. Their potential disadvantages are putative safety issues such as integration into the host cell genome. The slow development of the immune response to genetic immunization will make these vaccines unsuitable for treatment of some infectious disease such as postexposure vaccination to rabies virus, where a rapid immune response is warranted. Although only time will tell if genetic immunization provides a viable alternative for human immunization, in the meantime this approach provides immunologists with a powerful tool to gain further insight in the mechanisms that drive primary immune responses.

Immune effector mechanisms required for protection to rabies virus.

Genetically engineered mice with targeted mutations in genes encoding immunologically relevant molecules were used to elucidate the role of different immune effector mechanisms in protection against a rabies virus (RV) infection. In vaccinated animals challenged with a highly virulent strain of RV, antibodies were crucial in protection. In naive mice challenged with an attenuated strain of the virus that does not cause disease in adult fully immunocompetent mice but kills RAG mice that lack functionally active T and B cells, different immune effector mechanisms were shown to suffice for protection.

Immune responses to nucleic acid vaccines to rabies virus.

A plasmid vector expressing the full-length rabies virus glycoprotein (G protein) under the control of the simian virus 40 (SV40) promoter has previously been shown to induce upon intramuscular (i.m.) inoculation into mice a specific B- and T-cell-mediated immune response and protection against challenge with a virulent strain of the virus. Here we tested two parameters that might affect the efficacy of this DNA vaccine. First, we replaced the SV40 promoter of the original vector with the early promoter derived from cytomegalovirus leaving all other parameters of the plasmid intact. Although upon transfection in vitro the two vectors showed a striking difference in their ability to cause stable expression of the rabies virus G protein, upon i.m. inoculation into mice both constructs induced comparable immune responses. Second, we constructed a vector that induces expression of a secreted form of rabies G protein by inserting a stop codon just upstream of the transmembrane domain of the rabies G protein gene. The immune responses to the DNA vaccines expressing the two different forms of the G protein, secreted and membrane bound, were compared and found to be similar in magnitude. The long-term effect of DNA vaccination was also investigated especially with regard to adverse immunological reactions such as the induction of unresponsiveness against rabies virus and the development of antibodies to DNA. DNA vaccination was found to induce long-lasting immunity to rabies virus without apparent negative side effects such as development of T cell tolerance or generation of anti-DNA antibodies.

Comparison of the effects of amino acid substitutions and beta-N- vs. alpha-O-glycosylation on the T-cell stimulatory activity and conformation of an epitope on the rabies virus glycoprotein.

The first potential N-glycosylation site of the rabies virus glycoprotein, the antigen that carries epitopes for glycoprotein-specific T-cells and virus neutralizing antibodies, is glycosylated inefficiently. Recently, we showed that addition of a beta-N-acetyl-glucosamine moiety to the asparagine residue in the corresponding synthetic fragment V V E D E G C T N L S G F (amino acids 29-41), significantly diminished the T-cell stimulatory activity and reduced the characteristic alpha-helicity of the peptide. The amino acid sequence of the glycoprotein in this region exhibits some degree of variability among different rabies virus and rabies virus related strains, including the replacement of the asparagine residue with aspartic acid or threonine. In the current study, stimulation of a specific T-cell clone by various viral strains and appropriate tridecapeptide sequences and their analogs was investigated. The T-cell recognition pattern of the rabies and rabies-related viruses was identical to that of the synthetic peptides representing the respective epitope sequences. While the asparagine could be replaced without complete loss of T-cell stimulatory activity, amino acid modifications at the C-terminus of the peptide were not tolerated. In contrast to glycosylation of the asparagine, coupling of an N-acetyl-galactosamine moiety at the serine, or galactosyl-N-acetyl-galactosamine moieties at the threonines preceding or replacing the asparagine (all O-linked sugars in the natural alpha-anomeric configuration) resulted in epitopes that lowered rather than abolished the T-cell stimulatory activity. All non-glycosylated peptides assumed a low-to-medium helicity in trifluoroethanol. O-glycosylation was more efficient than N-glycosylation in breaking the helical conformation of the peptides to result in the formation of reverse-turns or unordered structure.