Immunization with RBD-P2 and N protects against SARS-CoV-2 in nonhuman primates

Since the emergence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), various vaccines are being developed, with most vaccine candidates focusing on the viral spike protein. Here, we developed a previously unknown subunit vaccine comprising the receptor binding domain (RBD) of the spike protein fused with the tetanus toxoid epitope P2 (RBD-P2) and tested its efficacy in rodents and nonhuman primates (NHPs). We also investigated whether the SARS-CoV-2 nucleocapsid protein (N) could increase vaccine efficacy. Immunization with N and RBD-P2 (RBDP2/N) + alum increased T cell responses in mice and neutralizing antibody levels in rats compared with those obtained using RBD-P2 + alum. Furthermore, in NHPs, RBD-P2/N + alum induced slightly faster SARS-CoV-2 clearance than that induced by RBD-P2 + alum, albeit without statistical significance. Our study supports further development of RBD-P2 as a vaccine candidate against SARS-CoV-2. Also, it provides insights regarding the use of N in protein-based vaccines against SARS-CoV-2.

Quantification of trivalent non-replicating rotavirus vaccine antigens in the presence of aluminum adjuvant

Parenterally administered rotavirus vaccines may overcome the low efficacy observed in resource-poor regions that use live oral formulations. We have reported work on a trivalent nonreplicating rotavirus vaccine (NRRV) for parenteral administration consisting of the recombinant tetanus toxoid P2 CD4 epitope fused to a truncated VP8* fragment (P2-VP8*) for the P[4], P[6], and P[8] serotypes of rotavirus adjuvanted with aluminum. An essential part of developing this vaccine candidate was devising quantification methods for each antigen in the trivalent NRRV in the presence of aluminum adjuvant. This report describes the development of quantitative inhibition enzyme-linked immunosorbent assays (ELISAs) for in vitro antigenicity determination of the adjuvanted trivalent NRRV using serotype-specific monoclonal antibodies (mAbs) against each of the P2-VP8* antigens. Adjuvanted trivalent vaccine samples are titrated and incubated with a constant concentration of specific mAbs against each NRRV P2-VP8* antigen variant. Unbound mAbs are measured by ELISA to indirectly quantify the amount of each antigen present in the trivalent vaccine. Sensitive, specific, and reproducible inhibition ELISAs were developed and qualified for each antigen and used for final product quantification and release testing without desorption of the vaccine antigen.

Comparative pathogenomics of Clostridium tetani

Clostridium tetani and Clostridium botulinum produce two of the most potent neurotoxins known, tetanus neurotoxin and botulinum neurotoxin, respectively. Extensive biochemical and genetic investigation has been devoted to identifying and characterizing various C. botulinum strains. Less effort has been focused on studying C. tetani likely because recently sequenced strains of C. tetani show much less genetic diversity than C. botulinum strains and because widespread vaccination efforts have reduced the public health threat from tetanus. Our aim was to acquire genomic data on the U.S. vaccine strain of C. tetani to better understand its genetic relationship to previously published genomic data from European vaccine strains. We performed high throughput genomic sequence analysis on two wild-type and two vaccine C. tetani strains. Comparative genomic analysis was performed using these and previously published genomic data for seven other C. tetani strains. Our analysis focused on single nucleotide polymorphisms (SNP) and four distinct constituents of the mobile genome (mobilome): a hypervariable flagellar glycosylation island region, five conserved bacteriophage insertion regions, variations in three CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR-associated) systems, and a single plasmid. Intact type IA and IB CRISPR/Cas systems were within 10 of 11 strains. A type IIIA CRISPR/Cas system was present in two strains. Phage infection histories derived from CRISPR-Cas sequences indicate C. tetani encounters phages common among commensal gut bacteria and soil-borne organisms consistent with C. tetani distribution in nature. All vaccine strains form a clade distinct from currently sequenced wild type strains when considering variations in these mobile elements. SNP, flagellar glycosylation island, prophage content and CRISPR/Cas phylogenic histories provide tentative evidence suggesting vaccine and wild type strains share a common ancestor.

Tumor endothelial marker 1-specific DNA vaccination targets tumor vasculature

Tumor endothelial marker 1 (TEM1; also known as endosialin or CD248) is a protein found on tumor vasculature and in tumor stroma. Here, we tested whether TEM1 has potential as a therapeutic target for cancer immunotherapy by immunizing immunocompetent mice with Tem1 cDNA fused to the minimal domain of the C fragment of tetanus toxoid (referred to herein as Tem1-TT vaccine). Tem1-TT vaccination elicited CD8+ and/or CD4+ T cell responses against immunodominant TEM1 protein sequences. Prophylactic immunization of animals with Tem1-TT prevented or delayed tumor formation in several murine tumor models. Therapeutic vaccination of tumor-bearing mice reduced tumor vascularity, increased infiltration of CD3+ T cells into the tumor, and controlled progression of established tumors. Tem1-TT vaccination also elicited CD8+ cytotoxic T cell responses against murine tumor-specific antigens. Effective Tem1-TT vaccination did not affect angiogenesis-dependent physiological processes, including wound healing and reproduction. Based on these data and the widespread expression of TEM1 on the vasculature of different tumor types, we conclude that targeting TEM1 has therapeutic potential in cancer immunotherapy.

[Recent progress of the research on spore surface display]

Spore surface display is one of attractive microorganism surface display systems. With the advantage of resistance attribute and specific assembly pattern, the technology of spore surface display now is attracting more and more attention. According to the current reports and main achievements of spore surface display, the structure and assembly of spores, the principle for construction and some existing spore surface display systems were elaborated in this paper. Now with the unique property of spores, the technique is not only widely used in production of vaccines but also has great applied potential in the field of biocatalysis and cell-factory.

A novel DNA vaccine targeting macrophage migration inhibitory factor protects joints from inflammation and destruction in murine models of arthritis

OBJECTIVE

Previous studies have demonstrated that neutralization of macrophage migration inhibitory factor (MIF) by anti-MIF antibodies decreases joint inflammation and destruction in a type II collagen-induced arthritis model in mice. The aim of this study was to develop and describe a simple and effective method of active immunization that induces anti-MIF autoantibodies, which may neutralize MIF bioactivity.

METHODS

We developed a MIF DNA vaccine by introducing oligonucleotides encoding a tetanus toxoid (TTX) Th cell epitope into the complementary DNA sequence of murine MIF. Mice were injected with this construct in conjunction with electroporation. The ability of this immunization to inhibit the development of collagen antibody-induced arthritis (CAIA) in BALB/c mice and spontaneous autoimmune arthritis in interleukin-1 receptor antagonist (IL-1Ra)-deficient mice was then evaluated.

RESULTS

Mice that received the MIF/TTX DNA vaccine developed high titers of autoantibodies that reacted to native MIF. Compared with unvaccinated mice, vaccinated mice also produced less serum tumor necrosis factor alpha after receiving an intravenous injection of lipopolysaccharide. In addition, vaccination with MIF/TTX DNA resulted in significant amelioration of both CAIA in BALB/c mice and symptoms of autoimmune arthritis in IL-1Ra-knockout mice.

CONCLUSION

These results suggest that MIF/TTX DNA vaccination may be useful for ameliorating the symptoms of rheumatoid arthritis.

Reduction of the ganglioside binding activity of the tetanus toxin HC fragment destroys immunogenicity: implications for development of novel tetanus vaccines

In this study, the immunogenicities of the nontoxic H(C) fragment of tetanus toxin and derivatives lacking ganglioside binding activity were compared with that of tetanus toxoid after subcutaneous immunization of mice. Wild-type H(C) (H(C)WT) protein and tetanus toxoid both elicited strong antibody responses against toxoid and H(C) antigens and provided complete protection against toxin challenge. Mutants of H(C) containing deletions essential for ganglioside binding elicited lower responses than H(C)WT. H(C)M115, containing two amino acid substitutions within the ganglioside binding site, provided reduced protection against tetanus toxin challenge compared with H(C)WT, consistent with lower anti-H(C) and anti-toxoid antibody titers. Circular-dichroism spectroscopy and intrinsic fluorescence spectroscopy showed minimal structural perturbation in H(C)M115. We conclude that the presence of the ganglioside binding site within H(C) may be essential for induction of a fully protective anti-tetanus response comparable to that induced by tetanus toxoid by subcutaneous injection.

Production and purification of recombinant human BLyS mutant from inclusion bodies

B lymphocyte stimulator (BLyS), a member of the tumor necrosis factor superfamily, is an important regulator of B cell homeostasis. In BLyS-deficient mice, B cell development is severely perturbed. On the other hand, mice transgenic for BLyS developed autoimmune disorders, such as increased germinal center formation, production of autoantibodies, and Ig deposition in kidneys. The overexpression of BLyS was found in some human autoimmune diseases. These findings suggest that BLyS has a crucial role in the humoral immune response and may be a therapeutic target for some human autoimmune diseases. To construct and express the therapeutic vaccine BLyS, we coupled a foreign immunodominant T-helper epitope to the N terminus of BLyS (named recombinant BLyS mutant, rBLySM) and expressed rBLySM in Escherichia coli. We have developed a purification process of rBLySM from inclusion bodies. A step-down urea concentration strategy was applied to the rBLySM renaturation process. By this strategy, a stable yield of 4.5mg purified rBLySM per gram of cell paste could be obtained.

Ultrasensitive Detection and Phenotyping of CD4+ T Cells with Optimized HLA Class II Tetramer Staining

HLA class I tetramers have revolutionized the study of Ag-specific CD8+ T cell responses. Technical problems and the rarity of Ag-specific CD4+ Th cells have not allowed the potential of HLA class II tetramers to be fully realized. Here, we optimize HLA class II tetramer staining methods through the use of a comprehensive panel of HIV-, influenza-, CMV-, and tetanus toxoid-specific tetramers. We find rapid and efficient staining of DR1- and DR4-restricted CD4+ cell lines and clones and show that TCR internalization is not a requirement for immunological staining. We combine tetramer staining with magnetic bead enrichment to detect rare Ag-specific CD4+ T cells with frequencies as low as 1 in 250,000 (0.0004% of CD4+ cells) in human PBLs analyzed directly ex vivo. This ultrasensitive detection allowed phenotypic analysis of rare CD4+ T lymphocytes that had experienced diverse exposure to Ag during the course of viral infections. These cells would not be detectable with normal flow-cytometric techniques.

New advances in the production of edible plant vaccines: chloroplast expression of a tetanus vaccine antigen, TetC

Vaccines are a proven method of controlling disease. However there are issues with the delivery and administration of vaccines. A particular problem is that the majority of vaccines currently used are injected, which can be unsafe if needles are reused in areas where blood-borne diseases are prevalent. Vaccines targeting the mucosal immune system avoid many of the problems associated with injections. One potential form of mucosal vaccine is based on the expression of vaccine antigens in plants. Current research in this area has focused on the expression of immunogens from the plant's nuclear genome but low expression levels generally achieved using this system have limited progress. In recent work we have used the model antigen, TetC, which confers resistance to Tetanus infection, to demonstrate the feasibility of expressing vaccine antigens at high levels in the plant chloroplast.

Gene expression after vaccination of mice with formulations of diphtheria toxoid or tetanus toxoid and different adjuvants: identification of shared and vaccine-specific genes in spleen lymphocytes

We immunized mice with four different combinations of diphtheria toxoid or tetanus toxoid with aluminum phosphate or Freund's adjuvant and studied the resulting gene expression profiles in spleen lymphocytes. Genes, which are unique for each combination or shared in several combinations, were found activated, with functions in immune response but also in other cellular processes like apoptosis or signal transduction. Using bioinformatic tools we show, that some of the genes may serve as indicators for adverse reactions, while other genes may be new immune response markers. The results also suggest that adjuvant participates in the formation of an immunological memory.

Signal sequence deletion and fusion to tetanus toxoid epitope augment antitumor immune responses to a human carcinoembryonic antigen (CEA) plasmid DNA vaccine in a murine test system

Carcinoembryonic antigen (CEA, CEACAM5) is expressed on several human carcinomas including colon cancer. CEA contains signal peptides that target the protein through the endoplasmic reticulum and to the cell membrane. We constructed a plasmid DNA vaccine encoding a truncated CEA (deltaCEA), devoid of its signal peptides, and demonstrated that it was retained inside the cell, while full-length CEA (wtCEA) was expressed on the membrane. We hypothesized that intracellular retention of deltaCEA would enhance MHC class I presentation of CEA peptides, thus favoring cellular immune responses. In addition, a promiscuous T-helper epitope (Q830-L844 of tetanus toxoid) was fused to the N-terminal of the truncated CEA gene (tetdeltaCEA). C57BL/6 mice immunized with DNA encoding wtCEA or tetdeltaCEA developed both humoral and cellular immune responses to CEA. SCID mice transplanted with spleen cells from tetdeltaCEA but not wtCEA-immunized C57BL/6 mice showed strong suppression of tumor growth after inoculation of human CEA-expressing colon carcinoma cells. Immune spleen cell populations depleted for either B, T or both B and T cells were active, indicating that effector cells might also reside in other populations. The present approach to manipulating antigen presentation may open new possibilities for immunotherapy against colon and other CEA-secreting carcinomas.

Protection against tetanus toxin after intragastric administration of two recombinant lactic acid bacteria: impact of strain viability and in vivo persistence

Non-pathogenic lactic acid bacteria (LAB) are attractive as live carriers to deliver protective antigens to the mucosal immune system. Both persisting and non-persisting strains of lactic acid bacteria have been evaluated and seem to work equally well by the systemic and nasal routes of administration. However, it is not known if persistence and viability of the strain play a critical role when immunizing by the oral route. To address this question, recombinant LAB strains, able to persist (Lactobacillus plantarum NCIMB8826/pMEC127) or not (Lactococcus lactis MG1363/pMEC46) in the gastro-intestinal tract of mice and producing equivalent amounts of the tetanus toxin fragment C (TTFC) were compared to each other. A very strong ELISA TTFC-specific and protective humoral response was elicited by either live or UV-inactivated recombinant Lb. plantarum strains. In a similar protocol, recombinant Lc. lactis seemed to be somewhat less efficient than the former host. It is thus tempting to propose that the difference in the capacity of the bacterial vector to persist in the gastro-intestinal tract impacts on its immunogenicity and on the level of protection it may induce. Protection was slightly superior after administration of live strains.

Comparison of the immune responses induced by local immunizations with recombinant Lactobacillus plantarum producing tetanus toxin fragment C in different cellular locations

Lactobacillus plantarum NCIMB8826 was selected as a bacterial carrier for the development of live mucosal vaccines. This strain was reported to display interesting pharmaco-kinetic properties when fed to human volunteers and is also able to persist in the mouse intestine. The non-toxic C fragment of tetanus toxin (TTFC) was used as a model antigen. Recombinant strains producing TTFC in three cellular locations, intracellular, secreted or cell-surface exposed were compared to each other by immunizing mice through the subcutaneous, intranasal and intragastric routes. The three types of constructs were able to induce strong specific immune responses against TTFC by all routes tested. While cell-surface presentation required lower antigen doses to be immunogenic, the highest IgG serum antibody titers were obtained with the strain producing large amounts of TTFC in the cytoplasm.

Surface display of recombinant proteins on Bacillus subtilis spores

We developed a novel surface display system based on the use of bacterial spores. A protein of the Bacillus subtilis spore coat, CotB, was found to be located on the spore surface and used as fusion partner to express the 459-amino-acid C-terminal fragment of the tetanus toxin (TTFC). Western, dot blot and fluorescent-activated cell sorting analyses were used to monitor TTFC surface expression on purified spores. We estimated that more than 1.5 x 10(3) TTFC molecules were exposed on the surface of each spore and recognized by TTFC-specific antibodies. The efficient surface presentation of the heterologous protein, together with the simple purification procedure and the high stability and safety record of B. subtilis spores, makes this spore-based display system a potentially powerful approach for surface expression of bioactive molecules.

The potential of oligodeoxynucleotides as mucosal and parenteral adjuvants

Synthetic oligodeoxynucleotides (ODN) containing immunostimulatory CpG motifs (CpG ODN) are potent adjuvants in mice when delivered by parenteral (intramuscular, subcutaneous) and mucosal (intranasal, oral and intrarectal) routes. We have recently shown that with mucosal delivery non-CpG ODN can also have immunostimulatory properties which, in contrast to the Th1-bias characteristic of CpG ODN, are predominantly Th2-like. Herein, using hepatitis B surface antigen (HBsAg) and tetanus toxoid (TT) as model antigens in BALB/c mice, we have examined a number of different ODN (CpG, non-CpG, poly-T, poly-CG) to determine their effects on immune responses after mucosal (oral) and parenteral (IM) immunizations. Our findings demonstrate that with mucosal delivery, there is a Th2-biased immunostimulatory effect that is associated with non-CpG ODN, and that the presence of CpG motifs can shift this towards a Th1 response. The adjuvant effect of non-CpG ODN was much less evident after parenteral immunization.

Mucosal immune responses and protection against tetanus toxin after intranasal immunization with recombinant Lactobacillus plantarum

The use of live microorganisms as an antigen delivery system is an effective means to elicit local immune responses and thus represents a promising strategy for mucosal vaccination. In this respect, lactic acid bacteria represent an original and attractive approach, as they are safe organisms that are used as food starters and probiotics. To determine whether an immune response could be elicited by intranasal delivery of recombinant lactobacilli, a Lactobacillus plantarum strain of human origin (NCIMB8826) was selected as the expression host. Cytoplasmic production of the 47-kDa fragment C of tetanus toxin (TTFC) was achieved at different levels depending on the plasmid construct. All recombinant strains proved to be immunogenic by the intranasal route in mice and able to elicit very high systemic immunoglobulin G (IgG1, IgG2b, and IgG2a) responses which correlated to the antigen dose. No significant differences in enzyme-linked immunosorbent assay IgG titers were observed when mice were immunized with live or mitomycin C-treated recombinant lactobacilli. Nevertheless, protection against the lethal effect of tetanus toxin was obtained only with the strains producing the highest dose of antigen and was greater following immunization with live bacteria. Significant TTFC-specific mucosal IgA responses were measured in bronchoalveolar lavage fluids, and antigen-specific T-cell responses were detected in cervical lymph nodes, both responses being higher in mice receiving a double dose of bacteria (at a 24-h interval) at each administration. These results demonstrate that recombinant lactobacilli can induce specific humoral (protective) and mucosal antibodies and cellular immune response against protective antigens upon nasal administration.

Assessment of a vaccinia virus vectored multi-epitope live vaccine candidate for Plasmodium falciparum

We constructed a live recombinant vaccinia virus vaccine candidate containing a synthesised hybrid gene termed 'HGFSP' encoding circumsporozoite protein (CSP), major merozoite surface antigen-1(MSA1), major merozoite surface antigen-2 (MSA2), and ring-infected erythrocyte surface antigen (RESA) of Plasmodium falciparum, interleukin-1 (IL-1) and tetanus toxin (TT) epitopes. Anti-recombinant vaccinia virus rabbit sera and IgG were tested in inhibition experiments in vitro. Results showed that the recombinant vaccinia virus had some capability to inhibit the growth of P. falciparum in vitro. The sera of rabbits, rats, and mice immunised with recombinant virus showed obvious IL-2 activity 4-6 weeks after immunisation. The interferon (IFN) level of sera from these animals 6 weeks after immunisation was significantly higher than before immunisation. These results indicate that the recombinant vaccinia virus can stimulate cell mediated responses (Th1 cell response) in immunised animals, and has the capability to inhibit multiplication of in vitro cultured P. falciparum. Thus this recombinant vaccinia virus is an appropriate vaccine candidate for further evaluation in Aotus monkey or human clinical trails.

Influence of codon usage on the immunogenicity of a DNA vaccine against tetanus

Two related DNA vaccine vector plasmids, harbouring either wild-type (pcDNA3/ntetC) or synthetic codon optimised (pcDNA3/stetC) DNA encoding fragment C (TetC) of tetanus toxin were constructed. COS-7 cells transformed with pcDNA3/stetC reproducibly expressed higher levels of TetC than similar cells transformed with pcDNA3/ntetC. BALB/c mice immunised intramuscularly with pcDNA3/stetC produced significantly higher levels of anti-TetC antibodies in their serum in the weeks following vaccination compared to mice immunised with pcDNA3/ntetC, even when differences in the CpG content between the two sequences were controlled for using non-expressing DNA.

Enhanced immunogenicity of hepatitis B surface antigen by insertion of a helper T cell epitope from tetanus toxoid

The currently marketed hepatitis B vaccines in the U.S. are based on the recombinant major hepatitis B surface antigen (HBsAg) of hepatitis B virus. Although a large majority of individuals develop protective immunity to HBV-induced disease after three immunizations, routinely a small but a significant percentage of the human population does not respond well to these vaccines. In this report, we describe the generation of a novel HBsAg molecule containing a Th epitope derived from tetanus toxoid (TT). Using recombinant DNA technology. the TT Th epitope (TTe) was inserted into the HBsAg coding sequence. Using a recombinant adenovirus expression system, HBsAg TTe chimeric protein was produced in A549 cells and found to be secreted into culture medium as 22 nm particles. The chimeric HBsAg particles were readily purified by immunoaffinity chromatography and their immunogenicity was evaluated relative to native HBsAg produced in an adenovirus expression system. When evaluated in inbred and outbred strains of mice, HBsAg TTe was shown to enhance several-fold the anti-HBs response relative to native HBsAg. Further enhanced responses were observed in mice primed with TT. This highly immunogenic form of HBsAg has promise as an improved HBsAg subunit vaccine.

Are DNA-based vaccines useful for protection against secreted bacterial toxins? Tetanus toxin test case

Polypeptide and DNA vaccine alternatives to the conventional tetanus toxoid were compared. Mouse immunizations with plasmid DNA that encoded the tetanus toxin C fragment polypeptide induced consistently lower antibody responses than direct immunization with the C fragment polypeptide or toxoid, yet provided some degree of protection from a lethal toxin challenge. Cytotoxic T-cell responses dominated DNA immunizations, while specific T-cell proliferation resulted from all vaccines tested. Immune responses to the DNA vaccine exhibited a T-helper type-1 propensity, while polypeptides elicited T-helper type-2 responses. The lower antibody response to the plasmid vaccine was not due to insufficient quantity of C fragment in vivo but was likely the result of a mode of antigen presentation that was less efficient for supporting antibody production. Collectively, these results suggest that polypeptide or toxoid vaccines are preferable to plasmid-based vaccination for control of diseases caused by tetanus toxin.

Temperature-induced expression of human-mouse chimeric Fab

The temperature-induced expression vector pHZ01 with lambda PRPL promoter for the efficient expression of human-mouse chimeric Fab was constructed. Three kinds of chimeric Fab were expressed in E. coli: anti-prostate specific antigen (PSA) chimeric Fab, anti-lysozyme (HEL) chimeric Fab, and anti-tetanus toxoid (TT) chimeric Fab. All the soluble chimeric Fabs expressed showed specific antigen-binding activities.

Oral vaccination of mice against tetanus with recombinant Lactococcus lactis

To determine whether a protective immune response could be elicited by oral delivery of a recombinant bacterial vaccine, tetanus toxin fragment C (TTFC) was expressed constitutively in Lactococcus lactis and administered orally to C57 BL/6 mice. The antibody titers elicited were lower than those following intranasal immunization (a route already known to result in high-level systemic anti-TTFC immune responses) but the protective efficacy was the same order of magnitude. The serum antibody isotypes elicited were predominantly IgG1 and IgG2a. TTFC-specific fecal IgA responses could be detected following oral or intranasal immunization. Chemically killed lactococci administered via the intranasal route were also able to elicit serum antibody responses of similar levels and kinetics to those induced by live bacteria.

Immunization of mice with poliovirus replicons expressing the C-fragment of tetanus toxin protects against lethal challenge with tetanus toxin

In this study, we describe the construction of poliovirus genomes or "replicons" which contain the C fragment gene of tetanus toxin substituted for the poliovirus P1 capsid. Upon transfection of replicon RNA into cells, we immunoprecipitated a protein corresponding to the C-fragment of tetanus toxin using tetanus-specific antibodies. Using a recombinant vaccinia virus expressing poliovirus P1 capsid protein (VV-P1) to provide P1 protein, the replicon RNA was encapsidated; stocks of the replicons were generated by passage with VV-P1. The immunogenicity of the replicons was determined by immunization of transgenic mice which are susceptible to poliovirus. A serum antibody response to poliovirus and tetanus toxoid was detected in all of the immunized mice. Protection against a lethal dose of tetanus toxin generally correlated with the levels of serum anti-tetanus antibodies. To address whether pre-existing antibodies to poliovirus limit the effectiveness of the replicon as a vaccine vector, mice were first immunized with the inactivated poliovirus vaccine followed by immunization with the replicons expressing C-fragment protein. Anti-tetanus antibodies were detected in these mice after a single administration of the replicon; these antibodies conferred protection upon challenge with tetanus toxin. These results demonstrate the potential use of poliovirus replicons encoding foreign proteins to induce a protective antibody response, even in the presence of pre-existing antibodies to poliovirus.

Factors affecting the immunogenicity of tetanus toxin fragment C expressed in Lactococcus lactis

The relative immunogenicity of tetanus toxin fragment C (TTFC) has been determined in three different strains of inbred mice when expressed in Lactococcus lactis as a membrane-anchored protein (strain UCP1054), as an intracellular protein (strain UCP1050), or as a secreted protein which is partly retained within the cell wall (strain UCP1052). Protection against toxin challenge (20 x LD50) could be obtained without the induction of anti-lactococcal antibodies. When compared in terms of the dose of expressed tetanus toxin fragment C required to elicit protection against lethal challenge the membrane-anchored form was significantly (10-20 fold) more immunogenic than the alternative forms of the protein.

Utilization of soluble fusion proteins for induction of T cell proliferation

A peptide display library was evaluated as a means to identify peptide binding motifs for class II molecules. Peptides expressed as part of a soluble fusion protein with a maltose binding protein (malE) were produced by Escherichia coli. Constructs containing the high-affinity binding influenza hemagglutinin peptide 307W-319 (mal-HA) or the low-affinity binding tetanus toxoid peptide 830-843 (mal-TT) were used as controls. mal-HA, but not mal-TT, inhibited synthetic biotinylated-HA peptide from binding to purified DR4 Dw4 molecules in a dose-dependent manner. The fusion-peptide presentation system was also evaluated for its ability to induce antigen-specific T cell proliferation. DR4 Dw4+ B cells pulsed with mal-HA, but not mal-TT, induced dose-dependent proliferation of an HA-specific DR4 Dw4-restricted T cell line to the same extent as synthetic HA peptide. Using this type of peptide display library, it may be possible to determine the antigenic specificity of T cell clones isolated from patients with autoimmune diseases.

Antibody synthesis induced by endogenous internal images

In this study, immunization with a vaccine consisting of multiple F(ab')2 fragments of affinity-purified antitetanus toxoid antibodies covalently bound to a carrier protein successfully induced antitetanus toxoid antibodies. Further studies showed that this vaccine preparation contained no biologically detectable tetanus antigen. The induced antitetanus antibody (Ab1') titer was higher than the titer of antibodies binding control antigens. The immunizing F(ab')2 preparation did not elicit a secondary antitetanus response from mice primed with tetanus toxoid and, hence, appeared free of tetanus epitopes. The specificity of Ab1' was established by absorption and inhibition with antigen. Immunization with antitetanus F(ab')2 (Ab1') fragments appears to have elicited naturally occurring autologous antitetanus toxoid antibody (Ab1') through an idiotypic pathway. As predicted by network theory, anti-idiotype (Ab2) and antitetanus (Ab1') cycled reciprocally. Clonotypic characterization of Ab1' using isoelectric focusing and affinity immunoblotting showed increases in Ab1' titer to be the result of increased synthesis by limited subsets of antitetanus toxoid B-cell clones and not increased synthesis by multiple clones, as is characteristic of antigen-driven Ab1 responses. Many Ab1 and Ab1' clonotypes had identical pIs, suggesting that they either share V region genes or are the product of the same B-cell clones. These findings indicate that immunization with polyclonal multivalent Ab1 preparations can trigger active synthesis of antibodies with the same specificity. The results provide further evidence for naturally occurring idiotypic cascades that could be exploited for studies of catalytic antibodies.

Use of the nirB Promoter to Direct the Stable Expression of Heterologous Antigens in Salmonella Oral Vaccine Strains: Development of a Single–Dose Oral Tetanus Vaccine

Plasmid pTETnir15, which directs the expression of the non-toxic immunogenic fragment C of tetanus toxin from the anaerobically inducible nirB promoter, was introduced into the Salmonella typhimurium aroA aroD live oral vaccine strain BRD509. The resulting strain, designated BRD847, was used to vaccinate orally BALB/c mice and was tested for plasmid stability and its ability to protect against a lethal tetanus toxin challenge. pTETnir15 was stably inherited by bacteria growing or persisting in the tissues of immunized mice whereas another BRD509 derivative, designated BRD753, harboring plasmid pTET85 which directs fragment C expression from the tac promoter, was highly unstable. Mice immunized with a single oral dose of BRD847 developed high levels of circulating anti-fragment C antibodies and were solidly protected against tetanus toxin challenge. Mice immunized with a single oral dose of BRD753 developed no detectable anti-fragment C antibodies. After boosting, antibodies were detected, but the mice were only partially protected against tetanus toxin challenge. Thus the use of an in vivo inducible promoter such as nirB may be a generally applicable approach to obtaining the stable in vivo expression of heterologous antigens in Salmonella vaccine strains.

Construction of a genetically defined Salmonella typhi Ty2 aroA, aroC mutant for the engineering of a candidate oral typhoid-tetanus vaccine

The construction of a Salmonella typhi Ty2 strain harbouring defined deletions in both the aroA and aroC genes is described. These deletions have been fully defined at the molecular level by DNA sequencing and have been introduced in such a way that no foreign DNA remains in the S. typhi genome. This strain is attenuated in mice when given by the intraperitoneal route suspended in hog gastric mucin and is attenuated to a similar level to strains harbouring deletions in aroA or aroC alone indicating that both lesions are capable of attenuating independently. We have used this defined S. typhi aroA aroC strain to express stably a non-toxic 50 kDa fragment of tetanus toxin (fragment C) from a gene incorporated into the chromosome. This strain has the advantage of harbouring no antibiotic-resistance markers and we consider it to be a candidate bivalent oral typhoid-tetanus vaccine.

High-level expression of tetanus toxin fragment C in Pichia pastoris strains containing multiple tandem integrations of the gene

We have used the methylotrophic yeast, Pichia pastoris, to express high levels of tetanus toxin fragment C, a potential subunit vaccine against tetanus. In high biomass fermentations fragment C was induced to 27% of total cell protein or about 12 g/l of culture. The purified protein was as effective as native fragment C in immunizing mice. In order to optimize fragment C production, we have examined the parameters affecting foreign gene expression in Pichia. The level of expression was found to be largely independent of the site of chromosomal integration of the gene (AOX1 or HIS4), the type of integrant (insertion or transplacement), and the methanol utilisation phenotype of the host strain (Mut+ or Muts). The most important factor in obtaining high levels was the presence of multiple integrated copies of the fragment C expression cassette. Multicopy clones could be isolated from transformations using DNA fragments targeted for single-copy transplacement into the chromosome. These multicopy transformants were surprisingly stable over multiple generations during growth and induction in high cell density fermentations. Analysis of chromosomal DNA from these clones suggests that they arose by circularization of the transforming DNA fragment in vivo followed by multiple insertion into the chromosome via repeated single crossover recombination, in addition to the expected transplacement event. We have found this to be a general phenomenon and have used these multicopy "transplacement" clones to obtain high-level expression of several other foreign genes in Pichia.