Immunization of mice with DNA encoding fragment C of tetanus toxin

Discovery and engineering of the antibody response against a prominent skin commensal

The ubiquitous skin colonist Staphylococcus epidermidis elicits a CD8 + T cell response pre-emptively, in the absence of an infection 1 . However, the scope and purpose of this anti-commensal immune program are not well defined, limiting our ability to harness it therapeutically. Here, we show that this colonist also induces a potent, durable, and specific antibody response that is conserved in humans and non-human primates. A series of S. epidermidis cell-wall mutants revealed that the cell surface protein Aap is a predominant target. By colonizing mice with a strain of S. epidermidis in which the parallel β-helix domain of Aap is replaced by tetanus toxin fragment C, we elicit a potent neutralizing antibody response that protects mice against a lethal challenge. A similar strain of S. epidermidis expressing an Aap-SpyCatcher chimera can be conjugated with recombinant immunogens; the resulting labeled commensal elicits high titers of antibody under conditions of physiologic colonization, including a robust IgA response in the nasal mucosa. Thus, immunity to a common skin colonist involves a coordinated T and B cell response, the latter of which can be redirected against pathogens as a novel form of topical vaccination.

Fusion to chicken C3d enhances the immunogenicity of the M2 protein of avian influenza virus

BACKGROUND

Current vaccines to avian influenzae virus (AIV), a highly contagious disease of birds, need to be constantly updated due to the high level of variation in the target antigens. Therefore, a vaccine that could induce broad cross protection against AIV is required. The M2 membrane protein is structurally conserved amongst AIV subtypes but tends in induce a poor immune response, whereas C3d has been shown in many species to enhance immunogenicity. In this study, we investigated the potential of M2-avian C3d fusion proteins to provide effective immunity.

RESULTS

We fused chicken complement C3d to sM2 (M2 protein with the transmembrane region deleted) of AIV and expressed four fusion proteins, GST (Glutathione S-transferase tagged proteins in pGEX expression vector) -C3d-sM2, GST-C3d-L2-sM2, GST-C3d-L1-C3d-sM2 and GST-C3d-L1-C3d-L2-sM2 were used to immunize mice. In addition, Specific pathogen free (SPF) chickens were inoculated with the plasmids pcDNA-sM2, pcDNA-C3d-L1-C3d-L2-sM2, GST-sM2 and GST-C3d-L1-C3d-L2-sM2. The immune response was monitored by an enzyme-linked immunosorbent assay (ELISA) for sM2 antibody, and all the test animals were challenged with A/chicken/Bei Jing/WD9/98 (H9N2) virus. Results revealed that the anti-sM2 antibody in mice and chickens vaccinated with these proteins was higher than the nonfused forms of sM2, the GST-C3d-L1-C3d-L2-sM2 groups have conferred the highest 30% and 20% protection ratio in mice and chickens respectively. In addition, the pcDNA-C3d-L1-C3d-L2-sM2 also enhances the antibody responses to sM2 compared to pcDNA-sM2 in chickens, and acquired 13.3% protection ratio.

CONCLUSION

These results indicated that chicken C3d enhanced the humoral immunity against AIV M2 protein either fused proteins expressed by the prokaryotic system or with the DNA vaccine. Nevertheless, in view of the poor protection ratio for these animals, we speculated that this is not a worthy developing of vaccine in these constructs.

The synthetic peptide Trp-Lys-Tyr-Met-Val-D-Met as a novel adjuvant for DNA vaccine

Trp-Lys-Tyr-Met-Val-D-Met (WKYMVm) is a synthetic peptide known to activate human neutrophils, monocytes and dendritic cells, resulting in the enhancement of superoxide generation, bactericidal activity, chemotactic migration and survival. In this study, we demonstrated that WKYMVm enhanced the surface expression of CD80, but not that of CD40, CD86 and MHC class II, on mouse bone marrow-derived dendritic cells which is one of the essential costimulatory signals for the induction of immune responses. Furthermore, when WKYMVm was codelivered with HIV, HBV and Influenza DNA vaccines, WKYMVm selectively enhanced the vaccine-induced CD8(+) T cell responses in a dose-dependent manner, in terms of IFN-gamma secretion and cytolytic activity. Our results indicate that a synthetic peptide, WKYMVm can function as a novel adjuvant for DNA vaccine.

DNA vaccines to attack cancer

Delivery of antigens by injection of the encoding DNA allows access to multiple antigen-presenting pathways. Knowledge of immunological processes can therefore be used to modify construct design to induce selected effector functions. Expression can be directed to specific intracellular sites, and additional genes can be fused or codelivered to amplify responses. Therapeutic vaccination against cancer adds a requirement to overcome tolerance and to activate a weakened immune repertoire. Induction of CD4(+) T helper cells is critical for both antibody and T cell effector responses. To activate immunity against tumor antigens, we fused the tumor-derived sequences to genes encoding microbial proteins. This strategy engages T helper cells from the large antimicrobial repertoire for linked help for inducing antibody against cell-surface tumor antigens. The principle of linked T cell help also holds for induction of epitope-specific antitumor CD8(+) T cells, but the microbial sequence has to be minimized to avoid competition with tumor antigens. Epitope-specific DNA vaccination leads to powerful antitumor attack and can activate immunity from a profoundly tolerized repertoire. Vaccine designs validated in preclinical models are now in clinical trial with immune responses detected against both tumor antigens and fused microbial antigens. DNA priming is highly efficient, but boosting may benefit from increased antigen expression. Physical methods including electroporation provide increased expression without introducing additional competing antigens. A wide range of cancers can be targeted, and objective assays of response will determine efficacy.

DNA-Salmonella enterica serovar Typhimurium primer-booster vaccination biases towards T helper 1 responses and enhances protection against Leishmania major infection in mice

Successful resolution of infections by intracellular pathogens requires gamma interferon (IFN-gamma). DNA vaccines promote T helper 1 (Th1) responses by triggering interleukin-12 (IL-12) release by dendritic cells (DC) through Toll-like receptor 9 (TLR9). In humans TLR9 is restricted to plasmacytoid DC. Here we show that DNA-Salmonella enterica serovar Typhimurium primer-booster vaccination, which provides alternative ligands to bind TLR4 on myeloid DC, strongly biases towards Th1 responses compared to vaccination with DNA alone. This results in higher immunoglobulin G2a (IgG2a) responses compared to IgG1 responses, higher IFN-gamma responses compared to IL-10 CD4(+)-T-cell responses, and enhanced protection against Leishmania major infection in susceptible BALB/c mice.

DNA fusion gene vaccines against cancer: from the laboratory to the clinic

Vaccination against target antigens expressed by cancer cells has now become a realistic goal. DNA vaccines provide a direct link between identification of genetic markers in tumors and vaccine formulation. Simplicity of manufacture facilitates construction of vaccines against disease subsets or even for individual patients. To engage an immune system that exists to fight pathogens, we have developed fusion gene vaccines encoding tumor antigens fused to pathogen-derived sequences. This strategy activates high levels of T-cell help, the key to induction and maintenance of effective immunity. We have dissected the immunogenic tetanus toxin to obtain specific sequences able to activate antibody, CD4+, or CD8+ T cells to attack selected fused tumor antigens. Principles established in preclinical models are now being tested in patients. So far, objective immune responses against idiotypic antigen of neoplastic B cells have been observed in patients with B-cell malignancies and in normal transplant donors. These responses provide a platform for testing physical methods to improve DNA delivery and strategies to boost responses. For cancer, demands are high, because vaccines have to activate powerful immunity against weak antigens, often in a setting of immune damage or tolerance. Vaccination strategies against cancer and against microbes are sharing knowledge and technology for mutual benefit.

Pluronic® F127-based systemic vaccine delivery systems

We have developed a vaccine delivery system based on the non-ionic block copolymer, Pluronic F127 (F127), combined with selected immunomodulators. F127-based matrices are characterized by a phenomenon known as reverse thermogelation, whereby the formulation undergoes a phase transition from liquid to gel upon reaching physiological temperatures. Protein antigens (tetanus toxoid (TT), diphtheria toxoid (DT) and anthrax recombinant protective antigen (rPA)) were formulated with F127 in combination with CpG motifs or chitosan, as examples of immunomodulators, and were compared to more traditional adjuvants in mice. IgG antibody responses were significantly enhanced by the F127/CpG and F127/chitosan combinations compared to antigens mixed with CpGs or chitosan alone. In addition, the responses were significantly greater than those elicited by aluminum salts. Furthermore, the functional activity of these antibodies was demonstrated using either in vivo tetanus toxin challenge or an anthrax lethal toxin neutralization assay. These studies suggest that a block-copolymer approach could enhance the delivery of a variety of clinically useful antigens in vaccination schemes.

DNA fusion vaccines against B-cell tumors

DNA vaccination is currently being explored as a potential strategy for combatting cancer. However, tumor antigens are often weak and the immune system of patients may be compromised. For B-cell tumors, immunoglobulin idiotypic antigens provide defined targets but are poorly immunogenic. Fusion of a sequence derived from tetanus toxin to the genes encoding idiotypic determinants has proved highly effective in activating protective anti-tumor immunity. DNA fusion vaccines containing immuno-enhancing sequences can augment and direct immune attack on a range of target antigens. Gene-based fusion vaccines offer ease of manipulation and flexible design to activate effective attack on cancer.

Successful DNA immunisation of rats against fasciolosis

The liver fluke Fasciola hepatica contributes to great economic and health losses in the cattle industry in many countries, including Poland. Unfortunately, no vaccine against fasciolosis is commercially available. We have designed a DNA vaccine and tested it in rats. Groups of male or female rats received one intramuscular injection of 50 microg of a pcDNA 3.1 vector carrying cDNA encoding for a cysteine proteinase of F. hepatica. The plasmid was diluted in saline containing 0.05% bupivacaine. Control rats were injected with empty plasmid or not injected at all. All rats were challenged with 45 metacercariae of the fluke on day 28 of the experiment. Seven weeks after the challenge infection fluke burdens were evaluated in vaccinated and control rats. Male rats vaccinated with cysteine proteinase cDNA revealed 100% protection against F. hepatica infection. Females immunised in the same way exhibited the reduction of fluke burden by 74%.

DNA vaccination using the fragment C of botulinum neurotoxin type A provided protective immunity in mice

Botulinum neurotoxin (BoNT) is one of the most toxic substances known to produce severe neuromuscular paralysis. The currently used vaccine is prepared mainly from biohazardous toxins. Thus, we studied an alternative method and demonstrated that DNA immunization provided sufficient protection against botulism in a murine model. A plasmid of pBoNT/A-Hc, which encodes the fragment C gene of type A botulinum neurotoxin, was constructed and fused with an Igkappa leader sequence under the control of a human cytomegalovirus promoter. After 10 cycles of DNA inoculation with this plasmid, mice survived lethal doses of type A botulinum neurotoxin challenges. Immunized mice also elicited cross-protection to the challenges of type E botulinum neurotoxin. This is the first study demonstrating the potential use of DNA vaccination for botulinum neurotoxins.

Gene gun mediated vaccination is superior to manual delivery for immunisation with DNA vaccines expressing protective antigens from Yersinia pestis or Venezuelan Equine Encephalitis virus

Plasmids expressing the V antigen of Yersinia pestis or the E2 glycoprotein of Venezuelan Equine Encephalitis (VEE) virus were used to vaccinate mice by intra-dermal or intra-muscular injection, or by particle-mediated bombardment using the Helios gene gun. After two immunizations, groups of mice which had received 4 microg doses of plasmid DNA using the gene gun had IgG levels which were higher than in other groups manually immunised with 12-fold more plasmid DNA. The immunoglobulin isotype profile was predominantly IgG1 following inoculation with either plasmid. Our results indicate that gene gun mediated vaccination can be used to increase the magnitude of the immune response to both bacterial and viral antigens expressed by plasmid DNA.

Nucleic acid immunization: concepts and techniques associated with third generation vaccines

A radical change in vaccine methodology arrived nine years ago with the advent of nucleic acid immunization. Aspects such as plasmid design, gene selection, the use of immunostimulatory complexes and clinical trials are discussed in this review. Furthermore, concepts and protocols involved in the construction, evaluation and immunization of a DNA vaccine have been examined as new strategies to enhance this technology continues to grow.

Genetic vaccines

In a few short years, genetic vaccine technology has moved rapidly from a novel concept to an important strategy for the development of human and veterinary vaccines, for numerous indications. This article discusses current areas in which further refinements in technology will influence a variety of infectious disease treatments, including intramuscular and intradermal inoculation, gene gun inoculation, the mechanism of antigen presentation, and the use of genetic adjuvants.