Recombinant viruses as vaccines and immunological tools

Overview of the current promising approaches for the development of an effective severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine

Coronavirus disease 2019 (COVID-19) is a pandemic infectious disease caused by the novel coronavirus called SARS-CoV-2. There is a gap in our understanding regarding the immunopathogenesis of COVID-19. However, many clinical trials are underway across the world for screening effective drugs against COVID-19. Nevertheless, currently, no proven effective therapies for this virus exists. The vaccines are deemed as a significant part of disease prevention for emerging viral diseases, since, in several cases, other therapeutic choices are limited or non-existent, or that diseases result in such an accelerated clinical worsening that the efficacy of treatments is restricted. Therefore, effective vaccines against COVID-19 are urgently required to overcome the tremendous burden of mortality and morbidity correlated with SARS-CoV-2. In this review, we will describe the latest evidence regarding outstanding vaccine approaches and the challenges for vaccine production.

Vaccination strategies to combat novel corona virus SARS-CoV-2

The 2019-novel coronavirus disease (COVID-19) is caused by SARS-CoV-2 is transmitted from human to human has recently reported in China. Now COVID-19 has been spread all over the world and declared epidemics by WHO. It has caused a Public Health Emergency of International Concern. The elderly and people with underlying diseases are susceptible to infection and prone to serious outcomes, which may be associated with acute respiratory distress syndrome (ARDS) and cytokine storm. Due to the rapid increase of SARS-CoV-2 infections and unavailability of antiviral therapeutic agents, developing an effective SAR-CoV-2 vaccine is urgently required. SARS-CoV-2 which is genetically similar to SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV) is an enveloped, single and positive-stranded RNA virus with a genome comprising 29,891 nucleotides, which encode the 12 putative open reading frames responsible for the synthesis of viral structural and nonstructural proteins which are very similar to SARS-CoV and MERS-CoV proteins. In this review we have summarized various vaccine candidates i.e., nucleotide, subunit and vector based as well as attenuated and inactivated forms, which have already been demonstrated their prophylactic efficacy against MERS-CoV and SARS-CoV, so these candidates could be used as a potential tool for the development of a safe and effective vaccine against SARS-CoV-2.

Parasites or cohabitants: cruel omnipresent usurpers or creative "éminences grises"?

This paper presents many types of interplays between parasites and the host, showing the history of parasites, the effects of parasites on the outcome of wars, invasions, migrations, and on the development of numerous regions of the globe, and the impact of parasitic diseases on the society and on the course of human evolution. It also emphasizes the pressing need to change the look at the parasitism phenomenon, proposing that the term “cohabitant” is more accurate than parasite, because every living being, from bacteria to mammals, is a consortium of living beings in the pangenome. Even the term parasitology should be replaced by cohabitology because there is no parasite alone and host alone: both together compose a new adaptive system: the parasitized-host or the cohabitant-cohabited being. It also suggests switching the old paradigm based on attrition and destruction, to a new one founded on adaptation and living together.

SARS vaccines: where are we?

In this review, the current state of vaccine development against human severe acute respiratory syndrome (SARS) coronavirus, focusing on recently published data is assessed. We discuss which strategies have been assessed immunologically and which have been evaluated in SARS coronavirus challenge models. We discuss inactivated vaccines, virally and bacterially vectored vaccines, recombinant protein and DNA vaccines, as well as the use of attenuated vaccines. Data regarding the correlates of protection, animal models and the available evidence regarding potential vaccine enhancement of SARS disease are discussed. While there is much evidence that various vaccine strategies against SARS are safe and immunogenic, vaccinated animals still display significant disease upon challenge. Current data suggest that intranasal vaccination may be crucial and that new or combination strategies may be required for good protective efficacy against SARS in humans.

Gene therapy for disorders affecting children, progress and potential

For over two decades gene therapy has been actively pursued as a treatment modality for the inherited diseases that affect the paediatric population, however, it is still to make a real impact in the clinic. There are many reasons for this including inadequate technology and a lack of understanding of the biological complexities that impact on the efficiency of gene delivery and its outcomes, both positive and negative. However, recent progress is now addressing these issues and indicates that these problems can be overcome, and that gene therapy will play a significant role in the treatment of at least some of these disorders. This review will first give a short overview of relevant gene delivery technologies, what strategies can be used and which diseases are potential targets for gene therapy, and then illustrate several specific diseases for which gene therapy is actively being developed.

Cancer vaccines: preclinical studies and novel strategies

The development of cancer vaccines, aimed to enhance the immune response against a tumor, is a promising area of research. A better understanding of both the molecular mechanisms that govern the generation of an effective immune response and the biology of a tumor has contributed to substantial progress in the field. Areas of intense investigation in cancer immunotherapy will be discussed here, including: (1) the discovery and characterization of novel tumor antigens to be used as targets for vaccination; (2) the investigation of different vaccine-delivery modalities such as cellular-based vaccines, protein- and peptide-based vaccines, and vector-based vaccines; (3) the characterization of biological adjuvants to further improve the immunogenicity of a vaccine; and (4) the investigation of multimodal therapies where vaccines are being combined with other oncological treatments such as radiation and chemotherapy. A compilation of data from preclinical studies conducted in vitro as well as in animal models is presented here. The results from these studies would certainly support the development of new vaccination strategies toward cancer vaccines with enhanced clinical efficacy.

Pox Viral Vaccine Approaches

Recent advances in understanding tumor-specific immunity have introduced new excitement in the clinical development of vaccines for the treatment of cancer. A better understanding of basic immunologic principles has led to a variety of techniques for enhancing tumor-specific immunity through vaccination. Approaches to antigen-specific immunotherapy have included: (1) peptides, usually in combination with various immunological adjuvants; (2) soluble proteins; (3) dendritic cells pulsed with specific antigens; (4) monoclonal antibodies; (5) recombinant plasmid DNA; (6) autologous and allogeneic tumor cells; and (7) recombinant viral vectors. This review will focus on the use of viral vectors, which offer unique advantages as both gene delivery vectors and as agents supplying additional adjuvant activity for vaccination. Viral vectors are particularly attractive for immunotherapy since they mimic natural infection and can induce potent immune responses. Replicating and nonreplicating members of the poxvirus family have been widely studied for expression of tumor antigens and other immunomodulatory genes, such as cytokines and costimulatory molecules. Although a large number of TAAs are available for insertion into viral vectors, this review will discuss the preclinical and clinical development of prostate-specific antigen (PSA) and carcinoembryonic antigen (CEA) poxviral vaccines, as models of the pox viral vaccine approach.

Immune responses against a single CD8+-T-cell epitope induced by virus vector vaccination can successfully control Trypanosoma cruzi infection

In order to develop CD8+-T-cell-mediated immunotherapy against intracellular infectious agents, vaccination using recombinant virus vectors has become a promising strategy. In this study, we generated recombinant adenoviral and vaccinia virus vectors expressing a single CD8+-T-cell epitope, ANYNFTLV, which is derived from a Trypanosoma cruzi antigen. Immunogenicity of these two recombinant virus vectors was confirmed by the detection of ANYNFTLV-specific CD8+ T cells in the spleens of immunized mice. Priming/boosting immunization using combinations of these two recombinant virus vectors revealed that the adenovirus vector was efficient for priming and the vaccinia virus vector was effective for boosting the CD8+-T-cell responses. Moreover, we also demonstrated that the ANYNFTLV-specific CD8+-T-cell responses were further augmented by coadministration of recombinant vaccinia virus vector expressing the receptor activator of NFkappaB (RANK) ligand as an adjuvant. By priming with the adenovirus vector expressing ANYNFTLV and boosting with the vaccinia virus vectors expressing ANYNFTLV and RANK ligand, the immunized mice were efficiently protected from subsequent challenge with lethal doses of T. cruzi. These results indicated, for the first time, that the induction of immune responses against a single CD8+-T-cell epitope derived from an intrinsic T. cruzi antigen was sufficient to control lethal T. cruzi infection.

Immune properties of recombinant vaccinia virus encoding CD154 (CD40L) are determined by expression of virally encoded CD40L and the presence of CD40L protein in viral particles

Expression of costimulatory molecules by recombinant poxviruses is a promising strategy for enhancing therapeutic vaccines. CD40-CD40L interactions are critical for conditioning dendritic cells (DC) and priming T- and B-cell immunity. We constructed a vaccinia virus expressing murine CD40L (rV-CD40L) and studied its immunomodulatory properties in vitro. Direct DC infection with control vaccinia or psoralen/UV-inactivated rV-CD40L stimulated high levels of interleukin 12 (IL-12) release. However, replication-competent rV-CD40L did not stimulate IL-12 under similar conditions. We observed a high level of CD40L protein on purified viral particles and demonstrated that induction of IL-12 by nonreplicating rV-CD40L was blocked by anti-CD40 antibodies suggesting that functional CD40L on viral particles contributed to alterations in IL-12 synthesis. Since cross-presentation of tumor-associated antigens by DC is augmented by viral infection of tumor cells, we infected MC38 murine colon carcinoma cells with rV-CD40L. Infected cells stimulated IL-12 secretion by DC and proliferation of B cells and DX5(+) (NK/NKT) cells through direct CD40-CD40L interaction. A subpopulation of NKT cells expressing CD40 (NK1.1(+), CD3(lo)) appeared to be a major effector population responding to MC38/rV-CD40L. These results highlight the complex immune regulatory effects of rV-CD40L defined by the cumulative effects of CD40L expression, presence of CD40L protein in viral particles, and the replication potential of the virus.

The multivalent minigene approach to vaccine development

Epitope based minigenes (epigenes) have been under investigation for several years as an experimental approach to vaccination against infectious diseases. The essence of this technology is that short DNA sequences, encoding well-defined cytotoxic T-lymphocyte- (CTL), antibody- (Ab) or helper T-lymphocyte- (HTL) specific epitopes are used as immunogens. Compared to other vaccine strategies, several potential advantages are apparent. These include the increased 'safety' of an immunisation strategy that mimics antigen processing and presentation during natural infections, without actually causing disease, and the 'flexibility' in epitope selection, which allows induction and optimisation of the desired type of immunity. In addition, the 'high immunogenicity' of epitope based constructs relative to constructs based on whole antigenic proteins is an important factor. This paper presents and discusses recent developments in the use of minigenes or multiple epitope genes that allow vaccines to be designed. The preclinical studies available to date clearly demonstrate the great potential of this vaccine approach, in terms of both prophylaxis and therapy.

A natural vaccinia virus promoter with exceptional capacity to direct protein synthesis

A survey of vaccinia virus promoters, through a reporter gene approach, has identified the viral I1L promoter as having exceptional activity. The I1L promoter exhibited over 10 times the activity of other vaccinia promoters and even rivaled the activity of the bacteriophage T7 promoter in the hybrid vaccinia/T7 expression system. The I1L promoter had high activity in both transient transfection experiments and in the context of recombinant viruses. The I1L promoter should be useful for high-level protein synthesis and poxvirus studies in general.

NY-ESO-1 protein formulated in ISCOMATRIX adjuvant is a potent anticancer vaccine inducing both humoral and CD8+ t-cell-mediated immunity and protection against NY-ESO-1+ tumors

NY-ESO-1 is a 180 amino-acid human tumor antigen expressed by many different tumor types and belongs to the family of "cancer-testis" antigens. In humans, NY-ESO-1 is one of the most immunogenic tumor antigens and NY-ESO-1 peptides have been shown to induce NY-ESO-1-specific CD8(+) CTLs capable of altering the natural course of NY-ESO-1-expressing tumors in cancer patients. Here we describe the preclinical immunogenicity and efficacy of NY-ESO-1 protein formulated with the ISCOMATRIX adjuvant (NY-ESO-1 vaccine). In vitro, the NY-ESO-1 vaccine was readily taken up by human monocyte-derived dendritic cells, and on maturation, these human monocyte-derived dendritic cells efficiently cross-presented HLA-A2-restricted epitopes to NY-ESO-1-specific CD8(+) T cells. In addition, epitopes of NY-ESO-1 protein were also presented on MHC class II molecules to NY-ESO-1-specific CD4(+) T cells. The NY-ESO-1 vaccine induced strong NY-ESO-1-specific IFN-gamma and IgG2a responses in C57BL/6 mice. Furthermore, the NY-ESO-1 vaccine induced NY-ESO-1-specific CD8(+) CTLs in HLA-A2 transgenic mice that were capable of lysing human HLA-A2(+) NY-ESO-1(+) tumor cells. Finally, C57BL/6 mice, immunized with the NY-ESO-1 vaccine, were protected against challenge with a B16 melanoma cell line expressing NY-ESO-1. These data illustrate that the NY-ESO-1 vaccine represents a potent therapeutic anticancer vaccine.

Prostate-specific antigen vaccines for prostate cancer

Prostate cancer is the most common malignant tumour in men and there are few treatment options available once the tumour becomes refractory to hormonal manipulation. Prostate-specific antigen (PSA) is a secretory glycoprotein that is commonly expressed by prostatic epithelial cells and is found in elevated levels in the serum of men with prostate cancer. The identification of T cell specific epitopes within the coding sequence of PSA has led to the development of various vaccine strategies that target PSA in an attempt to treat established prostate cancer. These strategies have included human leukocyte antigen-restricted PSA peptides, dendritic cells pulsed with PSA, recombinant viruses expressing PSA and combinations of different vectors. In addition to PSA, several other antigens have been described that may be useful for targeting prostate tumours by vaccines. Animal studies have established the feasibility and safety for many of these agents and clinical trials are now in progress to evaluate the immunological and clinical responses of PSA vaccines. Further research in manipulating anti-PSA immunity with cytokines, costimulatory molecules and other immune modulating agents will likely improve the therapeutic effectiveness of PSA vaccines. Clinical trials designed to evaluate the effects of vaccination in different stages of disease and through different routes of administration need to be performed to define the optimal schedule for PSA vaccines in patients with prostate cancer, or for those at high risk of developing the disease.

Kunjin virus replicon vaccine vectors induce protective CD8+ T-cell immunity

The ability of self-replicating RNA (replicon) vaccine vectors derived from the Australian flavivirus Kunjin (KUN) to induce protective alphabeta CD8+ T-cell responses was examined. KUN replicons encoding a model immunogen were delivered by three different vaccine modalities: (i) as naked RNA transcribed in vitro, (ii) as plasmid DNA constructed to allow in vivo transcription of replicon RNA by cellular RNA polymerase II (DNA based), and (iii) as replicon RNA encapsidated into virus-like particles. A single immunization with any of these KUN replicon vaccines induced CD8+ T-cell responses at levels comparable to those induced by recombinant vaccinia virus encoding the same immunogen. Immunization with only 0.1 microg of DNA-based KUN replicons elicited CD8+ T-cell responses similar to those seen after immunization with 100 microg of a conventional DNA vaccine. Naked RNA immunization with KUN replicons also protected mice against challenges with recombinant vaccinia virus and B16 tumor cells. These results demonstrate the value of KUN replicon vectors for inducing protective antiviral and anticancer CD8+ T-cell responses.

Progress toward a malaria vaccine: efficient induction of protective anti-malaria immunity

Malaria can be a very severe disease, particularly in young children, pregnant women (mostly in primipara), and malaria naïve adults, and currently ranks among the most prevalent infections in tropical and subtropical areas throughout the world. The widespread occurrence and the increased incidence of malaria in many countries, caused by drug-resistant parasites (Plasmodium falciparum and P. vivax) and insecticide-resistant vectors (Anopheles mosquitoes), indicate the need to develop new methods of controlling this disease. Experimental vaccination with irradiated sporozoites can protect animals and humans against the disease, demonstrating the feasibility of developing an effective malaria vaccine. However, developing a universally effective, long lasting vaccine against this parasitic disease has been a difficult task, due to several problems. One difficulty stems from the complexity of the parasite's life cycle. During their life cycle, malaria parasites change their residence within the host, thus avoiding being re-exposed to the same immunological environment. These parasites also possess some distinct antigens, present at different life stages of the parasite, the so-called stage-specific antigens. While some of the stage-specific antigens can induce protective immune responses in the host, these responses are usually genetically restricted, this being another reason for delaying the development of a universally effective vaccine. The stage-specific antigens must be used as immunogens and introduced into the host by using a delivery system that should efficiently induce protective responses against the respective stages. Here we review several research approaches aimed at inducing protective anti-malaria immunity, overcoming the difficulties described above.

Role of type I IFNs in the in vitro attenuation of live, temperature-sensitive vaccine strains of human respiratory syncytial virus

The contributions of type I interferons (IFNs) to the in vitro attenuation of three temperature-sensitive (Ts) subgroup A and one subgroup B deletion mutant RSV strains were evaluated. The ability of these vaccine viruses to induce IFNs at their permissive and restrictive temperatures and their sensitivity to the antiviral effects of exogenous I IFNs were tested in human lung epithelial A549 cells. Our results show that the highly attenuated and immunogenic subgroup A vaccine strain Ts1C produced higher levels of IFN-beta than its parent RSS-2 or two related strains, Ts1A and Ts1B, at their permissive temperature. Growth of RSV-infected A549 cultures at restrictive temperatures or prior UV inactivation of the virus abolished the observed induction of IFN-beta, suggesting a strict requirement of viral replication for cellular IFN induction. The enhanced induction of IFN-beta by the highly immunogenic Ts1C at permissive temperature may be an advantageous characteristic of a live intranasal vaccine candidate. The subgroup B strain RSV B1 and its mutant cp-52 (with SH and G gene deletions) both induced similar but low levels of IFN-beta. Hence the observed overattenuation of cp-52 in human infants is probably not due to enhanced IFN induction during its replication in the host. The ability of cp-52, which does not express the SH and G proteins, to induce IFN-beta levels similar to those of its parent strain suggests that these viral proteins may not have a role in the induction of IFN-beta in the host. In addition, both subgroup A and B mutants and their respective parent strains were similarly resistant to the antiviral effects of exogenous IFN-alpha or -beta. Therefore, increased sensitivity of the mutants to IFNs does not seem to contribute to their attenuation.

Postexposure vaccination massively increases the prevalence of gamma-herpesvirus-specific CD8+ T cells but confers minimal survival advantage on CD4-deficient mice

Mice that lack CD4(+) T cells remain clinically normal for more than 60 days after respiratory challenge with the murine gamma-herpesvirus 68 (gammaHV-68), then develop symptoms of a progressive wasting disease. The gammaHV-68-specific CD8(+) T cells that persist in these I-A(b-/-) mice are unable to prevent continued, but relatively low level, virus replication. Postexposure challenge with recombinant vaccinia viruses expressing gammaHV-68 lytic cycle epitopes massively increased the magnitude of the gammaHV-68-specific CD8(+) population detectable by staining with tetrameric complexes of MHC class I glycoprotein + peptide, or by interferon-gamma production subsequent to in vitro restimulation with peptide. The boosting effect was comparable for gammaHV-68-infected I-A(b-/-) and I-A(b+/+) mice within 7 days of challenge, and took more than 110 days to return to prevaccination levels in the I-A(b+/+) controls. Although the life-span of the I-A(b-/-) mice was significantly increased, there was no effect on long-term survival. A further boost with a recombinant influenza A virus failed to improve the situation. Onset of weight loss was associated with a decline in gammaHV-68-specific CD8(+) T cell numbers, though it is not clear whether this was a cause or an effect of the underlying pathology. Even very high levels of virus-specific CD8(+) T cells thus provide only transient protection against the uniformly lethal consequences of gammaHV-68 infection under conditions of CD4(+) T cell deficiency.

Use of recombinant viruses to deliver cytokines influencing the course of experimental bacterial infection

The feasibility of using viral constructs expressing cytokine genes to influence the course of bacterial infection was tested in mice. The mice were first infected with vaccinia or fowlpox viruses expressing the cytokine of interest, then challenged with the facultative intracellular bacterial pathogen Listeria monocytogenes. The course of infection was assessed by subsequent bacterial counts. Expression of IFN-gamma or TNF was protective. Vaccinia virus was more efficient at delivering IFN-gamma-mediated protection than was fowlpox virus, which is unable to proliferate in mammalian cells. The effect of vaccinia-IFN-gamma was more apparent in the liver, where vaccinia proliferates to high titres (> 109), than in the spleen, where only 103 vaccinia were isolated. Vaccinia virus expressing IL-4 exacerbated infection. Interleukin-4 exacerbation was T cell independent and was reflected in the failure of macrophage activation, possibly due to suppression of NK cells, which are a source of IFN-gamma early in infection. The clear indication of protection by some cytokines in this prophylactic model appears to justify further study of the therapeutic effects of cytokine-expressing viruses in chronic bacterial infections, especially where a cytokine defect is suspected.

Interferon gamma expressed by a recombinant respiratory syncytial virus attenuates virus replication in mice without compromising immunogenicity

Interferon gamma (IFN-gamma) has pleiotropic biological effects, including intrinsic antiviral activity as well as stimulation and regulation of immune responses. An infectious recombinant human respiratory syncytial virus (rRSV/mIFN-gamma) was constructed that encodes murine (m) IFN-gamma as a separate gene inserted into the G-F intergenic region. Cultured cells infected with rRSV/mIFN-gamma secreted 22 microg mIFN-gamma per 10(6) cells. The replication of rRSV/mIFN-gamma, but not that of a control chimeric rRSV containing the chloramphenicol acetyl transferase (CAT) gene as an additional gene, was 63- and 20-fold lower than that of wild-type (wt) RSV in the upper and lower respiratory tract, respectively, of mice. Thus, the attenuation of rRSV/mIFN-gamma in vivo could be attributed to the activity of mIFN-gamma and not to the presence of the additional gene per se. The mice were completely resistant to subsequent challenge with wt RSV. Despite its growth restriction, infection of mice with rRSV/mIFN-gamma induced a level of RSV-specific antibodies that, on day 56, was comparable to or greater than that induced by infection with wt RSV. Mice infected with rRSV/mIFN-gamma developed a high level of IFN-gamma mRNA and an increased amount of interleukin 12 p40 mRNA in their lungs, whereas other cytokine mRNAs tested were unchanged compared with those induced by wt RSV. Because attenuation of RSV typically is accompanied by a reduction in immunogenicity, expression of IFN-gamma by an rRSV represents a method of attenuation in which immunogenicity can be maintained rather than be reduced.

Induction of CD8+ T cell-mediated protective immunity against Trypanosoma cruzi

Trypanosoma cruzi was transformed with the Plasmodium yoelii gene encoding the circum-sporozoite (CS) protein, which contains the well-characterized CD8+ T cell epitope, SYVPSAEQI. In vivo and in vitro assays indicated that cells infected with the transformed T. cruzi could process and present this malaria parasite-derived class I MHC-restricted epitope. Immunization of mice with recombinant influenza and vaccinia viruses expressing the SYVPSAEQI epitope induced a large number of specific CD8+ T cells that strongly suppressed parasitemia and conferred complete protection against the acute T. cruzi lethal infection. CD8+ T cells mediated this immunity as indicated by the unrelenting parasitemia and high mortality observed in immunized mice treated with anti-CD8 antibody. This study demonstrated, for the first time, that vaccination of mice with vectors designed to induce CD8+ T cells is effective against T. cruzi infection.

Out on the farm with DNA vaccines

DNA vaccination is a rapidly developing technology that offers new approaches for the prevention of disease. This technology may permit the production of new vaccines against diseases that have no current vaccine, as well as allowing the development of improved vaccines to replace existing products. We describe how DNA vaccination is being developed for use in commercial animal production, with an emphasis on viral diseases, and discuss the existing hurdles to its development and use.

Cytokine responses in virus infections: effects on pathogenesis, recovery and persistence

During the past year, significant advances have been made in our understanding of cytokine regulation and the respective roles played by T helper cells type 1 and 2 immune responses during virus infection. Numerous mechanisms by which viruses may evade host immune defences have now been identified, some directly influencing cytokine activity. Major advances have also been made in delineating the roles of cytokines and chemokines at different stages in the pathogenesis of HIV infection.

Cytokines: principles and prospects

Cytokines participate in the induction and effector phases of all immune and inflammatory responses. They are therefore obvious tools and targets for strategies designed to promote, inhibit or redirect these responses. However, the complexity of the cytokine network has hindered the widespread clinical application of many cytokines and it has become clear that a deeper understanding of the normal operation of this system in health and disease is needed for the therapeutic potential of cytokines to be fully realized. This review summarizes some of the principles that are now thought to underlie the diverse functions of the interleukins, interferons, colony-stimulating factors and tumour necrosis factors in immune and inflammatory reactions in vivo. Genetic and structural relationships between these cytokines, the regulation of their synthesis, and the structures and functions of their receptors are outlined. Current knowledge of these parameters suggests ways in which multiple positive and negative regulatory mechanisms are integrated to balance cytokine benefits and harm under physiological conditions and offers new prospects for rational exploitation of this system.

Delivery of epitopes by the Salmonella type III secretion system for vaccine development

Avirulent strains of Salmonella typhimurium are being considered as antigen delivery vectors. During its intracellular stage in the host, S. typhimurium resides within a membrane-bound compartment and is not an efficient inducer of class I-restricted immune responses. Viral epitopes were successfully delivered to the host-cell cytosol by using the type III protein secretion system of S. typhimurium. This resulted in class I-restricted immune responses that protected vaccinated animals against lethal infection. This approach may allow the efficient use of S. typhimurium as an antigen delivery system to control infections by pathogens that require this type of immune response for protection.

Poliovirus vaccine vectors elicit antigen-specific cytotoxic T cells and protect mice against lethal challenge with malignant melanoma cells expressing a model antigen

Recombinant polioviruses expressing foreign antigens may provide a convenient vaccine vector system to induce protective immunity against diverse pathogens. Replication-competent chimeric viruses can be constructed by inserting foreign antigenic sequences within the poliovirus polyprotein. When inserted sequences are flanked by poliovirus protease recognition sites the recombinant polyprotein is processed to mature and functional viral proteins plus the exogenous antigen. It previously has been shown that poliovirus recombinants can induce antibody responses against the inserted sequences but it is not known whether poliovirus or vaccine vectors derived from it can elicit effective cytotoxic T lymphocyte (CTL) responses. To examine the ability of the recombinant poliovirus to induce CTL responses, a segment of the chicken ovalbumin gene, which includes the H2-Kb-restricted CTL epitope SIINFEKL, was cloned at the junction of the P1 and P2 regions. This recombinant virus replicated with near wild-type efficiency in culture and stably expressed high levels of the ovalbumin antigen. Murine and primate cells infected with the recombinant virus appropriately processed the SIINFEKL epitope and presented it within major histocompatibility complex class I molecules. Inoculation of mice with recombinant poliovirus that expresses ovalbumin elicits an effective specific CTL response. Furthermore, vaccination with these recombinant poliovirus induced protective immunity against challenge with lethal doses of a malignant melanoma cell line expressing ovalbumin.

Induction of protective immunity against Japanese encephalitis in mice by immunization with a plasmid encoding Japanese encephalitis virus premembrane and envelope genes

A DNA vaccine plasmid containing the Japanese encephalitis (JE) virus premembrane (prM) and envelope (E) genes (designated pcDNA3JEME) was evaluated for immunogenicity and protective efficacy in mice. Two immunizations of 4-week-old female ICR mice with pcDNA3JEME by intramuscular or intradermal injections at a dose of 10 or 100 microg per mouse elicited neutralizing (NEUT) antibodies at titers of 1:10 to 1:20 (90% plaque reduction), and all immunized mice survived a challenge with 10,000 50% lethal doses of the P3 strain of JE virus. A single immunization with 100 microg of pcDNA3JEME did not elicit detectable NEUT antibodies but induced protective immunity. Spleen cells obtained from BALB/c mice immunized once with 10 or 100 microg of pcDNA3JEME contained JE virus-specific memory cytotoxic T lymphocytes (CTLs). BALB/c mice maintained detectable levels of memory B cells and CTLs for at least 6 months after one immunization with pcDNA3JEME at a dose of 100 microg. The CTLs induced in BALB/c mice immunized twice with 100 microg of pcDNA3JEME were CD8 positive and recognized mainly the envelope protein. These results indicate that pcDNA3JEME has the ability to induce a protective immune response which includes JE virus-specific antibodies and CTLs.