Variable effects of the co-administration of a GM-CSF-expressing plasmid on the immune response to flavivirus DNA vaccines in mice

Gaston Ramon's Big Four

When immunology was still in its infancy, Gaston Ramon made several major contributions to humoral immunology [...].

DNA Vaccines: History, Molecular Mechanisms and Future Perspectives

The history of DNA vaccine began as early as the 1960s with the discovery that naked DNA can transfect mammalian cells in vivo. In 1992, the evidence that such transfection could lead to the generation of antigen-specific antibody responses was obtained and supported the development of this technology as a novel vaccine platform. The technology then attracted immense interest and high hopes in vaccinology, as evidence of high immunogenicity and protection against virulent challenges accumulated from several animal models for several diseases. In particular, the capacity to induce T-cell responses was unprecedented in non-live vaccines. However, the technology suffered its major knock when the success in animals failed to translate to humans, where DNA vaccine candidates were shown to be safe but remained poorly immunogenic, or not associated with clinical benefit. Thanks to a thorough exploration of the molecular mechanisms of action of these vaccines, an impressive range of approaches have been and are currently being explored to overcome this major challenge. Despite limited success so far in humans as compared with later genetic vaccine technologies such as viral vectors and mRNA, DNA vaccines are not yet optimised for human use and may still realise their potential.

Hepatitis C virus DNA vaccines: a systematic review

BACKGROUND

Vaccination against HCV is an effective measure in reduction of virus-related public health burden and mortality. However, no prophylactic vaccine is available as of yet. DNA-based immunization is a promising modality to generate cellular and humoral immune responses. The objective of this study is to provide a systematic review of HCV DNA vaccines and investigate and discuss the strategies employed to optimize their efficacies.

METHODS

MEDLINE (PubMed), Web of Science, Scopus, ScienceDirect, and databases in persian language including the Regional Information Centre for Science & Technology (RICeST), the Scientific Information Database and the Iranian Research Institute for Information Science and Technology (IranDoc) were examined to identify studies pertaining to HCV nucleic acid vaccine development from 2000 to 2020.

RESULTS

Twenty-seven articles were included. Studies related to HCV RNA vaccines were yet to be published. A variety of strategies were identified with the potential to optimize HCV DNA vaccines such as incorporating multiple viral proteins and molecular tags such as HBsAg and Immunoglobulin Fc, multi-epitope expression, co-expression plasmid utilization, recombinant subunit immunogens, heterologous prime-boosting, incorporating NS3 mutants in DNA vaccines, utilization of adjuvants, employment of less explored methods such as Gene Electro Transfer, construction of multi- CTL epitopes, utilizing co/post translational modifications and polycistronic genes, among others. The effectiveness of the aforementioned strategies in boosting immune response and improving vaccine potency was assessed.

CONCLUSIONS

The recent progress on HCV vaccine development was examined in this systematic review to identify candidates with most promising prophylactic and therapeutic potential.

Dengue Virus and Vaccines: How Can DNA Immunization Contribute to This Challenge?

Dengue infections still have a tremendous impact on public health systems in most countries in tropical and subtropical regions. The disease is systemic and dynamic with broad range of manifestations, varying from mild symptoms to severe dengue (Dengue Hemorrhagic Fever and Dengue Shock Syndrome). The only licensed tetravalent dengue vaccine, Dengvaxia, is a chimeric yellow fever virus with prM and E genes from the different dengue serotypes. However, recent results indicated that seronegative individuals became more susceptible to develop severe dengue when infected after vaccination, and now WHO recommends vaccination only to dengue seropositive people. One possibility to explain these data is the lack of robust T-cell responses and antibody-dependent enhancement of virus replication in vaccinated people. On the other hand, DNA vaccines are excellent inducers of T-cell responses in experimental animals and it can also elicit antibody production. Clinical trials with DNA vaccines have improved and shown promising results regarding the use of this approach for human vaccination. Therefore, in this paper we review preclinical and clinical tests with DNA vaccines against the dengue virus. Most of the studies are based on the E protein since this antigen is the main target for neutralizing antibody production. Yet, there are other reports with DNA vaccines based on non-structural dengue proteins with protective results, as well. Combining structural and non-structural genes may be a solution for inducing immune responses aging in different infection moments. Furthermore, DNA immunizations are also a very good approach in combining strategies for vaccines against dengue, in heterologous prime/boost regimen or even administering different vaccines at the same time, in order to induce efficient humoral and cellular immune responses.

The immune enhancement effects of recombinant NDV expressing chicken granulocyte-macrophage colony-stimulating factor on the different avian influenza vaccine subtypes

Avian influenza is an acute and highly contagious infectious disease that is caused by the influenza virus. Avian influenza has been widely spread all over the world, has caused property loss and has threatened human life and security. In this study, the recombinant plasmid rClone30-chGM-CSF was constructed and rescued to the recombinant virus rClone30-chGM-CSF successfully. After 8 days of immunization with the recombinant virus, the titre of NDV HI (haemagglutination inhibition) antibodies in SPF chickens reached its peak. The average titre of the rClone30-chGM-CSF group reached 6 log2 and was significantly higher than the protection critical value of 4 log2 ; the titres of the rClone30 group and the blank group were 2.86 log2 and 1 log2 , respectively, indicating that the recombinant virus can effectively improve the NDV antibody titre. Then, SPF chickens were co-immunized with the recombinant virus and with three different vaccine subtypes of inactivated avian influenza. The results indicated that the SPF chickens that were immunized with the vaccine plus rClone30-chGM-CSF showed significantly higher avian influenza antibody levels than those in the single vaccine groups. Furthermore, the SPF chickens in the vaccine plus rClone30-chGM-CSF group elicited stronger CD4+ and CD8+ T-cell proliferative responses and also had upregulated transcriptional levels of interleukin-1β (IL-1β), IL-4, IL-6 and IL-17 compared with those in the single vaccine groups. This study has shown that the recombinant virus expressing chicken granulocyte-macrophage colony-stimulating factor (chGM-CSF) can be used not only as an NDV vaccine to effectively improve the titre of NDV antibodies but also as a biological adjuvant to enhance the immune effects of the avian influenza vaccine. Therefore, this recombinant virus can also be used as a biological adjuvant for other poultry vaccines.

The Genetic Adjuvants Interleukin-12 and Granulocyte-Macrophage Colony Stimulating Factor Enhance the Immunogenicity of an Ebola Virus Deoxyribonucleic Acid Vaccine in Mice

In previous studies, we showed that deoxyribonucleic acid (DNA) vaccines expressing codon-optimized filovirus envelope glycoprotein genes protect mice and nonhuman primates from viral challenge when delivered by intramuscular (IM) electroporation (EP). To determine whether we could achieve equivalent immunogenicity and protective efficacy by a simplified delivery method, we generated DNA vaccine plasmids expressing genetic adjuvants to potentiate immune responses. We tested the Th1-inducing cytokine interleukin-12 and the granulocyte growth factor granulocyte-macrophage colony stimulating factor, both of which have demonstrated significant adjuvant effect when included in clinical DNA vaccine formulations. In addition, because interferon (IFN)-αβ is required for DNA vaccine-induced immunity, we tested inclusion of a potent stimulator of the IFN-αβ pathway. Our data suggest that IM vaccination of mice with plasmid DNA encoding genetic adjuvants enhances vaccine immunogenicity, resulting in increased anti-Ebola virus (EBOV) immunoglobulin G and T-cell responses. Codelivery of genetic adjuvants also improved EBOV neutralizing capability compared with vaccine alone. Finally, IM vaccination with plasmid EBOV and genetic adjuvants provided complete protection against EBOV challenge. Overall, our data suggest that codelivery of genetic adjuvants with filovirus DNA vaccines using IM delivery can provide comparable efficacy to the same DNA vaccines when delivered using IM-EP devices.

The genetic adjuvant IL-12 enhances the protective efficacy of a DNA vaccine for Venezuelan equine encephalitis virus delivered by intramuscular injection in mice

We have previously shown that DNA vaccines expressing codon-optimized alphavirus envelope glycoprotein genes protect both mice and non-human primates from viral challenge when delivered by intramuscular electroporation (IM-EP). To determine if we could achieve equivalent immunogenicity and protective efficacy in the absence of electroporation, we co-delivered our Venezuelan equine encephalitis virus (VEEV) DNA vaccine with DNA plasmids expressing genetic adjuvants designed to augment immune responses. We tested the T_h1-inducing cytokine IL-12 as well as the granulocyte growth factor GM-CSF, both of which have demonstrated significant adjuvant effect when included in clinical DNA vaccine formulations. Additionally, as multiple reports have described the necessity of IFN-αβ in DNA vaccine immunogenicity, we tested vaccine plasmids encoding a potent stimulator of the IFN-αβ pathway. Our data suggest that IM vaccination of mice with plasmid DNA encoding genetic adjuvants enhances VEEV vaccine immunogenicity, resulting in improved T cell responses, as well as skewing of the anti-VEEV IgG antibody isotype. Additionally, IM vaccination of VEEV DNA vaccine and IL-12 provided complete protection against aerosol VEEV challenge. Overall, our data suggest that co-delivery of genetic adjuvants with alphavirus DNA vaccines using IM delivery can influence the type of immune response obtained and provide comparable protective immunity to that achieved by IM-EP delivery of the vaccine without adjuvants.

Stable incorporation of GM-CSF into dissolvable microneedle patch improves skin vaccination against influenza

The widely used influenza subunit vaccine would benefit from increased protection rates in vulnerable populations. Skin immunization by microneedle (MN) patch can increase vaccine immunogenicity, as well as increase vaccination coverage due to simplified administration. To further increase immunogenicity, we used granulocyte-macrophage colony stimulating factor (GM-CSF), an immunomodulatory cytokine already approved for skin cancer therapy and cancer support treatment. GM-CSF has been shown to be upregulated in skin following MN insertion. The GM-CSF-adjuvanted vaccine induced robust and long-lived antibody responses cross-reactive to homosubtypic and heterosubtypic influenza viruses. Addition of GM-CSF resulted in increased memory B cell persistence relative to groups given influenza vaccine alone and led to rapid lung viral clearance following lethal infection with homologous virus in the mouse model. Here we demonstrate that successful incorporation of the thermolabile cytokine GM-CSF into MN resulted in improved vaccine-induced protective immunity holding promise as a novel approach to improved influenza vaccination. To our knowledge, this is the first successful incorporation of a cytokine adjuvant into dissolvable MNs, thus advancing and diversifying the rapidly developing field of MN vaccination technology.

Advancements in DNA vaccine vectors, non-mechanical delivery methods, and molecular adjuvants to increase immunogenicity

A major advantage of DNA vaccination is the ability to induce both humoral and cellular immune responses. DNA vaccines are currently used in veterinary medicine, but have not achieved widespread acceptance for use in humans due to their low immunogenicity in early clinical studies. However, recent clinical data have re-established the value of DNA vaccines, particularly in priming high-level antigen-specific antibody responses. Several approaches have been investigated for improving DNA vaccine efficacy, including advancements in DNA vaccine vector design, the inclusion of genetically engineered cytokine adjuvants, and novel non-mechanical delivery methods. These strategies have shown promise, resulting in augmented adaptive immune responses in not only mice, but also in large animal models. Here, we review advancements in each of these areas that show promise for increasing the immunogenicity of DNA vaccines.

Molecular mechanisms for enhanced DNA vaccine immunogenicity

In the two decades since their initial discovery, DNA vaccines technologies have come a long way. Unfortunately, when applied to human subjects inadequate immunogenicity is still the biggest challenge for practical DNA vaccine use. Many different strategies have been tested in preclinical models to address this problem, including novel plasmid vectors and codon optimization to enhance antigen expression, new gene transfection systems or electroporation to increase delivery efficiency, protein or live virus vector boosting regimens to maximise immune stimulation, and formulation of DNA vaccines with traditional or molecular adjuvants. Better understanding of the mechanisms of action of DNA vaccines has also enabled better use of the intrinsic host response to DNA to improve vaccine immunogenicity. This review summarizes recent advances in DNA vaccine technologies and related intracellular events and how these might impact on future directions of DNA vaccine development.