Preclinical study of a DNA vaccine targeting SARS-CoV-2

DNA vaccine prime and replicating vaccinia vaccine boost induce robust humoral and cellular immune responses against MERS-CoV in mice

As of December 2022, 2,603 cases laboratory-identified Middle East respiratory syndrome coronavirus (MERS-CoV) infections and 935 associated deaths, with a mortality rate of 36%, had been reported to the World Health Organization (WHO). However, there are still no vaccines for MERS-CoV, which makes the prevention and control of MERS-CoV difficult. In this study, we constructed two vaccine candidates of DNA and replicating Vaccinia Tian Tan (VTT) vector that carried the MERS-CoV Spike (S) protein. Compared with homologous immunization with either vaccine, mice immunized with DNA vaccine prime and VTT vaccine boost exhibited much stronger and durable humoral and cellular immune responses. The mice immunized generated robust binding antibodies and broader neutralizing antibodies against the EMC2012, England1 and KNIH strains of MERS-CoV. Prime-Boost immunization also induced strong MERS-S specific T cells responses, with high memory and poly-functional (CD107a-IFN-γ-TNF-α) effector CD8+ T cells. In conclusion, the research demonstrated that DNA-Prime/VTT-Boost strategy could elicit robust and balanced humoral and cellular immune responses against MERS-CoV-S. This study not only provides a promising set of MERS-CoV vaccine candidates but also proposes a heterologous sequential immunization strategy worthy of further development.

Nanoparticle-based DNA vaccine protects against SARS-CoV-2 variants in female preclinical models

A safe and effective vaccine with long-term protection against SARS-CoV-2 variants of concern (VOCs) is a global health priority. Here, we develop lipid nanoparticles (LNPs) to provide safe and effective delivery of plasmid DNA (pDNA) and show protection against VOCs in female small animal models. Using a library of LNPs encapsulating unique barcoded DNA (b-DNA), we screen for b-DNA delivery after intramuscular administration. The top-performing LNPs are further tested for their capacity of pDNA uptake in antigen-presenting cells in vitro. The lead LNP is used to encapsulate pDNA encoding the HexaPro version of SARS-CoV-2 spike (LNP-HPS) and immunogenicity and protection is tested in vivo. LNP-HPS elicit a robust protective effect against SARS-CoV-2 Gamma (P.1), correlating with reduced lethality, decreased viral load in the lungs and reduced lung damage. LNP-HPS induce potent humoral and T cell responses against P.1, and generate high levels of neutralizing antibodies against P.1 and Omicron (B.1.1.529). Our findings indicate that the protective efficacy and immunogenicity elicited by LNP-HPS are comparable to those achieved by the approved COVID-19 vaccine from Biontech/Pfizer in animal models. Together, these findings suggest that LNP-HPS hold great promise as a vaccine candidate against VOCs.

The development of DNA vaccines against SARS-CoV-2

BACKGROUND

The COVID-19 pandemic exerted significant impacts on public health and global economy. Research efforts to develop vaccines at warp speed against SARS-CoV-2 led to novel mRNA, viral vectored, and inactivated vaccines being administered. The current COVID-19 vaccines incorporate the full S protein of the SARS-CoV-2 Wuhan strain but rapidly emerging variants of concern (VOCs) have led to significant reductions in protective efficacies. There is an urgent need to develop next-generation vaccines which could effectively prevent COVID-19.

METHODS

PubMed and Google Scholar were systematically reviewed for peer-reviewed papers up to January 2023.

RESULTS

A promising solution to the problem of emerging variants is a DNA vaccine platform since it can be easily modified. Besides expressing whole protein antigens, DNA vaccines can also be constructed to include specific nucleotide genes encoding highly conserved and immunogenic epitopes from the S protein as well as from other structural/non-structural proteins to develop effective vaccines against VOCs. DNA vaccines are associated with low transfection efficiencies which could be enhanced by chemical, genetic, and molecular adjuvants as well as delivery systems.

CONCLUSIONS

The DNA vaccine platform offers a promising solution to the design of effective vaccines. The challenge of limited immunogenicity in humans might be solved through the use of genetic modifications such as the addition of nuclear localization signal (NLS) peptide gene, strong promoters, MARs, introns, TLR agonists, CD40L, and the development of appropriate delivery systems utilizing nanoparticles to increase uptake by APCs in enhancing the induction of potent immune responses.

Intradermal administration of DNA vaccine targeting Omicron SARS-CoV-2 via pyro-drive jet injector provides the prolonged neutralizing antibody production via germinal center reaction

Emerging SARS-CoV-2 Omicron variants are highly contagious with enhanced immune escape mechanisms against the initially approved COVID-19 vaccines. Therefore, we require stable alternative-platform vaccines that confer protection against newer variants of SARS-CoV-2. We designed an Omicron B.1.1.529 specific DNA vaccine using our DNA vaccine platform and evaluated the humoral and cellular immune responses. SD rats intradermally administered with Omicron-specific DNA vaccine via pyro-drive jet injector (PJI) thrice at 2-week intervals elicited high antibody titers against the Omicron subvariants as well as the ancestral strain. Indeed, the Omicron B.1.1.529-specific antibody titer and neutralizing antibody were higher than that of other strains. Longitudinal monitoring indicated that anti-spike (ancestral and Omicron) antibody titers decreased toward 30 weeks after the first vaccination dose. However, neutralization activity remained unaltered. Germinal center formation was histologically detected in lymph nodes in rats immunized with Omicron DNA vaccine. Ancestral spike-specific immune cell response was slightly weaker than Omicron spike-specific response in splenocytes with Omicron-adapted DNA vaccine, evaluated by ELISpot assay. Collectively, our findings suggest that Omicron targeting DNA vaccines via PJI can elicit robust durable antibody production mediated by germinal center reaction against this new variant as well as partially against the spike protein of other SARS-CoV-2 variants.

Co-delivery of a trimeric spike DNA and protein vaccine with aluminum hydroxide enhanced Th1-dominant humoral and cellular immunity against SARS-CoV-2

Protein subunit vaccines have been used as prophylactic vaccines for a long time. The well-established properties of these vaccines make them the first choice for the coronavirus disease 2019 (COVID-19) outbreak. However, it is not easy to develop a protein vaccine that induces cytotoxic T lymphocyte responses and requires a longer time for manufacturing, which limits the usage of this vaccine type. Here, we report the combination of a recombinant spike (S)-trimer protein with a DNA vaccine-encoded S protein as a novel COVID-19 vaccine. The recombinant S protein was formulated with different adjuvants and mixed with the DNA plasmid before injection. We found that the recombinant S protein formulated with the adjuvant aluminum hydroxide and mixed with the DNA plasmid could enhance antigen-specific antibody titers, neutralizing antibody titers. We further evaluated the IgG2a/IgG1 isotype and cytokine profiles of the specific boosted T-cell response, which indicated that the combined vaccine induced a T-helper 1 cell-biased immune response. Immunized hamsters were challenged with severe acute respiratory syndrome coronavirus 2, and the body weight of the hamsters that received the recombinant S protein with aluminum hydroxide and/or the DNA plasmid was not reduced. Alternatively, those that received control or only the DNA plasmid immunization were reduced. Interestingly, after the third day of the viral load in the lungs, the viral challenge could not be detected in hamsters immunized with the recombinant S protein in aluminum hydroxide mixed with DNA (tissue culture infectious dose < 10). The viral load in the lungs was 109 , 106 , and 107 for the phosphate-buffered saline, protein in aluminum hydroxide, and DNA-only immunizations, respectively. These results indicated that antiviral mechanisms neutralizing antibodies play important roles. Furthermore, we found that the combination of protein and DNA vaccination could induce relatively strong CD8+ T-cell responses. In summary, the protein subunit vaccine combined with a DNA vaccine could induce strong CD8+ T-cell responses to increase antiviral immunity for disease control.

A Promising Needle-Free Pyro-Drive Jet Injector for Augmentation of Immunity by Intradermal Injection as a Physical Adjuvant

Current worldwide mRNA vaccination against SARS-CoV-2 by intramuscular injection using a needled syringe has greatly protected numerous people from COVID-19. An intramuscular injection is generally well tolerated, safer and easier to perform on a large scale, whereas the skin has the benefit of the presence of numerous immune cells, such as professional antigen-presenting dendritic cells. Therefore, intradermal injection is considered superior to intramuscular injection for the induction of protective immunity, but more proficiency is required for the injection. To improve these issues, several different types of more versatile jet injectors have been developed to deliver DNAs, proteins or drugs by high jet velocity through the skin without a needle. Among them, a new needle-free pyro-drive jet injector has a unique characteristic that utilizes gunpower as a mechanical driving force, in particular, bi-phasic pyrotechnics to provoke high jet velocity and consequently the wide dispersion of the injected DNA solution in the skin. A significant amount of evidence has revealed that it is highly effective as a vaccinating tool to induce potent protective cellular and humoral immunity against cancers and infectious diseases. This is presumably explained by the fact that shear stress generated by the high jet velocity facilitates the uptake of DNA in the cells and, consequently, its protein expression. The shear stress also possibly elicits danger signals which, together with the plasmid DNA, subsequently induces the activation of innate immunity including dendritic cell maturation, leading to the establishment of adaptive immunity. This review summarizes the recent advances in needle-free jet injectors to augment the cellular and humoral immunity by intradermal injection and the possible mechanism of action.

Progress and prospects on vaccine development against Monkeypox Infection

The monkeypox virus (MPOX) is an uncommon zoonotic illness brought on by an orthopoxvirus (OPXV). MPOX can occur with symptoms similar to smallpox. Since April 25, 2023, 110 nations have reported 87,113 confirmed cases and 111 fatalities. Moreover, the outspread prevalence of MPOX in Africa and a current outbreak of MPOX in the U.S. have made it clear that naturally occurring zoonotic OPXV infections remain a public health concern. Existing vaccines, though they provide cross-protection to MPOX, are not specific for the causative virus, and their effectiveness in the light of the current multi-country outbreak is still to be verified. Furthermore, as a sequel of the eradication and cessation of smallpox vaccination for four decades, MPOX found a possibility to re-emerge, but with distinct characteristics. The World Health Organization (WHO) suggested that nations use affordable MPOX vaccines within a framework of coordinated clinical effectiveness and safety evaluations. Vaccines administered in the smallpox control program and conferred immunity against MPOX. Currently, vaccines approved by WHO for use against MPOX are replicating (ACAM2000), low replicating (LC16m8), and non-replicating (MVA-BN). Although vaccines are accessible, investigations have demonstrated that smallpox vaccination is approximately 85% efficient in inhibiting MPOX. In addition, developing new vaccine methods against MPOX can help prevent this infection. To recognize the most efficient vaccine, it is essential to assess effects, including reactogenicity, safety, cytotoxicity effect, and vaccine-associated side effects, especially for high-risk and vulnerable people. Recently, several orthopoxvirus vaccines have been produced and are being evaluated. Hence, this review aims to provide an overview of the efforts dedicated to several types of vaccine candidates with different strategies for MPOX, including inactivated, live-attenuated, virus-like particles (VLPs), recombinant protein, nucleic acid, and nanoparticle-based vaccines, which are being developed and launched.

Next-Generation Vaccines: Nanovaccines in the Fight against SARS-CoV-2 Virus and beyond SARS-CoV-2

The virus responsible for the coronavirus viral pandemic is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Emerging SARS-CoV-2 variants caused by distinctive mutations within the viral spike glycoprotein of SARS-CoV-2 are considered the cause for the rapid spread of the disease and make it challenging to treat SARS-CoV-2. The manufacturing of appropriate efficient vaccines and therapeutics is the only option to combat this pandemic. Nanomedicine has enabled the delivery of nucleic acids and protein-based vaccines to antigen-presenting cells to produce protective immunity against the coronavirus. Nucleic acid-based vaccines, particularly mRNA nanotechnology vaccines, are the best prevention option against the SARS-CoV-2 pandemic worldwide, and they are effective against the novel coronavirus and its multiple variants. This review will report on progress made thus far with SARS-CoV-2 vaccines and beyond employing nanotechnology-based nucleic acid vaccine approaches.

Modified DNA vaccine confers improved humoral immune response and effective virus protection against SARS-CoV-2 delta variant

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to a global pandemic. New technologies have been utilized to develop several types of vaccines to prevent the spread of SARS-CoV-2 infection, including mRNA vaccines. Our group previously developed an effective DNA-based vaccine. However, emerging SARS-CoV-2 variants of concern (VOCs), such as the delta variant, have escaped mutations against vaccine-induced neutralizing antibodies. This suggests that modified vaccines accommodating VOCs need to be developed promptly. Here, we first modified the current DNA vaccine to enhance antigenicity. Compared with the parental DNA vaccine, the modified version (GP∆-DNA vaccine) induced rapid antibody production. Next, we updated the GP∆-DNA vaccine to spike glycoprotein of the delta variant (GP∆-delta DNA vaccine) and compared the efficacy of different injection routes, namely intramuscular injection using a needle and syringe and intradermal injection using a pyro-drive jet injector (PJI). We found that the levels of neutralizing antibodies induced by the intradermal PJI injection were higher than intramuscular injection. Furthermore, the PJI-injected GP∆-delta DNA vaccine effectively protected human angiotensin-converting enzyme 2 (hACE2) knock-in mice from delta-variant infection. These results indicate that the improved DNA vaccine was effective against emerging VOCs and was a potential DNA vaccine platform for future VOCs or global pandemics.

Phase I Study to Assess the Safety and Immunogenicity of an Intradermal COVID-19 DNA Vaccine Administered Using a Pyro-Drive Jet Injector in Healthy Adults

We conducted a nonrandomized, open-label phase I study to assess the safety and immunogenicity of an intradermal coronavirus disease 2019 (COVID-19) DNA vaccine (AG0302-COVID-19) administered using a pyro-drive jet injector at Osaka University Hospital between Yanagida November 2020 and December 2021. Twenty healthy volunteers, male or female, were enrolled in the low-dose (0.2 mg) or high-dose (0.4 mg) groups and administered AG0302-COVID19 twice at a 2-week interval. There were no adverse events that led to discontinuation of the study drug vaccination schedule. A serious adverse event (disc protrusion) was reported in one patient in the high-dose group, but the individual recovered, and the adverse event was not causally related to the study drug. In the analysis of the humoral immune response, the geometric mean titer (GMT) of serum anti-SARS-CoV-2 spike glycoprotein-specific antibody was low in both the low-dose and high-dose groups (246.2 (95% CI 176.2 to 344.1, 348.2 (95% CI 181.3 to 668.9)) at the 8 weeks after first vaccination. Regarding the analysis of the cellular immune, the number of IFN-γ-producing cells responsive to the SARS-CoV-2 spike glycoprotein increased with individual differences after the first dose and was sustained for several months. Overall, no notable safety issues were observed with the intradermal inoculations of AG0302-COVID19. Regarding immunogenicity, a cellular immune response was observed in some subjects after AG0302-COVID19 intradermal inoculation, but no significant antibody production was observed.

Immune response induced in rodents by anti-CoVid19 plasmid DNA vaccine via pyro-drive jet injector inoculation

There is an urgent need to stop the coronavirus disease 2019 (COVID-19) pandemic through the development of efficient and safe vaccination methods. Over the short term, plasmid DNA vaccines can be developed as they are molecularly stable, thus facilitating easy transport and storage. pVAX1-SARS-CoV2-co was designed for the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) S protein. The antibodies produced led to immunoreactions against the S protein, an anti-receptor-binding-domain, and a neutralizing action of the pVAX1-SARS-CoV2-co, as previously confirmed. To promote the efficacy of the pVAX1-SARS-CoV2-co vaccine a pyro-drive jet injector (PJI) was used. An intradermally adjusted PJI demonstrated that the pVAX1-SARS-CoV2-co vaccine injection caused a high production of anti-S protein antibodies, triggered immunoreactions, and neutralized the actions against SARS-CoV-2. A high-dose pVAX1-SARS-CoV2-co intradermal injection using PJI did not cause any serious disorders in the rat model. A viral challenge confirmed that intradermally immunized mice were potently protected from COVID-19. A pVAX1-SARS-CoV2-co intradermal injection using PJI is a safe and promising vaccination method for overcoming the COVID-19 pandemic.