Recombinant protein subunit SARS-CoV-2 vaccines formulated with CoVaccine HT adjuvant induce broad, Th1 biased, humoral and cellular immune responses in mice

Current Progress, Challenges and Prospects in the Development of COVID-19 Vaccines

The COVID-19 pandemic has resulted in over 772 million confirmed cases, including nearly 7 million deaths, according to the World Health Organization (WHO). Leveraging rapid development, accelerated vaccine approval processes, and large-scale production of various COVID-19 vaccines using different technical platforms, the WHO declared an end to the global health emergency of COVID-19 on May 5, 2023. Current COVID-19 vaccines encompass inactivated, live attenuated, viral vector, protein subunit, nucleic acid (DNA and RNA), and virus-like particle (VLP) vaccines. However, the efficacy of these vaccines is diminishing due to the constant mutation of SARS-CoV-2 and the heightened immune evasion abilities of emerging variants. This review examines the impact of the COVID-19 pandemic, the biological characteristics of the virus, and its diverse variants. Moreover, the review underscores the effectiveness, advantages, and disadvantages of authorized COVID-19 vaccines. Additionally, it analyzes the challenges, strategies, and future prospects of developing a safe, broad-spectrum vaccine that confers sufficient and sustainable immune protection against new variants of SARS-CoV-2. These discussions not only offer insight for the development of next-generation COVID-19 vaccines but also summarize experiences for combating future emerging viruses.

Research progress on emulsion vaccine adjuvants

Vaccination is the most cost-effective method for preventing various infectious diseases. Compared with conventional vaccines, new-generation vaccines, especially recombinant protein or synthetic peptide vaccines, are safer but less immunogenic than crude inactivated microbial vaccines. The immunogenicity of these vaccines can be enhanced using suitable adjuvants. This is the main reason why adjuvants are of great importance in vaccine development. Several novel human emulsion-based vaccine adjuvants (MF59, AS03) have been approved for clinical use. This paper reviews the research progress on emulsion-based adjuvants and focuses on their mechanism of action. An outlook can be provided for the development of emulsion-based vaccine adjuvants.

Thermostable bivalent filovirus vaccine protects against severe and lethal Sudan ebolavirus and marburgvirus infection

Although two vaccines for Zaire ebolavirus (EBOV) have been licensed and deployed successfully to combat recurring outbreaks of Ebolavirus Disease in West Africa, there are no vaccines for two other highly pathogenic members of the Filoviridae, Sudan ebolavirus (SUDV) and Marburg marburgvirus (MARV). The results described herein document the immunogenicity and protective efficacy in cynomolgus macaques of a single-vial, thermostabilized (lyophilized) monovalent (SUDV) and bivalent (SUDV & MARV) protein vaccines consisting of recombinant glycoproteins (GP) formulated with a clinical-grade oil-in-water nanoemulsion adjuvant (CoVaccine HT™). Lyophilized formulations of the vaccines were reconstituted with Water for Injection and used to immunize groups of cynomolgus macaques before challenge with a lethal dose of a human SUDV or MARV isolate. Sera collected after each of the three immunizations showed near maximal GP-binding IgG concentrations starting as early as the second dose. Most importantly, the vaccine candidates (monovalent or bivalent) provided 100% protection against severe and lethal filovirus disease after either SUDV or MARV infection. Although mild, subclinical infection was observed in a few macaques, all vaccinated animals remained healthy and survived the filovirus challenge. These results demonstrate the value that thermostabilized protein vaccines could provide for addressing an important gap in preparedness for future filovirus outbreaks.

The Promising Potential of Reverse Vaccinology-Based Next-Generation Vaccine Development over Conventional Vaccines against Antibiotic-Resistant Bacteria

The clinical use of antibiotics has led to the emergence of multidrug-resistant (MDR) bacteria, leading to the current antibiotic resistance crisis. To address this issue, next-generation vaccines are being developed to prevent antimicrobial resistance caused by MDR bacteria. Traditional vaccine platforms, such as inactivated vaccines (IVs) and live attenuated vaccines (LAVs), were effective in preventing bacterial infections. However, they have shown reduced efficacy against emerging antibiotic-resistant bacteria, including MDR M. tuberculosis. Additionally, the large-scale production of LAVs and IVs requires the growth of live pathogenic microorganisms. A more promising approach for the accelerated development of vaccines against antibiotic-resistant bacteria involves the use of in silico immunoinformatics techniques and reverse vaccinology. The bioinformatics approach can identify highly conserved antigenic targets capable of providing broader protection against emerging drug-resistant bacteria. Multi-epitope vaccines, such as recombinant protein-, DNA-, or mRNA-based vaccines, which incorporate several antigenic targets, offer the potential for accelerated development timelines. This review evaluates the potential of next-generation vaccine development based on the reverse vaccinology approach and highlights the development of safe and immunogenic vaccines through relevant examples from successful preclinical and clinical studies.

Nanoparticle-Based Adjuvants and Delivery Systems for Modern Vaccines

Ever since the development of the first vaccine, vaccination has had the great impact on global health, leading to the decrease in the burden of numerous infectious diseases. However, there is a constant need to improve existing vaccines and develop new vaccination strategies and vaccine platforms that induce a broader immune response compared to traditional vaccines. Modern vaccines tend to rely on certain nanotechnology platforms but are still expected to be readily available and easy for large-scale manufacturing and to induce a durable immune response. In this review, we present an overview of the most promising nanoadjuvants and nanoparticulate delivery systems and discuss their benefits from tehchnological and immunological standpoints as well as their objective drawbacks and possible side effects. The presented nano alums, silica and clay nanoparticles, nanoemulsions, adenoviral-vectored systems, adeno-associated viral vectors, vesicular stomatitis viral vectors, lentiviral vectors, virus-like particles (including bacteriophage-based ones) and virosomes indicate that vaccine developers can now choose different adjuvants and/or delivery systems as per the requirement, specific to combatting different infectious diseases.

SARS-CoV-2 S1 Subunit Booster Vaccination Elicits Robust Humoral Immune Responses in Aged Mice

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants has raised concerns about reduced vaccine effectiveness and the increased risk of infection, and while repeated homologous booster shots are recommended for elderly and immunocompromised individuals, they cannot completely protect against breakthrough infections. In our previous study, we assessed the immunogenicity of an adenovirus-based vaccine expressing SARS-CoV-2 S1 (Ad5.S1) in mice, which induced robust humoral and cellular immune responses (E. Kim, F. J. Weisel, S. C. Balmert, M. S. Khan, et al., Eur J Immunol 51:1774-1784, 2021, https://doi.org/10.1002/eji.202149167). In this follow-up study, we found that the mice had high titers of anti-S1 antibodies 1 year after vaccination, and one booster dose of the nonadjuvanted rS1Beta (recombinant S1 protein of SARS-CoV-2 Beta [B.1.351]) subunit vaccine was effective at stimulating strong long-lived S1-specific immune responses and inducing significantly high neutralizing antibodies against Wuhan, Beta, and Delta strains, with 3.6- to 19.5-fold increases. Importantly, the booster dose also elicited cross-reactive antibodies, resulting in angiotensin-converting enzyme 2 (ACE2) binding inhibition against spikes of SARS-CoV-2, including Omicron variants, persisting for >28 weeks after booster vaccination. Interestingly, the levels of neutralizing antibodies were correlated not only with the level of S1 binding IgG but also with ACE2 inhibition. Our findings suggest that the rS1Beta subunit vaccine candidate as a booster has the potential to offer cross-neutralization against broad variants and has important implications for the vaccine control of newly emerging breakthrough SARS-CoV-2 variants in elderly individuals primed with adenovirus-based vaccines like AZD1222 and Ad26.COV2.S. IMPORTANCE Vaccines have significantly reduced the incidences of severe coronavirus disease 2019 (COVID-19) cases and deaths. However, the emergence of SARS-CoV-2 variants has raised concerns about their increased transmissibility and ability to evade neutralizing antibodies, especially among elderly individuals who are at higher risks of mortality and reductions of vaccine effectiveness. To address this, a heterologous booster vaccination strategy has been considered as a solution to protect the elderly population against breakthrough infections caused by emerging variants. This study evaluated the booster effect of an S1 subunit vaccine in aged mice that had been previously primed with adenoviral vaccines, providing valuable preclinical evidence for elderly people vaccinated with the currently approved COVID-19 vaccines. This study confirms the potential for using the S1 subunit vaccine as a booster to enhance cross-neutralizing antibodies against emerging variants of concern.

The Vaccine World of COVID-19: India’s Contribution

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) eruption has left not only illness and mortality in its wake, but also an overwhelming threat to health policy, human regality, food security, and struggle worldwide. The accessibility and potential distribution of a protective and successful vaccination to communities throughout the world are being considered now not just, as a potential of overcoming these hurdles, but also as an example of human perseverance in the face of catastrophe. A vaccine is the only tool that can efficaciously deal with the COVID-19 catastrophe. Currently, more than 47 vaccines are permitted for emergency use in distinct parts of the world. India will play a significant role in the development of the high-priced Moderna shots and Pfizer Inc, therefore assisting in the immunization of a large portion of the world. Moreover, many of the internationally researched and developed vaccine laboratories seek manufacturing in Indian firms and companies for efficient and low-cost production of vaccines intending to provide to the world, hence, making India, a major role player during these pandemic times. This review highlights the Indian contribution to the globe for COVID-19 management.

COVID-19: vaccines, efficacy and effects on variants

PURPOSE OF REVIEW

We reviewed three leading strategies of vaccine development against coronavirus disease 2019 (COVID- 19): mRNA vaccines, adenoviral vector vaccines and recombinant nanoparticles. We also considered the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and their impact on the effectiveness of the most widely implemented vaccines.

RECENT FINDINGS

General properties, efficacy, safety and global uptake of Pfizer/BioNTech's Comirnaty (BNT162b2), Moderna's Spikevax (mRNA-1273), Oxford/AstraZeneca's ChAdOx1 nCoV-19, J&J/Janssen's Ad26.COV2.S and Novavax's NVX-CoV2373 vaccines at the end of the year 2021 were presented. We summarized the information on the effectiveness against COVID-19 infection, severe disease and death. We then focused on important missense mutations in the five variants of concern (VoC): Alpha, Beta, Gamma, Delta and Omicron. We explored the evidence for the effectiveness of the vaccines against those five VoC.

SUMMARY

It is difficult to predict the further development of the COVID-19 pandemic. The development of vaccines of an increasingly broad spectrum against coronaviruses, more easily deliverable and conferring more durable immune protection is likely. However, the very large number of infections may lead to new mutations with unpredictable impacts. Interventions that would control COVID-19 more effectively and enable a safer coexistence with the SARS-CoV-2 virus and its emerging variants are still needed in early 2022.

A Recombinant Subunit Vaccine Induces a Potent, Broadly Neutralizing, and Durable Antibody Response in Macaques against the SARS-CoV-2 P.1 (Gamma) Variant

FDA-approved and emergency use-authorized vaccines using new mRNA and viral-vector technology are highly effective in preventing moderate to severe disease; however, information on their long-term efficacy and protective breadth against severe acute respiratory syndrome coronavirus 2 variants of concern (VOCs) is currently scarce. Here, we describe the durability and broad-spectrum VOC immunity of a prefusion-stabilized spike (S) protein adjuvanted with liquid or lyophilized CoVaccine HT in cynomolgus macaques. This recombinant subunit vaccine is highly immunogenic and induces robust spike-specific and broadly neutralizing antibody responses effective against circulating VOCs (B.1.351 [Beta], P.1 [Gamma], and B.1.617 [Delta]) for at least three months after the final boost. Protective efficacy and postexposure immunity were evaluated using a heterologous P.1 challenge nearly three months after the last immunization. Our results indicate that while immunization with both high and low S doses shorten and reduce viral loads in the upper and lower respiratory tract, a higher antigen dose is required to provide durable protection against disease as vaccine immunity wanes. Histologically, P.1 infection causes similar COVID-19-like lung pathology as seen with early pandemic isolates. Postchallenge IgG concentrations were restored to peak immunity levels, and vaccine-matched and cross-variant neutralizing antibodies were significantly elevated in immunized macaques indicating an efficient anamnestic response. Only low levels of P.1-specific neutralizing antibodies with limited breadth were observed in control (nonvaccinated but challenged) macaques, suggesting that natural infection may not prevent reinfection by other VOCs. Overall, these results demonstrate that a properly dosed and adjuvanted recombinant subunit vaccine can provide protective immunity against circulating VOCs for at least three months.

Adjuvants Differentially Modulate the Immunogenicity of Lassa Virus Glycoprotein Subunits in Mice

Lassa Fever (LF) is an acute viral hemorrhagic fever caused by Lassa virus (LASV) that is primarily transmitted through contact with wild rodents in West Africa. Although several advanced vaccine candidates are progressing through clinical trials, some effective vaccines are virally vectored and thus require a stringent cold-chain, making distribution to rural and resource-poor areas difficult. Recombinant subunit vaccines are advantageous in this aspect as they can be thermostabilized and deployed with minimal storage and transportation requirements. However, antigen dose and adjuvant formulation must be carefully selected to ensure both the appropriate humoral and cell-mediated immune responses are elicited. In this study, we examine the immunogenicity of a two-step immunoaffinity-purified recombinant LASV glycoprotein (GP) with five clinical- and preclinical-grade adjuvants. Swiss Webster mice immunized intramuscularly with 2 or 3 doses of each vaccine formulation showed complete seroconversion and maximal GP-specific antibody response after two immunizations. Formulations with GPI-0100, LiteVax, Montanide™ ISA 51, and Montanide™ ISA 720 induced both IgG1 and IgG2 antibodies suggesting a balanced Th1/Th2 response, whereas formulation of LASV GP with Alhydrogel elicited a IgG1-dominant response. Splenocytes secreting both Th1 and Th2 cytokines i.e., IFN-γ, TNF-α, IL-2, IL-4 and IL-5, were observed from mice receiving both antigen doses formulated with ISA 720, LiteVax and GPI-0100. However, robust, multifunctional T-cells were only detected in mice receiving a higher dose of LASV GP formulated with GPI-0100. Our results emphasize the importance of careful adjuvant selection and lay the immunological basis for a recombinant subunit protein LF vaccine formulation.