Protection from COVID-19 with a VSV-based vaccine expressing the spike and nucleocapsid proteins

The Key to Increase Immunogenicity of Next-Generation COVID-19 Vaccines Lies in the Inclusion of the SARS-CoV-2 Nucleocapsid Protein

Vaccination is one of the most effective prophylactic public health interventions for the prevention of infectious diseases such as coronavirus disease (COVID-19). Considering the ongoing need for new COVID-19 vaccines, it is crucial to modify our approach and incorporate more conserved regions of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to effectively address emerging viral variants. The nucleocapsid protein is a structural protein of SARS-CoV-2 that is involved in replication and immune responses. Furthermore, this protein offers significant advantages owing to the minimal accumulation of mutations over time and the inclusion of key T-cell epitopes critical for SARS-CoV-2 immunity. A novel strategy that may be suitable for the new generation of vaccines against COVID-19 is to use a combination of antigens, including the spike and nucleocapsid proteins, to elicit robust humoral and potent cellular immune responses, along with long-lasting immunity. The strategic use of multiple antigens aims to enhance vaccine efficacy and broaden protection against viruses, including their variants. The immune response against the nucleocapsid protein from other coronavirus is long-lasting, and it can persist up to 11 years post-infection. Thus, the incorporation of nucleocapsids (N) into vaccine design adds an important dimension to vaccination efforts and holds promise for bolstering the ability to combat COVID-19 effectively. In this review, we summarize the preclinical studies that evaluated the use of the nucleocapsid protein as antigen. This study discusses the use of nucleocapsid alone and its combination with spike protein or other proteins of SARS-CoV-2.

Single dose recombinant VSV based vaccine elicits robust and durable neutralizing antibody against Hantaan virus

Hantaan virus (HTNV) is a pathogenic orthohantavirus prevalent in East Asia that is known to cause hemorrhagic fever with severe renal syndrome (HFRS), which has a high fatality rate. However, a Food and Drug Administration (FDA)-approved vaccine is not currently available against this virus. Although inactivated vaccines have been certified and used in endemic regions for decades, the neutralizing antibody (NAb) titer induced by inactivated vaccines is low and the immunization schedule is complicated, requiring at least three injections spanning approximately 6 months to 1 year. Replication-competent vesicular stomatitis virus (VSV)-based vaccines provide prolonged protection after a single injection. In this study, we successfully engineered the HTNV glycoprotein (GP) in the VSV genome by replacing the VSV-G open reading frame. The resulting recombinant (r) rVSV-HTNV-GP was rescued, and the immunogenicity of GP was similar to that of HTNV. BALB/c mice immunized with rVSV-HTNV-GP showed a high titer of NAb against HTNV after a single injection. Notably, the cross-reactive NAb response induced by rVSV-HTNV-GP against Seoul virus (an orthohantavirus) was higher than that induced by three sequential injections of inactivated vaccines. Upon challenge with HTNV, rVSV-HTNV-GP-immunized mice showed a profoundly reduced viral burden in multiple tissues, and inflammation in the lungs and liver was nearly undetectable. Moreover, a single injection of rVSV-HTNV-GP established a prolonged immunological memory status as the NAbs were sustained for over 1 year and provided long-term protection against HTNV infection. The findings of our study can support further development of an rVSV-HTNV-GP-based HTNV vaccine with a simplified immunization schedule.

A T cell-targeted multi-antigen vaccine generates robust cellular and humoral immunity against SARS-CoV-2 infection

SARS-CoV-2, the etiological agent behind the coronavirus disease 2019 (COVID-19) pandemic, has continued to mutate and create new variants with increased resistance against the WHO-approved spike-based vaccines. With a significant portion of the worldwide population still unvaccinated and with waning immunity against newly emerging variants, there is a pressing need to develop novel vaccines that provide broader and longer-lasting protection. To generate broader protective immunity against COVID-19, we developed our second-generation vaccinia virus-based COVID-19 vaccine, TOH-VAC-2, encoded with modified versions of the spike (S) and nucleocapsid (N) proteins as well as a unique poly-epitope antigen that contains immunodominant T cell epitopes from seven different SARS-CoV-2 proteins. We show that the poly-epitope antigen restimulates T cells from the PBMCs of individuals formerly infected with SARS-CoV-2. In mice, TOH-VAC-2 vaccination produces high titers of S- and N-specific antibodies and generates robust T cell immunity against S, N, and poly-epitope antigens. The immunity generated from TOH-VAC-2 is also capable of protecting mice from heterologous challenge with recombinant VSV viruses that express the same SARS-CoV-2 antigens. Altogether, these findings demonstrate the effectiveness of our versatile vaccine platform as an alternative or complementary approach to current vaccines.

Effectiveness of VSV vectored SARS-CoV-2 spike when administered through intranasal, intramuscular or a combination of both

A critical feature of the VSV vector platform is the ability to pseudotype the virus with different glycoproteins from other viruses, thus altering cellular tropism of the recombinant virus. The route of administration is critical in triggering local and systemic immune response and protection. Most of the vaccine platforms used at the forefront are administered by intramuscular injection. However, it is not known at what level ACE2 is expressed on the surface of skeletal muscle cells, which will have a significant impact on the efficiency of a VSV-SARS-CoV-2 spike vaccine to mount a protective immune response when administered intramuscularly. In this study, we investigate the immunogenicity and efficacy of a prime-boost immunization regimen administered intranasally (IN), intramuscularly (IM), or combinations of the two. We determined that the prime-boost combinations of IM followed by IN immunization (IM + IN) or IN followed by IN immunization (IN + IN) exhibited strong spike-specific IgG, IgA and T cell response in vaccinated K18 knock-in mice. Hamsters vaccinated with two doses of VSV expressing SARS-CoV-2 spike, both delivered by IN or IM + IN, showed strong protection against SARS-CoV-2 variants of concern Alpha and Delta. This protection was also observed in aged hamsters. Our study underscores the highly crucial role immunization routes have with the VSV vector platform to elicit a strong and protective immune response.

Overview of Nucleocapsid-Targeting Vaccines against COVID-19

The new SARS-CoV-2 coronavirus, which emerged in late 2019, is a highly variable causative agent of COVID-19, a contagious respiratory disease with potentially severe complications. Vaccination is considered the most effective measure to prevent the spread and complications of this infection. Spike (S) protein-based vaccines were very successful in preventing COVID-19 caused by the ancestral SARS-CoV-2 strain; however, their efficacy was significantly reduced when coronavirus variants antigenically different from the original strain emerged in circulation. This is due to the high variability of this major viral antigen caused by escape from the immunity caused by the infection or vaccination with spike-targeting vaccines. The nucleocapsid protein (N) is a much more conserved SARS-CoV-2 antigen than the spike protein and has therefore attracted the attention of scientists as a promising target for broad-spectrum vaccine development. Here, we summarized the current data on various N-based COVID-19 vaccines that have been tested in animal challenge models or clinical trials. Despite the high conservatism of the N protein, escape mutations gradually occurring in the N sequence can affect its protective properties. During the three years of the pandemic, at least 12 mutations have arisen in the N sequence, affecting more than 40 known immunogenic T-cell epitopes, so the antigenicity of the N protein of recent SARS-CoV-2 variants may be altered. This fact should be taken into account as a limitation in the development of cross-reactive vaccines based on N-protein.

OVX033, a nucleocapsid-based vaccine candidate, provides broad-spectrum protection against SARS-CoV-2 variants in a hamster challenge model

Spike-based COVID-19 vaccines induce potent neutralizing antibodies but their efficacy against SARS-CoV-2 variants decreases. OVX033 is a recombinant protein composed of the full-length nucleocapsid (N) protein of SARS-CoV-2 genetically fused to oligoDOM^®, a self-assembling domain which improves antigen immunogenicity. OVX033 including N as an antigenic target is proposed as new vaccine candidate providing broad-spectrum protection against sarbecoviruses. OVX033 demonstrated its ability to trigger cross-reactive T cell responses and cross-protection against three variants of SARS-CoV-2 (B.1 Europe, Delta B.1.617.2, and Omicron B.1.1.529) in a hamster challenge model, as evidenced by lower weight loss, lower lung viral loads, and reduced lung histopathological lesions.

Exosome-Based Multivalent Vaccine: Achieving Potent Immunization, Broadened Reactivity, and Strong T-Cell Responses with Nanograms of Proteins

Currently approved vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have focused solely on the spike protein to provide immunity. The first vaccines were developed rapidly using spike mRNA delivered by lipid nanoparticles but required ultralow-temperature storage and have had limited immunity against variations in spike. Subsequently, protein-based vaccines were developed, which offer broader immunity but require significant time for development and the use of an adjuvant to boost the immune response. Here, exosomes were used to deliver a bivalent protein-based vaccine in which two independent viral proteins were used. Exosomes were engineered to express either SARS-CoV-2 delta spike (Stealth X-Spike [STX-S]) or the more conserved nucleocapsid (Stealth X-Nucleocapsid [STX-N]) protein on the surface. When administered as a single product (STX-S or STX-N) or in combination (STX-S+N), both STX-S and STX-N induced strong immunization with the production of potent humoral and cellular immune responses. Interestingly, these results were obtained with the administration of only nanograms of protein and without an adjuvant. In two independent animal models (mouse and rabbit), the administration of nanograms of the STX-S+N vaccine resulted in increased antibody production, potent neutralizing antibodies with cross-reactivity to other variants of spike, and strong T-cell responses. Importantly, no competition of immune responses was observed, allowing the delivery of nucleocapsid with spike to offer improved SARS-CoV-2 immunity. These data show that the StealthX exosome platform has the enormous potential to revolutionize vaccinology by combining the advantages of mRNA and recombinant protein vaccines into a superior, rapidly generated, low-dose vaccine resulting in potent, broader immunity. IMPORTANCE The pandemic emergency has brought to light the need for a new generation of rapidly developed vaccines that induce longer-lasting, potent, and broader immune responses. While the mRNA vaccines played a critical role during the emergency in reducing SARS-CoV-2 hospitalization rates and deaths, more efficient approaches are needed. A multivalent, protein-based vaccine delivered by exosomes could meet this urgent need due to the high speed of development, manufacturability, and the ability to produce a strong antibody response, with neutralizing antibodies and a strong T-cell response able to broadly combat viral infection with a minimum number of injections.

Next-Generation Vaccines Against COVID-19 Variants: Beyond the Spike Protein

Vaccines are among the most effective medical countermeasures against infectious diseases. The current Coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spurred the scientific strategies to fight against the disease. Since 2020, a great number of vaccines based on different platforms have been in development in response to the pandemic, among which mRNA, adenoviral vector, and subunit vaccines have been clinically approved for use in humans. These first-generation COVID-19 vaccines largely target the viral spike (S) protein and aim for eliciting potent neutralizing antibodies. With the emergence of SARS-CoV-2 variants, especially the highly transmissible Omicron strains, the S-based vaccine strategies have been faced constant challenges due to strong immune escape by the variants. The coronavirus nucleocapsid (N) is one of the viral proteins that induces strong T-cell immunity and is more conserved across different SARS-CoV-2 variants. Inclusion of N in the development of COVID-19 vaccines has been reported. Here, we briefly reviewed and discussed COVID-19 disease, current S-based vaccine strategies, and focused on the immunobiology of N protein in SARS-CoV-2 host immunity, as well as the next-generation vaccine strategies involving N protein, to combat current and emerging SARS-CoV-2 variants.

Heterologous chimpanzee adenovirus vector immunizations for SARS-CoV-2 spike and nucleocapsid protect hamsters against COVID-19

Available COVID-19 vaccine only provide protection for a limited time due in part to the rapid emergence of viral variants with spike protein mutations, necessitating the generation of new vaccines to combat SARS-CoV-2. Two serologically distinct replication-defective chimpanzee-origin adenovirus (Ad) vectors (AdC) called AdC6 and AdC7 expressing early SARS-CoV-2 isolate spike (S) or nucleocapsid (N) proteins, the latter expressed as a fusion protein within herpes simplex virus glycoprotein D (gD), were tested individually or as a mixture in a hamster COVID-19 SARS-CoV-2 challenge model. The S protein expressing AdC (AdC-S) vectors induced antibodies including those with neutralizing activity that in part cross-reacted with viral variants. Hamsters vaccinated with the AdC-S vectors were protected against serious disease and showed accelerated recovery upon SARS-CoV-2 challenge. Protection was enhanced if AdC-S vectors were given together with the AdC vaccines that expressed the gD N fusion protein (AdC-gDN). In contrast hamsters that just received the AdC-gDN vaccines showed only marginal lessening of symptoms compared to control animals. These results indicate that immune response to the N protein that is less variable than the S protein may potentiate and prolong protection achieved by the currently used S protein based genetic COVID-19 vaccines.