Preliminary nonclinical safety and immunogenicity of an rVSV-ΔG-SARS-CoV-2-S vaccine in mice, hamsters, rabbits and pigs

A review of the scientific literature on experimental toxicity studies of COVID-19 vaccines, with special attention to publications in toxicology journals

Since the reports of the first cases of COVID-19, in less than 5 years, a huge number of documents regarding that disease and the coronavirus (SARS-CoV-2), responsible for the infection, have been published. The tremendous number of scientific documents covers many topics on different issues directly related to COVID-19/SARS-CoV-2. The number of articles-including reviews-reporting adverse/side effects of the approved COVID-19 vaccines is considerable. A wide range of adverse/side effects have been reported in humans after COVID-19 vaccination: thrombotic events/thrombocytopenia, myocarditis/pericarditis, cutaneous reactions, immune-mediated effects, psychiatric adverse events, systemic lupus erythematosus, reproductive toxicity, and other miscellaneous adverse effects. In contrast, information on nonclinical studies conducted to assess the potential toxicity/adverse effects of the COVID-19 vaccines in laboratory animals, is comparatively very scarce. The present review was aimed at revising the scientific literature regarding the studies in laboratory animals on the toxic/adverse effects of COVID-19 vaccines. In addition, the investigations reported in those specific toxicology journals with the highest impact factors have been examined one by one. The results of the present review indicate that most nonclinical/experimental studies on the adverse/toxic effects of the COVID-19 vaccines and/or potential candidates showed-in general terms-a good safety profile. Only in some animal studies were certain adverse effects found. However, a rather surprising result has been the limited number of available (in the databases PubMed and Scopus) nonclinical studies performed by the companies that have been the largest manufacturers of mRNA vaccines in the world. It is assumed that these studies have been conducted. However, they have not been published in scientific journals, which does not allow the judgment of the international scientific community, including toxicologists.

Induction of Superior Systemic and Mucosal Protective Immunity to SARS-CoV-2 by Nasal Administration of a VSV-ΔG-Spike Vaccine

The emergence of rapidly spreading variants of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) poses a major challenge to vaccines' protective efficacy. Intramuscular (IM) vaccine administration induces short-lived immunity but does not prevent infection and transmission. New vaccination strategies are needed to extend the longevity of vaccine protection, induce mucosal and systemic immunity and prevent viral transmission. The intranasal (IN) administration of the VSV-ΔG-spike vaccine candidate directly to mucosal surfaces yielded superior mucosal and systemic immunity at lower vaccine doses. Compared to IM vaccination in the K18-hACE2 model, IN vaccination preferentially induced mucosal IgA and T-cells, reduced the viral load at the site of infection, and ameliorated disease-associated brain gene expression. IN vaccination was protective even one year after administration. As most of the world population has been vaccinated by IM injection, we demonstrate the potential of a heterologous IM + IN vaccination regimen to induce mucosal immunity while maintaining systemic immunity. Furthermore, the IM + IN regimen prevented virus transmission in a golden Syrian hamster co-caging model. Taken together, we show that IN vaccination with VSV-ΔG-spike, either as a homologous IN + IN regimen or as a boost following IM vaccination, has a favorable potential over IM vaccination in inducing efficient mucosal immunity, long-term protection and preventing virus transmission.

Immunogenicity of mucosal COVID-19 vaccine candidates based on the highly attenuated vesicular stomatitis virus vector (VSVMT) in golden syrian hamster

COVID-19 is caused by coronavirus SARS-CoV-2. Current systemic vaccines generally provide limited protection against viral replication and shedding within the airway. Recombinant VSV (rVSV) is an effective vector which inducing potent and comprehensive immunities. Currently, there are two clinical trials investigating COVID-19 vaccines based on VSV vectors. These vaccines were developed with spike protein of WA1 which administrated intramuscularly. Although intranasal route is ideal for activating mucosal immunity with VSV vector, safety is of concern. Thus, a highly attenuated rVSV with three amino acids mutations in matrix protein (VSVMT) was developed to construct safe mucosal vaccines against multiple SARS-CoV-2 variants of concern. It demonstrated that spike protein mutant lacking 21 amino acids in its cytoplasmic domain could rescue rVSV efficiently. VSVMT indicated improved safeness compared with wild-type VSV as the vector encoding SARS-CoV-2 spike protein. With a single-dosed intranasal inoculation of rVSVΔGMT-SΔ21, potent SARS-CoV-2 specific neutralization antibodies could be stimulated in animals, particularly in term of mucosal and cellular immunity. Strikingly, the chimeric VSV encoding SΔ21 of Delta-variant can induce more potent immune responses compared with those encoding SΔ21 of Omicron- or WA1-strain. VSVMT is a promising platform to develop a mucosal vaccine for countering COVID-19.

VSV-ΔG-Spike Candidate Vaccine Induces Protective Immunity and Protects K18-hACE2 Mice against SARS-CoV-2 Variants

Since the emergence of the original SARS-CoV-2, several variants were described, raising questions as to the ability of recently developed vaccine platforms to induce immunity and provide protection against these variants. Here, we utilized the K18-hACE2 mouse model to show that VSV-ΔG-spike vaccination provides protection against several SARS-CoV-2 variants: alpha, beta, gamma, and delta. We show an overall robust immune response, regardless of variant identity, leading to reduction in viral load in target organs, prevention of morbidity and mortality, as well as prevention of severe brain immune response, which follows infection with various variants. Additionally, we provide a comprehensive comparison of the brain transcriptomic profile in response to infection with different variants of SARS-CoV-2 and show how vaccination prevents these disease manifestations. Taken together, these results highlight the robust VSV-ΔG-spike protective response against diverse SARS-CoV-2 variants, as well as its promising potential against newly arising variants.

Application of Nanotechnology in COVID-19 Infection: Findings and Limitations

There is an urgent need to address the global mortality of the COVID-19 pandemic, as it reached 6.3 million as of July 2022. As such, the experts recommended the mass diagnosis of SARS-CoV-2 infection at an early stage using nanotechnology-based sensitive diagnostic approaches. The development of nanobiosensors for Point-of-Care (POC) sampling of COVID-19 could ensure mass detection without the need for sophisticated laboratories or expert personnel. The use of Artificial Intelligence (AI) techniques for POC detection was also proposed. In addition, the utilization of various antiviral nanomaterials such as Silver Nanoparticles (AgNPs) for the development of masks for personal protection mitigates viral transmission. Nowadays, nano-assisted vaccines have been approved for emergency use, but their safety and effectiveness in the mutant strain of the SARS-CoV-2 virus remain challenging. Methodology: Updated literature was sourced from various research indexing databases such as PubMed, SCOPUS, Science Direct, Research Gate and Google Scholars. Result: We presented the concept of novel nanotechnology researched discovery, including nano-devices, electrochemical biosensing, nano-assisted vaccine, and nanomedicines, for use in recent times, which could be a formidable step for future management of COVID-19.

Viral Vector Vaccine Development and Application during the COVID-19 Pandemic

With the accumulation of mutations in SARS-CoV-2 and the continuous emergence of new variants, the importance of developing safer and effective vaccines has become more prominent in combating the COVID-19 pandemic. Both traditional and genetically engineered vaccines have contributed to the prevention and control of the pandemic. However, in recent years, the trend of vaccination research has gradually transitioned from traditional to genetically engineered vaccines, with the development of viral vector vaccines attracting increasing attention. Viral vector vaccines have several unique advantages compared to other vaccine platforms. The spread of Omicron has also made the development of intranasal viral vector vaccines more urgent, as the infection site of Omicron is more prominent in the upper respiratory tract. Therefore, the present review focuses on the development of viral vector vaccines and their application during the COVID-19 pandemic.

rVSV-ΔG-SARS-CoV-2-S vaccine: repeated intramuscular (IM) toxicity, local tolerance, immunogenicity and biodistribution study in NZW rabbits

BriLife^®, a vector-based vaccine that utilizes the recombinant vesicular stomatitis virus (VSV) platform to express and present the spike antigen of SARS-CoV-2, is undergoing testing in a phase 2 clinical trial in Israel. A nonclinical repeated-dose (GLP) toxicity study in New Zealand white rabbits was performed to evaluate the potential toxicity, local tolerance, immunogenicity and biodistribution of the vaccine. rVSV-ΔG-SARS-CoV-2-S (or vehicle) was administered intramuscularly to two groups of animals (10⁶, 10⁷ PFU/animal, n = 10/sex/group) on three occasions, at 2-week intervals, followed by a 3-week recovery period. Systemic clinical signs, local reactions, body weight, body temperature, food consumption, ophthalmology, urinalysis, clinical pathology, C-reactive protein, viremia and antibody levels were monitored. Gross pathology was performed, followed by organs/tissues collection for biodistribution and histopathological evaluation. Treatment-related changes were restricted to multifocal minimal myofiber necrosis at the injection sites, and increased lymphocytic cellularity in the iliac and mesenteric lymph nodes and in the spleen. These changes were considered related to the inflammatory reaction elicited, and correlated with a trend for recovery. Detection of rVSV-ΔG-SARS-CoV-2-S vaccine RNA was noted in the regional iliac lymph node in animals assigned to the high-dose group, at both termination time points. A significant increase in binding and neutralizing antibody titers was observed following vaccination at both vaccine doses. In view of the findings, it was concluded that the rVSV-ΔG-SARS-CoV-2-S vaccine is safe. These results supported the initiation of clinical trials.

Toxicity and Local Tolerance of a Novel Spike Protein RBD Vaccine Against SARS-CoV-2, Produced Using the C1 Thermothelomyces Heterothallica Protein Expression Platform

Coronavirus disease 2019 (COVID-19) has caused the ongoing COVID-19 pandemic and there is a growing demand for safe and effective vaccines. The thermophilic Thermothelomyces heterothallica filamentous fungal host, C1-cell, can be utilized as an expression platform for the rapid production of large quantities of antigens for developing vaccines. The aim of this study was to evaluate the local tolerance and the systemic toxicity of a C1-cell expressed receptor-binding domain (C1-RBD) vaccine, following repeated weekly intramuscular injections (total of 4 administrations), in New Zealand White rabbits. The animals were sacrificed either 3 days or 3 weeks following the last dose. No signs of toxicity were observed, including no injection site reactions. ELISA studies revealed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific immunoglobulin G antibodies in the sera of C1-RBD-treated animals starting from day 13 post injection, that were further elevated. Histopathology evaluation and immunohistochemical staining revealed follicular hyperplasia, consisting of B-cell type, in the spleen and inguinal lymph nodes of the treated animals that were sustained throughout the recovery phase. No local or systemic toxicity was observed. In conclusion, the SARS-CoV-2 C1-RBD vaccine candidate demonstrated an excellent safety profile and a lasting immunogenic response against receptor-binding domain, thus supporting its further development for use in humans.