Nonclinical safety assessment of an mRNA Covid-19 vaccine candidate following repeated administrations and biodistribution

Nonclinical safety and biodistribution evaluation of HC009 mRNA vaccine against COVID-19 in rat

mRNA-based technology has been evaluated in clinical trials for rapid control and prevention of emergencies and diseases. HC009, a mRNA vaccine encoding the full-length SARS-CoV-2 spike protein delivered via the QTsome platform, was tested in rats for immunogenicity, toxicity, and biodistribution. For immunogenicity and toxicity, rats received three intramuscular injections of HC009 at 3-week intervals followed by a 4-week observation period. In the biodistribution study, rats received a single intramuscular injection, with mRNA levels measured in organs at various time points. Results showed that HC009 elicited effective, long-lasting humoral immunity and Th1-biased cellular responses. The mRNA primarily localized to the injection site and spleen, with no observed vaccine-related toxicological reactions. These findings support HC009's potential for inducing an effective immune response with a favorable safety profile, warranting further clinical investigation.

Proceedings of the 2023 Annual Scientific Meeting of the French Society of Toxicologic Pathology (SFPT) on Preclinical Development and Therapeutic Applications of mRNA-Based Technologies

The 2023 annual scientific meeting of the French Society of Toxicologic Pathology (Société Française de Pathologie Toxicologique, SFPT), entitled "mRNA-based technologies: preclinical development and therapeutic applications," was held in Lyon (France) on May 25 to 26, 2023. The aim of the meeting was to discuss the biology, immunology, and preclinical development of messenger RNA (mRNA)-based vaccines and therapeutics, including immuno-oncology and rare diseases, as well as the regulatory aspect of the COVID-19 vaccines and an overview of the principles and applications of in situ hybridization techniques. This article presents the summary of five lectures along with selected figures, tables, and key literature references on this topic.

Impact of administration routes and dose frequency on the toxicology of SARS-CoV-2 mRNA vaccines in mice model

The increasing use of SARS-CoV-2 mRNA vaccines has raised concerns about their potential toxicological effects, necessitating further investigation to ensure their safety. To address this issue, we aimed to evaluate the toxicological effects of SARS-CoV-2 mRNA vaccine candidates formulated with four different types of lipid nanoparticles in ICR mice, focusing on repeated doses and administration routes. We conducted an extensive analysis in which mice received the mRNA vaccine candidates intramuscularly (50 μg/head) twice at 2-week intervals, followed by necropsy at 2 and 14 dpsi (days post-secondary injection). In addition, we performed a repeated dose toxicity test involving three, four, or five doses and compared the toxicological outcomes between intravenous and intramuscular routes. Our findings revealed that all vaccine candidates significantly induced SARS-CoV-2 spike protein-specific IgG and T cell responses. However, at 2 dpsi, there was a notable temporary decrease in lymphocyte and reticulocyte counts, anemia-related parameters, and significant increases in cardiac damage markers, troponin-I and NT-proBNP. Histopathological analysis revealed severe inflammation and necrosis at the injection site, decreased erythroid cells in bone marrow, cortical atrophy of the thymus, and increased spleen cellularity. While most toxicological changes observed at 2 dpsi had resolved by 14 dpsi, spleen enlargement and injection site damage persisted. Furthermore, repeated doses led to the accumulation of toxicity, and different administration routes resulted in distinct toxicological phenotypes. These findings highlight the potential toxicological risks associated with mRNA vaccines, emphasizing the necessity to carefully consider administration routes and dosage regimens in vaccine safety evaluations, particularly given the presence of bone marrow and immune organ toxicity, which, though eventually reversible, remains a serious concern.

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.

Toxicologic Pathology Forum: mRNA Vaccine Safety-Separating Fact From Fiction

SARS-CoV-2 spread rapidly across the globe, contributing to the death of millions of individuals from 2019 to 2023, and has continued to be a major cause of morbidity and mortality after the pandemic. At the start of the pandemic, no vaccines or anti-viral treatments were available to reduce the burden of disease associated with this virus, as it was a novel SARS coronavirus. Because of the tremendous need, the development of vaccines to protect against COVID-19 was critically important. The flexibility and ease of manufacture of nucleic acid-based vaccines, specifically mRNA-based products, allowed the accelerated development of COVID-19 vaccines. Although mRNA-based vaccines and therapeutics had been in clinical trials for over a decade, there were no licensed mRNA vaccines on the market at the start of the pandemic. The rapid development of mRNA-based COVID-19 vaccines reduced serious complications and death from the virus but also engendered significant public concerns, which continue now, years after emergency-use authorization and subsequent licensure of these vaccines. This article summarizes and addresses some of the safety concerns that continue to be expressed about these vaccines and their underlying technology.

Specific long-term changes in anti-SARS-CoV-2 IgG modifications and antibody functions in mRNA, adenovector, and protein subunit vaccines

Various vaccine platforms were developed and deployed against the COVID-19 disease. The Fc-mediated functions of IgG antibodies are essential in the adaptive immune response elicited by vaccines. However, the long-term changes of protein subunit vaccines and their combinations with messenger RNA (mRNA) vaccines are unknown. A total of 272 serum and plasma samples were collected from individuals who received first to third doses of the protein subunit Medigen, the mRNA (BNT, Moderna), or the adenovector AstraZeneca vaccines. The IgG subclass level was measured using enzyme-linked immunosorbent assay, and Fc-N glycosylation was measured using liquid chromatography coupled to tandem mass spectrometry. Antibody-dependent-cellular-phagocytosis (ADCP) and complement deposition (ADCD) of anti-spike (S) IgG antibodies were measured by flow cytometry. IgG1 and 3 reached the highest anti-S IgG subclass level. IgG1, 2, and 4 subclass levels significantly increased in mRNA- and Medigen-vaccinated individuals. Fc-glycosylation was stable, except in female BNT vaccinees, who showed increased bisection and decreased galactosylation. Female BNT vaccinees had a higher anti-S IgG titer than that of males. ADCP declined in all groups. ADCD was significantly lower in AstraZeneca-vaccinated individuals. Each vaccine produced specific long-term changes in Fc structure and function. This finding is critical when selecting a vaccine platform or combination to achieve the desired immune response.

Specific long-term changes in anti-SARS-CoV-2 IgG modifications and antibody functions in mRNA, adenovector, and protein subunit vaccines

Various vaccine platforms were developed and deployed against the COVID-19 disease. The Fc-mediated functions of IgG antibodies are essential in the adaptive immune response elicited by vaccines. However, the long-term changes of protein subunit vaccines and their combinations with mRNA vaccines are unknown. A total of 272 serum and plasma samples were collected from individuals who received first to third doses of the protein subunit Medigen, the mRNA (BNT), or the adenovector AstraZeneca vaccines. The IgG subclass level was measured using enzyme-linked immunosorbent assay, and Fc-N glycosylation was measured using LC-MS/MS. Antibody-dependent phagocytosis (ADCP) and complement deposition (ADCD) of anti-spike (S) IgG antibodies were measured. IgG1 and 3 reached the highest anti-S IgG subclass level. IgG1, 2, and 4 subclass levels significantly increased in mRNA- and Medigen-vaccinated individuals. Fc-glycosylation was stable, except in female BNT vaccinees, who showed increased bisection and decreased galactosylation. Female BNT vaccinees had a higher anti-S IgG titer than that of males. ADCP declined in all groups. ADCD increased in Medigen-vaccinated individuals after the third dose. Each vaccine produced specific long-term changes in Fc structure and function. This finding is critical when selecting a vaccine platform or combination to achieve the desired immune response.