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

Abstract

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.

Filamentous Fungus-Produced Human Monoclonal Antibody Provides SARS-CoV-2 Protection in Hamster and Non-Human Primate Models

“…These studies have used different subunits, such as the hemagglutinin for In uenza A virus, the RBD for SARS-CoV-2 and part of the Gc glycoprotein for Schmallenberg virus 18,19,23 . A previous study testing C1-derived SARS-CoV-2 RBD protein in rabbits for toxicology did not show any local or systemic side effects of fungal produced proteins, indicating its potential safety for use in humans 24 .…”

Preclinical immunogenicity and protective efficacy of a SARS-CoV-2 RBD based vaccine produced with the thermophilic filamentous fungal expression system Thermothelomyces heterothallica, C1.

“…Moreover, in the study done by Ramot et. al., it was shown that in New Zealand rabbits, the SARS-CoV-2-RBD produced with the C1 system, did not induced any adverse effects or systemic toxicity and induced the production IgG antibodies against SARS-CoV-2 36 . Furthermore, Lazo and colleagues, proved that immunization with SARS-CoV-2-RBD produced in the C1 system, induced a similar humoral response in mice as recombinant SARS-CoV-2-RBD produced in HEK293 cells 17 .…”

Evaluation of non-clinical toxicity studies of COVID-19 vaccines

“…The majority of the observed findings are immunostimulatory effects, which, together with their reversible nature, can be considered non-adverse. Inflammatory reactions at the injection site are considered as intended reactions representing the immune response to the antigen ( Ramot et al, 2022 ). This has been described earlier in a workshop report ( Van Der Laan et al, 2009 ).…”