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

Abstract The emergency use of vaccines has been the most efficient way to control the ongoing COVID-19 pandemic. However, the emergence of SARS-CoV-2 variants of concern has reduced the efficacy of currently used vaccines. The receptor-binding domain (RBD) of the SARS-CoV-2 spike protein is the main target for virus neutralizing (VN) antibodies. Here, we evaluated the immunogenicity and efficacy of a SARS-CoV-2 RBD vaccine candidate produced in the Thermothelomyces heterothallica (formerly Myceliophthora thermophila), C1 protein expression system, in a Syrian golden hamster (Mesocricetus auratus) infection model. One dose of 10 µg RBD vaccine based on SARS-CoV-2 Wuhan strain, coupled to a nanoparticle in combination with aluminum hydroxide as adjuvant, efficiently induced VN antibodies and reduced viral load and lung damage upon SARS-CoV-2 challenge infection. The VN antibodies, neutralized SARS-CoV-2 variants of concern D614G, Alpha, Beta and Gamma. Our results support the use of the Thermothelomyces heterothallica, C1 protein expression system to produce recombinant vaccines against SARS-CoV-2 and other virus infections, in order to help overcome limitations associated with the use of mammalian expression systems.