pYD1

The global pandemic of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has highlighted the urgent need to develop safe and effective vaccines. Here, researchers generated a S. cerevisiae-based SARS-CoV-2 vaccine, EBY100/pYD1-RBD, in which the full-length receptor-binding domain (RBD) of the SARS-CoV-2 spike protein is expressed on the surface of the yeast. Mice orally administered the unadjuvanted EBY100/pYD1-RBD vaccine developed significant humoral and mucosal responses as well as a robust cellular immune response. Notably, EBY100/pYD1-RBD elicited mixed Th1/Th2-type cellular immune responses and Th1-biased immune responses in mouse models.

In this study, the RBD gene of SARS-CoV-2 spike protein was inserted into plasmid pYD1, and then the RBD protein was fused to Aga2, and Aga2 was expressed as a subunit of α-lectin receptor by pYD1 through the Gly-Ser linker. Furthermore, Aga2 then binds to Aga1 (a subunit of yeast) via two disulfide bonds (Figure 1a). Western blot analysis identified the expression of RBD protein in EBY100/pYD1-RBD. As shown in Figure 1b, no specific band was obtained in EBY100/pYD1, while the expected band appeared in EBY100/pYD1-RBD, with a molecular weight of approximately 32 kDa and consisting of Aga2 and RBD.

Figure 1. Schematic diagram and expression analysis of EBY100/pYD1-RBD. (Gao, Tong, et al. 2021)