Traditionally, measuring the infectivity of SARS-CoV-2 requires a live virus which creates serious biosafety concerns. We wanted to create a safe alternative, utilizing a general assay system, to identify the infectivity of different current and future strains of SARS-CoV-2, as it is critical for assessing outbreak control and immunity of potential vaccines.
Infectivity of different strains can be measured by the binding affinity between the receptor-binding domain (RBD) of Spike protein (S protein) and its human ACE2 receptor, which is how the virus gains entry into human cells. Various genetic mutations in the S protein affect the RBD-ACE2 interaction, therefore contributing to different infectivities.
We engineered a pseudovirus to recap this crucial interaction by expressing S proteins corresponding to the original and the predominant G614D SARS-CoV-2 strains and used a luciferase assay to quantitatively measure infectivity.