Novel S2-based fusion inhibitors also need further study, such as nanobodies and aptamers, that can specifically recognize antigen epitopes with high affinity.159,160 Numerous studies have reported that nanobodies and aptamers can effectively neutralize SARS-CoV-2 infection by blocking the RBD-ACE2 interactions.161–164 Due to their small size and unique conformation, they are more likely to bind the cryptic epitopes that are usually inaccessible to conventional antibodies. This evidence concerns the gene ACE2 and COVID-19.