DPP4 and Middle East respiratory syndrome: Although DPP4 was initially described as receptor for SARS-CoV, which induced Middle East respiratory syndrome (MERS), recently an affinity between DPP4 and the spike (S) receptor-binding domain of SARS-CoV-2 was shown by a bioinformatics approach, indicating that DPP4 is also a potential binding target for SARS-CoV-2 (Fig. 1a).