Previous studies have suggested that CTSL inhibitors effectively prevent the infection of many other coronaviruses, including SARS-CoV-1, Middle East respiratory syndrome coronavirus (MERS-CoV), and human coronavirus (HCoV)-229E.39–41 CTSL is thought to be a potential target for the treatment of COVID-19,19,20 although no systematic study has been conducted. This evidence concerns the gene CTSL and COVID-19.