ACE2 and COVID-19: Among other clusters, Ye et al.'s (37) “The pathogenesis and treatment of the “Cytokine Storm” in COVID-19”, Leng et al.'s (21) “Transplantation of ACE2—Mesenchymal Stem Cells Improves the Outcome of Patients with COVID-19 Pneumonia”, and Nishiga et al.'s (41) “COVID-19 and cardiovascular disease: from basic mechanisms to clinical perspectives” had the highest citation frequency.