These findings suggest that in severe COVID-19 patients, NK cells are highly exhausted and fail to kill virus-infected macrophages that produce proinflammatory cytokines.91 To evaluate the efficacy of engineered allogenic cord blood NK cells, clinical trial NCT04324996 (Table 1) is evaluating NKG2D-ACE2 CAR-NK targeting the S protein of SARS-CoV-2 and NKG2DL on the surface of infected cells with ACE2 and NKG2D, respectively. Here, ACE2 is linked to COVID-19.