Ex vivo NK cells from peripheral blood of COVID-19 patients have reduced intracellular expression of CD107a, Ksp37, granzyme B, and granulysin, suggesting an impaired cytotoxicity, as well as an impaired production of chemokines, IFN-ɣ, and TNF-α (Wilk et al., 2020, Zheng et al., 2020b).