ACE2 and lung carcinoma: By contrast, in H1299 lung cancer epithelial cells, HeLa-ACE2 cells (overexpressing ACE2), and HEK293T cells overexpressing ACE2 and deleted for TMPRSS2 (293T-A2ΔT2), we did not observe large differences in the entry efficiency of Delta and Omicron (Fig. 3a).