CD9 and lung adenocarcinoma: To analyze whether the tetraspanin CD9 facilitates the infection by SARS-CoV-2, the colorectal SW480/WT and SW480/CD9 KO cells, and the lung adenocarcinoma A549/WT and A549/CD9 KO cells, were generated using a home-made CRISPR/Cas9 system (see Materials and Methods section).