KRT18 and infection: In a subsequent experiment where mice were sacrificed 2 days post-infection, we observed slight fold increases in SARS-CoV-2 N-gene RNA levels (Additional file 1: Figure S4) in SARS-CoV-2 infected hCD147KI-NSG mice compared to WT-NSG mice, confirming viral presence in hCD147KI-NSG mice 48 h post-infection, albeit not to the degree of that in hACE2KI-NSG mice or the significantly infected K18-hACE2-B6 transgenic mice.