PCNA and COVID-19: Immunofluorescence staining also showed that the expression of KRT14, KRT10, proliferating cell nuclear antigen (PCNA), P63, COL4A1, and ITGA6 downregulated in the COVID‐19 skin tissues or organoids, compared with the control group, which was consistent with the proteomics results (Figure 4b and Figure S4a, Supporting Information).