Culturing MCC Cell Lines and Fibroblasts

MCPyV-positive, WaGa and MKL-1, and -negative, UM-MCC 34, MCC cell lines have been previously described (Schrama et al. 2019 (link); Fan et al. 2018 (link)). All the cell lines were cultured under standard conditions (37 °C, 5% CO₂) in RPMI 1640 medium (PAN-Biotech, Aidenbach, Germany) supplemented with 10% fetal bovine serum (FBS; PAN-Biotech) and 1% penicillin–streptomycin (P/S; PAN-Biotech). Primary skin fibroblasts isolated from healthy skin (F1.15) were cultured in DMEM medium (PAN-Biotech) and DMEM/F12 (1:1) medium (Lonza, Cologne, Germany), supplemented with 10% FBS and 1% P/S under standard conditions (Fan et al. 2021 (link)). The cell lines were regularly tested to ensure the absence of mycoplasma and their identity was verified by DNA finger printing.