The neonatal foreskin human melanocytes purchased from Cascade Biologics (C-102-5C, Gibco) were maintained in Medium 254 supplemented with human melanocyte growth supplement containing basic FGF (3 ng/mL), insulin (5 µg/mL), transferrin (5 µg/mL), bovine pituitary extract (0.2%), FBS (0.5%), heparin (3 µg/mL), hydrocortisone (0.18 µg/mL), and phorbol 12-myristate 13-acetate (10 ng/mL). The human fibroblasts Hs68 cells derived from male foreskin (ATCC® CRL-1635™) were obtained from the Food Industry Research and Development Institute (FIRDI, Hsinchu, Taiwan) and cultured in DMEM supplemented with 10% FBS and 1% antibiotic. All cells were incubated at 37 °C under 5% CO2 .