Colony-forming efficiency analysis of NHEK transduced with p14ARF, p16INK4A, p53 and TRF2ΔBΔM. NHEKs were transduced with amphotropic retroviral particles using spinfection and, 48 h later, trypsinised and seeded at clonal density (7 × 103 cells per 6-well plate). Cells were cultured for 2 weeks under drug selection and finally fixed and stained with Rhodamine B to reveal keratinocyte colonies. Colony-forming efficiency, displayed as percentage and relative to the respective EV control, was calculated by dividing the total number of colonies obtained per well by the total number of cells seeded per plate (7,000). Photos show wells representative of the results obtained for each construct. Legend: GFP, empty vector control for p14ARF, p16INK4A and p53; EV, empty vector control for TRF2ΔBΔM (DN). This is the result of a single experiment.