This invention relates to a culture system for the growth of epidermal keratinocyte stem cells comprising, a. processing the feeder cells economically with Mitomycin C; and b. providing a substratum in the form of such feeder cells; c. achieving better growth stimulation of epidermal keratinocyte stem cell growth than γ-irradiated feeder cells; characterized in that the optimal concentration of mitomycin C is combined further with respect to the dose per cell to derive a range of concentration-dose permutations, where the concentration of mitomycin C is in the range of 3 to 10 μg per ml and the dose is in the range of 15 to 450 pg per cell.
