The invention relates to a method of cell culture where the cells are modified to reduce the level of synthesis of growth and/or productivity inhibitors by the cell. The invention also relates to a method of cell culture for improving cell growth and productivity, in particular in fed-batch culture of mammalian cells at high cell density. The invention further relates to a method of producing cells with improved cell growth and/or productivity in cell culture and to cells obtained or obtainable by such methods.