base medium or as a medium additive in steps a and or b and or c preferably conditioned medium is used in step c in particular conditioned medium is used in step c as the base medium or as a medium additive the proportion of conditioned medium may be from 10 100 of the total volume of medium a proportion of 30 75 particularly preferably 50 consists of conditioned medium the present invention also relates to a cell which is generated by a method according to the invention the present invention preferably also relates to a method for producing a protein of interest in a cell preferably a cho cell under serum free and insulin free culture conditions comprising the following steps a preparing a cell population containing a gene of interest that codes for a protein of interest b culturing these cells under culture conditions that permit cell growth c isolating a single cell and depositing it in a container preferably in a 96 well dish d culturing the said single cell in serum free and insulin free medium containing igf optionally in the presence of albumin and or feeder cells e selecting a cell according to its level of expression of a protein of interest f harvesting.