The microcarriers were prepared as according to instructions from Pharmacia. They were prepared in a siliconised Schott bottle of suitable size. All microcarriers were conditioned by washing with DMEM (5% FBS) prior to addition to the vessel. The microcarriers for the 1 l cultures were washed twice with 250 ml of complete medium whilst the microcarriers for the 15 l cultures were washed twice with 1500 ml of medium.