Process for cell culturing by continuous perfusion

A method for limiting cell aggregation during cell culture to a level wherein no more than 5% of the animal cells in suspension in the culture comprise aggregates of at least 5 cells, comprising:

• culturing of a cell culture comprising cell culture medium and animal cells that easily or inherently form aggregates during culturing, wherein the culturing comprises:
• (a) circulating the cell culture through a filter module comprising hollow fibers, in an alternating tangential flow resulting in an outflow of cell culture liquid through the pores of the filter module having a lower animal cell density per ml than the cell culture prior to circulating through the filter module;
• and
• (b) adding cell culture medium to the cell culture, and
• wherein no more than 5% of the animal cells in the culture form aggregates in suspension of at least 5 cells during the culturing, and wherein the culturing is continued until animal cells are present in the cell culture at a density of at least 80×106 viable animal cells/ml.