The present invention relates to a method of increasing biosimilarity of a TNF α binding protein to a reference TNF α binding protein by modifying the charge profile of the binding protein produced by cell culture in a cell culture medium, by making an adjustment to a cell culture condition The adjustment is an increase in the concentration of a metal ion in the cell culture medium and the adjustment occurs on one or more days during the cell culture method, whereby the adjustment in the cell culture condition results in the modification of the charge profile of the binding protein. The present invention also relates to a biosimilar protein obtainable by such a process.
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