Herein is reported a method for producing an immunoconjugate with reduced product- and process-related impurities by culturing mammalian cells that contain one or more nucleic acids encoding the immunoconjugate of interest in a cell culture medium, wherein the one or more nucleic acids are expressed under the conditions of cell culture comprising the steps of:culturing the mammalian cells in a cell culture medium at a first temperature and at a first pH；reducing the first temperature of the cell culture medium to a second temperature； and increasing the first pH of the cell culture medium to a second pH；recovering the immunoconjugate from the cells or the cell culture medium,and thereby producing the immunoconjugate.
