I am currently working on ocrelizumab purification process. After harvest step of cell culture, cell and other debris was removed by depth filters and sterilized by 0.22 micrometer filter. It was stored at 2-8 centigrade. Quality of protein after first step of purification (affinity chromatography by mabselect resin) in different set point was investigated:(sterile supernatant was kept and in different time quality of eluated protein was investigated)

-After harvest followed by filtration, 0 day sup was kept and purified, in first step of chromatography by mabselect ,acidic charge variant 17.2%, basic variant 14 %.

-After harvest followed by filtration, 2 days sup was kept, and purified , in first step of chromatography by mabselect ,acidic charge variant 19.2%, basic variant 17.2 %.

-After harvest followed by filtration ,4 days sup was kept and purified,in first step of chromatography by mabselect , acidic charge variant 23.4%, basic variant 14.5 %.

-After harvest followed by filtration,10 days sup was kept and purified ,in first step of chromatography by mabselect , acidic charge variant 35.4%, basic variant 24.5 %.

Dynamis (from thermo) and ex-cell feed (from sigma) was applied in cell culture step. Does anyone have any suggestion in order to increase stability of supernatant after filtration? what I mean is increasing supplement or changing condition like EDTA ,pH or some thing like that?

Thanks a million