You have the pure protein. Now, how do you store it? Proteins are fragile; they can denature (unfold) with changes in temperature or pH.
The cell line development process involved several rounds of cloning and screening to identify a cell line with the desired characteristics, including: A Mab A Case Study In Bioprocess Development
The drug substance was formulated in 20 mM Histidine, 5% Sucrose, 0.02% Polysorbate 80, pH 6.0. Note: Polysorbate 80 was selected over PS20 due to lower hydrolysis risk observed in accelerated stability studies (40°C for 1 month). You have the pure protein