Hi, I am going to do T cell expansion and later will do experiments using those cells. I see some protocol is using RPMI 1640 with FBS as medium, activate cell using CD3/CD28 antibody, add IL-2 10ng/ml in medium. Some company suggested using their medium which is Serum Free, and can increase viability (the medium is expensive), I am wondering how to choose the medium. If I use serum free medium to expand, later for my co-culture with other cells, I need to add serum, so will it cause problem (serum free to serum?) Thanks.