We routinely cryopreserve our reporter expressing stable cell lines. We use this method: Trypsinize, neutalize and centrifuge to collect cell pellet. Re-suspend cell pellet in the culture media with 10% FBS only (no antibiotics) and add 5% DMSO. Tranfer cells to cryotubes and move right away to -80C (in foam/thermocol/
I assume you have already, in the past, viably frozen down the untransfected animal cells you are using. You should be able to freeze your stably transfected cells with the same method that you freeze the untransfected cells. You are probably already aware that DMSO can cause differentiation. So if the cells you are using are prone to differentiation you just want to make sure that, upon thawing the cells, you get the DMSO diluted quickly (with culture medium or PBS) after you thaw the cells and pellet the cells quickly to resuspend in your cell culture medium.